Consumers always seem to want thinner and lighter electronic products, and computer laptops are no exception. One of the challenges of producing extremely thin and light laptops is the manufacturing of the touch pads. In particular, touch pads are difficult to align. A common complaint is that one corner is higher or lower than another, resulting in what is known as “tilting.” Tilting makes navigation difficult, so touch pad manufacturers have strict limits on the amount of tilting that they will allow in a pad.
A company producing touch pads will want to ensure that the pads are flat to within a certain acceptable tolerance. One possible measure is the total deviation from flatness as measured by the maximum difference in height between any two corners (in mm). In the data file QC Control you will find this flatness measure for 250 touch screens produced during a period that was judged to be in control.
Using the mean and standard deviation from this control period, examine the next 150 samples of 5 pads (in the data file QC Production). Using various quality control rules and appropriate graphs, do you think the process is still in control? Explain.
Instead of samples of size 5 suppose they had used a run chart on the individual pads. Would your answer change? Explain.
Suppose the engineers establish 14 mm as the maximum flatness deviation they will tolerate and want to use that as an upper specification limit. Does your answer change now? Explain.
A qualitative measure is clarity of the pad. Batches of 100 pads are produced and defects are counted where defect is defined as a pad that does not pass the clarity test. From a period that was deemed to be in control, the mean number of defects per 100 was 0.5. Using this mean, determine whether the process stayed in control for the next 50 batches (QC Clarity)