Sizing: an in-depth examination
There's a Wall Street saying often quoted to those who see no limits to a favorite stock's prospects: "Trees don't grow to the sky." In other words, everything has its limits. And so it is with Protomold's molding capabilities. We can deliver great parts incredibly fast and at amazing prices, but due to a number of factors related to our existing molding equipment we do have size limitations. We are, of course, always striving to expand our capabilities.
Until recently, our production was limited to parts cut no more than two inches deep into each mold half. In other words, the depth of a carefully designed part could be a full four inches, but only if the depth of the part were divided equally between the two mold halves. (See Figure 1)
Figure 1
With the addition of new technology, we can now produce parts with a total depth of six inches as long as neither mold half is cut more than three inches deep. (See Figure 2)
Figure 2
Regardless of the depth of the part, its total volume cannot exceed 22.1 cubic inches. The reason is simple: that is the volume of resin our largest press can currently inject into a mold in a single "shot."
The next issue is maximum part outline. Imagine that you sat your part on a flat surface running parallel to the part's parting line. The shadow of the part projected downward onto the surface is the part outline or "projected area." (Light shining through holes in your part don't count toward the projected area.) For parts up to two inches in depth in each mold half, the part outline must fit within a rectangle measuring 7.5 x 14 inches. For parts up to three inches in depth in each mold half, the part outline must fit a rectangle measuring 6 x 8 inches. The reason for this limitation is the size of the raw mold stock we use for molds of different depths.
The final issue is total mold area. This is the actual area of the opening where the two mold halves meet, and it cannot exceed 75 square inches. This limitation is based on the maximum closing force our molding presses can exert. That force must exceed the injection pressure, typically measured in psi, of the resin multiplied by the total mold area or the press will be unable to hold the mold closed during injection.
To summarize the above data:
| Maximum depth per mold half | 2 inches | 3 inches |
| Maximum part outline | 7.5" x 14" | 6" x 8" |
| Maximum projected part area | 75 in2 | 75 in2 |
| Maximum part volume | 15.75 in3 | 15.75 in3 |
Finally, there is the issue of draft. A good rule of thumb is that parts should be drafted one degree for each inch of depth cut into the mold half. In other words, one inch of depth requires one degree of draft; two inches requires two degrees; three inches of depth gets three degrees. Parts of one half inch or less require a minimum of one half degree of draft.
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It shouldn't come as a surprise that researchers are turning some of the four billion pounds of chicken feathers produced each year into fabric, but Walter Schmidt, a chemist with the Agricultural Research Service has other ideas. Into what item has Schmidt incorporated processed chicken feathers as a major component? (The feathers help lighten the resulting composite.)
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