3.injection molding process

7/28/2019 3.Injection Molding Process

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CENTRAL INSTITUTE OF PLASTICS

ENGINEERING AND TECHNOLOGY

BY

R.T. NAGARALLI


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I NJECTION MOULDING PROCESS -

RESOURCES

MATERIALMACHINE

MOULD

MAN POWER


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MATERIAL

THERMOPLASTIC

MATERIAL

THERMOSET

MATERIAL

PLASATIC MATERIAL


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HEAT COOLSOLID

PRESS.

IT CAN BE RECYCLED

THERMPLASTIC MATERIAL

SOFT


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HEAT HEATSOLID

PRESS.

IT CAN NOT BE RECYCLED

THERMOSET MATERIAL

SOFT

CHARCOAL


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MACHINE

HEATING

PRESURISING AND CONVEYING MOULD CLAMPING


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MOULD

THE MOLD HAS 4 MAIN FUNCTIONS

RECEIVE & DISTRIBUTE THE MATERIAL

SHAPE FORMING

COOLING(Water & oil)

DISPOSAL


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MANPOWER

TO SET UP A PROCESS

TO MONITOR AND TROUBLE SHOOT

TO OPARATE MACHINE


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PLUNGER TYPE

PLUNGER-PLUNGER TYPE

TYPES OF INJECTION MOULDING MACHINES


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SCREW

PLUNGER

TYPE

IN LINERESIPROCATING

SCREW TYPE


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The rotation of the screw produces frictional and sheartogether with the heat input from heater bands around the

barrel cause the material to melt. These two sources of heat ,

combined with the mixing effect of the screw , provide a

homogenous melt

Screw Rotation


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It is important that the speed the screw is kept constant from cycle to

cycle. If the speed of rotation of the screw is increased, or if takes

longer to refill the amount of sheer put in to melt will be increased.

Screw stroke:

The return stroke of the injection is determined by the amount of

material to be injected ( shot weight). The longer the stroke larger

the volume.

Screw Speed


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Injection Pressure and Hold on Pressure


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MELT TEMPARATURE

CAN BE CHANGED BY

BARREL TEMPARATURE

BACK PRESSURE

SCREW RPM

CYCLE TIME


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PRESSURE PROFILE IN CAVITY


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NOZZLE

It provides thermal&mechanical connection

from hot cylinder to cold injection mold

TYPES

An open channel with no mechanical valve

An internal check - valve held closed by spring

A shut off valve


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Standard / Open

Channel nozzle

Reverse tapered /

Nylon nozzle


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Needle type shutoff nozzle


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Ring type

Ball Type

Non-return valve


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Standard

Type

P.V.CPurpose


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SCREW-TYPES

GENERAL PURPOSE SCREW

ENTED SCREW

BARRIER SCREW

SCREW FOR THERMOSET


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Screwnomenclature


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SCREW-L/D RATIO

The flighted length of screw to the dia. Of screw

Generally L/D ratio varies 20:1 to 30:1

Generally L/D ratio for PVC is 16:1 The larger the L/D ratio greater the opportunity

for mixing,resulting in better homogeneity of melt

Greater the resident time of the plastic in thebarrel permitting faster cycles of larger shots &

more output


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SCREW- VARIOUS ZONES IN SCREW

FEED ZONE: Promotes pumping/output rateadequately-It can be 50 to 60% of L

COMPRESSION ZONE: Promotes shearing andhence melting of polymers at the output rate offeed zone-It can be 20 to 25% of L

METERING ZONE: Promotes homogenization ofentire melt stream emerging from compressionzone- It can be 20 to 25% of L


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SCREW

SIGNIFICANCE OF LENGTH OF EACHZONE

Longer feed zone creates greater potential throughputLonger compression zone results in less shear heatand more to compress and melt the plastic

Longer meter zone allows screw to develop more

pumping pressure and greater opportunity tohomogenize

Shorter meter zone allows less time to assure uniformmelt temperature and viscosity


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SCREW-CHANNEL DEPTH

Higher channel depth in feed zone conveys more materialand hence more torque is required to rotate.Shallowchannel depth screw requires higher rpm and lower torquefor a given output rate.Shear rate is lower on the polymerin screws with deeper channel depth at lower rpm.Hence it

is preferred for shear sensitive polymers

A shallow screw channel

Increases the exposure of plastic to the heated barrelwall

Increases the shear heat imparted to the polymer

Reduces potential throughput of the screw


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COMPRESSION RATIO

IT IS THE RATIO OF THE VOLUME OF FIRST TURNOF SCREW TO VOLUME OF LAST TURN OF THESCREW

IT IS NORMALLY BETWEEN 1.5 to 4.5 FORGENERAL PURPOSE SCREW

LOWER CR SUITS LOW VISCOCITY MELTS ANDHIGHER CR SUITS HIGHER VISCOCITY MELTS

HIGHER THE CR,GREATER THE RESULLTING

Shear heat imparted to the polymer

Heat uniformity of melt

Potential for creating stresses in some polymers

Energy consumption


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CLAMPPING-TYPES

MAJORLY OF TWO TYPES

HYDAULIC CLAMPING

TOGGLE CLAMPING


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Hydraulic Clamping

Toggle Clamping


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HYDRAUL IC Vs TOGGLE-COMPARISION

