Hot working is a process that combines heat and mechanical pressure to create hard, brittle metals from high purity metal powders. It is used to improve the physical properties of metals and produces higher purity levels. The sintering process used in hot metal working is essential for the manufacture of a variety of metal products.
The metalworking term “hot working” refers to a powder metallurgy process that combines the alternating action of heat and mechanical pressure or vacuum to create hard, brittle metals from high purity metal powders. It is widely used in the metalworking industry to improve the physical properties of metals such as steel, titanium and aluminum. Hot working is also called hot pressing or hot isostatic working. The process uses three types of heating: inductive, indirect resistance, and direct hot pressing.
As a result of hot working, the worked metal takes on the physical characteristics of the worked metals, developing both hardness and fragility. This increased hardness makes the hot worked metal useful for a variety of applications where extreme durability is required. The metals and alloys created in this way are commonly used for heavy cutting equipment, such as carbide-tipped drill bits and saw blades.
Hot working is done through sintering, which is the heating of a powdered material to a state just below its melting point where it becomes pliable like a plastic. This causes the powdered metal to fuse together, forming strong molecular bonds. The hot work technique also produces higher purity levels because the metal powder used for hot work is generally a high purity material at the start of the operation.
During the hot working process, the metal structure is condensed and stabilized. Using vacuum hot pressing, an inert gas, usually argon, is used to exert a constant pressure on all sides of the forming metal. This pressure, combined with heat and sintering, creates a highly compacted and dense final product that is many times harder than untreated metal would be. Additionally, the process removes voids and imperfections in the metal as pressure pushes inward on the former metal to further enhance the metal’s natural properties and further refine the metal’s impurities.
The sintering process used in hot metal working is essential for the manufacture of a variety of metal products. Liquid sintering is used in creating tungsten carbide or cemented carbide for cutting tools. Bronze is sintered for use in wheel bearings due to its physical characteristics and porosity. Stainless steel is sintered and used for filters in the food and pharmaceutical industries. Hot working and sintering could also be used to refine and condition precious metals used in the production of jewellery, aircraft parts and surgical equipment.
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