Precision Control of Plastic Molds for Automotive High-Voltage Wire Harness Sheaths

Automotive high-voltage wire harness sheaths are core protective components in the circuit systems of new energy vehicles, featuring excellent insulation and voltage resistance, high and low temperature resistance, aging resistance, and impact resistance. Their complex structure and strict wall thickness uniformity requirements determine that dimensional accuracy directly affects assembly tightness and overall vehicle electrical safety. Precision control of molds in processing, assembly and molding processes is essential to achieve stable mass production of qualified sheath products.

1. Precision Control in Early Mold DesignAccurate shrinkage rate calculation is the foundation of dimensional stability. Common materials for sheaths including PP, TPE and modified PA have obvious shrinkage differences. Designers shall revise shrinkage parameters according to actual molding temperature and injection pressure on site to avoid overall dimensional deviation. Reasonable parting surface layout is required aiming at buckles, clamping grooves, threading holes and sealing bosses on products to prevent parting misalignment, flash and wall thickness errors.

2. Material Selection and Heat Treatment Precision ManagementSelect mold steel according to production volume. P20 and 718H are suitable for trial production, while S13 and NAK80 with high hardness and wear resistance are preferred for mass production, maintaining hardness between HRC48 and HRC52. Strict vacuum quenching and tempering processes are implemented to eliminate internal structural stress and prevent deformation and cracking in subsequent processing and service.

Different materials are allocated for mold bases and forming parts. Hardened mold bases ensure overall stability, while high-polish forming steel guarantees surface finish to meet insulation appearance standards of wire harness sheaths.

3. Full-process Precision Control in Mechanical ProcessingEven finishing allowance shall be reserved in rough machining, and workpieces shall be placed statically to release processing stress before fine machining to reduce structural distortion. Adopt CNC finish milling, wire cutting and mirror polishing to control tolerance of key positions such as hole positions and sealing grooves within ±0.02mm.

Ensure coaxiality and verticality of inserts, pins and ejector pins. Slim threading pins shall be processed without bending and deflection to guarantee concentricity of molded holes. Unified processing benchmarks are applied to guarantee interchangeability of all mold components. Complete dimensional inspection with calipers, micrometers and two-dimensional measuring instruments after finishing processing.

4. Precision Adjustment in Mold Assembly and ClosingRemove burrs, iron scraps and oil stains thoroughly before assembly to ensure close fitting of joint surfaces. Adjust clearance of guide components to realize smooth opening and closing without excessive looseness or jamming. Optimize parallelism of ejection systems to achieve synchronous ejection and avoid product deformation caused by unbalanced stress.

Gradually adjust mold locking force to prevent surface damage from excessive locking and flash from insufficient locking. Conduct repeated no-load opening and closing tests after assembly to eliminate hidden troubles such as jamming and eccentric wear in advance.

Keep uniform mold temperature to reduce internal molding stress and structural distortion. Carry out small-batch trial production after passing trial mold inspection, and start formal mass production only after confirming stable precision of finished products.

6. Daily Precision Maintenance in Mass ProductionClean carbon deposits and glue dirt in exhaust grooves and runners regularly to prevent forming size changes caused by wear. Inspect wear conditions of positioning parts and inserts periodically and replace worn accessories timely to avoid positioning offset. Implement standardized daily maintenance including lubrication and anti-rust treatment to maintain original mold precision for a long time.

Conduct regular dimensional sampling inspection during production. Stop operation immediately once size deviation and assembly failure occur to troubleshoot mold deformation and assembly clearance problems. Control ambient temperature in workshops to reduce dimensional changes caused by thermal expansion and cold contraction of molds.

ConclusionPrecision control of molds for automotive high-voltage wire harness sheaths runs through the whole process including design, material selection, processing, assembly, trial production and daily maintenance. Stable control of machining tolerance, stress elimination, accurate mold closing and consistent molding environment can ensure unified product size and precise assembly effect, satisfying strict service standards of high-voltage circuits for new energy vehicles. Standardized precision management can also extend mold service life, reduce maintenance costs and realize high-efficiency and high-quality large-scale production.