University of University of CambridgeCambridge

New approaches to Materials Education - a course authored by Mike Ashby and David Cebon, Cambridge, UK, 2005

The CES EduPackThe CES EduPack

Unit 4. Selecting processes:shaping, joining and surface treatment

© MFA and DC 2005

Outline

• Processes and their attributes

• The selection strategy

• Screening by attributes

• Ranking by economic criteria

• Case study + demos

More info:

• “Materials Selection in Mechanical Design”, Chapters 7 and 8

© MFA and DC 2005

Manufacturing processes

Process: a method of shaping, joining or surface-treating a material

Sand casting

Shaping

Blow moulding

Shaping

Fusion welding

Joining

Induction hardening

Surface treating

© MFA and DC 2005

Data organisation: the PROCESS TREE

Family

Joining

Shaping

Surfacing

Class

Casting

Deformation

Moulding

Composite

Powder

Machining

Rapid prototyping

Member

Compression

Rotation

Injection

RTM

Blow

Attributes

A process record

Material

Shape

Size Range

Min. section

Tolerance

Roughness

Economic batch

Supporting information

-- specific

-- general

Material

Shape

Size Range

Min. section

Tolerance

Roughness

Economic batch

Supporting information

-- specific

-- general

Structured

information

Unstructured

information

Difficult !Kingdom

Processes

© MFA and DC 2005

Shape classification

Some processes can make only simple shapes, others, complex shapes.

Wire drawing, extrusion, rolling, shape rolling: prismatic shapes

All shapes

Prismatic Sheet 3-D

Circular Non-circular Flat Dished Solid Hollow

Casting, molding, powder methods:

3-D shapes

Stamping, folding, spinning, deep drawing:

sheet shapes

© MFA and DC 2005

Structured data for injection moulding*

INJECTION MOULDING of thermoplastics is the equivalent of pressure die casting of metals. Molten polymer is injected under high pressure into a cold steel mould. The polymer solidifies under pressure and the moulding is then ejected.

Injection moulding (Thermoplastics)

*Using the CES EduPack Level 2 DB

Process CharacteristicsDiscrete TruePrototyping False

ShapeCircular Prism TrueNon-circular Prism TrueSolid 3-D TrueHollow 3-D True

Physical AttributesMass range 0.01- 25 kgRoughness 0.2 - 1.6 µmSection thickness 0.4 - 6.3 mmTolerance 0.1 - 1 mm

Economic AttributesEconomic batch size 1e+004 - 1e+006Relative tooling cost highRelative equipment cost high

+ links to materials

© MFA and DC 2005

Unstructured data for injection moulding*

Design guidelines. Injection moulding is the best way to mass-produce small, precise, plastic parts with complex shapes. The surface finish is good; texture and pattern can be moulded in, and fine detail reproduces well. The only finishing operation is the removal of the sprue.

The economics. Capital cost are medium to high; tooling costs are high, making injection moulding economic only for large batch-sizes (typically 5000 to 1 million). Production rate can be high particularly for small mouldings. Multi-cavity moulds are often used. The process is used almost exclusively for large volume production. Prototype mouldings can be made using cheaper single cavity moulds of cheaper materials. Quality can be high but may be traded off against production rate. Process may also be used with thermosets and rubbers.

Typical uses. The applications, of great variety, include: housings, containers, covers, knobs, tool handles, plumbing fittings, lenses, etc.

The environment. Thermoplastic sprues can be recycled. Extraction may be required for volatile fumes. Significant dust exposures may occur in the formulation of the resins. Thermostatic controller malfunctions can be extremely hazardous.

The process. Most small, complex plastic parts you pick up – children’s toys, CD cases, telephones – are injection moulded. Injection moulding of thermoplastics is the equivalent of pressure die casting of metals. Molten polymer is injected under high pressure into a cold steel mould. The polymer solidifies under pressure and the moulding is then ejected.

Various types of injection moulding machines exist, but the most common in use today is the reciprocating screw machine, shown schematically here. Polymer granules are fed into a spiral press like a heated meat-mincer where they mix and soften to a putty-like goo that can be forced through one or more feed-channels (“sprues”) into the die.

