Precise control of injection molding process parameters is crucial to avoiding flash issues in shock absorber cushions. This requires coordinated optimization across multiple dimensions, including material properties, mold condition, equipment parameters, and environmental conditions. Flash, a common surface defect in injection molding, primarily results from molten plastic overflowing from the parting line or core gap after mold closing. Its formation is closely related to parameters such as injection pressure, clamping force, and melt temperature, requiring systematic adjustments to achieve dynamic balance.
Matching injection pressure and speed is the primary factor in controlling flash. Excessive injection pressure forces the melt into the tiny gaps in the mold, while excessive injection speed can cause the parting line to open due to excessive impact force at the melt front. For shock absorber cushions, which require a balance between elasticity and structural strength, a multi-stage injection process is typically employed: the initial stage uses lower pressure and speed to fill the runner and prevent premature melt solidification; the middle stage gradually increases the pressure to a reasonable range to ensure the melt fully fills the cavity; and the final stage reduces pressure and speed to prevent a sudden increase in cavity pressure. Simultaneously, the injection speed needs to be adjusted according to the wall thickness difference of the damping pad. The speed should be appropriately increased in thin-walled areas to prevent premature solidification of the melt, while the speed should be reduced in thick-walled areas to prevent internal stress concentration.
Precise setting of the clamping force is crucial to preventing flash. Insufficient clamping force will cause elastic deformation of the mold under injection pressure, leading to increased parting line clearance and melt overflow, forming flash. The mold design for the damping pad must fully consider its structural complexity, such as the rigidity of side core pulling and angled ejector mechanisms, as well as the impact of cavity depth on the clamping force. In actual production, the minimum effective clamping force needs to be determined through trial molding, typically 1.1-1.2 times the theoretical calculation value, ensuring tight mold closure while avoiding mold wear or energy waste due to excessive clamping force. Furthermore, the parallelism of the mold and the fitting accuracy of the guide pillars and bushings need to be checked regularly to ensure uniform distribution of clamping force.
The control of melt temperature directly affects its fluidity and viscosity. Excessive temperature reduces melt viscosity, increases fluidity, and makes it easier to penetrate the mold gaps; excessively low temperature may lead to insufficient filling or surface defects. Commonly used elastomer materials for shock-absorbing pads, such as TPU and TPE, are highly sensitive to temperature, requiring strict temperature control in each zone of the barrel: the feeding section temperature should be slightly below the material's melting point to promote plasticization; the compression section temperature should be gradually increased to the material's flow temperature; and the metering section temperature should be kept stable to prevent decomposition. Simultaneously, the nozzle temperature needs to be adjusted according to the mold structure to ensure the melt maintains suitable fluidity before entering the cavity, preventing flash or underfilling due to temperature fluctuations.
The uniformity of mold temperature is crucial to the molding quality of the shock-absorbing pad. Excessively high mold temperatures lead to prolonged melt cooling time, resulting in persistent pressure within the cavity and increasing the risk of flash; excessively low temperatures may cause rapid melt solidification, preventing sufficient cavity filling. Shock-absorbing pad molds are typically controlled by a mold temperature controller, using circulating water or oil for precise temperature regulation. For complex shock-absorbing pads, independent temperature control circuits should be set up for the core and cavity to ensure consistent temperature across all areas. Furthermore, mold surface treatments, such as chrome plating or nitriding, can improve thermal conductivity and reduce flash caused by localized overheating.
Properly setting the holding pressure and time is crucial to avoiding flash. Sufficient pressure must be maintained during the holding phase to compensate for melt cooling and shrinkage. However, excessive pressure or prolonged holding time can cause a continuous increase in cavity pressure, forcing the melt to seep into the mold gaps. The holding pressure parameters of the damping pads need to be dynamically adjusted according to material characteristics and product structure: for elastomer materials with low shrinkage, the holding pressure is typically 50%-70% of the injection pressure, and the holding time is based on the solidification time of the mold core, avoiding premature pressure release leading to shrinkage marks or delayed pressure release causing flash. Simultaneously, the gate design needs to be optimized, such as using a submarine gate or pin gate, to shorten the holding time and reduce residual stress.
Equipment precision and maintenance status are fundamental to stable process parameters. The precision of the injection molding machine's clamping mechanism, injection unit, and hydraulic system directly affects parameter control effectiveness. Regularly check the parallelism of the clamping mechanism, the wear of the guide pillars, and the pressure stability of the hydraulic system to ensure accurate transmission of clamping force and injection pressure. Furthermore, the clearance between the screw and barrel must be maintained within a reasonable range to avoid injection pressure fluctuations due to melt backflow. For the production of shock absorber cushions, it is recommended to use a servo-driven injection molding machine, whose closed-loop control system can adjust parameters in real time, improving molding stability.
Environmental factors have a significant impact on the injection molding process. Fluctuations in workshop temperature can lead to changes in mold temperature, thus affecting melt flowability; excessive humidity may cause material hydrolysis, altering melt viscosity. The shock absorber cushion production workshop must maintain a constant temperature and humidity environment, with temperature controlled between 20-25℃ and humidity below 60%. Simultaneously, the raw material storage and pre-drying processes must be standardized to ensure the material moisture content meets requirements, avoiding abnormal melt flowability due to moisture evaporation, which indirectly leads to flash issues. By systematically controlling process parameters and environmental conditions, the yield and quality stability of injection molding accessories shock absorber cushions can be significantly improved.
