IFS Cloud Routing Lead Time: Fixed, Variable and Overlap

The calculation produces a lead time for a manufactured part, and the page states that routing lead time is used in several places, among them MRP and Master Scheduling. The MRP page adds that for a manufactured or remanufactured part MRP calculates the lead time for a supply based on the valid routing.

Routing lead time calculations can be based on machine time, labor time or the maximum of machine and labor time. The calculation considers setup, transport and operation times, efficiency factor, overlap and eventually also the operation quantity factor entered for the operations. It also considers the information about queue time and shifts, such as the number of work hours per day, from the work center. The result can be calculated for the current and future revisions and for all routing alternates for a part, and optionally the inventory part can be updated with the lead time calculated for the default routing alternate and the current revision.

The capacity basis is a further choice. The page explains that the average capacity represents the projected usage based on the current work center parameters, and the demonstrated capacity represents the past actual usage. The planning side is covered in dynamic structures in MRP.

Fixed time does not depend on the lot size, and variable time is time per unit. The page states the sums for a routing alternate having no parallel or overlapping operations: the fixed lead time is the sum of setup time, transport time and queue time for all operations, and the variable lead time is the sum of machine or labor time for all operations.

Queue time is added as fixed time. The page notes that in its examples the work centers are assumed to have no queue time, and that if queue time had been defined, that time would be added as a fixed lead time. The calculation takes the queue time and the shifts from the work center, so that data belongs in the review.

The lot size is normally the standard lot size specified on the inventory part. If an Operation Qty Factor is defined for an operation, that percentage of the standard lot size is used for it.

The page also says it is possible to simulate lead time for other lot sizes using Calculate Lead Time from the Routing, Routing Alternate or Routing Alternates pages. A simulation is the way to see what a different lot size does to the total before anyone changes the standard lot size of the part.

For parallel operations only the operation that takes the longest to complete is considered when calculating the fixed and variable lead time. A shorter operation that runs in parallel therefore adds nothing to the total, and changing its time has no effect unless it becomes the longest.

Overlap lets a succeeding operation start before the preceding operation has finished, and it is defined on the routing operation. The page on operation overlap belongs to scheduling and not to the lead time calculation. It states that the overlap time can be defined either as a percentage of the preceding operation’s scheduled manufacturing lead time or as a number of units. It also states that if the part routing has operation overlap defined, the lead time calculation will accommodate the overlap times and the calculated lead time value will be reduced.

The two pages state limits that matter for data maintenance:

• For an operation that overlaps with the previous operation, the contribution depends on the overlap and on the difference in run time between the operations.
• It will not be possible to finish the succeeding operation before the preceding operation’s scheduled end time plus transportation time plus the time it takes the succeeding operation to manufacture the last delivered overlap quantity.
• If an overlap time is defined on the first operation in an operation structure, with no defined preceding operation, it has no effect.
• Operations defined as parallel simply overwrite the overlap functionality.

The routing page is explicit that the formula does not cover calculations for operations with overlap, so the fixed and variable sums of section 2 hold only for routings without overlap. The overlap information is transferred automatically to the order operation when an order operation is created from a routing revision, and it can be modified there.

The page works examples with a lot of 5 pieces, and three of them show how the total follows from the inputs.

The page also contains an example whose stated fixed time and calculated total do not agree with each other, and this article does not use it. Where a page example and its formula disagree, test the routing in your own system and compare.

The routing figure assumes that all parts are available from inventory. When components can be missing, the expected lead time field is the one the documentation points to, as described in the lead time article. Order promising is covered in high-fidelity discrete order promising and, for capable-to-promise, in CTP in IFS Cloud.

Manufacturing engineering owns the routing times, the overlap definitions and the work center queue time, and planning owns the standard lot size and the choice between average and demonstrated capacity. Agree who changes each value and how often it is reviewed. A related argument about static manufacturing set-up is made in the architectural failure of static manufacturing.

Test routing lead time with one routing per case, calculate the expected total by hand from the page’s rules, and compare it with the system’s result.

Routing data is ready for go-live when each of the checks below has a record behind it.

1. Setup, transport and run times are entered for every operation.
2. Queue time is defined on the work centers and its source is known.
3. The standard lot size is set on the inventory part, and any operation quantity factor is intended.
4. Parallel operations are marked and the longest one is the one that should count.
5. Overlap is defined as a percentage or in units, and operations defined as parallel do not also carry overlap.
6. The capacity basis, average or demonstrated, is decided.
7. The five test cases are recorded with evidence.
8. Each value has an owner and a review date.

Dariusz Myśliwiec: 18 years hands-on with IFS, including IFS Cloud. Based in Kraków, delivering remotely across Europe and globally through an independent practice. You talk to the consultant who does the work, not a sales layer.

IFS is a registered trademark of IFS AB; this practice is not affiliated with IFS AB.