Isostatic powder compaction is a type of cold compacting. Fine metal particles are introduced into the cavity of a flexible mold. High liquid or gas pressure is pressed upon it to form a workpiece. To bond the powdered metal particles together metallurgically the workpiece is then sintered in a furnace.
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Workpiece Geometry and Common Material
Many types of shapes can be created. Typical workpiece sizes range from 0.25 in (6.35 mm) to 0.75 in (19.05 mm) thick and 0.5 in (12.70 mm) to 10 in (254 mm) long. It is possible to compact workpieces that are between 0.0625 in (1.59 mm) and 5 in (127 mm) thick and 0.0625 in (1.59 mm) to 40 in (1,016 mm) long. Many metals and alloys can be used in this process, depending on the characteristics desired in the work workpiece. Iron, copper, bronze, tungsten carbide and other materials are commonly used.
Setup and Equipment
Equipment consists of a flexible mold, a pressure vessel in which the mold is placed, and equipment for supplying high pressure. It can operated with either liquid or gas. A control unit is used to regulate pressure and pressing time.
Design Considerations
Listed are some of the design considerations for isostatic powder compaction. Advantages over standard powder compaction are the possibility of thinner walls and larger workpieces. lubricants are not required. Height to diameter ratio has no limitation. No specific limitations exist in wall thickness variations, undercuts, reliefs, threads, and cross holes. All are possible with few restrictions.
- Minimum wall thickness 0.005 in (0.127 mm)
- Maximum workpiece weight 40 lb (18 kg) to 300 lb (136 kg)
- 25% to 45% shrinkage during compaction and up to 25% during sintering
- No limitation on wall thickness variations
- No limitations on height to diameter variations
- Undercuts, reliefs, threads, crossholes are all possible with minor exceptions
Factors Affecting Process Results
Tolerance and surface finish depend upon the following:
- Type of powder material
- Size of powder particles
- Mold material and quality
- Tool style (fixed or free mold)
- Size of workpiece
- Production quantity and rate
- Subsequent treatment (i.e., sintering, barrel tumbling, coating)
- Compaction pressure
Process Conditions
Compacting pressures range from 15,000 psi (100,000 kPa) to 40,000 psi (280,000 kPa) for most metals and approximately 2,000 psi (14,000 kPa) to 10,000 psi (69,000 kPa) for non-metals. The density of isostatic compacted parts is 5% to 10% higher than with other powder metallurgy processes.
Source
- Manufacturing Processes Reference Guide by Robert H. Todd and Dell K. Allen
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