Heat treatment method of hot forging die
(1) Heat treatment should adopt a reasonable process to reduce heat treatment deformation (generally use multi-stage heating process, while preventing heating cracking), while considering the heat treatment method adopted, the evaporation of alloying elements should be avoided, and under the condition that the hardenability of the material allows, vacuum heat treatment and gas quenching technology should be used as far as possible to reduce heat treatment deformation and avoid a large processing allowance after heat treatment, resulting in surface overheating and affecting the life of the mold. However, for materials with poor hardenability or materials with volatile elements at high temperatures, such as high Ni, salt bath heat treatment is appropriate.
(2) It is recommended to use supersaturated carburizing heat treatment technology, that is, to apply carburizing technology to prevent the decarburization of the heat treatment surface, and at the same time improve the wear resistance of the surface, and use the carburizing and quenching to form high-pressure stress on the surface to improve the fatigue resistance of the mold.
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(3) The mold material generally contains high CR, mo, v, w, nb and other high-temperature, strong carbide forming elements, so as to improve the strength, red hardness and other properties of the mold, in the heat treatment tempering treatment, it has obvious secondary hardening characteristics, that is, in the low temperature tempering and high temperature tempering to form two high hardness. Therefore, according to the actual use temperature range of the mold, the tempering temperature can be optionally applied, but the high-temperature tempering process should be used for the hot forging die to avoid the reduction of the mold performance during use caused by the secondary tempering hardening effect.
On the other hand, because the mold material generally contains high CR, mo, v, w, nb and other high-temperature, strong carbide forming elements, it has strong anti-tempering performance, so it is necessary to temper many times to avoid early failure (fracture and cracking) caused by insufficient tempering, and generally require at least 2 times of high-temperature tempering (more use of three tempering processes).
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Key points of industrial aluminum extrusion die design
1. Reasonably adjust the flow speed of aluminum metal
Reasonable adjustment of the flow speed of aluminum metal is to ensure that each particle on the aluminum profile section should flow out of the die hole at the same speed. The design of the extrusion die should be arranged as symmetrically as possible, and the sizing belt of unequal length should be designed according to the shape of the aluminum profile, the difference in the wall thickness of each part and the difference in the circumference and the distance from the center of the extrusion cylinder. Generally speaking, the thinner the wall thickness of the aluminum profile somewhere, the larger the circumference, the more complex the shape, and the farther away from the center of the extrusion cylinder, the shorter the sizing zone here should be. If it is still difficult to control the flow rate of aluminum metal with the sizing belt, the section shape of the aluminum profile is particularly complex, the wall thickness is very thin, and the part far from the center can be used to accelerate the flow of aluminum metal. For those parts with much larger wall thicknesses or close to the center of the extrusion cylinder, the obstruction angle should be used to supplement the obstruction to slow down the flow rate here. In addition, the flow rate of aluminum can also be adjusted by using process balance holes, process allowances, or by using front chamber molds, guide molds, and changing the number, size, shape and position of manifold holes.
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2. Check the strength of the extrusion die
Because the working conditions of the mold are very harsh when the aluminum profile is extruded, the strength of the mold is a very important issue in the mold design. In addition to the reasonable arrangement of the position of the die hole, the selection of appropriate mold materials, the design of a reasonable mold structure and shape, it is also very important to accurately calculate the extrusion force and check the allowable strength of each dangerous section. At present, there are many formulas for calculating the extrusion force, but the modified Belling formula still has engineering value. The upper limit solution method of extrusion force also has good application value, and it is relatively simple to calculate the extrusion force by empirical coefficient method. As for the verification of mold strength, it should be carried out separately according to the type of product, mold structure, etc. Generally, the flat mold only needs to check the shear strength and flexural strength. Tongue molds and planar manifold molds need to check the shear, bending and compressive strength, and the tensile strength of the tongue and needle tip parts also need to be considered. An important basic issue in strength verification is to select the appropriate theoretical formula of strength and the more accurate allowable stress. In recent years, the finite element method can be used to analyze the force and check strength of particularly complex molds.