Let's start the second part of our look at Theory of Constraints (TOC) by examining a principle called Drum-Buffer-Rope (DBR).
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PHOTO COURTESY OF PHOTODISC/GETTY IMAGES
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DBR involves locating and handling some part of your repair process that is limited in what it can produce. That thing is
known as the Drum.
The drum is a "set" limitation. It's a part of the repair process that creates capacity constraints (time or units). It's
a process limited by the amount of its output or the time it takes to process this output. When this particular drum beats
(when its part is the process is completed), another unit or car can then move through it.
Two vehicles can now be kitted in an area at Smail that previously stored parts in inventory. Now the company installs parts
rather than inventory them.
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In our industry, the most common drum is the paint booth since it is limited by capacity (the number of parts of vehicles
that can be processed in it at one time) along with time (set times are used for the work completed in it).
Because the Drum is limited to what it can do in a given amount of time, it sets the cadence for production.
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Two techs working in Smail Collision Center's metal area keep the buffer full. There are only three metal workers inside the
$5.2-million sales operation.
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The Buffer is the part of the process that precedes the Drum. When we keep the Drum beating continuously, we maximize throughput.
If we miss a beat, there are delays, and money and opportunity are forever lost. The purpose of the Buffer is to keep the
Drum filled in the event something else goes wrong (which inevitably happens) in the repair process. This way, the Drum doesn't
skip a beat. In order to produce maximum throughput, shops must make sure the Drum producing constantly.
The Buffer here is prep work. We strive to always have a car ready for the booth even if the booth isn't quite ready. That
way when something goes wrong at the booth, which it always does, we have another car ready for the Drum.
The Rope is the lead time to the Buffer. Keeping the Buffer full ahead of the Drum is critical for maximum velocity. DBR allows
the Rope to be shorter than in traditional models because the production ahead of the Drum is only needed to fill the Buffer.
Overproducing or under producing extends cycle times and therefore creates throughput problems.
The Rope here, for us, is the metal and frame work ahead of the Buffer. We can keep this Rope short because we're able to
determine our capacity and properly schedule our work using our TOC scheduling software.
The booth also acts as a control point. The time needed at the booth is a reliable factor for scheduling capacity.
Using this methodology, our inventory in parts has been reduced by 70 percent. We no longer have parts waiting weeks for cars.
Our parts inventory used to run around $85,000 all the time. These days it is rare to have $25,000 in parts inventory. If
it does bridge this, we will sell the excess in the next five working days.
Previously, it was not uncommon for our store to have 20 to 30 cars on the lot at any time that were not being worked on.
We now average 10 to 12. Early in our implementation we watched both inventories diminish quickly.
Using TOC, all the money that was stuck in our system was turned into sales. This was a one-time cash event for the owner
of our store. Increased throughput changed the environment.
