Heat treatment of die casting mold parts:
1.The quenching equipment is a high pressure and high flow rate real air 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 and cavities that affect this point, they should be filled and blocked, and the mold can be heated and cooled evenly as far as possible; At the same time, pay attention to the way of furnace loading to prevent deformation of die casting die caused by dead weight at high temperature.
(2) Mold heating: in the heating process, it should be slowly heated (heating with 200℃/h), and two-stage preheating method should be adopted to prevent excessive temperature difference between inside and outside the mold caused by rapid heating, causing excessive thermal stress, and reducing phase transformation stress. Titanium Hao machinery is machine tool spindle, rotary thimble, lead screw screw, shaft processing, CNC CNC processing, tool handle tool rod, chuck joint rod, non-standard parts processing for the company's main products, quality assurance, trustworthy!
(3) Quenching temperature and holding time: the lower limit quenching heating temperature should be adopted, and the heating time should not be too short or too long. Generally, the heating time is determined by the wall thickness and hardness.
(4) Quenching cooling: using pre-cooling, and by adjusting the air pressure and wind speed, effectively control the cooling speed, so as to maximize the ideal cooling. That is, after pre-cooling to 850℃, increase the cooling speed and quickly pass through the nose of the "C" curve. When the mold temperature is below 500℃, the cooling speed is gradually reduced, and when it is below the Ms point, the cooling method of approximate isothermal transformation is adopted to minimize the quenching deformation. When the mold is cooled to about 150℃, turn off the cooling fan and let the mold cool naturally.
2.Annealing includes spheroiding annealing after forging and stress relief annealing in the process of mold making. Its main purpose: to improve the crystalline structure in the raw material stage; Easy to process and reduce hardness; To prevent deformation and quenching crack after processing and remove internal stress.
(1) Spheroidization annealing. After the die steel is forged, the internal structure of the steel becomes unstable crystal, and the hardness is high and the cutting is difficult. Moreover, the steel in this state has large internal stress, which is easy to be deformed and quenched after processing, and the mechanical properties are poor. In order to make the carbide crystal become spheroidized stable structure, spheroidized annealing must be carried out.
(2) Stress relief annealing. The die steel with residual stress will be deformed after mechanical processing. If there is still stress after mechanical processing, great deformation or quenching crack will occur during quenching. Titanium Hao machinery is the main machine tool spindle, rotary thimble, lead screw, shaft processing, CNC CNC processing, tool shank tool rod, chuck joint rod, non-standard parts processing for the company's main products, in order to prevent these problems, must carry out stress annealing.
In the process of mold making, stress relief annealing is generally carried out three times:
(1) When cutting off the shape of more than 1/3 of the volume of raw materials or the depth processing of the thickness of raw materials 1/2, the processing allowance is 5 ~ 10mm, for the first time to relieve the stress annealing.
(2) in finishing with a margin (2 ~ 5mm), the second stress relief annealing.
(3) After mold test, stress relief annealing is carried out for the third time before quenching.
3.When the tempered and quenched die is cooled to about 100 ° C, it is necessary to temper immediately to prevent further deformation and even cracking. Tempering temperature is determined by the hardness of the work, generally three tempering.
4.Nitriding treatment can be used after quenching and tempering (45 ~ 47HRC), but in order to improve the wear resistance, corrosion resistance and oxidation resistance of the die, prevent sticking to the die and extend the life of the die, nitriding treatment must be carried out. The depth of nitride layer is generally 0.15 ~ 0.2mm. After nitriding, it is necessary to polish and grind off the white bright layer (about 0.01mm thick).
5.A few notes
(1) The heat treatment deformation of the mold is caused by the joint action of phase transformation stress and thermal stress, which is affected by many factors. Therefore, on the premise of correct material selection, but also pay attention to the forging of blank, to use six forging method, repeatedly upsetting. At the same time, in the mold design stage must pay attention to, make the wall thickness as uniform as possible (when the wall thickness is not uniform to open the process hole);
For the mold with complex shape, it is necessary to use the inlaid structure rather than the overall structure; For the die with thin wall and sharp corner, it is necessary to use the rounded corner transition and increase the radius of the rounded corner. In the heat treatment, the data should be well recorded, the upward deformation of the long, wide and thick sides, the heat treatment conditions (furnace loading mode, heating temperature, cooling rate, hardness, etc.), so as to accumulate experience for the heat treatment of the mold in the future.
(2) There are generally two kinds of technological processes for die casting die processing, which are determined according to the actual situation. The first kind: general die casting mold. Forging → spherification annealing → roughing → the first stress-relieving annealing (with a margin of 5 ~ 10mm) → roughing → the second stress-relieving annealing (with a margin of 2 ~ 5mm) → finishing → the third stress-relieving annealing (after mold testing and before quenching) → quenching → tempering → pliers repair → nitriding. The second kind: especially complex and quenched very easy deformation mold. Forging → spheroidization annealing → rough machining → secondary stress relief annealing (with a margin of 5 ~ 10mm) → quenching → tempering → machine, electrical machining → second stress relief annealing (with a margin of 2 ~ 5mm) → machine, electrical machining → third stress relief annealing (after mold testing) → pliers repair → nitriding.
