Approach to Production Scheduling Wave 13

5/19/2018 Approach to Production Scheduling Wave 13

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Pragmatic Approach to Production Scheduling

Introduction:An effective and reliable production scheduling system is must for a manufacturing organization to achievetrue operations excellence. Many organizations often struggle to implement an effective production planning system whichoften leads to shop-floor inefficiencies, large Inventory and WIP levels. Lack of accurate Production Scheduling alsoaffects timely delivery and quality of goods thus impacting overall customer satisfaction.

Based on my experience I've tried to present a pragmatic approach to production planning and scheduling through thisseries comprising of five Articles. The series primarily focuses on Production Scheduling and Capacity Planning utilizingOracle Inventory, Bills of Material (BOM), Work in Process (WIP), Advanced Supply Chain Planning (ASCP) and

Production Scheduling (PS) modules.

I've described five waves of implementing an effective production scheduling system taking into view the complexities,pre-requisites and business maturity required for each wave.


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This article is the first of a five-article series "Pragmatic Approach to Production Scheduling" and describes the "Wave 1"of the above discussed approach.

Wave 1:Accurate Lead Time computation and WIP based Job scheduling

The main pre-requisite for any production scheduling system to work effectively is accurate master data. It is essential tovalidate the correctness of data and practically understand the lead time computation & detailed scheduling logic beforeproceeding ahead with an advance planning system such as Oracle ASCP or PS. Following is the fine print of criticalmaster data elements and their exact impact on production scheduling.

Assumption: Unconstrained material availability and production scheduling can be carried out on the basis of availablemachine and manpower resources (Hours).

Four Scenarios are discussed below to demonstrate the lead time calculation and its impact on Job scheduling. Twocritical attributes required towards manufacturing lead time computation and scheduling are:

Lead Time %: Percent of manufacturing (processing) lead time required for previous operations, calculated from the startof a job to the start of an operation.

Offset %: Percent of manufacturing (processing) lead time required for previous Manufacturing Lead Times operations,calculated from the start of the job to the start time of a resource at an operation.


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Scenario A:Sequential Operations with single Assigned Units

Let's discuss a typical case of component manufacturing where multiple operations and activities need to be carried outsequentially one after another with no parallel / overlapping activities.

1) Routing def ini t ion:A Routing is defined for TA0001 (Test Assembly for demonstration) in following fashion. Criticaldetails are mentioned below in tabular format. (Navigation: Bill of materials Routings Routings New)

OperationSequence

Department Resource Usage (Hrs) Scheduling flag Assigned Units Basis

5 MACHINING R001 12 Yes 1 Item

10 ASSEMBLY R002 12 Yes 1 Item

10 ASSEMBLY R003 24 Yes 1 Item20 FINISHING R004 36 Yes 1 Item

Note: 24 hour production and resource availability is assumed for simplification and highlighting computation logic

2) Lead Time and Offset % Computat ion:Manufacturing lead time computation is carried out based on this Routingdata ((Navigation: Bill of materials Routings Routings Find Tools Compute Lead Time) with followingresults. "Lead Time %" and Resource "Offset %" are estimated.

OperationSequence

Department LeadTime %

Resource Usage(Hrs)

Schedulingflag

Offset %

5 MACHINING 0 R001 12 Yes 0

10 ASSEMBLY 14.29 R002 12 Yes 14.29

10 ASSEMBLY R003 24 Yes 28.57

20 FINISHING 57.14 R004 36 Yes 57.14

"Lead Time % (LT)" and "Offset % (OT)" parameters are updated based on above listed definition.


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Detailed Illustration:

Since there is no operation prior to first operation ("Operation 5") both LT as well as OT are set to zero (0). Total hours consumed in first operation = (12/84)*100 => 14.29% , hence LT for "Operation 10" is set as 14.29%

which is same as OT for R002 resource assigned to this operation Total hours consumed in until the start of this resource activity = (24/84)*100 => 28.57% , hence OT is set to

28.57% Total hours consumed in until the start of "Operation 20" = (48/84)*100 => 57.14% , hence LT for "Operation 20" is

set as 57.14% which is same as OT for R004 resource assigned to this operation

3) Detai led Schedul ing from Oracle WIP

Oracle WIP uses detailed up-to-minute Job scheduling based on Routing details (as defined above) and does not referItem Lead time attributes. Lead time computation logic which updates the item level lead time attributes for MRP/ASCPplanning is discussed in next section.

Let's have a quick snapshot of Job based scheduling and validate our routing data. Following Gantt chart (Navigation:WIP Discrete Job Workbench) shows the Job operations being scheduled sequentially as per the details mentionedabove.

Job 254215 is created for Quantity 1 using the above defined routing for assembly "TA0001".


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Snapshot of resource loading for the concerned resources (against all jobs scheduled to use these resources)


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Scenario B:Sequential Operations with Multiple Assigned Units

Lets repeat the above analysis with just one change i.e. No. of assigned units for Resource R004 is changed to 2 insteadof 1.

