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Stress relief and aging treatment of die-casting molds, prevention and control of residual stress-induced deformation and cracking
After the processing, heat treatment, and welding of mold steel, residual stress comes with it. When it is heated and stacked on the machine, it can cause premature deformation, cracking, and dimensional drift. The root cause of many mold failures is that the stress is not fully released.
1、 Source of residual stress
Original stress of forging blank, CNC rough machining cutting stress, quenching and tempering stress, EDM discharge stress, weld overlay welding stress, polishing and grinding stress. The internal stress of EDM white layer is extremely high, making it a high-risk area for microcracks.
2、 Classification of stress relief methods
1. Forging billet aging: Pre aging by steel mills to release forging stress;
2. Stress relief tempering after rough machining: insulation at 550-600 ℃ to release cutting stress;
3. Quenching and tempering: Heat treatment of hot work steel core, balancing hardness and toughness;
4. EDM、 Low temperature stress relief after welding: insulation at 200-300 ℃ to eliminate surface stress;
5. Vibration aging: suitable for large items, assisting in stress relief.
3、 Typical consequences of not relieving stress
After running thousands of molds on the machine, the mold cavity deforms and the size drifts; Irregular cracking at sharp corners and gate positions; Slowly deform after polishing, with dimensions exceeding tolerance; After the assembly of the insert, it slowly shifts and there are flying edges. Alloy wheel mold has a larger wheel cavity, which increases the risk of stress deformation.
4、 Taboo of process sequence
Cannot be stress relieved after precision machining, high temperature aging will change the size; Must undergo rough machining → stress relief → precision machining; After EDM, the stress is removed first, followed by polishing and nitriding.
5、 Data requirements for delivery of foreign trade molds
Heat treatment reports and stress relief tempering records are often requested by European and American host customers; Many low-priced molds omit the rough machining and stress relief process, resulting in no visible problems in the short term and concentrated failures in the later stages of mass production. Google's "die casting mold stress relief process" is aimed at heat treatment engineers.
FAQ
Is quenching and tempering equivalent to stress relief?
Quenching and tempering are essential for obtaining hardness and toughness, and independent stress relief tempering after rough machining cannot be omitted.
Why is the stress on the EDM white layer high?
Rapid melting and rapid cooling during discharge, surface tissue distortion, and high residual tensile stress.
Can vibration aging replace tempering to relieve stress?
Auxiliary methods cannot replace heat treatment and tempering.
Is it better to have a higher stress relief temperature?
When the temperature exceeds the tempering temperature, the hardness directly decreases.
5. If the mold is deformed, can stress correction still be applied?
Mild deformation can be corrected by pressure tempering, while severe deformation is scrapped.
6. Should the inlay be individually stressed?
After rough machining, the embedded parts also need to be stress relieved.
7. Will polishing and grinding generate stress?
Fine grinding and high-speed polishing will generate surface grinding stress.
8. Which step is easiest to omit with low-priced molds?
Stress relief tempering after rough machining.
MOLDES DE FUNDICIÓN A BAJA PRESIÓN (LPDC)
MOLDES DE FUNDICIÓN POR GRAVEDAD
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MOLDE DE FUNDICIÓN POR PRESIÓN DIFERENCIAL PARA CUBOS DE RUEDA
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MOLDE DE FUNDICIÓN A BAJA PRESIÓN PARA CUBOS DE RUEDA
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