Much higher original

cost

Higher horse powerneeded.Therefore more

expensive to run

Unlimited stroke

potential Direct readout of clamp

force

Lower original cost

Lower horse powerneeded.More economical

to run

Limited stroke potential

No Direct readout ofclamp force


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HYDRAUL IC Vs TOGGLE-COMPARISION

Easy adjustment ofclamp force

Easy mold setup

Varies stroke to moldheight

Clamp speed easily

controlled or stopped atany point

Low maintenance asparts are self lubricated

More difficult

More involvement inmold setup

Constant mold stroke

Clamp speed more

difficult to control andstop

Higher maintenance cost

MACHINE SELECTION


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MACHINE SELECTION

INJECTION

UNIT

TO UNDERSTAND

Maximum swept volume,cc Shot weight for a material

Max.Inj.Speed, gm/sec or

cc/sec

How it ensures melt to spread

throughout when in fluid condition-

before it freezes

Max.Inj.Pressure,Kg/cm2 How it overcomes to flow during

filling on account of flow ratio and

viscosity

Max.Plasticizing rate,gm/sec

or Kg/hrHow it influences cycle time

Max.Injection power,

Kg-cm/sec

How it takes care of difficulty in

filling of thinner walled and

high flow ratio parts


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MACHINE SELECTION

CLAMPING UNIT TO UNDERSTAD

Clearance between tie bar and

platen sizeHow it accommodates mold

Max.day light and mold open

stroke

Max.day light =

mold open stroke + min.day light

(it`s significance for ejection of

deep parts)

Clamping force in tons Depends on cavity pressure

HYDROMOTOR


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MACHINE SELECTION

DRIVE POWER TO UNDERSTANDPower supply frequency 60

or 50 hzIts influence on speeds

Pump-motor raring,Kw To match the application-usage ofmachine

Controlls

Conventional/Proportional valve

hydraulic controls

Electrical/microprocessor controlsOpen/closed loop controls

No load cycle time

It indicates the time for non

processing part of the cycle time


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MACHINE

SELECTION

Force on melt

(F1)= Force in

Hydraulic cylinder( F2)

Pm As = Ph Ah

Ph D2hPm = _-------------

D2s


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I NJECTION MOULDING PROCESS

MATERIAL PREPARATIOIN

PLASTICIZING

INJECTION

COOLING

EJECTION PACKING


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Elements of the Injection Moulding Cycle


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POLYMER MATERIALTEMP.RANGE 0 C MOLD TEPMP.

Nylon-6 230-260 80-90

Nylon-6 with GF 230-280 70-90

Nylon-66 270-290

80-90

Nylon11 210-240 30-60

Polysulphon 33-400 100-160

LDPE 160-240 30-50

LLDPE 200-280 30-50

HDPE 160-220 30-50

EVA copolymer 160-230 30-50

PP homopolymer 220-280 20-70

PP,20% Talc 200-280 20-70

PP,copolymer 170-230 20-60

PP,20% glass 220-280 20-80

GPPS 170-280 20-70

GPPS with GF 210-280 60-80

HIPS 190-260 50-80

SAN 200-280 30-80

ABS 240-280 40-80


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POLYMER MATERIAL TEMP.RANGE 0 C MOLD TEPMP.

PVC,Rigid 190-220 30-60

PVC,Soft 140-200 20-40

Acrylic 220-250 60-90

PET 280-295 5-15

PET,Not reinforced 235-280 20-70

PBT,30%GF 235-280 20-90

PET/PBT copolymer 235-280 20-90

PC 280-310 80-120

PC 40% GF 270-310 80-120

PPS 300-360 120-180

POM copolymer 180-230 60-120

PPO modified with GF 250-280 110-13

PPS/PS 270-300 70-110

PUR 170-220 10-30


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THREMOSET INJECTION MOULDING PROCESS


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ADVANCED INJECTION MOULDING PROCESS

VENTED

BARRELTYPE

SCREW

COOLING

TYPE


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REACTION INJECTION MOULDING PROCESS


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TWO COLORMOULDING

MULTICOLORED

MOULDING


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GAS ASSISTED

INJECTION

MOULDING

PROCESS


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In closed loop controls the effect of disturbances in the

process is eliminated by counter acting or by opposing the

effects of disturbance by automatically triggering certainreaction

The above is done in response of feedback which is compared

with the set value to take the required corrective action

CLOSED LOOP CONTROLS SYSTEM


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Set process parameters in open loop control influences the

process. But does not make correction by providing the

feedback, if there is any disturbance is effecting the process .

In open loop controls the effect of disturbances in the

process is eliminated or held constant to ensure the

uniformity in the process

OPEN-LOOP CONTROLS SYSTEM


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SRUCTURAL FOAM MOULDING

( SANDWHICH )


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THANK YOU

3.injection molding process

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