W 02-04 ME6093 Mfg Process

Composites Manufacturing &

Manufacturing Process Selection Strategy

(the Ashby approach)Week 3 - 4

Dept of Mechanical Engineering,

Mohammad Ali Jinnah University

Dr. Rizwan Saeed [email protected]

Material selection charts in this slide are copyright of GranataDesign and should only be used for educational purpose

COMPOSITES MANUFACTURING

FULLY AUTOMATED CAR BONNET

MANUFACTURE AT BMW

MANUAL CAR BONNET MANUFACTURE

USING VARI

Click on image to play video

PROCESS SELECTION! - COMPOSITES DRIVING FORCES

Criteria on which composites are selected depend on the industry in

which they will be used same is the case for Processes Selection!

Aerospace: mainly weight reduction with increased stiffness/strength High scrap levels are (were?) tolerated

There is a preference for high performance materials in order to reach the

weight savings

5

Fibres need to be continuous and volume

fractions need to be high

Transportation: Emphasis is on decreasing cost

Return on investment, complex

shapes, recycling, etc.

Need to reduce weight as increased

safety requirements = heavier

vehicles = worse fuel economy

Manufacturing routes need to be

low-cost and high speed: fibre

volume fractions not so much of an

issue

Aerospace:Strength, stiffness,

weight, quality control

Mechanical Industry:Design, strength, quality

Automotive:Automated fabrication

Perf

orm

an

ce

1/Cost

6 Prepreg (autoclave) prepregs were expensive Capital equipment (Autoclaves, tape layers) are expensive, material

deposition rates and processing are slow

More than 70% of part cost from fabrication!

INEFFICIENT MANUFACTURING PROCESSES

COSTS

Car

Materials Design

Manufacturing

SYSTEMS APPROACH TO DESIGNING WITH

COMPOSITES

PROCESS SELECTION! - WHY THE FUSS!

Effects of manufacturing

Manufacturing route has to be chosen at part design as

this has a huge influence on the final properties of the

composite

Influences include component geometry, reinforcement

type/format, matrix, quality problems, etc.

9

Knockdown factors

Main cause of safety margins

introduced are due to

manufacturing problems:

Up to a 40% reduction in the

composite value is due to

manufacturing issues

It is essential to know/

understand the different

manufacturing routes in order

to prevent these problems

RELATIONSHIP OF MATERIAL PROPERTY WITH PROCESSING

PROCESSING FOR PROPERTIES

PROCESS SELECTION

Process

Economics

THE PROCESS SELECTION CONSTRAINTS / PROCESS

ATTRIBUTES

Material

1. Type of composite matrix (e.g. Polymeric , Thermoset or thermoplastic, metallic or ceramic)

2. The type of preform (i.e. the form of reinforcement) i.e. yarn, non-crimp fabric, woven fabric, chopped strand, braded etc.

Shape

3. Achievable shapes and geometries

4. The requirement of dimensional control (accuracy and repeatability)

Function & Material

5. Achievable reinforcement volume fraction

6. Achievable control of fibre orientation

7. The dictates of quality control

Process Economics / Environment

8. The requirement of number of parts (production rate)

9. The organizational budget (cost of process)

10. Trade Embargos, Environmental legislation, Local Laws etc.

MANUFACTURING PROCESSES (UNDERSTANDING

MATERIAL CONSTRAINT)

Open Mould Techniques

Contact moulding

Hand lay-up, spray

lay-up

Filament winding

15

Closed Mould Techniques

Liquid composite moulding

Hot press moulding

Injection moulding

Centrifugal casting

Before formally developing the strategies for Process Selection lets revisit

some of the very widely used manufacturing processes and compare then for

the ten constraints/attributes discussed

Manufacturing can be divided into two separate techniques depending on how

the resin is infiltrated into the reinforcement

The techniques can also be classified on the basis of type of preform type.

Preforming may be performed in-house or they may be purchased directly

from an external supplier.

