9.(15 pts) The Ace Hexnut Company sells hex nut and bolt assemblies. Their rather primitive assembly method is to have the operator place the bolt, head down, into the holding fixture. The operator then places the hex nut on the threaded end and manually tightens the nut. The completed assembly is then removed from the fixture and placed in a shipping barrel. Each operator is provided with two fixtures, two stockpiles of raw material, and two shipping barrels. These materials permit the operator to simultaneously assemble two products at one time. The following elements have been developed for performing a time study: 1) Reach for and grasp bolt. 2) Place bolt in fixture. 3) Release bolt; reach for and grasp hex nut. 4) Place hex nut on end of bolt. 5) Fasten nut to bolt. 6) Place bolt in shipping barrel. Ten cycles were timed and each element was rated. These results appear in the table on the next page. (Note the timing data is in hundredths of a minute.) Use a PDF allowance of 12 percent. a. Calculate the standard time to complete one assembly b. How many hours per thousand are required? C . How many assemblies should the worker be able to complete in one hour? d. The worker normally is expected to earn $40 a day for this task. How many assemblies would the worker be expected to complete in a normal eight-hour work day? How much is the labor in each assembly worth? e. How would the standard be affected if element 5 were performed by an air wrench instead of manually? Is there a sufficient number of samples to have 90% confidence that the standard time you calculated is within 10% of the actual standard time to complete the assemblies? Cycles/Elements 1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 Rating 8 8 a 7 5 8 8 11 1 100 58 132 199 260 320 393 458 525 610 4 4 4 4 5 4 4 4 2 120 12 72 136 203 264 325 397 462 529 614 10 10 10 10 10 10 9 10 3 100 22 82 146 214 274 |335 407 472 538 624 5 7 6 6 6 5 6 6 5 6 4 110 27 89 152 220 280 340 413 478 543 630 25 27 26 25 27 37 29 28 b 26 5 80 52 116 178 245 307 377 442 506 593 656 8 8 8 8 8 6 100 60 124 186 253 315 385 450 514 664 a - sneeze b - dropped hex nut c - missed reading