The charging gun shell of new energy vehicle belongs to automotive precision appearance and structural part, mostly made of flame retardant PA66 glass fiber reinforced and ABS+PC modified engineering plastics. It has strict requirements of high and low temperature resistance, impact resistance, flame retardancy, insulation, dustproof and waterproof. The product features complex curved surface, multiple buckles and uneven wall thickness, putting forward high standards for mold parting structure, gating system, cooling system, exhaust system and demoulding mechanism. Rational mold structure design is the key to ensure dimensional accuracy, appearance quality and stable mass production of products.
Product Structure and Forming Process AnalysisThe charging gun shell adopts upper and lower butt combined structure, with mounting buckles, sealing grooves, positioning columns and wiring grooves. The overall curved surface is smooth, and no welding line, shrinkage and flash defects are allowed on the appearance surface. The product wall thickness is controlled at 1.8 to 2.5mm, and the thickness of local reinforcing ribs shall not exceed 60% of the main wall thickness to avoid shrinkage depression during injection molding. Commonly used raw materials include flame retardant reinforced PA66 and weather-resistant ABS+PC, which have moderate melt fluidity and large curing shrinkage. Glass fiber filled materials accelerate cavity wear and produce corrosive gas, so wear-resistant and corrosion-resistant mold steel shall be preferred. Injection pressure, holding time and mold temperature should be optimized to reduce product deformation and dimensional deviation.
Mold Steel Selection and Hardness Configuration
Affected by flame retardant agent and glass fiber, the charging gun shell mold bears dual working conditions of wear and corrosion. Cavity and core adopt S136 and STAVAX mirror corrosion-resistant mold steel, quenched and tempered to HRC 48-52, with excellent polishing performance, rust resistance and glass fiber erosion resistance. The mold base is made of P20 or 45# tempered steel to meet overall rigidity and assembly precision requirements. Sliding blocks and inclined tops adopt high-hardness SKD61 and DC53, treated by vacuum heat treatment and ion nitriding to improve wear resistance and adapt to mass production of millions of shots.
Parting Surface and Cavity Layout DesignFollow the demoulding direction to adopt curved conformal parting surface, avoiding the straight appearance surface to reduce flash generation and facilitate later mold repair. Mass production molds adopt one mold two-cavity symmetrical layout to balance filling efficiency and reduce mold occupation space. One mold one-cavity structure is suitable for small-batch trial production to reduce mold cost. The parting surface avoids key assembly surfaces such as buckles and sealing positions, and adopts tiger mouth positioning and conical surface locking structure to prevent mold closing misalignment and ensure uniform product wall thickness.
Gating System DesignNo gate mark is allowed on the appearance surface of the charging gun shell. The main runner adopts standard conical structure, and the runner is designed with trapezoidal section to reduce flow resistance and facilitate condensate removal. Submerged side gate and horn hidden gate are adopted, arranged on the inner buckle and edge non-appearance position. Automatic gate breaking is realized after injection molding without manual trimming to ensure appearance integrity. For large-area shells prone to insufficient filling and obvious welding lines, multi-point balanced gating is adopted to shorten filling path, reduce injection pressure and inhibit warping deformation.
Cooling System DesignAiming at uneven wall thickness and fluctuating curved surface of the shell, combine straight water channel and conformal water channel design. The distance from water channel to cavity wall is controlled at 15-20mm, arranged closely along the product contour to realize uniform cooling. Independent cooling loops are set for cavity and core with separated water nozzles to avoid water channel interference. Built-in cooling water channels are added at thick wall and deep rib positions to solve local heat accumulation, shrinkage and overlong molding cycle, effectively shorten cooling time and improve production efficiency and product yield.
Exhaust System DesignGlass fiber modified raw materials produce a large amount of gas during injection molding. Poor exhaust will cause burning marks, air lines and obvious welding lines. Exhaust grooves are opened at parting surface, welding line convergence position and rib end with depth 0.02-0.03mm to discharge gas smoothly without overflow flash. Micro exhaust gaps are reserved at the matching surface of sliding blocks and inclined tops, and exhaust inserts are added at dead corners to ensure full cavity exhaust and adapt to the forming characteristics of flame retardant glass fiber raw materials.
Demoulding and Core-Pulling Mechanism Design
There are many undercuts, buckles and hole structures on the side of the shell, which cannot be directly demoulded by forced ejection. Combined mechanism of sliding block core-pulling and inclined top demoulding is adopted. Large-area outer undercuts are completed by sliding block mechanism with wear-resistant guide rail and limit locking device for stable movement and accurate positioning. Small inner buckles and narrow grooves are demoulded by inclined tops with reasonable angle design to avoid movement interference and product whitening deformation. The ejection system adopts the combination of round ejector pins and sleeve pins, evenly arranged at reinforcing ribs and flange edges to increase ejection stress area and prevent product whitening, deformation and cracking during demoulding.
Mold Surface Treatment and ProtectionThe mold cavity appearance surface is processed by high-gloss mirror polishing to meet the high-gloss texture requirement of the shell. Fine finishing is carried out on non-appearance matching surfaces to reduce friction resistance. Ion nitriding and PVD coating are applied on the cavity surface to improve surface hardness, corrosion resistance and self-lubricating performance, reducing demoulding adhesion and cavity scratching. The parting surface and sliding block matching surface are precisely ground to control fitting gap and fundamentally eliminate flash overflow.
Key Design NotesReserve machining allowance according to product shrinkage rate, simulate warping trend in advance and compensate deformation in mold design. Strengthen mold rigidity by thickening template and adding support columns to prevent template deformation under long-term high injection pressure. Reserve maintenance allowance for all movable mechanisms to facilitate later disassembly, repair and parts replacement. Match injection machine parameters, mold hoisting and water circuit layout to meet the mass production requirements of high precision, long service life and high yield.