MANUFACTURING COMPOSITES

(MATERIAL CONSTRAINT)

Raw

Material

(Fibre & Resin)

Preforms

Wet preformsDry Preform

1D Preform

(yarn,

roving)

2D Preforming

Technical textiles

incl. woven fabrics,

uni-weave (UD

fabric), Non Crimp

Fabric,

Mats (Chopped &

Continuous)

2D braids

1. Prepregs

(UD and

Woven (2D

and 3D)

2. Moulding

compounds

3D Preforms

(3D Woven

and braided)

Appropriate Product Manufacturing Processes

(Primary shaping, Secondary shaping and joining)

MANUFACTURING THERMOSET

COMPOSITES Appropriate Product Manufacturing Processes(Primary shaping)

Dry Preform1D Preform

2D Preform3D Preform1. Filament

winding

2. Spray up

3. Pultrusion1. Hand layup

2. VARI/SCRIMP/

Fastrac

3. VARTM

4. TERTM

5. SRIM/RRIM

6. Pultrusion

Wet preforms

Prepreg

1. Vacuum bag moulding

2. Blow moulding

Moulding compounds

1. Compression Moulding for

(SMC and BMC)

2. Injection Moulding (BMC)

Secondary shapping and joining

(water jet cutting, machining, laser

cutting, adhesive bonding and

cocuring, riveting, painting etc

EXAMPLE OF A COMPLETE PRODUCT

MANUFACTURING ROUTE

PrepreggingMatrix

Fibres

Lay-up &

BaggingAutoclaving Finishing

Part

Assembling

Continuous Batch Batch Batch

Batch

Adhesive &

Core Materials

Overall process scheme for manufacturing of autoclaved

prepreg based composites

Property testing feedback loop

PROCESSES REVISITEDA quick review of the more widely used thermoset

composites manufacturing processes

9/2

0/2

015

HAND AND SPRAY LAY-UP

Resins are impregnated by

hand into fibres which are in

the form of woven, knitted,

stitched or bonded fabrics. This

is usually accomplished by

rollers or brushes, with an

increasing use of nip-roller type

impregnators for forcing resin

into the fabrics by means of

rotating rollers and a bath of

resin. Laminates are left to

cure under standard

atmospheric conditions.

21

Coat tool with release agent

Spray gel-coat onto mould tool. Gel coat produces Class-A surface finish on outer surface

Gel coat is hardened before laying the fibres

22

Select dry reinforcement

form:

Mats, fabrics but not UD

rovings

Cut and trim to size, and

stipple onto wet/tacky gel

coat layer

23

Resin applied using brush rollers

either manually or through

pumped systems

Product is consolidated by hand using

steel rollers

Helps remove air bubbles and

achieves desired compaction

Thick parts are built up in stages

to prevent excessive exotherm

If necessary a core is bonded and

then lamination continues

Cost:

24

Similar to wet lay-up initially

Resin and reinforcement applied through use of spray gun

Chops fibre rovings into lengths of 1070mm (typically 40mm)

Mixes resin, catalyst and accelerator

Fibres deposited on surface through action of resin pump

Part rolled for consolidation

Resin cured at room temp

Spray-up (or spray lay-up)

25

Fibre feed (rovings cheap)

Resin is supplied to

the gun in 2 streams:

Catalyst

Resin

plus accelerator

Typical spray-up gun arrangement

26

Big sections very

suitable for spray.

Machine: 5K-10K

Mould: 150-15K

Size: ~10m2

Prod. Rate: 5-50kg/hr

Quantity: 5-2000/yr

27

AdvantagesSimilar to wet lay-up but:

Faster deposition rates

Suitable for small- to medium-volume parts

Labour costs lower than for hand laminating

Allows easy part thickness variation

Easily automated

Limitations Reinforcement in chopped format Only

Concerns about styrene emissions

Different types of chopper guns produce different styrene emissions due to different mixing methods

Inconsistent quality

Product quality dependent on operator skill dimensional inconsistencies within and between batches

Difficult to remove trapped air from moulding

Low volume fraction of fibres also limited to chopped fibres

High levels of waste due to overspray

28

Easily automated !

Spray lay-up can be easily

automated using robots (e.g.

