Thermoplastic injection molding machines are the backbone of modern precision manufacturing, enabling the mass production of complex plastic components with micron-level accuracy. These systems operate through a meticulously engineered four-stage process:

1. Material Preparation & Feeding
   Plastic pellets (typically ABS, polycarbonate, or nylon) are fed into a heated barrel via a hopper. Advanced machines incorporate hygroscopic resin dryers to maintain material moisture below 0.02%, critical for preventing structural defects.
2. Plasticization & Injection
   A reciprocating screw with L/D ratios of 20:1–25:1 rotates at 50–200 RPM, generating shear heat to melt pellets into a homogeneous fluid (viscosity range: 100–10,000 Pa·s). The molten plastic (180–320°C depending on polymer) is then injected into mold cavities at pressures up to 210 MPa (30,000 psi), achieving fill times as short as 0.5 seconds.
3. Cooling & Solidification
   Precision temperature control systems maintain mold surfaces within ±0.5°C of setpoints (typically 20–120°C) using cascading water circuits. Cooling accounts for 70–80% of cycle time, with advanced systems reducing this through conformal cooling channels.
4. Ejection & Post-Processing
   Ejector pins remove the solidified part, while automated systems perform gate trimming, surface texturing (Ra 0.05–12.5 μm), or secondary CNC machining for critical features (±0.005 mm tolerances).

Technical Comparison Table

Parameter	Injection Molding	CNC Machining
Optimal Batch Size	1,000–1M+ units	1–500 prototypes
Per-Unit Cost (USD)	$0.10–$5.00	$20–$500+
Lead Time	2–6 weeks (incl. tooling)	1–5 days
Minimum Wall Thickness	0.4–1.5 mm	0.8 mm+
Surface Finish Options	VDI 3400 A1–D3	Ra 0.4–6.3 μm

Industry Applications

• Medical: Sterilizable PEEK components for surgical instruments (ISO 13485 compliance)
• Automotive: Glass-fiber reinforced polyamide engine components (IATF 16949 standards)
• Consumer Electronics: EMI-shielding PC/ABS housings with UL94 V-0 flammability ratings