How to heat-treat die-casting mold parts?

Heat treatment of Die Casting mould parts:

1. The quenching equipment is a high pressure and high flow vacuum quenching furnace.

(1) Before quenching: The heat balance method is used to improve the overall consistency of heating and cooling of the mold. For all the thin-walled holes, grooves, cavities, etc. that affect this point, they must be filled and plugged, as far as possible to achieve a balanced heating and cooling of the mold; at the same time, attention should be paid to the charging method to prevent the die-Casting mold from being heated at high temperatures. Deformation caused by gravity.

(2) Heating the mold: During the heating process, heat slowly (heating at 200°C/h) and adopt two-stage preheating method to prevent the rapid temperature rise from causing excessive temperature difference between the inside and outside of the mold, causing excessive thermal stress. At the same time reduce the phase change stress.

(3) Quenching temperature and holding time: To use the lower limit quenching heating temperature, the soaking time should not be too short or too long. Generally, the soaking time is determined by the wall thickness and hardness.

(4) Quenching and cooling: The pre-cooling method is adopted, and the air-cooling speed is effectively controlled by adjusting the air pressure and the wind speed so as to realize ideal cooling. Namely: After precooling to 850°C, increase the cooling rate, quickly pass through the nose of the "C" curve. The cooling rate is gradually reduced when the mold temperature is less than 500°C, and the cooling method is applied to approximate the isothermal temperature below the Ms point. Limit the quench deformation. When the mold is cooled to about 150°C, the cooling fan is turned off and the mold is naturally cooled.

2. Annealing includes both the spheroidizing annealing after Forging and the stress relief annealing during the mold making process. Its main purpose: to improve the crystal structure at the raw material stage; to facilitate processing and reduce the hardness; to prevent deformation and quenching cracks after processing to remove internal stress.

(1) Spheroidizing annealing. After the die steel is forged, the internal structure of the steel becomes an unstable crystal, high hardness and difficult to cut, and the steel in this state, the internal stress is large, easily deformed and quenched after processing, poor mechanical properties, in order to crystallize carbides Spheroidized stable tissue must be spheroidized.

(2) Stress relief annealing. Mechanical processing of die steels with residual stresses can cause distortions after processing. If stress remains after machining, large deformations or quench cracks occur during quenching. To prevent these problems from occurring, stress relief annealing must be performed.

Three stress relief anneals are generally performed during the mold making process:

(1) When cutting 1/3 or more of the raw material volume or 1/2 depth of the raw material thickness, the machining allowance is 5 to 10 mm, and the first stress relief annealing is performed.

(2) The second stress relief annealing is performed when there is a margin (2 to 5 mm) for finishing.

(3) After the trial test, a third stress relief annealing is performed before quenching.

3. When the tempered and quenched mold is cooled to about 100°C, tempering must be carried out immediately to prevent further deformation or even cracking. The tempering temperature is determined by the working hardness, and three temperings are generally performed.

4. Nitriding treatment Generally, the die casting mold can be used after quenching and tempering (45 to 47HRC), but in order to improve the wear resistance, corrosion resistance, and oxidation resistance of the mold, to prevent sticking, and to extend the life of the mold, Nitriding treatment. The depth of the nitrided layer is generally 0.15-0.2 mm. After nitriding, it needs to be polished and the white bright layer (about 0.01mm thick) is polished.

5, some instructions

(1) The heat treatment deformation of the mold is caused by the combined effect of phase change stress and thermal stress and is affected by various factors. Therefore, under the premise of correct material selection, we must pay attention to the forging of blanks, and we must use the method of six-sided forging and repeated drawing. At the same time, care must be taken in the design stage of the mold to make the wall thickness as uniform as possible (though the process hole must be opened when the wall thickness is not uniform); for the complex shape of the mold, the insert structure should be adopted instead of the overall structure; For sharp angle molds, use rounded corners and increase fillet radius. In the heat treatment to make a good data record, the length, width, thickness of all the upward deformation, heat treatment conditions (installed furnace, heating temperature, cooling rate, hardness, etc.), for the future heat treatment mold accumulation experience.

(2) There are generally two kinds of technological processes for the processing of die casting moulds, which are determined according to actual conditions. The first kind: General die casting mold. Forging→Spheroidizing Annealing→Roughing→First Stress-Relief Annealing (with a margin of 5-10mm)→Roughing→Second Stress-Relief Annealing (with a margin of 2-5mm)→Finishing→Third Secondary stress relief annealing (after mold trial, before quenching) → quenching → tempering → nipper repair → nitriding. The second type: a mold that is particularly complex and hard to quench. Forging→Spheroidizing Annealing→Roughing→First Stress Relief Annealing(Leave 5~10mm)→Quenching→Tempering→Machine/Electric Machining→Second Stress Relief Annealing (Leave 2~5mm )→Machine, Electromachining → Third stress relief annealing (after mold trial) → Clamp repair → Nitriding.