Fanuc P200-T modfied paint

robot with AccuChop control

software Fanuc Robotics)

Improves product quality

More consistent products

Reduced waste material usage

monitoring

Feedback on amount of material

applied to a part

Click on image to play video

29

Filament winding is one of the first techniques used in mass

production

A carriage unit carrying the fibres moves back and forth while the

mandrel rotates at a specified speed

Controlling the motion of the carriage unit and the mandrel allows the

desired fibre angle to be generated

Fibre tows or rovings are impregnated in bath or resin and wound under

tension over a mandrel in a defined geometric pattern

Process ideal for rotational symmetrical shapes e.g. tubes, pressure

vessels, pipes, rocket motor casings and launch tubes, and storage

tanks

FILAMENT WINDING

Click on image to play

video

Polar Winding:

Mandrel rotates,

feed stays fixed

Chopped fibres dispensed onto

feed section

Used for making pipes and

tanks

VARIATIONS

31

Advantages Filament winding places fibres in exact

orientations for maximum structural efficiency

High volume fractions possible (up to 70%)

For certain applications, e.g. pressure vessels and

fuel tanks it is the only method for manufacturing

cost-effective composite parts

Raw materials and mandrels are low-cost, so parts

are cost-effective

Can be automated for high-volume production

Multi-axis winding allows complex shapes

(examples connection rods, prostheses, branched pipe work)

32

Disadvantages A mandrel is needed therefore only hollow sections are

possible

It is difficult to obtain uniform fibre distribution and resin

content throughout the thickness of the part

High (>1%) void content without use of vacuum, especially at

high winding speeds

Complex programming is required for multi-axial parts

Cannot wind into concave surfaces

Need to follow geodesic paths during winding:

Not all fibre angles are easily produced: 0 to 15 is difficult

Open mould process therefore there are emissions concerns

The outer surface of the wound component is not smooth

A teflon coated bleeder cloth or shrink tape can be applied over the

surface once winding is complete

MSc Composites Science & Engineering 33

Filament winding

Machine: 30k-150k

Tools: 1k-20k

Size: 50150cm longProd. Rate: 3-50m/hr

Quantity: >1500m/yr

35

Similar to extrusion but fabric/roving is pulled through a die rather

than pushed

Continuous reinforcements are drawn from a spool and pulled into

pultrusion die

Guides or bushings in front of the die preform the reinforcement

Impregnation with liquid resin is performed either in an open bath (=

cheap) or under pressure in die (= more expensive dies)

Resin is typically filled with calcium carbonate or fire retardants etc

Heated part of die consolidates tool curing is essentially complete as part emerges

Sections are cut to desired length

PULTRUSION

Cost: 7k-300k

Size: ~30cm2mCycle time: ~4hr

Quantity: 1-10000/yrClick on image to play video

PULTRUSION PROCESS ANIMATION

Click on image

to play video

37

Processing for prepreg

Vacuum bag moulding Basically an extension of the hand lay-up process where pressure is

applied to the laminate once laid-up:

Improves consolidation.

Click image for video

38

Vacuum bag moulding: processing

Lamination & Bagging performed at ambient temperature &

pressure

Vacuum is applied once the resin is of sufficient viscosity to

prevent excess resin bleed (i.e. excessive removal of resin)

The vacuum is held until the resin has reacted beyond the gel point

Uniform pressure is needed such that perforated tubes and/or extra

breather cloth may be required to provide a network of air paths

Vacuum bagging is a useful procedure for bonding core

materials and for forming curved panels where there is a need

for uniform pressure to hold the core in place

In this case the pressure is held until the adhesive bond is strong

enough to hold the core in place

39

Advantages Higher fibre content and lower void content than with standard hand

lay-up.

