SCP Presentation

•N I K H I L K J O S E P H - F R A N K L I N J O S E P H - S I M O N S C H Ü L E R

PRODUCTION PLANNING AND SCHEDULING

Nikhil k Joseph Franklin Joseph Simon Schüler

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CONTENTS

1. Description of the Decision Situation.2. Planning Decentralization.3. How to proceed from a model to a Production

Schedule.4. Production Process Model (PPM).5. Objectives of Production Planning and

Scheduling6. Updating Production Schedule.7. Incremental Planning.8. Number of Planning Levels & Limitations.

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DESCRIPTION OF THE DECISION SITUATION

• Production schedule indicates for each order to be executed within the planning period its start and end time and also resources required for various processes.• It can be visualised by using a Gantt chart.• The planning period for production and scheduling

varies from one day to weeks depending on the industrial sector.• It should cover the largest throughput time of an order

within the production unit.• It mostly depends on availability of known customers

and accurate demand forecasting.

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DESCRIPTION OF THE DECISION SITUATION... CONT’D

• For some production types like Job Shop production planning and scheduling requires sequencing and scheduling of orders on potential bottlenecks.• For other production types like group technology

an automated bucket-oriented capacity check can be used sequencing can then be performed manually.•

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PLANNING DECENTRALIZATION

• Planning tasks should be done decentraly utilizing the expertise of the staff at each location and their current knowledge of the state of the Job shop.

• The master plan would set the frame work within which production planning and scheduling at the decentralized units can be performed.

• The directives used are• The amount of overtime or additional shifts to be done .• The availability of items from upstream units in the

supply chain at different points in time.• Purchase agreements concerning input materials from

suppliers.

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PLANNING DECENTRALIZATION…CONT’D

• Master plan also give additional directives like• The amount of seasonal stock of different items

to be built up by the end of the planning horizon • Due dates for orders to be delivered to the next

downstream unit in the supply chain.

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I

1. Model Building

2. Extracting required data from ERP system, Master Planning,...etc

3. Generating a set of assumptions (a scenario)

4. Generating a (initial) production schedule

5. Analysis of the production schedule and interactive modifications

7.Executing and updating the production schedule via the ERP-System until an “even” requires reoptimization

6. Approval of a

scenario

III

III

II

II

No

Yes

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HOW TO PROCEED FROM A MODEL TO A PRODUCTION SCHEDULE

• Step 1: Model building• A model of the shop floor has to capture the

specific properties of the production process and the corresponding flow of materials in a detail that allows to generate feasible plans at minimum costs.• Only a subset of the existing resources which can

result into a bottleneck need to be modelled seperately

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HOW TO PROCEED FROM A MODEL TO A PRODUCTION SCHEDULE…CONT’D

• Step 2: Extracting required dataProduction planning and scheduling utilizes data

from ERP systemMaster planning systemDemand Planning Only a subset of the data available in these

modules is used so it is necessary to specify which data will be used.

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• Step 3:Generating a set of assumptions(A scenario)• In addition to the data received from sources like

ERP the decision maker at the plant or production unit may have some further knowledge or expectations about the current and future situation of the shop floor not available in software modules .• Therefore the decision maker must have the

ability to modify data and thereby set up a certain sceanrio

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• Step 4:Generating an initial production schedule.• Next an initial production schedule would be

created automatically from the above given scenario.• This can be done either by a two level planning

hierarchy or in one step.

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• Step 5 : Analysis of the production schedule and interactive modifications.

• If we are using a bucket –oriented upper planning level then this production plan must be analysed first before a detailed schedule is generated.

• If the plan is infeasible the decision maker may indicate some course of action interactively to balance capacities(like introduction of overtime or the specification of a different routing).

• This would be easier than modifying a detailed sequence of operations on individual resources we can also incorporate the experience and knowledge of the decision maker interactively.

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• Step 6 :Approval of a scenario• Once the decision maker has evaluated all

available alternatives he/she can choose the most promising production schedule relating to a specific scenario.

