Restroom and Wet-Bench Equality, Now!

CB028861Sign for Men's Restroom

The simplest—and highest-profit-margin—modeling project that Simitar founder Bob Kotcher has ever done demonstrates the power of simulation modeling for operations improvement.

Celebrate your inner Seinfeld

At a restaurant one day, my inner Seinfeld came out (we all have one—come on).

Since the Americans With Disabilities Act was passed in 1990, many restaurants had to remodel their restrooms to make them wheelchair accessible. This often required them to remove internal partitions that comprised the stalls. With privacy gone, they put locks on the restroom doors and made each restroom single-user.

BUT…many businesses failed to remove the male or female signs from the doors. Furthermore, even some new restaurants, building new single-user restrooms from scratch, put male and female signs on the respective doors. Why not put unisex signs on each door? We now often have the problem of going to such restrooms, seeing a line in front of “ours,” and having to wait (and wait, and wait, and wait…) while the other restroom sits enticingly empty (as our meal buddy out on the table grows increasingly bored).

This calls for an engineering analysis…

Suppose we did a time study on the restrooms (yes, I am an engineer) and used the results to make a static capacity model in a spreadsheet? We’d almost certainly find that each restroom is loaded far below capacity—maybe 75% at peak hours. If we made them unisex, average loading would remain the same. So what’s the problem with them being dedicated by gender?

Well, a computer simulation model would show how, by replacing the two restrooms’ signs with unisex signs, average queue time would decrease.  This is because, due to random variation, there are times when there are women in line when the men’s room is wide open, and vice versa.  Making the restrooms unisex would reduce waiting time in such situations.  Reduced waiting would perhaps result in more satisfied customers and more repeat customers—all for about $20 for new signs.

From restaurant to wafer fab (they both offer chips)

Now, I doubt that restaurants will be conducting simulation analyses to see if spending $20 for new signs would be a profitable investment or not. But one internal client at a wafer fab did something similar.  You see, in wafer fabs and other factories, there are often several identical machines processing in parallel at a particular operation.  If they’re running different recipes, process engineers often like to dedicate each machine to a particular recipe.  This makes process control easier.  But it increases average waiting time due to the above phenomenon.  What is the best tradeoff?

At this client, a process engineer oversaw a wet bench with two parallel identical baths, the only difference being that they were set at different temperatures (dedicated by gender, if you will). Recipe A required temperature A, and all other recipes required temperature B.  The engineer found that he could run the Recipe A wafers at the B temperature if he made Recipe A’s processing time longer.  This would reduce average queue time for all wafers…but increase the processing time for Recipe A wafers.  His question to me was: if I set both baths to the same temperature, will the reduced queue time for all wafers outweigh the increased processing time for Recipe A wafers?

I pretty quickly did a simulation analysis and found that, yes, setting both baths to temperature B and increasing Recipe A’s processing time would actually reduce  average cycle time.

Act on the analysis results, bank the savings

Armed with the analysis results, the engineer made the change. And the result was the biggest return on investment of any simulation project I’d ever done! Not because the savings were so mammoth, but because the cost of the rather simple analysis plus the cost of making the ensuing change were so low. But the change never would have been made had the simulation model not been available to test it out, because nobody in his right mind would approve a change that would increase loading on a machine in order to reduce  cycle time. Until a simulation analysis showed that it did.

Simitar, Inc. permits republication of all or part of this article, provided that (1) it is attributed to Robert Kotcher of Simitar, Inc., and (2) a link is provided to either the Simitar Home Page (if article is wholly republished) or to this article’s page (if the article is partly republished).

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Bob Kotcher

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    • “At Western Digital, I brought in Bob Kotcher based on his exemplary job performance, project management skills, academic & practical knowledge, and teamwork/communications skills, all of which Bob had repeatedly demonstrated to me when I had the opportunity to work with him prior to Western Digital. Bob brought with him world-class academic credentials and a simply outstanding knowledge of Factory Physics, including Capacity Modeling, Cycle-Time Simulation, and Lean Manufacturing. Bob is a great guy to work with and would be a valued member of any operations staff wanting to improve its productivity and/or lower operating costs. He won’t let you down.”

      Guy Harper – Engineering Projects Director
      Calisolar, Inc.
    • “At MMC, Bob initiated and led numerous cross-functional process improvement teams that made significant improvements to our production. For example, in one area, he linked together several disparate operations into a cell, reducing cycle time and WIP by 97% and saving $220,000 a year in labor and damaged product.”

      John Kim – Director, Thermal Reactor Process Engineering
    • “At Headway Technologies, we were planning a major capital investment in an additional photolithography stepper tool in order to improve throughput at this bottleneck. Bob did a Monte Carlo simulation analysis of this area and found something that none of us had suspected. The capacity at this work-center was actually operator-constrained, not machine-constrained. He showed us how, by adding operators, we could meet the required capacity increase. A few additional operators in the photolithography area kept these tools at an optimum utilization and this extra Opex was a small fraction of the capital depreciation that another stepper would have cost.” 

      Guy Harper – Engineering Projects Director
      Calisolar, Inc.
    • “At each company that he works with, [Simitar founder Bob Kotcher] strives to improve day-to-day operations, and thus to improve the bottom line.  Bob is not afraid to present politically unpalatable truths, if his work suggests that a change will lead to overall improvement.”

      Dr. Jennifer Robinson – Chief Operating Officer
      Fabtime, Inc.
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