Volume fractions of 58% and void contents below 2% easily achievable

Improved mechanical properties are achieved as a result

Better fibre wet-out due to pressure and resin flow

Heavier fabrics than those commonly used in hand lay-up can be easily wet out

The additional consolidation pressure helps the reinforcement conform to tight

curvatures

Health and safety

The vacuum bag reduces the amount of volatiles emitted

Pre-preg layup can be Automated for faster production and accurate

control (Click for video)

40

Disadvantages During lamination there are still health & safety issues due to styrene

emissions

Therefore there are still the cost issues of extracting the VOCs (volatile

organic compounds)

The extra process adds cost both in labour and in disposable bagging

materials

Production rates suffer due to extra labour for bagging: bags are only available

in certain widths and it can be difficult to seal adjacent pieces

Moulds need to be vacuum tight

Care needs to be taken with resins that emit volatiles: UPE and VE will lose

styrene under vacuum making them porous

A higher level of skill is required by the operators for the bagging

stage

There is a need to prevent vacuum leaks while at the same time work needs to

be quick so as to pull vacuum before the resin gels

Mixing and control of resin content still largely determined by

operator skill

Processing for prepreg - Blow Molding

Being used for

hockey stick

manufacture

After part layup it

is placed in a two

part heated mould

and high pressure

gas is blown in.

The layup takes the

shape of mould and

is allowed to cure

and then taken out

42

VARI VARI is a liquid moulding processing method popularized by Lotus to

manufacture the Elan, the Esprit, and the Excel automobiles.

Tooling can be matched or one-sided with a flexible tool

Vacuum is used to draw the resin through the preform and hold the mould closed

during processing.

Low volume of parts produced per year:

The process aims to compete with spray-up and hand lay-up as opposed to RTM

Mould prepared

and gel-coated

Filled with fabrics

and preforms

43

Vacuum tight upper tool covers reinforcement Evacuated to consolidate materials, trap on vacuum line to ensure no

resin drawn into vacuum pump.

Resin supply clamped

to stop resin flow

(gravity assisted!)

VARI (cont)

44

Resin flows and wets out

fabrics to fill cavity

VARI (cont)

45

Final part

46

Remember the BMW video in start

RTM is capable of satisfying the low-cost/high-volume 500-50,000 parts per

year of the automotive industry as well as the higher performance/lower

volume 50-5,000 parts per year of the aerospace industry.

Processing:

Two-part, matched-metal mould (or tool) is required

Reinforcement is preformed and placed into the mould

Cores and inserts are inserted into the preform as required

Mould is closed under hydraulic/pneumatic pressure or clamped at the edges

Resin is pumped under low pressure through injection ports into the mould and

follows pre-designed paths through the preform.

Both the mould and resin can be heated as needed for the application.

Resin Transfer Moulding (RTM)

Click for Video

MSc Composites Science & Engineering

Tooling

Important parts:

Seal

Clamping

High clamping pressures allow higher injection pressures

Injection port (s)

Important to control flow fronts and ensure no trapped air

or dry spots

Vent (s)

Must be located near last areas to be filled

Heating/Cooling system

Ejector pins

Sensors

Allow process monitoring

47


RTM Mould tool

48

Rigid supports

Clamps


Resin injection machine can

provide injection pressure

similar in many respects to

spray machine (costs about

15-20K)

Mould filling with reinforcement

is time consuming operation

often limiting step in determining

cycle time.

Loft of fabrics and especially

mats make it necessary to impart

pressure to close tool typically

200 psi.


Mould closed and clamped shut

Often use bolts or G-clamps

Hydraulic or pneumatics

produce a higher closing

force

Resin injected from suitable location

care needed to ensure all mould is

filled no dry spots.

Leaky moulds often used to allow air

to escape.


Mould opened

after cure.

Note resin/fibre

around edge of tool

High quality precision part

Cost: 3k-20k

Size: >0.2m2-10m2

Prod Rate: 2-10/hr

Quantity: 200-10,000/yr


Resin Injection

Pressure pot system

Low cost

Accurate mixing

Limited injection pressure

Piston based

Typically used for SRIM

High pressure injection

52


Resin Temperature

Important points:

Injection temperature

Preheating resin lowers overall

viscosity

Tool temperature

Ideally similar to injection

temperature to keep resin at

low viscosity during process

High injection temperature

lowers time to gel and time to

cure, therefore decreasing

cycle time

53


Advantages Low capital investment

Tooling and operating costs are low compared to injection and compression moulding

Good surface quality

Mouldings can be manufactured to close dimensional tolerances and with two good

surfaces: both surfaces can have similar or different finishes

Tooling flexibility

Large, complex shapes can be manufactured in a one-shot process

Ribs, cores and inserts can be placed into the preform allowing whole parts to be

produced in a single moulding

Range of available resin systems and reinforcements

Controllable fibre volume fraction

Up to 65% can be achieved with heavy tooling and high clamping pressures

Disadvantages Complex parts need a degree of trial and error to ensure that there are no dry

patches in the final moulding

Matched tooling costs are higher than for hand lay-up and spray-up processes

Tooling design is complex

54


SCRIMP/RIFT and associated processes

Hybridisation of RTM, VARI and vacuum bagging

One sided tooling only

Preform assembled and bagged with plastic bag

Vacuum pulled (1 atm.)

