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asignment 2 QC

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ASSIGNMENT 2 – CONTROL CHART FOR VARIABLES MECHANICAL ENGINEERING DEPARTMENT QUALITY CONTROL – J5124 INSTRUCTION: ANSWER ALL QUESTIONS. 1. The following table gives the average and range in kilograms for tensile tests on an improved plastic cord. The subgroup size is 4. Determine the trial central line and control limits. If any points are out of control, assume assignable causes and calculate revised limits and central line. SUBGROUP NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 R 476 466 484 466 470 494 486 496 488 482 498 464 484 32 24 32 26 24 24 28 23 24 26 25 24 24 SUBGROUP NUMBER 14 15 16 17 18 19 20 21 22 23 24 25 R 482 506 496 478 484 506 476 485 490 463 469 474 22 23 23 25 24 23 25 29 25 22 27 22 (25 Marks) 2. Control charts for the and s are to be established on the Brinell hardness of hardened tool steel in kilograms per square millimeter. Data for subgroup sizes of 8 are shown below. Determine the trial central line and control limits for the and s charts. If any points are out of control, assume assignable causes and calculate revised limits and central line. SUBGROUP NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 s 540 534 545 561 576 523 571 547 584 552 541 545 546 26 23 24 27 25 50 29 29 23 24 28 25 26 SUBGROUP NUMBER 14 15 16 17 18 19 20 21 22 23 24 25 S 551 522 579 549 508 569 574 563 561 548 556 553 24 29 26 28 23 22 28 33 23 25 27 23 (25 Marks) ASSIGNMENT 2 – CONTROL CHART FOR VARIABLES 3. Control charts for the and R are kept on the weight in kilograms of a color pigment for a batch process. After 25 subgroups with a subgroup size of 4, = 52.08 kg (114.8 lb), = 11.82 kg (26.1 lb). Assuming the process is in a state of control, compute the and R chart central line and control limits for the next production period. (8 Marks) 4. Control charts for and s are maintained on the resistance in ohms of an electrical part. The subgroup size is 6. After 25 subgroups, = 2046.5 and = 17.4. If the process is in statistical control, what are the central line and control limits? (8 Marks) 5. A new process is started, and the sum of the sample standard deviation for 25 subgroups of size 4 is 750. If the specifications are 700 80, what is the process capability index, Cp? (10 Marks) 6. What is the Cpk value for the information in Question 5 when the process average is 700, 740, 780 and 820? Explain. (24 Marks)
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