In the automotive manufacturing industry, the quality of interior parts directly impacts the sensory experience of drivers and passengers and the overall market competitiveness of the vehicle. From the dashboard to door panels, from the central tunnel to air conditioning vents, the vast majority of interior parts rely on the core technologies of "plastic molds" and "injection molding" for production. This article, based on current mainstream industry practices, systematically outlines the technical system, key control points, and future development direction of automotive interior plastic parts processing.
Molds: The "Master Template" of Injection Molding
Molds are the foundation for determining the precision, surface quality, and production efficiency of interior parts. An excellent injection mold must achieve a high degree of coordination in structure, manufacturing precision, and material selection.
Core Considerations in Structural Design
Parting Surface Design: Affects demolding smoothness and flash tendency. Reasonable selection of the parting surface position can avoid leaving obvious marks on the A-grade appearance surface.
Gating System: Directly determines whether the melt filling is uniform and rapid. For thin-walled or complex structural parts, multi-point gating or hot runner technology is often used to reduce flow resistance and material waste.
Cooling System: Occupying 50%–70% of the molding cycle, cooling time is a bottleneck to production efficiency. Conformal cooling channel design can make the mold temperature field more uniform, significantly shortening cooling time and reducing the risk of warpage.
Manufacturing Precision and Materials Modern mold manufacturing has fully adopted an integrated CAD/CAM/CAE process: after 3D design, precision equipment such as CNC and EDM is used for machining to ensure that critical dimensional tolerances are controlled within ±0.5mm. High-quality tool steels (such as P20 and H13) are mostly selected for mold steel, and nitriding or PVD coating is applied when necessary to resist wear and corrosion in the high-temperature, high-pressure injection molding environment.
Injection Molding Process: Parameters Equal Quality
Injection molding is not a simple three-step process of "melting-filling-cooling"; every process parameter is directly related to the defects of the final product.
Material Pretreatment
Hygroscopic engineering plastics such as polyamide (PA) and polycarbonate (PC) must be dried before injection molding. Generally, a moisture content of less than 0.2% is required, with a drying temperature of 80–120℃ and a drying time of 2–4 hours. Otherwise, silver streaks, bubbles, and even degradation black spots are very likely to appear on the product surface.
Key Parameter Control
Temperature Gradient: The barrel temperature increases gradually from the rear to the front (e.g., PP: 150℃→220℃); the mold temperature is set according to the material's crystallinity and appearance requirements. High-gloss parts often use a mold temperature controller for precise temperature control.
Pressure and Speed: Injection pressure is generally between 50–150 MPa. For thin-walled or long-flow parts, high-speed injection is required; while thick-walled parts require staged holding pressure to avoid shrinkage marks.
Time Allocation: Cooling time is the longest. Optimizing the cooling system design can significantly shorten the cycle time and directly increase single-machine output.
Common Defects and Countermeasures
Shortage of Material: Increase injection pressure/temperature, or increase the number/size of gates. Flash: Check if the clamping force is sufficient; repair wear on the mold parting surface.
Warpage: Optimize the holding pressure curve and cooling channel layout to reduce internal stress.
Weld lines: Increase melt temperature and injection speed; add venting grooves at corresponding locations in the mold.
Sink marks: Increase holding pressure and time, or design to reduce the wall thickness in certain areas of the product.
