Dr. Yan Wang

Dr. Dal Koshal

Contact: y.wang5@brighton.ac.uk

Tel: 01273 642328

ME245: Manufacturing Engineering

Non traditional Machining

Non-Traditional Processes Defined

A group of processes that remove excess material

by various techniques involving chemical,

electrical, mechanical and thermal energy (or

combinations of these energies)

• They do not use a sharp cutting tool in the

conventional sense

• Developed since World War II in response to new

and unusual machining requirements that could

not be satisfied by conventional methods

Limitations of Conventional Machining

Processes

• Machining processes that involve chip

formation have a number of limitations

– Large amounts of energy

– Unwanted distortion

– Residual stresses

– Burrs

– Delicate or complex geometries may be

difficult or impossible

• Non-traditional machining (NTM) processes

have several advantages

– Complex geometries are possible

– Extreme surface finish

– Tight tolerances

– Delicate components

– Little or no burring or residual stresses

– Brittle materials with high hardness can be

machined

– Microelectronic or integrated circuits (IC)

are possible to mass produce

Importance of Nontraditional Processes

• Need to machine newly developed metals and

non-metals with special properties that make

them difficult or impossible to machine by

conventional methods

• Need for unusual and/or complex part

geometries that cannot readily be accomplished

by conventional machining

• Need to avoid surface damage that often

accompanies conventional machining

Classification of Nontraditional Processes

• Chemical – chemical etchants selectively remove material

from portions of workpart, while other portions are protected

by a mask

• Electrical - electrochemical energy to remove material

(reverse of electroplating)

• Mechanical - typical form of mechanical action is erosion of

work material by a high velocity stream of abrasives or fluid

(or both)

• Thermal – thermal energy usually applied to small portion

of work surface, causing that portion to be fused and/or

vaporized

Chemical Machining Processes

• Chemical milling or industrial etching

uses baths of temperature-regulated

etching chemicals to remove material to

create an object with the desired shape.

• It was developed from armor-decorating.

• The process essentially involves bathing

the cutting areas in a corrosive chemical

known as an etchant, which reacts with

the material in the area to be cut and

causes the solid material to be dissolved;

• Inert substances known as maskants are

used to cover the specific areas that are

not machined.

Chemical Milling

Figure 27.2 (a) Missile skin-panel section contoured by chemical milling to improve the

stiffness-to-weight ratio of the part. (b) Weight reduction of space-launch vehicles by the

chemical milling of aluminum-alloy plates. These panels are chemically milled after the plates

first have been formed into shape by a process such as roll forming or stretch forming. The

design of the chemically machined rib patterns can be modified readily at minimal cost.

Chemical-Machining

Figure 27.3 (a) Schematic illustration of the chemical-machining process. Note that no

forces or machine tools are involved in this process. (b) Stages in producing a profiled

cavity by chemical machining; note the undercut.

Advantages and Disadvantages of Chemical

Machining

• Advantages– Process is relatively

simple

– Does not require highly skilled labor

– Induces no stress or cold working in the metal

– Can be applied to almost any metal

– Large areas

– Virtually unlimited shape

– Thin sections

• Disadvantages– Requires the handling

of dangerous chemicals

– Disposal of potentially harmful byproducts

– Metal removal rate is slow

http://www.precisionmicro.com/194/photo-etching/3-minute-process-video

• A chemical milling process used to fabricate sheet metal components

using a photoresist and etchants to corrosively machine away

selected areas.

• Photo etching can produce highly complex parts with very fine

detail accurately and economically.

• The tooling is inexpensive and quickly produced. This makes the

process useful for prototyping and allows for easy changes in mass

production.

• It maintains dimensional tolerances and does not create burrs or

sharp edges. It can make a part in hours after receiving the drawing.

• PCM can be used on virtually any commercially available metal or

alloy, of any hardness.

• It is limited to materials with a thickness of 0.02mm to 2mm).

