Micro injection parts refer to miniature plastic products with millimeter-level dimensions, wall thickness of 0.1~0.5mm and weight less than 1 gram, which are widely applied in medical devices, micro sensors, optical components and precision electronics. Due to tiny size and delicate structure, micro injection molding faces prominent difficulties in melt filling, mold manufacturing, dimensional stability, venting and automatic picking. Combined with practical production experience, this article analyzes core processing difficulties and puts forward targeted solutions.
1. Poor Melt Filling and Frequent Short ShotsMicro molds are featured with long thin runners, small cavity volume and ultra-thin walls. Melt flow resistance increases sharply during filling. Meanwhile, molten plastic cools down rapidly after contacting with cold mold surfaces, resulting in short shots, flow marks and obvious weld lines. Parts with tiny ribs, micropores and flanges have higher filling difficulty.
To solve filling problems, low-viscosity and high-flow special plastics are selected, such as high-flow PP, PC/ABS and medical-grade PA. Recycled materials are strictly forbidden. In terms of process parameters, raise barrel temperature by 10~20℃ to maintain melt fluidity. Multi-stage injection speed is adopted: medium speed for runners and high speed for thin-wall cavities. Optimize mold structure by shortening runners and designing large arc transitions to reduce flow resistance. Hot runner system and miniature vacuum venting devices are also applied to improve filling performance.
2. Insufficient Mold Precision, Flashes and Mold StickingMicro parts usually require a dimensional tolerance within ±0.01mm, which puts forward ultra-high precision requirements for molds. Excessive fitting gaps of parting lines and inserts will cause fine flashes, while too narrow gaps will lead to mold sticking and surface scratch under thermal expansion. Slender cores and tiny ejector pins are easy to bend and break under injection pressure.
High-hardness and wear-resistant mold steel such as S136 and STAVAX is adopted for micro molds, with mirror polishing treatment. Precision equipment including high-precision CNC, wire EDM and optical grinding is used to control fitting gaps between 0.005mm and 0.01mm. Integral structure is used for slender cores to enhance strength, and rounded transitions are designed at root positions to avoid stress concentration. Uniform multi-point ejection layout ensures balanced ejection force and prevents product damage.
3. Product Deformation and Poor Dimensional StabilityUneven wall thickness and thin structure easily cause inconsistent shrinkage after filling. Tiny deformation beyond micron level will exceed tolerance standards. Slight fluctuation of process parameters and ambient temperature will also lead to large dimensional deviation in mass production.
Uniform cooling water channels are arranged close to cavities to accelerate and balance cooling. Multi-stage packing mode with gradually reduced pressure is adopted to lower internal stress. Hygroscopic materials must be fully dried before molding. Appropriately increase mold temperature to reduce demolding resistance and deformation. Keep production parameters and workshop environment stable to control dimensional deviation.
4. Venting Defects Causing Burning and BubblesThe narrow space of micro cavities makes internal air compressed rapidly during high-speed filling. Compressed high-temperature air will burn plastic and form internal bubbles. Traditional natural venting cannot meet requirements, and it is difficult to open large vent grooves on compact micro molds.
Micro vent grooves with depth of 0.01~0.015mm are opened at gas gathering areas. For areas unable to set grooves, miniature vacuum venting system is equipped. Control barrel temperature strictly to prevent material decomposition and reduce volatile gas. Clean vent grooves regularly to avoid blockage.
5. Difficult Picking and Low Automatic Production EfficiencyMicro parts are light, fragile and easy to be damaged by manual picking. Ordinary suction cups and clamps cannot adapt to automatic operation, resulting in low picking success rate. Custom flexible clamps and micro vacuum suction cups are used for precision manipulators to control clamping force reasonably. Coat mold cavities with anti-stick coating to improve demolding effect. Integral molding and subsequent cutting separation are adopted for ultra-small parts to reduce picking difficulty.
Micro injection molding is a comprehensive precision technology covering materials, molds, processes and automation. Only by collaborative optimization of all links can enterprises improve product yield and realize stable mass production of micro parts.
