mddionline.com

July 2010

PREMIEREISSUE

a A Canon Communications LLC Publication

From the publisher of

Complex Molding PracticesGaining Design Freedom and Process Efficiency p. 20

Simulation TrendsCan Finite Volume Models Increase Accuracy?p. 24

Validation for DevicesGlobal Requirements Are Intensifying for Molded Components p. 12

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Contents

2 | JULY 2010 mddionline.com

JULY 2010 | Vol. 32, Number 7

28

24

20

Features12 Need A Little Validation?

Validating the injection molding process is no longer limited to

medical device components.

Ed Stockdale

17 When Molders Need to Be Choosy Medical devices often have to be molded in a cleanroom

environment. But which cleanroom option is best?

Stephen Moore

20 Using Complexity as a Competitive Advantage Complex injection molding can reduce costs and improve function

and aesthetics.

Dave Robinson

24 How Finite Volume Models Improve Accuracy Some commercially available tools have eschewed the finite element

method for the finite volume method.

John Cogger

28 So Fresh, So Clean A few analytical methods can help manufacturers keep residual

material product contamination away from their devices.

Tina May and Brent Shelley

31 Getting Up to Speed with Hot Runners Hot runner systems are boosting their importance to the medical

device industry thanks to speed and precision.

Craig Kovacic

Departments 4 Editor’s Page 6 Contributors 8 Molding News36 Molding Directory37 Advertisers Index

Cover images courtesy of Eastman Chemical Co., Fraunhofer IZM, Innova

Engineering Inc., Mack Molding, Kaysun Corp., and Nelson Laboratories.

17

MD+DI would like to extend a special thank you to its sister publications Modern Plastics Worldwide and Injection Molding Magazine for their contributions to this issue.

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FROM THE EDITOR

4 | July 2010 mddionline.com

W hen putting together a team for prod-

uct development, everything from the

material to the manufacturing must be

considered, and molding is just one of those pieces

of the puzzle. Recently, DD Studio put together a

team that included Eastman Chemical, Phillips Plas-

tics, and PolyOne to design and develop a mobile,

wireless, continuous vital signs monitoring system.

The ViSi Mobile by Sotera Wireless Inc. is composed

of a wireless device that straps to a patient’s arm

to monitor vital signs, such as blood pressure and

heart rate; a monitoring device to keep clinicians

connected to patients’ information; and a charging

station.

But according to Michael Swartz, growth strate-

gist, DD Studio, the result would not have been pos-

sible without a team pulled together from these four

companies. Swartz spoke at a press conference at

MD&M East in June.

Having the right material only works if

it can be manufactured successfully.

“When Sotera Wireless approached us with this

medical device design concept, it wanted the look

and feel of a small, user-friendly consumer product,

but had a number of specific demands. The device

had to be chemical resistant, durable, easy to clean,

and submersible under water. We weren’t sure the

design was possible,” said Swartz. “But, by working

with Eastman’s technical experts, we were able to

specify Eastman Tritan copolyester as a material

solution to make the innovative design a reality and

meet the device’s performance requirements.”

The device’s lens, housing, printed circuit board

assembly, and connectors are made with Eastman

Tritan copolyester MX711. The cold-swaging ability

of Tritan allows for fit and press assembly of the de-

vice, which offers a tight, smooth, continuous fit be-

tween parts; allows for joining parts without the use

of chemicals, adhesives, or mechanical fasteners;

and saves energy. By utilizing Tritan, Swartz said,

the device features superior resistance to chemicals

used in disinfectants and cleansers without crack-

ing or crazing. He said the material also exceeded

durability requirements, which he said was par-

ticularly valuable in mobile devices that are used

frequently or could be dropped or damaged should

a patient fall.

To protect the device from water and fluids found

in the hospital environment, it had to meet IPX7 re-

quirements of withstanding water

submersion for 60 minutes at a

depth of 1 m. DD Studio worked

with compatibility samples and

testing results from PolyOne to

select the thermoplastic elasto-

mer GLS Versaflex OM 3060. Ac-

cording to PolyOne, the material

adheres to the Eastman Tritan

copolyester substrate to seal the

device housing, including the

speaker port and microphone,

from water seepage and protects

internal electronics.

Having the right material only

works if it can be manufactured successfully. To en-

sure the manufacturability of the design, DD Studio

and the product development team worked with

Phillips Plastics Corp., which took the designs DD

Studio created and conducted a detailed design

for manufacturability exercise and created market-

entry prototype tooling.

“Contemporary plastic materials, such as East-

man Tritan copolyester, are well-positioned to re-

spond to the trend in the healthcare industry toward

durable, reliable wireless devices that enhance pa-

tient safety and comfort,” said Scott Hanson, global

industry leader, medical market segment, Specialty

Plastics Business, Eastman. “Development of the

Sotera Wireless device is an example of how early

and ongoing interaction between material suppli-

ers and designers is truly effective to bring next-

generation devices to the marketplace.”

Sherrie Conroysherrie.conroy@cancom.com

Molding: Just One Piece of the Manufacturing Puzzle

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6 | JULY 2010 mddionline.com

John Cogger is president of

Innova Engineering Inc. (Irvine,

CA), a full-service engineering

firm specializing in nonlinear

analysis of plastics. Cogger

originally formed the company

as Leading Edge Design in 1987. Reach him at

jcogger@innovaengineering.com.

Craig Kovacic is global

manager of hot runner systems

for DME Co. (Madison Heights,

MI), an essential mold

technologies resource to

customers worldwide. Reach

him at customer_service@dme.net.

Tina May is the chemistry

section manager at Nelson

Laboratories Inc. (Salt Lake City).

She has been with the company

since 2004. May previously held

the position of quality manager

of a certified EPA laboratory. Contact her at

clientservices@nelsonlabs.com.

Dave Robinson is vice

president of engineering at

Kaysun Corp. (Manitowoc, WI)

and brings a focus to tool

design. Robinson has worked in

the plastics industry since high

school, when he was a part-time machine operator

during school breaks. Reach him via e-mail at

drobinson@kaysun.com.

Brent Shelley is a study

director at Nelson Laboratories

Inc., where he directs the

quantification of extractable

residue test. Shelley has been

with Nelson Laboratories since

2006 and is an ASTM committee member. Contact

him at clientservices@nelsonlabs.com.

Ed Stockdale is a process

engineer at MackMedical/Mack

Molding, (Arlington, VT) where

his responsibilities include the

development and validation of

injection molding processes and

programs. He can be reached at ed.stockdale@

mack.com.

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MD100702_006 6MD100702 006 6 7/2/10 8:43:16 AM7/2/10 8:43:16 AM

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8 | JULY 2010 mddionline.com

MOLDING NEWS

Bioplastics: The Proof Is in the Isotopes 9 | Elastomer Grades Tailored for Medical Devices 10 | Eastman Opens Expanded Tritan Plant 10 |

OTHER STORIES

R esearchers from a

consortium of Eu-

ropean universities

and small-to-large medical

device developers and man-

ufacturers are using plastics

in various forms to create

tiny lab-on-a-chip devices.

Such devices could, for ex-

ample, enable consumers

to quickly analyze the risk of

blood clots in their legs prior

to a long-distance flight, or

warn pacemaker patients

when electric smog levels

approach dangerous levels.

One of the project’s goals is to use high-volume

printing and plastics processes to ensure that

such devices can be made and marketed at a price

attractive for consumers.

Not yet commercial but in an advanced testing

phase is the measuring device to ascertain the

danger of blood clots during long flights. The Eu-

ropean Union–supported project is called DVT-

Imp, and one of the active project members is the

Fraunhofer Institute for Reliability and Microin-

tegration IZM in Munich, Germany. The lab-on-

a-chip, which is the core of the diagnostic device

for deep vein thrombosis, was built and tested at

IZM. It is a small single-use cartridge, made of a

polycarbonate plate measuring 3 × 22 × 70 mm,

that acts as a tool for the biochemical analysis of

a drop of a passenger’s blood. The cartridge unites

two critical components in one device: a film

150 μm thick on which a filigree network with con-

ductor lines and gold sensors for blood analysis is

attached, as well as a 120-μm-deep fluid channel

for bringing blood to the analysis elements. Inside

the sensor chamber, antibodies are integrated on

electrodes that enable the analysis of the concen-

tration of blood-clotting markers. If the number is

elevated, then the risk of a thrombus (blood clot)

is forming.

“This example shows clearly the possibilities for

polytronics...In order to build up the infrastruc-

ture necessary for this, electronic systems have to

be produced in large quantities, in a cost-effective

manner on large substrates. And with polymer

electronics, this would be perfectly possible,” says

Karlheinz Bock, head of the Polytronic Systems

division at IZM. Polymer electronics combines

functional materials and electronics; for instance,

one technique involves dissolving polymers and

then recapturing them through a printing pro-

cess, structured on flexible sheets. The EU proj-

ect on the feasibility of the system runs until the

middle of 2010.

The sensor wristband (photo), which also was

engineered at IZM, is used for the long-term mon-

itoring of various body functions of older patients

or even athletes. Lighting elements, sensors,

and polymer resistors printed on films are con-

nected into one system with integrated circuits

made of silicon. A 0.003-mm-thin resonance cir-

cuit with an etched coil records electric smog. A

0.030-mm-thick interdigital capacitor attached

to a film detects skin moisture. Comb-shaped,

narrowly interlaced meanders made of copper

bands 0.5 μm thick measure body temperature.

—Matt Defosse

Lab-on-a-Chip Project Counts on Plastics

DuPont Expands Healthcare Off erings DuPont (Wilmington, DE) has

launched 10 new engineering

polymers targeting the healthcare

products and equipment market.

The company reports that its

healthcare offerings comply

with FDA, USP Class VI, and ISO

10993-5 and -11 regulations.

Sixteen of the products are

available as special control

grades that meet the standards

of manufacturing consistency

required of many nonimplantable

medical products, with 12 grades

available in even more stringent

premium control versions.

Masterbatch Squelches Smells and BacteriaFrom Polyvel (Hammonton,

NJ) comes two new series of

masterbatches. The first of the

developments, the VA-series of

masterbatches, contains silver,

trichlosan, or proprietary agents

that effectively kill microorganisms

such as fungus, E. coli, and

salmonella. These masterbatches

are suitable for inclusion in

most thermoplastics and can be

injection molded and extruded.

Because bacteria can emit

unpleasant odors, antimicrobials

are often used as a method of

controlling unwanted scents.

When the source of the smells is

not bacteria, Polyvel’s ZO-series of

odor-managing masterbatches help

end-product scent improvement.

PolyOne Distributes Dow SiliconesPolyOne and Dow Corning jointly

announced in June at the Medical

Design & Manufacturing East

show in New York City that

PolyOne is now distributing Dow

Corning’s silicone products to

healthcare device manufacturers

and fabricators in the United

States, Canada, and Mexico.

Imag

e co

urte

sy o

f FR

AU

NH

OFE

R I

ZM

Shown here is a sensor wristband with an electroluminescent display.