Provides compaction and positive pressure for resin to flow

Distribution medium on top of preform acts as path of low flow resistance for injected resin

Resin moves over this medium and down into the preform

55


Differences between Vacuum Infusion and SCRIMP

56

In conventional Vacuum

infusion, resin has to permeate

through the thickness of the

reinforcement stack and then

proceed towards the end of the

part slow process.

Permeation through bundles is slow.

Flow A to B is rate determining step

A

B

C

A

B

C

In SCRIMP, a distribution medium is inserted

between the vacuum bag and the reinforcement.

This lifts the bag slightly away from the reinforcement

allowing resin to rapidly travel across the surface of the

part.

Impregnation then involves permeation through the

thickness of the part much quicker. B to C is rate

determining step


SCRIMP/RIFT is now very popular in marine, and increasingly aerospace.


Typical products

59

Carbon epoxy

Fuselage section

Stitched Wing Box

Produced using SCRIMP

(USAF labs)


New variants: Fastrac

60

Dispenses with distribution layer instead uses profiles outer layer to create channels.

Inner vac bag is sucked onto this layer at the beginning to create channels (two vac bags!!).

Resin flows over part. Outer vacuum released eliminates surface roughness and waste of

resin trapped in distribution medium.


FASTRAC

61


Comparison between hand-lay up and other processes for the production of a 30x120 cm,

24-ply, 1.9 kg flat panel, 1200 units per year.

Machinery

cost

Relative production

timeProcess limitations

Hand lay-up - 1.000 None

Automated cutting 0.5-1.0 mio$ 0.895 None

Automated tape

lay-up 2.0-4.0 mio$ 0.460

Flat laminates only;

Unidirectional tape only

Filament winding 0.25-0.50 mio$ 0.662-0.376 Convex shapes only

Pultrusion N/A 0.04 Constant cross-section only;

No cores

RTM 40-80 k$ 0.087 Low resin viscosity;

No honeycomb cores


SRIM/RRIM

Extension to RTM

RIM mixes 2 to 4 fast reacting components with the mixing occurring just prior to injection

Moulds and reactants are preheated: temperatures of 50 to 90C are common

Cure occurs within 30 60s = cycle time of 12 min

Polyurethane resins are the most common polymer due to their high reaction rate

Very low viscosity resins needed (10 times less than for RTM)

RRIM (video)

Short or milled glass fibres (


Reinforced Reaction Injection Moulding - RRIM

64

The principle of RIM consists of injecting into a closed

mould and under low pressure (0.5 MPa), two or

more reactive components

These are mixed within a nozzle, just prior to

their injection into the mould.

The reaction, in the case of a polyol and an

isocyanate, leads to the formation of a polyurethane.

The introduction of short strands, such as

chopped fibres, directly into one of the two

reactive constituents, leads to the injection of a

pre-reinforced mixture

This is known as R-RIM (Reinforced Reaction

Injection Moulding).

The introduction of long strand reinforcement

such as continuous filament mats, fabrics,

complexes or chopped strand preforms into the

mould before the injection takes place is known as

S-RIM (Structural Reaction Injection Moulding.


SRIM

65

The RIM process is based

on the injection of the two

polyurethane components

(a polyol and an isocyanate)

inside a mould cavity.

The automotive market

offers the most important

applications for this process,

such as dashboards, interior

panels and under body

shields.


SRIM/RRIM

Advantages Suitable for high volume structural parts (SRIM only) at low cost

Small to large-sized parts with complex configurations possible

Disadvantages Large capital investment in equipment

High cost of tools

Maximum fibre volume fraction of 40%

66


Compression Moulding

Was specifically developed for replacement of metal components with

composite parts.

