Realizing the Benefits of Finite Capacity Scheduling to Manage Batch Production Systems

Transcription

1 Presented at the WBF North American Conference Baltimore, MD, USA 30 April - 4 May Alexander Drive PO Box Research Triangle Park, NC Fax: info@wbf.org Realizing the Benefits of Finite Capacity Scheduling to Manage Batch Production Systems Glen Wirth Requirements Analyst Rockwell Automation 2000 Marconi Drive Warrendale, PA United States Wk: Fax: gtwirth@ra.rockwell.com Vincent de Gast Applications Engineer Systems Navigator Delftechpark XH Delft The Netherlands Wk: +31 (0) Fax: +31 (0) vincent.de.gast@ systemsnavigator.com Marcus Tennant Product Manager Rockwell Automation 1201 S. 2nd Street Milwaukee WI United States Wk: Fax: matennant@ra.rockwell.com KEY WORDS Finite Capacity Scheduling, Batch Production Scheduling, ERP, B2MML ABSTRACT This paper defines the benefits of using a finite capacity scheduling (FCS) in a batch production process. It defines the modeling constructs that are available in FCS systems and how they can be used to improve batch production performance. The paper discusses the benefits of having a tight integration framework of the FCS with ERP and batch production systems. It also suggests a few implementation strategies that should be considered to ensure an FCS system is implemented successfully. Copyright 2007 WBF. All rights reserved. Page 1

2 INTRODUCTION PAPER In many of today s production systems, few decision support tools have been implemented to accurately model the production scheduling environment. Manufacturers rely on spreadsheets and white boards to make operational decisions for the factory floor. Most of the feedback to these systems is manual and untimely. This makes it difficult to accurately model the manufacturing process and react to changes on the manufacturing floor. The ERP system is another tool typically used to manage the production schedule. ERP systems are good for strategic and tactical decisions, but are poor on solving operational decisions. ERP systems are transactional based systems that define What is needed?, What is available? and What is required?. In manufacturing, the ERP system manages the generation of production orders based on customer orders and forecast as well as the purchasing of the raw material that support production. There are ERP systems in the market today that provide a limited set scheduling functionality. However, ERP systems generally have limited capabilities for modeling the manufacturing process and defining constraints. These limitations make it difficult for the ERP system to generate an accurate production schedule. Some of the limitations of an ERP system that are typically observed are: Often models operations on a higher level Assumes infinite or fixed resource capacities Real-time capacity of the facility is not considered Difficult to respond quickly to changes on the factory floor (downtime, poor material quality, rush orders) Cannot model many types of constraints (labor, fixtures, tanks, piping, resource sets, and dwell times) Does not take into account recipe complexity, alternate BOM items and alternate routings Bottleneck resources, work-in-process (WIP) inventory and WIP buffers are difficult to manage Cannot generate what-if scenarios Finite Capacity Scheduling (FCS) recognizes actual plant capacity limits, including time patterns, work centers, labor, and fixture resources. Realistic modeling of capacity constraints is the objective of accurate finite capacity scheduling. Some Finite Capacity Scheduling systems are extended by also recognizing material constraints, in regard to on-hand inventory as well as planned future material deliveries and planned allocations of materials tied to Purchase Orders. A finite capacity scheduling (FCS) system is an appropriate tool for managing the detailed operations of a manufacturing facility. FCS enables a manufacturing facility to generate a detailed schedule that presents a view into the future. FCS systems have many constructs for defining and managing production constraints. These constraints are used when constructing the production schedule to block the scheduling of order/operations when insufficient quantities of the constraint exist. Copyright 2007 WBF. All rights reserved. Page 2

3 An FCS system integrates well with ERP and MES systems. Most of the data needed to run the FCS already exists within the ERP and MES systems. FCS does not replace ERP functionality. It complements ERP and adds value to the ERP s functionality. FCS IN BATCH PRODUCTION There are many capabilities that FCS provides that enable it to thrive in a batch processing system. One of the biggest reasons is it gives visibility of the entire batch manufacturing process. An FCS provides visibility of manufacturing operations across multiple batch servers and multiple areas within a manufacturing process. This helps users understand the impact batch operations have with upstream and downstream operations. Graphical interfaces define views of orders, materials and constraints across multiple areas within the facility. Resource, material and tooling utilization can also be easily visualized (see Figure 1). Figure 1: Visibility of the entire batch production process An FCS is a logical location to stage orders coming down from an ERP system and determine when and where they should begin processing. An FCS system can then schedule the batches based on business rules to generate a production schedule. The business rules can be setup based on key performance indicators (KPIs). The strength of a schedule can be measured using KPIs to ensure that the manufacturing facility is meeting its goals. The production schedule can be adjusted to pro-actively ensure goals are met. Many FCS systems can use pegging (the linking one production order to another) to pre-assign bulk material components to packaging orders. If a bulk production order is delayed, the packaging order Copyright 2007 WBF. All rights reserved. Page 3

