Dynamic Lead Time
Dynamic lead time is production lead time that is dependent on order quantity as opposed to the information in fixed lead time.
Outcome
You understand how to use and calculate dynamic lead time both per manufacturing order and per operation, regarding within or beyond time fence, with or without shiftplanning, and forward and backward scheduling.
Dynamic lead time is used in both planning and executing manufacturing order.
Before you start
Whether lead time is fixed or dynamic is set for the product in field MO lead time method in 'Item. Connect Facility' (MMS003/F).
Lead time per manufacturing order
Lead time per manufacturing order (MO) is divided into the lead time to the first operation, the total lead time for each operation in the order, and lead time from the final operation to put-away.
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Start-up and transit time
Lead time to the first operation includes such considerations as safety time for short-term disturbances in component, capacity or tool availability. Lead time after the final operation includes such considerations as quality inspection, waiting time for transit, and transportation time to inventory.
These lead times are defined in 'Work Center. Enter Queue & Transit Time' (PDS020). The parameters include the phantom work center from which the time is counted. Lead time can only be set in workdays (to two decimal places). The transit U/M must be set for the first and last work center, respectively, so that lead time can be set.
Lead time for quality inspection can be included in queue and transit time or defined in the routing for an operation with fixed operation time at a work center for quality inspection.
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Lead time per operation
The lead time for an operation is the time required to complete the production step. It includes transit and other inter-operation time, queue time, setup time and production time.
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Planned total lead time
The start date for an MO is the same as when start-up is initiated, and the completion date is the same as when transit time is completed.
Calculating lead time per order
Dynamic lead time is calculated by totaling the lead time components defined for the product. A time fence in days is set to reduce the number of lead time calculations. When the finish date for an order is within the time fence, lead time is calculated using order quantity and available capacity. Actual load is also used when the work center is defined for finite loading. If the item has no time fence, the orders is calculated as if it used fixed leadtime. A time fence is set for each facility in 'Item. Connect Facility' (MMS003).
Lead times for released orders are always calculated as if they were within the time fence, regardless of the finish date.
The day factor that indicates the percentage available capacity at the work center in order for the up- or downstream work center to start the same day. It is specified per work center.
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Lead time beyond time fence
When beyond the time fence, lead time is calculated using the economic order quantity for the product. For this, the rated capacity per day is also considered, regardless of whether shift planning is used. Rated capacity per day is calculated using the work center data as follows:
(Capacity per unit and shift) x (Number of shifts) x (Utilization factor/100)
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Lead time within time fence
Within the time fence, lead time is calculated using the actual order quantity, considering the capacity calendar per work center. Also considered are whether shift planning is used, forward or backward scheduling is used, and whether scheduling is done using finite loading.
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Shift planning
When using shift planning, calculations are made to the minute. The start date and start time for downstream operations are calculated based on when the work center is open or available according to the capacity calendar. The open time for the receipt warehouse is checked against the capacity calendar of the work center with the final operation.
Example
Assume transit time is 6 hours, operation 1 ends at 16:00, and operation 2 is open from 08:00 - 08:30, 09:00 - 12:00 and from 12:30 - 20:00. Operation 2 will start at 10:30 the next day (16:00 + 6hrs = 22:00 > 20:00, so the operations starts 2 hours into the next day).
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No shift planning
When not using shift planning, calculations are made per day to two decimal places. The rated capacity per day and work center according to the capacity calendar represents the time the work center is available. The time the next operation can start is checked by comparing lead time to rated capacity.
Example
Assume transit time is 6 hours, operation 1 ends when 30% of the 12-hour rated capacity remains (approx. 4 hours), and rated capacity for operation 2 is 8 hours. Operation 2 will start 25% of a day (2 hours) into the following day ((6 - 4)/8 hrs) x 100 = 25%.
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Backward scheduling
Lead time is calculated starting at the entered time (if used, else the defined time on the order type ('General Distribution List. Open' (CRS250). on the order due date, or when the last shift ends (when using shift planning). Each lead time component is counted back to the start date. If the order is within the time fence, the calculation considers available capacity and load.
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Forward scheduling
Lead time is calculated from the entered time (if used, else the the defined time on the order type 'General Distribution List. Open' (CRS250) on the order start date or when the first shift starts (when using shift planning). Each lead time component is counted forward to the due date. If the order is within the time fence, the calculation also considers available capacity and load.
