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Prevention plan for thermal fatigue cracking of die-casting molds, extending the service life of fixtures

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  • Release time: 2026-11-07

Prevention plan for thermal fatigue cracking of die-casting molds, extending the service life of fixtures
Thermal fatigue cracking is the main failure mode of die casting mold, and periodic thermal shock continuously damages the surface of the mold cavity. Xinfeng Machinery has implemented effective prevention and control measures.

1、 Mold temperature fluctuation is the core cause of cracking
The temperature of the aluminum liquid is 650-720 ℃, and the mold release agent is sprayed and cooled instantly. The temperature difference on the surface of the mold cavity can reach over 400 ℃, and micro cracks are generated by the accumulation of alternating stress cycles. The daily production shift exceeds 16 hours without interruption, and the crack initiation speed is increased by about 2.1 times. The mold life of intermittent production and frequent start stop is actually better than that of continuous production molds.

2、 Design Standards for Cooling Water Circuit Layout
The distance between the waterway and the outer wall of the cavity is usually reserved at 12-18mm, with uniform spacing to avoid local hot spot concentration. If there is no waterway to take away heat in the hotspot area, network cracks will appear first after thousands of cycles. Many low-priced molds simplify the cooling circuit, reduce the drilling process, and offer low short-term prices, resulting in large-scale cracking and scrapping after 30000 to 50000 mold cycles.

3、 Purity of Steel and Internal Control of Heat Treatment
The location of impurity accumulation is the preferred channel for crack propagation, and high-purity electroslag remelting H13 and 8407 have significant advantages in thermal fatigue resistance. The tempering temperature of heat treatment should match the die-casting working conditions. Insufficient tempering can lead to high internal stress and premature cracking; Excessive tempering and insufficient hardness can easily lead to aluminum adhesion and deformation. Xinfeng Machinery prioritizes recommending high-purity material solutions for continuous mass production customers in steel solutions.

4、 The boundary of surface coating protection
TiN and AlTiN coatings can isolate aluminum liquid erosion and reduce aluminum adhesion tendency, but coatings cannot prevent thermal fatigue cracks. Coatings generally increase the lifespan of molds by 15% -25%. After the coating wears off, cracks will quickly propagate in the substrate. The coating is not suitable for repairing cavities that have already shown obvious cracks and can only be used for new mold protection.

5、 Key points for daily production operation and maintenance control
Preheat the mold thoroughly before starting up, and prohibit direct injection of aluminum material into the cold mold; Gradually reduce the mold temperature before shutdown to avoid sudden cooling and heating. Regularly polish and polish small cracks to prevent them from continuing to propagate, and arrange a cavity inspection every 20000 molds. Overseas Russian speaking auto parts factories have high continuous production intensity and a high proportion of inquiries related to thermal fatigue cracking, making them suitable for long tail content layout.

FAQ
Will minor cracks recur after polishing? The stress field at the root of the crack is still present, and it will continue to develop in the future. Grinding only delays the scrapping node.

What is the appropriate temperature for preheating the mold? Preheat the die-casting mold to above 180 ℃ before production to reduce the initial thermal shock strength.

Can cracks be repaired by welding and continue production? Shallow cracks can be repaired by welding, but if the depth exceeds 1.5mm, it is prone to cracking again after welding, and the repair value is low.

Can spraying more release agent prevent cracking? Excessive spraying brings severe chilling, increases temperature difference, and accelerates the growth of thermal fatigue cracks.

Is the cracking speed the same in different areas of the same mold? The gate, inner corner, and thick section correspond to the position of the mold cavity, with the highest heat load and earlier cracking.

Are there many thermal fatigue cracks in low-pressure casting molds? The filling temperature shock is alleviated, and the crack development rate is only about 30% of that of die-casting molds.

Is it better to have a higher tempering temperature for the mold? Tempering increases the hardness and reduces the risk of deformation and aluminum adhesion, requiring a balance between hardness and toughness.

Is the mold insulation cover effective in preventing cracking? Reduce the amplitude of shutdown cooling, suitable for long intermittent production conditions, and reduce the amplitude of cold and hot alternation.

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