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Email Us Today!Desigining for P/M
Designing for Powdered MetallurgyBearings are a natural product for PM because of its controlled porosity and the resulting self-contained lubrication. The shaping of a sintered bearing is essentially defined by the tool design and its manufacture. The appropriate layout of the components geometry and the selection of suitable material according to the PM process has a strong influence on tool life and consequently on the price of the part. It is therefore worthwhile to consider some of the guidelines of design related to the PM process.
Shapes
The P/M process is not shape-sensitive. Parts can be uniquely shaped or designed to combine two single parts into a complex, one-piece PM part. The part combinations are only limited to the design concept. Flanges A comparatively small flange, step, or overhang can often be produced by machining a shelf or step in the die. Too large a flange causes ejection difficulties. Bottom flange edge and juncture radii should be generous Shapes with uniform dimensions in the pressing direction are easiest to produce and eject from the press.
Wall Thickness
As a general rule, walls should not be thinner than 0.060 inch (1.52 mm) and the ratio of the length to wall should be less than 8:1 for tool strength and to ensure that the powder properly fills all sections of the die for proper part density. Avoid designing long, thin walls; they require tooling that is fragile and the parts themselves have a tendency toward density variation. Where the ratio of length-to-wall thickness is as high as 8:1 or more, special precautions must be taken to achieve uniform fill, and variations in density are unavoidable. The lower length to diameter and or length to wall thickness ratios, the easier it becomes to maintain uniform density throughout the part.
Edges
The edges of a part should be designed with chamfers rather than radii to prevent burring. A 30-45 Deg. chamfer with a 0.005-inch (0.13mm) to 0.015 inch 0.38mm) flat will eliminate feathered edges, which are undesirable.
Tolerances
The P/M process is cost effective in producing close-tolerance, parts to final dimensions with excellent part-to-part reproducibility. Contact us to discuss your specific part requirements.
Surface Finish
With some manufacturing processes, producing the desired surface finish on a part can require an additional finishing process. The overall smoothness and surface reflectivity depend on density and the tool finish.
Part Size
The size limitation of PM parts is based on powder compressibility and press tonnage. Since compaction occurs in the vertical direction, using only top and bottom motions, part lengths in the pressing direction are limited. Compression ratio—the ratio of the height of the loose powder filling the die to that of the compacted part—also tends to limit vertical part lengths
Part Use
The part specification or drawing should provide as much additional information regarding the part use as possible. The following questions are most important for the material and process selection:
Will the part operate under a pressure? Must it be leak tight?
Must the part be protected from corrosion—how severe?
Will the part be machined—which surfaces, what tolerances?
Will the part require heat treatment—what type?
Will the part be used in a high-impact-loaded application?
Will the part be used in a wear application—which surfaces? Is surface finish an important design feature, where, how to measure?
Will the part be used in a magnetic application?
Will the part be used in a thermally demanding application?
Must the part be burr-free—what type, amount of corner radius?
Will the part be welded?
Is there a region critical to the performance of the part?
Are there any unique packaging requirements?The operating environment should be carefully considered: external lubrication, cooling, and hardened or chromium-plated shafts tend to increase permissible loads. Repeated start-stop operation, oscillatory or reciprocating motion, high speeds, shock loads, and temperature extremes tend to decrease permissible loads.
If necessary, a sintered PM component can be finished or treated just like any other metal component to achieve desired characteristics—corrosion resistance, improved strength and hardness, surface wear resistance, edge-sharpness relief, porosity sealing, and control of size and surface finish. Plating, coating, deburring, welding, furnace brazing, heat treating, and steam treating are among the secondary operations that are used successfully in the process of fabricating finished PM parts.
Additionally, unlike components made using other metal forming processes, PM components can be repressed or coined, as well as sized, to densify or modify the surface shape and provide stricter dimensional control. Through oil impregnation, used on PM self-lubricating bearing components since the late 1920s, components can absorb 12% –30% oil by volume.
Material Specifications
| Material Specifications | |||||||
| Composition % |
Density (gm/cc) |
Porosity (% by Vol.) |
K Strength Constant |
Tensile Strength |
Elongation (in 1"%) |
Yield Strength PSI |
Comparable Designations |
|---|---|---|---|---|---|---|---|
| Copper 87.5-90.5 Iron 1.0 max. Tin 9.5-10.5 Carbon 1.75 Other Elements 0.5 |
6.4-6.8 | 19 min. | 26500 | 14000 | 1 | 11000 | ASTM B-438-70 GR1 Type 11 MPIF CT-1000-K26 SAE 841 Type I. Comp. A |
| Super Sintered Iron Material Specifications | |||||||
| Copper 18.0-22.0 Iron Balance Other Elements |
5.8-6.2 | 19 min. | 40000 | 22000 | 1 | 22000 | ASTM B-439-70 GR4 SAE 863, Type 3 Mil-B-5687C Type II. Comp. B |