Heater Screw

Granular PolymerMould

Nozzle

Cylinder

No.8-CMYK-5/01

*Using the CES EduPack Level 2 DB

© MFA and DC 2005

Finding data

Handbooks, compilations (see Appendix D of The Text)

Suppliers’ data sheets

The Worldwide Web (e.g. www.matweb.com)

Finding data using CES BROWSE: locate candidate on PROCESS TREE and double click, or

SEARCH: enter name or word string name (trade-name, or application)

3 levels of data, with increasing content

But no comparison or perspective

© MFA and DC 2005

Selection of processes

Step 2 Screening: eliminate processes that cannot do the job

Step 3 Ranking: find the processes that do the job most cheaply

Step 4 Supporting information: explore pedigrees of top-ranked candidates

Step 1 Translation: express design requirements as constraints & objectives

Process selection has the same 4 basic steps

Because there are thousands of variants of processes, supporting information plays a particularly important role

© MFA and DC 2005

Translation

More info: Cebon, D. “Handbook of Vehicle-Road Interaction”, Swets and Zeitler, Netherlands,1999

Example: casing for a road-pressure sensor

Function Casing for road-pressure sensor

Constraints Material: Al alloyShape: non-circular prismaticMinimum section: 2 0.025 mm

Objectives Minimise cost

Free variable Choice of process

The sensor lies across the road, covered by a rubber mat. Vehicle pressure deflects top face, changing capacitance between topface and copper conducting strip.

© MFA and DC 2005

All processes

Apply a series of screening stages

Screened sub-set of processes

Physical attributes Minimum Maximum

Mass range 0.6 kg

Section thickness mm

Tolerance mm

Roughness m

Batch size

Shape

Circular prismatic

Non-circular prismatic

Flat sheet

Dished sheet

Solid 3-D

Hollow 3-D

Limit stage

Ceramics

Metals

Polymers

Hybrids

Materials

Tree stage

Eco

nom

ic b

atch

siz

e B

B1 > B > B2

Graph stage

• A combination of limit selection, tree stage and bar-charts is the best way forward.

• Bar charts are better than bubble charts (ranges too wide)

© MFA and DC 2005

Processes for a spark-plug insulator

• Material class Alumina

• Shape class 3-D, hollow

• Mass 0.05 kg

• Min. section 3 mm

• Tolerance < 0.5 mm

• Roughness < 100 m

• Batch size >1,000,000

Constraints

Specification

Function Insulator

Free variables

Choice of process

Insulator

Bodyshell

Centralelectrode

Objective Minimise cost

© MFA and DC 2005

Screening: a tree stage and a limit stage

Tree stage: Select CERAMIC (or Alumina)

Rank: bar chart for ECONOMIC BATCH SIZE.

Limit stage: Physical attributes Minimum Maximum

Mass range 0.6 kg

Section thickness mm

Tolerance mm

Roughness m

Shape

Circular prismatic

Non-circular prismatic

Flat sheet

Dished sheet

Solid 3-D

Hollow 3-D

0.05 0.06

3

0.5

100

© MFA and DC 2005

Desired Batch Size

Screen on batch size*

*Using the CES EduPack Level 2 DB

Eco

no

mic

ba

tch

siz

e (

un

its)

1

10

100

1000

10000

100000

1e+006

1e+007

1e+008

Blow Moulding

Powder methods

Injection Moulding

Sheet forming

Die Casting

Compression Moulding

Expanded foam molding

Rotational Moulding

Rolling and forging

Resin transfermolding (RTM)

Electro-discharge machining

Thermoforming Rapid prototyping

Lay-Up methods

Sand castingPolymer Casting

Economic batch size

Demo: the Process data-table

© MFA and DC 2005

Data organisation: joining and surface treatment

Processrecords

Heat treat

Paint/print

Coat

Polish

Texture ...

Electroplate

Anodise

Powder coat

Metallize...

Material

Purpose of treatment

Coating thickness

Surface hardness

Relative cost ...