MD100702_008 8MD100702 008 8 7/2/10 8:47:59 AM7/2/10 8:47:59 AM

MOLDING TECHNOLOGIES JULY 2010 | 9

Bioplastics: The Proof Is in the Isotopes

B ioplastics continue to get a lot of press,

and are one of the fastest-growing seg-

ments of the plastics and packaging indus-

tries. More and more consumer packaged

goods companies have announced cam-

paigns to integrate bioplastics into their

packaging to reduce their carbon footprint,

and thus attract eco-conscious buyers. But

how can processors be certain that the

amount of bioplastic content that is promot-

ed in a material actually exists in the resin?

Picarro Inc., a Sunnyvale, CA, technology

company can help make that determination

with its Combustion Module-Cavity Ring-

Down Spectrometer (CM-CRDS) device for

stable carbon isotopic analysis. According

to Picarro’s CEO Mike Woelk, the CM-CRDS

makes analysis push-button simple for com-

panies to verify the bioplastics composition

of polymers or finished materials throughout

the supply chain, whether on the factory floor

or at the distributor’s warehouse.

There are two massive cycles going on,

explains Woelk—the carbon cycle and water

cycle, and both CO2 and H

2O are very dynam-

ic molecules. “You can determine how CO2

moves in the universe and where it originat-

ed—shale gas, coal, [and] natural gas all have

a distinctive isotopic pattern. We measure it

as a family of molecules based on the carbon

that is in it,” Woelk says.

Previously, this type of measurement re-

quired expensive and disruptive testing in

specialized labs, but Picarro’s method gives

both plastic consumers and suppliers a tool to

ensure that bioplastics content claims can be

verified in minutes without disrupting ongo-

ing production.

To determine whether a material is bio-

plastic or “petroplastic,” the material is

burned, and the composition of the CO2 is

measured to determine where it originat-

ed. “There are very distinct signatures for

CO2—soy, corn, rice, etc.,” Woelk says. “We

make it easy—shop ready—so that you can

put a piece of plastic into the device and im-

mediately determine the material’s integrity

throughout the supply chain.”

Woelk agrees that there’s a lot of hype sur-

rounding bioplastic products, and added that

the manufacturers of medical devices, “regard-

less of their philosophical point of view,” want

to support their consumers’ buying preferenc-

es with respect to being eco-friendly. “How do

you know the truth? That’s what we provide

and it’s as simple as you can get,” Woelk states.

“What we’re talking about is analytical-grade

results as good as any technology in the world

can produce, and you don’t need to be a scien-

tist to do the work.”

This material analyzer helps companies determine whether packaging actually contains the bioplastic specified.

[See Bioplastics, page 11]

Where innovation takes flight

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10 | JULY 2010 mddionline.com

Underlining its ongoing commitment to the

medical device industry, Arkema (Colomb-

es, France) now offers specialized grades for

medical devices marketed as the Pebax MED

series of resins.

According to the supplier, these grades rep-

resent the highest quality of Pebax polymers for

medical applications, including devices exposed

short term to bodily fluids (<30 days). Effective

January 1, 2011, Arkema will no longer offer

standard-grade Pebax SA resins for any medical

applications. Pebax is a polyether block amide

thermoplastic elastomer that can be injection

molded or extruded.

Pebax resin has been a preferred material

in medical devices, such as minimally invasive

catheters for angioplasty, since the mid-1990s.

It has gained recognition over other elasto-

mers for its excellent flexibility, kink resistance,

torque transfer, low coefficient of friction, and

resistance to softening in the body.

Over recent years, however, the functional

and processing requirements for polymers have

become more rigorous. Arkema is introducing

this new Pebax grade as part of an ongoing

commitment to the medical industry, offering a

range of grades specifically intended for today’s

devices. “Our highest-quality Pebax MED resin

will be instrumental in helping OEMs meet

the growing demands of minimally invasive

and intravascular devices by improving product

performance and manufacturing yields,” says

Basker Lalgudi, Arkema’s North American medi-

cal market manager.

All Pebax MED resin grades have passed

USP Class VI biocompatibility testing and are

sterilizable by EtO, gamma, and steam, key

requirements for minimally invasive devices.

Pebax thermoplastic elastomer is manufac-

tured in the United States by Arkema Inc. (Phila-

delphia, PA) and marketed in North America

through its strategic partner Foster Corp., a

PolyMedex Discovery Group company (Putnam,

CT).—Stephen Moore

Elastomer Grades Tailored for Medical Devices

Eastman Opens Expanded Tritan Plant

pursue the new monomer and polymer, a

team led by Rutstrom pushed forward in

2005 with the simultaneous creation of the

monomer and polymer production tech-

nologies, as well as market development.

The goal was to commercially launch the

material by 2007 at the triennial K show in

October in Düsseldorf, Germany. The com-

pany reached that goal and announced its

intention to expand production, with those

plans coming to fruition in the form of the

newly inaugurated line.

Making all of this possible was the work

of a handful of researchers, building from

an investigation of a new monomer, tetram-

ethyl cyclobutanediol (TMCD), that began

in the late 1950s. At the time, Eastman

felt that the research could present a path

to a high-heat material. That work, led by

Robert Hasek, was eventually abandoned.

But in 2001, Emmett Crawford, a recently

hired research scientist, saw promise in the

monomer that Hasek had studied. Work-

ing with fellow researcher David Porter,

he started Eastman on the path that, after

much trial and error, would eventually lead

to Tritan.

Some 60 years prior, Crawford said a num-

ber of companies investigated TMCD, look-

ing for a method to produce polycarbonate

(PC) from it. Eastman’s interest stemmed in

part from how well the chemical fit within

its technology footprint. “The reason [East-

man] looked at it in the 1950s,” Crawford

said, “is it’s a great fit for our company,” on

the basis of the chemicals and intermedi-

ates Eastman produces in Kingsport. The

company has capacity in all of the elements

that make up Tritan, helping it better con-

Eastman Chemical Co. (Kingsport, TN)

marked another important milestone

in the whirlwind development of its Tritan

copolyester material with the May 13 open-

ing of a dedicated Tritan production plant

at its Tennessee headquarters.

“I’ve been in R&D most of my career, and

taking something from lab scale to com-

mercial scale when you have to simulta-

neously develop a new monomer, a new

polymer, and the market, it’s just…we had

no right to believe we could actually do that,

but we did,” explained Dante Rutstrom, vice

president and general manager, specialty

plastics business, at the plant opening.

Eastman officials hosted trade and area

press as well as local and regional govern-

ment officials to mark the occasion, show-

ing visitors the new production line, as well

as the array of now-commercial products

Tritan is used in. Including the original de-

velopmental line, Eastman now has more

than 30,000 tn/yr of capacity for Tritan co-

polyester, all in Kingsport. The supplier has

plans in place to double that capacity by

2011 should demand continue to expand

at its current pace. Eastman said that in the

past 12 months, Tritan business has qua-

drupled in dollar and volume terms, with

applications expanding beyond the initial

markets of reusable sports water bottles,

house wares, and small appliances, to now

include medical, infant care, bulk water,

and signage. Eastman did not disclose its

investment to date in the material’s launch.

Company officials said that technology

development began in earnest in 2004. After

presenting a plan at the corporate level to

Eastman’s dedicated Tritan production plant opened in May.

MD100702_010 10MD100702 010 10 7/2/10 8:49:19 AM7/2/10 8:49:19 AM

MOLDING TECHNOLOGIES JULY 2010 | 11

trol costs and production.

Pushing past the reluctance of some to

pursue TMCD on the basis of past failures,

Crawford successfully found a route to cre-

ate the monomer and a new copolyester

from it. He would eventually share his work

with Hasek, who had toiled with the mol-

ecule decades before.

Mark Costa, Eastman’s executive vice

president, specialty polymers, coatings, and

adhesives and chief marketing officer, said

Tritan’s rise has been fueled by concerns

about the safety of PC, and more impor-

tantly, its chemical forerunner, bisphenol

A (BPA). In the past, where its heritage

copolyesters could compete with acrylic,

vinyl, and some styrenics, Tritan’s proper-

ties enable it to target PC—a market that

has a global annual volume of 700,000 tn by

Eastman’s estimation. “So, 60,000 tn out of

a 700,000-tn/yr market leaves a lot of room

for additional build for us,” Costa said, “but

PC is a huge market, and lots of things like

optical media, we have no interest in and

won’t be pursuing.”

In order for Eastman to target PC replace-

ment, it understood early on that its con-

sumer safety credentials would need to be

well established. To that end, in addition to

its own testing for endocrine disruption and

estrogenic and testosterone activity, it has

completed independent third-party testing

of the material. “Even when we began, we

had a sense that we really want to go the

extra mile here in understanding the safety

of our materials and the monomers that go

into them,” Rutstrom said. Motioning to a

spot on the conference table, he added, “if

the letter of the law stops here, we want to

stop here,” dropping his hand farther along

the surface. —Tony Deligio

Bioplastics [continued from page 9]

The CM-CRDS is a tabletop unit that per-

forms a bulk specific isotope analysis and de-

livers isotopic carbon measurements of plas-

tics and other packaging materials in roughly

10 minutes. The CM-CRDS is designed to run

up to 147 plastic samples consecutively with-

out operator intervention, and with minimal

training and setup time. Woelk notes that

Picarro is in the very early stages of commer-

cialization of its technology, even though it

has been around for several years.

Picarro sees the regulatory environment

evolving as a result of the green movement,

“More regulations will evolve by hook or by

crook,” Woelk says. “I think people think that

these bioplastics markets are all big estab-

lished markets, but they’re not. There are

very few companies that are making any

money in the green space. And there are is-

sues surrounding bioplastics, such as com-

mingling bioplastics and petroplastics, that

contaminate the resin stream. It will be im-

portant for manufacturers to produce scien-

tific results to match the suppliers’ claims.”

—Clare Goldsberry MT

The company’s copolyester material has a surprisingly long history.

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A successfully validated process is

stable, dimensionally centered

within the required tolerance, and

minimizes rejects with significantly fewer

adjustments from run to run. The adop-

tion of process validation principles and

disciplines has proven beneficial for both

new and existing programs. It is essential,

however, to first establish an agreed-upon

procedure for the validation, known as the

installation, operation, and process qualifi-

cations or IQ/OQ/PQ. This should be done

in conjunction with the customer.

Early interaction identifies and resolves

areas of concern between the two parties. It

also details the equipment needed to manu-

facture, test, and measure product, and it de-

fines dimensional tolerances, molding tech-

nique, engineering studies, the substance of

the qualifications themselves, and the quali-

fication approval and acceptance criteria.

Typically, the desired acceptance criterion

for critical dimensions is a Cpk of ≥1.33 (see

the sidebar “Definitions“ on p. 13).

The IQ/OQ/PQ procedures are outlined

below. It’s important to note that the use of

all or any of these disciplines has proven ben-

eficial for process and dimensional control.

Installation QualificationThe purpose of IQ is to demonstrate that the

equipment and facility used to manufacture,

measure, or test the product is maintained

and calibrated as required. Additionally, it

affords the opportunity to benchmark spe-

cific installation and process conditions that

can prove valuable over the life of a mold-

ing program. For example, if a process isn’t

yielding the same dimensional stability after

months of run time, the problem could be

attributed to a number of circumstances,

including restricted water circuit flow, a dif-

ferent style of nozzle body or tip, the use of

similar but different equipment, etc.

