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DESIGN AND ANALYSIS OF A COMPRESSION MOLDED CARBON COMPOSITE WHEEL CENTER

VINOTH KUMAR DHANANJAYANThesis Defense for MS Mechanical Engineering

April 3, 2013

Committee :Prof. Robert Woods, University of Texas at Arlington (Advisor)

Prof. Kent Lawrence, University of Texas at ArlingtonProf. Wen Chan, University of Texas at Arlington

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Background & Motivation

Alternate process development of a high strength part

Weight reduction Functional performance improvement Machining time reduction

FORGED COMPOSITE

FORGED CARBON

ADVANCED COMPRESSION MOLDING PROCESS

LAMBORGHINI CALLAWAYCycle time – minutesStrength – equal to quasi isotropic

Ref : Lambolab.com, composites world

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Objective

•Study on factors influencing the compression molding process

•Analysis of existing and proposed design of a part

•Raw material selection

•Mold design

•Thermal system identification and analysis

•Process parameters

Development of wheel center by compression molding process

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Importance of closed mold and short fibers

• Directional properties• High process time• High skill requirement• Intricate shapes not feasible• High part cost• Low volume

Open mold continuous fiber

• Near isotropic properties• Quicker cycle time in minutes• Minimal skill dependency• Near net shape part and ability to mold complex shapes• Low part cost• High volume

Closed mold short fiber

Advantageous closed mold process

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Compression molding

Minimal flow Less fiber breakage

Ref : Duqueine, Mazumdar composites mfg, lamborghini urus

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Compression molded parts

Ref : Hexcel, Lamborghini, Audemars piguet, Carbon Forge, Duqueine, excel sports, DUC -helices

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Process dependency

COMPRESSION MOLDING

resin type

formability

fiber content

fillers

Mold design

Thermal system

charge placement process temperature & pressure

Press parallelism, mold finish, ejection

Part strength

volumeThickness variation

Holes or mash off zones

Moldability

PART MATERIAL

fiber lengthresin process

parameters

PROCESS

Part Material Process

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Wheel center part study

• Most suitable for compression molding – 20% improvement yields 1.58 lbs weight saving/car

• Improve lateral stiffness – high deformation• High machining time and material wastage• Lateral Load

– Lateral load 750 lb– Normal reaction load 600 lb

• Braking Load– Braking load 600 lb– Normal reaction load 600 lb

Ref : UTA FSAE team (load values)

Reaction force due to weight

Braking force

Wheel center loads

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Raw material selection

Al 6061 T6HexMC

MS 1HMS 4A

0

2

4

6

8

10

12

10

5.5

10

9

10

5.5

9

8

10

4.35

10

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SMC market study

Tensile modulus msi Compressive modulus msi Flexural modulus msi

• Market study

• Hexcel, ten cate, Quantum composites

• 15 compounds

•Carbon epoxy and vinyl ester

Benchmark properties – Al 6061 T6

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Existing wheel center – lateral load

FOS – 0.96

Deformation – 0.049”

Elements Equiv Stress (ksi) Change %51831 36.4  60157 38.9 6.8 %70013 41.1 5.5 %93733 41.6 1.2 %

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Existing wheel center – Braking load

Deformation – 0.004”

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Inference

• Functional issue– Increase lateral stiffness– Strengthen riveting points

• Moldability– Provide drafts– Minimize pattern holes– Gradual thickness variation

L

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Proposed design

Other designs studied

Proposed

Existing

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Proposed design – Lateral load

30 %

>25 % Improvement

FOS – 1.48FOS - 0.96

27 % Stress

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Proposed design – Braking load

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Results comparison

LateralBraking

0

15

30

4541.6

9.0

30.5

4.0

Stress (ksi)

ExistingProposed

LateralBraking

0

0.02

0.04

0.06 0.049

0.004

0.035

0.004

Deformation (in)

Existing

Proposed

0.00 0.50 1.00 1.50 2.00

1.98

1.52

Weight (lb)

24 %

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Mold design

• Mold material - Al 6061 T6– Better machinability– Quick heat transfer– Better surface finish

• Shear edge design – Complete filling– Escape of air

• Mold size– Length 15”– Breadth 14”– Thickness 2.5”

Good mold design Better part quality

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Heating system

Cartridge heaters

Quantity – 4/moldCapacity – 450W

Wattage required for heating the mold in 30 min – 3.6 KW

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Heating system - analysis

Minimum temperature variation Uniform heat absorption by charge

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Cooling system

• Remove heat generated during curing reaction

• Depends on

– Location of cooling lines– Size of cooling lines– Types of cooling lines– Length of cooling circuit– Flow rate of coolant

• Position of channels and time taken for cooling are analyzed in solidworks

• Best suitable mass flow rate of water selected for individual molds to have uniform decrease in temperature

Uniform cooling Minimum warpage

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Cooling system analysis

0 100 200 300 400 500 6000

40

80

120

160

Bottom mold temp Vs time

B 2.5 m/s

Time (sec)

Tem

pera

ture

deg

C

0 100 200 300 400 500 600 7000

40

80

120

160

Top mold temperature vs time

T 2.5 m/s

Time (sec)

Tem

pera

ture

deg

C

0 100 200 300 400 500 6000

40

80

120

160Mold temperature Bottom vs Top

T0.5 m/s B 2.5 m/sTime (sec)

Tem

pera

ture

deg

C

Minimum temperature gradient b/w mold halves Min warpage

Ref : DSM design guide

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Mold assembly

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Process parameters

Material - MS 4A

Charge loading pattern – By trials during manufacturing

Press capacity – 85 ton

Press pressure – 2000 psi

Process temperature – 150 deg C

Mold pre heat time – 30 min

Heater bore clearance – 0.015 mm

Cure time – 20 min

Press parallelism – 0.001”/ft (recommended values)

Accurate control of the process High part repeatability

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Future Scope

• Software simulation to predict– Fiber orientation– Charge pattern– Warpage – Closing speed – Material flow

• Software– Moldex 3d– Cadpress– Express– Autodesk moldflow beta

Process simulation

Animation reference : Moldex 3d

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Conclusion

•Process dependency parameters are identified and analyzed•Process data sheet preparation•Future work involves manufacture of the mold and part

• Design• Analysis• Engineering drawingPart

• Material study• Material selectionMaterial

• Mold design• Engineering drawing• Heating system analysis• Cooling system analysis• Process parameters

Process

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Thank You

Questions and discussion

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Analysis conditions

Properties Units Al 6061 T6 Al alloy Carbon epoxy

Density lb / in3 0.097 0.0975 0.054Young’s modulus msi 10 10.297 8.357Poisson ratio   0.33 0.33 0.3

Parts  Wheel hub,

existing wheel center

Wheel rim Proposed wheel center

Static Structural analysis