A spaghetti diagram provides a visualization of the flow of material and/or people through a manufacturing or business process. A spaghetti diagram is primarily used to visualize transport and motion, two of the seven wastes in lean thinking.
A spaghetti diagram is easy to construct. The most important input is process knowledge. Assembling a small team is a great idea, especially if the process of interest spans multiple departments. Not much else is needed: a plant layout or schematic, colored pencils or felt tip pens, and maybe some sticky notes.
Start at the first step of the process. Where does this material go next? What happens when it gets there? Be sure to capture decision points. For example, defects go to a rework station before moving to the next process step. I like to use red for transport (e.g., forklift moves or conveyors) and blue for motion (e.g., picking, placing, stacking). Use whatever colors work best to visualize your process.
A spaghetti diagram is a qualitative tool. To make the analysis more quantitative, you can measure distances, take process times, count forklift moves, etc. There are no rules, use whatever metrics best quantify your process.
After establishing a baseline of the actual process flow, use a future state spaghetti diagram to visualize the benefits of plant and office rearrangements, capital investments in new or additional equipment, etc.
Here is a case study. A manufacturer was ramping up production of a new product line. Additional capacity was planned but where are the best locations for the new equipment?
The team was very surprised by the amount of transport in the current state spaghetti diagram. There were long red lines everywhere…a plate of spaghetti indeed!
Future state spaghetti diagrams were developed for layout alternatives with the new mold cells and assembly cell, the two planned capacity investments. It was quickly seen that an additional curing oven (not in the capacity plan) would dramatically reduce transport distances and forklift moves: the red lines are fewer and shorter.
A spaghetti diagram is a simple and effective method to analyze and compare plant layouts. Put one in your Plan-Do-Check-Act tool continuous improvement kit.