All of these and other deviations can con-

tribute to process and dimensional varia-

tion, as well as instability. By documenting

the initial installation settings, fewer per-

sonnel will be needed to investigate and de-

termine the root cause of the rejects. More

importantly, satisfying customer delivery

and quality requirements will be much more

consistent.

When selecting the molding machine of

choice, keep in mind the following criteria:

■ Real-time closed loop technology (electric

molding machines have recently demon-

strated more consistent repeatability and

reduced cycle times).

■ The shot size of the screw should utilize

25–75% of barrel capacity (ideally, 33–

66%) to avoid minimal or excessive resi-

dence time, either of which can influence

process variation.

■ Machine tonnage should provide enough

clamping pressure to keep the mold fully

closed and prevent flash; typically 5–10

tn/in.3 of the projected area of the molded

part is adequate.

Cooling circuits in the mold should be

adequately sized to satisfy the Reynolds

equation for turbulent flow for good ther-

mal coefficient (typically 1.0 gpm of flow

for each 0.5 in. of cooling line is adequate.

See the sidebar, “Definitions.”). Additionally,

the cooling lines should be sized equally to

achieve balanced cooling.

The inspection area of the molded prod-

uct should be benchmarked for location

and lighting influence, as well as cleanli-

ness attributes, e.g., lumens, particulate in

ppm, etc. The equipment and techniques

used to inspect and accept product must be

calibrated and documented. Additionally, all

equipment used in the direct manufacture

of the product needs to be calibrated in ac-

cordance with ISO and GMP guidelines.

Operation Qualification OQ is at the heart of evaluating and defin-

ing the injection molding process. Through

the use of analytical processes, engineer-

ing studies, and statistical and dimensional

evaluations, one can identify areas of con-

cern that need to be addressed early in the

program. Examples might include a small

runner system that would limit pressure,

a part that won’t fill evenly, or less-than-

desirable aesthetics that might result from

shear, dimensional concerns, and so forth.

In these cases, the mold can be modified to

address the concerns before building a pro-

Medical Molding: How to Validate the Process Validating the injection molding process is no longer limited to medical device components. It is increasingly becoming a requirement throughout global industries.

ED STOCKDALE

A metrologist conducts first article inspections, which consist of the measurement of all dimensional calloutson the molded product part print.

VALIDATION

MD100702_012 12MD100702 012 12 7/2/10 8:52:05 AM7/2/10 8:52:05 AM

MOLDING TECHNOLOGIES JULY 2010 | 13

duction tool, thereby minimizing lead times

to production.

For a new molding program, it is benefi-

cial to perform process development and a

design of experiments (DOE) with a proto-

type mold prior to building a production

tool. The purpose of performing process de-

velopment is to minimize areas of the pro-

cess that cause variation, e.g., pressure limi-

tations, shear rates or viscosity variations,

inadequate changeover definition, proper

pack and holding pressures, and time. The

DOE defines which process attributes affect

specific dimensional responses, the influ-

ence on the response, and the interactions

between them. From the two studies, one

can confidently define an ideal process with

a predicted dimensional outcome.

Process development consists of a short-

shot study, in-mold rheology, a stability or cav-

ity-to-cavity balance run, gate-seal analysis,

and a pack-pressure study, as well as a DOE

and first article inspection (FAI). As a starting

point for these studies, use the resin manufac-

turer’s recommended process settings.

The short-shot study demonstrates that

the cavity or cavities fill evenly or balanced,

the injection pressure required to fill the part

approximately 95–99% (used for velocity-to-

pressure-changeover definition) is not lim-

ited due to the runner system in the mold,

and there are no mechanical issues that pre-

vent the mold from successfully cycling.

In-mold rheology defines the best shear

rate (injection rate) to minimize variation

during fill. This rate varies from one resin to

another and is influenced by the geometry

of the mold and cavities. A level shear rate

slope is more desirable and will exhibit less

variation than one on a sharp incline or de-

cline (see Figure 1).

A stability or cavity-to-cavity balance run

demonstrates that the process to the point

of velocity-to-pressure changeover is stable

and balanced. It also validates process capa-

bility through the use of Cp and Cpk relative

to the molding process itself (see the side-

bar, “Definitions”).

A gate seal or freeze study (holding and

pack time) confirms when the influence of

injection within the cavity and runner system

is complete. An improper gate-seal or freeze-

time setting can cause process variation or

add unnecessary additional cycle time.

The pack-pressure study identifies the

influence that the pack and holding pres-

sure have on dimensional characteristics. It

defines a proper pack-pressure process win-

dow and evaluates how the mold operates

under these conditions. Dimensional studies

are then necessary to evaluate these progres-

sive influences on the molded product.

Once the process window for each pro-

cess attribute has been defined, these set-

tings can be used to define the DOE. The

DOE defines the optimum process win-

dow and its respec-

tive influence on

each dimensional

response. A series

of experiments are

run, and the influ-

ences are evaluated

statistically. A DOE

prediction is made,

and an additional

run confirms that

the DOE predic-

tion is accurate and

defines the optimal dimensional process

window. These process limits will then be

challenged and evaluated. The challenges

consist of three different runs: low, high,

and nominal process challenge runs. Each

run is equal in run time and evaluated for

dimensional, functional, and cosmetic

considerations in relation to the product

specifications and tolerance. The results

may demonstrate conditions that do not

meet the desired acceptance criteria, in

which case the process, tolerance, mold,

or specification needs to be modified and,

if necessary, the processes rerun to verify

conformance.

Beyond process development and DOE,

an in-mold cavity pressure transducer

equipped with a temperature sensor can

also be beneficial. This equipment illus-

trates and defines proper velocity-to-cavity

pressure settings and cooling time (see Fig-

ures 2 and 3, p. 14). The sensor and transduc-

er combination minimizes the difference in

cavity pressure between the beginning and

end of fill, thereby reducing in-mold stresses

while enhancing dimensional and product

stability. Recent studies comparing process

variation both with and without the use of a

sensor and transducer demonstrated a pro-

cess and dimensional stability improvement

A measuring machine is adjacent to its medical molding cell to minimize the time required for first article inspections on new medical molding programs.

HighProcess

Limit

Ap

pa

ren

t Vis

co

sity

PA

.S

0.5 0.6 0.7 1.0 1.1 1.20.3597264726972747279728472897294729972

1197210472

119721247212972

0.4 0.8 0.9

Low

Normal

Shear Rate, 1/s

Figure 1. Defining proper In-mold rheology process window.

DefinitionsThe following terms are commonly used in

validating molding processes.

4.1 Cp: Estimates what the process would

be capable of producing if it could be centered

in tolerance. Assumes that the process output

is normally distributed. Cp demonstrates that

the process is in control without respect to the

present dimensional tolerance, so tolerance

can be adjusted with confidence.

4.2 Cpk: A globally recognized measure-

ment of the process capability index or sta-

tistical prediction of potential product at risk

that could be out of dimensional tolerance.

Based on (4) sigma (standard deviation), a

Cpk of ≥1.33 is the commonly recognized ac-

ceptance specification for medical devices.

This means that 63 of every million parts

produced (ppm) are at risk of potentially being

out of dimensional tolerance (99.99%). A Cpk

of ≥1.67 based on (5) sigma potentially yields

a process that is at risk of producing one part

out of tolerance specification for every ppm

or 99.9999%. The benefit of these disciplines

is realized through the reduction of potential

risk of out-of-tolerance product, fewer assem-

bly issues with mating components, and less

scrap and down time due to rejects.

4.3 Reynolds number equation: The

measure and calculation of turbulent flow,

which translates into thermal heat transfer

or cooling.

MD100702_013 13MD100702 013 13 7/2/10 8:52:10 AM7/2/10 8:52:10 AM

14 | JULY 2010 mddionline.com

VALIDATION

of greater than 50% over time when the sen-

sor and transducer combination was used

(see Figure 3).

First Article Inspection An FAI consists of the measurement of all di-

mensional callouts on the molded product

part print. Typically two samples are taken

from the nominal process run or from the

DOE conformation run and submitted to

metrology for measurement. The dimen-

sional results are evaluated by the customer

and for conformity.

It is common to find out-of-specification

conditions, which need to be evaluated for

significance, followed by corrective action.

Usually this requires a dimensional change

on the part print or a tooling modification.

Once the FAI is approved by the customer,

process qualification begins.

Process Failure Effects and Mode Analysis (pFEMA)Depending on the end-use of the product, a

pFEMA may be conducted to identify poten-

tial areas of concern. There may be specific

critical dimensions, for example, that need to

be monitored closely, because if even one is

out of specification periodically, it may cause

significant failure or risk with the product.

Potential risks and safeguards are there-

fore assigned to these areas, e.g., special

measurement devices or equipment, 100%

inspection, etc., to ensure that product of

this nature is appropriately rejected.

Process QualificationPQ demonstrates that the process is stable

and dimensionally capable and that it produc-

es a molded part that meets the customer’s

expectations. Typically, PQ is accomplished

by running the defined or nominal process

through three separate runs. These runs are

a simulation of three separate production

runs and should be a minimum of four hours

in length for each run with a shutdown pe-

riod between each run. Additionally, three

different lots of resins should be used dur-

ing the PQ, which represents actual molding

conditions and variation over time. Samples

should be taken at even intervals through-

out each run, labeled sequentially, and then

submitted to metrology for measurement

and conformity. Once the PQ and FAI have

been approved, these samples should be kept

for the life of the program for reference. This

retaining policy helps with answering ques-

tions as programs develop and transition.

If the PQ is unsuccessful and the molded

part does not meet customer expectations,

the root cause needs

to be evaluated

and the two parties

must work together

to define and accept

a resolution.

The qualification

of spare mold or

tooling components

directly related to

the molded part,

e.g., spare core pins,

lifters, etc., should

be evaluated and

validated so that they are readily available

if needed. Typically, the spare part or com-

ponent validation process consists of one

similar PQ run that demonstrates accept-

able capability.

Other ConsiderationsDocument Control and Process Docu-

mentation. The ongoing documentation of

the process needs to be maintained in a con-

trolled environment in accordance with ISO

13485 standards. This is essential in main-

taining and ensuring that the same process

is run from one run to another.

Variation versus Profitability. The use

of these analytical and engineering concepts

will stabilize process and dimensions, as well

as profitability. It’s worth noting, however,

that sufficient resources and specific equip-

ment are necessary to successfully incorpo-

rate these concepts into a business strategy.

Resource requirements include management

staff; process, quality, and tooling engineers;

process technicians; metrologists; and tool-

ing personnel experienced in Cp/Cpk disci-

plines and tight- tolerance molding. Specific

equipment needs include well-maintained

peripherals and molding machines, check

ring and barrel assemblies capable of hold-

ing a molding process to a tight tolerance,

coordinate measurement machine and vi-

sion system equipment for measuring tight

geometric dimension and tolerance profiles,

and tool room equipment.

The business approach that integrates

process validation touches many areas of the

company, so the company’s commitment to

the process is essential to its success. And

while significant investment is required, it is

recouped through stable molding programs

where profitability is maintained over time.