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• Step 7: Executing and updating the production schedule • The production schedule selected would be

transferred to• The MRP module to explode the plan• The ERP system to execute the plan• The transport planning module for generating

routes and vehicle loadings to deliver customer orders

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• The MRP module performs the explosion of all planned activities on bottleneck resources to those materials that are produced on non-bottleneck resources.

• Changing the model of the plant is less frequent and if the structure remains unaltered and only quantities are affected the model can be updated automatically via the data that is downloaded from the ERP system however for major changes like the introduction of a new production stage with new properties a manual adaptation of the model is advisable.

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Cleaning Stirring Waiting

CleaningMaterial

Ingredients

Waste LiquidKetchup

-24h

0h0h

Cleaning Bottling Packaging

Liquid Ketchup, bottles

Cleaning Personnel

Boxes containing 24 Ketchup bottles

0h

0h0h

Primary Resource 1:Tub

Primary Resource 2:Packaging Line

PackagingPersonnel

(..Activities...) (..Products…) Material Flow with max Lead Time.

Explanations:

Secondary Resources:

Boxes

BottlingPersonnel

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PPM MODEL(PRODUCTION PROCESS MODEL)

• The number of items per order as well as the resource consumption per item are required for sequencing and scheduling of individual orders hence a combination of both called PPM model is used .

• Example for PPM : Two stage production of ketchup bottles of a specific size and brand.

• First part of PPM would represent the production of the ketchup-cleaning the tub, stirring the ingredients and waiting for the bottles to be filled up.

• Once the liquid is ready it has to be bottled within the next 24 hours.

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PPM MODEL(PRODUCTION PROCESS MODEL)…CONT’D

• The liquid can be bottled in bottles of different sizes.• For each size there will be an individual PPM.• The liquid ketchup can be used up for different

bottles simultaneously.• A PPM will at least consist of one operation and

each operation will consist of at least one primary resource( like tub) and secondary resources like personnel

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• Activities would require some input material and yield some material as output we need to specify the point of input and output though.• The technical sequence of activities within an

operation is called as precedence relationship represented by arcs in the diagram.

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Cleaning Stirring Waiting

CleaningMaterial

Ingredients

Waste LiquidKetchup

-24h

0h0h

Cleaning Bottling Packaging

Liquid Ketchup, bottles

Cleaning Personnel

Boxes containing 24 Ketchup bottles

0h

0h0h

PackagingPersonnel

Boxes

BottlingPersonnel

Primary Resource 1:Tub

Primary Resource 2:Packaging Line

Secondary Resources:

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• Pegging • The timing as well as the resource and material

requirement of a order may be derived by linking associated PPMs by the pegging arcs.• Pegging arcs connect the input material of one

PPM with the respective output material of the predecessor PPM.• PPMs are stored and updated solely in APS this

allows to take into account more details like –timing restrictions than when they are stored in an ERP system.

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• APS offers following information whether a plant or resource is operated in in one ,two, three shifts.• Situation dependent data varies with current

situation of the shop floor it includes.• Initial inventories ,including WIP.• Setup state of resources • Set of orders processed within a given interval of

time.

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• Operational procedures include• Lot –size rules• Priority rules • Choice of routings• The rules of building lot sizes would actually depend on

actual production situation APS provides some input like simple rules of priori like fixed lot size, minimum lot size, or a lot size between orders.

• Fixing lot sizes to the EOQ(economic order quantity )is not a wise decision because large deviations would result only in small cost increases instead there should be certain amount of flexibility in the system.

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OBJECTIVES OF PRODUCTION PLANNING AND SCHEDULING

• The objectives for production planning and scheduling are as follows minimizing the

• Makespan• Sum of lateness • Maximum lateness • Sum of throughput times• Sum of setup times• Three objectives related to costs are also important• Variable production costs • Setup costs • Penalty costs

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OBJECTIVES OF PRODUCTION PLANNING AND SCHEDULING..CONT’D

• If a decision maker wants to pursue several of the above objectives an ideal solution does not exist we have to look for a compromise solution which includes weighted sum of individual objectives .

