Strictly control the intrinsic quality of structural foam mold raw materials

Quench cracking is a critical defect that can occur in large injection molds after the heat treatment process. This issue not only leads to the rejection of the mold but also results in significant economic losses for manufacturers. Understanding the causes of quench cracking is essential for preventing such defects and ensuring the quality and longevity of injection molds. So, what are the main reasons behind quench cracking in injection molds? 1) The presence of severe network carbide segregation in the mold material can weaken its structure and make it more prone to cracking during quenching. 2) Residual stresses from machining or cold deformation can accumulate within the mold, increasing the risk of cracks when subjected to thermal stress during heat treatment. 3) Improper heat treatment practices—such as rapid heating or cooling, incorrect selection of quenching media, or inadequate cooling time—can lead to uneven thermal expansion and internal stress, resulting in cracks. 4) Molds with complex geometries, irregular thicknesses, sharp corners, or threaded holes are more susceptible to excessive thermal and structural stress, which can cause cracking. 5) Overheating due to excessively high quenching temperatures can cause microstructural damage, leading to quench cracking. 6) Inadequate tempering after quenching, or insufficient holding time, can leave the mold in a brittle state, making it more vulnerable to cracking. 7) Re-working and re-quenching without prior intermediate annealing can introduce additional stress and increase the likelihood of cracks. 8) Poor compatibility between heat treatment and grinding processes can introduce surface damage or residual stress, contributing to cracking. 9) EDM (Electrical Discharge Machining) performed after heat treatment may create tensile stress and micro-cracks in the hardened layer, increasing the risk of quench cracking. To prevent these issues, several preventive measures should be taken: 1) Ensure the raw materials used for structural foam molding meet strict quality standards to minimize inherent defects. 2) Optimize forging and spheroidizing annealing processes to eliminate carbide segregation and improve the uniformity of the microstructure. 3) After mechanical processing or cold deformation, perform stress-relief annealing above 600°C before proceeding with heat treatment. 4) For molds with complex shapes, use asbestos plugs to fill Screw holes and reinforce thin sections. Employ graded or isothermal quenching techniques to reduce thermal stress. 5) When reworking or refurbishing molds, ensure proper annealing or high-temperature tempering is carried out before re-quenching. 6) Preheat the mold before quenching and implement pre-cooling measures. Select an appropriate quenching medium based on the mold's geometry and material. 7) Control quenching temperature and time carefully to avoid overheating or over-hardening, which can compromise the mold’s integrity. 8) Immediately temper the mold after quenching, and allow sufficient holding time. For high-alloy molds, multiple tempering cycles (2–3 times) may be necessary. 9) Choose the right grinding process and suitable grinding wheels to avoid introducing surface damage or stress. 10) Improve the EDM process by incorporating stress relief and tempering steps to minimize the risk of micro-cracking. By following these guidelines, manufacturers can significantly reduce the occurrence of quench cracking in injection molds, improving product quality and reducing production costs.

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