1) Routing def ini t ion:A Routing is defined for TA0001 (Test Assembly for demonstration) in following fashion. Criticaldetails are mentioned below in tabular format. (Navigation: Bill of

materials Routings Routings New)

OperationSequence



10 ASSEMBLY R002 12 Yes 1 Item10 ASSEMBLY R003 24 Yes 1 Item

20 FINISHING R004 36 Yes 2 Item



OperationSequence


Resource Usage(Hrs)

Schedulingflag

AssignedUnits

Offset %

5 MACHINING 0 R001 12 Yes 1 0

10 ASSEMBLY 14.29 R002 12 Yes 1 18.18

10 ASSEMBLY R003 24 Yes 1 36.36

20 FINISHING 57.14 R004 36 Yes 2 72.73


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"Lead Time % (LT)" and "Offset % (OT)" parameters are updated based on above listed definition. Please note thatchaning no. of assigned units from1 to 2 actually reduces the total manufacturing lead time to 66 hours instead of 84

hours as in scenario A.


Since there is no operation prior to first operation ("Operation 5") both LT as well as OT are set to zero (0). Total hours consumed in first operation => (12/66)*100 => 18.18.% , hence LT for "Operation 10" is set as

18.18% which is same as OT for R002 resource assigned to this operation Total hours consumed in until the start of this resource activity = (24/66)*100 => 36.36% , hence OT is set to

36.36% Total hours consumed in until the start of "Operation 20" = (48/66)*100 => 72.73% , hence LT for "Operation 20" is

set as 72.73% which is same as OT for R004 resource assigned to this operation



Let's have a quick snapshot of Job based scheduling and validate our routing data. Following Gantt chart (Navigation:

WIP Discrete Job Workbench) shows the Job operations being scheduled sequentially as per the details mentionedabove.



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Please note that assigning 2 units to R004 actually resulted in job being completed by Friday itself instead of next Mondayas in scenario A. Though total resource usage for R004 increased on Friday resulting in Overload.

Scenario C: Parallel Resource Operations

Let's again repeat the above analysis with one more change i.e. making R002 and R003 as parallel resources

1) Routing def ini t ion:A Routing is defined for TA0001 (Test Assembly for demonstration) in following fashion. Criticaldetails are mentioned below in tabular format. (Navigation: Bill of materials Routings Routings New)

Operation

Sequence

Department Resource Usage

(Hrs)

Scheduling flag Assigned

Units

Schedule

Sequence No.

Basis

5 MACHINING R001 12 Yes 1 NA Item

10 ASSEMBLY R002 12 Yes 1 1 Item

10 ASSEMBLY R003 24 Yes 1 1 Item

20 FINISHING R004 36 Yes 2 NA Item


Schedule Sequence No. is kept as 1 (in Operation Resources scheduling tab) i.e. both resources are required to workparallel.


OperationSequence


Resource Usage(Hrs)

ScheduleSequence No.

AssignedUnits

Offset %

5 MACHINING 0 R001 12 NA 1 0


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10 ASSEMBLY 22.22 R002 12 1 1 22.22

10 ASSEMBLY R003 24 1 1 22.22

20 FINISHING 66.67 R004 36 NA 2 66.67

"Lead Time % (LT)" and "Offset % (OT)" parameters are updated based on above listed definition. Please note thatmaking R002 and R003 as parallel reduces the total manufacturing lead time to 54 hours instead of 66 hours as inscenario B. This change is due to the fact that for Operation second operation, processing time is considered as 24 whichis maximum of the two parallel resources


Since there is no operation prior to first operation ("Operation 5") both LT as well as OT are set to zero (0).

Total hours consumed in first operation => (12/54)*100 => 22.22% , hence LT for "Operation 10" is set as 22.22%which is same as OT for R002 resource assigned to this operation

Total hours consumed in until the start of this resource activity = (12/54)*100 => 22.22% , hence OT is set to22.22%

Total hours consumed in until the start of "Operation 20" = (36/54)*100 => 66.67% , hence LT for "Operation 20" isset as 66.67% which is same as OT for R004 resource assigned to this operation






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Please note that making R002 and R003 parallel resources resulted in further reduction in manufacturing lead time as twoactivities are carried out in parallel. Creating Job for Scenario C resulted in overloading of R001 as well on Wednesday.


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Please note that for demonstration purpose I am creating a new job for each scenario keeping the dates same which isleading to increasing in Resource loadings.


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Scenario D: Overlapping Operations with Schedule attribute as "Prior" / "Next" options

Let's again repeat the above analysis by adding one more change to scenario B i.e. setting "Schedule" attribute for R001as "Next" and for R004 as "Prior"

4) Routing def ini t ion:A Routing is defined for TA0001 (Test Assembly for demonstration) in following fashion. Criticaldetails are mentioned below in tabular format. (Navigation: Bill ofmaterials Routings Routings New)

OperationSequence

Department Resource Usage(Hrs)

Schedule AssignedUnits

Basis

5 MACHINING R001 12 Next 1 Item

10 ASSEMBLY R002 12 Yes 1 Item10 ASSEMBLY R003 24 Yes 1 Item

20 FINISHING R004 36 Prior 2 Item


Schedule Attributes:

Prior :WIP schedules the job such that last resource on the prior Routing Operation ends at the same time as thisresource.

