High-temperature plastic materials (such as PEEK, PEI, PSU) are widely used in high-end fields like semiconductors, new energy, and medical devices due to their excellent heat resistance, corrosion resistance, and high mechanical strength. However, these materials feature high melting temperatures (usually 280℃-400℃), poor fluidity, and unstable cooling shrinkage, imposing strict requirements on the heat resistance, adaptability, and precision of injection molds. Based on years of integrated molding practice, the design of injection molds for high-temperature plastics must focus on the following core points to ensure product molding quality and production stability.
Material selection is the fundamental guarantee for molds. Key components such as cavities and cores should be made of high-quality hot work die steel with heat resistance and thermal fatigue resistance, such as modified H13 and S136H. After vacuum quenching and cryogenic treatment, the hardness should reach HRC55 or higher to avoid deformation, wear, or corrosion under long-term high temperatures. Guide pillars, guide sleeves, and other guiding components should adopt high-temperature resistant alloy materials combined with graphite self-lubricating structures to reduce friction and wear in high-temperature environments. For high-temperature materials with strong corrosiveness, the cavity surface should undergo nitriding treatment or TiN coating to enhance corrosion resistance and demolding performance.
Cavity and runner design must adapt to material characteristics. Due to the poor fluidity of high-temperature plastics, runners should adopt large-diameter circular cross-sections with minimized length. The taper of the main runner should be controlled between 2°-3° to ensure smooth melt filling. Cavity design should avoid sharp corners and narrow gaps, using arc transitions to reduce melt flow resistance and stress concentration. Meanwhile, gate positions and quantities should be reasonably set according to product structures, preferably using sub-gates or pin gates. The gate size should be 1.2-1.5 times larger than that of ordinary plastic molds to avoid defects such as material shortage and weld lines. For products with complex structures, conformal runners can be adopted to ensure uniform melt filling of each cavity.
Cooling system design directly affects molding efficiency and product precision. High-temperature plastics have large cooling shrinkage, and uneven cooling is prone to product deformation and warpage. Cooling channels should be closely attached to the cavity surface with a spacing of 15-25mm and a diameter of 8-12mm to ensure uniform cooling. A parallel waterway layout is adopted, with each cooling circuit independently controlling water flow rate and temperature, which can be accurately adjusted according to the heat dissipation needs of different product areas. For thin-walled or complex-structured products, special-shaped waterways or insert-built cooling pipes can be used to improve cooling efficiency. Industrial water chillers are preferred as cooling media, with the inlet water temperature controlled at 25-35℃ to avoid insufficient cooling due to excessively high water temperature.
Ventilation structure design needs to solve the problem of high-temperature exhaust. A small amount of gas is generated when high-temperature plastics melt, and poor exhaust can easily cause air marks, burning, and material shortage. Mold exhaust grooves should be set at the positions where the melt fills last, such as the end of the cavity and near the gate. The groove width is 0.03-0.05mm and the depth is 0.8-1.2mm to ensure smooth gas discharge without flash. For closed cavities or complex structures, exhaust pins or exhaust inserts can be installed on the core to improve exhaust efficiency. Meanwhile, a 0.01-0.02mm exhaust gap should be reserved on the mold parting surface for auxiliary exhaust.
Ejection mechanism should balance demolding stability and product protection. High-temperature plastics have high hardness after cooling and strong adhesion to the cavity. The ejection mechanism should adopt a multi-point uniform ejection design to avoid product deformation caused by excessive local force. Ejector pins are made of high-temperature resistant alloys with a diameter of no less than 2mm. The fit clearance between ejector pins and pin holes is controlled at 0.01-0.02mm to prevent melt overflow. For thin-walled or easily deformable products, top plate ejection or gas-assisted ejection can be used to improve ejection stability. The ejection stroke should reserve sufficient margin to ensure complete product separation from the cavity.
Precision and wear protection design cannot be ignored. Molds experience significant thermal expansion and contraction in high-temperature environments. Reasonable thermal expansion gaps should be reserved during design, and the thermal expansion amount should be calculated based on mold materials and product sizes to avoid mold jamming or product dimensional deviations. The mold assembly precision should be controlled within 0.005mm, and positioning pins should be used for precise positioning to ensure the fit precision of the cavity and core. Meanwhile, wear-resistant inserts should be installed in easily worn parts such as mold parting surfaces and sprue bushes to extend mold service life. In addition, the mold should be equipped with temperature monitoring devices to real-time monitor the cavity temperature for timely adjustment of process parameters.
The design of injection molds for high-temperature plastics is a comprehensive embodiment of material characteristics, structural mechanics, and production processes, requiring precise control from multiple dimensions such as material selection, structural design, and cooling exhaust. Only through targeted design combined with actual product requirements and material characteristics can the performance advantages of high-temperature plastics be maximized, ensuring the dual improvement of production efficiency and product quality.