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Shift planning
Lead time per operation
The lead time for each operation is divided into queue time, external setup time, setup time, production time, and transit time. For fixed lead time, the lead time per operation is specified as the lead time offset for the operation start date. Transit and queue times do not affect lead time. Therefore, the description below is primarily for the components in dynamic lead time.
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Queue time
Queue time is the time an order waits at a work center before the operation is started. Queue time is defined (in workdays to two decimal places) in 'Work Center. Open' (PDS010). It cannot be changed for the operation.
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External setup time
External setup time measures setup that can be done while the work center is running. It is not included in load calculation or lead time. External setup is specified per operation. It is specified for the work center from which it is defaulted when the operation is created.
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Setup and production time
Setup and production time are the total operation time. The start date for the operation is the same as when setup is started. The finish date for the operation is the same as when production is completed. Total setup and production time equals the operation time.
Setup time is the time required to prepare and then close the operation. This normally has no relation to order quantity, but can vary depending on the previous operation at the work center (the tools used or items produced).
Production time is the time used for direct production of the order and is specified in the operation. It is calculated as the run time per unit multiplied by the order quantity per operation, divided by the number of resources in the work center. In work centers using machine time, a resource corresponds to the planned number of machines, and in work centers using labor time, to the planned number of labor units for the operation.
When calculating production time, the learning curve is taken into account by dividing run time for the operation by the efficiency factor.
Default setup and production times can be specified for the work center and copied to the operation when it is created. The time unit for the work center defines the unit (hours, minutes, or seconds) used and the price/time code for the operation indicates the quantity in which run and setup times are specified.
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Transit time
Transit time is the time needed to move the yield from one operation to the next. Negative transit time indicates overlapping.
The transit time to the next work center can be specified for the operation. A default transit time can be specified for the work center and copied to the operation when it is created. The transit time can also be set between any two work centers in PDS020 for when it is not set in the operation.
The Transit U/M field for the work center indicates how transit time is defined and the unit of measure, as follows:
U/M Sign Definition Days/hours
+
Slack – operation 2 starts X days/hours after operation 1 is finished.
Days/hours
–
Overlapping – operation 2 starts when X days/hours are left in operation 1.
Percent
+
Overlapping – operation 2 starts when X percent of operation time in operation 1 is left.
Quantity
+
Overlapping – operation 2 starts when X quantity is produced in operation 1.
Operation 1 is the upstream and operation 2 the downstream operation. X is the value for transit time.
Calculating lead time per operation
Lead time is calculated for an operation by totaling the parts as stated in the formula below.
Que + Set/Res + Pce * Qty/(Ptq * Res) + Trp,
where
Que = Queue time (days) * Work center capacity per day
Set = Setup time recalculated in hours based on the time unit selected
Res = Planned quantity resources (labor or machine, depending on work center capacity type)
Pce = Run time recalculated in hours based on the time unit selected
Ptq = Price per time unit on the operation
Qty = Order quantity for the operation (including planned scrap)
Trp = Transport time (days, hours, percentage, or quantity) in hours based on the capacity per day of the work center
Compressing lead time
With orders using dynamic lead time, the lead time can only be compressed if the lead time components are changed, or overlapping is implemented. This can be done by changing the operation start dates in 'MO Operation. Reschedule' (PMS020).
Example - Dynamic lead time with shift planning and backward scheduling
Assume the following to calculate dynamic lead time for shift planning and backward scheduling.
Op 020
|
Setup |
Runtime |
Queue |
|
|
Day 5 |
10:30-11:00 |
11:00-18:00 |
20:00-22:00 |
Op 010
|
Setup |
Runtime |
Queue |
|
|
Day 5 |
08:00-14:30 |
||
|
Day 4 |
08:00-12:00 |
13:00-16:30 |
|
|
Day 3 |
08:00-16:30 |
||
|
Day 2 |
13:36-14:51 |
13:36-14:51 |
Capacity
The capacity calendar for each work center indicates, in this example, when the product moved from the upstream operation can be received by the next (open time). Production is from Monday to Friday (five workdays per week). Each work center's capacity (operation capacity) is as follows.
|
Op. |
Open |
Cap/day |
|||
|---|---|---|---|---|---|
|
010 |
08:00-10:00 |
10:15-12:00 |
13:00-14:30 |
14:45-16:30 |
8 hrs |
|
020 |
05:00-08:00 |
09:00-13:00 |
14:00-18:00 |
19:00-22:00 |
14 hrs |
Order data
Order quantity is 60, planned scrap 15% in operation 010. The order finish date is day 5.
