For customer’s deeper understanding of our Metal Injection Molding technology, we will separately talk about every process of MIM, let’s start from the forming process today.
Powder forming technology is the process of filling pre-mixed powder into a designed cavity, applying a certain pressure through a press to form a product of the designed shape, and then removing the product from the cavity by the press.
Forming is a basic powder metallurgy process whose importance is second only to sintering. It is more restrictive and determines the entire production process of powder metallurgy than other processes.
1. Whether the forming method is reasonable or not directly determines whether it can proceed smoothly.
2. Affect the subsequent processes (including auxiliary processes) and the quality of the final product.
3. Affect production automation, productivity and production costs.
Forming press
1. There are two types of die surface in the forming press:
a) The middle mold surface is floating (most of our company has this structure)
b) Fixed mold surface
2. There are two types of mold surface floating forms in the forming press:
a) The demolding position is fixed, and the forming position can be adjusted
b) The forming position is fixed, and the demolding position can be adjusted
Generally, the fixed type of the middle die surface is adopted for the smaller pressure tonnage, and the middle die surface floats for the larger pressure tonnage.
Three Steps of Shaping
1. Filling stage: from the end of demolding to the end of the middle mold surface rising to the highest point, the operating angle of the press starts from 270 degrees to about 360 degrees;
2. Pressurization stage: It is the stage where the powder is compressed and formed in the cavity. Generally there are upper die pressurization and middle die surface descending (ie lower press) pressurization, sometimes there is final pressurization, that is, the upper punch pressurizes again after the end of the press, the operating angle of the press starts from about 120 degrees to 180 degrees End;
3. Demolding stage: This process is the process in which the product is ejected from the mold cavity. The operating angle of the press starts at 180 degrees and ends at 270 degrees.
Density distribution of powder compacts
1. One-way suppression
During the pressing process, the female mold does not move, the lower die punch (upper die punch) does not move, and the pressing pressure is only applied to the powder body through the upper die punch (lower die punch).
a) Typical uneven density distribution;
b) Neutral axis position: the lower end of the compact;
c) When H, H/D increase, the density difference increases;
d) Simple mold structure and high productivity;
e) Suitable for compacts with small height and large wall thickness
2. Two-way suppression
During the pressing process, the female mold does not move, and the upper and lower punches exert pressure on the powder.
a) It is equivalent to the superposition of two one-way suppression;
b) The neutral shaft is not at the end of the compact;
c)Under the same pressing conditions, the density difference is smaller than unidirectional pressing;
d) Can be used for pressing with larger H/D compacts