IPMD 14th Edition 2010-2011, 10 pages, 5817 words

Author: Dr.-Ing. Georg Schlieper, Ingenieurbüro Gammatec, Remscheid, Germany

The Metal injection moulding (MIM) industry continues to build on developments in materials and processing technologies, opening up new markets and applications.
Dr Georg Schlieper reviews the current status of MIM and presents a number of examples of innovative MIM components.

The idea to plastify powdered raw materials with the help of thermoplastic additives and subsequently using injection moulding to form complex components was first developed in ceramics technology. In the 1970’s this process was adapted to metal powders by Raymond Wiech in the USA. He is widely considered the inventor of the new metal forming process which was named metal injection moulding (MIM). Since its beginnings it has developed into a well-established manufacturing technology. The flow diagram in Fig. 1 shows the sequence of processing steps.

The principal technological problems that had to be solved before the MIM process could be industrialised included:

• Production of a homogeneous powder-binder mix with a high metal powder loading and sufficient viscosity for injection moulding

• Development of economical binder removal processes providing shape retention

• Sintering to high density and dimensional accuracy.

The raw materials for MIM are metal powders and a thermoplastic binder. While the binder is only an intermediate processing aid and removed from the products after injection moulding, the properties of the powder determine the final properties of the PIM product. The blended powder mix is worked into the plastified binder at elevated temperature in a kneader or shear roll extruder. The intermediate product is the so-called feedstock. It is usually granulated with granule sizes of several millimetres, as is common in the plastics injection moulding industry. MIM feedstock is a highly loaded compound of metal powder with a plastifiable binder phase that can be processed into complex, high precision components by plastic forming, followed by debinding to remove the plastic binder and sintering of the remaining powder body. Therefore, when we look at feedstock for MIM, we have to keep in mind that powder, binder and the processing conditions are mutually dependent, even if we do not mention this explicitly each time....

Further sections of this article include:

• Metal powders
• Binders and binder removal techniques
• Feedstock preparation
• Learning from the plastic moulders
• Sintering
• Materials
• Dimensional tolerances of MIM parts
• The maturing of MIM technology
• Applications
  - Medical and orthodontic applications
  - Ordnance applications
  - Watch cases and wristwatch bracelets
  - Mobile phone applications
  - Spectacle frame components
  - Automotive applications
  - Other recent innovative applications for MIM
  - Connector for hydraulic circuits
  - Housing for a fire resistant door lock
• Inherent advantages of MIM technology

Figures and Tables:

Fig. 1 The metal injection moulding process (Courtesy IFAM, Germany)

Fig. 2 MIM part a) as moulded, b) after binder removal, c) after sintering (Courtesy BASF AG, Germany)

Fig. 3 Carbonyl iron powder (SEM, left) and cross-section of a particle (Courtesy BASF, Germany)

Fig. 4 Array of solvent debinding tanks at Schunk, Germany (Photo: G. Schlieper)

Fig. 5 Twin screw extruder schematic (Courtesy Chris E Scott)

Fig. 6 Feedstock pellets (Courtesy Ryer, USA)

Fig. 7 Injection moulding machine in a MIM production workshop

Fig. 8 Continuous MIM furnace for solvent debinding and sintering (Courtesy Elino, Germany)

Fig. 9 Batch furnace for debinding and sintering (Courtesy Elnik, USA)

Fig. 10 Pore structure of a MIM stainless steel (Courtesy CETEHOR, France)

Fig. 11 Orthodontic brackets (Courtesy Dentaurum, Germany)

Fig. 12 Parts from an orthodontic tooth positioning system (Courtesy Flomet LLC, USA)

Fig. 13 Housing of a titanium port system for long term drug delivery (Courtesy TiJet Medizintechnik GmbH, Germany)

Fig. 14 Base plate for an infusion pump (Courtesy TiJet Medizintechnik GmbH, Germany)

Fig. 15 MIM trigger guard for rifle (Courtesy Megamet Solid Metals Inc., USA,)

Fig. 16 MIM turbine wheel (Courtesy Junghans Microtec GmbH, Germany)

Fig. 17 Swatch Irony watches were among the first to use stainless steel MIM parts and Rado watches use PIM ceramic and hardmetal watch cases

Fig. 18 Mobile phone flip slider and hinge barrel made by MIM (Courtesy MPIF, Princeton, NJ)

Fig. 19 Rotating spring hinge (Courtesy OBE, Germany)

Fig. 20 Fixing element for rimless spectacle frames (Courtesy OBE, Germany)

Fig. 21 Rocker arm (Courtesy Schunk MIM-Technik, Germany)

Fig. 22 Car door safety-catch (Courtesy Listemann AG, Liechtenstein)

Fig. 23 Injection nozzle (Courtesy Listemann AG, Liechtenstein)

Fig. 24 Valve holder (Courtesy Metal Injection Mouldings Ltd, UK)

Fig. 25 Nut for a tightener system (Courtesy Parmaco AG, Switzerland)

Fig. 26 Mounting unit (Courtesy Parmaco AG, Switzerland)

Fig. 27 Connector for hydraulic circuits: original design (left) and MIM design (right) (Courtesy Mimtech Alfa SA, Spain)

Fig. 28 Housing for a fire resistant door lock (Courtesy Mimtech Alfa SA, Spain)

Table 1 Standard mechanical properties issued by the European MIM industry

Table 2 Dimensional tolerances of MIM parts