Solid metal parts that are made from powdered metal via powder metallurgy are strong equipment components used in almost every industry. They are utilized in a variety of industrial applications in the automotive, hardware, electronic, computer and lawn and garden industries.
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Metal is formed and fabricated from powder to a finished part through a process called powder metallurgy. Metal powders are the main raw material, which is processed into powder form by pulverization, chemical reduction, electrolytic techniques, mechanical alloying, or most commonly, atomization. The resulting powder is then impregnated with a lubricant, which is added to the metal to reduce friction between the powder and the pressing dies. Next, the raw material undergoes a forming process, where it is pressed, forged or molded. A major final step in powder metallurgy is sintering, a high temperature process that develops the final properties of the metal part. The compacted raw materials, called green parts, are heated in a furnace at temperatures below their melting point to bond the particles together without changing part's shape. The sintering process also increases part strength and controls the porosity of the part. Secondary operations are not usually required, but parts may still need to be heated, sized, deburred or machined. Although the finished parts look solid, they actually consist of small interconnected capillaries, which cause the parts to be approximately 25% porous. They are sealed through steam treatment, infiltrated with a metal that has a lower melting point, or oil or plastic resin impregnation, which provides the best seal.
Sintered metal products have many benefits over parts produced through other methods. The process results in little waste, as approximately 97% of the materials are used during the procedures. Sintered products are not shape sensitive either. Powder metal part manufacturers create parts close to tolerances, often eliminating the need for secondary operations. Therefore, powder metallurgy is often the technique of choice for the production of intricate parts requiring bends, projections and depressions. A wide variety of shapes and designs can be sintered out of an almost infinite choice of alloys, composites and associated properties. Powder metal parts have controlled porosity for self-lubrication and for gas or liquid filtration.A powder metallurgy process called metal injection molding is sometimes used to produce smaller, more complex, high density and high performance metal parts. It combines the technologies of plastic injection molding and powder metallurgy to produce parts used in the automotive, medical and dental, firearms, hardware, computer, and electronics industries. It offers more design freedom, more complex detailing, reduced assembly costs, reduced waste and denser, stronger, more corrosion resistant and magnetic products. However, only smaller, thinner parts are produced this way, and tooling costs are higher than regular powder metallurgy. There are a few main differences in metal injection molding. During the initial mixing process, the metal powder is mixed with thermoplastics in addition to lubricants. The parts are only formed through molding, which uses standard plastic injection molding machines. The thermoplastics are then removed, or debindled from the parts by thermal or chemical means through an open pore network. The parts are then sintered and put through any necessary secondary operations.
Many different metals, including aluminum, copper, brass, iron, steel and bronze, are able to convert to powdered form and undergo a type of powder metallurgy to produce parts and products. Aluminum is a popular metal to use because of its light weight, conductivity and high flammability. It's often used in pyrotechnics and high strength structural applications. Copper parts exhibit good electrical and thermal conductivity, and are used in heat sink and electrical contractor applications. Iron powder is used to make structural parts, filters and bearings. It also contains graphite additive. Steel, often stainless steel or tool steel powders, are high strength and used in automobile weight reduction. Finally, bronze powder parts are used to produce self-lubricating bearings. It is a denser metal with a higher mechanical performance than brass.
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Metallurgy |
- Powder comprised of needle-shaped particles.
- A sintering
process whose rate is dramatically increased by something other than the
changing of temperature or time (e.g. adding a constituent to the powder,
thermal cycling or the atmosphere).
- A process
in which an air stream of controlled velocity is used to separate powder
into particle size fractions.
- The production
of metal powder by dispersing molten metal into individual particles through
mechanical methods or through the rapid movement of streams of liquids
or gases.
- A cementing medium
that is added to the powder to increase the green strength of the compact
and expelled during the sintering process. The term binder can also refer
to a material, typically having a lower melting point, that is added to
a powder mixture in order to bind powder particles together, which would
not have normally sintered into a strong body.
- An unfinished compact
that has already been pressed, presintered or fully sintered but requires
some other operation, such as cutting or machining, to bring it to its
completed form.
- The formation
of a metal compact through the compression of metal powder at room temperature.
- The process of
breaking down metal into individual particles through grinding and flaking
operations, among other procedures.
- A solid material consisting
of compressed metal powder that has been pressed in a die.
- A compact
consisting of more than one distinct substance.
- A press
tool consisting of a cavity and shaped according to part design requirements,
into which the metal powder is pressed to form a compact.
- Also referred to
as "sweating," it is the rising of a compact component to
the top of the compact. During sintering, the component has a lower melting
point than that of the main compact constituent.
- A term that refers to
an object that has not been sintered.
- An increase in the
size of a compact that occurs during the sintering process.
- Process occurring
after the sintering process in which a nonmetallic substance, such as
oil, is used to fill the pores of the compact.
- Process occurring
either before or after the sintering process in which the pores of a compact
are filled with a metal substance having a lower melting point than that
of the compact.
- The production
of a compact through the application of uniform pressure from all directions
to metal powder.
- A fluid substance applied to the punch and die walls or mixed
into the metal powder to aid in the compaction process and compact removal.
- Another term for pressing
metal powder into a compact.
- The production
of more than one compact at a time by pressing metal powder in different
dies.
- Measurement reflecting
the percentage of open spaces, or pores, on a powdered metal part compared
to the volume of the part.
- Die component responsible
for pressing the metal powder into a compact. The punch makes contact
with the metal powder during the formation of a compact.
- A decrease in the
size of a compact that occurs during the sintering process.
- Deformations in a
compact resulting from the sintering process.
