Analysis of Optimization Process for Shrinkage and Gap Defects in Injection Molded Busbar Shells

In the production of electrical insulation components, injection-molded housings are the mainstream solution for bar protection structures. Plastic insulated bars such as PA66 Plastic Insulation Bar and PP Plastic Insulation Busbar rely on injection-molded housings for isolation and protection. During mass production, defects such as surface shrinkage and excessively large assembly gaps often occur in the housings. This problem is not caused by a single factor, but rather by a combination of factors including raw material characteristics, injection molding process, mold structure, and product design. The industry generally adopts a systematic optimization approach of step-by-step investigation and layered adjustments. The basic optimization logic is to first adjust injection molding parameters to reduce mold modification costs; if process improvements do not meet expectations, then optimize the mold structure, simultaneously coordinating with product structure and material selection to avoid defects at the source.

Adjusting injection molding process parameters is the most efficient and cost-effective way to improve shell shrinkage and gap defects. During production, molding problems can be quickly improved by optimizing core parameters: setting the holding pressure to 80% of the injection pressure, calculating the holding time based on the wall thickness (2-3 seconds per millimeter for thin-walled parts, and extended holding time for thicker parts over 5 millimeters); reasonably increasing the mold temperature, controlling the temperature difference between the moving and fixed molds within 5℃, slowing down the melt cooling rate, and ensuring sufficient shrinkage compensation; appropriately reducing the material temperature while maintaining melt flowability, and using a slow-fast-slow segmented injection speed to avoid density unevenness caused by melt turbulence, effectively improving the overall molding accuracy and consistency of Insulated Busbar Pin Type shells.

If simply adjusting process parameters cannot eliminate shrinkage and gap defects, targeted improvements to the mold structure are necessary to address the defects at the molding carrier level. The gate should be located in a thick-walled area of ​​the product to ensure the holding pressure is fully transmitted to the melt. For large and complex busbar shells, a multi-point gating structure can be added to shorten the melt flow path. The gate thickness and diameter should match the product wall thickness to delay gate freezing and enhance the shrinkage compensation effect. A balanced cooling water channel layout can eliminate local shrinkage differences. The water channels should maintain a fixed distance from the product surface, with denser water channel arrangement in thick-walled areas. A conformal cooling structure should be used to balance the cooling rate throughout the mold cavity. The mold venting system is equally important. Gas easily accumulates on the back of ribs and at the ends of blind holes. Trapped gas can hinder melt filling, leading to short circuits and shrinkage. Standard-sized venting grooves and venting pins should be added at corresponding locations to ensure smooth gas discharge from the cavity, adapting to the production needs of various shell molds for the PP Plastic Insulation Busbar.

Standardized product structure design and appropriate material selection are core means to reduce molding defects at the source. Structural design must adhere to the principle of uniform wall thickness, controlling the proportion of wall thickness differences, and setting gentle, gradual slopes at the junctions of thick and thin sections. The thickness at the base of reinforcing ribs must be strictly limited within the main wall thickness range; exceeding this standard can easily lead to shrinkage and depressions. A reduced-plasticity volcano-shaped structure is used on the back of the pillars to achieve a smooth wall thickness transition. Standard rounded corners are uniformly set to avoid plastic buildup at corners that can induce shrinkage. For material selection, low-shrinkage plastic substrates are preferred, while low-shrinkage alloy materials offer better dimensional stability. Glass fiber modified materials can significantly reduce molding shrinkage, but glass fiber fillers exhibit molding anisotropy and are prone to warping, requiring higher standards for mold and process control. This is suitable for mass production of high-precision shells for PP Plastic Insulation Busbar.

As the requirements for dimensional accuracy and appearance quality of injection-molded busbar shells continue to increase, molding defects such as shrinkage and assembly gaps directly affect the assembly accuracy and safety of insulated bars. A four-tiered optimization approach-process fine-tuning, mold optimization, structural improvement, and material replacement-can systematically solve the molding defects of injection-molded shells, stabilize the molding quality of various plastic insulated bar shells, reduce production scrap rates, and promote the standardization and upgrading of injection-molded insulated busbar component molding processes.

If you need help with issues such as shrinkage and gaps in the injection-molded busbar casing, please contact us for a complete molding optimization solution and material selection advice.