composites manufacturing manufacturing process selection
TRANSCRIPT
College of Elect. & Mech. Engineering
Composites Manufacturing &
Manufacturing Process Selection Strategy
(the Ashby approach)
Dept of Mechanical Engineering,
NUST, College of E & ME, Rawalpindi, Pakistan
Dr. Rizwan Saeed Choudhry [email protected]
Material selection charts in this slide are
copyright of Granata Design and should only be used for educational purpose
College of Electrical and Mechanical Engineering
COMPOSITES MANUFACTURING
College of Electrical and Mechanical Engineering
FULLY AUTOMATED CAR BONNET
MANUFACTURE AT BMW
College of Electrical and Mechanical Engineering
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
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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 <1
Subway 15
Aircraft 200
Satellite 5,000
$ saved (Fuel) / kg weight reduction per lifetime
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
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 preforms Dry 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 Preform 1D Preform
2D Preform 3D Preform 1. Filament
winding
2. Spray up
3. Pultrusion 1. 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
Prepregging Matrix
Fibres
Lay-up &
Bagging Autoclaving 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 REVISITED A quick review of the more widely used thermoset
composites manufacturing processes
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014
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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: <£500
Size: 1-200m2
Prod. Rate: 1-10kg/hr
Quantity: 1-500/yr
24
• Similar to wet lay-up initially
• Resin and reinforcement applied through use of spray gun
– Chops fibre rovings into lengths of 10–70mm (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
Advantages Similar 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
College of Electrical and Mechanical Engineering 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)
College of Electrical and Mechanical Engineering 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: 50×150cm long
Prod. Rate: 3-50m/hr
Quantity: >1500m/yr
MSc Composites Science & Engineering 34
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: ~30cm×2m
Cycle time: ~4hr
Quantity: 1-10000/yr Click on image to play video
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PULTRUSION PROCESS ANIMATION
Click on image
to play video
37
• 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
38
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
39
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…)
40
Resin flows and wets out
fabrics to fill cavity
VARI (cont…)
41
Final part
42
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
43
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
44
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)
45
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
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COMPRESSION MOULDING AND THERMO-
FORMING FOR SMC AND BMC
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014
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SMC – Compression moulding 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.
PROCESS SELECTION – PERFORMANCE/VOLUME
CONSTRAINT FOR (FOR POLYMERIC COMPOSITES)
49 (& manufacturing cost)
50
?
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
2/2
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014
• 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
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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
College of Electrical and Mechanical Engineering
Composites Manufacturing &
Manufacturing Process Selection Strategy
(the Ashby approach)
Part 2 of 2
Dept of Mechanical Engineering,
NUST, College of E & ME, Rawalpindi, Pakistan
Dr. Rizwan Saeed Choudhry [email protected]
Material selection charts in this slide are
copyright of Granata Design and should only be used for educational purpose
College of Electrical and Mechanical Engineering
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 COMPOSITES
MANUFACTURING PROCESSES
• Material
• Shape
• Size
• Mass
• Tolerance
• Roughness
• Reinforcement Type and layup
Control on angles during layup Volume Fraction range Void 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 ?)
Constraints What 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
ń = 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
The cost of sharpening a pencil plotted against batch size
CASE STUDY :
FORMING A FAN (FOR VACUUM CLEANERS)
CASE STUDY :
FORMING A FAN (FOR VACUUM CLEANERS)
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Process - Material
Compatibility
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Process – Shape
Compatibility
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Process – Mass
Compatibility
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Process – Section thickness
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Process – Tolerance
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
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
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Relative cost of moulding the fan
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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
College of Electrical and Mechanical Engineering
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 functional p = p(F,G,M) where F = functional requirements; G = Geometric parameters; and M = material indices
THE ASHBY APPROACH[1-4]
College of Electrical and Mechanical Engineering
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
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CASE STUDY: MATERIAL FOR OARS
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
CASE STUDY: MATERIAL FOR OARS
CASE STUDY: MATERIAL FOR OARS
CASE STUDY: MATERIAL FOR OARS
• 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 3D
Mass – less than 4 kg
Tolerance - ?
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 cost
Free variables Choice of Process
Process parameters
CASE STUDY : FORMING A FAN (FOR VACUUM CLEANERS)
Process - Material
Compatibility
Oars
Process – Shape Compatibility
Process Loom Spoon
1. RTM ++ ++
2. VARI + ++
3. Vacuum
bagging Prep-preg
+++ +++
4. Spray-up +++ +++
5. Filament
Winding
+++ N/A
Process – Mass Compatability
All 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
CASE STUDY: PROCESS FOR CFRP OARS
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
CASE STUDY: PROCESS FOR CFRP OARS
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
CASE STUDY: PROCESS FOR CFRP OARS
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