Work in Progress (WIP) management is a broad topic encompassing everything that takes place between material start and order fulfillment. Various strategies exist for managing WIP ranging in scope from narrow, highly targeted measures like inventory management to comprehensive, end-to-end initiatives involving systems integrations and process automation. The ultimate motivations behind any of these strategies are to keep WIP moving efficiently, avoid buildup of excess inventories, and support multiple production priorities simultaneously. While efficiencies and improvements are realized when strategies are narrow in scope, WIP management strategies offering visibility into the entire supply chain will return the best results.

Well-Integrated Technology Layers

A comprehensive approach to WIP management involves several layers of well-integrated technology solutions to achieve end-to-end visibility of core business processes including production, procurement, distribution and insights into business resources such as cash, raw materials, production capacity, customer orders, purchase orders, and human resources. Typically, this structure includes an enterprise resource planning system (ERP), a manufacturing execution system (MES), a “digital backbone” to facilitate communication between systems and equipment, and automated production control systems with capabilities for data collection, analytics and reporting.

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Enterprise Resource Planning (ERP)

ERP solutions typically offer modules that provide real-time, or near real-time, access to data across accounting, human resources, manufacturing, order processing, supply chain management, project management and customer relationship management systems. Each of these components provide critical information which inform various phases of WIP management such as production, capacity and demand planning; scheduling; dispatching; and recipe management.

Production, capacity, and demand planning

Production planning is the process used to define, plan, and control long-term production goals. A production plan incorporates manufacturing capacity, sales forecasts and orders, and raw material requirements. These planning processes lay the foundation to ensure manufacturing has sufficient resources and capacity to build finished goods and meet forecasted as well as confirmed orders.

MES

A manufacturing execution system (MES) is critical for WIP management. The data collected and stored in the MES regarding the manufacturing process provides other automation systems the granularity of information required for the evaluation of real-time production events. This information can be used to ensure that the material is processed with the right equipment at the correct step in its process flow and facilitate data collection. By enabling information to flow freely between MES, ERP and automation systems, not only can dispatching and other automation systems gather key insights on the state of processes, it becomes possible to visualize the gathered data for reporting purposes and to further optimize production controls.

Scheduling

Scheduling is the process used to define, plan and control near- to mid-term production plans, typically at a daily or shift level (4-, 8-, or 12-hour increments). Scheduling is effective for calculating expected resource loading depending on number of tasks, how resources are expected to be utilized, and any known constraints.

Scheduling becomes inefficient the moment scheduled events are unable to be executed as planned and there is a real-time need to determine sequencing of tasks and resources. Some common events that interrupt the most carefully scheduled production plans include maintenance tasks, equipment failures, fluctuations in staffing levels, execution/misprocessing errors, bottlenecks, starvations, and changes in management priorities.

As unplanned events inevitably take place, the minutes and system resources invested in rescheduling efforts can—over time—add up to significant losses in potential revenue and valuable production time. As such, an event-driven dispatcher is recommended for the purposes of handling the real-time execution of scheduled production plans as it is specifically designed to accommodate and react to unanticipated events quickly and efficiently.

Event-Driven Dispatching

Event-driven dispatching systems respond to planned and unanticipated events on the production floor by evaluating events and resources in real-time in order to keep production flowing optimally. Event-driven dispatching keeps equipment operators informed of the best lot to run, at the current moment, on the equipment they are operating. These systems synthesize and evaluate real-time production dynamics in order to provide nearly immediate updates to operator dispatch lists so production experiences virtually no delay and helps to prevent excess tool wait times, which are common in the absence of automated dispatching systems.

Event-driven dispatching systems should seamlessly incorporate existing manual, or partially automated, WIP management methodologies. There should be no need to reinvent any working methodology. Production floors achieve improved equipment utilization, maximum manufacturing capacity and reduced labor costs by consistently applying processing rules and automating lot-prioritization evaluation factors such as batching requirements, timer conditions, equipment capability, equipment availability and management priorities.

Automated WIP Management

Automation (made possible through well-integrated systems and equipment) offers significant advantages over manual processes. The goals of integrated and automated WIP management include:

  • eliminate operator time spent collecting data and maintaining process job context
  • improved data quality by eliminating manual entry data transfer errors
  • improved yield based on data-driven process controls
  • avoidance of misprocessing by implementing automated processing verifications
  • improved throughput by executing processes with little to no operator intervention
  • prevention of starvations and bottlenecks
  • efficient movement of WIP through process steps

As WIP moves through automation steps, an abundance of data becomes available for collection and analysis to enable and further optimize process controls which will result in improved factory efficiency, improved product quality, increased profit, and reduced waste.

Example Automation Steps:

  • A lot is manually identified via scan of lot id and operator credentials. With advanced automation, a lot can be automatically identified by reading, for example, a carrier RFID and retrieving the lot ID from a material tracking system.
  • MES verifications check to see that the lot is in the correct state and is positioned at the right equipment for the current processing step for the lot.
  • The equipment may then be verified to be communicating and in the correct control state and material which will be consumed during the processing of the lot is available. With advanced automation, equipment recipes and setup requirements may also be verified along with additional lot verifications.
  • Lot is tracked in, processed and monitored
  • Collection of:
    • processing information (process start/end times, context info regarding lot, location, environmental conditions, tools involved and setup conditions, processing time),
    • measurement data,
    • material consumption,
    • and any modifications to setup data (equipment recipe & recipe parameters; equipment constants).
  • Verifications at end of process step (number of processed units equals expected; no critical equipment alarm or event occurred; processing time is within reasonable range)
  • Process results are captured and lot is tracked out
  • Lot is unloaded
  • Exception handling: Failed verifications at any time lead to actions such as setting the lot on HOLD, logging a piece of equipment or a capability “DOWN” in MES after an alarm, or sending an email alerting appropriate personnel

Short and Long-Term Automation Benefits

Surprisingly, the number one cause of production downtime is still human error. Reducing the opportunities for human error through automation strategies improves factory efficiency and product quality. By automating standard tasks, shop floor personnel can focus on problem-solving and more complicated tasks which are better suited to humans than software. Automation also enables more flexible workforce planning by reducing the amount of training required for equipment operators.

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Automated WIP management strategies cover the automation of standard production processes at equipment. Once in place, full equipment integration and automation along with carrier and material identification can significantly contribute to longer-term automation objectives such as automation of equipment engineering and production engineering processes, integration of adaptive process control (run-to-run) loops, and automated transport and equipment loading systems.