Wakefield Corporation

Sintered P/M Parts
Powder metallurgy, or P/M, offers designers and specifiers design freedom, production efficiencies and a wide range of engineering properties. Wakefield’s products allow that freedom through the following process of production:
MIXING: The combination of elemental or pre-alloyed metal powders. P/M powders are precisely engineered materials that can be categorized into two groups: elemental or pre-alloyed. Elemental powder is a single metal element that can be used by itself, as in the case of iron, or mixed with other elemental powders to form an alloy. Pre-alloyed powder is a metallic powder composed of two or more elements which are alloyed in the powder manufacturing process. All particles are the same nominal composition. The mixing operation combines the powders, elemental or pre-alloyed, with additives such as graphite and die lubricant, into a homogeneous mixture.
FORMING/COMPACTING: Compression of the mixed powder in the die. The compacting process places a controlled amount of mixed powder, approximately 2-1/2 times finish volume, into the die. Compression is conducted by punches moving simultaneously from above and below at pressures ranging between 20 and 50 tons per square inch. Dimensions and density are closely controlled in this process. The compacted component is called a "green compact".
SINTERING: The transformation of powdered metal by sintering. The green compacts are then placed on a moving belt and slowly fed into a controlled-atmosphere furnace. The parts are heated to a temperature below the melting point of the primary element so that the particles are bonded, or sintered, together into a solid mass. Sintering transforms the compacted mechanical bonds between the powder particles into metallurgical bonds. The physical properties of the final product are comparable to cast or wrought products of the same composition.
OPTIONAL MANUFACTURING STEPS: Infiltration, coining, and machining. Of the optional manufacturing steps, infiltration, coining and machining, infiltration is exclusive to the P/M process. Infiltration is the process of filling the voids or pores of a P/M compact during sintering with a metal or alloy of a lower melting point than the base material. The infiltrating material is normally copper or a copper alloy. The process begins by placing an infiltration slug or slugs directly on top of the compact surface. As it melts during sintering, it slowly filters down into the pores of the compact. Infiltration improves strength, seals parts and improves ductility and machinability. Coining's main application is sizing and the correction of heat distortion. It can also be used to increase densification. Machining operations add features not achievable in the P/M process such as undercuts, cross holes, sidewall grooves, sharp radii and threads.
OPTIONAL FINISHING STEPS: Improvements in material strength, appearance, and performance. Heat Treating A quench and temper operation to improve strength and hardness. Tumbling A deburring operation to remove sharp edges. Impregnation There are two types of impregnation with almost opposite results.Components impregnated with oil are intended to leach oil during the part's service life. This is the concept behind self-lubricating bearings. Resin impregnation fills and seals pores with a resin material. This results in improved machinability, pressure tightness and surface preparation for plating. Steam treating Steam treating provides surface hardness and wear resistance for ferrous parts. It also improves corrosion resistance and seals porosity. Plating High density and infiltrated parts can be plated using the same methods as those used on wrought parts. Lower density parts should have porosity sealed, usually through resin impregnation to avoid plating solution entrapment in the pores.

CALL: 781-245-1828 or 800-548-9253 | 29 Foundry Street - Wakefield, MA 01880 | Email: info@wake.com