March 26, 2002
Want know how lean manufacturing principles relate to your welding operation? You have to look further than just what is happening in the welding cell.
Following World War II and during the rebuilding of the Japanese industrial base manufacturers recognized that to restore production of manufactured goods and be globally competitive, new methods were necessary.
One of the pioneers in this re-engineering of manufacturing was Toyota, led by Taiichi Ohno, a company executive who was recognized as one of the most ferocious foes of waste humanity ever has produced. Ohno recognized waste ("muda") as the primary deterrent to a productive and efficient manufacturing operation. In a sense, the principles applied by Ohno and others at Toyota to eliminate muda, or nonvalue-added, steps in the manufacturing operation, became the basis for lean manufacturing.
One of the most recognized sources for a description of lean manufacturing and how it is applied is the book Lean Thinking.1
As described in this book, lean manufacturing principles provide a way to specify value, line up value-creating actions in the best sequence, conduct these activities without interruption whenever someone requests them, and perform them more and more effectively. In short, lean manufacturing is lean because it provides a way to do more and more with less and less—less labor, less equipment, less time, and less space—while coming closer to providing customers with exactly what they want.
Ohno and others at Toyota developed what has been know as the Toyota Production System (TPS), which is the most widely recognized lean manufacturing system in the world. Students of lean manufacturing will at some point study the TPS and how Toyota has used this system as the primary way to improve productivity and efficiency in their manufacturing operations.
By applying the TPS on an ongoing basis, companies can achieve continuous improvement, because one of the key elements of lean manufacturing is encouraging a work force to constantly look for ways to improve efficiency and productivity further in its manufacturing operation.
In many cases, these improvements are achieved through kaizen projects, which use a team-based, incremental approach to continual improvement. These kaizen projects are recommended and conducted by the employees themselves.
Incorporating lean manufacturing principles into welding operations offers a number of desirable benefits.
First, welding often is perceived to be an operation that is difficult to measure from a productivity standpoint. While numerous time studies could be conducted in an attempt to quantify the amount of time needed to produce a weldment, it is difficult to factor all of the variables, such as material irregularities, fit-up variations, and cleanliness of parts, that can have a direct effect on welding productivity.
Unlike a machining operation, welding quality and productivity can be affected dramatically by both prior and subsequent operations. With machining operations, we usually know what the incoming conditions are in terms of dimensions, material properties, and so forth, so we can predict, quite accurately, the amount of time required for a given operation in a specific machining work center. Similarly, the final condition of the component following machining is predicted easily and quite measurable.
However, these same conditions are not always known for welding operations. For example, the joint fit-up and exact joint geometry can vary significantly, even when they are controlled within accepted tolerances. This causes difficulty when we attempt to accurately predict the amount of time required to produce a given weld, let alone an entire weldment.
For a weldment with a 1/4-inch fillet weld, the amount of filler metal required for a 1/8-inch root opening is 2-1/4 times greater than that for a weld with a zero root opening (perfect fit-up), because the weld size must be increased to provide equivalent strength. From a productivity standpoint, the time required to weld the joint with imperfect fit-up is more than twice that for a joint with perfect fit-up.
Similarly, if welding is not done according to certain specifications, the as-welded properties of some components may be undesirable for subsequent operations, such as machining or anodizing. Situations such as this make it very difficult to include welding in a production system that relies on the uniform flow of components, as they do in a lean manufacturing environment.
As a result, the only way in which lean manufacturing can be applied to welding operations that include welding is to ensure that all the prior operations that could influence the welding quality or productivity are studied and controlled carefully so the components presented to the welding cell are as uniform as possible. Likewise, the welding operation must be controlled to a degree that the resulting condition of the weld metal and weldment is as uniform as possible so subsequent operations are not adversely affected.
The bottom line for deciding whether to implement lean manufacturing principles for welding operations is to consider much more that what is happening in the welding cell itself. While an initial study may show that the welding operation is the bottleneck for the overall manufacturing process, it is critical that the operation be carefully examined to ensure that the reduced productivity is not the result of inadequately controlled prior operations.
Further, in an attempt to speed up the welding itself, shortcuts may be taken that either reduce the weld quality or create undesirable conditions that adversely affect subsequent operations.
So, when making your welding operations lean, don't allow yourself to succumb to tunnel vision. To apply lean manufacturing ideas effectively, the overall operation must be studied carefully so that truly wasteful steps are eliminated and those that add value to the product are controlled carefully.
When that is accomplished, the adoption of lean manufacturing principles results in improved productivity and quality.
1. James C. Womac and Daniel T. Jones, Lean Thinking, (New York: Simon & Schuster, 1996).