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Article Revised: March 27, 2019
This is the fifth post in a series taken from a lesson in Pyzdek Institute Lean Six Sigma Black Belt training. Future posts will continue the topic. You can find all of the articles in the series by searching this site for the title.
Which non-value added activities can be eliminated immediately?
Of course, the standard work description, including the work element times, is just a starting point. Constant improvement is expected in the way the work is done and the time it takes to do it. For the long term, consider creating an opportunity map for the work within the cell and pursuing the opportunities over time. It’s a good idea to do this even before the original work cell design is complete. You can use the work element time data you just collected for this purpose. Create a stacked bar chart showing all of the work element in the work cell. One of the bars is for the work elements used currently, the other will show only the work elements that are actually included in the work cell design. In particular, you need to focus on eliminating non-value added work. You may recall from the lesson on opportunity maps that work is considered value added only if all of the following are true:
- It is done right the first time. Rework does not count as value-added work.
- The customer is willing to pay for it.
- It changes the thing being worked on. Moves, inspection, or storage are not value-added.
Figure 6 shows a stacked bar chart of the initial improvements that can be made to the weld + inspect process when changing the design from batch-and-queue to a continuous flow cell. The team focused on non-value work elements, mainly waiting and moving, and made the improvements shown.
Figure 6-Paper Kaizen
How should the workplace be arranged?
Cell design is performed in two phases.
- Phase 1: Document the current state. This topic has been covered in several earlier modules. At this point in your Lean Six Sigma project you have already created a lean value stream at the process level. Cell design begins from there.
- Phase 2: Convert to a process-based layout. Cause-and-effect diagrams are a useful tool here.
When creating a cause-and-effect diagram you were taught that they can be used to identify the causes of a problem you are trying to solve. Here the problem is one of achieving continuous flow. When creating a cause-and-effect diagram use the “4 Ms” as a starting point: Men (and women,) Methods, Machines, and Materials. How should these elements be combined to achieve maximum flow?
How should we layout the equipment so movement of people and materials is efficient?
Continuous flow work cells are nearly always shaped like either “U” or “C” to minimize walking. The equipment and workstations are arranged close together in the sequence of the work steps. This arrangement reduces walking distance to a minimum and results in the worker being near the start point of the next work cycle when he completes the work cycle. It is different than many traditional operation based work layouts where a worker sits or stands in one position and does a very simple repetitive task all day. The traditional work arrangement leads to psychological issues such as boredom or mental fatigue, as well as physical problems from repetitive stress injuries.
Where will WIP be stored?
Standard stock refers to the materials that are needed to begin work within a process, such as work-in-process inventory (WIP.) The design of the work cell will influence the WIP requirements; conversely, WIP requirements will influence the design of the work cell. Ideally, one piece will start at the beginning of the work cell and progress through each process step without the need to stop. However, there are circumstances that may require additional stock. For example, if part is welded at one step and needs to cool before it can be processed through the next step. Or if there is a need to perform an inspection before the part is placed in a subassembly where it can’t be accessed afterwards. Bottlenecks, by definition, can’t produce enough to meet takt time requirements. The bottleneck problem is sometimes solved by additional WIP to supplement the bottleneck’s output.
How can we rearrange the workplace quickly when we need to make a different item?
As discussed earlier, the equipment used for Lean production tends to be smaller and more mobile. It is usually possible to rearrange the equipment in a work cell quickly so different parts can be made using the same equipment. Work cell design should make this as simple to do as possible. Also consider where equipment, fixtures, WIP and other items will be placed when not needed for the item currently being produced. Storage areas should be nearby and clearly marked so workers know where to store unneeded resources, and where to find them when they are needed again. It should be easy to physically move the equipment and, if necessary, reconnect to power, plumbing, etc.
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