Exam 16: Quality Control and Spc

A Proctor and Gamble factory process fills boxes with detergent. Construct an appropriate set of control charts to monitor the process. Historical data for fill weight (in ounces) of eight samples is presented below. A sample size of eight was used. Sample Sample Mean Sample Range 1 15.80 0.42 2 16.10 0.38 3 16.02 0.08 4 15.95 0.15 5 16.12 0.42 6 16.18 0.23 7 15.87 0.36 8 16.20 0.40 a.Compute the limits for both an R-chart and x-bar chart. Compare the sample results to the limits of the charts. b.Briefly explain what the quality control charts tell you. What actions, if any, would you take?

Common causes of variation:

The time to check out guests at a hotel front desk was measured over the course of several weeks. Management believes that the target time for checking out guests should be between 2 and 3 minutes with a target of 2.5 minutes. The data gathered for the actual process had a mean time of 2.75 minutes with a standard deviation of 0.45 minutes. Find and interpret Cp, Cpl, Cpu, and Cpk in the context of this situation. Which one of the following statements is TRUE?

Larger sample sizes allow smaller changes in process characteristics to be detected with higher probability.

Fifteen samples of size 5 have been taken from a production process. The sum of the sample averages was found to be 92.54 cm, while the sum of the ranges was 115.36. Find the values of the center lines for the x-bar and R-charts.

Common causes of variation generally accounts for about 80 to 90 percent of the observed variation within a process.

Common causes of variations generally accounts for about 10 to 15 percent of the observed variation within a process.

Quality control ensures that a good or service conforms to specifications and meets customer requirements.

Testing whether a computer boots up the first time is an example of _____.

Quality control of front-office operations in services uses the same techniques that are applied in manufacturing.

A plastic cell phone case has been experiencing physical quality control problems. That is, the clear screen does not always fit (and snap into place) on the case. The dimensions of the screen have consistently been in statistical process control (SPC). A root cause quality initiative collected the following data about the plastic cell phone case. Analyze the width of the cell phone case using control charts and make a recommendation. Table 1 Cell Phone Plastic Case Widths in Centimeters Data* Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Observation \#1 6.02 5.92 5.88 5.99 6.05 5.94 6.00 \#2 5.97 5.83 5.97 6.08 6.06 5.96 5.95 \#3 5.90 5.87 5.88 6.08 5.98 5.99 5.82 Average 5.963 5.873 5.91 6.05 6.03 5.963 5.923 Range 0.12 0.09 0.09 0.09 0.08 0.05 0.18 *The sample averages and ranges helps in avoiding simple math errors and quickens the time to complete the SPC analysis. -Given the previous results and analysis for the R-chart, one would:

Five samples are taken, with five observations each. The sample findings are listed below. The sample values represent service times in minutes. ObservationNumber 1 2 3 4 5 1 10.1 10.6 9.8 9.9 10.9 2 9.7 9.5 10.3 9.9 10.5 3 10.1 10.7 9.2 10.0 10.1 4 9.9 9.8 10.5 10.4 10.1 5 10.4 10.1 10.9 9.9 10.3 a.Determine the control limits for the R-chart. b.Can it be concluded that the R-chart is in statistical control and proceed to develop the x-bar chart?

What is the purpose of a process capability study and what is a process capability index?

A system governed only by common causes is called a stable system.

In developing process control charts, if special causes are present, then they are not representative of the true state of statistical control, and the calculations of the center line and control limits will be biased.

If no special causes affect the output of a process, the process is said to be _____; and if special causes are present, the process is said to be _____.

A company that makes handheld computers is trying to improve one of its poorer selling products. They conducted some customer surveys and found that customers prefer the product to weigh between 10 and 14 ounces. At present, the mean of the process is 12 ounces and the standard deviation of the process is 0.4 ounces. They want to ensure that the production process will meet customer expectations; that is, the process capability index (C_p) will be greater than or equal to 1.00. a.What is the C_p of the current production process? b.What does the standard deviation of the process have to be for the C_p to equal 1.00?

Both the p-chart and c-chart use continuous data.

Flaws are counted on a standard steel plate (sheet). Each sheet has the exact same dimensions. If 10 sheets are selected at random and the number of flaws per sheet is as follows, determine the lower and upper control limits. Sheet Number of Flaws 1 3 2 1 3 3 4 0 5 2 6 2 7 0 8 1 9 1 10 2 The upper control limit (UCL) for the steel plate control chart is _____.

A c-chart _____.