Reply With QuoteMy book has the same thing I think it's a misprint or error. There should be an explanation on how to use the check sheet.
I'm trying to evaluate surface roughness against other machinability measures.
I recently purchased the Engineers Edge Design For Manufacturability and Assembly Book.
In the Appendix, there is a Generic Part Manufacturability Check Sheet. Though, I can not find explanation of its use.
I'm anticipating that the sheet can be used to identify areas which contribute most to DFM. The higher the Measure Quantity, the higher the contribution to manufacturability and thus cost.
The one item i'm not sure how to represent is Surface Roughness.
The sheet specifies the "Quantity or Measure" to be "micro-inch". But the "Unit Multiplier" is "One divided by %".
How do I derive a percent from the "micro-inch" units?
Thank you for your input.
My book has the same thing I think it's a misprint or error. There should be an explanation on how to use the check sheet.
No, microinches are not expressed as a percent. The DFM or DFMEA question is are the microinch finish requirements tighter than necessary for the proper fit form and function of the part. Are you paying for grinding when a machined surface will suffice?
If you can turn a steel shaft to the required tolerance and a 25 microinch finish but you specify a 10 microinch finish, the cost of improving the finish to 10 depends upon the function of the part. Do you need the 10 finish because the shaft runs in a seal? If you need the smoother finish, the grinding is not an added expense. If grinding is not necessary you can express the difference in cost between grinding to obtain the smoother finish and turning as a percentage of your product cost. Then the 15 extra microinches can be a percentage of your total product cost.
In order to determine if a specification is tighter than necessary, you need experience or knowledge of the product, materials and manufacturing methods. That type of knowledge and experience will not be found on a check list.
