Part.1 rational design
The mold is mainly designed according to the requirements of use, and its structure sometimes cannot be completely reasonable and evenly symmetrical. This requires the designer to take some effective measures when designing the mold without affecting the performance of the mold, and try to pay attention to the manufacturing process, the rationality of the structure and the symmetry of the geometric shape.
(1) Try to avoid sharp corners and sections with great differences in thickness
There should be a smooth transition at the junction of thick and thin sections of the mold. This can effectively reduce the temperature difference of the cross-section of the mold, reduce the thermal stress, and at the same time reduce the non-simultaneity of tissue transformation on the cross-section, and reduce the stress of the tissue. Figure 1 shows that the mold adopts transition fillet and transition cone.
(2) Appropriately increase the process holes
For some molds that cannot guarantee a uniform and symmetrical cross section, it is necessary to change the non-through hole into a through hole or increase some process holes appropriately without affecting the performance.
Figure 2a shows a die with a narrow cavity, which will be deformed as shown by the dotted line after quenching. If two process holes can be added in the design (as shown in Figure 2b), the temperature difference of the cross-section during the quenching process is reduced, the thermal stress is reduced, and the deformation is significantly improved.
(3) Use closed and symmetrical structures as much as possible
When the shape of the mold is open or asymmetrical, the stress distribution after quenching is uneven and it is easy to deform. Therefore, for general deformable trough molds, reinforcement should be made before quenching, and then cut off after quenching. The trough workpiece shown in Figure 3 was originally deformed at R after quenching, and reinforced (the hatched part in Figure 3 ), can effectively prevent quenching deformation.
(4) Adopt a combined structure, that is, makeing a diversion mold, separate the upper and lower molds of the diversion mold, and separate the die and punch
For large dies with complex shape and size >400mm and punches with small thickness and long length, it is best to adopt a combined structure, simplifying the complex, reducing the large to small, and changing the inner surface of the mold to the outer surface, which is not only convenient for heating and cooling processing.
When designing a combined structure, it should generally be decomposed according to the following principles without affecting the fit accuracy:
- Adjust the thickness so that the cross-section of the mold with very different cross-sections is basically uniform after decomposition.
- Decompose in places where stress is easy to generate, disperse its stress, and prevent cracking.
- Cooperate with the process hole to make the structure symmetrical.
- It is convenient for cold and hot processing and easy to assemble.
- The most important thing is to ensure usability.
As shown in Figure 4, it is a large die. If the integral structure is adopted, not only the heat treatment will be difficult, but also the cavity will shrink inconsistently after quenching, and even cause unevenness and plane distortion of the cutting edge, which will be difficult to remedy in subsequent processing. , therefore, a combined structure can be adopted. According to the dotted line in Figure 4, it is divided into four parts, and after heat treatment, they are assembled and formed, and then ground and matched. This not only simplifies heat treatment, but also solves the problem of deformation.
Part.2 correct material selection
Heat treatment deformation and cracking are closely related to the steel used and its quality, so it should be based on the performance requirements of the mold. Reasonable selection of steel should take into account the precision, structure and size of the mold, as well as the nature, quantity and processing methods of the processed objects. If the general mold has no deformation and precision requirements, carbon tool steel can be used in terms of cost reduction; for easily deformed and cracked parts, alloy tool steel with higher strength and slower critical quenching and cooling speed can be used; For example, an electronic component die originally used T10A steel, large deformation and easy to crack after water quenching and oil cooling, and the alkali bath quenching cavity is not easy to harden. Now use 9Mn2V steel or CrWMn steel, the quenching hardness and deformation can meet the requirements.
It can be seen that when the deformation of the mold made of carbon steel does not meet the requirements, it is still cost-effective to use alloy steel such as 9Mn2V steel or CrWMn steel. Although the material cost is slightly higher, the problem of deformation and cracking is solved.
While selecting materials correctly, it is also necessary to strengthen the inspection and management of raw materials to prevent mold heat treatment cracking due to raw material defects.
Edited by May Jiang from MAT Aluminum
Post time: Sep-16-2023
