Mold Design Feasability

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Designing for mouldability A quick-reference user guide for rapid injection moulding for engineers and designers 2nd edition

Real Parts. Really Fast.

www.protomold.co.uk

Proto Labs, Ltd. Unit A Hortonwood In dustrial Estate, Hortonwood H ortonwood 7, Telford, Shropshire, TF1 7GX, UK U K +44 (0) 1952 607447

DESIGNING FOR MOULDABILITY

TABLE OF CONTENTS What is injection moulding

2

What is Rapid Injection Moulding

3

What is injection moulding? 1 The hopper is loaded with the plastic stock material.

Applications of Rapid Injection Moulding

3

Wall thickness

4

Cored geometry

4

Recommended wall thickness

5

Warp

5

4 The part cools and solidifies.

Sharp corners Ribs

6 6

5 The mould is opened and the part ejected.

Bosses

7

Draft

7

Core-cavity

8

Deep (milling) impact

8

Texture

8

Straight pull mould

9

Side actions

9

Bump off Pick-outs

10 10

Steel core pins

10

Text

11

Tab gate

11

Self mating parts

12

Tolerance

12

Choosing a material

13

Select colours

14

Resin additives Be the hero!

14 15

2 A heated barrel is used to melt the beads into a molten form. 3 A screw apparatus is used to inject the polymer into a mould.

©2010 Proto Proto Labs. All rights reserved. reserved. 2

DESIGNING FOR MOULDABILITY

TABLE OF CONTENTS What is injection moulding

2

What is Rapid Injection Moulding

3

Applications of Rapid Injection Moulding

3

Wall thickness

4

Cored geometry

4

Recommended wall thickness

5

Warp

5

Sharp corners Ribs

6 6

Bosses

7

Draft

7

Core-cavity

8

Deep (milling) impact

8

Texture

8

Straight pull mould

9

Side actions

9

Bump off Pick-outs

10 10

Steel core pins

10

Text

11

Tab gate

11

Self mating parts

12

Tolerance

12

Choosing a material

13

Select colours

14

Resin additives Be the hero!

14 15

What is rapid injection moulding?

Applications of rapid injection moulding

Rapid mould fabrication

Prototypes. Refine your design with real



Moulds are made from aluminium



They are 3-axis CNC milled



Selective use of electrical discharge machining (EDM)

There are limits to complexity  Number of side actions at the parting line 

No internal threads

Fast real injection moulded plastic parts 

CAD to plastic as fast as 1 day



Standard delivery 10-15 business days

moulded parts 

Functional testing in product development cycle cycle



Test multiple materials



Try multiple versions

Bridge tooling 

Production parts until production mould is ready

Low to medium-volume production 



25 to thousands of parts Just-in-time parts, use your cash for something other than inventory

Panic situations 

Production line shutdown



Crash development projects

Markets that use Rapid Injection Moulding 

Medical



Automotive



Electronics

 

 

 



Consumer Products



Appliance



Other high volume parts

©2010 Proto Proto Labs. All rights reserved. reserved. 3

DESIGNING FOR MOULDABILITY

TABLE OF CONTENTS What is injection moulding

2

What is Rapid Injection Moulding

3

Applications of Rapid

Up against the wall (thickness)

A core issue Core out parts to eliminate thick walls. 

The most important design requirement for

Injection Moulding

3

Wall thickness

4

Cored geometry

4

Recommended wall thickness

5

Warp

5

Sharp corners Ribs

6 6

Bosses

7

Draft

7

Core-cavity

8

Deep (milling) impact

8

Texture

8

Straight pull mould

9

Side actions

9

Bump off Pick-outs

10 10

Steel core pins

10

Text

11

Tab gate

11

Self mating parts

12

Tolerance

12

Choosing a material

13

Select colours

14

Resin additives Be the hero!

14 15

getting good moulded parts - maintain

You get the s ame functionality in a good moulded part.

constant wall thickness.

Sink

Original geometry

As moulded

As designed

Warp

Cored geometry

Cored geometry

* Tip: Good injection moulded part design relies on a consistent wall thickness to minimize the p otential for warped or distorted parts.

* Tip: Unnecessary thickness can throw off part dimensions, reduce strength and necessitate post-process machining.

©2010 Proto Proto Labs. All rights reserved. reserved. 4

DESIGNING FOR MOULDABILITY

TABLE OF CONTENTS What is injection moulding What is Rapid Injection Moulding

2 3

Applications of Rapid Injection Moulding

3

Wall thickness

4

Cored geometry

4

Recommended wall thickness

5

Warp

5

Sharp corners Ribs

6 6

Bosses

7

Draft

7

Core-cavity

8

Deep (milling) impact

8

Texture

8

Straight pull mould

9

Side actions

9

Bump off Pick-outs

10 10

Steel core pins

10

Let’s get absolute

A warped personality

Recommended absolute wall thickness by resin.

moulded-in stress.

Eliminate sharp transitions which cause

Recommended Wall Resin

Thickness (mm)

ABS

1.14 - 3.50

Acetal

0.64 - 3.05

Acrylic

0.64 - 3.81

Liquid crystal polymer

0.76 - 3.05

Long-fibre reinforced plastics

1.90 - 2.54

Nylon

0.76 - 2.92

Polycarbonate

0.11 - 3.81

Polyester

0.64 - 3.17

Polyethylene

0.76 - 5.08 0.51 - 4.57

Text

11

Polyphenylene sulfide

Tab gate

11

Polypropylene

0.64 - 3.81

Self mating parts

12

Tolerance

12

Polystyrene

0.89 - 3.81

Choosing a material

13

Select colours

14

Resin additives Be the hero!

14 15

Note: These are general guidelines, subject to part geometry and moulded construction. Large parts shouldn’t be designed with the minimum wall thickness. * Tip: Protomold’s general rule for wall thickness is 0.040 - 0.140.

Design 3D structures that support themselves.

©2010 Proto Proto Labs. All rights reserved. reserved. 5

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