Ed Stockdale is a process engineer for Mack-

Medical/Mack Molding Co. (Arlington, VT). 2

A technician defines the optimal dimensional process window for a DOE.

46.75

44.7

5 A

ng

le

Serial #

43.75

42.75

44.75

45.75

1 6 11 16 21 26 31

With Psi Tranducer

Upper Control (UCL)Lower Control Limit (LCL)

With out Psi TranducerNominal

Without Transducer

Poor Cpk (.683)

WithTransducer

Good Cpk (8.75)

Figure 3. Typical cavity pressure transducer (with and without a sensor ).

80

70

30 1-1

17-1

40

90

100

50

60

CavityTemperature

CavityPressure

CavityTemperature

Stable

Gate SealedY1-1

Y17-2

Sca

le (%

)

Figure 2. In-mold pressure transducer and temperature sensor application.

MD100702_014 14MD100702 014 14 7/2/10 8:52:16 AM7/2/10 8:52:16 AM

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MOLDING TECHNOLOGIES JULY 2010 | 17

CLEANROOMS

C leanroom molding is essential

for serving the medical segment,

and various options exist for

manufacturing anything from discrete

components to complex assemblies in

a pristine environment. So what clean-

room alternative should you choose?

It very much depends on your application

and business strategy.

What may appear to be the simplest so-

lution to medical molding is to locate the

entire machine in a cleanroom. This is best

suited for molders that are operating several

machines under cleanroom conditions and

need to integrate large assembly systems

into the cleanroom concept, according to

Jochen Hirt, application department man-

ager at Arburg (Shanghai) Co. However, this

solution can only obtain ISO 7 standard at

best, which is essentially equivalent to the

Class 10,000 U.S. federal standard typically

required as a minimum for cleanroom mold-

ing. Good manufacturing practice (GMP)

standards are generally also required for

cleanroom molding, and these specify maxi-

mum bacterial count in addition to particle

count. GMP Level C equates to ISO 7.

One issue with the fully integrated ap-

proach is, “If the cleanroom malfunctions

and air quality is adversely affected, you

have to shut down all your machines,” says

Jack Liu, application engineering manager

at Demag Plastics Machinery (Ningbo) Co.

Ltd. A more flexible and lower-cost method

is to enclose only the mold space in a clean-

room environment by installing a laminar

flow element on top of the machine’s clamp-

ing end. The clean air module is mounted on A laminar flow box mounted over the mold area keeps molded parts clean while removing many contaminant sources from the clean area.

Robotic part placement onto a covered conveyor

enables transfer of fragile parts to a

separate cleanroom for postprocess operations.

Keeping It Clean Which cleanroom

option is best? Well, that depends.

STEPHEN MOORE

MD100702_017 17MD100702 017 17 7/2/10 8:54:40 AM7/2/10 8:54:40 AM

18 | JULY 2010 mddionline.com

CLEANROOMS

a traveling frame above the clamping unit,

allowing easy mold installation from above.

In its simplest form, parts are molded in

this miniature cleanroom area and dropped

onto a covered conveyor that then trans-

ports them to a cleanroom attachment for

robotic or manual assembly and packing.

“Being much smaller, ISO 5 is attainable in

this attachment,” says Liu.

With this modular clean air hood tech-

nique, the ambient air is drawn in via radial

fans and clean air is produced via a prefilter

and a suspended matter filter (HEPA H14).

An integrated ionization module produces

ionized air, which ensures the neutraliza-

tion of electrically charged components.

This reduces electrostatic charging of the

molded parts. Through the permanent air

flow, a high level of air circulation is ensured

within the clamping unit. The fan also cre-

ates an overpressure in the interior of the

mold, which effectively prevents the pen-

etration of particles from the ambient air.

Needless to say, for fragile parts that

might be damaged by free-fall and a sorter

flap, robotic takeout is essential. The clean-

room area must therefore be expanded to en-

compass the robot and conveyor placement

area. Arburg’s offering for this situation is a

cleanroom production cell with its Multilift H

horizontally operating robotic system.

KraussMaffei Technologies GmbH (Mu-

nich) has a different take on this option in

that the robot accesses the mold space from

an adjacent cleanroom. The overpressure in

the white room causes the clean air to flow

through the tunnel and flow out through

the chute on the injection machine. The

production area is isolated from the rest of

the machine. This solution achieves ISO 6/7

standards.

Room in a RoomKraussMaffei also offers a room-in-room

option whereby the clamping end of the

machine protrudes into a sealed clean-

room. This option can cater to cleanliness

up to the ISO 5 standard. For mold chang-

ing, service, and repairs, the machine is

retracted on rails until the clamp is in the

gray room area and the white room is com-

pletely sealed off by a second metal plate at

the front of the clamp end.

This option was adopted by Rexam

Pharma GmbH (Neuenburg, Germany) for

molding vials from cyclic olefin co polymer

(COC) with TPE closures for injectables.

The ready-to-fill vials leave the cleanroom

closed and packed. Thomas Hörl, who over-

sees product and technology management

at KraussMaffei, notes that when mold-

ing takes place under GMP Class B (ISO 5)

conditions, the surrounding gray room area

should be at least GMP Class C (ISO 7). Pro-

duction in a Class 5 cleanroom makes post-

mold cleaning or sterilization unnecessary

in many applications, although it may be

stipulated by end-users.

Demag’s decentralized method for in-

corporating an injection machine plus

automation into a cleanroom is dubbed a

cleanroom cabinet with roof construction.

Takeout, assembly, and packing are carried

out under an ISO 7 environment. The ma-

chine may also be enclosed in the cabinet

in its entirety.

Using a decentralized approach, Arburg’s

Hirt says that newcomers to cleanroom

molding can benefit in that they can start

with just one machine and add cleanroom

capacity as they go. “If individual machines

are temporarily not required for cleanroom

production, they may be undocked to pro-

duce standard parts,” he adds.

Cleanroom-Customized MachinesWorkers are the main source of particulate

contaminants, accounting for around 40%

of emissions in a cleanroom, and removing

them from the equation, or at least minimiz-

ing their presence, goes a long way toward

eliminating particles. The next largest source

on the list is the injection machine itself, and

here, various techniques exist to minimize

contamination. While Demag’s Liu says

that fully hydraulic machines are capable of

achieving ISO 7 standards when contained in

cleanrooms, all-electric machines can oper-

ISO 7-standard cleanrooms can be sufficient for medical molding tasks.

KraussMaffei’s room-in-room approach minimizes the volume of work area held at high cleanroom level, while facilitating machine servicing and toll changes.

MD100702_018 18MD100702 018 18 7/2/10 8:54:46 AM7/2/10 8:54:46 AM

MOLDING TECHNOLOGIES JULY 2010 | 19

ate at up to ISO 5 standards if water-cooled.

“Fan cooling is not as good for cleanroom

environments, although ISO 6 is technically

achievable,” says Liu, who adds that direct

drive is also preferable over belt drive. An-

tistat metal coatings and PVC coatings for

mobile elements are also employed, while

use of perforated metal sheet minimizes air

turbulence in the mold space.

“During production under cleanroom

conditions, it is very important that the [hy-

draulic] machine can be cleaned easily,” says

Arburg’s Hirt. “For this purpose, the dis-

tributor manifolds of the hydraulic circuit

can be contained in a powder-coated sheet

metal housing located at the machine base.

This allows the injection molding machine

to be kept clean much more effectively.” Fur-

ther, raising the machine by 100 mm using

antivibration pads makes cleaning under

the machine considerably easier.

Closer to the tool, multiple cooling cir-

cuits can be routed directly to the fixed or

moving mold platen for the mold cooling.

“This tidy routing prevents unnecessary

trailing of the hoses,” says Hirt. Powder

coating is also used throughout Arburg ma-

chines for wear and scratch resistance. Hirt

insists that a properly configured hydraulic

machine can run in a cleanroom equally as

well as a hybrid or all-electric machine.

KraussMaffei recommends its EX Series

all-electric machines for medical molding

applications. The Z-toggle has only eight

pivot points, all of which are lubricated

with completely encapsulated circulating

oil. All drives are water-cooled, and plas-

ticating and injection are driven by two

coupled direct drives.

Stephen Moore is senior editor of Modern

Plastics Worldwide. MT

In this cleanroom variant, parts are molded in a laminar flow clean area, and then drop onto a covered conveyor for transport to a separate cleanroom.

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MD100702_019 19MD100702 019 19 7/2/10 8:54:55 AM7/2/10 8:54:55 AM

20 | JULY 2010 mddionline.com

COMPLEX INJECTION MOLDING

C omplex injection molding repre-

sents a direct route to competi-

tive differentiation. It provides

the design freedom and process efficiency

required to create new features and incor-

porate new technologies as quickly and

cost-eff ectively as possible.

Complex injection molding is defined

by simultaneous complexity in four criti-

cal areas: part design, mold design, mate-

rial selection, and process control. To make

successful medical products, OEMs should

choose a molding partner that can offer

them expert guidance in these areas. This

article explores when to address pertinent

molding considerations in complex injec-

tion molding.

Why Use Complex Injection Molding?With complex injection molding, additional

materials—from dissimilar polymers to

metal components and other nonplastics—

can be integrated during molding. These

materials and features are combined in

the molding process to facilitate assembly

by adding metal inserts, threading for fas-

teners, and incorporating elements such

as lenses. Such features can also optimize

function by creating waterproof seals and

increasing durability.

Improving aesthetics can also drive the

decision to use complex molding. For ex-

ample, some OEMs may want to color a

polymer to make the device more appealing

to patients—notably in pediatric applica-

tions—or, they may want to integrate deco-

rative elements such as metal flake, gloss, or

some other proprietary pattern. Such visual

uniqueness can differentiate products with-

in a manufacturing line or separate them

from the competition.

In addition to streamlining production

and reducing costs, incorporating a deco-

ration or functional item into the injection

process improves quality. Machine-paced

production always yields higher quality

product by eliminating or greatly reducing

human involvement and inconsistency. It

also reduces potential process variances

introduced by secondary machining or

joining operations. Just as important,

complex molding yields more predictable

quality because manufacturers are able to

maintain consistency no matter how many

units are produced, ensuring that tight

tolerances are met and sterility is always

maintained.

Furthermore, the medical market is sub-

ject to regulatory compliance demands

from organizations such as FDA that dic-

tate the validation requirements for all

physical, chemical, and compositional

aspects of medical products. Regulatory

control of implanted devices is especially

critical, for example, because these types of

products carry the greatest risks. Complex

injection molding addresses the design and

production challenges posed by such strict

controls.

Part Design ConsiderationsMany of the crucial decisions involved in

complex injection molding should be made

as early as possible in the design phase,

when adjustments can be made without

a significant effect on the total costs and

product timeline. For example, the place-

ment of ejector pins and gating—the point

where the plastic enters the mold—is

Complex Injection Molding for Competitive AdvantageWith careful planning, complex injection molding can result in reduced costs, optimized function, and improved aesthetics.

DAVE ROBINSON

Decisions regarding each part’s unique cosmetic, functional, and volume characteristics should be made as early as possible in the design phase.

