Design Guidelines Injection MouldingEngineering Design

Presenter: Laszlo PatakiSABIC-Innovative Plastics

3Design Guidelines Injection Moulding

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

5Design 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

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Design Guidelines Injection Moulding

Part Design aspects

• Design for mould ability• Design for stiffness• Design for impact• Design for appearance• Design for precision.

7Design Guidelines Injection Moulding

1, Design for Mould ability

• Constant wall thickness recommended

• If not possible, transitions should be smooth.

Design Guidelines Injection Moulding

8Design Guidelines Injection Moulding

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

9Design Guidelines Injection Moulding

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

10Design Guidelines Injection Moulding

Design for Mould ability

• Undercuts should be avoided where possible. If needed, use undercuts without sliding cores.

Design Guidelines Injection Moulding

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Design Guidelines Injection Moulding

Design for Mould ability

• Draft angles

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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.

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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.

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Design Guidelines Injection Moulding

Design for Mould ability Gate shapesGate size is importantfor shear rate controlFlow simulation usefulfor predicting shear and pressure drop.

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Design Guidelines Injection Moulding

• VentingImportant for part quality.Good venting is always needed where air traps and weld linesare 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.

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Design for stiffnessPart stiffness determined by:1. Material E module2. Shape of the partStiffness increase • Higher E module• Ribs• Corrugations• Hollow parts

Design Guidelines Injection Moulding

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Design Guidelines Injection Moulding

Design for stiffnessStiffness to weight ratio.

Most efficient material use in corrugated design.Structural analysis can help to check mechanicalbehavior in advance.

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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.

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Design Guidelines Injection Moulding

Design for AppearancePossible surface defects• gate marks • sink marks due to ribbing or thick sections• weld lines• air traps.• voids• jetting

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Design Guidelines Injection Moulding

Design for AppearanceSink mark reduction

Gas assist can reduce sink marksUnder ribs

Design feature appliedTo eliminate visible sink mark

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Design Guidelines Injection Moulding

Design for Appearance

Sudden changes in thickness should be avoided

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Design Guidelines Injection Moulding

Design for Appearance

Try to avoid jetting when choosingthe gate location

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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)

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Design Guidelines Injection Moulding

Design for Precision

Volumetric Shrinkage Amorphous

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Design Guidelines Injection Moulding

Design for Precision

Volumetric Shrinkage Crystalline

26Design 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

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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.

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Design Guidelines Injection Moulding

Design for PrecisionThin long ribs shrink different compared to nominal wallthis can cause warpage.

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Thank you for your attention

Design Guidelines Injection Moulding