Limitations of Value Stream Mapping

Value Stream Mapping (VSM) is a visualization tool, oriented to the Toyota version of Lean Manufacturing. As with any tool, it has limits.

The Problem of Over-hype

Authors and consultants claim unrealistic benefits and applications for VSM. At the same time, customers and managers tend to look for the "silver bullet." This situation sets up unrealistic expectations and diverts attention from important aspects of complex problems.

As with the "miracle garden tools" advertised on television, beware of anything that promises to solve all your problems. It takes more than a claw hammer to build a house. One needs a saw, level, tape measure and many other tools.

Non-Technical Aspects of Lean

Value Stream Mapping is a technical tool that examines the physical system, processes and interconnections. Equally important for Lean Manufacturing success is the people side. Factories are complex socio-technical systems that require an integrated approach.

For example, Lean Manufacturing requires high teamwork for motivation, coordination and problem solving. It requires an effective mobilization of the collective intelligence of the organization. There may also be quality issues that the company could address through Six Sigma or TQM techniques. Five-S can clean up the plant, improve safety and further raise productivity. Value Stream Mapping addresses none of these directly. This is especially important in manufacturing where many managers have a technical bent and limited awareness of the human issues to begin with.

Fuzzy Definitions

The definition of "value stream" is rather fuzzy. For example: 

1) The map does not begin to capture "all specific actions."

2) The definition says "specific product" but the originators apply it to product families with little guidance as to what constitutes a family.

3) "Value Stream" conjures a vision of water running through a series of value-adding activities. But many icons do not depict value adding activities, do not touch the product and do not flow like a stream.

"The map is not the territory." -S.I. Hayakawa

High Variety Situations

VSM was developed and popularized in the automotive industry. Automotive plants are highly focused factories with a narrow family of products for a only few customers. VSM works well in these situations.

However, in high variety-low volume factories, VSM is cumbersome and unrealistic. Here we must supplement mapping with Group Technology and other tools.

Symbology Affects Thinking

Many VSM symbols correspond to specific Toyota techniques such as "Withdrawal Kanban" or "Workcells." This may lead the user to employ these techniques even when they are inappropriate. In addition, there are other solutions that might be more effective in specific cases. These tend to be ignored.

Overcoming the influence of symbology requires broad knowledge, creativity and awareness on the part of users. Rote thinking may lead to the wrong path.

Training

To be effective, a VSM group requires training on symbols and mapping techniques. They also need training on the Lean Manufacturing elements that the symbols represent. This contrasts with Process Mapping which only requires a trained facilitator.

Other Mapping Techniques

Other mapping techniques are also useful and give different perspectives. Process Mapping is an example. The original system invented by Frank Gilbreth in the early 1900's is still the most useful. The Gilbreth approach is fundamental, highly visual and discriminates between waste and value-added. It is also simple, intuitive and suitable for untrained groups.