WMBA 6040 Week 2 Swimlane Process Map Example

One Progressive Lens Job, Eleven Steps, 8.3 Business Days and Under Three Hours of Work: A Swimlane Map of a Coated Job Through an Optical Lab, With the Four Places It Stops Moving

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Walden University

WMBA 6040: Improving Business Performance

Instructor Name

Month Day, Year

One Progressive Lens Job, Eleven Steps, 8.3 Business Days and Under Three Hours of Work: A Swimlane Map of a Coated Job Through an Optical Lab, With the Four Places It Stops Moving

The Job Being Followed

This map follows a single job through Clearwater Optical Laboratory, the composite wholesale lab introduced in Week 1: a pair of progressive lenses with antireflective coating, ordered electronically by an optometry practice, to be mounted in a frame the practice sends separately. This job type was chosen because coated progressives are the lab's most common order and the type practices complain about most.

The figures come from tracking scans on about 400 such jobs over four weeks. Each tray is scanned when it enters and leaves a department, so the lab knows how long jobs sit between steps as well as how long the steps take.

The Map

Table 1

Swimlane Map of a Coated Progressive Job, With Average Elapsed and Work Time

Elapsed times are averages over all tracked jobs and sum to 8.3 business days; work time counts only hands-on or machine time for this job. Figures are composite.

Read down the elapsed column and the problem is plain. The job spends about 8.3 business days in the lab, and only about two and a half hours of that is work, counting the coating chamber's full cycle. Everything else is waiting. Because average work in process equals throughput multiplied by time in the system (Little, 1961), 8.3 days at about 650 jobs a day means roughly 5,400 jobs are somewhere in the building at any moment, most of them sitting in trays.

Walking Through the Map

The job begins in order entry, where a technician checks that the prescription is complete and consistent. About one order in seven arrives with a missing measurement, usually the pupillary distance or segment height, and the technician must query the practice, which adds half a day on average to those jobs. Then comes the first stop: if the frame has not arrived, the tray waits. Only about 22 percent of jobs wait for frames, but those wait about three days each, which adds 0.7 days to the average.

Surfacing is the next queue. Trays wait for a free generator for about a day, then spend less than an hour being cut and polished. This queue is long but steady, since surfacing runs two shifts.

Coating is the second and largest stop. The lab uses three coating formulations, and each chamber run can coat only one. With two runs a day, a given formulation comes up roughly every day and a half, and when a run fills, the remaining lenses roll to the next run of that type. A lens that leaves surfacing on a Tuesday morning may not be coated until Thursday.

Edging is the third stop. Coated lenses come out of the chamber in a batch of several hundred at once, so the edging department receives a wave twice a day and works through it while the next wave builds. The average wait there, 1.4 days, is a downstream effect of coating's batches.

Final inspection rejects about 9 percent of jobs, and the most common reasons are coating defects and lenses edged to the wrong axis. Rejected jobs start again at surfacing, which is the fourth stop: a remake adds about six days to the jobs affected.

Where Work Stops Moving

Four places account for most of the delay: the coating queue, the edging queue that coating creates, the surfacing queue and the frame hold. The coating queue and the edging wave together account for 3.8 of the 8.3 days. Goldratt and Cox (2004) argued that the constraint governs the whole system's flow, and the map supports treating the coating schedule as the constraint, since its batches also shape the edging queue.

Limits of the Current-State Map

The map shows averages, and averages hide variation: some coated jobs leave in five days, others take fourteen. It also shows where jobs wait, not why each department schedules as it does. Womack and Jones (2003) recommended mapping the flow of a single product family before redesigning any department, and this map is meant as that first step. Later weeks will measure the variation and test the causes.

How the Times Were Measured

The elapsed times come from scans the lab already records. Each department scans a tray's barcode when the tray arrives and again when it leaves, so the time between one department's exit scan and the next department's arrival scan is waiting in transit or in a queue, and the time between arrival and exit is time spent in the department, including any waiting inside it. Work time was measured separately: a supervisor timed twenty jobs at each step with a stopwatch and recorded the hands-on or machine time only. For the coating chamber, the full two-hour cycle is counted once per job even though the chamber holds hundreds of lenses, which overstates the work content and makes the contrast with elapsed time conservative. Business days exclude weekends, when the lab runs only a skeleton crew. Jobs that were remade are counted once, with the remake time added to their total, so the 9 percent of jobs that failed inspection raise the average for every job rather than appearing as separate orders.

References

Goldratt, E. M., & Cox, J. (2004). The goal: A process of ongoing improvement (3rd rev. ed.). North River Press.

Little, J. D. C. (1961). A proof for the queuing formula: L = λW. Operations Research, 9(3), 383-387. https://doi.org/10.1287/opre.9.3.383

Womack, J. P., & Jones, D. T. (2003). Lean thinking: Banish waste and create wealth in your corporation (Rev. ed.). Free Press.