Allowed design features

• Holes at angles to one another

• Stiffening ribs

• Protrusions and studs

• D-shaped and keyed holes

• Hexagonal, square, blind, and flat bottom holes

• Knurled and waffle surfaces

• External or internal threads

• Part number or identification in die

The particle size is a dictate for the minimum section thickness. The powder size needs to be less than one-tenth of the smallest thickness. Particle size limits the sharpness of all corners, because the minimum particle radius is the edge radius, but more typically several particles are needed to fill out the dimension. A conceptual limit on an edge radius is 0.05 mm and a corner radius is 0.1 mm.

Table 8 also lists options in the design or production of PIM compacts. These options include square holes, flat-bottomed holes, knurled surfaces, faces, twists, curls, helical geometries, and external or internal threads. Although these features are not needed to make a PIM compact viable, they are possible and add to the design flexibility. Certain attributes, such as component size and mass, will increase as experience and manufacturing optimization occur. Already components up to 10 kg and 1,000 mm maximum length have been fabricated by PIM. These require special efforts and are not routine products. With respect to changes in the section thickness, a ratio of 2 is typical; however, compacts have been successfully fabricated with thickness changes of 100:1.

Component design has a great influence on the success of PIM. Identification of injection molding as a production process in the design stage allows changes that increase the ease and lower the manufacturing cost. Possible design shifts that give essentially the same functional features are sketched in Fig. 9. Two alternatives are shown in each case. Both alternatives achieve the same design objectives, but one is better aligned with the specifics of the PIM approach.

Not good Preferred Better Not good Preferred Better

Not good Preferred Better Not good Preferred Better

Fig. 9 Recommended designs for powder injection molding components and suggestions for improved processing fi>

Fig. 9 Recommended designs for powder injection molding components and suggestions for improved processing

Table 9 summarizes the minimum and typical tolerances possible in PIM processing without secondary operations. Generally, the ability to hold tolerances increases with production experience. With little effort, dimensional tolerances can be held within 0.5% (one standard deviation). A controlled process with solvent, wicking, or catalytic debinding allows dimensions to be held with a deviation of 0.3% or less, and critical dimensions can be held within 0.1%. With newer binder systems and integrated process controls these values can be improved to 0.05%. In the production of jet engine ceramic casting cores, the mass ranges from 10 to 1200 g and part lengths range from 2 to 50 cm. These cores are produced with final dimensional scatter of ±0.05% on length (one standard deviation) in production quantities over

50,000 per week. Larger dimensions exhibit more scatter. Fortunately, the component density can be held within ±1% and weight variation to ±0.1%.

Table 9 Typical standard deviation of powder injection molding production components

Feature

Best possible

Typical

Angle

0.1°

Density

0.2%

1%

Weight

0.1%

0.4%

Dimension

0.05%

0.3%

Absolute dimension

0.04 mm

0.1 mm

Hole diameter

0.04%

0.1%

Hole location

0.1%

0.3%

Flatness

0.1%

0.2%

Parallelism

0.2%

0.3%

Roundness

0.3%

0.3%

Perpendicularity

0.1% or 0.1°

0.2% or 0.3°

Average roughness

0.4 .'■'m

10 .'-'m

0 0

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