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MOLDING TECHNOLOGIES JULY 2010 | 21

critical aesthetically and stylistically. A vis-

ible knit line, where the flow fronts of the

molten material meet, may be objection-

able to the customer. If such marks cannot

be strategically located to a place on the

part where they will not be visible, they can

sometimes be disguised by texturing the

mold. Either way, the part designer must

plan for them.

If multiple materials are to be used, the

polymers must be chosen carefully for com-

patibility to ensure a permanent chemical

bond. Different plastics undergo thermal

expansion at different temperatures, and

any incompatibility can become a serious

issue. For example, polysulfone, a polymer

commonly used in medical applications,

will not bond with polypropylene, which in

turn bonds weakly with nylon, styrenic, and

urethane-based elastomers.

Process complexity is added when a part

requires metal inserts or pass-through cor-

ing. For example, the metal elements being

added to a mold often require preheating to

reduce thermal shock, improve retention

properties, and prevent flash—thin, sharp,

or unsightly areas that can form in the pass-

throughs due to stress (e.g., molten plastic

meeting cold metal fasteners) during the

molding process. The presence of flash can

have an adverse effect on the performance

of the product or require secondary opera-

tions to be removed.

All of these issues highlight the impor-

tance of a robust part design that antici-

pates possible problems with complex in-

jection molding and prevents them through

thoughtful planning. A careless part design

can lead to weak points, aesthetic flaws, or

overall part failure.

A robust part doesn’t just meet the origi-

nal requirements its designer intended; it

also stands up to the wear and tear—or

even abuse—it is subjected to during daily

use. For example, many medical devices

are moved often, from room to room or

even between ambulances and hospitals,

so they must be designed and built to with-

stand the jostling and bumping that ac-

companies such use. Aesthetically, a device

must maintain its appearance. This means

no fading, hazing, or yellowing of the plas-

tic after exposure to sun, fluorescent light-

ing, chemicals, or other potentially harsh

elements.

Mold Design Considerations The development of the mold or tool is the

heart of the injection molding process, the

stage from which everything else flows. The

ultimate success of the part is determined

when the engineering team designs, cre-

ates, and maintains the mold—accounting

for the materials to be used and the quan-

tity of the item to be produced. Poor choices

in any aspect of the mold development pro-

cess ultimately results in poor products, re-

gardless of part design, material choice, or

process control.

The type and durability expectations for

a mold determine which material is used to

make it. For example, aluminum is relatively

inexpensive and easily machined but it of-

fers limited longevity. Therefore, it should

be used only for small and finite produc-

tion runs—a rare case in medical device

applications. As a result, molds for medical

applications are nearly always steel. They

can range from soft steels used for simple,

single-cavity prototype molds with smaller

runs to hardened steels used for complex,

multicavity molds to support greater pro-

duction volumes.

Because medical device production leans

toward high volume and high complexity,

these requirements increase the importance

of selecting the proper steel for building the

tool. The determining factors are based di-

rectly on the goals and expectations of the

project, ranging from total quantity sought

to the finish quality needed. Budgets for

both time and cost can influence material

choice as well (see Table I).

Softer metals, such as P20 steel and

aluminum, are easily machined and there-

fore less costly to mold. However, because

they are prone to wear faster, they are

less commonly used in medical device

manufacturing.

Stainless steel is an appropriate tool steel

for medical applications because it resists

corrosion, pitting, and wear while sup-

porting the smooth finishes required for

cleanliness in a medical setting. In general,

the harder the steel, the more effort and ex-

penditure is required. Each additional step

used to create the mold drives up time and

cost. But these harder steel molds also last

An OEM’s evaluation process for a complex injection molder should include a site visit to assess the quality of the plant’s environment and personnel.

<10,000 10,000—200,000 200,000—1 MM

Aluminum X

P-20 X X X

Tool steel (various grades) X X

Table I. Rules of thumb for material choices are based on project volume requirements.

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22 | JULY 2010 mddionline.com

COMPLEX INJECTION MOLDING

considerably longer and return high-quality

parts with consistency.

Other steels used for complex injection

molding medical devices and equipment

include high-carbon varieties, such as

H13. These varieties contains a negligible

amount of impurities—an important fac-

tor in heat treating—and are economical

to purchase in larger sizes. See Table II

for a breakdown of types of steel and their

characteristics.

Corrosion resistance in a mold is es-

pecially important with the use of ma-

terials that have a high degree of acid-

ity. These materials include resins in

the PVC family or those with certain

added agents, such as flame retar dants,

which are often required to meet the

UL standards for resins used in medical de-

vice manufacturing.

Materials ConsiderationsJust as important as selecting the

material for the mold is choosing

the material for the part. Deter-

mining the proper material for

a complex injection molding

application should begin with

a discussion between the plas-

tics engineer and the OEM.

This decision requires informa-

tion about five defining factors

(outlined below), as well as any

outstanding special needs, such

as the frequency and method of

sterilization.

Physical Load. The impact

expectations of the part must be

determined so that it will stand

up to the conditions of everyday

use without fatigue. Any degrada-

tion can lead to life-threatening

part failure.

Mechanical Function. The

particular polymer must be right for its ap-

plication. For example, a part of a surgical

device that holds a blade must be made

from a polymer with appropriate stiffness.

Thermal. Exposure to fluctuating and

extreme temperatures must be accounted

for. Most medical devices are kept indoors,

but some portable devices or ambulance

equipment may be exposed to extreme heat

or cold. Polymers must be chosen to endure

such conditions.

Environmental. Consider whether the

device will be implanted or used in direct

contact with bodily fluids. If so, the poly-

mers must be biocompatible in accordance

with FDA regulations (as well as further

testing requirements depending on the

device).

Chemical. Exposure to chemicals is also

a factor. Most hospital-grade disinfectants

are strong formulas, often in an alcohol

base. Plastics chosen for the exposed parts

of a device must stand up to their composi-

tion without breaking down. Certainty that

a part will be exposed to chemical steriliza-

tion will limit the list of polymer options,

as will applications in which medications

will be transmitted via plastic parts and

tubing.

Sterilization is another factor to con-

sider. Many medical devices must with-

stand regular sterilization treatment by

radiation, chemicals, or the high heat and

steam of autoclaving. Table III shows some

common material choices that steriliza-

tion requires.

The need to mold dissimilar plastics also

plays a role in material selection. One of the

most common complex injection molding

techniques used in medical device manu-

facturing is the multishot method, which

is required to add soft polymers for ergo-

nomic and waterproofing features (such

as keypads, grips, protective bumpers, and

seals) over a hard plastic substrate, as in an

impact-resistant device body. Other times,

overmolding of silicone tubing may be

required.

By accomplishing these steps during

molding, manufacturers eliminate costly

and inefficient secondary steps from the

production process. It can also result in

higher quality because the material it-

self can be monitored during production

through cavity pressure feedback—a pres-

sure reading of the resin as it is going into

the mold. The feedback provides data on

the consistency of the pressure and where

correction is needed. Causes for inconsis-

tent pressure include a change in the vis-

cosity of the molten material.

The mold and the process must be de-

signed to suit the part and materials. No

medical OEM would tolerate a soft-touch

keypad separating from one of its handheld

monitoring devices during use. Nor would

it accept a waterproof seal failing because

materials were improperly selected or the

process to manufacture it was not expertly

designed.

The last material concern of importance

is whether a project requires high-heat

resins. The high-heat resins such as poly-

sulfone, which are required to withstand

autoclaving, have their own set of process

considerations. These materials are more

difficult—and therefore more costly—to

work with, mainly due to their high melting

points, which complicates everything from

safety concerns to the molding process.

Type of Steel General Use Criteria

S-7 General all-purpose, heat-treatable tough steel. Normal wear resistance.

A-2General all-purpose, heat-treatable hard steel. Higher wear resistance and less

toughness.

D-2 High-wear applications.

420 SS Medium wear resistance, high polish, corrosion resistant, not as hard.

H-13 Medium wear resistance. Can be nitrided for surface lubricity with flex strength.

Table II. A profile of the different types of steel that can be used to make a mold.

The high-heat resins required to withstand autoclaving require specialized oil heating equipment to bring the molds to temperatures in excess of 325°F.

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MOLDING TECHNOLOGIES JULY 2010 | 23

As an example, polysulfone has a melting

point of 700°F versus 500°–550°F for typical

resins. Oil, rather than water, must be used

to control mold cooling, requiring a longer

molding process and different equipment—

with different risks involved. Heating oil

also takes longer and metal-braided hosing

must be used as opposed to rubber. These

higher demands mean higher risks for both

safety and deviation. Because the mold

itself can reach 325°F (whereas a water-

heated mold typically reaches 180°F), it is

subject to higher levels of thermal expan-

sion, which adds complexity to the overall

mold design process.

Supplier Considerations The importance of selecting the right

manufacturing partner increases in di-

rect proportion to the complexity of the

task at hand. With all that is at stake in

the medical device industry, the OEM’s

evaluation process should be rigorous.

The process should cover every aspect

of a partner’s operations, equipment,

personnel, track record, culture, and fi-

nancial health. A site visit should also be

part of this process because it provides

the best method for assessing the quality

of the supplier’s plants environment and

personnel.

ConclusionComplex injection molding can provide a

medical device and equipment manufac-

turer with competitive differentiation, but

it requires highly specialized equipment,

skills, and engineering expertise. OEMs

that take advantage of the complex injec-

tion molding process can enjoy the ben-

efits of high-quality parts and devices with

optimal efficiency and low total production

costs.

Dave Robinson is vice president of engi-

neering at Kaysun Corp. in Manitowoc,

WI. MT

Method Amorphous Polymers Semicrystalline Polymers

Autoclaving

Polyphenylsulfone (PPSU) offers best resistance.Polycarbonate and polysulfone can withstand finite

number of cycles.Acrylonitrile butadiene styrene (ABS) and polyester

should not be autoclaved.

Polyether ether ketone (PEEK) offers best resistance.Polyamides and polypropylene can withstand finite number of

cycles. Some polyethylenes can withstand shorter cycles at lower

temperatures. Polyethylene terephthalate (PET) should not be autoclaved.

Chemical (ethylene oxide) Withstand very well. Withstand very well.

Radiation Most withstand well; polycarbonates will discolor. Most withstand well.

Table III. Certain polymers are better suited for specific sterilization treatments.

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MD100702_023 23MD100702 023 23 7/2/10 8:56:32 AM7/2/10 8:56:32 AM

24 | JULY 2010 mddionline.com

SOFTWARE MODELING

M ost modern mold filling simu-

lation software uses some type

of solid or shell element mesh to

define the part geometry. These range from

simple midplane element models meshed

with 2-D shells to 2 ½-D surface meshing

strategies.

Increasingly, some of the high-end soft-

ware packages are using full 3-D elements.

With few exceptions, these codes almost

exclusively use four-noded tetrahedral el-

ements—not always the best choice when

modeling fluid behavior.

As the fundamental physics of mold fill-

ing simulation is really a fluid flow problem,

several codes are now commercially avail-

able that use the finite volume method as

opposed to the more common finite ele-

ment method.

