EXERCISES AND STUDY QUESTIONS FOR CHAPTER 4

1. A 12-station automatic assembly line has a station cycle time of 18 seconds, including index time. Calculate ideal line production rate per hour and throughput time.
2. A six-station dial indexing machine is driven by a geneva with driver rotation at 18 rpm. What are the production and throughput times of this machine?
3. An eight-station geneva with driver rotation 24 rpm is compared to a six-station geneva with driver rotation 20 rpm. Which system has the faster production rate? Which has the faster throughput?
4. An assembly system has five sequential stations with no storage between stations. Ideal production rate for the system is 150 units per hour. With station malfunctions, the actual production rate deteriorates to 120 units per hour. What is the percent downtime? What is the ideal throughput time? What is the actual throughput time?
5. A dial-indexing geneva assembly machine with an ideal cycle time of four seconds has a throughput time of 20 seconds. How many stations are in the system? What is the rpm of the driver?
6. Assume a station reliability of .99 for each of the stations in the dial-indexing system in Exercise 4.5, that is, on the average a malfunction will occur approximately once in 100 cycles. Every malfunction stops the entire machine and requires ten minutes to clear. What is the actual production rate of the system, taking into consideration downtime to clear malfunctions?
7. A six-station assembly machine has zero storage between stations and a breakdown rate of 2 percent for each station. Average time to clear a breakdown and restart the line is ten minutes. With an ideal cycle time of ten seconds for this machine, including index time, what is its actual production rate? Calculate the production efficiency. Calculate the ideal and actual throughput times.
8. In Exercise 4.7, suppose the station breakdown rate could be cut in half by introducing a component-quality improvement project that includes a more stringent receiving inspection of purchased parts, vendor rating, and closer specified tolerances on both purchased parts and parts fabricated in-house. How much would this improve the efficiency of the assembly machine?
9. A ten-station automatic assembly line with no buffer storage has a normal cycle time of three seconds when no malfunctions occur. To allow for parts jams, which require two hours to repair, the system is designed to tolerate a total average cycle time of ten seconds. For the sake of discussion, let us assume that the only reason that a cycle will malfunction is when an out-of-tolerance piece part jams it, Will the ten-second cycle time limit be met if the piece-part quality is "three sigma"?
10. In Exercise 4.9, suppose the piece-part quality is "four sigma." What would be the total average cycle time and production rate?
11. In Exercise 4.9, what piece-part quality would be required to hold system downtime to less than half the total average cycle time?
12. In Exercise 4.9, what piece-part quality would be required to hold system downtime to 10 percent of total average cycle time?
13. An eight-station automatic assembly line has buffer storage between stations of capacity 50 units each. The eight stations are reasonably similar in operating characteristics and downtime. How many units would you recommend to be in each buffer storage when the system is operating normally?
14. What procedure would you recommend for initial startup and loading of the eight station automatic assembly line described in Exercise 4.13?
15. Calculate average throughput time for the eight-station automatic assembly line described in Exercise 4.13.
16. (Design Case Study) Suppose a 50~-station transfer line with no storage or slack between stations is being planned for a major automation thrust in the manufacturing plant where you are employed as the automation engineer. A cycle time objective has been set at 12 seconds in order to meet production quotas of 2000 units per eight-hour shift. The plant manager is very excited about this new major automation project and plans to invite top management from corporate headquarters to observe the fruits of automation as soon as you are able to get the operation on-stream. Would you share in the plant manager's optimism about the project? Do you think the eight-hour shift production quota of 2000 units is realistic? Is the production quota compatible with the cycle time objective? If all preventive maintenance is performed on another shift so that theoretically the line could operate during a full eight-hour shift, what would be the ideal production rate for this line? What is the maximum average station breakdown rate per cycle to be tolerated if the average time required to service a line breakdown and restart the line is six minutes?