Defects in stainless steel powder metallurgy products

Stainless steel powder metallurgy products, injection molding defects in blank mostly in the process of injection forming. Some of the defects of injection molding are visible to the naked eye, and some may appear in the subsequent desorption or sintering process, but also to be traced back to the injection molding process. Therefore, the quality control of stainless steel powder metallurgy products is very important.

Stainless steel powder metallurgy products injection forming slab defects: appearance observed flying edge, foaming, corrugated surface, layered or skin, depression, and deformation of surface black spots, the green strength is low and the operation of die sticking. The causes and influencing factors of these defects are various, among which the injection temperature and injection pressure are the key factors.

By adjusting the injection temperature and injection pressure, most of the defects can be solved. When the temperature and pressure of the adjustment to some defects change, further tracing to the binder system is the right choice, powder and a node agent mixed refining homogeneous degree, feeding with or without contamination, moisture absorption and moisture factors, also check the mold cavity design, the sprue, distributary channel and the gate design is reasonable.

In short, injection molding normal operation and high quality injection molding compacts, many influencing factors to in practice constantly explore and summarize, accumulate experience, to the problems are compared with the exact analysis and judgment, and make timely adjustments.

Design points of stainless steel powder metallurgy structural parts

1, material selection

The choice of material of stainless steel powder metallurgy parts, in addition to the mechanical properties, should also to select the raw powder of the species and its composition, the density of the material, sintering conditions and subsequent processing in accordance with the requirements of part of wear-resistant, corrosion resistance and other characteristics.

Although, in high alloy powders as raw materials by material of high density and sintering conditions, or the carburizing and quenching heat treatment, the physical and mechanical properties of stainless steel powder metallurgy parts material increased, but parts of the production cost also correspondingly increased. Therefore, in the selection of materials, it is best not to pursue the excessive material properties, and increased production costs.

2, shape design

Stainless steel powder metallurgy structural parts are generally made of metal powder with single axial compression, so the shape of the parts are subject to various restrictions. When designing parts, we must pay attention to overcome these limitations, so as not to increase the production cost of parts or produce quality problems. In addition, the clever use of combination or sintering method, such as the legitimate, but also to overcome some of the limitations of the shape of the parts.

In addition, some parts of the shape of cutting and other methods can not or difficult to make, but it is suitable for stainless steel powder metallurgy process. Such examples are many, such as tooth in motor pulley, the transmission synchronizer gear hub etc.. This kind of parts fully embodies the characteristics of stainless steel powder metallurgy technology.

3, size accuracy

Generally speaking, although can be made very high dimensional accuracy of green compacts, but due to shrinkage or swell produced in the sintering process, powder metallurgy parts size precision reduced. When the size precision of stainless steel powder metallurgy parts can not meet the technical requirements, it is necessary to increase the finishing, cutting, grinding and other follow-up processing. Therefore, to determine the size accuracy of parts, to master the allowable size of each process accuracy, as far as possible to reduce the number of processing procedures, in order to reduce the production cost of parts.

Affecting Factors for MIM Products Size

Compared to machining, powder metallurgy PM process and casting process, accuracy performance is not its advantage of  metal injection molding MIM process. So what factors do exactly affecting size of MIM products? Shenzhen powder metallurgy factory –ZCMIM has made the following analysis based on years of stainless steel powder metallurgy experience and researches about metal injection molding industry:

Affecting Factors of metal injection molding MIM products size:
1. MIM mold size and its tolerance
2. Abrasion of  MIM mould
3. Matching error between moving parts of MIM mold
4. The structure of metal injection molding products
5. Weight deviation of metal injection molding product  in weight equal circumstances, the lower the density,  the larger size)
6.  Density deviation of MIM parts ( in density equal circumstances , the greater the weight, the larger the size)