Six Common Misunderstandings and Avoidance Methods in Precision Injection Molding
2026-05-20 13:07:12
Injection Molding
Precision injection molding is mainly used to produce electronic precision parts, medical devices, automotive sensor components and micro structural parts, which have extremely strict requirements on dimensional tolerance, flatness, geometric tolerance and product consistency. Many production sites are trapped in long-term operational misunderstandings in actual commissioning and mass production, resulting in batch dimensional deviation, warpage deformation and assembly failure. Clarifying typical misunderstandings and implementing targeted avoidance schemes are core prerequisites for high-standard precision injection molding production.
1. Misunderstanding 1: Increasing Injection Pressure Blindly for Complete FillingMost technicians tend to raise injection pressure directly when facing insufficient filling defects, believing that higher pressure brings fuller molding effect. Excessively high injection pressure will enhance melt impact force, easily cause edge flash and core deflection. Long-term high-pressure mold locking will loosen mold positioning components and damage geometric tolerances such as coaxiality and flatness. Meanwhile, huge residual internal stress will induce slow dimensional drift of finished products in later service.
Avoidance Method: Improve melt fluidity by optimizing material temperature and injection speed firstly instead of blind pressure increase. Adopt segmented pressure control in precision production, apply low pressure for feeding buffering, stable pressure for main filling and low pressure for final material collection to reduce internal stress and mold deformation and maintain basic dimensional precision.
2. Misunderstanding 2: Applying Unified Holding Pressure for All Structural PositionsFixed holding pressure and time are commonly used in actual production, ignoring unbalanced wall thickness and dense rib distribution of precision products. Insufficient holding pressure at thick-wall positions leads to sink marks and internal cavities, while excessive pressure at thin-wall positions causes ejection whitening, deformation and oversized size, resulting in unstable assembly clearance and unqualified precision matching effect.
Avoidance Method: Implement segmented gradient holding pressure to match shrinkage rules of different glue positions. Adjust holding time appropriately according to ambient temperature and raw material batches to realize sufficient shrinkage compensation at thick positions and moderate pressure control at thin positions, so as to unify shrinkage rate and stabilize key assembly dimensions.
3. Misunderstanding 3: Judifying Raw Material Dryness by Naked Eyes OnlyHigh-precision engineering plastics such as PA, PC, PBT and LCP have strong moisture absorption. Many workshops end drying operation within a short time and confirm qualified drying state simply by visual observation, while deep internal moisture cannot be completely removed. Residual moisture will form silver streaks and internal bubbles under high temperature, causing uneven product density and severe dimensional deviation of precision holes and shaft positions.
Avoidance Method: Formulate standardized drying standards: keep PC materials at 110℃-120℃ for 4-6 hours, and PA materials at 100℃-110℃ for constant-temperature drying. Store dried materials in sealed thermal insulation containers to prevent secondary moisture absorption. Conduct trial production verification before mass production to confirm defect-free molding.
4. Misunderstanding 4: Reducing Mold Temperature Excessively to Shorten CyclesIn pursuit of higher production efficiency, reducing mold temperature blindly will cause rapid surface solidification of melts after entering cavities, resulting in disordered molecular arrangement and frequent warpage, bending and hole position deflection. Such structural deformation cannot be corrected through later process adjustment.
Avoidance Method: Adhere to medium and high mold temperature molding principles for precision products. Stabilize mold temperature between 60℃ and 95℃ according to raw material properties to ensure uniform melt flow and orderly molecular orientation. Unify temperature difference inside molds to realize even cooling and shaping, and optimize cooling duration on the premise of guaranteed precision.
5. Misunderstanding 5: Reducing Back Pressure Excessively for Fast PlasticizingLow back pressure setting is widely adopted to accelerate screw retraction and shorten production cycles. Under low back pressure conditions, plastic particles cannot be fully melted and mixed, and melts are mixed with air and undissolved raw materials, leading to loose internal product structure, inconsistent batch tolerance and decreased weld line strength.
Avoidance Method: Set reasonable back pressure ranging from 8MPa to 15MPa for precision injection molding. Increase back pressure properly for high-viscosity and modified materials to realize sufficient plasticizing and air removal. Match screw speed with injection rhythm to ensure consistent melt output density and high unified product size.
6. Misunderstanding 6: Perfunctory Mold Maintenance Ignoring Precision Matching PositionsDaily mold maintenance is limited to simple surface glue cleaning, ignoring wear inspection of guide components, positioning pins, precision inserts and exhaust grooves. Long-term operation will increase matching clearance, decline mold closing precision, block exhaust passages and cause ejection deformation, all of which will directly affect finished product precision.
Avoidance Method: Establish standardized regular maintenance systems. Clean carbon deposits in runners and exhaust grooves daily, inspect wear conditions of positioning components weekly and replenish high-temperature resistant lubricants regularly. Calibrate mold closing precision and ejection parallelism periodically to delay precision attenuation and maintain long-term stable molding performance of molds.
ConclusionHigh-quality precision injection molding production depends on standardized operation concepts and refined whole-process management rather than extreme adjustment of single parameters. Abandon extensive production modes such as high pressure rapid cooling, fixed parameter copying and simplified raw material drying. Implement full-process standardized control covering raw material pretreatment, temperature matching, pressure combination and mold maintenance to eliminate various molding hidden troubles, strictly control dimensional tolerance and geometric precision, and realize high-efficiency, high-quality and low-cost stable mass production of precision plastic parts.
