Chinese Plastic Mold Standard for Insert Pre-Embedding Positioning Accuracy Control
1. Introduction
Insert embedding injection molding is widely used in electronic accessories, automotive plastic parts and household appliance structural components. Metal inserts such as copper nuts, steel pins and terminals are easily offset, tilted and height-deviated during high-pressure melt filling, resulting in unqualified assembly size, poor structural strength and batch defective products. To standardize mass production quality and unify inspection and mold making specifications, this standard regulates the full-process positioning accuracy control of insert pre-embedding for Chinese plastic mold manufacturing industry, covering incoming inspection, mold positioning structure, placement operation, injection molding control and mold maintenance.
2. Incoming Accuracy Control of Inserts
The precision of insert itself is the premise of stable embedding positioning. Precision electronic inserts shall control dimensional tolerance, flatness and deformation within ±0.01 mm. Ordinary structural plastic inserts shall adopt a tolerance standard of ±0.02 mm. The warpage deformation of all inserts must not exceed 0.015 mm, and deformed products are strictly prohibited from entering the mold production.
All inserts must be free of burrs, bending deformation and electroplating protrusions. Surface oil stains, cutting residues and oxide layers shall be completely cleaned and dried to prevent slipping and offset during manual or robotic placement. Each batch of inserts shall be sampled at 5% for two-dimensional precision inspection. Unqualified batches will be returned to ensure zero defect of incoming materials.
3. Precision Specification of Mold Positioning Structure
Mold positioning structures include positioning pins, profiling grooves, magnetic adsorption inserts and shaped cavities. For cylindrical nut inserts, the unilateral fitting clearance of positioning pins is controlled from 0.008 mm to 0.015 mm, which can avoid jamming caused by too small clearance and displacement caused by excessive melt impact due to too large clearance.
Sheet terminal inserts adopt profiling positioning grooves with unilateral enlargement of 0.01 mm, equipped with bilateral limit baffles to prevent lateral offset. Tiny lightweight inserts use magnetic positioning with moderate suction to ensure stable placement without tilting. All positioning inserts are heat-treated to HRC 52–56 with mirror polishing. The coaxiality and symmetry of positioning structures are controlled within 0.01 mm to avoid inherent eccentricity of inserts.
4. Accuracy Control of Insert Placement Process
Both manual and automatic placement processes have unified precision standards. During manual embedding, operators use auxiliary jigs to standardize placement direction and depth. The height deviation of inserts is inspected every 30 minutes, and production is suspended immediately if the error exceeds 0.02 mm.
For robot automatic embedding, the placement coordinate calibration shall be completed before daily production. If the coordinate offset exceeds 0.01 mm, servo parameters must be recalibrated. The clamping force of the gripper shall be moderate to avoid insert deformation or loose offset. The low-speed mold closing speed for insert molds is controlled within 25 mm/s to prevent impact displacement during mold clamping. After mold cleaning and material replacement, the first product must be fully inspected before continuous mass production.
5. Displacement Prevention Control During Injection Molding
Direct melt impact is the main cause of insert displacement. The gate position shall avoid facing the insert directly, and side gating or submarine gating is adopted to balance cavity pressure. Multi-point uniform feeding is used for multi-insert products to prevent local unbalanced thrust.
The filling speed is segmented: the front stage fills 70% of the cavity at low speed to reduce impact force, and the holding pressure is controlled at 70% of the conventional pressure to avoid slow extrusion deviation of inserts. The mold temperature fluctuation is controlled within ±3 ℃ to prevent uneven cooling shrinkage from pulling inserts. The allowable eccentricity of precision products is ≤0.03 mm, and ordinary products ≤0.05 mm.
6. Mass Production Wear Monitoring and Precision Maintenance
Regular inspection mechanisms are essential to maintain long-term positioning accuracy. Within 10,000 shots per day, the positioning structure is inspected once per shift. For high-volume production above 20,000 shots, the fitting clearance is rechecked every 4,000 shots. When the unilateral wear of positioning parts reaches 0.02 mm, the inserts must be replaced immediately.
Hard tools are prohibited from scratching the positioning surface during cavity cleaning. After production, residual glue and debris inside positioning grooves and pins shall be cleaned and rust-proof oil applied. A full three-coordinate precision test is conducted every 50,000 shots to correct structural deformation and wear.
7. Conclusion
This Chinese plastic mold insert positioning accuracy standard systematically controls the whole process from insert incoming quality, mold structural precision, placement operation, injection molding parameters to mold maintenance. By implementing hierarchical tolerance control, reasonable positioning clearance, anti-impact injection strategy and regular wear calibration, insert eccentricity, height deviation and tilting defects can be effectively suppressed. The standard ensures stable dimensional consistency of embedded plastic parts, improves product assembly qualification rate, and provides reliable technical specifications for high-precision and high-stability mass production of Chinese insert embedding injection molds.
