Applications for Metal Injection Molding: Medical and Orthodontic
Orthodontic components
Fig. 16 Parts from an orthodontic tooth positioning system manufactured by Flomet LLC, USA. (Image courtesy MPIF, USA)
One of the first major application areas for Metal Injection Molding was for orthodontic brackets and this still remains a major product for the industry.
These extremely small precision parts are usually made from 316L stainless steel, however Ceramic Injection Molding is increasing being used to make translucent brackets that have a much more discreet appearance.
Surgical instruments
Fig. 17 A 17-4 PH stainless steel articulation gear manufactured by Parmatech Inc, USA, and used in a surgical stapling unit (Image Courtesy MPIF, USA)
Metal Injection Molding has, over the last 20 years, become an essential manufacturing technology for the medical device industry, thanks to its ability to produce high volume precision components to net-shape.
The part shown in Fig. 17 is an articulation gear used in a surgical stapling unit. Produced by MIM to net shape from 17-4 PH stainless steel, the part has a density of more than 7.65g/cm3, ultimate tensile strength of 900 MPa (130,000 psi), yield strength of 730 MPa (106,000psi) and a 25 HRC hardness. This part won an MPIF Grand Prize in 2008.
Implantable Metal Injection Molded components
There has been much progress towards the development of implantable MIM products for applications such as drug delivery devices and joint replacements.
Fig. 18 MIM-Ti6Al4V base plate. (Courtesy Element 22 GmbH, Germany)
A base plate for an implantable infusion pump made from MIM-Ti6Al4V is shown in Fig. 18. The base plate, the most expensive part of the pump, combines several functional elements.
The extreme aspect ratio of 78 mm diameter and a wall thickness of only 1 mm is almost impossible to realise with conventional cold runner tooling, but, with a hot runner this mould can be completely filled with high reliability.
The moulded part weighs almost 50 g. Two small bores are moulded in, a conical one with 0.8 mm diameter at the top and 0.4 mm at the bottom, and a cylindrical one with 0.5 mm diameter.
Fig. 19 Metal Injection Molded knee implant parts made from Ti6Al4V. (Courtesy Maetta Sciences Inc., Canada)
Fig. 19 shows prototype MIM knee implant parts made from Ti6Al4V by Maetta Sciences Inc., Canada.
For load bearing surgical implants, the typical post-treatments are, after HIPping, bead blasting, polishing, electropolishing and anodising.
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