From Powder to Parts

A Powder Metal Primer

On of the major advantages of using Powder Metal for production of components is the wide variety of raw materials that can be used to match your needs with regard to cost, durability, quality control, and special needs applications. Metals commonly used include iron. steel. tin, nickel, copper, aluminum, and titanium. Refractory metals such as tungsten, molybdenum, and tantalum may be used as are bronze, brass, stainless steel, and nickel cobalt alloys.

Combining these metals to form special alloys that exactly meet the needs of your application is a standard part of the Powder Metal process. In addition to strength and hardness qualities, we can help you design self-lubrication, corrosion-resistance, and other characteristics as an integral part of the production process.

Using these special mixes of metal powders, we can press complicated shapes in a single operation and at production rates of up to 100 parts per minute

Once the proper alloy of powders is mixed, that mixture is fed into a vertical hydraulic or mechanical press where it is deposited in a tool steel or carbide die. PMCo can press parts with up to 4 unique levels in intricate detail. This process uses pressures up to 60 tons per square inch, depending upon size and density requirements, to create a “green” part that has all of the predetermined shape properties of the final design.

However, at this stage, the part has neither exact final dimensions nor mechanical properties. Those properties are finalized in the heat treatment, or “sintering” process that follows. Please use the animated demonstration on this page to view the compaction

Sintering-In order to achieve desired final strength, density and dimensional stability, the green parts are sent through a sintering furnace. During sintering, the metal powder particles of the part are molecularly bonded by heating in a protective atmosphere to temperatures below the melting point of the major powder constituent of the part. The contacts points between the compacted particles increase in size and strength to improve the techanical properties of the component.

Sintering, depending up the process design, can shrink, expand, increase conductivity and/or make the part harder in order to achieve the final part specifications.

In a sintering furnace, the parts are placed on a continuous conveyor and moved slowly through the chambers of the furnace to achieve three major functions. First, the parts are slowly preheated to remove unwanted lubricants introduced into the powder for the compaction process. Next, the parts move through the high heat zone of the furnace where carefully controlled temperatures ranging from 1450° to 2400° are used to determine the final properties of the parts. The atmosphere inside this chamber of the furnace is carefully balanced by adding specific gases to reduce existing oxides and prevent further oxidation of the parts during this high heat phase. Finally, the parts pass through a cooling chamber to finish them or prepare them for any secondary procedures needed. This whole cycle can take anywhere from 45 minutes to 1.5 hours, depending upon the materials used and the size of the parts.

Assembly-Infiltration of one metal into another in the sintering process may be used to seal porosity, improve machining, and improve mechanical properties.

This is done by placing a lower melting “slug” on or beneath the part prior to entering the sintering furnace. Typically, a metal such as copper will be used. When this secondary metal melts, it is absorbed into the pores of the part by capillary action and diffused into the particles of the primary metal. To make more complex components, individually compacted pieces can be fit together prior to sintering by designing in slots and keyways as assembly guides.

These assemblies are then finalized one of two ways. They may use the infiltration process to create a bond between the parts similar to brazing or soldering. Alternatively, the parts may be designed so that their component metals shrink or expand at different rates, locking them together in a type of super press fit.

Although one of the advantages of P/M is the production of net configuration, it is sometimes desirable to achieve even closer tolerances or different strength characteristics than are possibly during the basic P/M process. The coining and sizing processes involve submitting the sintered parts to the press a second time, with a different set of tooling.

Coining actually reduces the volume of the part in the press. The result is increased density, strength and hardness. Dimensional accuracy is also improved during this process. Coining may also be used to reshape or emboss the final surface of the part.

Sizing varies from coining in that it causes very little change in density or strength of the part. As the term indicates, the objective is to ensure dimensional accuracy of the finished piece. Sizing is achieved by burning the part with die or core rod sizing tools.

Impregnating-Because the P/M process permits us to control the porosity of the final part, we can design in the ability to impregnate that part with lubricants or resins. The most common way to infuse the part with lubricant is to simply immerse the parts in a container of desired lubricant and place the entire vessel in a vacuum chamber. The air in the pores of the part is removed and the oil replaces it. The lubricant can account for 2 30% of the final volume of the part.

Using polyester resins to impregnate a part can provide lubrication qualities
and seal the pores. This provides pressure tightness and allows the part to be impervious to solutions it may be exposed to in further process or in uses that could degrade it. Impregnation also improves the machining of a part.

Treating-Heat treatment techniques are similar to those used for wrought metals are also applicable to P/M parts. P/M parts with a specific alloy can be expected to respond to heat treatment in a similar manner to wrought component. Most processes that are commonly used to treat wrought and cast parts can also be used for P/M.

  • Austenizing
  • Quenching
  • Tempering
  • Normalizing
  • Case Hardening
  • Gas Nitriding
  • Annealing
  • Local Hardening
  • Induction
  • Flame
  • Laser
Machine and Surfacing- One Primary objective of using the P/M process to produce components is to minimize machining by incorporating as much of the finished configuration into the process as possible. However, the combination of P/M production and machining to resolve special shapes, cross holes, threads and extremely close tolerances can produce the most efficient method for the production of a complex part.

The beauty of the P/M process is that, knowing in advance that some machine will be necessary, materials may be added to the powder to facilitate the machining procedures. Ferrous powder may receive small amounts of sulfur, manganese sulfide or graphite. Non-ferrous powders may have a small addition of lead to improve machining. And, the addition of resin or oil impregnation will aid in machining the parts. Like machining, nearly all surface treatments that are used for wrought or cast parts may be used with P/M produced components.

  • Deburring
  • Burnishing
  • Blackening (bluing)
  • Steam Treating
  • Plating