Understanding Conwip: A Constant Work in Progress Approach

In the world of process optimisation and workflow management, Conwip is an intriguing methodology that stands out for its simplicity and effectiveness. Constant Work in Progress—or Conwip for short—is exactly what it sounds like. It ensures that work flows consistently through a process, preventing overloads and bottlenecks. But what exactly is Conwip, and how does it differ from other popular systems like Kanban?

What is Conwip?

Conwip is a system designed to keep the amount of work-in-progress (WIP) in a process stable. It sets a fixed number of products, services, or tasks that can be in progress at any given time. The idea is to maintain a constant flow of work, without letting it fluctuate too much. The goal is to prevent congestion in the system while ensuring every stage in the process has a manageable workload.

This is done by limiting the amount of work allowed into the system until current tasks are completed. Once a task is finished, it frees up space for the next one to enter. This method ensures that resources are used efficiently, without overwhelming any part of the process.

Example of Conwip in Action

Imagine a car manufacturing plant. The plant has decided that no more than ten cars can be worked on at any one time. This is their Conwip limit. By doing this, the workers at each stage—assembly, painting, inspection—can focus on a manageable number of tasks. No one is overloaded, and all resources are used efficiently.

Once a car is completed and leaves the system, a new car enters. This constant flow ensures smooth operation without piling up unfinished work.

Conwip vs. Kanban: What’s the Difference?

While both Conwip and Kanban are systems used to manage workflow and limit WIP, they operate in different ways.

In Kanban, each step in the process has its own WIP limit. For instance, the design stage might have a limit of 3 tasks, the production stage 5, and the testing stage 2. This means each stage works independently to manage its own workflow.

In Conwip, the WIP limit applies to the entire process. This means there’s a single limit for the whole system, not individual limits for each stage. Work flows through the system as a whole, based on overall capacity, rather than being constrained at individual steps.

Key Difference:

• Kanban controls WIP at each stage.
• Conwip controls WIP across the entire process, allowing for more flexibility in how tasks are handled.

Implementing Conwip

The most important factor in implementing Conwip is determining the right WIP limit. Set it too high, and you’ll overwhelm your process. Set it too low, and you won’t be using your resources efficiently. So how do you find the right balance?

A helpful tool is Little’s Law, which states that:

WIP = Throughput × Cycle Time

In other words, the amount of work-in-progress in your system should equal the rate at which tasks are completed (throughput) multiplied by how long it takes to complete a task (cycle time). By analysing these metrics, you can set an appropriate WIP limit that keeps work flowing without overloading the system.

Example

Take, for example, a local council department that processes building permits. The department can process 10 permits per day, but they have a backlog of 100 permits. By applying Conwip, they can set a limit on how many permits are worked on at once—let’s say 20. As each permit is processed and completed, a new one is started. This steady flow helps the council manage their backlog while improving completion times.

Benefits of Conwip

1. Consistent Workflow: Conwip ensures that tasks move steadily through the process, reducing the risk of bottlenecks and ensuring that resources are used effectively.
2. Simplified Management: By having a single WIP limit for the entire system, Conwip simplifies the management of work. This is especially useful in complex environments where it’s hard to predict how work will flow between stages.
3. Flexibility: Unlike Kanban, which sets limits at each stage, Conwip allows work to move freely between stages, making it easier to adapt to changes in demand or capacity.

Conclusion

Conwip provides a simple yet effective way to manage work-in-progress in any process. By maintaining a constant flow of tasks, it helps organisations make the most of their resources, avoid bottlenecks, and keep their processes running smoothly.

While Conwip is often compared to Kanban, it can also be used as a standalone method for managing complex workflows. Whether you’re running a production line, handling customer orders, or managing a service department, Conwip can help you streamline your operations, improve efficiency, and keep your processes under control.