Question #6: How should we level the production mix at the pacemaker process?
From the cell’s or line’s perspective this seems to make sense because in minimizes the number of required changeovers. However, from a value-stream perspective batching is the way to go. Batch-producing in assembly will increase the impact of problems, lengthen the lead time, and mean that the supermarket supplied parts has to be ready to meet sudden demand surges. “Being ready” means keeping more batched process parts in inventory in the supermarket, which again increases lead time, obscures quality problems and, in general, causes all those wastes associated with overproduction.
Instead, we need to level the mix of parts evenly over the shift at the pacemaker process. Reducing set-up times as much as possible, then we will have time to react to the cell’s / line’s “pulls” for parts.
With leveling, which requires much more frequent changeovers, the cell’s / line’s production mix looks like this:
By taking a few pains to level the production mix at the pacemaker process, which may seem unnatural at first at that location, the entire value stream will show improved lead time, quality, and cost. As we can imagine, these benefits are amplified greatly in value streams that are longer and more complex.
How can we ensure that kanban coming back to the pacemaker process, cell / line, which are the production instructions, come back in a sequence that levels the mix of products over the shift?
Production control places withdrawal (“move”) kanban corresponding to the customer order in a load-leveling box near the shipping dock in a mixed sequence. A material handler then pulls these kanban out of the leveling box one-by-one at eh pitch increment, and moves product from FG supermarket to the staging area one-by-one according to the withdrawal kanban.
Production control can send today’s order to the pick/ship material handler, who pulls all corresponding product out of the finished goods market at once and stages them for shipment. Pulling product produces a batch of production kanban, which are placed in a load leveling box near the cell / line, in a mixed sequence. The assembly material handler then pulls production kanban out of the leveling device one at a time at the pitch increment and as a result assembly produces in a mixed pattern.
The drawback of Option B compared to Option A is that in B an entire batch of finished goods is moved to shipping staging at once. Lean manufacturing strives to avoid or minimize batching as much as possible, always getting closer and closer to continuous flow.
Option A does require someone to repeatedly move product (at the pitch increment) not only from assembly to the FG supermarket, but also from finished goods to the shipping staging area.