Exam 18: Statistical Process Control

The specifications for a manifold gasket that installs between two engine parts calls for a thickness of 2.500 mm ± .020 mm.The standard deviation of the process is estimated to be 0.004 mm.What are the upper and lower specification limits for this product? The process is currently operating at a mean thickness of 2.50 mm.(a)What is the for this process? (b)The purchaser of these parts requires a capability index of 1.50.Is this process capable? Is this process good enough for the supplier? (c)If the process mean were to drift from its setting of 2.500 mm to a new mean of 2.497,would the process still be good enough for the supplier's needs?

What are the three possible results (or findings)from the use of control charts?

Which of the following is true of a p-chart?

A process is said to be in statistical control when assignable causes are the only sources of variation.

The process capability measures Cp and Cpk differ because

The Central Limit Theorem states that when the sample size increases,the distribution of the sample means will approach the normal distribution.

A Cp of 1.33 indicates how many sigma limits?

At your first job out of college you have been assigned to the production of bottled 20 oz.soda. The process has upper and lower limits of 20.5 and 19.5 oz,respectively,with a mean of 19.8 oz and standard deviation of .3 oz.Your manager has requested the process produce no more than 3.4 defects per 1 million bottles produced.Calculate and then determine if the process is capable or if you should be looking for assignable variation.

A p-chart is appropriate to plot the number of typographic errors per page of text.

What four elements determine the value of average outgoing quality? Why does this curve rise,peak,and fall?

The Central Limit Theorem

The probability of rejecting a good lot is known as consumer's risk.

In acceptance sampling,a manager can reach the wrong conclusion if the sample is not representative of the population it was drawn from.

Assignable variation

What is the basic objective of a process control system?

Pierre's Motorized Pirogues and Mudboats is setting up an acceptance sampling plan for the special air cleaners he manufactures for his boats.His specifications,and the resulting plan,are shown on the POM for Windows output below.Pierre wants acceptance sampling to remove ALL defects from his production of air cleaners.Explain carefully why this won't happen.

Cartons of Plaster of Paris are supposed to weigh exactly 32 oz.Inspectors want to develop process control charts.They take ten samples of six boxes each and weigh them.Based on the following data,compute the lower and upper control limits and determine whether the process is in control.

A department chair wants to monitor the percentage of failing students in classes in her department.Each class had an enrollment of 50 students last spring.The number of failing students in the 10 classes offered that term were 1,4,2,0,0,0,0,0,0,and 3,respectively.Compute the control limits for a p-chart at the 95% confidence level.Is the process in control?

Control charts for variables are based on data that come from

If a process has only natural variations,________ % of the time the sample averages will fall inside the (or)control limits.