Comprehensive Analysis of Core Injection Molding Processes and Key Control Factors

I. Overview of Injection Molding Process

Injection molding, an intermittent manufacturing technique, comprises the following stages:

1. Material Preparation: Feeding granular/powdered plastics into the hopper.

2. Melting and Plasticizing: Converting raw materials into a molten state via heating.

3. High-Pressure Injection: Injecting the melt into a closed mold under screw-driven high velocity.

4. Cooling and Solidification: Solidifying the product through mold temperature control.

5. Ejection: Retrieving the finished product via ejector mechanisms.

II. Pre-Molding Preparations

1. Material Pre-Treatment

   • Physical Property Testing:
     Includes color uniformity, particle size distribution, melt flow index (MFI), thermal stability, and shrinkage rate.

   • Drying Protocols:

     • Small-scale production: Hot-air circulating oven (80–120°C).

     • Mass production: Fluidized-bed drying or vacuum drying (30% efficiency improvement).

   • Typical Parameters: ABS: 80°C × 4h; PC: 120°C × 6h.

2. Equipment Setup

   • Barrel Cleaning: Use specialized purging compounds or disassembly for material/color changes.

   • Mold Preparation:

     • Release Agent Selection: Zinc stearate (general-purpose) or silicone oil (high-gloss surfaces).

     • Insert Preheating: Minimize thermal stress (recommended: 110–130°C).
       

III. Critical Process Stages

1. Plasticization Phase

   • Screw Speed & Back Pressure Control:

     • Back pressure range: 3–15 MPa (upper limit for engineering plastics).

     • Speed optimization: Avoid shear-induced overheating (<80 rpm for L/D >20).

2. Injection and Filling

   • Multi-Stage Pressure Control:

     • Primary Injection: High-speed filling (>80% cavity volume).

     • Secondary Pressure Holding: Compensate shrinkage (20–30% pressure decay).

   • V/P Switch Point: Determined by shot weight or cavity pressure sensors.

3. Cooling and Solidification

   • Cooling Time Formula:

     T=s2π2⋅α⋅ln⁡(Tm−TwTe−Tw)T=π2⋅αs2​⋅ln(Te​−Tw​Tm​−Tw​​)

     Where: $s$ = wall thickness; $\alpha$ = thermal diffusivity.

IV. Post-Processing Standards

1. Annealing Treatment

   • Applicable Materials: PC, PMMA, and other stress-prone polymers.

   • Parameters:

     • Temperature: Tg+10∘CTg​+10∘C to Thdt−20∘CThdt​−20∘C.

     • Time: 1.5–2 min/mm (gradient heating for thickness >6 mm).

   • Validation: Polarized light inspection for >90% stress elimination.

2. Humidification Treatment

   • For nylon-based materials: Boiling water immersion (2–4h to achieve 2.5% moisture content).

V. Process Parameter Optimization Matrix

VI. Defect Resolution Strategies

• Silver Streaks: Verify material moisture content (<0.02%).

• Sink Marks: Increase holding pressure (10–15%) + extend holding time.

• Flash Formation: Reduce injection speed (20%) + check mold clamping force.

VII. Industry Innovations

1. Microcellular Foaming (MuCell®): 15–30% weight reduction.

2. In-Mold Assembly: Simultaneous molding of metal/plastic components.

3. AI-Driven Monitoring: SPC real-time control (CPK >1.67).

Optimization Highlights

1. Hierarchical structure for logical clarity.

2. Critical formulas and parameter ranges for enhanced practicality.

3. Material comparison matrices and defect solutions for actionable insights.

4. Integration of cutting-edge technologies for technical depth.

5. Standardized units (MPa/°C/rpm) for professional consistency.

6. Tolerance ranges aligned with industrial practices.

This version ensures technical precision while aligning with global industry standards, suitable for technical manuals, training materials, or cross-border collaboration. Let me know if further adjustments are needed!