Process can be carried out with either thermosets or thermoplastics.

Compression moulding is the most common method of processing thermosets.

Compounds can be produced that are pre-combined forms of a composite

that include resin, fibres, curing agents and any other additives needed to

optimise physical properties

These compounds and shaped at higher temperatures and cure is triggered by

the high temperatures

High temperatures and high pressures ensure rapid forming and rapid curing to

allow short cycle times

67

There are various types of compounds used for compression moulding

Sheet Moulding Compound (SMC)

Dough/Bulk Moulding Compounds (DMC/BMC)

Glass Mat Thermoplastics (GMT)


Sheet Moulding Compounds

SMC is a variable system of components containing a large variety of

fillers and additives that makes it suitable for a wide range of

applications.

The SMC resin matrix can be adapted to the required characteristic profiles of

the final product

Resistance to chemicals and weathering, surface structure, flexibility, dyeability,

shrinkage, flame retardation, strength, dynamic characteristics, surface hardness, etc

The fibres influence the

Strength and rigidity characteristics, amount of shrinkage and warping

68

Resins tend to be UPEs and VEs that have additives to ensure lo shrink and

smooth surface finish

The resins are thickened with alkaline earth oxides and hydroxides to make a

paste

Fibres are typically chopped and random, though modern advances include the

addition of long fibres


SMC formulations

69

Monostyrene additive (10wt% of resin) can be

added to lower viscosity

Catalyst is an organic peroxide, though several

types may be combined for optimal curing

properties

Inhibitors can be added to improve the shelf-life

of the SMC

Fillers reduce thermal shrinkage and help the flow

of the fibres during moulding

CaCO3 has low oil absorption rates and can be added

in large amounts, it also gives a smooth surface finish

Aluminium trihydrate gives flame retardancy

SMC Formulation by weight %

Resin 2027%

Fibres 3050%

Catalyst 0.31.5%

Filler (CaCO3) 4050%

Detaching Agent (Ca & Zn stearate) 12%

Thickening Agent (MgO, MgOH2) 13%

LPA 34%

Pigment 15%

LPA is a thermoplastic additive:

Typically is a finely ground PE powder, but can also be PMMA, PVAc, etc. that are dissolved in styrene and

serve to reduce the shrinkage of the UPE resins

Mould release agents:

Zn or Ca stearates are added to allow trouble-free removal of the moulded parts. During cure, the stearate

becomes incompatible with the UPE and flows to the surface of the part

Thickeners serve to turn the UPE resin into a handleable non-sticky paste that is relatively rigid

Other fillers, e.g. pigments, carbon black, microshperes etc, can also be added


SMC Continuous fibres are chopped to a length of 25 to 50mm and fall onto a moving

carrier film that is coated with the resin mixture.

A doctor blade ensures that the correct thickness of paste is delivered on to the film

A second resin coated film is then brought into contact with the first and the

sandwich is passed through compaction rollers to compact material.

70


Additives effects on cure

71

Insufficient

viscosity for

handling

Slow initial thickening

allows fibres to be

completely wet out; slow

eventual thickening gives a

longer operating window in

which to process the SMC

Viscosity increases

too quickly


SMC can be cut and handled easily

weighed for use in moulding process.

Typical part

Charge is cut to shape but it is NOT a

net shape process. Typically SMC

charge only covers 50-70% of the mould

tool surface.


SMC

Time to produce a part is dictated by the time

for resin cure

Moulding pressure ~35 to 140bar:

Higher glass contents require higher closing

pressures

SMC moulds require positive closure, i.e. moulds

have to compress the material

73

Press: 30K-350K

Tools: 3K-70K

Size: >100cm2 3m2

Cycle time: 1 5 min.

Quantity : >5000


SMC curing cycle

Typical curing cycle for compression moulding

(1MPa = 10bar)

74

PROCESS SELECTION PERFORMANCE/VOLUME

CONSTRAINT FOR (FOR POLYMERIC COMPOSITES)

75(& manufacturing cost)

76

?

