Precision Injection Molding: Key Processes and Technical Specifications

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:

• 万彩网100线路Polycarbonate (PC): Applied in optical lenses and electronic enclosures for its transparency, heat resistance, and dimensional stability.

• 万彩网100线路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:

• 万彩网100线路Temperature: 80–120°C

• 万彩网100线路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:

• 万彩网100线路Gate type, location, and distribution

• Material crystallization orientation (anisotropy)

• 万彩网100线路Part geometry, size, and distance from the gate

• Tolerance: ≤±0.005 mm

• 万彩网100线路Surface roughness: Ra 0.1–0.05 μm

2. Gate Design

• 万彩网100线路Pin-point gate: For high-precision parts with minimal gate marks.

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

• 万彩网100线路Submarine gate: Hidden within the mold, suitable for aesthetic components.

3. Cooling System Design

• 万彩网100线路Maintain uniform mold temperature (±1°C variation) to minimize shrinkage and warpage.

• 万彩网100线路Use circulating water channels around the cavity.

• 万彩网100线路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.

• 万彩网100线路Wire-cut EDM: Cuts intricate features with ±0.005 mm accuracy.

• 万彩网100线路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

• 万彩网100线路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

• 万彩网100线路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.

• 万彩网100线路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:
  万彩网100线路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.