Next:WIP schedules the job such that first resource on the next operation begins at the same time as this resource.


OperationSequence


Resource Usage(Hrs)

Schedule AssignedUnits

Offset %


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5 MACHINING 0 R001 12 Next 1 0

10 ASSEMBLY 0 R002 12 Yes 1 0

10 ASSEMBLY R003 24 Yes 1 33.3320 FINISHING 50 R004 36 Prior 2 50

"Lead Time % (LT)" and "Offset % (OT)" parameters are updated based on above listed definition. Please note thatmaking changes to "Schedule" attributes as described above reduces the total manufacturing lead time to just 36 hoursinstead of 66 hours as in scenario B. This change is due to overlapping first and last operations.


Since there is no operation prior to first operation ("Operation 5") both LT as well as OT are set to zero (0).

Since there is a overlap from first operation LT for "Operation 10" is set as 0 % which is same as OT for R002resource assigned to this operation

Total hours consumed in until the start of this resource activity = (12/36)*100 => 33.33% , hence OT is set to33.33%

Total hours consumed in until the start of "Operation 20" = (18/36)*100 => 50% , hence LT for "Operation 20" isset as 50% which is same as OT for R004 resource assigned to this operation






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Please note that making changes to "Schedule" attribute as "Next" and "Prior" resulted in further reduction inmanufacturing lead time as it lead to overlapping first and last operation. Creating new Job for Scenario D resulted in

overloading at different points. Please note that for demonstration purpose I am creating a new job for each scenariokeeping the dates same which is leading to increasing in Resource loadings.

Manufactur ing Lead Time Comp utat ion

Following Item level Lead Time attributes are updated by "Compute Lead Time" program which are referred by OracleMRP/ASCP for computing material requirement dates and generating planned orders (Navigation:Inventory Organization Items Lead Times)

Routing Data:

OperationSequence





20 FINISHING R004 36 Yes 1 Item

Lead Time Computation:

Lead Time Attribute Lead Time

Total resource Usage (U) 84Fixed (F) 0Variable (V) 3.5Processing (P) 4Lead time Lot size (LS) 1

Average Shift Time (T) 24


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Fixed Lead Time (F) is sum total of resource usage amounts with basis type as "Lot". Lot basis type means that resourceusage will not depend upon the job quantity and would remain fixed. This basis type is generally used in scenarios where

"setup" time is significant.

Variable Lead time (V) depends on the quantity of the job. It is specified as resource usage per assembly. In Ourexample, V = 84/24 = 3.5 Days (all resources have 24 hours availability)

Processing Lead Time (P) = F + V*LS = 0 + 3.5*1 = 3.5 ~ 4 days (captured in integer days, for Lead Time Lot Size (LS) of1)

Processing Lead Time for make items is considered as manufacturing lead time. Pre-processing lead time is alsoconsidered by MRP/ASCP for generating planned order recommendations.

Lead Time Computation Logic

Oracle Master Scheduling / MRP use Dynamic Lead Time Offsetting as lead time computation logic which plans at Daylevel rather than up-to-minute detailed planning. It refers the item level lead time attributes as well as Lead Time andOffset % at Routing level and generates the plan as quick as possible with minimum load on resource intensive planningengine.

Dynamic lead time offsetting offsets dates in two steps, computing total lead time and offsetting the date by total leadtime. Total lead time contains both fixed lead time and the quantity-dependent portion of lead time. Preprocessing lead

time is also included for discrete items.

Total Lead Time = preprocessing lead time + fixed lead time + (order quantity x variable lead time)

Material Requirement dates: Master Scheduling/MRP computes component requirement dates for planned orders usingthe offset percentage for the operation where each component is used. Master Scheduling/MRP multiplies the operationoffset percentage times the planned order lead time to get offset days, and then finds the workday that is the number ofdays past the planned order start date.


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Since Oracle WIP uses detailed up-to-minute Job scheduling based on Routing details (as defined above) and does notrefer Item Lead time attributes, results from MRP/Unconstrained ASCP may differ from WIP level detailed Job scheduling.

Note:Oracle ASCP supports both day level as well as up-to-minute scheduling as per the chosen scheduling option (I'llcover this in my second post which will cover the scheduling cycle through ASCP).

References: Oracle User Guides, Oracle EBS R12.1.3 Vision Instance

Hope you found this Post interesting. Your valued comments and feedback are most welcome.

Best RegardsManu SinghalThe Oracle Manufacturing BlogEmail: [email protected]
http://www.oraclemfgblog.wordpress.com/http://www.oraclemfgblog.wordpress.com/http://www.oraclemfgblog.wordpress.com/

Approach to Production Scheduling Wave 13

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