DESIGN FOR MANUFACTURING:DESIGN FOR SECONDARY OPERATION

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DESIGN FOR SECONDARY OPERATION

Just as there should be careful analysis in the selection of the ideal basic or primary process, so must there be sound planning in the specification of the secondary processes. The parameters associated with all process planning include the size of the part, the geometric configuration or shape required, the material, the tolerance and surface finished needed, the quantity to be produced, and of course the cost. Just as there are several alternatives in the selection of a basic process, so there are several alternatives in determining how a final configuration can be achieved.

With reference to secondary removal operations, several guidelines should be observed in con- nection with the design of the product in order to help ensure its producibility.

1. Provide flat surfaces for entering of the drill on all holes that need to be drilled.

2. On long rods, design mating members so that male threads can be machined between centers, as opposed to female threads, where it would be difficult to support the work.

3. Always design so that gripping surfaces are provided for holding the work while machining is performed and ensure that the held piece is sufficiently rigid to withstand machining forces.

4. Avoid double fits in design for mating parts. It is much easier to maintain close tolerance when a single fit is specified.

5. Avoid specifying contours that require special form tools.

6. In metal stamping, avoid feather edges when shearing. Internal edges should be rounded, and corners along the edge of the strip stock should be sharp.

7. In metal stamping of parts that are to be subsequently press formed, straight edges should be specified, if possible, on the flat blanks.

8. In tapped blind holes, the last thread should be at least 1.5 times the thread pitch from the bottom of the hole.

9. Blind-drilled holes should end with a conical geometry to allow the use of standard drills.

10. Design the work so that diameters of external features increase from the exposed face and diameters of internal features decrease.

11. Internal corners should indicate a radius equal to the cutting tool radius.

12. Endeavor to simplify the design so that all secondary operations can be performed on one machine.

13. Design the work so that all secondary operations can be performed while holding the work in a single fixture or jig.

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