Micro-powder injection molding Z.Y. Liu a , N.H. Loh a,* , S.B. Tor a , K.A. Khor a , Y. Murakoshi b , R. Maeda b , T. Shimizu b a School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore b Institute of Mechanical Systems Engineering, National Institute of Advanced Industrial Science & Technology, 1-2 Namiki, Tsukuba, Japan Abstract Micro-system technology and related products will be used more widely in the new millennium. For their successful applications in various fields, e.g. in fluidic, medical, optical and telecommunications, economical mass production of the micro-components will be of great importance. Micro-powder injection molding (mPIM) reported in this work is being developed for possible mass production of metallic or ceramic micro-components. In the initial findings presented here, mPIM was processed using silicon mold inserts with square or round cavities in dimensions of 100 mm, with an aspect ratio of 2.5. Alumina, PZT and 316L stainless steel powders were tested with different binder systems such as PVA þ H 2 O; EVA þ PW and PAN250 þ EVA þ HDPE. Results show that all the powders can be used for the molding of micro- components: the finer the powder, the better is the surface finish. PVA þ H 2 O binder system can be used for room-temperature molding, but with difficulties during molding and de-molding. Micro-components were successfully molded with EVA þ PW binder and PZT powders. However, the green parts slumped during thermal de-binding. 316L stainless steel micro-components were successfully molded, de-bound and sintered using PAN250 þ EVA þ HDPE binder system. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Micro-powder injection molding; Powder injection molding; Micro-injection molding; Micro-system technology; 316L stainless steel 1. Introduction Micro-systems and related products will have increasing applications and potential huge markets in the new millen- nium. Micro-systems can be used in the fields of information and communication technology, medical and biotechnology, and micro-sensor and micro-actuator technology. Economic success of micro-systems technology requires cost-effective fabrication in large series as well as a great diversity of materials-processing technologies. Techniques such as X-ray lithography, electro-forming, micro-molding and exci- mer laser ablation are used for the production of micro- components out of silicon, polymer and a limited number of pure metals or binary alloys [1–3]. However, the production cost is very high in most cases, and the materials available are also limited. To overcome these drawbacks, micro- powder injection molding (mPIM), a variant of powder injection molding (PIM), has been developed in recent years [4,5]. mPIM inherits the features of conventional PIM such as low production cost, shape complexity, applicability to many materials, good tolerance and good mechanical prop- erties. mPIM can be used in the mass production of metal or ceramic micro-components possessing lateral dimensions in the sub-millimeter range, and structural details in the tens of micrometers range. As in conventional PIM, the four major processing steps of mPIM are: mixing of powder and binder to prepare the feedstock, molding to replicate the mold inserts topography, de-binding to remove the binder con- stituents and sintering to obtain good mechanical properties. However, as the detail structure dimensions is down to microns, the requirements for the powders, binders and facilities are more stringent. In this paper, initial work on mPIM using different binder systems and powders for micro- components in dimensions of 100 mm is presented. 2. Experimental materials and equipments In the initial findings reported here, mPIM was processed using silicon mold inserts with square or round cavities. The powders used were alumina, PZT and 316L stainless steel. PVA ðpolyvinyl alcoholÞþ H 2 O, EVA ðethylene vinyl acetateÞþ PW (paraffin wax), PAN250 ða patented binderÞ þEVAþHDPE (high-density polyethylene) binder systems were used. Differential scanning calorimetry (DSC) testing was conducted on a Perkin-Elmer DSC Model 7 machine. The heating rate of 10 8C/min was used to test the thermal properties of the binder constituents in the temperature Journal of Materials Processing Technology 127 (2002) 165–168 * Corresponding author. Tel.: þ65-790-5540; fax: þ65-791-1859. E-mail address: mnhloh@ntu.edu.sg (N.H. Loh). 0924-0136/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0924-0136(02)00119-X