Metal injection molding can simplify the manufacture of complex parts

September 4, 2020 By Nancy Crotti

The MIM process combines the design flexibility of plastic injection molding with the strength and integrity of wrought metals.

Deepak Garg, Indo-MIM

(Image courtesy of Indo-MIM)

Medical device manufacturers are designing and developing smarter, lighter and more intricate products using and experimenting with hard-to-machine materials such as martensitic, austenitic, and precipitation-hardened stainless steel, titanium and nickel-free alloys.

Instruments such as dissectors, conchotomes, knives, scalpels and spreaders for minimally invasive surgeries are becoming lighter and offer greater freedom of movement, but they are more complex.

Metal injection molding (MIM) meets the challenges of manufacturing complex medical device parts. Net-shaping MIM technology has the distinctive ability to produce highly complex components with intricate surface details and custom textures.

With the MIM process, parts can be manufactured using an array of off-the-shelf material solutions including case-hardened and tempered steel, tool steel, stainless steel, magnetic materials, tungsten and titanium alloys for strength, wear and corrosion application.

Metal injection molding can offer innovative solutions, such as manufacturing a part with multiple materials, allowing for the development of the feedstock from material powders to achieve specific properties, having gradient porosity, etc.

Different materials are more suitable for some MIM applications than others. (Graphic courtesy of Indo-MIM)

It is best suited for higher-volume production with hard-to-machine alloys for strength, wear and corrosion resistance. Extensive mold life enables the reproduction of hundreds of thousands of pieces while maintaining quality. It offers significant cost savings over the piece price, helps with reduction of parts count, and eliminates assembly time because complex or multiple features of a design can be incorporated in a single part.

The MIM process is comprised of four unique processing steps:

The MIM process starts with feedstock preparation, also known as compounding. Ultrafine metal powders are blended with thermoplastic and wax binders in a precise amount. The blend is mixed and heated for binders to melt. The mass is cooled down and then granulated into free-flowing pellets (feedstock) for molding.

The pelletized feedstock is fed into an injection molding machine where it is heated and the binder melts before the feedstock injected into the mold cavity/cavities under high pressure. The molded part (“green part”) is allowed to cool and then ejected from the mold. The green part is approximately 20% larger than the final part, and precisely calculated to compensate for shrinkage that takes place during sintering.

During debinding or binder removal, solvent extraction removes most of the binder. The part (now termed a “brown part”) is now semi-porous, which allows the remaining binder to easily escape during sintering.

The parts are loaded into an atmospherically controlled sintering furnace which slowly heats them to drive out the remaining binders. Once the binders are evaporated, the metal part is heated to a higher temperature and the metal particles fuse. The part shrinks isotropically to its designed dimensions and transforms into a dense solid. The sintered part achieves >= 97% density of the wrought material.

Based on the customer requirements, certain operations such as coining, machining, heat treatment, surface finishing, plating and coating may be applied to the sintered part.

MIM molds can last up to 500,000 shots to produce parts with highly repeatable dimensional accuracy. It offers significant cost savings compared with traditional manufacturing processes and can eliminate assembly processes because MIM can replace an assembly of parts with one single component.

Deepak Garg is a senior manager of business development with Indo-MIM. He holds master’s degrees in Engineering Technology and Business Administration and has more than 20 years of experience in mechanical components manufacturing, fastening and installation, materials, surface treatment and metal/ceramic injection molding.

The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design and Outsourcing or its employees.