Molds for Logistics Transfer Plastic Parts: High-Impact Material Selection and Molding
Logistics transfer plastic parts include turnover boxes, pallet supporting blocks, anti-collision corner guards, stacking gaskets and separation brackets. These products face repeated drop impact, stacking pressure, low-temperature impact and friction in the circulation process. Some products work outdoors with large temperature differences, and brittle cracking is the most common failure problem. The development focus of such molds is not high-precision appearance, but stable impact toughness of the product. Matching mold structure and molding process with material characteristics can ensure the service life of parts under long-term cyclic use. A variety of high-toughness materials can be selected for logistics parts, and each material has its own applicable working conditions.
HDPE has excellent low-temperature impact resistance, good chemical stability and low cost, suitable for cold chain and outdoor turnover products. Impact copolymer PP balances rigidity and toughness, with good fatigue resistance and fast molding cycle, which is widely used for turnover boxes with buckles and hinge structures. TPU and TPE elastomers are used for edge buffer protection and overmolding with hard plastic. High-impact ABS has stable size and is easy to print, but its low-temperature toughness is poor, only suitable for indoor normal-temperature small buckles. PC/ABS alloy has balanced comprehensive performance and is used for heavy-duty safety connecting parts, with high raw material cost and strict molding control requirements. Glass-filled materials are not recommended for impact-bearing positions, as glass fiber will reduce the toughness of the base material.
Mold design points adapted to high-impact materials
High-toughness plastics have a large shrinkage range, and the shrinkage rate should adopt the test data of the specific material grade. Large-section gates are used to reduce excessive shear. Small gates will cause serious molecular orientation, and the material is easy to crack along the orientation direction under impact. Vent slots must be set at the material convergence position, because HDPE and PP flow fast and are easy to trap air, resulting in weak weld lines. Uniform multi-point ejection or sleeve ejection is adopted to avoid local whitening and hidden microcracks caused by concentrated ejection force. The demolding draft angle is appropriately enlarged to reduce scratch damage during ejection. Pre-hardened steel such as 718H and P20 can meet the production requirements, and mirror polishing is not required.
Molding process control for impact performance
Hygroscopic materials such as TPU and PC/ABS must be fully dried before molding, and moisture will cause molecular chain degradation and toughness decline. HDPE and PP have low water absorption, but drying is still recommended in humid weather. The barrel temperature should be controlled reasonably. Overheating will degrade the material, while too low temperature will lead to poor weld fusion. The injection speed is controlled in sections, and the speed is reduced when the melt reaches the convergence area to improve the fusion quality. Excessive packing pressure will increase internal stress, and insufficient packing will cause shrinkage marks. Properly increasing the mold temperature helps the molecular chain relax and reduce residual stress, improving the impact performance, but the molding cycle will be prolonged.
Trial verification and mass production management
Drop impact and fatigue tests must be carried out in the trial mold stage, focusing on the weld line, buckle root and sharp corners which are easy to crack. If cracking occurs repeatedly, adjust the gate position, optimize exhaust and increase the fillet radius at the stress concentration position. The proportion of regrind material should be strictly limited. Repeated heating will reduce the impact toughness of the material, and regular impact sampling inspection is required to prevent batches of brittle defective products. The core of high-impact logistics plastic parts development is to reduce internal stress and improve weld quality through the cooperation of material selection, mold design and process adjustment.
