Resources Shared by Different Processes
Manufacturing, service, and healthcare systems often face a common problem. Expensive resources are often required to be shared by several production lines or used by multiple departments. At Boston Medical Center, the Emergency, Inpatient, and Outpatient departments all share multi-million dollar CT Scanning equipment. The equipment is expensive, requires highly trained personnel, and has a fairly large footprint so it can’t be moved. The usage of the system does not justify any one of the groups having their own CT Scanners. When using Value Stream Mapping (VSM) to create a picture of how the system looks and behaves, which department do you use — Emergency, Inpatient, or Outpatient? If changes are made to the value stream of one of the processes without the others, the result is often disastrous. Many shared resource problems in a wide variety of industries go unsolved because the issues are multi-dimensional. Because of this complex nature, the problem is difficult to solve using traditional VSM methods.
Product Mix Changes Frequently
In service systems and in assembly of expensive items it is common to run more than one type of “product” on the same line at the same time. This means that several products, each type having unique assembly times, assembly requirements and routing will be present on the same line at the same time. Furthermore, the product mix may change from day to day, and during the day. Creating a clear picture of the problem becomes difficult with traditional VSM methods. If a snapshot is created of how things look right now, in a few hours the picture would be completely different. A change to processing times causes buildup to occur in different areas. Traditional VSM becomes ineffective because many pictures would be needed to capture system. But which of those pictures would be used to make a change?
High Variability in Processing Times
In many service and health care systems, variability is a tougher problem to solve than in manufacturing systems, where the inputs can readily be controlled. With traditional tools the variability is changed to a simple average. Using averages to make decisions on a complex system is like using a chainsaw to perform surgery…the results are never going to be right.
High Variability in Routing Selection
When high variability in routing selection is first mentioned, it often conjures up pictures of a manufacturing job shop. Every order has the potential to move across the machines in a unique sequence. This high variability is often described as having “no process.” That description is simply inaccurate. Every single order has a tightly defined process. It is just difficult to describe with a single picture when trying to use an overview perspective. This problem is not limited to manufacturing job shops. Healthcare has a variety of these types of problems including the laboratory and the emergency department. Many general service processes exhibit the same behaviors including inbound call centers, insurance underwriting, etc. Again, traditional VSM methods can’t be used effectively to create a representative picture of this type of system because the single picture would provide little insight to the complex problem.
A lean practitioner will cringe at the very word “rework” because it means that the system has a built-in quality problem. In the “lean world” to allow the system to have built-in rework is costly, time consuming and just “wrong.” It goes against the very nature of lean teaching. That being said, reduction of rework may take time. In one company we observed that it took over one year to correct a design which caused manufacturing failures, and then incorporate those changes into products. In the meantime, this company still needed to meet the production requirements until the engineering changes rippled through the system. In many systems the problem of rework is resolved over time. The problem with rework is that it pushes work back into the existing processes. Calculating the effect of this random rework is difficult. If the rework is relatively small then a VSM can ignore the problem and provide a clean picture of the system. If rework is high then the variability of the process doesn’t allow VSM to paint a clear picture of the problem or show the result of changes to the system over time.