Like many of my contemporaries in the late 80s and early 90s, I had read Eli Goldratt's "The Goal" and enjoyed it immensely. Also, like many of those same contemporaries, implementing the lessons of "The Goal" seemed difficult if not impossible without Jonah, the philosopher-industrial engineer, being present.
My thinking changed in the fall of 1996. I assume the reader is familiar with the half-day seminars that seem to serve to get people out of the office in exchange for continuing education credits. I attended one of a different caliber; Debra Smith of Constraints Management Group presented a useful several hours of Drum-Buffer-Rope, or DBR, which was the named system for scheduling work that "The Goal" featured. The scales fell from the eyes, and I was able to envision how the wirebond area, which was the production line's bottleneck, could use the TOC philosophy to improve throughput.
I proceeded to set up training sessions for all of the assemblers and technicians using "The Goal" videotape. Training centered on how the wirebond area was the process bottleneck and what steps we would take from that day forth to subordinate decisions towards improving that process.
The basic concept underlying "The Goal" is this process:
- Identify the constraint
- Exploit the constraint
- Subordinate all other decisions to exploiting the constraint
- Elevate the Constraint
- Start over
In the video (and in real life at Interpoint), the huge pile of work-in-process was a dead giveaway as to the location of the constraint. Constraint identified!
The second step requires a bit more work. Exploiting the constraint requires looking at the input to it and how well the available process time at the constraint is used. Essentially, in Six Sigma terms, performing a Value Stream analysis through wirebond revealed many significant details that would assist in exploiting the constraint.
Each wirebond machine is subject to a certification process that lasts for 4 hours of production time. Scheduling assemblers around that certification time was the first subordination step. The first rule applied is that, except for the mandated break, certification means 4 hours of wirebonding.
The astute reader will note that the process of exploiting the constraint involves subordinating many decisions. The decision to exploit the constraint is treated separately as a "line in the sand" for management to communicate to other team members what the focus is.
The second subordination step was to examine batch sizes in wirebond. The concept behind this thought process was to ensure that 4 hours or some even fraction of that amount was transferred to the wirebond machine.
Implementing these two steps increased throughput in wirebond but did not result in first test yield improvements. The logical conclusion we reached is that while the throughput through wirebond is better, some of the product coming through was not capable of passing first step or even pre-cap (before hermetic sealing) inspection.
In my next post, the next subordination step will be presented and dissected.
