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Process Selection - From Design to Manufacture Episode 1 Part 8

Tham khảo tài liệu 'process selection - from design to manufacture episode 1 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 124 Selecting candidate processes 3.11 Powder metallurgy Process description Die compaction of a blended powdered material into a green compact which is then sintered with heat to increase the bond strength. Usually secondary operations are performed to improve dimensional accuracy surface roughness strength and or porosity see 3.11F . 3.11F Powder metallurgy process. Materials All materials typically metals and ceramics. Iron copper alloys and refractory metals most common. Can process materials not formable by other methods. Powder production atomization electrolysis and chemical reduction methods. Process variations Cold die compaction performed at room temperature. Gives high porosity and low strength. Hot forging deformation of reheated sintered compact to final density and shape. Continuous compaction for strip or sheet product. Slower than conventional rolling. Isostatic compaction hot or cold compaction of powder in a membrane using pressurized fluid oil water or gas. Permits more uniform compaction and near-net shapes. Undercuts and reverse tapers possible but not transverse holes. Used for ceramics mainly. Extrusion high pressure ram forces powder through an orifice determining the section profile. Injection molding fine powder coated with thermoplastic injected into dies. Relatively complex shapes with thin walls achievable. Spark sintering gives magnetic and electrical properties. Powder metallurgy 125 Pressureless compaction for porous components. Secondary operations include repressing sizing and machining. Economic considerations High production rates small parts up to 1800 pieces hour. Cycle times dictated by sintering mechanisms. Lead times several weeks. Dies must be carefully designed and made. Production quantities of 20000 preferred but may be economic for 5000 for simple parts. Material utilization very high. Less than 5 per cent lost in scrap. Powders expensive to produce. Automation of process common. New set of die and punches required for