Finite Element versus Finite VolumeMost mold flow simulation is finite ele-

ment based, a technology made popular in

structural analysis codes. Some of the newer

codes, such as Moldex3D, are finite volume.

There is a significant difference in how these

tools work.

The finite volume method differs in that

the mesh grid nodes and integration points

are fixed, and the fluid moves within the

fixed mesh grid. In the finite element meth-

od, the mesh grid points actually move,

simulating the flow behavior.

There are pros and cons to both ap-

proaches, the main practical advantage

of finite volume codes being the accuracy

of the solution for fluid flow and the speed

with which you can get a solution. Finite ele-

ment codes tend to be computationally ex-

pensive, as a large mesh can create inordi-

nately large numbers of nodes, all of which

must translate to simulate the flow behav-

ior. Typically, the finite element method is

more stable, and provides better results for

those primarily interested in stress tensor

outputs, such as in structural analysis. Fi-

nite volume codes are useful for fluid and

gas flow problems, and are used extensively

in CFD codes.

The speed advantage inherent in finite

volume codes is significant for simulating

thermoplastic flow when using full 3-D ele-

ments, because it is necessary to create large

numbers of elements to accurately capture

the part geometry. For example, a good rule

of thumb is to provide a mesh density of at

Using Finite Volume Models in Mold Filling SimulationsFinite volume simulation can increase accuracy in models.

JOHN COGGER

Figure 1. 2 ½-D element filling simulation.

Figure 2. High-order 3-D element filling simulation.

Figure 3. High-order 3-D elements with gate modeled.

Figure 5. A cutaway shows inner mesh resolution.

Figure 4. High-order 3-D elements, hybrid mesh hexahedrals with tetrahedrals.

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MOLDING TECHNOLOGIES JULY 2010 | 25

least three 3-D elements spanning the cross

section of a wall thickness. Propagated over

even a small part, this can create element

counts in the hundreds of thousands, which

can make it difficult to get timely solutions.

Larger parts can and do create 3-D element

counts in the millions.

The use of finite volume technologies

can substantially reduce the solution

time to run these types of mold fill simu-

lations. These jobs are very large, and the

Moldex3D solver allows for parallel pro-

cessing (we typically use an eight-core

machine) to get a solution of a model this

size in a few hours. Such a large model may

not even run on a finite element solver,

and many mold filling codes do not sup-

port parallel processing.

High-Density 3-D Elements. Armed

with a high-performance finite volume

solver, we can now use high-quality 3-D el-

ements to model plastic f low, and get solu-

tions in minutes or hours instead of days,

with high-fidelity results. Figure 1 shows

a mold filling analysis using typical 2 ½-D

fusion elements, while Figure 2 shows the

Figure 6. High-order boundary layer elements used with solid tetrahedrals.

Figure 7. Predicted results in the simulation.Figure 8. Actual molded part results (short shot).

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26 | JULY 2010 mddionline.com

SOFTWARE MODELING

same part using high-order 3-D elements in

a finite volume solver. The differences are

dramatic. With computationally efficient

finite volume solvers, we can also expand

our element library to include higher-order

elements, such as hexahedrals, to capture

much more accurate fluid flow behavior.

Drilling into the mesh resolution, we can

see a typical high-order mesh in Figures 3,

4, and 5 (p. 22). Note that these mesh struc-

tures are a hybrid of several element types.

In addition to using these types of hybrid

meshes, we can combine these methods

into a boundary layer strategy, allowing

higher-order elements to be used on the

part bounding surfaces and lower-order

3-D elements to be used in the part interior

for better resolution of temperature effects

on the critical boundary layer. An example

can be seen in Figure 6 (p. 23).

Gate/Runner Modeling. One of the

most important parts of mold filling sim-

ulation is the gate and runner modeling.

This is an area that is often overly simpli-

fied by software applications, and poor

accuracy here can negatively influence

results. Best results can be achieved using

high-order 3-D elements in the gate and

runners as well as in

the part geometry.

Results Correla-

tion. One of the best

ways to validate the pre-

dicted results of a mold

flow is to compare with

a short shot study after

the fact (Figures 7-9).

Fiber Orientation

and Postprocessing.

One of the more inter-

esting aspects of this

type of analysis is the

ability to import mold

filling analysis results

into structural analysis software for more

realistic loads analysis. Most structural

finite element analysis uses the flawed as-

sumption that thermoplastics are isotropic

(uniform material properties) and therefore

cannot accommodate the effects of molding

on structural part performance. This can

lead to unanticipated part failures when

weld lines, material flow lines, and part den-

sity changes occur in highly loaded areas.

When the mold filling solver runs the

warp load case in a typical molding simu-

lation, we (automatically) convert to the

finite element method, as we are now inter-

ested in finite strains and residual stresses

to predict warp accurately. This output file

can then be used as an initial condition for

a structural FEA, bringing along the follow-

ing attributes:

■ Fiber orientation.

■ Material density variations.

■ Residual stresses (f low and thermally

induced).

■ Initial strain.

ConclusionThese attributes are critical to under-

standing the part performance when

structural loads are applied. When cou-

pled with orthotropic or anisotropic mate-

rial data, accurate structural FEA can be

performed on injection molded parts. Fig-

ure 10 depicts a cross section of a molding

simulation showing fiber orientation of a

glass-filled part, while Figures 11 and 12

show the warp prediction with and with-

out consideration of fiber orientation.

John Cogger is president of Innova Engineer-

ing Inc. (Irvine, CA). MT Figure 12. Typical fiber warp results plot without fiber orientation.

Figure 11. Typical fiber warp results plot with fiber orientation.

Figure 10. Typical fiber orientation plot.

Figure 9a (left) and 9b. Predicted results versus actual short shots.

MD100702_026 26MD100702 026 26 7/2/10 9:19:52 AM7/2/10 9:19:52 AM

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28 | JULY 2010 mddionline.com

MATERIALS ANALYSIS

M ost medical device manufac-

turers know the importance

of putting a product through

rigorous cleaning and testing before it is

released into the market. Standard sterility

and biocompatibility tests are an essential

part of manufacturing protocols. However,

some manufacturers may not fully under-

stand the different ways a product can be

contaminated during the production, pack-

aging, and cleaning processes. To avoid

detrimental contamination, manufacturers

should test their devices, including those

made via injection molding, using residual

manufacturing materials (RMM) analysis.

The Basics of RMM AnalysisAny contaminants such

as oils, lubricants, releas-

ing agents, and detergents

transferred to the product

during the manufactur-

ing or cleaning process are

RMM. From extracting the

device out of the mold to

cleaning and packaging,

device contamination can

occur just about anywhere

along the production pro-

cess. Those residues that

remain on a product can be

potentially cytotoxic and

harmful, particularly for de-

vices implanted inside the

body. For example, a metal

device may be designed

to integrate with a patient’s bone, but oils

remaining on the metal could reduce new

bone growth or inhibit integration, causing

the device to be ineffective or unsafe.

RMM analysis quantifies the residuals on

the device and identifies them. It establishes

a baseline against which manufacturers can

discover if the amount of residuals changes

as they improve their assembly process.

Manufacturers can use RMM analysis

as a tool to monitor the cleanliness of pro-

duction at any point, including the final

product. Knowing how much residue is on

a device or component allows for the estab-

lishment of effective cleaning procedures

that are crucial to the release of clean and

safe medical devices.

RMM analysis uses three methods to

evaluate the different phases of manufac-

turing and cleaning—gravimetric analy-

sis, total organic carbon (TOC) analysis,

and detergent residual analysis by ultra-

violet/visible (UV/VIS) spectroscopy. All

three tests are quantitative and designed

to remove surface contamination but are

not intended to remove or assess leachable

components from a device. The assess-

ment from these tests can be used to de-

termine cleaning efficiency as well as aid

in the validations of cleaning and rinsing

methods.

Gravimetric Analysis

(ASTM F2459-05). Quantify-

ing extractible residue by gravi-

metric analysis involves using

aqueous and nonaqueous sol-

vents to extract contaminants

such as oils, salts, and other

materials from the surface of

medical devices.1 After the de-

vice is extracted, the solvent

is evaporated and the remain-

ing residuals are weighed and

quantified. Gravimetric analy-

sis does not determine the

specific elements making up

the residue, but it measures the

quantity of the total amount of

residue coming off the device.

If the analysis quantifies

significant residue, the labo-

ratory may also identify, or

qualify, residue by Fourier

transform infrared spectros-

copy. A general analysis or

Analyze This: Device Cleanliness TestingThree analytical methods can help manufacturers avoid residual material product contamination.

TINA MAY AND BRENT SHELLEY

Scientists are shown weighing a crucible for gravimetric analysis. Im

ages

cou

rtes

y of

NEL

SO

N L

AB

OR

ATO

RIE

S

MD100702_028 28MD100702 028 28 7/2/10 9:21:10 AM7/2/10 9:21:10 AM

MOLDING TECHNOLOGIES JULY 2010 | 29

interpretation of the sample

spectrum can reveal the pres-

ence of certain types of com-

pounds such as hydrocarbons

and amines. The laboratory can

also identify the compounds by

comparing the sample spectrum

to the spectra of target com-

pounds. Identifying the residue

may be important when a manu-

facturer is trying to control the

source of residue production.

TOC Analysis. TOC analy-

sis is the most sensitive of the

RMM series of tests. The analy-

sis is quantitative and detects

carbon-based materials such as

oils, adhesives, and detergents on a prod-

uct, but does not pick up inorganic residue

such as metals and salts.

TOC analysis involves extracting devic-

es in USP-purified water by sonicating or

shaking, to remove surface contaminants.

An aliquot of the extraction solvent is ana-

lyzed on a TOC instrument to determine

how much organic carbon is on a device or

component. Alternatively, the manufac-

turer can use swabs to evaluate clean-in-

place components and equipment. After

swabbing the targeted component, the

swab is sent to the lab to be immersed in

USP-purified water and analyzed.

The manufacturer must evaluate the

results and determine how much residual

material is allowable based on the device’s

designed use. For example, if a device is

designed to be implanted in the body, it

needs to carry fewer organic residuals

than if it is a smaller, functional part of a

bigger device used outside the body, such

as a gear in a machine.

Detergent Residual Analysis. Manu-

facturers use a variety of cleaning agents

to clean their devices. Unfortunately,

these cleaning agents can leave behind po-

tentially harmful residual material. Deter-

gent residual analysis detects detergents

by UV/VIS spectroscopy.

Because each detergent absorbs UV

light differently, the laboratory validates

each one for accuracy, precision, linearity,

limit of detection, and limit of quantita-

tion. For this validation method, manufac-

turers must provide a full-strength sample

of detergent that is used in the cleaning

process. Detergent residual analysis also

uses water extraction and sonication to

identify the detergent left on a device. The

lab compares device extracts to the deter-

gents calibration curve for quantification

(see Figure 1).

Detergent residual analysis confirms that

devices are being adequately rinsed. Manu-

facturers, including molded de-

vice manufacturers, should con-

sider having this analysis method

performed on each type and size

of device because different devices

may require different or addition-

al rinsing to completely remove

detergent residuals. For example,

rinsing a smooth artificial knee is

much easier than rinsing a device

with grooves, pockets, lumens, or

mated surfaces.

