What is High Temperature Powder Metal?
High Temperature PM (or the Powder Metal Sintering process) focuses on providing a cost-effective alternative to forging, stamping, casting, and machining processes. It combines the high volume process of PM compaction with superior physical properties achieved through an increased temperature-controlled atmosphere called "sintering".
Raised Temperature PM Benefits
Raised Temperature PM offers advantages that are not readily available with other forms of stainless steel metallurgy. Consequently, PM components are rapidly becoming an effective alternative to castings, forgings, and machined parts.
Design Advantages of Raised Temperature PM:
- Material Efficiency: One of the powdered metallurgy advantages of the PM process cost-wise is that the finished powdered product uses virtually 100% of the PM consumed. This eliminates the waste found in the stamping, fineblanking, or machining processes when producing components with holes or varying thickness.
- Intricate Shapes: With essentially no cost added, PM is easily able to provide internal or external splines, gears, knurls, or knobs. Features can be off-center or partially through, such as eccentric holes or hidden pockets.
- Close Tolerances: Precision dies, punches, and core rods produce net shape components with closer tolerances than castings, forgings, and stampings. Sintered steel components may be coined or machined if additional dimensional precision is required.
- Unique Material Properties: PM stainless steel offers a variety of standard alloys to suit a majority of requirements; however, custom blends of any size can easily be manufactured to meet specific material requirements.
- Labor Efficiency: Automatic, rapid cycle presses produce PM stainless steel components consistently. While intricate tooling set-ups may be somewhat lengthy, longer press runs and continuous sintering efficiently amortize this portion of the cost.
- Reduced Assemblies: In many cases, functions that would require intricate multiple parts and assembly steps are consolidated into a single PM component that minimizes manufacturing steps and reduces cost.
Defining The Process and History
PM is a mature process, beginning with decorative applications as early as 3000 BC and evolving to high volume, industrial production just over 100 years ago. Advances in equipment and materials over the past 50 years have led to significant improvements.
Elevated temperature stainless steel components use those advances to achieve better properties than conventional PM while continuing to provide cost benefits when compared to other metal forming processes.
While conventional PM processing sinters parts to 82-88% of the theoretical density, High Temperature materials are carefully processed to achieve change in densities ranging from 88% - 94% of theoretical density. Since material properties such as elongation, yield strength, corrosion resistance, and magnetic properties are directly related to density, High Temperature materials significantly outperform their conventional counterparts.
Really pure PM and additives are selected to provide unique physical properties tailored to the customer's requirements. The PM is blended with lubricants which aid flow, green density, and green strength. Mixing PM in the solid state provides opportunities to engineer a wide variety of material properties unique to PM.
PM flows from the feedshoe into the die cavity where multiple punches compress it to half its original volume. Intense compacting forces the steel to first realign, then deform the metal particles, creating localized mechanical bonds, forming a 'green' part. Green parts are ejected and conveyed mechanically to minimize handling damage. With presses from 4 to 550 tons capable of multiple motions, we are able to produce even the most complicated stainless steel parts.
Our high temperature stainless steel (above 2300F) capabilities yield many advantages such as improved metallurgical bonding, densification, ductility, and impact energy. The initial sintering stage removes binders and lubricants and cleans the surface of the metal particles, ensuring excellent mechanical properties in the finished stainless steel component. Time at temperature provides the energy that transforms the mechanical bonds into metallurgical bonds. Sintering below the melting point creates components with 88% to 94% of the alloy's theoretical density.
The strength of PM is the net shape capability — often providing a finished stainless steel component after the stainless steel powder, sintering operation. Sizing or coining operations are used for more demanding dimensional requirements. Additional feature complexity can be gained using a variety of machining applications including grinding, turning, milling, tapping, etc. Oil impregnation utilizes PM's porous pathways as a built in lubrication reservoir. Other surface treatments are also available to achieve specific requirements.