Tailoring materials to the task

Medical Design Magazine - Aug 1, 2007 12:00 PM, Ashley Nichols Metallurgist FloMet Inc. Deland, Fla.

 
The high cost of forming advanced materials frequently stalls the effort to make a better product. For example, the wide range of properties in metal alloys often makes them a best material candidate. But it turns out that the higher the values in an alloy's property list, the more difficult it is to process. Fortunately, there are ways to clear that hurdle thanks to net shape and near-net-shape forming techniques.

Powder metallurgy and Metal Injection Molding (MIM) have been successful at making complex net shape parts from high-performance alloys. MIM is similar to the injection molding of plastic, and mechanical properties are actually better than those of metal castings.

Two of the most common MIM-formed alloys are stainless 316L and 17-4PH. The 316L alloy is widely used because of its good ultimate strength of 84 ksi, high elongation of 40%, and excellent corrosion resistance. Pick the 17-4PH alloy when the application needs higher strength, good corrosion resistance, and a lower cost. The 17-4PH alloy has an ultimate strength of 185 ksi, as high as Titanium 6Al-4V.

Designs, of course, involve more than corrosion resistance and strength. For instance, if a design originally called for a plastic part and testing showed it did not have enough stiffness or wear resistance, replacing the plastic design with a metal one easily solves the material shortcomings. MIM often makes it possible to swap the plastic part with a metal version that requires little or no redesign and minimal-cost impact when compared to a machined component.

Magnetic shielding is also critical in many applications. Soft magnetic alloys such as iron-nickel and iron-cobalt can have customized saturation and permeability based on alloy composition, and so provide magnetic shielding or magnetic cores for solenoids and motors. But to be effective in these applications, the shape of the part is often complex. It's possible to optimize the design by selecting from a wide range of magnetic properties based on the alloy and then manufacturing it with the design flexibility of MIM.