(This is the fifth post in a series about the 14 Principles of The Toyota Way.)
As previously stated, the ideal process will have implemented continuous flow featuring time-balanced process steps with very few peaks and valleys in production rates.
However, that is very difficult to achieve when demand goes up and down sharply and with limited predictability. One strategy to combat this is with pull/kanban systems. It adds a lot of flexibility when other process steps lack continuous flow and incorporate batching (like having to buy in larger quantities and reorder intervals are not steady).
Another viable way to handle spikes in demand (or valleys) is NOT to make process operators work faster or harder (“haste makes waste”) but through scaling the process up or down to meet demand or with adding or taking away process operators and shifting process steps up or down the line.
And this is the fourth principle of The Toyota Way:
“Level out the workload (work like the tortoise, not the hare.)”
Like with the fable about the tortoise and the hare, “slow and steady wins the race.” Maintaining optimal effort from operators is important, whether demand goes up or down. You don’t want to slow the process effort down when demand falls, nor do you want to double the individual efforts applied by operators when demand doubles.
So how do we handle this?
Using an example where demand doubles, a “simple” way to handle this is by replicating the entire process. Instead of using one assembly line to complete a process, create a second flexible assembly line to handle the additional demand.
However, in most cases of demand rising or falling, it isn’t so easy. Maybe demand fluctuates by 10% one way or the other.
Using a second simplified example, let’s say a four-operator process is balanced and each operator carries out five process steps to complete the assembly of a part. There are twenty individual process steps needed to complete the process (operator 1 gets steps 1-5, operator 2 gets steps 6-10, etc).
Now let’s say demand jumps up 25%. If process steps are standardized and balanced properly to handle fluctuating demand, you could add a fifth operator to the process and shift process steps up or down (depending on where the fifth operator is placed) and give each of the five operators four process steps to complete. Therefore you still have the twenty process steps to complete, but the effort given to each operator remains the same and they can devote adequate time to completing each process step in the same amount of time as before (operator 1 gets steps 1-4, operator 2 gets steps 5-8, etc).
In the real world, not all steps are balanced and demand doesn’t always scale so easily. That being said, there are strategies you can apply to find interesting ways to balance the workloads.