Plastic Parts DesignPlastic Parts DesignKevin Schneider, AutodeskMA32-2.

Plastics PolymersPlastics - Polymers

Poly(many) Mer(parts):A large molecule made up of one or moreA large molecule made up of one or more

repeating units(mers) linked together by covalentchemical bonds Example:covalentchemical bonds. Example: polyethylene or poly(ethylene)

n = number of monomers reacting >> 1 2

Effect of Molecular Weight on the Properties of Polyethylene

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OutlineOutline

FundamentalsConcept Models and LayoutsConcept Models and LayoutsSplittingTechnical ModelingThe Assembly ProcessThe Assembly Process

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Design ExampleDesign ExampleFile namingWall thicknessFillets, Draft and RibsDesign For Manufacturing

FUNDAMENTALS

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The DesignThe Design

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File namingFile naming Define a simple logical naming schemeDefine a simple logical naming scheme Stick with it

Names for1. Skeletons (skl XXXX.ipt)1. Skeletons (skl_XXXX.ipt)2. Keepouts (ko_XXXX.ipt)3. Tooling (tooling_XXXX.ipt/iam)4 Intermediate files like derives or wrapper assemblies(na XXXX ipt/iam)4. Intermediate files like derives or wrapper assemblies(na_XXXX.ipt/iam)5. Top level assemblies (_XXXX.iam)

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Wall thicknessWall thickness Uneven wall thickness present challenges to the plastic molder manufacturer.

Designing your part with uniform walls and cross section will simplify Designing your part with uniform walls and cross section will simplify manufacturing and costing.

At wall intersection or "tees" sinking will occur. Thick walls cool slower and greater shrinking will occur. Thin walls cool faster as thus, less shrinkage.

Ways to deal with this "shrikage

a) Unwanted sinkb) Disguise (texture)c) Core out topd) Core out bottome) Foaming agent (structfoam)

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f) Gas assist moldingg) Spread sink over more area

Fillets, Draft and RibsFillets, Draft and Ribs Your rules may be differentYour rules may be different

Fillets should be min X Wall thickness Fillets should be min X Wall thickness High stress parts, x Wall thickness Draft min of 1 deg Finish affects draft Draft min of 1 deg. Finish affects draft Ribs should be 1/2 to 2/3 of the nominal wall

thickness and less than 3 times thickness in heightthickness and less than 3 times thickness in height. Taper of 1 deg. is typical. Note: excess thickness promotes shrinkage Excess rib height combinedpromotes shrinkage. Excess rib height combined with taper will produce thin sections requiring extra fill time at the mold.

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t e at t e o d

Designing for ManufacturingDesigning for Manufacturing Is your idea manufacturable?Is your idea manufacturable? What is your budget?

Complex parts = complex tooling = $$$$

Do you need to model:Parting line/Surfaces Parting line/Surfaces

Shrinkage DraftDraft Ejector pin locations/pads

What do you need to deliver 2D or 3D?

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What do you need to deliver 2D or 3D?

Designing for ManufacturingDesigning for ManufacturingThis Class assumes:This Class assumes: Your idea is manufacturable - YES You like KISS principles You like KISS principles You do need to model: Parting line/Surfaces Parting line/Surfaces Shrinkage Draft Ejector pin locations/pads You are building the tool in-house

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Basic ParametersWorking with internal componentsLayoutsThe working Model

CONCEPT MODELS AND O SLAYOUTS

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Make a plastics TemplateMake a plastics Template Make 5 User ParametersMake 5 User Parameters

1. Wall thickness2. Inside Radius3. Outside Radius4. Rib5. Draft

Add materials

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MaterialsMaterialsCommon Materials.xls

