Plastic Parts Design

Plastic Parts Design Kevin Schneider, Autodesk MA32-2 .

Plastics -“Polymers” Polymers Poly(many) Mer(parts): A large molecule made up of one or more repeating units(mers) linked together by covalentchemical bonds bonds. Example: polyethylene or poly(ethylene)

n = number of monomers reacting >> 1

2

Effect of Molecular Weight on the Properties of Polyethylene

3

Outline Fundamentals Concept Models and Layouts Splitting Technical Modeling The Assembly Process

4

Design Example File naming Wall thickness Fillets, Draft and Ribs Design For Manufacturing

FUNDAMENTALS

5

Autodesk Confidential © 2006

The Design

6


File naming • Define a simple logical naming scheme • Stick with it • Names for 1. 2. 3. 4 4. 5.

Skeletons (skl (skl_XXXX.ipt) XXXX.ipt) Keepouts (ko_XXXX.ipt) Tooling (tooling_XXXX.ipt/iam) Intermediate files like derives or wrapper assemblies(na assemblies(na_XXXX.ipt/iam) XXXX ipt/iam) Top level assemblies (_XXXX.iam)

7


Wall thickness • • • • •

Uneven wall thickness present challenges to the plastic molder manufacturer. 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) b) c) d) e) f) g)

Unwanted sink Disguise (texture) Core out top Core out bottom Foaming agent (structfoam) Gas assist molding Spread sink over more area

8


Fillets, Draft and Ribs • Your rules may be different… • • • •

Fillets should be min ¼ X Wall thickness High stress parts, ¾ x Wall thickness Draft min of 1 deg. deg Finish affects draft Ribs should be 1/2 to 2/3 of the nominal wall thickness and less than 3 times thickness in height height. Taper of 1 deg. is typical. Note: excess thickness promotes shrinkage. shrinkage Excess rib height combined with taper will produce thin sections requiring extra e at tthe e mold. od fill ttime 9


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

Complex parts = complex tooling = $$$$

• Do you need to model:

Parting line/Surfaces Shrinkage Draft Ejector pin locations/pads

• What do you need to deliver 2D or 3D? 10


Designing for Manufacturing This Class assumes: • Your idea is manufacturable - YES • You like KISS principles • You do need to model:

Parting line/Surfaces Shrinkage Draft Ejector pin locations/pads You are building the tool in-house

11


Basic Parameters Working with internal components Layouts The working Model

CONCEPT MODELS AND LAYOUTS O S 12


Make a plastics Template • Make 5 User Parameters 1. 2. 3. 4. 5.

Wall thickness Inside Radius Outside Radius Rib Draft

• Add materials

13


Materials Common Materials.xls Plastic Properties Young's Poisson's Shear Mass Density, Modulus, psi Ratio Modulus, psi lb/in3

Matieral

Thermal Exp Coef, 1in/in/F

Ultimate Tensile, psi

Ultimate Compressive, psi

Ultimate Shear, psi

Thermal Conductivity, Btuin/hrft2F

Specific Heat, Btu/lb/F

3.90E‐05

13000

NA

NA

NA

NA

Cycolac DH

380000

0.35

14000

0.03788

Cycolac GSM

320000

0.35

12000

0.03752

NA

10700

NA

NA

1.22

NA

Cycolac KJB

320000

0.35

12000

0.04401

5.50E‐05

10000

NA

NA

NA

NA

Delrin 100/500/900

410000

0.35

NA

0.05123

4.20E‐05

14100

5200

9500

1.6

0.35

Lexan 101/201

340000

NA

114000

0.04329

3.75E‐05

14200

12500

10000

1.35

0.3

Lexan 121/221 /

340000

NA

114000

0.04329

3.75E‐05

14000

12500

10000

1.35

0.3

Lexan 141/241

340000

NA

114000

0.04329

3.75E‐05

14000

12500

10000

1.35

0.3

Lexan 141L/241L

340000

NA

114000

0.04329

3.75E‐05

14000

12500

10000

1.35

0.3

Lexan 150

340000

NA

114000

0.04329

3.75E‐05

13500

12500

10000

1.35

0.3

Lexan 161/261

340000

NA

114000

0.04329

3.75E‐05

14200

12500

10000

1.35

0.3

Lexan 181/281 Lexan 181/281

340000

NA NA

114000

0.04329

3.75E‐05 3.75E 05

14200

12500

10000

1.35

0.3

Lexan 3412(20%GF)

800000

NA

203000

0.04878

1.49E‐05

19000

16000

10000

1.47

0.28

Lexan 3413(30%GF)

1100000

NA

260000

0.05181

1.21E‐05

23000

18000

10500

1.5

0.27

Lexan 3414(40%GF)

1400000

NA

319000

0.05495

9.30E‐06

27000

21000

11000

1.53

0.25 0.29

Lexan 500/503

500000

NA

147000

0.04505

1.79E‐05

15000

14000

8500

1.41

Lexan 920/940/950

325000

NA

114000

0.04329

3.80E‐05

13200

12500

10000

1.35

0.3

Lexan PPC4501

294000

NA

NA

0.04329

5.10E‐05

13800

NA

9800

1.46

0.3

Lexan PPC4701

338000

NA

NA

0.04329

4.50E‐05

14100

NA

10600

1.43

0.3

14


Working with internal components • Define logical working groups for Internals

15


Layout Process Create Layout Assembly A bl

Create Layout Part

Define character curves

Position Internal components

Finish Layout exterior

Add work geometry for Split

Add work geometry for Joining 16


Keepout Process Derive Layout

Select specific Internal group

Define work geometry

Model Keep outt volume l 17


PCB Keepout - solid

18


Speaker Keepout - surface

19


The working Model PCBKeepout. ipt

Layout.iam Speaker.iam

Speaker Keepout.ipt

PCB.iam Skeleton ipt Skeleton.ipt

20


Basics Hard the Impossible Workarounds

SPLITTING

21


Basics • Linear Parting lines

22


Hard • Non linear, but clear edge

23


the Impossible • Silhouettes

24


Spliting Derive finished layout

Define split geometry

Split

Shell

Technical ec ca Model 25


26


Snapping and Fastening features Tips for iFeatures

TECHNICAL MODELING

27


Snapping features

28


Snapping Features

29


Snapping Features

30


Snapping features and ejection

31


Snapping Features and ejection

32


Fastening features

33


Fastener Limitations • • • • • • •

Mechanical fasteners are point fasteners. Localized regions of potentially high stress. Holes >>> stress concentration and weld line formation. Thermal expansion mismatch. mismatch Additional pieces / parts. G k t to Gasket t achieve hi a fluid fl id or gas tight ti ht seal. l

34


Fastener Advantages • Operable (or reversible) joints or permanent assembly. • An 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. • Metal “fastener’s” properties are independent of temp., te p, • The assembly strength is achieved quickly. 35


Bosses

36


Tips for iFeatures • Custom Icons • Custom Help files • Table driven for standard sizes

37


THE FINAL ASSEMBLY PROCESS OC SS 38


WCS • Simpley put everything at the origin • All parts are built off the Layout coordinate system and there for fit with few to no constraints

39


40


The final file tree Prepping for MFG and Rapid Prototyping

REVIEW

41


The final file tree

42


Material sources: David O. Kazmer, P.E., Ph.D. Department of Plastics Engineering U i University it off Massachusetts M h tt Lowell L ll One University Avenue

Lowell, Massachusetts 01854

43


44


Plastic Parts Design

Recommend Documents