# Statistical Process Control

## Presentation on theme: "Statistical Process Control"— Presentation transcript:

Statistical Process Control
BPS chapter 27 © 2006 W.H. Freeman and Company

Flowcharts In the following flowchart, what happens if the “check for size” is not O.K.? Deburr Heat billet to the required temperature. Check to see if oversize. Scrap.

Flowcharts (answer) In the following flowchart, what happens if the “check for size” is not O.K.? Deburr Heat billet to the required temperature. Check to see if oversize. Scrap.

Flowcharts In the following flowchart, what happens if the item is oversized? Scrap. Bar code and store. Heat billet to required temperature. Cut to the billet length.

Flowcharts (answer) In the following flowchart, what happens if the item is oversized? Scrap. Bar code and store. Heat billet to required temperature. Cut to the billet length.

Control charts True or false? Once the mean and standard deviation have been determined for a process by careful observations over a long period of time, then this mean and standard will always be correct for this process. True False

True or false? Once the mean and standard deviation have been determined for a process by careful observations over a long period of time, then this mean and standard will always be correct for this process. True False

Control charts Which control chart should you look at first? s p

Which control chart should you look at first? s p

s control charts Which is an example of a cause that would affect the variation shown on an s control chart? A new employee’s first day on the job, when he sometimes does well and sometimes doesn’t. A gradual loosening of a screw on a piece of equipment. A switch from oak to maple for the wood used in the manufacturing process.

Which is an example of a cause that would affect the variation shown on an s control chart? A new employee’s first day on the job, when he sometimes does well and sometimes doesn’t. A gradual loosening of a screw on a piece of equipment. A switch from oak to maple for the wood used in the manufacturing process.

control charts Which is an example of a cause that would affect the variation shown on an control chart? A new employee’s first day on the job, when he sometimes does well and sometimes doesn’t. A gradual loosening of a screw on a piece of equipment. Combining results from several different employees in a single sample.

Which is an example of a cause that would affect the variation shown on an control chart? A new employee’s first day on the job, when he sometimes does well and sometimes doesn’t. A gradual loosening of a screw on a piece of equipment. Combining results from several different employees in a single sample.

Loss of control Why don’t we want to add lots of signals to help us detect various kinds of loss of control? The more signals you have, the more false alarms you will have. Too many signals cancel each other out. Signals are hard to implement. We do want as many signals as possible.

Why don’t we want to add lots of signals to help us detect various kinds of loss of control? The more signals you have, the more false alarms you will have. Too many signals cancel each other out. Signals are hard to implement. We do want as many signals as possible.

Control charts True or false? When setting up a control chart, you should use a “target value” for the process standard deviation  instead of estimating from past data. True False

True or false? When setting up a control chart, you should use a “target value” for the process standard deviation  instead of estimating from past data. True False

Control charts True or false? It is better and less expensive to inspect the final product than to take small samples at each of the key manufacturing points and to check that those steps are in control. True False Impossible to answer unless more is known about the manufacturing process.

True or false? It is better and less expensive to inspect the final product than to take small samples at each of the key manufacturing points and to check that those steps are in control. True False Impossible to answer unless more is known about the manufacturing process.

Capability Which is a true statement about capability?
If a process is in control, we know that it has adequate capability. If a process is not in control, we know that it does not have adequate capability. If a process is not in control, we would have a hard time telling if it is capable. A variable that continues to be described by the same distribution when observed over time is said to be capable.