Question

In the manufacture of roll-on deodorant, deodorant is discharged into a container and a plastic (polypropylene) ball is forced into the top of the container. Following this operation, samples are collected to test product functionality. Each item in a sample is placed into a device with the ball pointed downward. An apparatus moves the ball into contact with a two foot strip of vinyl. Pressure is applied until product is dispensed. If product is not dispensed when the pressure reaches 700 grams, the dispenser is considered nonconforming. Two hundred bottles are tested each day. Results for the past 25 days are given the following table.

or 211 14 12-6 7859-86 456789 012345 De | | | | | 1 | 1 | 1 222222 744137 0857093 al 23456 789 10 11-11

The control chart below is an np chart for this data. Interpret this chart. Is the process stable over this time period? Why or why not?

Choose what you believe is the best answer from the following answers:

i) There are no special causes signaled on this control chart, this suggests that the process is operating in a stable and consistent manner.

ii) This is the wrong chart to use for this data.

Answer 1

An np-chart is an attributes control chart used with data collected in subgroups that are the same size. np-charts show how the process, measured by the number of nonconforming items it produces, changes over time.

Since all the points lies within the control limits this implies that there is no assignable cause present in the manufacturing process.

Hence the best answer is:

i) There are no special causes signaled on this control chart, this suggests that the process is operating in a stable and consistent manner.