Methods for Machining Precision Control of Precision Injection Molds
2026-05-26 13:58:28
Plastic Molds
Precision injection molds are widely used for small plastic shells, electronic components and optical plastic parts. These molds have strict requirements on dimensional tolerance, surface roughness and fitting clearance. Their machining accuracy directly determines the quality of molded products, assembly performance and mold service life. Combining with on-site machining procedures and practical experience, this article introduces a complete set of accuracy control methods from pre-machining preparation, accuracy management of each process, assembly and commissioning, detection and verification to daily protection.
Pre-machining Preparation and Basic ControlAccuracy control of mold machining starts from early planning. Conduct drawing review and process decomposition firstly. Verify 3D product data, dimensional tolerance, draft angle and fitting requirements, and define machining datums and tolerance distribution for key components such as cavities, cores, inserts and ejection systems to avoid machining errors caused by misunderstanding. Select qualified mold steel according to mold precision grade. Prioritize mold steel with small thermal deformation and uniform structure for precision molds. Inspect flatness and hardness uniformity of raw materials after incoming inspection, and perform aging treatment on blanks to release internal stress and prevent deformation after subsequent machining and heat treatment.
Plan machining routes reasonably and follow the progressive sequence of rough machining, semi-finishing and finishing. Leave uniform machining allowance in roughing and control cutting depth to reduce deformation induced by cutting stress. Unify machining datums of all components to eliminate cumulative errors from inconsistent references. Calibrate processing equipment regularly, including CNC machine tools, grinders, EDM and wire cutters. Inspect spindle runout, guide rail clearance and worktable level, and repair old equipment timely to meet the requirements of precision machining.
Key Points for Accuracy Control of Core Processes
Milling MachiningMilling is the main process for processing mold bases, cavities and inserts. Rough machining is mainly for material removal, and semi-finishing corrects part profiles step by step. Use high-rigidity cutters and appropriate cutting parameters in finishing, and adopt layered cutting to reduce deformation caused by cutting force. Reduce cutting speed and shorten cutter overhang for thin walls, thin ribs and sharp corners to improve machining stability. Leave machined parts to stand naturally after milling to release cutting stress before proceeding to the next process.
Heat TreatmentHeat treatment is a high-risk stage for precision mold deformation. Formulate exclusive quenching and tempering parameters according to steel grades. Control heating rate, holding time and cooling mode strictly to prevent distortion and dimensional deviation caused by dramatic temperature changes. Apply multi-stage tempering to fully release internal stress generated in heat treatment and minimize deformation in subsequent machining and long-term service. Measure dimensional changes of core forming parts such as cavities and cores after heat treatment comprehensively, and reserve trimming allowance for parts with deviations.
Grinding and Electrical MachiningSurface grinding and cylindrical grinding guarantee flatness, parallelism and dimensional accuracy. Control grinding feed to avoid part annealing and deformation caused by excessive grinding heat, and demagnetize workpieces after grinding. Wire electrical discharge machining and EDM are applied for complex cavities, narrow grooves and tiny holes. Calibrate electrodes before machining to ensure even electrode wear. Set reasonable discharge parameters to reduce errors from discharge gaps. Adopt multi-step trimming for complex structures to improve surface quality and dimensional accuracy gradually.
PolishingHigh surface finish is required for precision plastic products. Improper polishing will not only affect appearance, but also change local dimensions. Polish step by step from coarse oil stone to fine abrasive paper and polishing paste. Control polishing force and direction to avoid undersize dimensions and arc deformation caused by excessive polishing. Polish appearance surfaces and fitting surfaces separately, and protect sharp corners, thin walls and sealing areas from collision and dimensional damage.
Accuracy Control in Mold Assembly and CommissioningClean all metal chips, burrs and dust thoroughly before assembly, as burrs will lead to abnormal fitting clearance and part jamming. Assemble components in specified order. Match parting surfaces, inserts, ejector pins, lifters and slides gently. Adjust clearances manually to ensure flexible movement and qualified fitting tolerance.
Focus on checking ejection systems, guide pillars, guide sleeves and positioning structures. Keep uniform clearance between guide pillars and sleeves to prevent mold offset during opening and closing. Verify template parallelism and cavity alignment before trial run, and confirm no interference among moving parts. Conduct low-pressure and low-speed mold opening and closing in the first trial run, observe mold operation status, and adjust fitting clearance and forming dimensions slightly according to burrs and dimensional errors of molded products.
Detection, Verification and Post-protection
Establish a full-process detection system. Measure dimensions with micrometers, calipers, height gauges and coordinate measuring instruments after each process. Rework unqualified parts timely to prevent defective components from flowing into subsequent procedures. Inspect key dimensions of forming surfaces and positioning holes comprehensively and keep detection records for traceability.
Protect mold accuracy during delivery and mass production. Wrap forming surfaces with protective films during handling and storage to avoid scratches and collision. Maintain molds regularly in mass production, inspect wear of moving parts and template deformation, and replace aging accessories timely. Conduct anti-rust treatment during long-term shutdown to prevent dimensional changes caused by rust.
SummaryThe machining accuracy of precision injection molds runs through the whole process including material selection, machining, heat treatment, assembly and detection. To maintain stable accuracy, it is essential to guarantee basic conditions of equipment, raw materials and process routes, refine operation standards for core processes to control deformation and dimensional errors, standardize assembly and detection systems, and implement post-use protection. Multi-link collaborative management can keep mold dimensions, fitting clearance and surface quality meeting the requirements of precision plastic products and extend mold service life.