4 will also be delayed. Other orders can be scheduled in place to keep resources utilized. An FCS system can also provide simple Manufacturing Resource Planning (MRP) calculations. An FCS system can determine the bulk batch requirements for packaging orders. Batches can be generated based on min/max batch sizes. An FCS system can also be used to determine the appropriate time to schedule CIP operations. MODELING CONSTRUCTS Most FCS systems have the capability to accurately model the constraints of the batch production system. These are categorized as additional resources, materials and tooling, but can used to model labor, raw materials, intermediate materials, WIP constraints, piping, tanks, molds and other constraints. The quantity and availability of the constraints can be managed by an FCS system. Another type of constraint an FCS can model is an operational constraint. An operational constraint defines the rules in which operations can be scheduled in relation to one another. These rules are useful for modeling minimum and maximum dwell times such as maturation time and shelf life requirements. Operational constraints can also be used to model flow production where one operation can start prior to the completion of the previous operation. This strategy can help decrease an order s cycle time. Order cycle time reductions can help enable the reduction of WIP and finished goods inventory. The system usually has the ability to define resource sets. Resource sets are a grouping of resources that have similar capabilities. Batches can be setup to execute on any of the resources in a resource set. Each resource in the set can have a different process time. These are usually defined based on product or product family. Sequencer dependent setup time can also be defined for each resource based on a product or product family. Using these types of criteria, an FCS will choose the best resource to execute the operation based on availability, setup time and processing time (see Figure 2). Copyright 2007 WBF. All rights reserved. Page 4

5 Figure 2: Various Modeling Constructs Alternate routings, operations and bill-of-materials can also be defined with an FCS. Alternate operations and alternate routings are used by an FCS system to choose different paths through the process based on the availability of resources. Alternate bill-of-materials are used by an FCS system to allocate materials based on rules or availability. BATCH INTEGRATION Once a production schedule is generated, this information needs to be communicated to the batch system. An FCS system makes the decision on which batches to run and the schedule that each batch should be run on for each batch server. The resources, material allocations and other processing parameters also need to be sent down to the batch system. Actual performance information also needs to be captured by the batch system and sent back to the FCS system. The actual performance data will enable an FCS system to automatically adjust batch durations and resource allocations. Also if equipment goes down on one batch server, the FCS system can reroute jobs to another batch server. An FCS system can usually be setup to re-schedule batches and determine which resources should be used in a relatively short timeframe. The schedule of batches should be followed by the batch server to ensure the schedule adheres to previous and subsequent orders/operations requirements. Batch systems should also use the materials and resources allocations determined by an FCS system. The schedule of batches and allocation of Copyright 2007 WBF. All rights reserved. Page 5

6 resources, materials and tooling could have dependencies that are outside the knowledge of the batch system. Choosing to run orders/operations out of sequence could largely impact the schedule of downstream operations. There are cases when an FCS system will not make all the necessary resource allocation decisions. In some environments, it is challenging to incorporate transient data (e.g. temperature, value, equipment status) into an FCS system. The batching system might be a better location to make decisions on what resource to use based on a certain condition. If this is the case, the batch system can make real-time decisions. The decisions made by the batch system needs to be captured and sent back to the FCS system to record the resources that were used. INTEGRATION NEEDS One of the biggest difficulties with installing an FCS system is getting all the data needed to accurately model the production environment. An FCS system needs a large amount of data. The types of data that are necessary include resources, resource availability, materials, material lots, tooling, routes, billof-materials, orders, and actual performance information. Gathering all this information manually is an insurmountable task. There has to be methods developed to pull the data from other systems. A good majority of the time during the implementation of an FCS is spent developing automated interfaces to pull the necessary data from other systems. In today s batch production environments, most of this data already exists in other information systems. The ERP system usually contains most of the order, routing material lot and bill-of-material information. The batch system has the actual production information. The information from all these systems needs to be identified and interfaces need to be developed. B2MML INTEGRATION FRAMEWORK A framework needs to be developed to synchronize data from external systems into FCS. As events happen in other systems, they need to be published. An FCS system will subscribe to these messages and update its information as the information is received. An FCS system can choose to react to certain messages. If an FCS system receives a rush order message or a resource failure message, the FCS can automatically reschedule and publish a new dispatch list. The FCS system could also wait until a point in time where it chooses to use this information. An example of this would be if an FCS receives a set of low priority orders, the FCS system will not schedule the orders until the start of the next shift. B2MML is the logical message structure for transferring data to an FCS. B2MML has many benefits for simplifying this integration. These benefits include: - B2MML standard is a well known data model. Copyright 2007 WBF. All rights reserved. Page 6

