Comparing Metal Injection Moulding and Powder Metallurgy

Manufacturers worldwide are always seeking to create higher-performing metal components. They want greater design freedom without compromising cost. When traditional casting methods no longer meet requirements, manufacturers turn to other moulding processes to advance their products.

If you are familiar with powder metallurgy (PM), you know that parts are formed from metal powder compacted in a die and then sintered. Metal injection moulding (MIM) is a complementary process that also uses metal particles—only much finer—to produce high-density components with three-dimensional design flexibility.

How Metal Injection Moulding differs

Materials

Powder metallurgy and metal injection moulding use the same base powders, and both processes allow the use of custom alloys; however, the key material difference is particle size. The coarser powders used in PM are widely available and inexpensive to produce. MIM powders are much smaller, so the process and energy required to produce them within that size range are more expensive.

The cost of metal powder is a key factor when comparing MIM and PM materials. MIM powders are typically more expensive than PM powders because they are finer (-20 micron vs. +100 micron). However, due to the finer material, MIM produces significantly less porosity.

Did you know?  PM achieves its full density during the compaction stage (85-92% density), whereas MIM density is achieved through sintering—a diffusion bond. (95%+ density)

Design freedom

Engineers often confuse MIM with conventional PM because both begin with metal powder. PM relies on high-pressure uniaxial compaction. PM is better suited to simple shapes that can be easily ejected from the die cavity. This is where MIM differs. With MIM, there are few, if any, geometric restrictions, allowing three-dimensional design freedom.

 Other design improvements for MIM components include:

• Part consolidation
• Uniform wall thickness
• Coring and mass reduction
• Holes and slots
• Undercuts
• Threads
• Knurling, lettering and logos

Physical properties

Although the MIM and PM processes may seem similar, the major differences lie in the final properties of the finished component—mainly final density. In the PM process, friction between the powder and tooling makes the final component non-uniform, whereas MIM parts are uniform in all directions.

In addition, MIM sintering takes place at much higher temperatures than PM (2350-2500F° vs. 1800-2000F°). The larger PM metal powders combined with lower sintering temperatures inherently result in lower physical properties in the final PM component, making MIM components about two times stronger, with significantly better toughness and fatigue strength. 

When is Metal Injection Moulding the right choice?

Although more expensive feedstock and tooling increase costs, savings are achieved with high-density, highly complex components that cannot be made by any other manufacturing process. PM may be a cost-effective alternative for simple parts, but MIM can produce part geometries that eliminate secondary operations, resulting in significant cost savings.

Many of our customers achieve substantial savings when they combine two or more subcomponents into a single MIM component. Additional savings can be achieved by considering the material, design, assembly and logistics benefits of the MIM process.

OptiMIM - Leading Metal Injection Moulding Manufacturer

For every project, we aim to deliver more consistent parts more efficiently and at lower cost. At OptiMIM, our goal is to eliminate the costs associated with secondary processes such as machining by achieving net-shape parts first time. We therefore build more efficient moulds for high-volume production and incorporate as much complexity as required at the outset to avoid costly machining and secondary operations.