Photochemical machining (PCM)

Electrical- Electrochemical Machining Processes

• Electrical energy used in combination with

chemical reactions to remove material

• Reverse of electroplating

• Work material must be a conductor

• Processes:– Electrochemical machining (ECM)

– Electrochemical grinding (ECG)

http://www.youtube.com/watch?v=VzmVrJAIhew

Electrochemical Machining

• Electrochemical machining (ECM) removes material by anodic

dissolution with a rapidly flowing electrolyte

• The tool is the cathode and the workpiece is the anode

Advantages and Disadvantages of

Electrochemical Machining

• Advantages– ECM is well suited for the

machining of complex two-dimensional shapes

– Delicate parts may be made

– Difficult-to machine geometries

– Poorly Machinablematerials may be processed

– Little or no tool wear

• Disadvantages

– Initial tooling can be

time consuming

and costly

– Environmentally

harmful by-products

Parts Made by Electrochemical Machining

Figure 27.7 Typical parts made by electrochemical machining. (a) Turbine blade made

of nickel alloy of 360 HB. Note the shape of the electrode on the right. (b) Thin slots

on a 4340-steel roller-bearing cage. (c) Integral airfoils on a compressor disk.

Knee Implants

Figure 27.8 (a) Two total knee replacement systems showing metal implants

(top pieces) with an ultra-high molecular-weight polyethylene insert (bottom

pieces). (b) Cross-section of the ECM process as applies to the metal implant.

Source: Courtesy of Biomet, Inc.

• Combines electrochemical machining with conventional grinding.

• Grinding wheel in which an insulating abrasive, such as diamond

particles, is set in a conducting material. This wheel becomes the

cathode tool .

• Deplating responsible for 95% of metal removal. Because machining is

mostly by electrochemical action, grinding wheel lasts much longer

• Suitable in grinding very hard materials where wheel wear can be very

high in traditional grinding.

Electrochemical

Grinding (ECG)

• One of the most widely used nontraditional processes

• Shape of finished work surface produced by a shape of electrode tool

• Sparks occur across a small gap between tool and work

• Requires dielectric fluid, which creates a path for each discharge as fluid becomes ionized in the gap

• Work materials must be electrically conducting

• Hardness and strength of work material are not factors in EDM

• Material removal rate depends on melting point of work material;

Electric Discharge

Machining (EDM)

https://www.youtube.com/watch?v=L1D5DLWWMp8

EDM Applications

• Tooling for many mechanical

processes: molds for plastic

injection molding, extrusion

dies, wire drawing dies, forging

and heading dies, and sheet

metal stamping dies

• Production parts: delicate

parts not rigid enough to

withstand conventional cutting

forces, hole drilling where hole

axis is at an acute angle to

surface, and machining of hard

and exotic metals

Electrical-Discharge Machining Process

Figure 27.10 (a) Schematic illustration of the electrical-discharge machining process. This is one of the

most widely used machining processes, particularly for die-sinking applications. (b) Examples of cavities

produced by the electrical-discharge machining process, using shaped electrodes. Two round parts (rear)

are the set of dies for extruding the aluminum piece shown in front (c) A spiral cavity produced by EDM

using a slowly rotating electrode similar to a screw thread. (d) Holes in a fuel-injection nozzle made by

EDM; the material is heat-treated steel. Source: (b) Courtesy of AGIE USA Ltd.

Stepped Cavities Produced by EDM Process

Figure 27.11 Stepped cavities produced with a square electrode by the EDM

process. The workpiece moves in the two principle horizontal directions (x – y), and

its motion is synchronized with the downward movement of the electrode to produce

these cavities. Also shown is a round electrode capable of producing round or

elliptical cavities. Source: Courtesy of AGIE USA Ltd.

Wire EDM

• Special form of EDM uses small diameter wire as electrode to cut a

narrow kerf in work

• Work is fed slowly past wire along desired cutting path, like a

bandsaw operation

• CNC used for motion control

• While cutting, wire is continuously advanced between supply spool

and take-up spool to maintain a constant diameter

• Dielectric required, using nozzles directed at tool-work interface or

submerging workpart

• Ideal for stamping die components.

http://www.youtube.com/watch?v=pBueWfzb7P0

Manufacturing,

Engineering &

Technology, Fifth Edition,

Wire EDM

(a) (b)

Figure 27.13 (a) Cutting a thick plate with wire EDM. (b) A computer-

controlled wire EDM machine. Source: Courtesy of AGIE USA Ltd.

Advantages and Disadvantages of EDM

Advantages

• Applicable to all materials that are fairly good electrical conductors

• Hardness, toughness, or brittleness of the material imposes no limitations

• Fragile and delicate parts

Disadvantages

• Produces a hard recast surface

• Surface may contain fine cracks caused by thermal stress

• Fumes can be toxic

• A tool of desired shape vibrates at an ultrasonic

frequency (19 ~ 25 kHz) with an amplitude of around 15 –

50 μm over the workpiece. Generally the tool is pressed

downward with a feed force, F.

