Technical Articles

• Size: The MIM process can be employed for virtually any size part. However, MIM is extremely effective for the manufacture of parts with a volume of, or less than, a golf ball or deck of playing cards.

• Complexity: One factor that makes MIM so attractive is the ability to mold cross-drilled holes, radii, blind holes, and other difficult-to-machine part geometries with tight tolerances in a single process, using little or no secondary machining. If the component has complex geometries in high volumes, MIM is an ideal solution. Typically if a part has more than 25 measurable dimensions it will make a good candidate for MIM.

• Volume: The quantity of parts plays a major role in the cost effectiveness of MIM. Generally speaking, quantities of more than 10,000 pieces per year translate to the highest level of cost savings when considering MIM versus other forming processes. 

These are sound guidelines, yet they are by no means the sole criteria. There are some cases where the above may not apply, but MIM is still the process of choice. For example, there are some fairly large parts or parts in low quantities that are MIM-produced, simply because they are just too costly to machine using traditional methods. 

Clearly, MIM technology offers manufacturers specific, quantifiable advantages over alternative metal-forming techniques. There are other advantages that, while not quantifiable, are no less significant. The MIM process allows engineers more latitude when designing a component, no longer constrained by the parameters of cost, size, or shape. The value of removing these restrictions from the engineer's thought process cannot be overstated. 

While MIM technology is often compared to the Pressed and Sintered (P&S) process, there are several differences. In P&S forming, a metal powder with a small amount of binder is poured into a mold, pressed and then sintered. MIM technology is closer to plastic injection molding, where a powder with a binder is heated into slurry and then injected into a mold.

A major difference between the two technologies is the geometries that can be achieved with P&S parts are somewhat limited. Tight radii, cored sections, and side- through holes are unattainable via P&S; with MIM, a part is formed without secondary machining. What's more, there is a major disparity in the density of the finished product. Uniform densities consistently around 98%+ can generally be attained through MIM, while a P&S part will achieve a non-uniform density of only about 85%. Using the Hot Isostatic Pressing (HIP) process, the densities of these parts can be raised to roughly 90%, but that typically only affects the outer surfaces of the part and is not uniform throughout, and it adds costs. 

The MIM process historically was based in carbon and stainless steels, but as the technology advances, more materials are being manufactured using MIM. MAC currently offers the ability to mold several stainless steels (17-4 PH, 316L, 304L), along with popular materials such as Kovar (F15 alloy) Nickel iron, Tungsten, OHFC copper, Molybdenum copper and Tungsten alloys. Additionally, mixtures of compatible materials can yield composite materials that offer special or added qualities. 

Unquestionably, MIM offers myriad tangible advantages over other manufacturing processes. In fact, where small part size, part complexity, and high volume are primary factors, this sophisticated, time-saving, and cost-effective technology is often the optimal solution.