7 - Hides the complexities of each applications API - Interfaces are extended based on a design pattern - B2MML provides elements for message routing and data aggregation - Interfaces that use B2MML can be easily modified and reused B2MML already provides all the messages necessary to translate the master and transactional data used by the FCS. The B2MML messages that an FCS system might subscribe to include: FCS Subscription Resources Resource Availability Materials Material Lots Tooling Routes Bill-Of-Materials Orders Actual Performance B2MML Message Equipment Resource Capacity Material Material Equipment Product Definition Product Definition Production Schedule Production Performance In addition to subscribing to information from the ERP and production systems, the FCS also needs to publish its scheduling results. The FCS results need to be published so they can be used by ERP and batch systems. B2MML can be used as well to publish the schedule information. The B2MML messages that an FCS system could publish include: FCS Publication Dispatch list Resource Allocation Material Allocation Tooling Allocation B2MML Message Production Schedule Resource Capacity Resource Capacity Resource Capacity From FCS published information, the ERP systems can use production schedule dates to plan raw materials more accurately then using the ERP scheduling dates. Batch systems will use the dispatch list information to give the operations a prioritized list of batches that need to be run. A batch system may choose to run a batch outside of sequence or use alternative materials or resources. If this occurs, the Copyright 2007 WBF. All rights reserved. Page 7

8 actual data used will be communicated back to the FCS system using the Production Performance message. FCS IMPLEMENTATION SUGGESTIONS When implementing an FCS system, there are a lot of items that need to be considered. These include resources, materials, tooling, operational constraints, shift-patterns, production rules, etc. A number of these factors need to be modeled by the FCS system. Some of these factors are necessary for the success of the project while others are not. When developing the initial model, start with a simple model. Don't get caught up in all the details in modeling the FCS environment or developing the scheduling rule. Focus on getting ample feedback from the production floor. This information is necessary to update the schedule on what were the actual resources, materials and tooling used by the operation. The production schedule and production performance data provide a continuous feedback loop between the batch production and the FCS systems. With integration in place, schedules can be run and compared against current production. Modifications can be made to the FCS model and its results can be compared to how operations are run in production. The development of the scheduling rules is another significant task. In a batch production system, there are a large number of rules that go into developing a production schedule. These rules are usually well know by production personnel, but are rarely written down. The rules need to be broken down into a logical format. It will take several iterations between business and production personnel to get a strong understanding of the production process and to understand the scheduling rules. The rules that are defined should always be linked to meet the business objectives. Once the scheduling rules are defined, it is also important to provide parameters that will permit simple adjustments to scheduling rules. The business drivers of batch production system can change. Any FCS system needs to be adjusted by the users to meet the changes. Adding parameters to the scheduling rules changes the impact the rules have on the system. Exposing the scheduling logic in a simplified user interface has a great advantage. The user interface gives end-users the ability to change scheduling rule criteria and measure the impact the change has on performance. An FCS system should provide feedback to the user to assist them with the schedule. The system should be able to highlight exceptions to schedule. FCS systems generate a lot of data. This makes it difficult to evaluate the schedule. Simplified views of scheduling results should be developed using a reporting framework. Use KPI wherever possible. KPIs, such as equipment utilization, responsiveness, minimize WIP, should help determine the appropriate scheduling rules that should be applied based on business drivers. Copyright 2007 WBF. All rights reserved. Page 8

9 What-if scenarios are very useful for evaluating schedules and determining the best scheduling rule. The FCS should provide an environment to develop what-if scenarios. The what-if environment should give users the ability to test multiple scenarios and compare the results against one another. Once the best schedule is determined, the system should give the ability to release the schedule to publish the results to the ERP and batch production systems. CONCLUSION There are limitations with the current set of decision support tools used to define production schedules for batch production. These limitations impact the ability for a manufacturer to accurately model their batch production system. FCS systems fill these gaps by providing a robust framework for modeling the batch production system. Through the implementation of an FCS system, a batch process manufacturer can realize many benefits to their operations. Being able to accurately model their processes and applying constraints can have positive impact on reducing order cycle time. Reduced order cycle times facilitates the reduction of WIP and finished goods inventory. Customer service levels can still be met without carrying large inventory buffers. Raw material can also be reduced based on the accuracy of the production schedule. If a production schedule is accurate, the arrival of raw materials can be timed to the schedule of operations. Schedule accuracy can help increase resource utilization. It can help make sure bottleneck resources are not starved and operations are scheduled to reduce setup times. The FCS provides visibility across the entire production process. Bulk production and packaging can be synchronized through the pegging of production orders. Scheduling rules can be based on business drivers and the results can be measured using KPIs. What-if scenarios help compare scheduling strategies against one another. The data to run an FCS system already exists in other information systems. B2MML provides the necessary messaging structure to synchronize the information. By establishing a real-time feedback loop between the FCS, EPR and batch systems, the FCS information can be keep accurate and the benefits of an FCS system can be realized. Copyright 2007 WBF. All rights reserved. Page 9