Metal Injection Molding (MIM)

Last updated: 7 Apr 2023 | 385 Views |

Metal Injection Molding (MIM)

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Metal injection molding (MIM) is a metalworking process in which finely-powdered metal is mixed with binder material to create a "feedstock" that is then shaped and solidified using injection molding. The molding process allows high volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debinding) and densify the powders. Finished products are small components used in many industries and applications.

The behavior of MIM feedstock is governed by rheology, the study of sludges, suspensions, and other non-Newtonian fluids.

Due to current equipment limitations, products must be molded using quantities of 100 grams or less per "shot" into the mold. This shot can be distributed into multiple cavities, making MIM cost-effective for small, intricate, high-volume products, which would otherwise be expensive to produce. MIM feedstock can be composed of a plethora of metals, but most common are stainless steels, widely used in powder metallurgy. After the initial molding, the feedstock binder is removed, and the metal particles are diffusion bonded and densified to achieve the desired strength properties. The latter operation typically shrinks the product by 15% in each dimension.

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Feature

1. It is possible to manufacture small, complex-shaped, difficult-to-machine parts at a relatively low cost.

2. It is possible to respond with the same high precision as die casting.

3. Unlike normal sintering, it is possible to form complex three-dimensional shapes.

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Injection Molded Body and MIM Sintered Body
The one on the left is the molded body, and the one on the right is sintered body. It is possible to produce highly precise products because the shrinkage is approximately equal.

MIM
The body made by MIM has excellent mechanical strength properties because its density reaches over 95% and its vacancies are spherical and independent.

Conventional Sintering
The body made by standard sintering has poor mechanical strength properties because its density reaches only 88% and its vacancies exist along the grain boundary irregularly.

It indicates properties similar to that of molten material such as torsion and spring. (The products in the photo are made of SUS304)

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Manufacturing process

01 Feedstock Preparation