Introduction to metal injection molding process!

Introduction to metal injection molding process!

The basic process steps of metal injection molding are as follows: first, select the metal powder and binder that meet the requirements of MIM, and then mix the powder and binder into a uniform feed at a certain temperature by appropriate methods. After granulation, the injection molding is carried out. The formed blank is sintered and densified into a finished product after degreasing treatment. Now let's have a brief introduction.

1. Metal injection molding powder and powder manufacturing technology. There is a high requirement for the raw powder of metal injection molding, and the selection of powder should be conducive to mixing, injection molding, degreasing and sintering, which is often contradictory. The research of MIM raw powder includes: powder shape, particle size, particle size composition, specific surface area, etc.

2. Binder. Binder is the core of metal injection molding technology. In metal injection molding, the binder has two basic functions, namely, improving the fluidity to fit for injection molding and maintaining the shape of the blank. In addition, it should be pollution-free and cost reasonable. For this reason, a variety of adhesives have emerged. In recent years, according to the requirements of degreasing methods and adhesive functions, the selection of adhesives has gradually developed from experience to targeted design of adhesive systems.

3. Mixing. Mixing is the process of mixing metal powder and binder to obtain uniform feed. Because the nature of the feed determines the performance of the injection molding product, the mixing process is very important. This involves many factors, such as the way and sequence of adding binder and powder, mixing temperature, characteristics of mixing device, etc. At present, this process step is still at the level of empirical exploration. An important indicator for evaluating the mixing process is the uniformity and consistency of the feed obtained.

4. Injection molding. The purpose of injection molding is to obtain a MIM green with the required shape, which has no defects and particles are evenly arranged. First, heat the granular material to a certain high temperature to make it flowable, then inject it into the mold cavity, cool it to obtain the required shape of a certain rigid blank, and then take it out of the mold to obtain the MIM shape blank. This process is consistent with the traditional plastic injection molding process, but due to the high content of metal injection molding powder, there are great differences in the process parameters and other aspects of the injection molding process, Improper control can easily lead to various defects.

5. Degreasing. Since the appearance of metal injection molding technology, different binder systems have formed various metal injection molding process paths and degreasing methods, and the degreasing time has been shortened from a few days to several hours now.

6. Sintering. Sintering is an important step in the metal injection molding process. It removes the pores between the powder particles and makes the metal injection molding product completely dense or nearly completely dense. In the metal injection molding technology, a large number of binders are used, so the shrinkage during sintering is large, and its linear shrinkage generally reaches 13% - 25%, so there are problems of deformation control and dimensional accuracy control.

Due to the complex shape and large sintering shrinkage of metal injection molding products, most products still need post-sintering treatment after sintering, including molding, heat treatment (carburizing, nitriding, carbonitriding, etc.) and surface treatment (fine grinding, ion nitriding, electroplating, shot peening, etc.).