CONWIP is a system of production control that seeks to improve overall efficiency in the workplace. It stands for Constant Work In Progress and is similar in many ways to the Kanban system of production, originally developed for Toyota. Both are popular manufacturing workforce solutions that promote increased efficiency in production. There are distinct differences between the two. CONWIP can help your contingent workforce in certain aspects of the production process that Kanban can not.
Push vs. Pull
The push system of production states that as soon as a new product is ordered, the materials immediately go into the production line. No matter how many other products are still waiting on production, each new production order is placed immediately into the queue. It waits patiently until the assembly line is ready for it.
A pull system waits until one product assembly process is complete. Then it pulls the next one into production. This is a good way of allowing workers to learn where there are bottlenecks in the production process—e.g. a machine breakdown, shortage of a particular material, etc. In a pull system, these problems can be spotted immediately and resolved quickly. It also caps inventory levels helping to eliminate excess inventory and the costs that come with it such as storage.
CONWIP vs. Kanban
CONWIP and Kanban use pull systems of production to cap inventory and identify problems in production. However, they are often used in different ways to different ends. Kanban is good for mass production of a single product. Every part involved in production is assigned a specific card. Only a certain number of cards are issued for each type of part. Since no part is allowed into production without a corresponding card, it effectively caps production at whatever level you deem necessary.
CONWIP also issues cards to correspond with parts in production. However, the cards don’t correspond with any specific type of part-only with the quantity that’s allowed. The products made using CONWIP can be made to order using specialized or unusual parts that the other products in the production order don’t necessarily call for.
It’s even possible to combine the two systems into a single hybrid which assigns Kanban cards to uniform parts and CONWIP cards to specialized parts. This allows both to be kept track of with equal ease.
Advantages and Disadvantages of CONWIP
Kanban makes it difficult to keep track of more unusual parts and products that are made to order since each card is specifically numbered according to part type. CONWIP is more flexible and handles these production orders with ease. However, the numbering system on Kanban cards allows you to manage the production sequence of a particular product automatically. Whereas with CONWIP, products must be tracked and recorded by hand. While this isn’t necessarily a big deal, it does allow for human error. Assigning cards to the wrong parts can lead to production—even mass production—of the wrong product. With Kanban, this kind of error isn’t a factor since the parts for each product in the production order are always the same.
Simply by exercising a little bit of looking before leaping, problems can be easily avoided. By implementing a hybrid of CONWIP and Kanban into your manufacturing process, you can track both mass production and specialized production. Eliminating waste and immediately finding and fixing errors in the production process will be your new normal. Adopting both workforce solutions as needed can help you eliminate waste, save time and money and increase production overall.