Metal powder injection molding process parameters of MIM should be how to choose?

Many MIM metal injection molding process, even if in the industry do a few years, may not be able to understand all processes have to understand, here, and we share of MIM316L powder injection process parameter selection problems, mainly include:

1, metal powder how to choose?

Sintered density of PF-3F, PF-5F, PF-10F and PF-15F four kinds of metal powders at different sintering temperatures. It can be seen that, at a certain temperature range, the higher the sintering temperature, the greater the sintering density, which changes little with the sintering temperature. In a certain range, the larger the size of the powder, the greater the sintering density. Spherical powder is beneficial to increase the density of vibration, increase the loading capacity and improve the sintering density.

2, metal powder and binder ratio?

The viscosity increases with the increase of the solid content, when the solid content reached 62% after the injection, the viscosity increased sharply, that the limit of solid content value (maximum 62%).

When the binder is insufficient, there is a gap between the powder will affect the mechanical strength of the products, the binder; excessive, solid content is too low, influence of degreasing, sintering, shrinkage rate.

3, the gate and overflow hole how to choose the design?

The gate should be higher position in space, thus reducing the melt feeding in the mold friction, reduce injection pressure, reduce the possibility of deformation of the products. In addition, the design of the flash point is also very important, the flash point is used to cold material loading in injection process, to ensure the uniformity of the products.

4, C, N and O on the sintering of 316L?

During the sintering process of C, N and O will have a bad effect on sintering 316L. Carbon has a strong affinity for chromium, generation of Cr23C6, the grain boundary decreased chromium content of solid solution, the formation of chromium depleted zone; nitrogen in stainless steel in the supersaturated solid solution, cooling in the form of Cr2N in the grain boundaries, thereby reducing the MIM corrosion resistance of the products; oxygen and chromium can form oxide film Cr2O3, and the liquid wettability is not good, the influence of liquid flow, hinder the densification process.

5, how to choose the sintering atmosphere?

This is because in Ar+H2 atmosphere, low dew point protection powder surface is not oxidized, powder C and O C-O remove more than 900 DEG C; in vacuum atmosphere, gas gap more easily excluded, accelerate the densification process; in N2 atmosphere, the dew point is not low enough, resulting in the oxide film forming powder that is not conducive to the formation of the sintered parts, hinder the diffusion of atoms.

In addition, in the process of sintering, the slower heating rate is conducive to the formation of grain boundary rules and reduce the isolation of obturator, increase sintering time, sintering density increased slightly, but the decline of the mechanical properties (grain). The increase of sintering platform at 800 DEG to 1100 DEG C, lower heating rate is a good choice!