Why RMM Analysis is EssentialSeveral critical reasons why

medical device manufacturers

should perform RMM analysis include the

following:

■ Cleanliness of device: RMM analysis

helps manufacturers determine wheth-

er they are producing a clean and safe

device.

■ Cleanliness of manufacturing process:

RMM analysis can determine cleanliness

throughout the manufacturing process.

Without this series of tests, manufactur-

ers may not know whether they are over-

cleaning their devices and molds and

therefore wasting time and money on

unnecessary rinses and cleaning cycles.

The analysis also informs the manufac-

turer whether its cleaning processes are

working by showing how much residue is

left behind on the products.

■ Designing cleaning processes: Manufac-

turers design their cleaning processes to

remove residue from a device, but clean-

The manufacturer must evaluate the results and determine how much residual

material is allowable based on the device’s designed use.

280250 270260230 240210 220190 200

0.6

0.8

1

1.2

0.4

0.2

0

Ab

sorb

an

ce

(AU

)

Wavelength (nm)

Figure 1. An example of a detergent residual analysis U/V printout.

A scientist loads samples on a TOC analyzer.

MD100702_029 29MD100702 029 29 7/2/10 9:21:15 AM7/2/10 9:21:15 AM

30 | JULY 2010 mddionline.com

MATERIALS ANALYSIS

ing agents can add additional contami-

nants to a device and render it unclean

and possibly cytotoxic. In some cases,

the cleaning process can makes the de-

vice more cytotoxic than before cleaning.

RMM analysis can help manufacturers

ensure that cleaning and rinsing process-

es are effective and producing a device

that is safe and patient ready.

■ Increased FDA involvement: FDA is in-

creasingly examining the cleanliness of

medical devices. RMM analysis provides

substantiated proof that products have

undergone meticulous cleanliness test-

ing. This documentation can be extreme-

ly useful to support a regulatory submis-

sion or in the event of an FDA or notified

body audit.

■ Mold-release agent transfer: Manufac-

turers often use mold-release agents

to remove devices from a mold, which

can leave residue on the device. RMM

analysis ensures that the device is not

picking up unexpected residues or that

these residuals are at acceptable levels

postproduction.

■ Creating a baseline measurement: RMM

analysis creates a baseline or a gauge for

a cleaning process. This can serve as a

useful validation criterion to ensure con-

sistent production of a safe product.

ConclusionThere are no established regulatory limits

of cleanliness for residual analysis. Manu-

facturers should perform a risk assessment

to determine acceptable levels of residue

based on the application and patient-con-

tact duration. They should also establish

limits for the cleanliness and safety of their

medical products.

Medical device manufacturers can save

time and money down the road if they ana-

lyze their devices, including those made

in molds, for RMM. The analysis method

streamlines and enhances process efficien-

cy to ensure safety while reducing product

and regulatory liabilities. Conducting such

analysis can prevent manufacturing from

halting when a problem or changes in the

process arises.

References1. ASTM F2459-05. 2005, “Standard Test Method

for Extracting Residue from Metallic Medical

Components and Quantifying via Gravimetric

Analysis” (West Conshohocken, PA: ASTM In-

ternational, 2005).

Tina May is chemistry section manager at

Nelson Laboratories (Salt Lake City). Brent

Shelley is study director at the company. 2

Manufacturers can use RMM analysis as a tool to monitor the cleaniness of production at any

point, including the final product.

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MOLDING TECHNOLOGIES JULY 2010 | 31

INJECTION MOLDING

M old makers, mold designers, and mold-

ers in industrial manufactur-

ing have used hot runner

technology for at least 40 years. The

systems are becoming especially im-

portant within the medical products

industry. Hot runners may help de-

vice OEMs reduce costs, improve

part quality, and increase speed

to market.

Hot runner systems are well-

suited for molding medical prod-

ucts for multiple reasons. The tech-

nology opens the door to a variety of options for molders, all

of which provide reduced material use and faster cycle times.

Recent innovations in technology can also provide power and

speed in cleanroom environments, which are required for pro-

ducing many medical products.

Hot Runner BasicsA hot runner system is an assembly of heated components used

in plastic injection molds that inject melted plastic into the cavi-

ties of the mold. A hot runner system usually includes a heated

manifold and a number of heated nozzles. The main task of the

manifold is to distribute the plastic entering the mold to the vari-

ous nozzles, which then meter it precisely to the injection points

in the cavities.

By contrast, a cold runner is simply a channel formed between

the two halves of the mold, for the purpose of carrying plastic from

the injection molding machine nozzle to the cavities. Each time

the mold opens to eject the newly formed plastic parts, the mate-

rial in the runner is ejected as well, resulting in waste.

Hot runner systems consist of a steel block, machined with an

internal passageway for molten resin. Heaters affixed to the pe-

rimeter of the steel block heat the manifold from the outside in,

enabling an even heat inside the block. Melt is then distributed

throughout the heated manifold block, fed into a heated nozzle,

then sent into the final gate well—or bubble—just prior to passing

into the part cavities. When designed properly, the system achieves

maximum material processing capability while eliminating resin

waste per injection cycle.

Hot Runners for Medical ProcessingThe primary benefit of hot runner systems is speed. Fractions of

a second in cycle time add up quickly and can significantly affect

the bottom line.

Hot runners also cut cost by reducing waste. The technology

eliminates runner waste and any costs necessary to regrind or dis-

pose of scrap. The technology also enables a variety of increased

process efficiencies, as well as the capability for extreme precision.

An example of how exact hot runner systems can be is the electric

valve gate. This machine has variable pin positioning in 0.001-in.

increments, giving a significant level of control to molders.

Top Considerations for Selecting a Hot Runner System Hot runner systems were created out of a need to mold plastic parts

fast and at a low cost. When they are selected, installed, and work-

ing properly, these systems can improve part quality, as well as en-

able fast processing speeds, low scrap, low labor costs, high-volume

production, and efficiency. But achieving the maximum potential

requires proper knowledge, planning, design, and execution.

The primary consideration for selecting a hot runner system is

to determine whether the product needs to be molded in a clean-

room. A contaminant-free environment is often a prerequisite for

producing medical products, especially Class II and Class III medi-

cal devices. Producing these types of items outside a cleanroom can

create serious risks for both patients and medical staff.

There are products, however, such as bedpans or food trays, that

do not require cleanroom standards. These types of items can often

Hot Runners and the Evolving Medical Industry Hot runner innovations may be able to provide speed and precision for medical molding.

CRAIG KOVACIC

An electric valve gate system provides technology for precision molding while also reducing waste.

MD100702_031 31MD100702 031 31 7/2/10 9:25:44 AM7/2/10 9:25:44 AM

32 | JULY 2010 mddionline.com

INJECTION MOLDING

be sanitized after the standard molding process due to advance-

ments in gamma radiation and other sterilization procedures.

Once you’ve established whether the application requires clean-

room molding, the next step is to determine the tolerance for gate

vestige based on the nature of the part. From there, you can ulti-

mately choose which nozzle, and therefore which system, is the

most appropriate for the application.

Preparation for Hot Runner Systems

Before starting a project, meet with

the materials supplier, the toolmaker,

and the hot runner manufacturer to

determine how each will contribute.

Working together from the beginning

allows the OEM to consider options

and ensure that all parts of the pro-

cess will fit together.

The most important recommenda-

tions should come from the material

supplier. The residence time of the ma-

terial is important. The supplier should

provide information on how much sheer

the material can take and on the proper flow

materials. Figuring this out first is especially

important for producing medical products,

because the resins used for medical devices

are typically highly engineered with specific processing parameters.

In medical applications, it’s also important for a material’s sur-

face to be as nonporous as possible to prevent bacterial growth.

Producing this type of resistant surface usually demands highly

engineered machines. This is also common when producing parts

for the food industry.

With the material supplier, determine whether a hot runner sys-

tem is even an option. Due to residence time, a highly engineered

resin may need to be injected right into a part once it comes out of

the molding machine. If a particular material only has a short amount

of time it can be fluid, a hot runner system might not be viable.

All of the specs provided by the material supplier will ultimately

determine which nozzle is selected. And knowing everything you

can about a material will help you “think like a pellet” when design-

ing the hot runner system for optimal operation.

Hydraulic, Pneumatic, or ElectricHot runner equipment comes in three varieties: hydraulically pow-

ered, pneumatically powered, and electrically powered. Whether a

cleanroom is required dictates which of these options is used.

Hydraulic systems provide powerful valve gate shutoff, contrib-

uting to maximum part quality. However, due to the risk of oil leaks

and contamination, they are unsuitable for use in cleanrooms.

Pneumatic systems, a much cleaner option, have long been the hot

runner of choice, but these also have a downside. Their relatively

weak shutoff force is less than ideal for the high speeds and preci-

sion the market demands.

Electrically powered hot runner systems are a relatively new

innovation. These systems provide more power, speed, and pre-

cision than pneumatic or hydraulic options. And they use power

that doesn’t require hoses, oil, or other potential contaminants. The

electric technology is suited for cleanrooms.

Thermal Gate versus Valve GateOnce the power source has been chosen, molders must determine

whether to use a thermal gate or a valve gate. This decision is based

primarily on whether the final part has any tolerance for gate ves-

tige, the mark a gate can create on the part.

Although gate vestige can be undesirable for many plastic prod-

ucts, it’s particularly problematic in the medical field. Surgical gloves

prevent the spread of disease within medical facilities and are a criti-

cal part of overall safety for patients and medical staff. Plastic parts

produced with any sharp or jagged edges, as a result of gate vestige,

can potentially tear through thin gloves and pose an assortment of

safety risks. Vestige points can be trimmed off of plastic items if nec-

essary, but these secondary processes reduce efficiency.

Thermal gates are generally the more common and less expensive

gate option. They are particularly suited for high-cavity-count molds

with close cavity pitch dimensions. With thermal gates, plastic hard-

ens in the gate area as it cools, creating a barrier between the molten

plastic and the cooled part, and leaving a small vestige point. The

molder must take this into consideration ahead of time and accom-

modate accordingly. It is not uncommon for molders to put a dimple

in a part so that the vestige is below the surface and not easily felt.

Valve gates, the other type of gate option, typically do the best job

eliminating vestige and producing suitable medical products. They

function by shutting off the flow of plastic mechanically, with a

physical barrier between molten and cooled plastic. They are good

for superior gate cosmetics, sequential part filling, and eliminating

the potential for sharp edges.

Some circumstances exist in which plastic parts are too small to

use a valve gate. In those cases, use a hot-to-cold runner technique

to feed a tiny runner into the small part. When the part ejects from

the mold, it makes a clean break from the cold runner, leaving no

sharp edges.

Selecting NozzlesThe appropriate nozzle for a hot runner

system is determined by the type of mate-

rial going through the flow channels. If the

nozzle is too small, sheer is created. If it is too

large, the system cannot be flushed out through

the manifold or the nozzle.

When choosing a nozzle, it is important to

consider how many shots of material are in the

manifold. Typically, it is standard to have within

three shots of material between the machine

barrel and the part. Sometimes this changes due to high cavitation

(the formation of vapor bubbles of a flowing liquid). Resin can only

be heated for a certain amount of time before losing its properties.