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UPDATING PRODUCTION SCHEDULE

• Used to cope with uncertainty.• Softwares and simulations for real-time updates

of estimated orders completion time.• Before the actual schedule is delivered to the

shop floor.• Time is of essence.• Assumes that decision situation is deterministic.

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INCREMENTAL PLANNING

• It is a two step planning process.• A new order can be accepted if;• It can be added into the current sequence of Production

Planning and Scheduling.• Only minor changes in the timing of orders result.

• Reoptimization is done time to time, depending on the different sequence of orders.

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E.G. FOR INCREMENTAL PLANNING• Assume • Four Orders are currently scheduled with due dates

given as;

• Processing times for all orders are 1 unit.• We cannot interrupt the processing of any order that

has already begun.• Objective:-To minimize the Sum of Sequence

dependent Setup Times.

Orders A B C DDue

Dates102 104 107 108

A B C D

100 01 02 03 04 05 06 07 08t

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E.G. FOR INCREMENTAL PLANNING...CONT’D

• Now if we need to add a new order E, with due date 107 • Given the Setup Times for all process as;

• Between A & E there is a positive Setup Time;• However, E cannot be inserted before, as it will affect B’s

due date.

To A B C D EA 0 0 1 1 1B 1 0 0 0 2/3C 1 1 0 0 1/3D 1 1 1/3 0 1E 1 1 2/3 1 0

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E.G. FOR INCREMENTAL PLANNING…CONT’D

• The Three Alternative Solutions are;• 1) Sum of Setup Times= 2 1/3

• 2) Sum of Setup Times= 2 1/3

• 3) Sum of Setup Times= 2

A B C D

100 01 02 03 04 05 06 07 08t

E

A B C D

100 01 02 03 04 05 06 07 08t

E

A B C D

100 01 02 03 04 05 06 07 08t

E

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E.G. FOR INCREMENTAL PLANNING..CONT’D

• After reoptimization we get; Setup Time 1 2/3

Explanation:Setup Time-Production-

A B CD

100 01 02 03 04 05 06 07 08t

E

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Software modules usually generate either one or two planning levels for production planning and scheduling, depending on production type and the repetition of operations

Production types:

• Flow lines no separation into multiple planning levels

• Process organization divided into two planning levels• Upper planning level: Time buckets of days and weeks, resources

are grouped in resource groups• Lower planning level: assignment of orders to individual resources

NUMBER OF PLANNING LEVELS AND LIMITATIONS

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Time buckets:• Big time bucket:

• Small time bucket:


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Time buckets:• In a big time bucket…• Operation started in time bucket has to be finished within

the time bucket• Setup stage can not preserved from one period to next• Aggregation of resources to resource groups

• In a small time bucket…• Setup stage can be preserved from one period to next• Usually only one setup per time bucket


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Sometimes, even through a possible big bucket plan exists, it might not be possible to disaggregate the plan into a production schedule because…

- Sequence dependent setup time:Planning in time buckets might not be possible because loading of time bucket is done without sequencing. Portion reserved for setup time, be to small or to large.


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- Loading of resource groups:Bucket size is 3 periods and 2 resources allocated 6 time units within bucket.3 operations with 1 time unit per operation and 1 time unit setup time each 6 time units needed


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- Lead time offset of zero time units between successive operations

Two successive operations loaded into same big time bucket. Operation B is successor of operation A. Both need 9 hours processing time.


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Possible solution:

Mixture of big and small time bucket big time bucket with linked lot sizes

-“Last“ lot within time bucket gets chosen which can be linked with a „first“ lot in next time bucket-If these two lots concern the same product, a setup can be saved

Allows model a setup over two or more big time buckets, like in the small bucket model


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Limitations due to computational efforts:

For finding best production schedule, there usually are many alternatives for sequencing orders (n! sequences for n orders per period).Combined with choise of use of paralell resources, excessive number of possibilities.


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