university of cambridge new approaches to materials education - a course authored by mike ashby and...
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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