Supporting information

Material

Purpose of treatment

Coating thickness

Surface hardness

Relative cost ...

Supporting information

Adhesives

Welding

Fasteners

Braze

Solder

Gas

Arc

e -beam ...

Material

Joint geometry

Size Range

Section thickness

Relative cost ...

Supporting information

Material

Joint geometry

Size Range

Section thickness

Relative cost ...

Supporting information

Class AttributesMember

Surfacetreat

Joining

Family

Shaping

Kingdom

Processes

© MFA and DC 2005

A joining record*

Gas Tungsten Arc (TIG)Tungsten inert-gas (TIG) welding, the third of the Big Three (the others are MMA and MIG) is the cleanest and most precise, but also the most expensive. In one regard it is very like MIG welding: an arc is struck between a non-consumable tungsten electrode and the work piece, shielded by inert gas (argon, helium, carbon dioxide) to protect the molten metal from contamination. But, in this case, the tungsten electrode is not consumed because of its extremely high melting temperature. Filler material is supplied separately as wire or rod. TIG welding works well with thin sheet and can be used manually, but is easily automated.

Physical AttributesComponent size non-restrictedWatertight/airtight TrueProcessing temperature 870 - 2250 KSection thickness 0.7 - 8 mm

Joint geometryLap TrueButt TrueSleeve TrueScarf TrueTee True

Materials Ferrous metals

Economic AttributesRelative tooling cost lowRelative equipment cost mediumLabor intensity low

Typical usesTIG welding is one of the most commonly used processes for dedicated automatic welding in the automobile, aerospace, nuclear, power generation, process plant, electrical and domestic equipment markets.

*Using the CES EduPack Level 1 DB

+ links to materials

© MFA and DC 2005

A surface-treatment record*

Induction and flame hardeningTake a medium or high carbon steel -- cheap, easily formed and machined -- and flash its surface temperature up into the austenitic phase-region, from which it is rapidly cooled from a gas or liquid jet, giving a martensitic surface layer. The result is a tough body with a hard, wear and fatigue resistant, surface skin. Both processes allow the surface of carbon steels to be hardened with minimum distortion or oxidation. In induction hardening, a high frequency (up to 50kHz) electromagnetic field induces eddy-currents in the surface of the work-piece, locally heating it; the depth of hardening depends on the frequency. In flame hardening, heat is applied instead by high-temperature gas burners, followed, as before, by rapid cooling. Both processes are versatile and can be applied to work pieces that cannot

readily be furnace treated or case hardened in the normal way. Physical AttributesCoating thickness 300 - 3e+003 µmComponent area restrictedProcessing temperature 727 - 794 KSurface hardness 420 - 720 Vickers

Economic AttributesRelative tooling cost lowRelative equipment cost mediumLabor intensity low

Typical usesThe processes are used to harden gear teeth, splines, crankshafts, connecting rods, camshafts, sprockets and gears, shear blades and bearing surfaces.

MaterialCarbon steel

Purpose of treatmentFatigue resistanceFriction controlWear resistanceHardness

*Using the CES EduPack Level 2 DB

+ links to materials

© MFA and DC 2005

Selecting joining & surface treatment processes

Joining -- the most important criteria are:

The material(s) to be joined

The geometry of the joint

Apply these first, then add other constraints

Surface treatment -- the most important criteria are:

The purpose of the treatment

The material to which it will be applied

Apply these first, then add other constraints

SUPPORTING INFORMATION

Matdata.net (“Search web” button)

Kelly’s Register, Thomas Register.

© MFA and DC 2005

Demo -- process selection with CES

Browse Select Search Toolbar Print Search web

Opens

Matdata.netFind what?

Which table?

Choose what you want to explore (materials, processes..)

ProcessesCastingMouldingPowder etc

© MFA and DC 2005

The main points

• Processes can be organised into a tree structure containing records for structured data and supporting information

• The structure allows easy searching for process data

• Select first on primary constraints

• Shaping: material and shape

• Joining: material(s) and joint geometry

• Surface treatment: material and function of treatment

• Then add secondary constraints as needed.

Supporting information in CES, and http://matdata.net