Delta Plastics

DELTA PLASTICS, INCORPORATED

Prepare a 3-sigma control chart for both production processes, using the new and standard material (use of quality report in “Delta Plastics, Inc, Case A,” Chapter

The quality report for the Delta Plastic case in Chapter 5 list the number of defects found over the last 4 weeks for both types of plastic and for 5 types of defects. As these are defect counts, the appropriate chart type is a C-chart. Of the 5 defect types, cracks and air bubbles seem to be the most serious. Below are C-charts for these two defects for each plastic type. For C-charts the center line is the average number of defects per period (in this case, days) and the limits are:

UCLc =

LCLc =

therefore

UCL Cstd = 6.3

LCL Cstd = -2.2

UCL Bstd = 7.7

LCL Bstd = -2.26

UCL Csup = 11.1

LCL Csup = -1.8

UCL Bsup = 9.2

LCL Bsup = -2.1

As the counts cannot be less than zero, use zero for all negative lower control limits.

The first three carts are in control. All observations are positive and below the upper control limits. Further, none shows a trend. The chart for bubbles with the super plastic should be considered out of control. Even though all observations are within limits, the chart shows a clear increasing trend in defect counts.

Discuss whether or not both processes are in control and what conclusion may be drawn.

Being in control does not tell the whole story. While the crack counts for the super plastic may be stable (in control), they are also much higher than the standard material.

Discuss whether or not both materials are equally subject to defects.

As observed above, the Super Plastic has more defects than the standard plastic, primarily in terms of cracks and scratches.

Given your findings, advise Jose on the action he should take.

Clearly, manufacturing has problems with the new Super Plastic. The number of crack and bubble defects are higher with the Super Plastic when compared to the Standard...