How to Solve Product Shedding Problems in Insert Molding
1. Mold Design and Structure Optimization
1.1 Precise positioning structure
Accurate positioning ensures insert stability during injection, avoiding uneven plastic filling caused by displacement that impairs bonding force. Common methods include locating pins and grooves. Pin diameter is selected based on insert size and precision needs, generally 2-8mm (small pins start at 2.5mm), with positioning accuracy controlled within ±0.02-±0.05mm to guarantee correct placement.
1.2 Improved exhaust system
Untimely air discharge in the cavity forms bubbles/cavities between plastic and inserts, weakening bonding force. Exhaust grooves should be properly designed: depth 0.015-0.025mm for high-fluidity plastics (PE, PP) and 0.025-0.04mm for low-fluidity ones (TPE, PC). Width is generally 3-5mm, length determined by mold structure. For complex products, exhaust pins can be added to optimize efficiency.
1.3 Optimized gating system
Reasonable gate location and size ensure uniform molten plastic filling, reducing bonding force differences from uneven flow. For complex inserts, multi-point gating is adopted for simultaneous filling from multiple directions. Gate diameter is 1.5-5mm for ordinary plastics; larger sizes are needed for high-viscosity materials (TPE) to ensure smooth filling.
2. Material Selection and Surface Treatment
2.1 Material selection
Compatibility between insert and plastic is key (e.g., PC plastic with aluminum alloy inserts boosts bonding strength). Plastics with good fluidity and low shrinkage are preferred, as they better fill insert gaps and reduce defects. Shrinkage ranges should refer to material technical manuals.
2.2 Insert surface treatment
Sandblasting metal inserts increases surface roughness from Ra 0.8μm to ~3.2μm, improving bonding force by 30%-50% via enhanced mechanical interlocking. Nickel plating on copper inserts (1-8μm thick; ≥0.4μm for weldable, ≥0.2μm for non-weldable) achieves 5B-level adhesion. Chemical treatment forms special compound layers (phosphating, silane coupling) to further enhance interface bonding.
3. Process Parameter Control and Monitoring
3.1 Temperature control
Excessively high barrel temperature causes plastic decomposition; too low leads to poor fluidity. Barrel temperature is generally 10-30℃ above melting point (380-400℃ for PEEK, fine-tuned via experiments). Mold temperature affects cooling and crystallization: 40-80℃ for ABS, 120-180℃ for PEEK-metal inserts to reduce shrinkage stress.
3.2 Pressure control
Injection pressure (80-150MPa, 80-120MPa for PEEK) must be sufficient to fill the cavity without causing insert deformation or plastic overflow. Holding pressure (60%-80% of injection pressure) compensates for shrinkage. Back pressure (0.5-5MPa) enhances plasticization uniformity.
3.3 Real-time monitoring and post-treatment
Temperature and pressure sensors in the mold monitor parameters in real time; the system alarms and adjusts automatically when parameters deviate. High-precision products require annealing (160-200℃ for 2-4 hours) to release internal stress and improve bonding reliability.
