Concrete methods of conception of system of piloting of line in mode Conwip

This article describes the principles and implementation of the CONWIP (CONstant Work In Process) method. CONWIP enables you to control the flow of a production line by keeping the work-in-process constant, so as to keep manufacturing lead times under control. This method is suitable for all types of manufacturing production, from rates of a few units per month, to rates of millions of parts per month. It can be applied to manufacturing workshops as well as to repair or recycling lines.

The CONWIP method is particularly well suited to workshops characterized by high variability, which are difficult to manage using MRP (Manufacturing Resources Planning) alone, and impossible to manage using pull-flow Kanban techniques.

This variability may stem from the diversity of parts to be manufactured within a single family, each part having a different operating time linked to its own morphology or variants. It can also stem from the intrinsic characteristics of a manufacturing process that is highly demanding and difficult to control completely, requiring rework on parts, scrap, frequent machine stoppages, all of which lead to delays and desynchronization of flows. These complex and not always stable manufacturing processes are often characteristic of very high value-added companies. What might sometimes be seen as industrialization problems must more often than not be seen as a mark of technological advance, innovation, differentiation from the competition, and minimized time-to-market. Under conditions of rapid product renewal, the learning curves that enable the gradual stabilization of production processes no longer come into play. Complexity here is an asset in the face of competition from low-cost production zones, where there is less variety in the products manufactured and more standardized production lines. However, it is essential to know how to manage these highly variable production lines with the best possible performance.

For these complex lines, it turns out that operational flow management using the CONWIP (CONstant Work In Process) method gives very interesting results in terms of in-process control, lead-time management and customer service levels.

The CONWIP method for managing production flows mobilizes several production management concepts:

• MRP (or any other planning tool) for selecting item numbers and quantities to be produced;

• theory of constraints for special attention to bottlenecks and permanent dynamic balancing of the line;

• just-in-time, using pull-flow techniques to engage work on the line;

• visual management for responsive, decentralized capacity...