The next mapping step is to draw the basic production processes. To indicate a process we use a process box. The general rule of thumb for the door-to-door map is that a process box indicates a process in which the material is flowing. Since drawing one box for every single processing step would make the map unwieldy we use the process box to indicate one area of material flow, ideally a con- The process box stops wherever processes are discon tinuous flow nected and the material flow stops.
For example, an assembly process with several connected workstations, even if there is some WIP inventory between stations, would be drawn as one process box. But if one assembly process is disconnected from the next assembly process downstream, with inventory stagnating, accumulating, and being moved in batches between them, then two process boxes would be used.
Likewise, a machining line of say 15 sequential machining opera- tions, such as drilling, tapping, etc., that are connected by a transfer line between each operation would be shown with only one process box on the door-to-door map, even if some inventory accumulates between machines. (If a detailed process-level map is later made for the machining area alone, then you would draw one box for every indi- vidual machining step.) But if there are distinctly separate machining processes in the plant, with inventory between them stagnating and transferred in batches, then each gets its own process box.
Material flow is drawn from left to right on the bottom half of the map in the order of processing steps; not according to the physical layout of the plant. At Acme Stamping we find six processes in the steering bracket material flow, which occur in the following order:
• Stamping
• Spot-Welding Workstation 1
• Spot-Welding Workstation 2
• Assembly Workstation 1
• Assembly Workstation 2
• Shipping