THE IMPACT OF WORLD-CLASS MANUFACTURING PRACTICES ON SMALL MANUFACTURERS - by
David K. Johnson

Kanbans and Pull Production Methods

Kanbans are simple visual signals that are used to regulate the flow of material through the production system. The use of kanbans creates a pull system in which the production rate is dictated by upstream demand. Tying production to upstream demand avoids the problem of overproduction as well as inventory buildup, both of which hinder continuous improvement and lean manufacturing. Most kanbans, while surprisingly low tech, are extremely effective at the complicated task of production scheduling. Kanbans can be as simple as taped squares on the table, which signal the operator to produce product to fill the squares when they become empty.

The most effective kanbans include the following attributes:

1. Simple - inexpensive and low tech
2. Visual - the visual signal makes it obvious what the operator should do next
3. Automatic - always current without the need to enter information

One mistake often made by companies who are implementing lean manufacturing is to automatically jump to using kanbans. Using kanbans to pull the product through the production processes reduces inventory, which serves as a buffer to variation in process flow. In order for a company to successfully use pull scheduling the company must also reduce the need for inventory buffering by using other lean manufacturing techniques.

Cellular Manufacturing

Cellular manufacturing is a technique, which eliminates waste by matching the appropriate production equipment and sequencing in order to produce a selected product family. It is a technique that is often imitated, but seldom implemented correctly. To avoid the pitfalls of poor implementation one must first understand the philosophy behind the practice. Designing a manufacturing cell is more complicated than simply arranging equipment into a U-shape. The selection and sequencing of the equipment must be arranged so that the cell layout encourages the lean principles of communication, single-piece-flow, flexibility, waste reduction, and elimination of unnecessary transport. Although the U-shape is often advocated the shape of the cell is not as important as the principles behind the layout.

When designing a manufacturing cell a product family is selected on the basis of similar processing requirements. It should be noted, that since correctly selecting the product family often determines the performance of the manufacturing cell, extra attention should be paid to the selection of the product family. Processing databases can help simplify the selection process, but it shouldn’t substitute for careful analysis and judgment in regard to the processing requirements. The equipment selected for the cell must be flexible enough to process each of the members of the product family. The equipment should also be sequenced so that individual products within the family flow through the cell in a common direction. Batching and queuing within the cell should be strongly discouraged because of its disruptive effect on process flow. An effective method to discourage the natural urge to produce in batches is to design the cell so that there is no place to store unnecessary WIP. The results of cellular manufacturing are much more dramatic when those who design and manage the manufacturing cell understand the philosophy behind cellular manufacturing.

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Copyright © 2005. David K. Johnson. All Rights Reserved.