Technical Paper: PIM International, Vol.1 No. 2 June 2007, pages 48-53, 2554 words

Author: T. Gietzelt [1], O. Jacobi [2], V. Piotter [2], R. Ruprecht [2] and J. Hausselt [2] 

[1] Institute of Micro Process Engineering, Research Center Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany
[2] Institute for Materials Research III, Research Center Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany

Abstract

Powder injection moulding (PIM) is a very sophisticated, and for large scale series, a comparably cost-effective technique to generate parts with a complex shape made of hard to machine materials like ceramics. In this paper several Catamold feedstocks were used for manufacturing of micro parts made from alumina, zirconia, precipitation hardening steel 17-4PH and some other sorts of steel. A way to achieve very tight tolerances of isolated ceramic micro parts is described. Specific problems for micro parts are addressed being without interest in the macroscopic world. For example, the use of ultra fine powders, preferably in the submicron range, are a prerequisite to realise tiny details, to improve dimensional accuracy, decrease the surface roughness and to guarantee reasonable mechanical properties of micro parts to ensure the function of a micro system. Additionally, the reasons for limitations of micro parts made of metal alloys are pointed out and specific problems for micro parts are addressed

Introduction

PIM is a near net shape manufacturing process and well established for large scale production. Limitations arise from the multiplicity of operation steps from raw material to the final part incorporating powder production, feedstock preparation, injection moulding, debinding, sintering and perhaps finishing (Fig. 1).

PIM is well suited for small and complex shaped parts. The process is especially favourable for parts made from ceramics due to the excessive hardness where grinding with diamond tools can reach up to 80 % of the overall costs [1]. Since high pressure injection moulding requires a metallic mould that has to be amortised over the product cycle a minimum number of parts depending also on the complexity of the shape are necessary. Hence, large scale series are favourable for PIM.

The PIM-process uses feedstocks consisting of a polymeric binder containing 50-60 vol-% of metal or ceramic powders, depending on particle shape and particle size distribution. The use of smaller powders with high specific surface area leads to a decreasing amount of incorporable powder amount since the whole surface of all particles must be coated with the binder for good rheological properties of the feedstock. Consequently, small powders lead to a greater shrinkage and make it more difficult to control the dimensions of a part. A solution to this problem is the use of bimodal powder mixtures where small particles fill the gaps between......

Further sections of this article include:

- Design and preparation
- Methods and procedures
- Results and discussion

Figures and Tables:

Fig. 1 PIM-Process route

Fig. 2 Design of the micromould for gearwheels with details

Fig. 3 Design of the micro annular gear pump with in- and outlet slice, rotor bearing slice, external and internal rotors, bearing slice and sealing slice

Fig. 4 Details of the rotor with minimal wall thickness

Fig. 5 Tolerance variation of the external shape of the external and internal rotors

Fig. 6 Assembled mould inserts and demoulded part demonstrator micro gearwheel mould insert

Fig. 7 LIGA-mould insert and demoulded part demonstrator micro annular gear pump

Fig. 8 Reduction of height variation of micro parts due to distortion of LIGA-mould

Fig. 9 Isolated micro parts of both demonstrators

Fig. 10 Surface distortion of a micromold for gearwheels made of alumina

Fig. 11 Surface of a micromould for gearwheels made of zirconia, surface as sintered

Fig. 12 Powder particle shape of alumina CT3000SG, Alcoa (left) and zirconia TZP-3Y, Tosoh

Fig. 13 Shell surface of a micromould for gearwheels made of zirconia as sintered

Fig. 14 Assembled micro annular gear pump (not working)

Fig. 15 Microstructure of sintered zirconia TZP-3Y

Fig. 16 Bonding of isolated micro parts

Fig. 17 Isolated ceramic micro parts: milled off in the green state (left) and lapped (middle) and polished (right) in the sintered state

Fig. 18 Microstructure of 17-4PH sintered 3 h @ 1380 °C (left) and after 0.5 h @ 1360 °C with nanoscale alumina as grain growth inhibitor (right)

Fig. 19 Microstructure of micromoulds for gearwheels made of 100Cr6

Fig. 20 Microstructure of micromoulds for gearwheels made of M2

Fig. 21 Side walls of micromoulds for gearwheels made of 17-4PH, 100Cr6 and M2

Table 1 Sinter condition for Catamold® TZP-A [6]

Table 2 Sinter condition for Catamold® 17-4PHA according BASF [7]

Table 3 Modified sinter conditions for 17-4PHA-Feedstock, taking into account the max. heating rate of the tube furnace