The difference in the structural shape and cross-sectional dimension of the Chair Mould(FURNITUREMOULD) part, the heat-heating (heat-heat-cooling) process, due to the different heating and cooling rates, under the combined effects of thermal stress, tissue stress and phase change volume, cause the volume expansion of the part Or shrinkage, which causes the size and shape to deviate, cause deformation, and even cause cracking.

The reasons that affect the heat treatment deformation and cracking of the chair mould are various, mainly related to the chemical composition of the steel and the original structure, the structural shape and section size of the part, and the heat treatment process. Heat treatment deformation is often difficult to avoid, but cracking is preventable.

1. Protection of hardened parts

Quenching and tempering are important steps that affect the heat treatment deformation or cracking of the chair mould parts. For parts of the chair mould parts (such as punches and dies) that are important for quenching, deformation or cracking is required. Effective protective measures should be taken to make the shape and section of the part symmetrical and the internal stress balanced.

2. Improvement of heating method

For some small stamping embossing dies or elongated cylindrical parts (such as small punches), it can be preheated to 520–580 °C before being heated in a medium temperature salt bath furnace to quenching temperature, compared to using electric furnace or reflection directly. The deformation of the furnace hardened parts is significantly reduced, and the tendency to *** can be controlled.

3. Determination of heating temperature

When the quenching heating temperature is too high, the austenite grains are coarse, and oxidation and decarburization are caused, and the tendency of deformation and cracking of the parts is increased. In the specified heating temperature range, the quenching heating temperature is low, which causes the inner hole of the part to shrink and the pore size to become smaller.

4, the choice of coolant

For alloy steels, the best way to reduce quenching deformation is to use isothermal quenching or fractional quenching of potassium nitrate and sodium nitrite hot baths. This method is especially suitable for processing stamping dies with complex shapes and precise dimensions. Some porous mould parts (such as porous die), the austempering time should not be too long, otherwise, it will cause the aperture or hole distance to become larger.

5. Optimization of cooling method

Before the parts are taken out of the furnace and placed in the coolant, they should be placed in the air for proper pre-cooling and then quenched in the coolant. This is one of the effective ways to reduce the quenching deformation of the parts and prevent the parts from cracking.

6. Control of tempering treatment

After the mould parts are taken out from the coolant, it is not suitable to stay in the air for a long time. It should be placed in the tempering furnace for tempering. When tempering, low-temperature temper brittleness and high-temperature temper brittleness should be avoided.

7. Quenching before wire cutting

For some wire-cutting stamping parts, prior to wire-cutting, staged quenching and multiple tempering (or high-temperature tempering) heat treatment processes should be used to improve the hardenability of the parts and to make the internal stress distribution uniform. In a state of less internal stress.

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