• Between the tool and workpiece, the machining zone is

flooded with hard abrasive particles generally in the

form of a water based slurry.

• As the tool vibrates over the workpiece, the abrasive

particles act as the indenters and indent both the work

material and the tool. The abrasive particles, as they

indent, the work material, would remove the same,

particularly if the work material is brittle, due to crack

initiation, propagation and brittle fracture of the material

Mechanical NTP: Ultrasonic Machining (USM)

http://www.bullentech.com/animation

Applications: brittle and non conductive materials

Mechanical NTP: Ultrasonic Machining (USM)

Mechanical NTP: Ultrasonic Machining (USM)

Abrasives contained in a slurry are driven at

high velocity against work by a tool vibrating at

low amplitude and high frequency

• Tool oscillation is perpendicular to work surface

• Abrasives accomplish material removal

• Tool is fed slowly into work

• Shape of tool is formed into part

• Uses high pressure, high velocity stream of water directed at work surface for cutting

Water jet cutting.

Mechanical NTP: Water jet cutting

• When WJC is used on metals, abrasive particles must

be added to jet stream usually

Mechanical NTP: Water abrasive jet cutting

https://www.youtube.com/watch?v=_FIsrYzyvlg

Applications:

• Usually automated by CNC or industrial robots to

manipulate nozzle along desired trajectory

• Used to cut narrow slits in flat stock such as plastic,

textiles, composites, floor tile, carpet, leather, and

cardboard

• Not suitable for brittle materials (e.g., glass)

Advantages

• No crushing or burning of work surface

• Minimum material loss

• No environmental pollution

• Ease of automation

Mechanical NTP: Water jet cutting

Abrasive

Waterjet

and

Waterjet

examples

©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

• Uses high velocity stream of electrons focused on workpiece surface to remove material by melting and vaporization

• EB gun accelerates a continuous stream of electrons to about 75% of light speed

• Beam is focused through electromagnetic lens, reducing diameter to as small as 0.025 mm (0.001 in)

• On impinging work surface, kinetic energy of electrons is converted to thermal energy of extremely high density which melts or vaporizes material in a very localized area

Thermal NTM:

Electron Beam

Machining (EBM)

EBM Applications

• Works on any material

• Ideal for micromachining– Drilling small diameter holes - down to 0.05 mm

(0.002 in)

– Cutting slots only about 0.025 mm (0.001 in.) wide

• Drilling holes with very high depth-to-diameter

ratios

– Ratios greater than 100:1

• Uses the light energy from a laser to remove material by vaporization and ablation

• Drilling, slitting, slotting, scribing, and marking operations

• Drilling small diameter holes - down to 0.025 mm (0.001 in)

• Generally used on thin stock

• Work materials: metals with high hardness and strength, soft metals, ceramics, glass and glass epoxy, plastics, rubber, cloth, and wood

Laser Beam Machining (LBM)

Laser-Beam

Machining (LBM)

Figure 27.14 (a) Schematic

illustration of the laser-beam

machining process. (b) and (c)

Examples of holes produced in

nonmetallic parts by LBM. (d)

Cutting sheet metal with a laser

beam. Source: (d) Courtesy of

Rofin-Sinar, Inc.

Conventional Machining VS

NonConventional Machining

• The cutting tool and workpiece are always in physical contact, with arelative motion against each other, which results in friction and asignificant tool wear.

• In non-traditional processes, there is no physical contact between thetool and workpiece. Although in some non-traditional processes toolwear exists, it rarely is a significant problem.

• Material removal rate of the traditional processes is limited by themechanical properties of the work material. Non-traditionalprocesses easily deal with such difficult-to-cut materials likeceramics and ceramic based tool materials, fiber reinforced materials,carbides, titanium-based alloys.

Continue…

• In traditional processes, the relative motion between the tooland work piece is typically rotary or reciprocating. Thus, theshape of the work surfaces is limited to circular or flatshapes. In spite of widely used CNC systems, machiningof three-dimensional surfaces is still a difficult task. Mostnon-traditional processes were develop just to solve thisproblem.

• Machining of small cavities, slits, blind or through holesis difficult with traditional processes, whereas it is a simplework for some non-traditional processes.

• Traditional processes are well established, use relativelysimple and inexpensive machinery and readily availablecutting tools. Non-traditional processes require expensiveequipment and tooling as well as skilled labor, whichincreases significantly the production cost.