Lean manufacturing's goal is to slim down production while maintaining the output. By studying where manufacturing "eats" wastefully -- gorging on money, time or raw materials, say -- a company can figure out how to put the process on a diet. A spaghetti diagram is a method for analyzing workflow and the flow of materials to look for possible improvements. It gets the name because the diagrams are often convoluted, creating a spaghetti-like tangle.
Make the Diagram
Don't try to spaghetti diagram at your desk. To understand how workflow and product flow really happen, visit the manufacturing floor, or task one of your foremen with getting the facts for you. Map out the workspace, keeping everything to scale. Then chart how the workers and the materials move from machine to machine. Mark where anything is stopped -- for example, to inspect the products. Don't be alarmed if the spaghetti gets tangled and confusing; that's normal.
After you finish the spaghetti diagram, draw up an idealized diagram showing the same processes as if they'd achieved the lean ideal. Compare the two charts and see what you can change or trim from the real diagram to bring it closer to the ideal. Pumping hot water to the machines, for instance, may eliminate workers having to go back and forth to a tap. A scrap bin under each machine can reduce time spent throwing things away and encourage employees to discard flawed material. The exact changes will depend on what you're making and the process you're using.