PlasticProperties

MatieralYoung's

Modulus,psiPoisson'sRatio

ShearModulus,psi

MassDensity,lb/in3

ThermalExpCoef,1in/in/F

UltimateTensile,psi

UltimateCompressive,

psiUltimateShear,psi

ThermalConductivity,Btuin/hrft2F

SpecificHeat,Btu/lb/F

CycolacDH 380000 0.35 14000 0.03788 3.90E05 13000 NA NA NA NA

CycolacGSM 320000 0.35 12000 0.03752 NA 10700 NA NA 1.22 NA

CycolacKJB 320000 0.35 12000 0.04401 5.50E05 10000 NA NA NA NA

Delrin100/500/900 410000 0.35 NA 0.05123 4.20E05 14100 5200 9500 1.6 0.35

Lexan101/201 340000 NA 114000 0.04329 3.75E05 14200 12500 10000 1.35 0.3

/Lexan121/221 340000 NA 114000 0.04329 3.75E05 14000 12500 10000 1.35 0.3

Lexan141/241 340000 NA 114000 0.04329 3.75E05 14000 12500 10000 1.35 0.3

Lexan141L/241L 340000 NA 114000 0.04329 3.75E05 14000 12500 10000 1.35 0.3

Lexan150 340000 NA 114000 0.04329 3.75E05 13500 12500 10000 1.35 0.3

Lexan161/261 340000 NA 114000 0.04329 3.75E05 14200 12500 10000 1.35 0.3

Lexan 181/281 340000 NA 114000 0.04329 3.75E05 14200 12500 10000 1.35 0.3Lexan181/281 340000 NA 114000 0.04329 3.75E 05 14200 12500 10000 1.35 0.3

Lexan3412(20%GF) 800000 NA 203000 0.04878 1.49E05 19000 16000 10000 1.47 0.28

Lexan3413(30%GF) 1100000 NA 260000 0.05181 1.21E05 23000 18000 10500 1.5 0.27

Lexan3414(40%GF) 1400000 NA 319000 0.05495 9.30E06 27000 21000 11000 1.53 0.25

Lexan500/503 500000 NA 147000 0.04505 1.79E05 15000 14000 8500 1.41 0.29

Lexan920/940/950 325000 NA 114000 0.04329 3.80E05 13200 12500 10000 1.35 0.3

LexanPPC4501 294000 NA NA 0.04329 5.10E05 13800 NA 9800 1.46 0.3

LexanPPC4701 338000 NA NA 0.04329 4.50E05 14100 NA 10600 1.43 0.3

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Working with internal componentsWorking with internal components Define logical working groups for InternalsDefine logical working groups for Internals

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Layout ProcessLayout ProcessCreate Layout

A blAssembly

Create Layout Part

Define character curves

Position Internal components

Finish Layout exterior

Add work geometry for Split

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Add work geometry for Joining

Keepout ProcessKeepout Process

DeriveDerive Layout

Select specific Internal groupInternal group

Define work geometry

Model Keep t l

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out volume

PCB Keepout - solidPCB Keepout solid

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Speaker Keepout - surfaceSpeaker Keepout surface

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The working ModelThe working Model

PCBKeepout.ipt

Speaker.iam

Layout.iam

Speaker Keepout.ipt

PCB.iam

Skeleton iptSkeleton.ipt

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BasicsHardthe ImpossibleWorkarounds

SPLITTING

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BasicsBasics Linear Parting linesLinear Parting lines

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HardHard Non linear, but clear edgeNon linear, but clear edge

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the Impossiblethe Impossible SilhouettesSilhouettes

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SplitingSplitingDeriveDerive

finished layout

Define split geometry

Split

Shell

Technical

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ec caModel

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Snapping and Fastening featuresTips for iFeatures

TECHNICAL MODELING

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Snapping featuresSnapping features

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Snapping FeaturesSnapping Features

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Snapping FeaturesSnapping Features

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Snapping features and ejectionSnapping features and ejection

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Snapping Features and ejectionSnapping Features and ejection

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Fastening featuresFastening features

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Fastener LimitationsFastener Limitations Mechanical fasteners are point fasteners.Mechanical fasteners are point fasteners. Localized regions of potentially high stress. Holes >>> stress concentration and weld Holes >>> stress concentration and weld line formation. Thermal expansion mismatch Thermal expansion mismatch. Additional pieces / parts.

G k t t hi fl id ti ht l Gasket to achieve a fluid or gas tight seal.

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Fastener AdvantagesFastener Advantages Operable (or reversible) joints or permanentOperable (or reversible) joints or permanent

assembly. An effective method for joining mostAn effective method for joining most

thermoplastic & thermosetting parts (except very flexible items).)

Join parts produced in similar or dissimilar materials.

Available in a variety of sizes and materials. The joining practices are very conventional.The joining practices are very conventional. Metal fasteners properties are independent of

temp.,

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te p , The assembly strength is achieved quickly.

BossesBosses

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Tips for iFeaturesTips for iFeatures Custom IconsCustom Icons Custom Help files Table driven for standard sizes Table driven for standard sizes

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THE FINAL ASSEMBLY OC SSPROCESS

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WCSWCS Simpley put everything at the originSimpley put everything at the origin All parts are built off the Layout coordinate system

and there for fit with few to no constraintsand there for fit with few to no constraints

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The final file treePrepping for MFG and Rapid Prototyping

REVIEW

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The final file treeThe final file tree

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Material sources:David O. Kazmer, P.E., Ph.D.Department of Plastics EngineeringU i it f M h tt L llUniversity of Massachusetts Lowell

One University AvenueLowell, Massachusetts 01854

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