The Dictionary.com definition of sched·ule: a plan of procedure, usually written, for a proposed objective, especially with reference to the sequence of and time allotted for each item or operation necessary to its completion.

An early practitioner who became famous in our field, Ollie Wight, described a good, realistic schedule as basic and fundamental to the health and integrity of a good MRP planning process.  He also described the aftermath result of poor unrealistic scheduling as the informal systems of hotlists and shortage meetings engulfing the formal planning process.  The MRP planning process still exists, today, in its original form, as the foundation of our evolved MRP, Closed Loop MRP, MRPII and ERP systems.

Back in 1973, I was a young college graduate living in Columbus, Ohio.  I was very fortunate in my first job as a Materiel Controller (Buyer/Planner) to work with the first computerized MRP software package developed by IBM and APICS, the IBM PICS (Production and Inventory Control System) Package.  During those two years I learned a lot about the computerized MRP planning process and wondered how this complicated and detailed process was ever achieved prior to the invention of the computer.

IBM in cooperation with APICS modeled this software package from the most efficient manual planning processes of manufacturing companies such as Steelcase and Black and Decker.  These manual planning systems utilized Fixed Lead Times for purchased parts and a combination of fixed and variable lead time elements (fixed move, queue, setup and variable run time per unit) for the manufacturing lead times of make assemblies. Mfg. LT = Move + Queue + Setup + (Order Qty. * Run Time per Unit).

A week after being walked out the door due to the 1975 recession I found employment again in Columbus, as an Inventory Control Analyst (Shop Floor Scheduler) for a heavy equipment manufacturer of electric driven coal mining machinery.  This company was in business since the late 1800’s and it was there I found the manual planning process that preceded computerized MRP planning.  It was a complete manual MRP planning process utilizing Acme Visible index cards with lots of clerks running around posting entries to transactions.

I had to be totally retrained by some senior schedulers who wore green cellophane visors as headwear and striped long-sleeved shirts with arm bands.  I thought to myself that these were the type of schedulers who planned the production of the bombers of WWII and the 1957 Chevy Bel Air.  Wow!

There was one retraining session that will always remain in my mind.  The senior scheduler was judiciously studying one of his ledgers and said to me “Here, we have to create two manufacturing orders for this gearbox assembly, a 10 piece order for final assembly and a 5 piece order for a spares requirement.  They are both due on the same due date but we have to release the final assembly order on June 1^st and the spares order on June 15^th”.

I questioned him and asked since the orders were both for the same gearbox and due on the same date, why not set the release dates the same for both orders?  He stated that the orders were for different quantities and releasing them both on the same date would unnecessarily overload the broaching and Bridgeport machining operations.  He was doing CRP in his head!  He was also using the true manufacturing lead time elements of move, queue, setup and runtimes so the smaller quantity spares order could be released at a later date than the larger quantity production requirement.

The most important lesson I learned from the senior schedulers was the impact of the accuracy of the true manufacturing lead time elements to the success of the overall schedule.  The lead times elements had to be accurate with as little padding as possible.  Too much padding and you will overload limited resources and start the jobs too early along with bringing in purchased material too soon thus inflating inventory levels.  Too little padding or lack of lead time would release the jobs too late and not give the shop floor enough time to complete the orders on time.  Too little manufacturing lead times also schedules the purchased materials in too late and then when the informal shortage meetings are held you are in a constant expedite mode to move up the jobs on the shop floor and pull in the purchased material.

Stay tuned for part two tomorrow where I’ll discuss Manufacturing Lead Time Overrides.

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Tags: Enterprise resource planning (ERP), Manufacturing resource planning, Material Requirements Planning
Posted in Best practices, Sales and operations planning (S&OP)
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