Performance versus Production

Ideal situation for composite takeup

would be to have high modulus

parts capable of being produced at

over 1000 parts per day


Process selection chart

77

9/2

0/2

015

Low volume production favours RTM

Large scale production favours SMC

e.g. Renault Espace: Production had to shift to SMC due

to large demand

PROCESS SELECTION COST/VOLUME CONSTRAINT

SMC vs. RTM

PROCESS SELECTION COST/VOLUME CONSTRAINT

Pigmentation adds to value

of final product

SMC allows modification of

parts allowing easy

production of Special

Editions

SMC vs. Steel

PART 1 SUMMARY A huge variety of processes can

be used for manufacturing

composites

Each process has certain

advantages and certain

limitations.

Comparing the processes

attribute using a formal

methodology that takes into

account the interaction of

materials, shapes, functions,

process, and economics can

allow us to make a rational

choice

USEFUL REFERENCES

PROCESS SELECTION

Process

Economics

CLASSIFYING PROCESSES

MEMBER ATTRIBUTES - THE BASIS FOR

PROCESS SELECTION

MEMBER ATTRIBUTES - THE BASIS FOR PROCESS

SELECTION

EXAMPLE MEMBER ATTRIBUTES FOR COMPOSITESMANUFACTURING PROCESSES

Material

Shape

Size

Mass

Tolerance

Roughness

Reinforcement Type and layup

Control on angles during layupVolume Fraction rangeVoid Content achievable

Batch Size

Cost Model

Production rate

Documentation

PROCESS SELECTION

Translation of process

requirements

Function:What must the process do ? (e.g.

moulding? joining? finishing ?)

ConstraintsWhat technical limits must be met? (i.e.

Material and shape compatibility)

What quality limits must be met

(Precision, porosity/void content, volume

fraction, fibre orientation control )

Objectives

What is to be maximized or minimized?

(Cost? Time ? Quality)

Free variables

Choice of process and process-operating

conditions

SCREENING USING

CONSTRAINTS

Process - Material

Compatibility

SCREENING USING

CONSTRAINTS

Process Shape Compatibility

SCREENING USING CONSTRAINTS Process Mass Compatibility

SCREENING USING CONSTRAINTS Process Section thickness Compatibility

SCREENING USING CONSTRAINTS Process Tolerance Compatibility

SCREENING USING CONSTRAINTS Process Surface Roughness Compatibility

RANKING THE COST OBJECTIVE

The Cost function and economic batch size

m= component weight (mass)

f = scrap function

n = number of components

L = load factor

two = write-off time

= production rate (units per hour)Int = integer value function

RANKING THE COST OBJECTIVE Understanding economic batch size

The cost of sharpening a pencil plotted against batch size

RANKING THE COST OBJECTIVE Process-vs-Economic batch size

COMPUTER AIDED PROCESS SELECTION

Cambridge Engineering Selector

CASE STUDY :

FORMING A FAN (FOR VACUUM CLEANERS)

CASE STUDY : FORMING A FAN(FOR VACUUM CLEANERS)

Process - Material

Compatibility


Process Mass Compatibility


Process Section thickness


Process Tolerance


Process Roughness

CASE STUDY : FORMING A FAN(FOR VACUUM CLEANERS) Economic Batch Size

CASE STUDY : FORMING A FAN(FOR VACUUM CLEANERS) Final recommendation

Exploring the cost further


Relative cost of moulding the fan

College of Electrical and Mechanical Engineering

Traditional and still the most prevalent approach - Trial

and Error based on historic data of usage and availability

Scientific approach: Most Popular theses days

Ashby approach Cambridge Engineering Selector

Other scientific approaches include Matrix methods such

as Multiple Criteria Ranking Methods, Digital Logic

Method and Analytical Hierarchical Method (AHP)

All scientific approaches to material selection attempt to

ensure that the desired functionality is achieved while

satisfying the constraint(s) and maximizing the desirable

objective(s)

MATERIAL SELECTION PROCESS


Function:

The desirable operation to be performed by the material; e.g. in mechanical design this can be usually translated into quantities that relate directly to material properties; for example a tie-rod resists axial loads and the functional requirement can be expressed in terms of both strength and stiffness.

