Zero Defects & On-target: There are two manufacturing philosophies of manufacturing. Zero-defects is primarily practiced by American manufacturers and on-target is generally adopted by Japanese companies.

For more information, read this paper: 2010 10 IIE Kick Down the Goal Post.pdfDownload For more information, read this paper: 2010 10 IIE Kick Down the Goal Post.pdf

The following example explains the concept further:

Say the dimension and tolerance given to you is 100 mm (+2 mm / -0 mm). This means the dimension will have the lower specification limit (LSL) of 100 mm and the upper specification limit (USL) of 102 mm, with a needed target of 100 mm. Now say you ran the parts on the machine and found the SD for a set of 30 parts to be 0.03 mm.

With this information we can now find the target value that you should aim the machine at. Ideally the target will be 100 mm but because of the variation in the process, it cannot be 100 mm, but we can be as close to it as possible. The distance we can be away from it for 68% of the output to be good will be 1x SD, for 95% it will be 2 x SD and for 99.73% it will be 3 x SD.

Hence the targets will be as follows:

1) 68% will be 100 + 1x SD = 100 + (1 x 0.03) = 100.03 mm

2) 95% will be 100 + 2x SD = 100 + (2 x 0.03) = 100.06 mm

3) 99.73% will be 100 + 3x SD = 100 + (3 x 0.03) = 100.09 mm

Hence, the dimensions will:

1) For 68% will be 100.03 mm, +0.03 / -0.03

2) For 95% will be 100.06 mm, +0.06 / -0.06

3) For 99.73% will be 100.09 mm, +0.09 / -0.09

Assignment Question:

If the dimension is 1000 mm (+5mm / -0 mm), and the SD for a set of 30 parts came out to be 0.10 mm.

1) What should be the target that you should aim.

2) If you would like to specify a bilateral tolerance to the machinist, what will be the dimension.

Calculate the target value and the bilateral tolerances for staying 1 x SD, 2 x SD and 3 x SD away from the target.

You may conduct this assignment with another student if you would like. Both will get the same grade.