Solving Your Complex Scheduling Problems

Posted by Sasi Padmanabhan on 28-Jul-2020 14:09:04

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(6-8 min read)

Quite often, specially in process industries it is observed that there are some specific production restrictions. The restrictions may be in the form viz. a specific sequence of processes using the processing units. The sequence may be derived due to the upstream semi-finished goods complexity or availability of several downstream resources. It is a good practise to decide which downstream resources are to be used before the production process starts.

These kinds of business requirements are modelled using an object called “Resource Networks” in SAP world. In this blog, the intention is to do a deep dive on how “Resource Networks” can be used in SAP APO Production Planning and Detailed Scheduling scenarios.

A “Resource Network” helps to describe the physical connection between Resources of different production lines. It models the flow of materials through these lines from one Resource to another.

General Business Scenarios

  • Scheduling across the allowable connections between Upstream lines and Downstream goods lines
  • Recognising the prioritisation across multiple semi-finished goods lines feeding into a Finished goods line
  • Providing flexibility to switch between alternative input lines in the case of capacity constraints

Resource Networks can also be used to manage and utilize production assets, ensuring the input/output of material flows between resources is optimised.

Industries where this maybe applicable include FMCG, Chemical, Pharmaceutical and Food & Beverage.

Customer Use Case

As an example, Olivehorse implemented PP/DS Resource Networks for an FMCG customer (toothpaste and shampoo/lotions manufacturing facilities). In both manufacturing units, there were two levels of manufacturing: Finished Goods (FG) and Semi-Finished Goods (SFG). Multiple SFG mixers could feed the SFG material into the FG packaging line and there were also intermediate storage tanks that held the SFG material for a defined period as an intermediate material staging.

Pic 1

In general, the storage tank capacity was based on the batch size of the SFG material produced on the SFG mixer. Modelling the capacity of the intermediate storage tanks was done using Min/Max stock levels of tanks which was respected by the planning algorithm and could be visualised graphically (see previous blog on scheduling SFG ).

The key business requirement for scheduling the mixers was “multiple semi-finished mixers feeding a single finished good line as well as the mixers had predefined priorities”.

A PP/DS scheduling solution was delivered which considered all these constraints.

Benefits Achieved 

  • Overall Asset Utilization increased at both Finished and Semi Finished goods levels, due to reduced waiting time of semi-finished mixers to fill the intermediate storage tanks.
  • The solution generated a more reliable production plan through better synchronization between the upstream and downstream levels.
  • The solution provided advancement in automation with minimal manual intervention for re-scheduling activities.

Sneak Peek of Resource Networks 

Below is a simple schematic of a Resource Network showing the relationships between FG packaging lines and SFG mixers.

Pic 2

The arrows indicate the flows from SFG to FG lines, with the red arrows indicating the highest priority of the Resource Network and all others represent lower priorities. Every FG packaging line is connected to one or more SFG mixer line and every FG packaging line has a preferred SFG mixer line from which to source the SFG material from.

Resource Networks provide the scheduling flexibility to utilize the priorities for sourcing SFG material from alternative mixers in case of capacity overload, down time and other scheduling constraints.

The prioritization in Resource Network will be triggered by requirement of SFG material in FG orders. The machine operators and planners play a key role in deciding which FG resources need to be connected to a corresponding SFG resource.

The design will be made based on various factors on the shop floor such as compatibility of the resource, distance between the resource, resource grouping based on homogenous products etc.

Challenges

Resource Networks can grow in complexity as the number of machines involved increases. The more complex it becomes; the more challenges and constraints will arise for the businesses to handle.

  • Priorities between upstream and down streamlines needs to be managed carefully. It might require a compromise while defining the prioritization rules.
  • Other scheduling factors such as Finiteness levels, overloads and downtimes need to be investigated thoroughly.
  • Alternative SFG mixer priorities, intermediate storage capacities and bottle neck resources need to be considered.
  • Lot sizes (fixed and lot for lot) logic needs to be determined to make the models work effectively.

Planning and Scheduling Techniques 

To apply Resource Network logic onto a scheduling model, there are two methods available via PP/DS Heuristics or PP/DS Optimiser. Both methods require certain system prerequisites

  • Resource Network together with the prioritisation logic
  • Routings/Recipes in ECC modelled accordingly
  • Multiple PDS (Product Data Structure) modes enabling to be scheduled dynamically across alternative resources

PP/DS Heuristics 

In case of Heuristics method, based on business requirement there will be sequence of Heuristics steps that would be required to be modelled and executed to derive the expected result.

Optimisation with Resource Network Costs 

The PP/DS Optimiser uses different weightings (costs) such as overall make span, total setup time / cost, total delay cost to arrive at an optimised plan.

As per the standard PP/DS optimiser, cost parameters will not be considered for Resource Network priorities. Olivehorse however have developed enhanced functionality by adding costs for Resource networks and running PP/DS optimiser to consider these costs during optimised scheduling. Weightings will be added to the Optimiser logic to consider priorities and costs of Resource Networks along with other standard weightings.

Conclusion

At Olivehorse, we have seen first-hand how PP/DS Resource Network functionality has provided real advantages to businesses where multi-level manufacturing is a requirement. We have gained extensive experience in handling and implementing complex planning and scheduling scenarios and would be happy to discuss any specific requirements.

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SasiSasibhushan Padmanabhan is a Senior SCM consultant. In total, he has 13 years of manufacturing and IT experience. SAP certified in the areas of S/4 Hana Production Planning and Manufacturing, SAP IBP, SAP-ARIBA Supply Chain Collaboration(SCC).