I. Raw Material Preparation

1. Material Selection
   Engineering plastics for precision molding require high mechanical strength, dimensional stability, creep resistance, and environmental stress cracking resistance. Common materials include:

• Polycarbonate (PC): Applied in optical lenses and electronic enclosures for its transparency, heat resistance, and dimensional stability.

• Polyoxymethylene (POM): Suitable for precision gears and mechanical parts, featuring high rigidity, low friction, and fatigue resistance.

2. Drying Treatment
   Moisture in plastic pellets can cause surface defects like silver streaks and bubbles, and reduce mechanical properties. For hygroscopic materials such as Nylon (PA), drying parameters are critical:

• Temperature: 80–120°C

• Duration: 2–4 hours

• Moisture content: ≤0.1%

II. Mold Design and Manufacturing

1. Mold Precision Design
   Cavity dimensions are calculated based on shrinkage rates, influenced by:

• Gate type, location, and distribution

• Material crystallization orientation (anisotropy)

• Part geometry, size, and distance from the gate

• Tolerance: ≤±0.005 mm

• Surface roughness: Ra 0.1–0.05 μm

2. Gate Design

• Pin-point gate: For high-precision parts with minimal gate marks.

• Edge gate: Versatile for various shapes, requiring careful placement to avoid weld lines.

• Submarine gate: Hidden within the mold, suitable for aesthetic components.

3. Cooling System Design

• Maintain uniform mold temperature (±1°C variation) to minimize shrinkage and warpage.

• Use circulating water channels around the cavity.

• For complex molds, adopt zone-controlled cooling for uneven heat distribution.

4. Mold Manufacturing Processes

• Electrical Discharge Machining (EDM): Achieves ±0.01 mm precision for complex shapes.

• Wire-cut EDM: Cuts intricate features with ±0.005 mm accuracy.

• Grinding: Ensures surface flatness within ±0.002 mm.

III. Process Parameter Settings

1. Injection Speed
   Apply segmented injection for complex molds:

• Stage 1: Slow filling (30% speed, 40 bar) to avoid jetting.

• Stage 2: Medium speed for intricate sections.

• Stage 3: Fast filling to 95% of cavity volume.

• Stage 4: Slow buffer for packing.

2. Packing Pressure and Time

• Pressure: 60–80% of injection pressure.

• Time: 10–20 seconds for 2 mm-thick parts (adjust based on shrinkage).

3. Injection Pressure

• Range: 100–200 MPa (higher for low-flow materials or thin walls).

4. Barrel Temperature

• PP: 180–230°C

• PC: 270–320°C

• Example ranges:

5. Mold Temperature

• Crystalline plastics (e.g., PE, PP): Higher temperatures for uniform crystallization.

• Amorphous plastics (e.g., PS, PMMA): Optimized for flow and surface finish.

• Control within ±1°C:

IV. Equipment Selection

1. Injection System Precision

• Screw diameter and L/D ratio tailored to part size.

• Shot volume accuracy: ≤±0.5%.

• Pressure control: ≤±1 MPa fluctuation.

2. Clamping System Rigidity

• Calculate clamping force:
  Force (kN) = Projected area (cm²) × Injection pressure (MPa) × Safety factor (1.2–1.5).

3. Control System Stability

• Digital control with real-time monitoring of speed, pressure, and temperature.

• Fault diagnosis and alarm functions.

V. Post-Processing

1. Annealing

• Reduce internal stresses by heating below the material’s heat deflection temperature (e.g., PC at 120°C for 1 hour).

2. Moisture Conditioning

• Immerse hygroscopic parts (e.g., PA) in hot water (90–100°C) for 2–4 hours to stabilize dimensions.

3. Surface Treatment

• Options include polishing, electroplating, and painting to enhance aesthetics and functionality.