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For items that you plan and cost by the same lot size, you can specify a value only for the standard lot size. Bills of Material then computes manufacturing lead time using the standard lot size quantity.
Note: If an item's routing references another item's routing as a common, set both items' lead time lot size to the same value. If you do not specify a lead time lot size, ensure that both items' standard lot sizes are equal.
For items that you plan with one lot size and cost with a different lot size, you can enter a lead time lot size. Bills of Material then calculates manufacturing lead time using this value (rather than the standard lot size). If an item does not have a value for the standard or lead time lot size, Bills of Material uses a quantity of one to compute manufacturing lead times.
Note: If you enter a lead time lot size for an item, consider the item's planning lot size to accurately offset lead times. For planned items with a fixed order quantity, set the lead time lot size to the fixed order quantity. If a planned item has varying lot sizes, assign a lead time lot size that represents the typical lot size.
When computing manufacturing lead times, primary routings are automatically updated with lead time and offset percents. As with the item lead time attributes, you can also manually assign these values.
For example, if an item's manufacturing lead time is two days and the primary routing has two operations with the same duration (1 day), the first operation's lead time percent is zero and the second operation's lead time percent is 50%.
For example, both operations in the previous example for lead time percent require one day(eight hours) to perform. If you have two different resources assigned to the second operation, and each resource requires four hours to complete their task, the offset percent is 50% for the first resource and 75% for the second resource.
A value of zero is assigned to the fixed, variable, and processing lead times of a manufactured item that does not have a routing and is not assigned to a production line.
Using detailed scheduling, fixed and variable lead times are computed as the difference between the total time required for two scheduled jobs. In other words, Bills of Material plots total time required for a work in process job as a function of order quantity for both order quantities and computes the slope of the line that the two points define.
Attention: Although Bills of Material uses detailed scheduling to compute lead times, all calendar days are considered workdays regardless of days off, workday exceptions, or shift exceptions.
Bills of Material uses the following formulas to compute fixed and variable lead times:
Schedule a job for zero quantity beginning on the system date and compute fixed lead time as follows:
Schedule a job for the lead time lot size beginning on the system date and compute variable lead time (rate) as follows:
The following terms apply to repetitive schedules:
| Day | A day is equal to the number of hours the production line is active. If the line is active from 8:00 to 16:00, the day is 8 hours long. |
| Production Rate (Line Speed) | The number of assemblies built per line, per hour. |
| Line Fixed Lead Time | The fixed lead time of the production line, that is, the amount of time for one assembly to travel down a production line. |
| Production Interval | The time between two assemblies on a production line. If the production rate (line speed) is 10 assemblies per hour, then the production interval is .1 hours or once every .0125 days, or 1/(10*8), for a line that runs 8 hours per day. |
1 / (production rate * day)
The Calculate Manufacturing Lead Times program calls the scheduler twice, first using a quantity of 1, then using a quantity of 0. For each case, the scheduling lead time (expressed in days) is returned. This is the total time taken to build the assemblies. The program then converts the two values into the fixed lead time and the variable lead time item attributes, respectively.
illustrates how scheduling lead times are calculated:
| Assembly's Routing | Scheduling Basis | Quantity | Scheduling Lead Time |
|---|---|---|---|
| No routing | routing | 0 | 0 |
| 1 | production interval | ||
| fixed | 0 | line fixed lead time | |
| 1 | line fixed lead time + production interval | ||
| Assembly with item-based resources only | routing | 0 | fixed lead time - production interval |
| 1 | (fixed lead time - production interval) + production interval | ||
| fixed | 0 | line fixed lead time | |
| 1 | line fixed lead time + production interval | ||
| Assembly with item- and lot- based resources | routing | 0 | fixed lead time - production interval |
| 1 | (fixed lead time - production interval) + production interval | ||
| fixed | 0 | line fixed lead time | |
| 1 | line fixed lead time + production interval | ||
| Table 4 - 30. (Page 1 of 1) | |||
For fixed lead time lines, the fixed and variable lead times are not based on whether a routing exists. The fixed lead time is always the line fixed lead time, the amount of time for one assembly to travel down a production line. The variable lead time is always the production interval:
For a routing-based line, the fixed lead time is the time required to build one assembly; the fixed lead time includes the time for both item and lot-based resources.
Processing lead time is presented in whole days rounded to the next day.
For example, if the routing operations for item A had the following start dates (on a job for 10 assemblies), Bills of Material would compute and update the following operation lead time percentages:
Bills of Material also computes, for each operation resource in an item's primary routing, the percent of total lead time required for previous resource operations in that routing.
For example, if your resource start and end times were as follows, Bills of Material would compute these resource offset percents:
Calculating Manufacturing Lead Times
Overview of Work in Process Scheduling
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