Objective:

For example minimize mass and cost

Constraints:

E.g. Availability, minimum strength requirements, allergies

Defines the performance (p) for a design problem as functionalp = p(F,G,M)

where F = functional requirements; G = Geometric parameters; and M = material indices

THE ASHBY APPROACH


If this functional can be written in separable form such as

p = p1(F).p2(G).p3(M) then for a given set of F and G the

problem of Material selection reduces to the one of optimizing

M; i.e. the material indices.

Based on above the Material index is a combination of

materials properties that characterizes the Performance of a

material in a given application [1].

Function, Objective, and Constraint Index

Tie, minimum weight, stiffness E/r

Beam, minimum weight, stiffness E1/2/r

Beam, minimum weight, strength s2/3/r

Beam, minimum cost, stiffness E1/2/Cmr

THE ASHBY APPROACH


CASE STUDY: MATERIAL FOR OARS


Constraints:

Deflection limits:

Soft = 50 mm, Hard = 30 mm

Weight limit:

As light as possible:

Shape:

Hollow Shaft with variable diameter and flat spoon

Weight hung 2.05 m

from collar


Wooden oars made of laminated spruce wood Requires around 2 weeks to settle down after lamination and gluing Weighs between 4 to 4.3 kg Quality consistency also depends on availability of same grade of

wood and workers skill.

CFRP is also better because 1. Possibility of faster production rates

2. More control over stiffness by precisely varying the fibre resin content

3. Weight can be easily lowered to 3.9 kg

4. More consistency of part quality

CASE STUDY: PROCESS FOR CFRP OARS

Process Requirements:

Function Moulding (shapping) Constraints Material (CFRP)

Shape Hollow/Solid 3DMass less than 4 kgTolerance - ?

Roughness - ?

Control on angles < 2.5o variation ?

Volume fraction > 40% Void Content < 2%

Reinforcement Type Continuous (Multidirectional layup)

Batch Size ? (1000)Production Time - ? (less than 2 weeks)

Same Process for Spoon and Loom

Objective Minimize costFree variables Choice of Process

Process parameters


Process - Material

Compatibility

Oars


Process Loom Spoon

1. RTM ++ ++

2. VARI + ++

3. Vacuum

bagging Prep-preg

+++ +++

4. Spray-up +++ +++

5. Filament

Winding

+++ N/A

Process Mass CompatabilityAll Five Processes

Process Fibre Type and Layup Compatibility

Process Loom Spoon

1. RTM ++ ++

2. VARI ++ ++

3. Vacuum

bagging Prep-preg

+++ +++

4. Spray-up N/A N/A

5. Filament

Winding

+++ N/A

Process Production Time Compatability

All Five Processes


Process Batch Size Compatibility

Process Loom Spoon

1. RTM +++ +++

2. VARI + +

3. Vacuum

bagging Prep-preg

++ +

4. Spray-up +++ +++

5. Filament

Winding

+++ +++

Process Fibre Orientation Control Compatibility

Process Loom Spoon

1. RTM + ++

2. VARI + +

3. Vacuum

bagging Prep-preg

+++ +++

4. Spray-up N/A N/A

5. Filament

Winding

+++ N/A


Process Volume fraction /Void Content Compatibility

Process Loom Spoon

1. RTM ++ ++

2. VARI + +

3. Vacuum bagging Prep-preg +++ +++

4. Spray-up N/A N/A

5. Filament Winding N/A N/A

Process Shape Layup Vf/Void Orient.. Batc

h

Aggregate

1. RTM 4 4 4 3 6 21

2. VARI 3 4 2 2 2 13

3. Vacuum

bagging

Prep-preg

6 6 6 6 3 27

Cumulative Ranking after elimination of processes which were not applicable on one or more counts


Vacuum bagging with curing is better for the criteria

considered however it may require secondary curing using

oven or autoclave depending on design specifications

On rigorous cost analysis RTM may turn out to be cheaper

in long run especially if part count is increased

CONCLUSION

Process

Economics

USING THE SELECTION CHARTS

Documents

W 02-04 ME6093 Mfg Process