Because all material has this residence time, it is important that the

nozzle be small enough to constantly contain fresh material.

Reusing Hot Runner SystemsThere are situations in which a processor can use the same hot

runner system for different parts that are within the gram weight

capacity of the system’s nozzles.

Thermal gates are a common option that can accommodate high-cavity molds.

Choosing nozzles and manifolds depends on the individual needs of the part.

MD100702_032 32MD100702 032 32 7/2/10 9:25:49 AM7/2/10 9:25:49 AM

MOLDING TECHNOLOGIES JULY 2010 | 33

For example, a part may be 5 g, but the same nozzle can also han-

dle a part that is 10 g. If the molding is within the same limitation of

that nozzle itself, A-plates and cavities can be pulled off and placed

on other A-plates and cavities, as long as they match the capacity of

the nozzles that were chosen first.

Reusing hot runner systems generally requires forethought on

the part of the mold maker to design molds and part cavities that

are spaced appropriately for a specific hot runner system. A mold

maker can put small cavities into a large footprint, which is an im-

portant planning consideration.

If one part can work in a 1-in. pitch, but the other part requires

a 1.5-in. pitch, the drops must be 1.5 in. apart. That way, the larger

spacing is run first, and it becomes the reference point before run-

ning the smaller part. A molder can always go large to small, but

not the other way.

Tip Style SelectionOnce the nozzle type is selected—which also determines the hot

runner model provided by the supplier—an OEM should select the

nozzle tip style. A variety of tips are designed for different types of

hot runner applications.

Sprue gate tips are used for situations in which gate vestige is

not a concern. They offer minimal flow resistance and handle most

resins effectively. Extended styles of sprue gates provide additional

stock for machining runner profiles or part contours. Sprue gate

tips can be used with either valve gates or thermal gates, but gener-

ally go from thermal to a cold runner. They keep the sheer of the ma-

terial down until it goes into the part, which prevents plastic from

degrading before it has achieved a fully fluid state.

Point gate tips are used only for thermal gate systems and are

suitable for direct part gating. They’re generally used for applica-

tions needing optimal gate cosmetics and can run a wide range of

resins. As a general rule, point gate vestige will be one half of the

gate diameter. If a 0.04-mm gate is used, up to 0.02 mm of material

could stick up. That excess can be removed, if necessary, depending

on where it is on the part.

Through-hole tips, also used for thermal gating, have nothing in

the tip to split material molecules. Their gate vestige is equal to the

gate diameter. A 0.04-mm gate will produce a 0.04-mm vestige.

Many preforms use through-hole tips. They’re also commonly

used for parts with secondary operations, like blow molding, when

the processor doesn’t want to sheer the material and wants to mini-

mize gate vestige as it moves to a secondary operation.

Valve gates eliminate vestige completely, leaving only a witness line

where the part is sealed off, similar to those left by an ejector pin. This

makes valve gate tips essential for many delicate medical molding ap-

plications in which surface quality and precision are critical.

Sourcing the ManifoldsOnce the nozzle type and tip style are determined, they need to

be housed in a manifold, which takes the melt from the molding

machine and distributes it evenly to each of the hot runner system

nozzles. Often, manifolds are sourced from the nozzle supplier as

part of a nozzle and manifold system due to the precision machin-

ing required. However, some mold makers may have the capabilities

needed to do this in-house as well.

Manifolds are generally made of P20 or stainless steel for the

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INJECTION MOLDING

part of the design. This is helpful if the part requires a screw hole or

similar element. The pin can be set to open at 0.0001-in. increments

along its 0.75-in. stroke range. All other hot runner options are ei-

ther open or closed, without the ability to stop the pin midway.

Besides design benefits, variable pin positioning also enables

even filling of a family mold in which one cavity may be larger than

another. Without this level of control, the mold may become out of

balance in the filling process or uneven pressure buildup may be-

come a problem.

Electric valve gate machines provide faster mold changeovers as

well. With these systems, a molder merely hooks up the electric from

the hot runner system to the control box. Air

and hydraulic require hooking up hoses and

cables and make the process much more

time consuming.

Electric valve gate hot runner systems

also have variable speed capability, which

is perfect for coinjection and family molds.

This capability helps balance the mold and

allows for sequencing on larger parts. When the molder wants to

move the knit line across, the machine enables the plastic to flow

from one nozzle to the next as they open and close in sequence.

Most molding requires the pins to all open or all close at the same

time within a mold. However, there are times when a molder might

want to partially open one gate while another is fully open to help

balance out the mold as it fills. The electric valve gate is the only

machine that can accomplish this.

Limitations of the Electric Valve GateBecause the electric valve gate is still fairly new technology, there

may be some applications for which it is not the right solution. This

is often due to the 3-sq in. size of the motors that currently operate

each valve gate. The measurements are somewhat large for close

center-to-center distances.

That means that three pins share the same plate if a molder needs

one inch of distance between pins. All of the pins have to fire at the

same time. That isn’t generally a problem for small, high-quantity,

high-cavitation parts. But it does create limitations for larger parts

with multiple gates.

ConclusionThe benefits of hot runner technology, specifically the electric valve

gate, are only getting better. The future of this technology includes

faster and smaller motors. In addition, the cost of the machines is

also anticipated to come down in the coming years.

Hot runners are an extension of a molding machine nozzle, but

they offer a unique opportunity for efficiency and cost savings. They

offer problem solving for complex applications.

Craig Kovacic is global manager of hot runner systems for DME Co.

(Madison Heights, MI). MT

medical industry. It is crucial that they be properly extrude honed,

a process by which flow channels are rounded and highly polished.

This eliminates friction and removes any spots where materials

could potentially get stuck or degrade.

Because extrude honing is an advanced and critical process,

medical molders or mold makers rarely build their own manifolds.

By buying an entire hot half (defined later), or a whole system from

a manufacturer, molders know the manifolds have been extrude

honed to the highest specifications.

The final step in creation of a hot runner system is developing

what is called a full hot half. This includes the nozzles, the manifold,

the mold plate that houses the manifold so that it can fit into a mold

base system, along with all of the wiring. Again, the level of sourc-

ing for a full system versus in-house development depends on the

capabilities of the molder or mold maker and the best use of their

resources and core competencies.

The Electric Valve GateGiven quality and contamination considerations in molding medi-

cal products, it’s no wonder the industry is moving toward electric

machines—both electric molding machines and electric valve gate

hot runner systems. Hydraulic-powered hot runner systems are not

an option for cleanrooms, and the cylinders in pneumatic systems

cannot match the speed or the 35,000-psi shutoff power of an elec-

tric valve gate.

Pneumatic systems have a moving solenoid, which takes time to

move. A mechanical process has to occur before the machine can

send air to the valve gate cylinder. With the electric valve gate, it

takes mere nanoseconds for an electric signal to fire a valve.

Another downside is the common maintenance and performance

issues of pneumatic systems caused by poorly tightened air or water

lines that don’t properly cool the plates. When this happens, the O-

rings can bake on the cylinders, lose their integrity, and cause air

leaks that contaminate the parts and decrease system pressure.

Since a motor moves the cylinder on an electric valve gate, there are

no O-rings that can dry out or that need to be maintained.

Eliminating leaks reduces scrap as well. A fast, precise, and power-

ful closing force reduces the gate vestige into which scrap can enter.

With oil or air, leaks can occur, which change the viscosity of the

material. The change in viscosity prevents the valve from opening or

closing all the way, creating a nub on the parts. Electric valve gate hot

runners have such a great closing force that they will close up on the

material flow as programmed even if the viscosity of the material has

changed. This results in better part quality and reduced scrap.

The electric valve gate and its variable pin-positioning feature can

also make design elements easier. The molder can control how far

the pin sticks out. This means it can even protrude into the product

if desired, allowing the valve pin to make a hole in the product as

Given quality and contamination considerations in molding medical

products, it’s no wonder the industry is moving toward electric machines.

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Crescent Industries Inc.70 E. High St.New Freedom, PA 17349717/235-3844info@crescentind.comwww.crescentind.comCrescent Industries is a single-source pro-

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MOLDING TECHNOLOGIES JULY 2010 | 37

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Plastics One Inc.6591 Merriman Rd.Roanoke, VA 24018540/772-7950info@plastics1.comwww.plastics1.comPlastics One specializes in custom injection

molding of medical device components

with complex requirements and unique

specifications. It provides a range of servic-

es including design and research, in-house

tooling, prototyping, and assembly.

PolyMedex Discovery Group45 Ridge Rd.Putnam, CT 06260860/928-4102info@polymedexgroup.com

www.polymedexgroup.comPolyMedex Discovery Group serves medi-

cal device manufacturers with comprehen-

sive development and manufacturing ser-

vices for intravascular, minimally invasive,

and implantable applications. It supports

its customers with polymer distribution,

custom compounds, bioresorbable and

drug delivery formulations, thermoplas-

tic and thermoset tubing, and custom

components.

Proto Labs Inc.5540 Pioneer Creek Dr.Maple Plain, MN 55359877/479-3680customerservice@protolabs.comwww.protolabs.comProto Labs through its First Cut and Proto-

mold services uses proprietary computing

technologies and automated manufactur-

ing systems to provide prototype parts and

short-run production services. All compo-

nents are made by standard production

methods and can be shipped in as fast as

one day.

Vesta 5400 W. Franklin Dr.Franklin, WI 53132414/423-0550sales@vestainc.comwww.vestainc.comVesta is a manufacturing services com-

pany that provides molding, extrusion, and

assembly for the medical device industry.

The company provides expertise in design

assistance, material selection, and quality

standards within ISO-certified facilities. It

offers a range of molding capabilities in-

cluding liquid injection, transfer, and insert

molding of medical-grade silicone. 2

Look for the following upcoming directories in MD+DI :

■ Who’s Who in Contract Manufacturing■ Outsourcing Showcase* ■ Packaging and Sterilization Showcase*■ LitPak*

*advertisers only

Contact your local sales representative to see whether your company qualifies.

Canon Trade Events ...............................30, 35

310/445-4200 • www.canontradeshows.com

Crescent Industries Inc. ..............................33

717/235-3844 • www.crescentind.com

Donatelle .......................................................... 7

651/633-4200 • www.donatellemedical.com

Foster Printing ...............................................25

866/879-9144 • www.fosterprinting.com

Medical Extrusion Technologies Inc. .....11

800/618-4346 • www.medicalextrusion.com

Plastics One Inc. ...........................................25

540/772-7950 • www.plastics1.com

PolyMedex Discovery Group ....................15

860/774-1559 • www.polymedex-possible.com

Proto Labs Inc. ................................................. 3

877/479-3680 • www.protolabs.com

Saint-Gobain Performance Plastics ........19

800/236-7600 • www.medical.saint-gobain.com

Sil-Pro (Silicone Professionals) ................. 5

763/972-9206 • www.sil-pro.com

Smiths Medical OEM .................................... 9

866/216-8808 • www.smiths-medical.com/oem

Vesta Inc. ........................................................23

414/423-0550 • www.vestainc.com

Wacker Chemical Corp...............................27

888/922-5374 • www.wacker.com

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