Design Guidelines Injection Moulding Engineering Design

2 Design Guidelines Injection Moulding Design can be split into 2 main activities: 1.Industrial Design ( concepts, styling) 2.Engineering Design ( mould ability, functionality) This presentation is about Engineering Design. Design Guidelines Injection Moulding

3 Successful injection moulding depends on the good interaction between: 1.Part Design 2.Mould Design 3.Processing Equipment and process control 4.Material selection. Design Guidelines Injection Moulding

4 Part Design Aspects Mould Design aspects (general, Hot runner) Flow Simulation examples.

5 Design Guidelines Injection Moulding 1, Part Design Aspects Firstly, part requirements have to be defined. Mechanical behavior ( stiffness, impact) Thermal behavior ( stiffness, Creep) Chemical resistance ( material selection) Cosmetics (surface finish, color, gate location, ribs, weld line) Mould ability ( wall thickness, flow length, gating …) Assembly ( screws, welding, bonding…) Painting Design Guidelines Injection Moulding

6 Part Design aspects Design for mould ability Design for stiffness Design for impact Design for appearance Design for precision.

7 Design Guidelines Injection Moulding 1, Design for Mould ability Constant wall thickness recommended If not possible, transitions should be smooth. Design Guidelines Injection Moulding

8 Design for Mould ability Ribs - if needed - max.0.6 x nominal wall at root, min.0.5 degree draft on each side. Filling thin ribs can be problematic Design Guidelines Injection Moulding

9 Design for Mould ability Bosses for screws same rule as ribs, to increase stiffness boss can be supported with gussets. Sharp corners rounded off, better release, better strength. Design Guidelines Injection Moulding

10 Design Guidelines Injection Moulding Design for Mould ability Undercuts should be avoided where possible. If needed, use undercuts without sliding cores. Design Guidelines Injection Moulding

11 Design Guidelines Injection Moulding Design for Mould ability Draft angles

12 Design Guidelines Injection Moulding Design for Mould ability Ejection Allow for sufficient ejection locations, specially complex shapes with many ribs and pockets can be critical with higher viscous materials. Ribs are best ejected on the rib itself with blade ejectors. Use as large as possible ejector pins, lowest deformations will occur.

13 Design Guidelines Injection Moulding Gating Flow should be from thick to thin, if not constant wall thickness. Gate location(s) to be considered to prevent filling issues. Flow curves can be used for first check.

14 Design Guidelines Injection Moulding Design for Mould ability Gate shapes

15 Design Guidelines Injection Moulding Venting Important for part quality. Good venting is always needed where air traps and weld lines are expected, also at the end of flow. Dynamic vents ( using ejectors with facets) are suitable for local air traps, mould parting line should always be vented. Size of venting depending on material viscosity.

16 Design for stiffness Part stiffness determined by: 1.Material E module 2.Shape of the part Stiffness increase Higher E module Ribs Corrugations Hollow parts Design Guidelines Injection Moulding

17 Design Guidelines Injection Moulding Design for stiffness Stiffness to weight ratio. Most efficient material use in corrugated design. Structural analysis can help to check mechanical behavior in advance.

18 Design Guidelines Injection Moulding Design for impact Avoid stress concentrators ( sharp corners, transitions, notches) Avoid impact load near gates and weld lines Avoid poor processing conditions (moulded in stress) Choose the right material ( ductile /brittle transition) In critical cases perform structural analysis.

19 Design Guidelines Injection Moulding Design for Appearance Possible surface defects gate marks sink marks due to ribbing or thick sections weld lines air traps. voids jetting

20 Design Guidelines Injection Moulding Design for Appearance Sink mark reduction Gas assist can reduce sink marks Under ribs Design feature applied To eliminate visible sink mark

21 Design Guidelines Injection Moulding Design for Appearance Sudden changes in thickness should be avoided

22 Design Guidelines Injection Moulding Design for Appearance Try to avoid jetting when choosing the gate location

23 Design Guidelines Injection Moulding Design for Precision Important factors: material choice (GF, GB, CF, Amorphous, Crystalline), shrinkage behavior gating (type and size of gate) mould design ( cooling, gating) processing ( temperatures, pressures, orientation)

24 Design Guidelines Injection Moulding Design for Precision Volumetric Shrinkage Amorphous

25 Design Guidelines Injection Moulding Design for Precision Volumetric Shrinkage Crystalline

26 Design Guidelines Injection Moulding Design for Precision (shrinkage control) Design related aspects for precision Wall thickness distribution gate location, gate size, gate type Processing related aspects melt-mould temperature, injection profile Post moulding effects Expansion, post shrinkage, moisture absorption Design Guidelines Injection Moulding

27 Design Guidelines Injection Moulding Design for Precision Gating type and size important for orientation shrinkage differences between flow and cross flow for Crystalline and glass filled materials.

28 Design Guidelines Injection Moulding Design for Precision Thin long ribs shrink different compared to nominal wall this can cause warpage.

29 Thank you for your attention Design Guidelines Injection Moulding