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home / study / business / operations management / questions and answers / the dean door corporation (ddc) manufactures steel ... Question The Dean Door Corporation (DDC) manufactures steel and aluminum exterior doors for commercial and residential applications. DDC landed a major contract as a supplier to Walker Homes, a builder of residential communities in several major cities. Because of the large volume of demand, DDC had to expand its manufacturing operations to three shifts and hire additional workers. Not long after DDC began shipping doors to Walker Homes, it began receiving some complaints about excessive gaps between the door and the frame. This problem was somewhat alarming to DDC, because its reputation as a high-quality manufacturer was the principal reason that it was selected as a supplier to Walker Homes. DDC placed a great deal of confidence in its manufacturing capability because of its well-trained and dedicated employees, and it never felt the need to consider formal process control approaches. In view of the recent complaints, Jim Dean, the company president, suspected that the expansion to a three-shift operation and the pressures to produce higher volumes and meet just-in-time delivery requests was affecting their quality. On the recommendation of the plant manager, DDC hired a quality consultant to train the shift supervisors and selected line workers in statistical process control methods. As a trial project, the plant manager wanted to evaluate the capability of a critical cutting operation that he suspected might be the source of the gap problems. The nominal specification for this cutting operation is 30.000 inches with a tolerance of 0.125 inches; therefore, the upper and lower specifications are LSL = 29.875 inches and USL = 30.125 inches. The consultant suggested inspecting five consecutive door panels in the middle of each shift over a ten-day period and recording the dimension of the cut. Table 1 shows 10 days data collected for each shift. Having seen the data (Table 1) in this initial study, Jim wants to know answers to the following questions: Is the process in a state of statistical control? Why or why not? If the process is out of control, what might be the likely cause(s)? What recommendations might you make to improve the situation i.e., reduce or eliminate the cause(s)? Finally, is the process capable of meeting the specifications given? Why or why not? The plant manager implemented the recommendations that resulted from the initial study. Because of the success in using control charts, DDC made a decision to continue using them on the cutting operation. After establishing control, additional samples were taken over the next 20 shifts, shown in Table 2. Jim now wants to know: Has the process changed? Explain Is the process capable? Explain Shift Operator Sample 1 2 3 4 5 1 Theo 1 30.046 29.978 30.026 29.986 29.961 2 Jolene 2 29.972 29.966 29.964 29.942 30.025 3 Don 3 30.046 30.004 30.028 29.986 30.027 1 Theo 4 29.997 29.997 29.980 30.000 30.034 2 Jolene 5 30.018 29.922 29.992 30.008 30.053 3 Don 6 29.973 29.990 29.985 29.991 30.004 1 Theo 7 29.989 29.952 29.941 30.012 29.984 2 Jolene 8 29.969 30.000 29.968 29.976 29.973 3 Chuck 9 29.852 29.978 29.964 29.896 29.876 1 Theo 10 29.987 29.976 30.021 29.957 30.042 2 Jolene 11 30.028 29.999 30.022 29.942 29.998 3 Don 12 29.955 29.984 29.977 30.008 30.033 1 Theo 13 30.040 29.965 30.001 29.975 29.970 2 Jolene 14 30.007 30.024 29.987 29.951 29.994 3 Don 15 29.979 30.007 30.000 30.042 30.000 1 Theo 16 30.073 29.998 30.027 29.986 30.011 2 Jolene 17 29.995 29.966 29.996 30.039 29.976 3 Don 18 29.994 29.982 29.998 30.040 30.017 1 Theo 19 29.977 30.013 30.042 30.001 29.962 2 Jolene 20 30.021 30.048 30.037 29.985 30.005 3 Chuck 21 29.879 29.882 29.990 29.971 29.953 1 Theo 22 30.043 30.021 29.963 29.993 30.006 2 Jolene 23 30.065 30.012 30.021 30.024 30.037 3 Chuck 24 29.899 29.875 29.980 29.878 29.877 1 Theo 25 30.029 30.011 30.017 30.000 30.000 2 Jolene 26 30.046 30.006 30.039 29.991 29.970 3 Don 27 29.993 29.991 29.984 30.022 30.010 1 Theo 28 30.057 30.032 29.979 30.027 30.033 2 Jolene 29 30.004 30.049 29.980 30.000 29.986 3 Don 30 29.995 30.000 29.922 29.984 29.968 TABLE 2 Observations Shift Operator Sample 1 2 3 4 5 1 Theo 31 29.970 30.017 29.898 29.937 29.992 2 Jolene 32 29.947 30.013 29.993 29.997 30.079 3 Don 33 30.050 30.031 29.999 29.963 30.045 1 Theo 34 30.064 30.061 30.016 30.041 30.006 2 Jolene 35 29.948 30.009 29.962 29.990 29.979 3 Don 36 30.016 29.989 29.939 29.981 30.017 1 Theo 37 29.946 30.057 29.992 29.973 29.955 2 Jolene 38 29.981 30.023 29.992 29.992 29.941 3 Don 39 30.043 29.985 30.014 29.986 30.000 1 Theo 40 30.013 30.046 30.096 29.975 30.019 2 Jolene 41 30.043 30.003 30.062 30.025 30.023 3 Don 42 29.994 30.056 30.033 30.011 29.948 1 Theo 43 29.995 30.014 30.018 29.966 30.000 2 Jolene 44 30.018 29.982 30.028 30.029 30.044 3 Don 45 30.018 29.994 29.995 30.029 30.034 1 Theo 46 30.025 29.951 30.038 30.009 30.003 2 Jolene 47 30.048 30.046 29.995 30.053 30.043 3 Don 48 30.030 30.054 29.997 29.993 30.010 1 Theo 49 29.991 30.001 30.041 30.036 29.992 2 Jolene 50 30.022 30.021 30.022 30.008 30.01
Explanation / Answer
1) The process is in statistical control if you allow the devition provided +/- 0.125 as every reading is in range specified. though for a perfect item you must have perfect reading but as approved is within limits.
2) If the process is out of control then the main reason behind this would be either error at the end of process or random error generation which went un-noticed. There can also be a reason that the company they are supplying would be having error in thier door size with possibility of less deviation allowed at their end, say +/- 0.025 that would be resulting in error.
3) I would suggest to overview the items supplied at their end with a consultant for rechecking the dimension at their end and also seeing thier part of deviation allowed. If deviation allowed at their end is less as compaired to the DDC their we might have to change the production process in accordance with the customer demand.
4) If the above techniques are followed then for sure their would be least amount of deviationa nd will also be able to deliver the items without any possible complain from buyer side.
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