Project Management Project

Note: This is a sample outline of how to proceed with this case. The data here are not the same as the data in your case. DO NOT USE THESE DATA in your case. This tutorial uses the template provide in the case. Most find using this template makes the completion of this case much easier.

Scenario/Summary

1. A transmission manufacturing company has been having process difficulties at one its assembly stations. Thirty samples of four gears (n = 4) have been selected from the process and are provided below.

2. Calculate X-bar-bar, R-bar, and associated control limits using the data in the table above.

3. Create X-bar • R (average and range) control charts from the data in table above.

4. Discuss notable out-of-control conditions displayed in the completed X-bar • R (average and range) control charts. Only consider points outside the control limits. Do not consider runs, set of points within certain zones, and so on.

5. If the conditions you note could be defined as assignable conditions and they are removed from the process, what will happen to the X-bar • R control chart?

(a) Remove the data related to the out-of-control points you observed from the original data and recalculate a new X-bar-bar, R-bar, and associated control limits.

(b) Create new X-bar • R (average and range) control charts from your updated data.

6. Discuss how the two sets of control charts are different. What has changed?

Problem 1:

Calculate X-bar-bar, R-bar, and associated control limits using the data in the table above and create X-bar • R (average and range) control charts.

Solution:

1. Using the template provided, click on the Data and Calculation tab. In the upper left corner, enter 30 for the number of samples and enter 4 for the sample size.

2. Enter the data into the yellow data area. Note: You will have to rotate your data to fit this table. When you are done you should have 30 observations (30 columns ), each with four results.

3. The template does all the calculations and plotting. The calculations are grouped into two parts, one for Averages (top group) and one for Ranges (bottom group). The X-bar-bar number we want in the top set of results titled Center. X-bar-bar = 5.057. The Center result the bottom set of data is R-bar. R-bar = 1.069.

3. Click on the X-bar Chart tab to view the X-bar chart; you should see a chart that looks like the one below. (It’s called an X-bar chart because you plot averages, or X-bars, on it.) We can see that one point, Point 22, is below the lower control limit (LCL).

4. Click on the R-Chart tab to view the R-chart and you should see a chart that looks like the one below. No points outside the control limits can be seen.

5. We now have enough information to answer Questions 1, 2, and 3 in the case study.

Problem 2:

If the conditions you note could be defined as assignable conditions and they are removed from the process, what will happen to the X-bar • R control chart? Calculate new X-bar-bar, R-bar, and associated control limits, and create a new X-bar • R (average and range) control charts.

Solution:

1. Click on the Data and Calculations tab. Point 22 was noted as being out of control. Highlight the data results (four numbers) under 22 and press Delete on your keyboard.

2. Highlight all the data for points 23–30. Right click and select Copy, then paste the data into the top blank cell under 22.

3. Delete the four data points under 30 by highlighting them and pressing Delete on your keyboard. You new data table should look like the following.

4. In the upper left corner, change the number of samples from 30 to 29. If you forget to do this, the control limit calculations will not be correct. Do not change the sample size.

6. Your new means and control limits have been recalculated and are as follows.

7. Click on the X-bar Chart tab to view the X-bar chart; you should see a chart that looks like the one below. No points outside the control limits can be seen.

8. Click on the R-Chart tab to view the R-chart and you should see a chart that looks like the one below. No points outside the control limits can be seen.

9. We have enough information to complete Steps 4a and 4b.

Problem 3:

How are the two sets of control charts different? What has changed?

Solution:

1. First, the most obvious observation we can make is that when we remove Point 22, the new control chart does not have any out-of-control points.

2. With the removal of Point 22, we can see the new X-bar-bar has increased, while the new R-bar has decreased.

3. We can also see the Control Limits on the new X-bar and R-charts have changed as well. The control limits for the X-bar chart have come tighter, which should not surprise us, because we removed the point that was outside the lower control limit. No changes occurred to the control limits of the range chart.

4. We have now have enough information to produce the Word document to complete the project.

44.24.44.64.855.25.45.65.86135791113151719212325272931333537394143454749

AveragesSample number

X-bar Chart

AveragesLower control limitUpper control limitCenter line

0

0.5

1

1.5

2

2.5

3

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

R

a

n

g

e

s

Sample number

R

-

Chart

Ranges

Lower control limit

Upper control limit

Center line

Average

4.603

LCLx-bar

4.315

Center

5.091

UCLx-bar

5.867

Range

0.68

LCLrange

0

Center

1.064

UCLrange

2.429

44.24.44.64.855.25.45.65.86135791113151719212325272931333537394143454749

AveragesSample number

X-bar Chart

AveragesLower control limitUpper control limitCenter line

00.511.522.53135791113151719212325272931333537394143454749

RangesSample number

R-Chart

RangesLower control limitUpper control limitCenter line