To get continuous-flow systems to flow for more than a minute or two at a time, every machine and every worker must be completely “capable.” That is, they must always be in proper condition to run precisely when needed and every part made must be exactly right. By design, flow systems have an everything-works-or-nothing-works quality which must be respected and anticipated. This means that the production team must be cross-skilled in every task (in case someone is absent or needed for another task) and as the machinery must be made 100 percent available and accurate through—a series of techniques called Total Productive Maintenance (TPM). It also means that work must be rigorously standardized (by the work team, not by some remote industrial engineering group) and the employees and machines must be taught to monitor their own work through a series of techniques commonly called poka-yoke, or mistake-proofing, which make it impossible for even one defective part to be sent ahead to the next step.’
A simple example of a poka-yoke is installing photo cells across the opening of each parts bin at a workstation. When a product of a given description enters the area the worker must reach into the boxes to get parts, breaking the light beam from the photo cells on each box. If the worker attempts to move the product on to the next station without obtaining the right parts, a light flashes to indicate that a part has been left out.
These techniques need to be coupled with visual controls, as mentioned earlier, ranging from the 5Ss (where all debris and unnecessary items are removed and every tool has a clearly marked storage place visible from the work area) to status indicators (often in the form of andon boards), and from clearly posted, up-to-date standard work charts to displays of key measurables and financial information on the costs of the process. The precise techniques will vary with the application, but the key principle does not: Everyone involved must be able to see and must understand every aspect of the operation and its status at all times.
Once the commitment is made to convert to a flow system, striking progress can be made very quickly in the initial kaikaku exercise. However, some tools (for example, massive paint booths with elaborate emission control equipment) will be unsuited for continuous-flow production and won’t be easy to modify quickly. It will be necessary to operate them for an extended period in a batch mode, with intermediate buffers of parts between the previous and the next production step. The key technique here is to think through tool changes to reduce changeover times and batch sizes to the absolute minimum that existing machinery will permit. This typically can be done very quickly and almost never requires major capital investments. Indeed, if you think you need to spend large sums to convert equipment from large batches to small batches or single pieces you don’t yet understand lean thinking Excerpted from Page numbers 60-61 of ‘Lean Thinking’ by Womack and Jones