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Look around you, and there’s probably something made of metal. And the tools used to make it were likely made of metal, as well as something called powdered metals. Manufacturers rely on powdered metals not only for precision but also to save money on metal removal processes. We’ll cover the applications of metal powder and the techniques used in shaping it for industrial use.
Uses of Powdered Metals
Powdered metals are used primarily for manufacturing. You can use them for 3D printing, surface coating, or toolmaking. Powder metallurgy is the various ways in which metal powders are made into materials and components. Aluminum, bronze, nickel, and stainless steel are often powdered to form crucial parts for products like automobiles and diamond tools.
Methods of Producing Powdered Metals
You can form metal powder in three ways:
1) Atomization – This is the process of separating something, often a liquid, into fine particles. When atomization is used to produce metal powder, a base metal takes a molten form and is poured into a container. While being poured, a gas is sprayed into the stream, turning the molten form into little droplets. The droplets freeze before making contact with the surface. Since atomization requires metals with lower melting points, this process is typically used on iron, bronze, and brass.
2) Solid-State Reduction – During this process, a gas, typically carbon, is mixed with crushed metal ore before entering a furnace. The blistering heat of the furnace forces a reaction, cutting down the metal’s carbon and oxygen levels. All that's left are the remnants, which produce a powder once filtered through a sieve.
3) Centrifugal Atomization – This process also starts with molten metal, which is poured into a container with perforations. The metal then settles onto a rotating disc, and a gas is released. A motor triggers varying speeds to transform the molten into powder. The powder particles are sorted afterward.
Methods of Consolidating/Pressing Powdered Metals
After reaching powder form, the powdered metal must be consolidated and shaped for manufacturing via the following methods:
1) The powder is molded or died/cut for consolidation.
2) The powder is densified into a compact. The higher the metal’s density, the higher its performance will be.
3) The powder is converted into a “green,” or softened, state. Then, the particles are joined together to create a compact.
4) The powder is transferred to a sintering furnace with three heating zones: pre-heat, high-heat, and cool-down. In the high-heat zone, the furnace heats the metal to a temperature just below its melting point. The high temperature metallurgically bonds individual particles.
Hot or Cold Pressing
Hot pressing is when metal powders are heated during a sintering process and compacted simultaneously.
Cold pressing relies on pressure rather than high temperatures. A column of loose metal powder is pressurized until it's formed into a green, or soft, compact. Factors such as the metal powder’s size, shape, distribution, and composition affect cold pressing. If the proper pressure is applied based on those factors, the resulting press will be ideal.
Hot pressing is often a go-to for the formation of carbide cutting tools. Cold pressing, on the other hand, is used for the majority of powder metallurgy.
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