Operation data
The order includes two operations, 010 and 020. Operation 010 overlaps to operation 020. The number of resources indicates both setup and production resources. The table indicates the settings for each operation.
|
Op. |
Queue (days) |
Setup |
Run |
Price/ time code |
Trnst time |
No. rsrces |
Qty |
|---|---|---|---|---|---|---|---|
|
010 |
1.00 |
1 hrs |
0.2 hrs |
10 |
-2 hrs |
1 |
67 |
|
020 |
0.25 |
1 hrs |
0.2 hrs |
1 |
1 hrs |
2 |
60 |
Lead time per operation
Lead time is calculated back from the finish date at 23:00. Operation 010 is expected to be finished at 10:30. Therefore, production for operation 010 on day 5 can be between 10:15 and 10:30, and between 08:00 and 10:00. The remaining production is done from day 4 to day 2.
|
Op. |
Fin day |
Fin time |
Lead time operation |
Start day |
Start time |
|---|---|---|---|---|---|
|
020 |
5 |
22:00 |
0.25*8+(1/2+0.2*60/2)+1 = 9.50 hrs |
5 |
10:30 |
|
010 |
5 |
10:30 |
1.00*8+(1+0.2*67)-2 = 20.33 hrs |
2 |
13:36 |
Example - Dynamic lead time with backward scheduling, no shift planning
This example is for calculating dynamic lead time for backward scheduling and order without using shift planning. Assume the same basic data as in the previous example.
Op 020
|
Setup |
Runtime |
Queue |
|
|
Day 5 |
10:30-11:00 |
11:00-18:00 |
20:00-22:00 |
Op 010
|
Setup |
Runtime |
Queue |
|
|
Day 5 |
08:00-14:30 |
||
|
Day 4 |
08:00-12:00 |
13:00-16:30 |
|
|
Day 3 |
08:00-16:30 |
||
|
Day 2 |
13:36-14:51 |
13:36-14:51 |
Capacity
The capacity calendar per work center indicates when the product from the upstream operation can be received by the next (open time). The capacity calendar indicate the capacity per day when shift planning is not used. Production is from Monday to Friday (five workdays per week). Each work center's capacity (operation capacity) is as follows:
|
Op. |
Cap/day |
Op. |
Cap/day |
|---|---|---|---|
|
010 |
8 hrs |
020 |
16 hrs |
Order Data
The order quantity is 60, planned scrap is 15% for operation 010. The order finish date is day 5 at 23.00.
Operation Data
The order includes two operations, 010 and 020. Operation 010 overlaps to operation 020. The number of resources indicates both setup and production resources. The table indicates the settings for each operation.
|
Op. |
Queue (days) |
Setup |
Run time |
Price/ time code |
Trnst time |
No. rsrces |
Qty |
|---|---|---|---|---|---|---|---|
|
010 |
1.00 |
1 hr |
0.2 hrs |
10 |
-2 hrs |
1 |
67 |
|
020 |
0.25 |
1 hr |
0.2 hrs |
1 |
1 hrs |
2 |
60 |
Lead time per operation
Lead time is calculated back from the finish date at 24:00. Operation 020 uses (9.5/16) * 100 = 59.38% of available capacity on day 5. Therefore, production in operation 010 on day 5 can be 100 - 59.38% (= 40,62% of the days total capacity)), or 8 * 40.62 / 100 = 3.25 days. The remaining 17,08 hours is done ; day 4 (8h), day 3 (8h) and finaly 1,08 hour; day 2. In day 2 the production is experted to start when 1,08/8 * 100 = 13,5% remaining of the day.
For instance if the production runs from 8.00 to 16.00 it is expected to start at 14.55. Please note that when not using shift planning the start will only be stated in the date. The calculated time in this exemple is just to explain how M3 calculates.
|
Op. |
Finish day |
Cap avl. in % |
Lead time operation |
Start day |
|---|---|---|---|---|
|
020 |
5 |
100 |
0.25*8+(1/2+0.2*60/2)+1 = 9.50 hrs |
|
|
010 |
5 |
40.62 |
1.00*8+(1+0.2*67)-2 = 20.33 hrs |