Feature article: PIM International, Vol.3 No. 2 June 2009, pages 37-42, 2401 words

Authors: Dr. Dieter Martischius, Dr. Hans Wohlfromm, Andreas Kern, Johan ter Maat, Arnd Thom and Martin Blömacher, BASF SE, Germany 

BASF SE, Global Business Unit Inorganic Specialities, Powder Injection Molding, G-CAS/BP - J513, 67056 Ludwigshafen, Germany

The unique ability of metal injection molding (MIM) to produce complex components from materials that are difficult to process by other routes makes it ideally suited to the manufacture high performance turbocharger components.

As BASF SE’s Catamold® Group explains, a unique adaptation of the company’s Catamold® process may help to overcome some major challenges in the development of new metal injection molded components for this sector.

Introduction

Turbochargers have been the central driving force behind the growth in popularity of diesel engined passenger cars and SUV’s in recent years, particularly within Europe (Fig. 1). The turbocharger has ensured that key consumer purchasing criteria such as the “fun of driving” and “agility” are now widely associated with diesel engine technology, which itself is already widely appreciated for its fuel efficiency.The turbocharger is also experiencing an enormous surge in growth outside the sphere of diesel technology, thanks to a trend towards smaller gasoline engines, driven primarily by efforts to reduce fuel consumption. Combined with direct fuel injection, turbochargers are therefore increasingly being seen as a key technology for future gasoline engines (Fig. 2).

The story of MIM turbocharger components

Metal injection moulding (MIM) was used relatively early in the production of parts for turbochargers. However, although MIM offers an enormous potential for materials and absolute freedom in the design of components, those made using MIM have, until now, been limited to a few small components in the VTG (variable turbine geometry) charger. The reasons for this cautious approach are not easy to quantify, especially since the components manufactured by way of MIM have been used in large numbers over the last few years and have proven themselves in practice.

As a relatively new manufacturing process, MIM is competing with other processes such as investment casting, which benefits from many more years of experience with the materials used and the tolerances achieved in production. Furthermore, with regard to the development of new components, it is often not possible for the designers and engineers to introduce a new production technique. The pressures of time, combined with a lack of experience and knowledge of the process, frequently leads to MIM not being considered as an alternative.

Further sections of this article include:

- The potential for MIM turbine wheels
- The challenges
- Lost core technology
- Sintering
- Modelling of turbocharger guide vanes
- Materials
- Summary
- References

Figures and Tables:

Fig. 1 Percentages of vehicles equipped with a turbocharger; based on diesel engines (passenger automobiles and SUV’s) Source: ABOUT Publishing Group “The global market for automotive superchargers and turbochargers”
Fig. 2 Percentages of vehicles equipped with a turbocharger; based on gasoline engines (passenger automobiles and SUVs) Source: ABOUT Publishing Group
Fig. 3 A typical automotive turbocharger
Fig. 4 An investment cast turbine wheel from an automotive turbocharger
Fig. 5 Filling time for turbine wheel with gate, complete component
Fig. 6 Filling time for turbine wheel with gate, cross section
Fig. 7 Solidification pressure after 40 s cooling time; sectional view
Fig. 8 Unsolidified area after a cooling time of 40s
Fig. 9 Principle of the lost core for the Catamold® Process
Fig. 10 Solidification time
Fig. 11 Guide vane
Fig. 12 Dilatometer curves
Fig. 13 Position and shrinkage of a guide vane; green part is shown on left, with the sintered part on the right.
Fig. 14 Guide vane shrinkage; the dark-blue represents the greatest shrinkage
Fig. 15 Strength curves of various heat-resistant materials
Fig. 16 Microstructure of Catamold Inconel 713 C

Table 1 Typical composition of Inconel 713 C
Table 2 Mechanical properties