Question: FB Badpoore Aerospace makes carbon brake discs
FB Badpoore Aerospace makes carbon brake discs for large airplanes with a proprietary “cross weave†of the carbon fibers. The brake discs are 4 feet in diameter but weigh significantly less than conventional ceramic brake discs, making them attractive for airplane manufacturers, as well as commercial airliners.
Processing the discs at FB Badpoore requires heat treating the discs in a sequence of 12 electric, high pressure, industrial grade furnaces (simply called Furnace A, Furnace B, Furnace C, . . . , Furnace L), each of them fed with a proprietary mixture of chemicals. All brake discs visit each of the 12 furnaces in the same order, Furnace A through Furnace L. Each of these furnaces follows its own very specific set of simultaneous temperature and pressure profiles. An example of one such profile is depicted in Figure 13.6. All profiles are 12 hours in duration.
All 12 furnaces are top loading. Additionally, each of them is cylindrical in shape, 15 feet in diameter, and about 10 feet in depth. They are arranged in an “egg-carton-like†array (six on one side and six on the other), loaded and unloaded via their top facing round ends by three overhead 10-ton bridge cranes, and located in part of the factory known as the furnace deck.
Each furnace can process seven stacks of 20 discs at a time. This equates to a batch size of 140 discs. Each batch is loaded onto a ceramic furnace shelf that is sturdy, round, and 14 feet in diameter. The furnace deck is said to be fully loaded when all 12 furnaces are processing discs.
Loading and unloading the discs is a labor-intensive process requiring high-level coordination of the three overhead bridge cranes. Bridge crane Alpha (BC-A) serves the incoming area; furnaces A, B, K, and L; and the outgoing area, where discs are stored when they have finished processing in all 12 furnaces. Bridge crane Beta (BC-B) serves Furnaces C, D, I, and J, while bridge crane Gamma (BC-G) serves Furnaces E, F, G, and H. When discs travel within a service area, they are moved by the crane assigned to that area. When discs have to travel between service areas, they are first deposited in a waiting area before being moved into the next service area. For example, discs being moved from Furnace D to Furnace E would be unloaded from Furnace D by BC-B, which would deposit them in the waiting area. Then BC-G would pick up the batch and load it into (an already empty) Furnace E.
Due to energy restrictions by the local electric utility company, all furnace processing must be performed at night between 8:00 p.m. and 10:00 a.m. daily. This, in turn, requires all loading and unloading operations to be performed during the day. Indeed, the main shift is from 1:00 p.m. (allowing the discs to cool after processing and before unloading) and 9:00 p.m. (allowing the shift to end by starting up all 12 furnaces after 8:00 p.m.).
Figure 13.6:
Each furnace has a known yield rate with no noticeable variation according to the following:
That is to say, 1 in 20 batches fails at Furnace A and must be scrapped, whereas only 1 in 1,000 batches fails at Furnace L. As one might expect, upstream batch failures are very disruptive to the downstream operations. Scrapping batches causes downstream furnaces to sit idle under the current “zero in queue†work in process (WIP) inventory policy as they wait for good batches to arrive from upstream operations. Design, build, and perform a 1,000-day simulation model study of the system described above in Excel, incorporating the random number generator function, RAND(). Start your simulation with a fully loaded furnace deck.
Discussion Questions
1. Determine and comment on the overall yield (the number of batches that make it all the way through Furnace L divided by the number that started at Furnace A) of disc brakes at FB Badpoore.
2. Determine the utilization of Furnace L.
3. Suggest improvements to the system.
Transcribed Image Text:
Pressure (kPa) Temperature (C°) 12 hours FURNACE A В C D E F H I J K L Yield 0.95 0.975 0.975 0.975 0.975 0.975 0.975 0.995 0.995 0.995 0.995 0.999
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