Lean Accumulation
Lean Manufacturing and accumulation can coexist, as long four key elements are addressed: Location, Size, Training, and Consolidation.
Toyota pioneered modern Lean manufacturing and created a highly efficient and reliable manufacturing system the rest of the world adopted. Lean philosophy says to closely examine manufacturing processes, find unnecessary steps, and eliminate them. By only allowing room for “value added” steps, product will be produced simpler and faster. Value added steps are defined as any step that creates value for the customer. Accumulating work in process does not add value, so conventional Lean thinking is to eliminate this wasteful step.
To get the same results in throughput, cost per case, and overall operation efficiency, you need to spend additional time and money making sure value added steps are running at ultra-high, possibly unattainable, efficiencies. A line with six 97% efficient machines only operates at 83% due to their compounding effect. Even getting each machine to 99% only raises overall line efficiency to 94%. The most efficient way for production lines to maximize efficiency is to employ Lean Accumulation.
Lean Accumulation uses four key elements. The desired results will not occur if one or more is neglected.
Location:
The accumulator should be located to prevent downtime on the line’s constraint operation. It should either maintain a constant flow of material to the constraint or be ready to accept finished product from the constraint.
Size:
Excessive accumulation wastes floor space and insufficient accumulation causes downtime, so how do you appropriately size an accumulator? Every machine on the line has a Mean Time to Repair (MTR). In Lean Accumulation, your accumulator size is equal to the line’s longest MTR (ie. a three minute MTR needs three minutes of accumulation).
Training:
Every accumulator has a normal state. Upstream from the constraint, its normal state is full. Downstream from the constraint, its normal state is empty. Operators need to know how accumulation fits into the team’s production goals and make decisions that always bring the accumulator back to its normal state. Decisions may include when to raise or lower machine rates, which problems to fix first, or when it is ok to briefly leave a station unattended.
Consolidation:
Every production line has several other non-value added steps, such as single filing, multi-laning, orienting, hand loading/unloading, etc. Combining these operations into the accumulator reduces cost, energy usage, and overall floor space.