Making A Good Plastic Chair Mould

Making a good plastic chair mould requires getting design, material, tooling, and process control right from the beginning. Below is a practical, industry-proven guide, aligned with how high-quality injection moulds are built in professional mould company like SWY MOULD.

1. Chair Product Design (Foundation of the Mould)

A good mould starts with a correct chair design.

Key design rules:

• Uniform wall thickness (typically 2.5–4.0 mm)
  → Prevents sink marks, warpage, and weak points

• Ribs instead of thick walls
  → Rib thickness = 50–60% of wall thickness

• Proper draft angle
  → 1.5°–3° minimum (more for textured surfaces)

• Rounded corners
  → Avoid sharp edges to reduce stress cracking

• Load-bearing reinforcement
  → Legs, backrest joints, and seat center must be strengthened

CAE / Moldflow analysis is strongly recommended to check:

• Flow balance

• Weld lines

• Shrinkage & warpage

• Gate location

2. Plastic Material Selection

Common materials for plastic chairs:

Material shrinkage must be confirmed before mould design (critical for chair size accuracy).

3. Mould Structure Design

Plastic chair moulds are large, high-pressure, high-cycle moulds.

Core structure requirements:

• Single cavity (mostly)
  Chairs are large → single cavity ensures strength & stability

• Strong core & cavity support

• Thick backing plates

• Extra pillars under seat & legs

• Insert design

• Wear areas use replaceable inserts

• Heavy mould base

• Prevents deformation during injection

4. Gate & Runner System

Recommended gate types:

• Fan gate (most common)

• Edge gate with wide opening

Why?

• Smooth material flow

• Less stress marks

• Better surface finish

Runner:

• Hot runner system (highly recommended)

• Saves material

• Shorter cycle time

• Stable filling

• Brands often used: YUDO, Synventive, Husky, Chinese own brand, etc.

5. Cooling System (Very Important)

A good chair mould must cool evenly.

Best practices:

• Dense cooling lines under:

• Seat area

• Leg roots

• Backrest

• Use baffle tubes & bubblers for deep areas

• Keep cooling line distance:

• 2–2.5 × wall thickness from cavity surface

Poor cooling = warpage + long cycle time.

6. Ejection System

Plastic chairs require strong but even ejection.

Common ejection methods:

• Ejector pins + ejector blocks

• Stripper plate (for smooth ejection)

• Extra ejectors at:

• Seat center

• Leg roots

Avoid ejector marks on visible surfaces.

7. Mould Steel Selection

Chair moulds run high tonnage & long cycles, so steel quality is critical.

Heat treatment hardness: HRC 30–36 (P20/718H)

8. Surface Finish & Texture

• Polish for glossy chairs

• Texture (MT / VDI) for matte & scratch resistance

• Texture depth must match draft angle

9. Trial, Testing & Optimization

During T1–T3 trials:

• Check filling balance

• Adjust packing pressure

• Measure warpage

• Load test the chair (static & impact)

Modify gates, cooling, or ribs if needed.

10. Mass Production & Maintenance

To keep mould quality long-term:

• Daily cleaning during production

• Weekly lubrication of sliders & ejectors

• Regular checking of cooling lines

• Record shot count & maintenance history

Key Summary

A good plastic chair mould must:
✅ Have a correct chair design
✅ Use suitable material & shrinkage data
✅ Be strong, well-supported, and well-cooled
✅ Use proper gating & ejection
✅ Be built with reliable mould steel
✅ Be maintained carefully during production

If you want, I can:

• Review a chair 3D design

• Recommend exact steel grades based on production volume

• Suggest hot runner & gate layout

• Provide a professional mould specification checklist

Just tell me