China Precision Injection Mold Development Scheme for Sensor and PLC Housings
Sensor and PLC housings belong to industrial electronic precision plastic parts, which carry circuit boards, terminal blocks and sealing structures. They have strict requirements on dimensional consistency, flatness, coaxiality of mounting holes, flame retardant performance and assembly clearance. Mold development needs to take molding structure, deformation control, mass production stability and electrical safety specifications into consideration simultaneously. Risk points such as tolerance, wall thickness, weld lines and sealing grooves should be identified in advance at the DFM stage to avoid a large number of mold modifications in the later stage.
Product Forming and Material Preliminary Review
Most sensor housings are equipped with sealing grooves, sensing windows, positioning posts and metal insert holes; PLC housings are mostly large-plane box structures with screw posts, buckles, side wiring holes and heat dissipation ribs. These two types of products generally adopt flame-retardant PBT, PC/ABS and glass fiber reinforced PC. The materials need to meet UL94 V-0 flame retardant standard. For glass fiber reinforced materials, the warpage caused by anisotropic shrinkage should be focused on. The wall thickness design should be as uniform as possible. Transition fillets are added at positions with sudden wall thickness change, and reinforcing ribs are set at the root of screw posts to reduce the risk of surface sink marks. The sealing grooves and mounting reference holes adopt a unified reference system, and tolerance chain checking is completed to avoid assembly jamming caused by superposition of multiple dimensional tolerances. At the same time, confirm the material drying parameters. Insufficient drying of glass fiber materials is very easy to cause bubbles and silver streaks, affecting the insulation performance of the housing.
Mold Flow Simulation and Gating System Design
Mold flow analysis is carried out before formal mold opening to simulate melt filling, packing, cooling, fiber orientation and warpage trend, predict the position of weld lines, and avoid weld lines on sealing surfaces, sensing windows and high-frequency signal areas. Balanced runners are preferred for multi-cavity molds. Valve hot runners are selected for mass production projects to control multi-point sequential injection, reduce internal stress of large-plane products and reduce warpage deformation. Cold runner three-plate molds can be adopted for small-batch projects to realize automatic gate breakage. Gate positions are kept away from appearance surfaces and sealing mating surfaces to prevent gate residues from affecting sealing and assembly. For large thin-walled areas, exhaust is reasonably arranged. Exhaust grooves are arranged at the melt convergence positions and the ends of ribs. The exhaust clearance is controlled according to material characteristics to prevent burning and short shot.
Mold Steel and Cavity Processing Scheme
S136, NAK80, H13 and other materials are preferred for steel of electronic precision housing molds. Flame retardant plastics contain corrosive additives, which will corrode the cavity surface after long-term production. For cavities and inserts with large-volume production demand, PVD coating can be added to improve corrosion resistance and wear resistance and extend mold service life. Standard precision mold bases are selected to control the parallelism of mold bases. The parting surface is fully ground to prevent flash. The cavity adopts insert split design. Sealing grooves, side core pulling and tiny positioning posts are split into separate inserts, which can be replaced separately once worn, reducing maintenance cost. The processing flow includes CNC finishing, wire EDM and optical grinding. Key dimensions are detected by CMM. The cavity size is pre-set according to the material shrinkage rate. For glass fiber reinforced materials, the shrinkage difference between flow direction and vertical direction should be distinguished.
Cooling, Core Pulling and Demolding Structure Design
PLC housings have large planes, and uneven cooling is the main cause of warpage. Cooling water channels are as close to the cavity surface as possible, adopting conformal cooling layout with uniform channel spacing and arc transition at corners to ensure stable mold temperature. Tiny inserts in partial areas of sensor housings cannot arrange water channels, and heat dissipation relies on heat conduction through insert bases. A mold temperature controller is used for precise temperature control during production. Side wiring holes and buckle grooves adopt slider core pulling structures. The slider fit clearance is strictly controlled to prevent flash from falling into the assembly area. Deep holes and tiny positioning posts adopt tube ejector or sleeve ejection to avoid whitening and cracking during ejection. The ejection layout is evenly distributed. Ejector pins are arranged on non-appearance areas such as screw posts and reinforcing ribs as much as possible. Ejector blocks are added on large planes to reduce local ejection force and control product deformation.
Trial Mold Verification and Dimensional Control Process
Trial mold is divided into multi-stage verification. T0 trial mold firstly confirms filling, exhaust and demolding status, records process windows and collects samples. T1 focuses on full dimensional inspection of size, flatness and hole coaxiality, compares simulation data, and adjusts shrinkage compensation, mold temperature and packing parameters. Sealing grooves and mounting reference surfaces are taken as key control dimensions, and SPC statistical process control is established to monitor dimensional fluctuation during continuous mass production. For glass fiber reinforced housings, warpage should be checked emphatically, which can be optimized by adjusting mold temperature difference, packing curve and gate timing. The trial samples are also verified for flame retardancy, insulation, drop and assembly performance to confirm that they meet the application requirements of electronic control products.
Mass Production Maintenance and Risk Control Scheme
Daily mold inspection focuses on slider fit clearance, carbon deposit in exhaust grooves, wear of sealing inserts and hot runner temperature control status. Flame retardant materials are more likely to produce carbon deposits, so runners and exhaust grooves need to be disassembled and cleaned regularly. Drying machines and mold temperature controllers are equipped in the production workshop. Standard process documents of raw material drying, injection temperature, packing and cooling time are fixed to reduce quality fluctuation caused by artificial parameter changes. Spare parts are prepared in advance. Wearing parts such as slider inserts, sleeves, ejector pins and valve pins are managed separately, which can be replaced quickly when worn to reduce downtime. In view of the special requirements of electronic control housings, isolation is carried out during production to prevent oil stains and release agents from polluting sealing surfaces and ensure the sealing and electrical safety performance of housings.
Supporting Delivery Documents
Mold delivery is accompanied by 2D part drawings, 3D mold drawings, mold flow reports, steel material certificates, heat treatment reports, first article inspection reports and standard process cards, facilitating subsequent production, mold modification and quality traceability for customers.
