study note of FDM : Specific Design Rules

Post by **subham** » Fri Oct 12, 2012 12:16 pm

A number of DFM rules for design, more specific than the preceding guidelines, have been developed.
1. Space holes in machined, cast, molded, or stamped parts so they can be made in one operation without tooling weakness. This means that there is a limit on how close holes may be spaced due to strength in the thin section between holes.

2. Avoid generalized statements on drawings, like “polish this surface” or “tool marks not permitted,” which are difficult for manufacturing personnel to interpret. Notes on engineering drawings must be specific and unambiguous.

3. Dimensions should be made from specific surfaces or points on the part, not from points in space. This greatly facilitates the making of gages and fixtures. The use of GD&T methods makes this point moot.

4. Dimensions should all be from a single datum surface rather than from a variety of points to avoid overlap of tolerances.

5. The design should aim for minimum weight consistent with strength and stiffness requirements. While material costs are minimized by this criterion, there also will usually be a reduction in labor and tooling costs.

6. Whenever possible, design to use general-purpose tooling rather than special dies, form cutters, and similar tools. An exception is high-volume production where special tooling may be more cost-effective.

7. Use generous fillets and radii on castings and on molded, formed, and machined parts.

8. Parts should be designed so that as many operations as possible can be performed without requiring re-positioning. This promotes accuracy and minimizes handling.

It is valuable to have manufacturing engineers and specialists involved in design decision making so that these guidelines and others they bring can inform the process.

**Sponsor**