Powder-Based Processes Flashcards
Describe major steps and equipment for powder-based manufacturing processes, in particular: powder metallurgy, powder injection molding, and tape casting
o Powder metallurgy: Steps are pre-treatment (additives, binders ), Shaping (die compaction, casting, molding, extrusion, rolling), post treatment (isostatic pressing, green machining, drying), Sintering, Finishing (machining, grinding, etc.). Equipment needed: dies and press, furnace to sinter, any machines needed for post machining.
o Powder injection molding: same general steps as above, with the same equipment as injection molding (material hopper, an injection ram or screw-type plunger and presses to hold mold together) with the addition of furnace for sintering.
o Tape casting: for ceramics, a ceramic slurry is applied to a carrier film evenly by a doctor bade, the ceramic film passes under drying chamber to harden, the finished film is then wound on to a take-up spool. Whole process is continuous, happens on a conveyor type system
Define and explain the need for sintering in powder-based processes, and explain what is meant by “green” state in the context of powder sintering
o Sintering: The thermal treatment of a powder or compact at a temperature below the melting point of the main constituent, for the purpose of increasing its strength by bonding together of the particles
o Green state: the product has not been sintered, a non-finished state, relatively fragile
Describe different methods and relative benefits of shaping and compaction strategies, in particular mechanical die compaction and isostatic pressing
o Mechanical die compaction: Die compaction represents the most widely used method this involves rigid dies and special mechanical or hydraulic presses. The friction between the powder and die wall and between individual powder particles hinders the transmission of pressure, resulting in unequal compaction. Pressing force only applied in one direction (typically top and bottom)
o Isostatic pressing: Powder is fed into a moulding bag inside the isostatic press, the press is sealed ant the pressure is increased powder compacts and forms a solid in shape of moulding. Benefit is that the pressure or compaction is equal on all side of the part.
• Compare relative merits of powder-based manufacturing against other processes such as forging, casting, and machining
o The benefits: Net-shape production with high productivity and minimal scrap. Applies to any material than can be made in powder form (ceramics, metals, polymers). Can be used to shaping high melting point, hardness, or other extreme properties. Can have mixed material compositions for custom-engineered properties or behavior (e.g. damping, magnetism, etc.)
o The limitations: High cost of preparing fine, uniform powder, Limited geometric complexity, Inferior mechanical properties unless fully-dense, Poor scaling law in terms of defect density
