Comparing metal injection moulding and powder metallurgy

Manufacturers worldwide are continually seeking to produce higher-performing metal components. They require greater design freedom without compromising cost. When conventional 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. Coarser powders used in PM are widely available, and the processes used to produce them are inexpensive. MIM powders are much smaller, so the process and energy required to produce them within that size range are more costly.

The cost of metal powder is a key consideration 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 density during the compacting stage (85-92% density), while MIM density comes from sintering—a diffusion bond. (95%+ density)

Design freedom

Engineers often confuse MIM with conventional PM because both start with metal powder. PM relies on high-pressure uniaxial compaction. PM is more suitable for simple shapes that can be easily ejected from the die cavity. This is where MIM differs. With MIM, there are few—if any—geometrical 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 MIM and PM processes may appear similar, the major differences are found in the final properties of the finished component—primarily the final density. When using the PM process, friction between the powder and tooling makes the final component non-uniform, whereas MIM parts are uniform in all directions.

Additionally, sintering for MIM 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 for 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 add cost, savings are realised for high-density, high-complexity components that cannot be produced 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, potentially resulting in significant cost savings.

Many of our customers achieve substantial savings by combining 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 expenses associated with secondary processes such as machining by achieving net-shape the first time. We therefore build moulds that are more efficient for high-volume production and incorporate as much complexity as required upfront to avoid costly machining and secondary operations.