Studies on the fabrication of tool steel components with micro-features by PIM

Abstract

Fabrication of structures with fine features has been a challenge and has required sophisticated equipment. In the current work, the use of a cost-effective method, PIM (powder injection molding) was evaluated to fabricate structures with fine features such as sharp edges with dimension in microns. The selected component consisted of micro features of two steps having a cross-section dimension of 0.6×0.07 mm and 0.6×0.06 mm. In order to achieve good mechanical properties coupled with wear resistance, an M2 tool steel material was selected. The mould tip region with two-step micro features was fabricated using into multi-mould pieces to ensure the edge sharpness of the two-step micro features in the mould cavity and to create an air vent to release the entrapped gas at the moulding stage. The moulded samples were first debound and then sintered at different temperatures. The results of actual sintering at 1,244, 1,252, 1,260, and 1,280°C were analyzed, since transition to liquid phase sintering occurs in this region. Visual observation, microstructural analysis and hardness distribution were carried out on the samples sintering at different temperatures. Incomplete sintering occurred at 1,244°C while at 1,252°C distortion of the samples was identified. Sintering at 1,260°C yielded parts with good integrity and strength and a further increase of sintering temperature deteriorated the characteristics. Five samples were chosen randomly from three batches of 100 pieces for a pilot production scale. Their dimensional flatness was measured and the result showed that flatness less than ±0.3% can be achieved under optimized sintering temperature of 1,260°C ± 0.3°C. This means that the M2 tool steel component with micro features can be possibly produced by PIM process in mass production.