A Soft Molding Process for Fabrication of Micromachine Parts from Stainless Steel Powder

Abstract

Micrometallic machine parts have important applications watch making industry, instrumentation and medical devices [1] and its related fabrication technology has been widely studied. Microelectro-discharge machining (micro-EDM) is one of the fabrication techniques in which different types of miniatures components are fabricated. [2][3] EDM is limited in the fabrication of the nonconductive materials. Laser micromachining is another fabrication technique used for drilling and cutting microcomponents [4] This method is expensive; because of the equipment it relies on, and produces a relatively rough edge with burnt traces, which affect the applications of the microcomponents. Electroforming is another techniques used for fabrication metallic microparts, [5][6] but its slow fabrication process makes the production of 0.5 mm or thicker components very difficult. In addition, Microinjection molding (MIM) is a fabrication process which has been used for polymers, [7] metals, [8] alloys, [9] and ceramics. [10] MIM usually replies on precise metal molds fabricated either by micro-EDM and the metallic components are limited by the precision of micro-EDM.This paper presents an approach to fabricate 316-L stainless steel micromachine parts. Figure 1 shows a linking rod with all dimensions. The thickness of the component is 1000 mm and the diameters of the two holes are 500 and 250 mm, respectively. The fabrication is based on soft lithography and powder metallurgical process, which are further developed from the previous successful experience in fabrication of microcomponents. [11][12][13] The process includes production of high quality micro-SU-8 master molds and their negative replicas in polydimethylsiloxane (PDMS). Then the PDMS soft molds are filled with stainless steel slurry containing 316-L stainless steel particles and binder. After the slurry is dry, the green patterns are removed from the PDMS molds, de-bound, and sintered in the tube furnace at 1300 containing forming gas atmosphere. Figure 2 gives a schematic diagram of the complete fabrication process from producing master mold to the final metallic components. The fabrication processes were investigated. SU-8 Master Molds and PDMS Negative ReplicasSU-8 is a negative tone epoxy type photo resist and has very low UV absorbance in wavelengths ranging from 360 to 420 nm. This property enables a homogenous exposure from the top to the bottom of the resist layer and results in excellent vertical sidewalls. UV lithography is one of the most important SU-8 fabrication techniques and 1 mm thick SU-8 components were produced. [14] The process costs much less when compared with X-ray lithography. [15] The fabrication process of SU-8 master mold used in this research was based on the previews work, [11][12]14] and modifications were made due to the change of the SU-8 type. In this work, SU-8 2075 (MicroChem, USA) was used for fabricating microconnecting rod master mold with dimension shown in Figure 1. TheSU-8 mold fabrication steps were carried out as follow: i) cast SU...