Click here to view Part 1: Does the Art of Scheduling Still Exist?
In the late 1980's I was working for a large government electronics manufacturer located in Scottsdale, Arizona. This was the first time that I was on a complete MRPII (Manufacturing Resource Planning) implementation team. My duty on this team was that of a Training Instructor, responsible for the development of the training materials and the facilitation of the courses.
During the initial training sessions I attended given by the software developers, one of the instructors introduced me to a field I had never heard of called fixed Manufacturing Lead Time Override. He explained that it was to be used on an exception basis. True manufacturing lead times were always to be used but on occasion, when some assemblies were bought outside or brought in from another division, you could temporarily override fixed and variable elements of true manufacturing lead times.
To my surprise, at completion of the implementation, fixed Manufacturing Lead Time Override was, in fact, the norm and not the exception. All of the make parts were being planned utilizing fixed lead times. This means that once you set a fixed manufacturing lead time, all of the manufacturing orders will use this one lead time. If you have a 10 piece spares order, it will be back-scheduled with the same lead time offset as a 1,000 piece manufacturing order. There is no variable element to give the 1,000 piece manufacturing order the correct amount of lead time it deserves.
When I questioned the use of Manufacturing Lead Time Override, I was told that the studies that were conducted found that the start dates of the assembly manufacturing orders were only off by about 2 — 3 manufacturing days and usually within the same week. Besides, it takes a lot of work to come up with all of the move, queue, setup and runtimes and it is much easier to input one Manufacturing Lead Time Override.
I believe that there is a law of physics that states "The whole is equal to the sum of the parts". We aren't just building and shipping assemblies, we are building an entire product. If you have ten levels in a bill of material and you short all of the assembly orders by 2 — 3 manufacturing days, you are shortening the planned build schedule of the product by an entire manufacturing month along with scheduling the purchased material to support that product build by the similar amount.
The 2 — 3 day start date variation argument might hold water if you are just shipping spares assemblies but from a Master Production Scheduling viewpoint that is concerned with forecasting and shipping finished product it results in a crapshoot. That's right, MPS success then depends on the roll of the dice. The manufacturing order quantities that closely align with fixed manufacturing lead times will succeed but the ones out of alignment will fail. What makes it an even bigger crapshoot the fact that very seldom will you ever wind up with all of the manufactured order quantities for a finished product that align properly. The odds against that go up as the number of levels in a bill of material increases.
Fixed manufacturing lead times appear to be the norm in just about every company I've come in contact with and so my question is: Does the art of scheduling still exist?
Those senior schedulers were undervalued by their company but in my opinion, they were worth their weight in gold. Who knows, if we redeveloped the art of scheduling, we might be mass producing aircraft as fast as they did back in WWII and maybe a 2012 Chevy Bel Air might cost $2500 again.
Originally posted by Ray Karaffa at http://blog.kinaxis.com/2011/11/part-2-does-the-art-of-scheduling-still-exist/