Page 284 - How To Implement Lean Manufacturing

Using the Pr escription—Thr ee Case Studies 261

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• The takt calculation was: Takt = (22 – 2.5) 60/165 = 7.09 minutes. It was based
on two shifts each lasting 11 hours. Each shift included 1.25 hours of meal and
rest breaks. Production was 3550 units per month—with 21.5 days/mo = 165
motors/day.
• The processing time for the ten models was relatively straightforward to
calculate and it made model-mix leveling easy. All models of small stators take
one particular time, while all models of large stators take a longer time. Since
large stator motors comprise 52 percent of the total, we decided to level with an
initial model mix of 50/50, large and small stators. We were not comfortable
designing a perfectly leveled system, rather we would level production based
on stator size and work in the specific model planning with the heijunka board.
For our design, at this point, that was all we needed to do.
• To size the buffer and safety stocks, we did not have good information, so we
chose to do it rather arbitrarily. For buffer and safety stock combined, we
decided to have two weeks for all weekly pickups and three days for all daily
pickups. For cycle stock we used the pick-up volume, as a starting point.
Table 16-9 shows the outcome of the plan for the inventories.

Synchronizing the Production, Internally

Defining the Work
This was very difficult, and when we were doing it, I was convinced it would need to
be done again because the processes were unstable and cycle times had large variations.
Nonetheless, you need to start somewhere, so we elected to use process, not element
times. (For example, in the process to Hipot, the motor needed several steps, or work

Safety
Monthly Pickup Daily Weekly and Total
Model Demand Frequency Prod Prod Cycle Buffer FG Inv.
Ia 1130 Daily 53 53 159 212
Ib 720 Daily 34 34 102 136
II 950 3/wk M, W, F 44 44 132 176
III 475 1/wk 110 110 220 330
IV 175 1/wk 41 41 82 123
V 90 1/wk 21 21 42 63
VI 50 1/wk 12 12 24 36
VII 20 1/wk 5 5 10 15
VIII 20 1/wk 5 5 10 15
IX 10 1/wk 2 2 4 6
Total 3550

TABLE 16-9 Inventory Plans