Application of powder metallurgy degreasing and sintering in stainless steel parts

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Metal Injection Molding (MIM) is a new type of powder metallurgy net forming technology that introduces plastic forming technology into the field of powder metallurgy. It is one of the hot spots in the current research of advanced manufacturing technology. The high-performance special-shaped metal parts with complex shapes prepared by MIM are low in cost, so MIM technology is increasingly valued by people. Stainless steel powder has good corrosion resistance, excellent formability and good fluidity. It has become an important raw material in industries such as injection molding, powder metallurgy and coating production. It has been widely used in the field of powder metallurgy, accounting for more than 50% of MIM parts.

The basic process of powder metallurgy degreasing and sintering is:

1) Mix the specific metal powder and organic binder evenly and form it by mechanical methods such as injection molding machine;

2) Remove the binder from the roughness of the formed parts;

3) Densify it by sintering to obtain the final product.

MIM can manufacture many parts with complex shape features, and the parts manufactured by MIM generally do not need to be machined, which reduces material consumption and ensures dimensional accuracy. Therefore, when producing large quantities of parts with complex shapes, MIM will be more economical than other traditional processing methods.

Technical characteristics of powder metallurgy degreasing and sintering

Because MIM technology uses a large amount of binder to enhance fluidity, MIM can arbitrarily form metal parts of various complex shapes, which is unattainable by traditional powder metallurgy molding and other processes. Moreover, since injection molding is a near-net forming process, it is generally no longer necessary to continue finishing, and the manufacturing cost of parts will be greatly reduced. Secondly, during injection molding, the powder flow can evenly fill the mold cavity, so that the density of MIM products is uniform, avoiding the inevitable disadvantage of uneven density distribution in other traditional processing technologies. Another process that can compete with MIM is precision casting. Compared with precision casting, MIM technology shows advantages in minimum diameter, minimum wall thickness, tolerance, surface roughness, etc.

The most widely used steels for MIM so far are austenitic Ni-Cr steel 316L and martensitic hardening steel 17-4PH. 316L stainless steel has excellent corrosion resistance in a variety of corrosive media, good comprehensive mechanical properties, excellent process performance and weldability, and has therefore been widely used. In European MIM, 316L accounts for about 80% of stainless steel. Japan is similar to Europe, mainly 316L stainless steel.

MIM stainless steel parts have been applied to the automotive industry, aircraft wing filters and construction, transportation, food industry, medical equipment and other fields, and have occupied an increasingly important position due to their complex shapes, excellent performance and low cost. However, as a new forming technology, there are still many shortcomings and limitations, especially the limitation on workpiece size, which greatly restricts the development of MIM.

Now, stainless steel powder injection molding represented by 316L steel (austenitic) and 17-4PH (precipitation hardening) accounts for more than 50% of the total sales of MIM parts, covering the main part of the application. Stainless steel itself has excellent mechanical properties and corrosion resistance but is difficult to process, and the good formability of MIM can just make up for the shortcomings of poor formability of stainless steel, so the application of MIM technology in the production of stainless steel powder parts has an optimistic prospect. From the correct selection of powder to the finished product, if the MIM process is correct, the MIM stainless steel parts that can be manufactured today will play a greater role.

MIM Debinding Sintering Furnace