Transcript New approaches in Materials and Manufacturing Education

University of
Cambridge
The CES EduPack
Unit 4. Selecting processes:
shaping, joining and surface treatment
New approaches to Materials Education - a course authored by
Mike Ashby and David Cebon, Cambridge, UK, 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
Shaping
Shaping
Sand casting
Blow moulding
Surface
treating
Joining
Fusion welding
Induction hardening
© MFA and DC 2005
Data organisation: the PROCESS TREE
Difficult !
Kingdom
Family
Member
Class
Material
Casting
Joining
Compression
Deformation
Rotation
Moulding
Processes
Shaping
Shape
Size Range
Min. section
Injection
Tolerance
RTM
Roughness
Composite
Powder
Surfacing
Attributes
Blow
Structured
information
Economic batch
Machining
Supporting information
Rapid prototyping
-- specific
Unstructured
information
-- general
A process record
© MFA and DC 2005
Shape classification
Some processes can make only simple shapes, others, complex shapes.
All shapes
Prismatic
Circular

Sheet
Non-circular
Wire drawing, extrusion,
rolling, shape rolling:
prismatic shapes
Flat
3-D
Dished
Stamping, folding,
spinning, deep drawing:
sheet shapes

Solid

Hollow
Casting, molding,
powder methods:
3-D shapes
© MFA and DC 2005
Structured data for injection moulding*
Injection moulding (Thermoplastics)
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.
Physical Attributes
Mass range
0.01Roughness
0.2 Section thickness 0.4 Tolerance
0.1 -
Economic Attributes
Economic batch size
Relative tooling cost
Relative equipment cost
25
1.6
6.3
1
Process Characteristics
Discrete
True
Prototyping
False
kg
µm
mm
mm
1e+004 - 1e+006
high
high
Shape
Circular Prism
Non-circular Prism
Solid 3-D
Hollow 3-D
True
True
True
True
+ links to materials
*Using the CES EduPack Level 2 DB
© MFA and DC 2005
Unstructured data for injection moulding*
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.
Mould
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.
Granular Polymer
Nozzle
Cylinder
Heater
Screw
No.8-CMYK-5/01
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. Multicavity 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.
*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)
But no
comparison or
perspective
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
© MFA and DC 2005
Selection of processes

Process selection has the same 4 basic steps
Step 1 Translation: express design requirements as constraints & objectives
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
Because there are thousands of variants of processes,
supporting information plays a particularly important role
© MFA and DC 2005
Translation
Example: casing for a road-pressure sensor
The sensor lies across the road, covered
by a rubber mat. Vehicle pressure deflects
top face, changing capacitance between top
face and copper conducting strip.
Function
Constraints
Objectives
Free variable
Casing for road-pressure sensor
Material: Al alloy
Shape: non-circular prismatic
Minimum section: 2  0.025 mm
Minimise cost
Choice of process
More info: Cebon, D. “Handbook of Vehicle-Road Interaction”, Swets and Zeitler, Netherlands,1999
© MFA and DC 2005
Apply a series of screening stages
• A combination of limit selection, tree stage and bar-charts is the
best way forward.
All processes
Limit stage
Minimum
Mass range
Tree stage
Maximum
0.6
kg
Section thickness
mm
Tolerance
mm
Roughness
m
Ceramics
Batch size
Materials
Shape
Circular prismatic
Non-circular prismatic
Metals
Polymers
Flat sheet
Dished sheet
Hybrids
Solid 3-D
Hollow 3-D
Graph stage
Economic batch size B
Physical attributes
• Bar charts are better than
bubble charts (ranges too wide)
B1 > B > B2
Screened sub-set of processes
© MFA and DC 2005
Processes for a spark-plug insulator
Specification
Function
Constraints
Insulator
• Material class Alumina
Insulator
• 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
Objective
Minimise cost
Free
variables
Choice of process
Body
shell
Central
electrode
© MFA and DC 2005
Screening: a tree stage and a limit stage
Limit
stage:
Physical attributes
Mass range
Minimum
0.05
Section thickness
Maximum
0.6
0.06
kg
3
mm
Tolerance
0.5
mm
Roughness
100
m
Shape
Circular prismatic
Non-circular prismatic
Flat sheet
Dished sheet
Solid 3-D
Hollow 3-D
Tree stage:

Select CERAMIC (or Alumina)
Rank: bar chart for ECONOMIC BATCH SIZE.
© MFA and DC 2005
Screen on batch size*
1e+008
1e+007
Desired
Batch Size
1e+006
Economic batch size (units)
Economic batch size
Blow Moulding
Powder methods
Injection Moulding
Sheet forming
Expanded foam molding
100000
Rolling and forging
Electro-discharge machining
10000
1000
100
10
Polymer Casting
Sand casting
Die Casting
Compression
Moulding
Rotational
Moulding
Lay-Up
methods
Resin transfer
molding (RTM)
1
Thermoforming
Rapid
prototyping
Demo: the Process data-table
*Using the CES EduPack Level 2 DB
© MFA and DC 2005
Data organisation: joining and surface treatment
Kingdom
Family
Class
Adhesives
Joining
Member
Braze
Material
Solder
Joint geometry
Welding
Gas
Fasteners
Arc
e -beam ...
Processes
Attributes
Size Range
Section thickness
Relative cost ...
Supporting information
Shaping
Material
Heat treat
Paint/print
Surface
treat
Coat
Polish
Texture ...
Electroplate
Purpose of treatment
Anodise
Coating thickness
Powder coat
Surface hardness
Metallize...
Relative cost ...
Supporting information
Process
records
© 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 Attributes
Component size
Watertight/airtight
Processing temperature
Section thickness
non-restricted
True
870
2250 K
0.7
8
mm
Ferrous metals
Economic Attributes
Joint geometry
Lap
Butt
Sleeve
Scarf
Tee
Materials
True
True
True
True
True
Relative tooling cost
Relative equipment cost
Labor intensity
low
medium
low
+ links to materials
Typical uses
TIG 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
© MFA and DC 2005
A surface-treatment record*
Induction and flame hardening
Take 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 workpiece, locally heating it; the depth of hardening depends on the
frequency. In flame hardening, heat is applied instead by hightemperature 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 Attributes
Coating thickness
Component area
Processing temperature
Surface hardness
300
restricted
727
420
-
3e+003
µm
Carbon steel
794
720
K
Vickers
Purpose of treatment
Fatigue resistance
Friction control
Wear resistance
Hardness
Economic Attributes
Relative tooling cost
Relative equipment cost
Labor intensity
Material
low
medium
low
+ links to materials
Typical uses
The processes are used to harden gear teeth, splines, crankshafts, connecting rods, camshafts, sprockets and gears,
shear blades and bearing surfaces.
*Using the CES EduPack Level 2 DB
© 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
Toolbar
Browse
Select
Choose what you want to
explore (materials, processes..)
Search
Find what?
Which table?
Print
Search web
Opens
Matdata.net
Processes
Casting
Moulding
Powder
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
© MFA and DC 2005