“You should strive for a U-shaped layout,” I said. “It is U-shaped!” responded the Engineering Manager. We were both looking at the same factory layout. He was looking at how the machines were placed so that they formed three sides of a square, or a U-shape, and I was looking at the process flow and material flow, which twisted and looped like the proverbial plate of spaghetti.
Batch and queue is the hallmark of a mass production system. Parts are processed, moved in large quantities to the next process, wait for their turn, are processed, and moved as a batch to the next process. Lean is characterized by having very small amounts of work-in-process (WIP) moving rapidly through the entire process to the customer. This is commonly referred to as flow.
When the goal is to have flow, the U-shaped cell, or something similar, is often the best solution. It might be an O, or a D, or a C, or something not alphabet-shaped, but the path does not cross itself and the start and end are very close to each other. The physical layout may not look like anything in particular but when you map process flow, material flow, and people flow, it tends to look somewhat circular.
Arranging machines into process sequence and minimizing material movement can create a straight line. Straight lines can cause lots of walking because the operators have to move the parts down the line and then return to the start position. A straight line process, also called an “I” line could also cause stacks of inventory if operators are static and inventory is between each position. By folding the line into something more U-shaped, the operators can now work on both sides and minimize the amount of time spent walking and maximize the time spent working. If operators are working instead of just walking, then material, and information, is moving.
The greatest advantage of the U-shape is the flexibility for line balancing. A line configuration only allows balancing with the operations to the right and left of a station. A U-shape cell allows balancing with stations right and left, but also behind and to the right and left. That doubles or triples the possible combinations of tasks and allows balancing even as there is variation in mix, model, and customer demand.
Do not focus on the layout of machines or equipment when striving for U-shaped cellular manufacturing solutions. Focus on flow: the flow of processes, material, and people. Optimize the flow and let the shapes fall where they may.
Robert H. Simonis is the Senior Consultant for Manufacturing and Operations at KCE Consulting LLC. Robert has over twenty years of leadership experience including ten years factory management and ten years of global responsibilities in automotive, electronics, machining, and complex assembly operations and is recognized as a Lean enterprise expert.