Process Background:
For this project we will be considering a manufacturing process that produces disposable diapers. In making a disposable diaper a top sheet (the outside surface of the diaper) is glued to the bottom sheet (the side of the diaper that touches the baby’s skin). One of the CTQs associated with this product is the bond strength (measured in pounds per square inch (PSI)) of the glue between the top sheet and the bottom sheet.
The top sheet material comes in rolls of material that last approximately 30,000 diapers (1 hour of production). The bottom sheet comes in rolls of material that last for approximately 45,000 diapers (1.5 hours of production). The glue used starts out as a solid that comes in a box and then is heated until it takes liquid form. This liquid glue is then squirted onto the top sheet and when the bottom sheet is added the bond is compressed. A box of glue lasts for approximately 120,000 diapers (4 hours of production).
For this particular glue bond the target strength is 9.50 with an upper specification limit of 10.00 and a lower specification of 9.00.
The Assignment:
Utilize the information above and the data stored on Niihka in the excel workbook project 2 data.xls to execute the following / answer the following questions:
1. Column PSI1 represents a retrospective study where 4 random samples were taken from 4 hours of production.
a. For this data create the appropriate control charts and determine if with this sampling plan the process is in control.
b. If necessary, eliminate out of control points to arrive at an in control process.
c. Considering the process described, what sources of variation contribute to within subgroup variability?
d. Considering the process described, what sources of variation contribute to between subgroup variability?
e. How well does this sampling scheme match the concept of rational subgrouping? Why?
f. Based on this data (with assignable causes removed) what is the estimate of process capability and the percent defective being produced?
2. After a process improvement team has implemented numerous improvements data is gathered again. Column PSI2 is this data and comes from 4 random samples were taken from every 30 minutes of production.
a. For this data create the appropriate control charts and determine if with this sampling plan the process is in control.
b. Considering the process described, what sources of variation contribute to within subgroup variability?
c. Considering the process described, what sources of variation contribute to between subgroup variability?
d. How well does this sampling scheme match the concept of rational subgrouping? Why?
e. Based on this data what is the estimate of process capability and the percent defective being produced?
f. The company wants a sampling plan that “quickly” detects a shift (either an increase or a decrease) in the average bond strength greater than or equal to 0.2 PSI. On average, how quickly will this sampling plan find such a shift?