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Material Requirements Planning e-book |
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Material Requirements Planning e-Book details - a practical, down to earth, run through the logic of material requirements planning which underpins all MRPII (manufacturing resource planning) and ERP (enterprise resource planning) systems. The e-Book explains how the process works, step by step and how to set up the process to provide the level of control you require. The book starts from the requirements for the input information and then shows how you can use the basic planning parameters of lead times, order policies and safety stock to manage and control the flow of information through the system. Finally the e-Book explains re-planning techniques to optimise and fine tune the plan as external factors change.
Contents:
You can purchase this e-book by credit card for £4.95 (about US$8 or €7) by clicking the "Buy Material Requirements Planning E-Book" image at the top of this page.
Cumulative Lead Time
The cumulative lead time for part 123 is the total time required to make part 123 from scratch and can be calculated from the lead times shown in the diagram. Every part has its own lead time and a cumulative lead time. For a purchased item like 405, the lead time and the cumulative lead time are the same, 15 days. The cumulative lead time of part 303 is 18 days, 15 days to purchase 405 plus 3 days to make it into part 303. For part 201 the cumulative lead time is 26 days, the longest cumulative lead time of its components, 18 days for part 303, plus 8 days for 201. For part 123 the cumulative lead time is 30 days, which is again the longest cumulative lead time of its components, 18 days for 201, plus 4 days to make 123. You can think of the cumulative lead time as the critical path or, if you drew the manufacture of the part on its side, as a timed Gantt chart, as the part which “sticks out” the furthest.
The importance of the cumulative lead time from a material planning point of view is that beyond the cumulative lead time, changes to the schedules can be accommodated without disrupting the flow of any active purchase orders or works orders at least from a material point of view. Inside the cumulative lead time changes may not be possible due to a shortage of one or more components and even those changes that are possible could cause disruption to current works orders, planned orders and/or purchase orders. Large increases to the schedule inside the cumulative lead time for one customer may therefore have a detrimental effect on other customers. Large reductions in schedules can result in surplus material and idle capacity.
It is important to notice that the cumulative lead time includes the lead time of purchased items. It is a measure of the importance of relationships with vendors to note that your vendors’ lead times, as part of the cumulative lead times, are integral to your planning process. Changes to a purchased part’s lead time affect the cumulative lead time of all parts that use the part. Purchase lead times are often longer than internal lead times.
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