Operations and Process Improvement
Domain 6 tests whether you can find the constraint in a process and prove that an improvement works.
Describe before you improve
Map the process, then measure it. Cycle time is elapsed time per unit; throughput is units completed per period. Little's Law states that work in process = throughput × cycle time, so 30 files in progress at 5 completions per day implies 6 days in the system. Takt time = available time divided by customer demand, and it sets the pace the process must meet.
Find the bottleneck
Capacity of a serial process equals the capacity of its slowest step. Adding capacity anywhere else adds inventory, not output. Theory of Constraints: identify the constraint, exploit it without starving it, subordinate everything else to it, elevate it, then repeat, because the constraint moves once relieved.
Improve
- Lean removes seven wastes: overproduction, waiting, transport, over-processing, inventory, motion, defects.
- Six Sigma DMAIC: define, measure, analyse, improve, control. Control is the step that keeps the gain.
- Root cause tools: 5 Whys, fishbone (people, process, equipment, materials, environment, management), and Pareto for prioritising the few causes producing most defects.
- SPC separates common-cause (system) variation from special-cause (assignable) variation; adjusting a stable process in response to routine noise makes it worse.
Worked example
A claims unit must process 200 claims daily. Each claim takes 20 minutes and each processor supplies 720 minutes a day. Capacity per person = 720 ÷ 20 = 36 claims, so demand needs 200 ÷ 36 = 5.6, meaning six processors. With five, capacity is 180 claims and a backlog of 20 a day grows indefinitely, pushing WIP and cycle time upward. Speeding up the intake desk changes nothing: the constraint is processing capacity at the bottleneck.
Traps that cost marks
- Improving a non-constraint and expecting throughput to rise.
- Confusing cycle time with touch time or processing time.
- Reacting to common-cause variation as if it were a special cause.
- Stopping at containment and never reaching root cause.