Key Points in Designing of Carbide Button Mold
1. Calculation and determination of the height of the forming area
It can be seen from the factors that affect the compaction density, in order to obtain a satisfactory compaction density, in addition to a reasonable selection of the pressing method, the powder loading height of each part of the cavity and the compression ratio and pressing rate of the powder body in each part must be correctly controlled. Therefore, when pressing alloy ball teeth with TPA press, it is necessary to correctly design and calculate the height of the cavity forming area. If the height of the forming area is too small, two phenomena will occur: one is that the pressing stroke of the upper punch is not enough, and the upward distance of the lower punch (also known as the ejector) is too large, so that the pressing pressure is concentrated at the bottom of the product, which is difficult to transmit. to the neutral layer, resulting in poor density in the middle of the compact, too high density at the bottom, and cracks at the bottom after sintering. The second is that the loading is too small, the unit weight of the product is too small, and the size is too negative.
If the height of the forming zone is too large, there will be three situations: one is that the pull-down stroke of the upper punch is too large, the pressing pressure is lost in the process of transferring to the neutral layer of the green compact, the density at the top of the green compact is relatively good, and the middle The density of the sexual layer is too poor, making it difficult for the product size to meet the requirements. However, due to the large depth of the punch into the cavity, the exhaust is not smooth, the punch sticks to the material, and it is difficult to move in the cavity, which is easy to damage the upper punch. The third is that the loading is too much, the weight of the product is increased, and the size is too large. Only when the height of the forming zone is moderate, the force on the top and bottom of the green compact can be evenly transmitted to the neutral layer, so that the green compact density is more uniform and the product quality is higher. Therefore, the cavity forming area height must be calculated.
Other relevant parameters and main technical conditions determine the loose specific gravity and fluidity of the powder. The size of the loose specific gravity directly determines the height of the mold, and the fluidity directly affects the time of automatic blanking. Although the metal powder has a certain fluidity, the fluidity is not good. During the pressing process, the flow of the powder is also related to the powder loading method, the friction between the powder and the die wall, and the cross-sectional shape of the compact. Therefore, it is very important to reasonably design the height of the cavity forming area.
2. Calculation of compact volume (or unit weight)
It can be known from the principle of powder metallurgy that metal powders with different compositions, different particle sizes and different single weights adopt the same pressing process parameters, and their compact density will be different. The green compact density directly affects the sintered product density. Therefore, the compact volume must be calculated correctly to strictly control the single weight of the compact, so as to obtain products with good quality.
3. Shrinkage
The shrinkage of the compact directly affects the size of the mold cavity. When designing, an overall shrinkage rate should be determined first according to the material properties of the product, and then combined with the specific shape and pressing process of the product, consider whether it is necessary to properly adjust the shrinkage rate of certain parts.
4. Die fit and surface roughness
The mold cavity needs to move relative to the upper punch and the ejector during the pressing process because the metal powder is loaded. Therefore, in addition to ensuring the dimensional accuracy requirements and surface roughness values of its various parts, it is also necessary to pay attention to its matching accuracy requirements. Otherwise, it is difficult to extrude high-precision products. If the clearance between the punch and the ejector and the die cavity is too small, it will make it unable to move freely, and the friction with the inner surface of the die cavity will be too large, which will damage the die hole and damage the sliding surface of the punch and the ejector. Cause the mold to be scrapped. If the clearance between the punch and ejector and the die cavity is too large, it will cause material leakage during pressing, resulting in excessive product burrs and affecting product accuracy.
Conclusion:
The compact mold of our carbide buttons for mining is designed according to the requirements of mold manufacturing and use and the principle of powder metallurgy forming.
After this mold is used in production, all aspects are well reflected. The press workers reported that the mold was easy to operate, the scrap rate was low, and the production efficiency was high. After the compact is sintered, the density of each part is uniform, and the dimensional accuracy is ideal.
Our customers also reported that the product quality is excellent, both wear resistance and hardness are very good, and the service life is long.
