质量管理与卓越绩效 (10)
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When deleting sample data, be sure to update the number of samples used in the calculations to compute the statistics or the control charts will not display correctly.
3. Determine initial control limits
Compute the upper and lower control limits Draw the center line (average) and control limits on the
chart
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
8
La Ventana Case Data
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
4
Constructing x-bar and R-Charts
Collect k = 25-30 samples, with sample sizes generally between n = 3 and 10
Compute the mean and range of each sample Compute the overall mean and average range:
7
Case Study: La Ventana
Window Company
La Ventana received some complaints about narrow, misfitting gaps between the upper and lower window sashes
The plant manager wants to evaluate the capability of a critical cutting operation that he suspects might be the source of the gap problem.
11
Control Charts
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
13
Using the Template
You may need to rescale the vertical axis of the charts to eliminate blank space and make them more visually appealing. See the appropriate Excel help files for the version you are using. This is rarely necessary.
3
Control Charts for Variables Data
x-bar and R-charts x-bar and s-charts Charts for individuals (x-charts)
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in pang and Control
After a process is determined to be in control, the charts should be used on a daily basis to monitor performance, identify any special causes that might arise, and make corrections only as necessary.
9
Control Limit Calculations
n = 5; A2 = 0.577 and D4 = 2.114
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
Compute control limits:
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
10
Spreadsheet Template
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
5
Estimating Process Capability
Estimate of standard deviation using control chart data:
Use this estimate in process capability index calculations
Not as accurate as calculating the standard deviation using the complete set of data.
Attribute results to special cause variation and delete these samples
New control limits
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
The nominal specification for this cutting operation is 25.500 inches with a tolerance of 0.030 inch.
Inspect five consecutive window panels in the middle of each shift over a 15-day period and recording the dimension of the cut
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
Measuring and Controlling Quality
Part 2
MANAGING FOR QUALITY AND PERFORMANCE EXCELLENCE, 9e, © 2014 Cengage Publishing
1
Developing and Using Control
Charts
12
Interpretation
Sample 24 out of control in R-chart Samples 9, 21, and 24 out of control in x-bar chart Common characteristic: Shane was process operator
Workers who run a process should use control charts and need to be trained to use them properly.
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
5. Use for ongoing control
Continue collecting data and plotting on the chart(s)
Stop the process when an out-of-control condition is identified and make necessary corrections or adjustments.
2
Developing and Using Control Charts
4. Analyze the chart
Determine if it is in control Identify and eliminate out-of-control points and
recompute control limits
When a sample is deleted from a data set in the templates, do not enter zero for the data; instead, leave the cells blank (just delete the data using the (“delete” key). The charts are set up to interpolate between non-missing data points.
1. Prepare
Choose the variable or attribute measurement Determine the basis, size, and frequency of sampling
2. Collect Data
Record the sample observations Calculate relevant statistics: averages, ranges, proportions… Plot statistics on chart(s)
3. Determine initial control limits
Compute the upper and lower control limits Draw the center line (average) and control limits on the
chart
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
8
La Ventana Case Data
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
4
Constructing x-bar and R-Charts
Collect k = 25-30 samples, with sample sizes generally between n = 3 and 10
Compute the mean and range of each sample Compute the overall mean and average range:
7
Case Study: La Ventana
Window Company
La Ventana received some complaints about narrow, misfitting gaps between the upper and lower window sashes
The plant manager wants to evaluate the capability of a critical cutting operation that he suspects might be the source of the gap problem.
11
Control Charts
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
13
Using the Template
You may need to rescale the vertical axis of the charts to eliminate blank space and make them more visually appealing. See the appropriate Excel help files for the version you are using. This is rarely necessary.
3
Control Charts for Variables Data
x-bar and R-charts x-bar and s-charts Charts for individuals (x-charts)
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in pang and Control
After a process is determined to be in control, the charts should be used on a daily basis to monitor performance, identify any special causes that might arise, and make corrections only as necessary.
9
Control Limit Calculations
n = 5; A2 = 0.577 and D4 = 2.114
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
Compute control limits:
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
10
Spreadsheet Template
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
5
Estimating Process Capability
Estimate of standard deviation using control chart data:
Use this estimate in process capability index calculations
Not as accurate as calculating the standard deviation using the complete set of data.
Attribute results to special cause variation and delete these samples
New control limits
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
The nominal specification for this cutting operation is 25.500 inches with a tolerance of 0.030 inch.
Inspect five consecutive window panels in the middle of each shift over a 15-day period and recording the dimension of the cut
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
Measuring and Controlling Quality
Part 2
MANAGING FOR QUALITY AND PERFORMANCE EXCELLENCE, 9e, © 2014 Cengage Publishing
1
Developing and Using Control
Charts
12
Interpretation
Sample 24 out of control in R-chart Samples 9, 21, and 24 out of control in x-bar chart Common characteristic: Shane was process operator
Workers who run a process should use control charts and need to be trained to use them properly.
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
© 20114 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part..
5. Use for ongoing control
Continue collecting data and plotting on the chart(s)
Stop the process when an out-of-control condition is identified and make necessary corrections or adjustments.
2
Developing and Using Control Charts
4. Analyze the chart
Determine if it is in control Identify and eliminate out-of-control points and
recompute control limits
When a sample is deleted from a data set in the templates, do not enter zero for the data; instead, leave the cells blank (just delete the data using the (“delete” key). The charts are set up to interpolate between non-missing data points.
1. Prepare
Choose the variable or attribute measurement Determine the basis, size, and frequency of sampling
2. Collect Data
Record the sample observations Calculate relevant statistics: averages, ranges, proportions… Plot statistics on chart(s)