Plastic Box Injection Mould

Making a good plastic box mould (crate, storage box, turnover box, container, etc.) requires special attention to warpage control, strength, and fast cycle time. Below is a practical, mould-maker–oriented guide, suitable for industrial and commercial box production.

1. Plastic Box Product Design (Most Important)

Most box problems come from poor product design, not the mould itself.

Key design rules:

• Uniform wall thickness
  2.5–4.0 mm (avoid thick corners)

• Ribs instead of thick walls

• Rib thickness = 50–60% of wall

• Corner reinforcement

• Large fillet radius inside & outside

• Bottom strengthening

• Grid or cross-rib structure

• Draft angle

• ≥ 1.5° (≥ 3° for textured surfaces)

Perform Moldflow analysis to check:

• Filling balance

• Weld lines at corners

• Warpage on long side walls

2. Plastic Material Selection

Common materials for plastic boxes:

Confirm shrinkage before mould design
(PP: ~1.5–2.0%, HDPE: ~1.8–2.5%).

3. Mould Structure Design

Plastic box moulds are large, flat, and prone to deformation.

Structural requirements:

• Single cavity mould

• Strong core support

• Dense support pillars under bottom area

• Replaceable inserts

• Corners

• Gate area

• High-wear areas

• Thick backing & clamping plates

Weak support = bottom warpage & flash.

4. Gate & Runner System

Recommended gate types:

• Fan gate

• Multiple edge gates

• Ring gate (for round boxes)

Why?

• Uniform filling

• Reduced weld lines

• Lower internal stress

Runner system:

• Hot runner preferred

• Shorter cycle time

• Less material waste

• Cold runner acceptable for low-cost moulds

5. Cooling System (Key to Box Quality)

Cooling determines flatness and cycle time.

Best practices:

• Dense cooling lines under:

• Bottom panel

• Long side walls

• Independent cooling zones for:

• Bottom

• Side walls

• Use baffles & bubblers for deep cores

• Cooling distance:
  2–2.5 × wall thickness from cavity surface

Uneven cooling = bottom sink & side wall bending.

6. Ejection System

Boxes have large contact area with the core.

Common ejection solutions:

• Stripper plate (best for thin boxes)

• Ejector pins + ejector blocks

• Large ejector pads under bottom ribs

Ensure uniform ejection force to avoid distortion.

7. Venting System

Very important for box moulds.

Venting locations:

• Corner areas

• End of flow paths

• Bottom ribs

Vent depth:

• PP / HDPE: 0.02–0.04 mm

8. Mould Steel Selection

Box moulds often run high volume production.

Hardness: HRC 30–36

9. Surface Finish & Texture

• Smooth polish → Easy cleaning

• Texture (MT / VDI) → Scratch resistance

• Match texture depth with draft angle

10. Mould Trial & Box Testing

During mould trials:

• Check bottom flatness

• Measure side wall deformation

• Perform:

• Stacking test

• Drop test

• Load test

Adjust gate size, packing pressure, or cooling if needed.

11. Production & Maintenance

For long mould life:

• Daily cleaning

• Weekly lubrication

• Regular cooling line flushing

• Track shot count

Key Differences: Box vs Chair / Stool Mould

Final Summary

A good plastic box mould must:
✅ Fill evenly
✅ Cool uniformly
✅ Resist warpage
✅ Eject smoothly
✅ Be structurally strong
✅ Support long-term mass production

If you want, I can:

• Review your box 3D design

• Recommend gate quantity & positions

• Design a cooling layout

• Suggest steel grade based on output volume

Just tell me the box size, material, and production target