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Lean operations strive to move materials through processes in the smallest quantity possible. As a value stream approaches one piece flow, inventory tends to drop and productivity rises.

Unfortunately, this streamlined flow is often interrupted by large, fixed pieces of equipment that are difficult to move or replace.

This type of equipment is often referred to as a monument. Because of their size and the time it takes to load them and run the process, these monuments create a batch and queue process. A full lot must be collected prior to running the machine, driving inventory up.

Monuments stick around for two main reasons. The first is that there are no known alternatives. The second is more emotional. There is often a large expense sunk into a monument, and people confuse expense with value.

Examples include large paint systems, ovens, conveyors, and in some cases, software systems.

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One of the telltale signs of a monument is the accumulation of inventory before or after it to accommodate the vast size of its batches. An example in the manufacturing world might be a curing oven after a paint process. The oven might take hours to properly ramp up to the proper temperature and cure the products. The paint booths that feed the oven may be painting a product every fifteen minutes. If the oven is in the middle of a curing cycle, these freshly painted products will have to sit. Due to the mismatch in timing, the inventory accumulates until the oven can be run at its capacity. If it takes 3 hours to run, the batch size would be 12 for the 15 minute example.

When a monument is not removed, there are ways to accommodate it. Note that I said ‘not removed’ and didn’t say ‘can’t be removed.’ Monuments often are treated as being more sacred than they really are. For this reason, people seldom look seriously at alternatives. One issue is that there are often tremendous sunk costs associated with a monument.

The most effective way to deal with a monument is to treat it as virtual flow, or create what is known as a curtain process. In effect, it as if you put a big curtain around the monument, and when you stick some unfinished goods in one side, you get your finished goods out the other. What happens inside the curtain is not visible to the upstream or downstream person. Generally, this is done by establishing Standard WIP. In the example above, your Standard WIP would be 24 pieces. You would always have 12 pieces in the oven, and the other 12 would be in some combination in piles coming in, or being drawn off the last run. The last item would be pulled from the downstream pile just as the 12th one hit the upstream pile, making a complete batch to load into the monument.

In addition to the obvious issues with inventory, space, and travel between machines, there is another big drawback to monuments. They can lock in a process and make it hard to do improvements. This is particularly true for things like software packages and phone systems for call centers. Coming up with a great idea is not enough. It has to be one that can also be supported by how the software package runs. Many potential improvements are tabled because of the requirements of monuments.

The best method for dealing with monuments is one of avoidance. You should never knowingly buy a monument if you are trying to establish flow. On some occasions it may be unavoidable, but make sure you don’t add a monument to your process until you have exhausted all other alternatives.

More frequently, though, monuments are inherited. In these cases, do what you can to create a process that gets as close to flow as possible. Standardize the processes. Even if you can’t reduce the inventory, make sure you are controlling it with kanban. Finally, continuously challenge the assumption that the monument is really needed.

  • Make sure that cost estimates about replacing monuments include the extra inventory required, maintenance costs, lost productivity, and the cost to production if the monument goes down. Your monument probably doesn’t provide as big of a benefit as you think it does.
  • The immobility of a monument will hamper your Lean efforts for years. Your layout will be far less flexible, and you often be limited in your improvement options.
  • Don’t let the costs sunk into a monument impact your decision making. If you find a better way to do things, the $2 million you spent on a giant automatic machine should not factor into your decisions.

Monuments present a significant leadership challenge because they act as a barrier to flow, and inspire people to operate with larger batches. Your most important task is to create a process that links your other processes to the monument in a way that is least disruptive to flow.

Most monuments come into processes as a result of false efficiencies. People become enamored at the speed of a machine, but forget to look at all the factors that actually go into production. Make sure to look at how the whole system will operate before investing in a big, immobile machine. If possible, run a simulation to see the machine’s impact on inventory and flow.

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