Injection molding (also called injection moulding) is the most widely used plastic manufacturing process. Plastic pellets are heated until molten, then injected under high pressure (700-2000 bar) into a metal mold cavity where they cool and solidify into the finished part.
The complete cycle: Material drying → Barrel heating (3-zone temperature control) → Screw metering → Injection filling → Holding pressure → Cooling → Mold opening → Ejection → Post-processing
Injection Pressure: 700-2000 bar (depends on material and mold design)
Injection Speed: High for thin walls, low for thick sections
Melt Temperature: 180-320°C (material dependent)
Mold Temperature: 20-120°C
Holding Time: 30-70% of total cycle
Cooling Time: 50-80% of total cycle — this is usually the bottleneck
In China, most molders will provide a 'T0 sample' (first shot) within 15-30 days of tool completion.
Thermoplastics (most common): ABS, PP, PE, PS, PC, Nylon (PA), POM (Acetal/Delrin), PMMA (Acrylic), PET, PBT, TPU, TPE
Engineering Plastics: PEEK (high temp/sterilization), PSU, PEI (Ultem)
Thermosets (limited): Phenolic resin, Epoxy
Most Chinese molders stock ABS, PP, PC and PA as standard — special materials require pre-order (1-3 day lead).
1. Sink Marks — Extend hold time, increase injection pressure, lower mold temp
2. Flash — Insufficient clamp force, reduce injection pressure, check mold parting line
3. Short Shot — Increase injection speed, raise melt temperature, increase shot size
4. Bubbles — Insufficient material drying, low back pressure, poor gate location
5. Warpage — Uneven cooling, mold temperature differential, anisotropic shrinkage
6. Weld Lines — Higher melt temperature, faster injection speed, adjust gate location
7. Silver Streaks — Moisture in material, insufficient back pressure, poor venting
An injection mold consists of:
• Mold base (standard: HASCO, DME, FUTABA, LKM) — the frame that holds everything together
• Cavity & Core — the shaped parts that form the plastic
• Cooling system — channels for temperature control
• Ejection system — ejector pins, sleeves, stripper plate
• Gating system — sprue, runner, gate, cold slug well
• Venting system — 0.02-0.05mm deep vents
• Sliders & Lifters — for undercuts and side features
China is the world's largest injection molded parts producer, with annual output exceeding ¥800 billion. Key clusters:
Dongguan & Shenzhen (Guangdong) — Consumer electronics, home appliances
Taizhou & Ningbo (Zhejiang) — Tooling and mold manufacturing base
Suzhou & Kunshan (Jiangsu) — Automotive parts
Qingdao & Weihai (Shandong) — Home appliances, daily necessities
Typical lead times: 1-2 weeks for samples, 2-4 weeks for production after sample approval. Most Chinese molders work on a 'net 30-day' payment term with established clients.