| Design Fundamentals for the Powdered Metal Process |
The powdered metallurgical process starts with the blending of raw metal powders and other
additives. The blend is compacted and the “green” part is sintered in a controlled atmosphere and
at a temperature well below the melting point of the blended materials.
Powdered metal parts may be used after sintering, or further processed to achieve special surface
qualities or added mechanical characteristics. They may also be joined by riveting, brazing or any
other conventional method. The end result is complete flexibility for the part designer.
Understanding a few basic considerations in powdered metal part design will insure production
feasibility. Powdered metal is poured into the die cavity, resulting in a mass corresponding loosely
to the shape of the cavity, but without the lateral flow that is found in molten metals, or in plastics.
Compression of the powder is then applied in a vertical direction only, from above, or from above
and below in a sequence of motions necessary to attain proper density throughout the part. Under
such compression, sometimes up to 140,000 psi, the powder mass will take the shape of the die,
with density very much increased.
Although these molded parts can be held to very close limits, tolerances should be as liberal as
possible. When they are more restrictive than ordinary tolerances, the inclusion of costly added
operations is required. Because of die wear and other factors, it is generally possible to quote a
lower price when tolerances are less restrictive.
All powder metal parts should have the edges beveled and fillet radii on inside corners. This will
prevent flash or burrs on wearing surfaces. Tolerances on broken corners should be as liberal as
possible since close control requires expensive tooling and costly maintenance. Practically any
contour in the direction of pressing can be molded of powder metal.
additives. The blend is compacted and the “green” part is sintered in a controlled atmosphere and
at a temperature well below the melting point of the blended materials.
Powdered metal parts may be used after sintering, or further processed to achieve special surface
qualities or added mechanical characteristics. They may also be joined by riveting, brazing or any
other conventional method. The end result is complete flexibility for the part designer.
Understanding a few basic considerations in powdered metal part design will insure production
feasibility. Powdered metal is poured into the die cavity, resulting in a mass corresponding loosely
to the shape of the cavity, but without the lateral flow that is found in molten metals, or in plastics.
Compression of the powder is then applied in a vertical direction only, from above, or from above
and below in a sequence of motions necessary to attain proper density throughout the part. Under
such compression, sometimes up to 140,000 psi, the powder mass will take the shape of the die,
with density very much increased.
Although these molded parts can be held to very close limits, tolerances should be as liberal as
possible. When they are more restrictive than ordinary tolerances, the inclusion of costly added
operations is required. Because of die wear and other factors, it is generally possible to quote a
lower price when tolerances are less restrictive.
All powder metal parts should have the edges beveled and fillet radii on inside corners. This will
prevent flash or burrs on wearing surfaces. Tolerances on broken corners should be as liberal as
possible since close control requires expensive tooling and costly maintenance. Practically any
contour in the direction of pressing can be molded of powder metal.
Additional Design Considerations:
• Powdered metal parts must be designed to allow for easy ejection from the
die. Sidewalls should be perpendicular and hole axes should be parallel to the
direction of the opening and closing of the die.
• Holes and even complicated profiles are permissible in the direction of
compressing. The minimum hole diameter is 1.5 mm (0.060 in).
• The wall thickness should be compatible with the process, and is typically
1.5 mm (0.060 in) minimum. Length to thickness ratio can be up to 18:1
maximum. This is to ensure that tooling is robust. However, wall thicknesses do
not have to be uniform, which offers the designer a greater amount of flexibility
than is found in other processes.
• Undercuts are not acceptable, so designs have to be modified to work
around this limitation or secondary machining is required. Threads for
screws cannot be made in the die and will also have to be machined later.
• Drafts are not required except for recesses formed by a punch making a
blind hole. In such a case a 2-degree draft is recommended. Note that the
requirement of no draft is more relaxed than other forming processes such
as casting, molding etc.
• Tolerances are 0.3 % on dimensions. If repressing is done, the tolerances
can be as good as 0.1 %. Repressing, however, increases the cost of the
product.
• When chamfers are required a PM flat is required for tool longevity.
NOTE: It is always beneficial to meet with your powder metal applications
engineer prior to and during the design phase to achieve desired results.
• Powdered metal parts must be designed to allow for easy ejection from the
die. Sidewalls should be perpendicular and hole axes should be parallel to the
direction of the opening and closing of the die.
• Holes and even complicated profiles are permissible in the direction of
compressing. The minimum hole diameter is 1.5 mm (0.060 in).
• The wall thickness should be compatible with the process, and is typically
1.5 mm (0.060 in) minimum. Length to thickness ratio can be up to 18:1
maximum. This is to ensure that tooling is robust. However, wall thicknesses do
not have to be uniform, which offers the designer a greater amount of flexibility
than is found in other processes.
• Undercuts are not acceptable, so designs have to be modified to work
around this limitation or secondary machining is required. Threads for
screws cannot be made in the die and will also have to be machined later.
• Drafts are not required except for recesses formed by a punch making a
blind hole. In such a case a 2-degree draft is recommended. Note that the
requirement of no draft is more relaxed than other forming processes such
as casting, molding etc.
• Tolerances are 0.3 % on dimensions. If repressing is done, the tolerances
can be as good as 0.1 %. Repressing, however, increases the cost of the
product.
• When chamfers are required a PM flat is required for tool longevity.
NOTE: It is always beneficial to meet with your powder metal applications
engineer prior to and during the design phase to achieve desired results.
| Bob Fox, Applications Engineer E-mail smp-rfox@cbpu.com Contact Bob with any technical questions about your project. Phone (517) 278-8750 |
| Coldwater Sintered Metal Products 300 Race St. Coldwater, Mi 49036 - Phone: 517 278 8750 Fax: 517 781 4632 Contact Us Types of parts we produce: Powdered Metal parts, Machined Parts, Gears (Bevel Gears, Planetary Gears, Helical Gears, Oil Pump Gears, Sector Gears, Spur Gears, etc.), Gear Forms, Sprockets, Bearings, Bearing End Caps, Bearing Shields, Bushings, Rollers, Cams, Cam Followers, Racks, Pinions, Spacers, G-Rotors, Pole Pieces, Soft Magnets, Sensor Rings, Pulse Rings, Impellers, Shaft Couplers, Counterweights, Support Members, Brackets, and any complex, tight tolerance, powdered metal or machined part. |