RP, ERP in the early commitment of the orders, plans are important to set parameters. Most of the advance of the concept is easy to obtain. Queuing time (Queue Time) theoretical explanation of the ERP feel more mysterious, abstract and metaphysical are not sufficient to guide practice. ERP required textbook way, also need case studies of the device. This article talk a "device."
Ahead of many, mainly 2 large family, order lead time and production (manufacturing) lead. Order lead time is the sum of the following composition of lead:
Product Design Lead
Procurement Lead
Production lead time
Other treatments lead
Release lead
Among them, the production lead time can be further broken down into:
Production lead time
Production lead time
Demolition time
Wait time
Transit time
Queuing time
Most ERP software include at least the production lead time, production lead time, transit time, queuing time.
Queuing time is the work of the center workpiece to reach waiting time. In the work center to become the bottleneck of the process route, the queuing time arises.
When the technology to work on the center line does not match the processing capacity, the bottleneck will result, queuing time will result. Figure 1.
Figure 1
Work centers on the process line, although the matching processing capacity, but the number of product lines in the work centers on the process cross, the bottleneck will result, queuing time will result. Figure 2.
Figure 2
Work center queue time is often dynamic.
Yield fixed the dynamic, for example, generally the work center a batch / hour, the bottleneck work center 0.5 batch / hour, the processing of cases in the bottleneck work center queue time, batch 1 is 0 hours 1 hour 2 is approved, the first 3 batches of 2 hours 3 hours 4 is approved, ... ..., 8th is 7 hours.
At present most of the ERP software is only a static set of queuing time, textbooks should be based on historical data that averaging set. The above example, queuing time to take 3.5 hours. There are no more reasonable settings, we analyze the work center's calendar, work centers 1, 2 job centers, work centers should be 8 hours 4 calendars, work centers should be 16 hours 3 calendar. Otherwise, the work center 3 OEM products will queue full of workshops, full of plants. We look at the first four batches of 2 if the work center output in the first 5 hours, 3 in the work center queue processing 2 hours 3 hours, the work center 4 has been off work. 5th batch, batch 6, 7 approved, 8 groups of people, so we can say that 5 to 8 award award although a longer waiting time, but they use the "spare time." Now we get the arithmetic average queuing time is 1.5 hours ((0 +3) / 2). Since the 8th of 7 hours queuing time is the use of "amateur" time, queuing time is 0 hours, so we get the weighted average queue time is 1.5 hours.
Discrete manufacturing is not practical as the process type as a stable rhythm. Fluctuations in production, work in different parts machining line in the center stack, queue processing center will lead to fluctuations in queue length, using the above method, to the right time to the processing center to adjust the time line is necessary.
In essence, in the manufacture of discrete time queue is dynamic. Conditions for calculating queue is full time. However, existing ERP software bottleneck work centers on the dynamic queue time is very limited processing power, APS, and TOC theory is the way to solve this problem.
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