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The Perfect Production Schedule Doesn’t Exist

By Bernard Milian
production schedule - stopwatch

Industry 4.0 and digitalization are on the rise. Technology is moving into our shop floors. LCD touch screens are gradually replacing physical boards and post-its.

However, we must recognize that the vast majority of our workshops, however complex, are planned or scheduled in Excel, right?

The promise of scheduling algorithms

Scheduling solutions have existed for decades, with promises of results that every production manager should be delighted with: optimizing the use of production resources, real-time response, advanced algorithms, etc.

If you look at the websites of some of the specialized publishers, you will find some tempting promises: “multi-level production plan optimized in real time,” “synchronized load smoothing with multiple constraints,” “real time planning,” “finite capacity MRP calculation,” “resource utilization optimization”…

Finite capacity, synchronization, optimization…

It sounds relevant, yet we encounter multiple companies that tried to implement a scheduling tool and gave up after a while, to once again entrust Excel and the knowledge of their planners to orchestrate production.

There are probably several reasons: advanced but obscure algorithms, difficulty in taking into account particular situations, etc.

Murphy’s law

But probably the main reason is that as soon as an optimized production schedule is established, it is immediately out of date because one of the small events that make the life of a factory so special has occurred: a batch is blocked, the machine is out of order, a component is out of stock, Marcel is sick and he is the one who knows how to do it…

So we have to redo the plan – with a lot of technology to resynchronize everything in a “chamboule-tout” … and this new plan may be obsolete within a few hours.

In other words, the optimized production schedule is a chimera. To manage a workshop, we need a roadmap and visibility that allows us to define the right priorities, and to delegate to the teams on the field the adjustments to contingencies.

What is the purpose of a production schedule?

If there is no such thing as an “ideal” production schedule, how can we establish a “relevant” production schedule that will meet our key expectations?

What is the ultimate purpose of our production schedule?

  • To promise our customers reliable availability dates that are as close as possible to their expectations
  • To make the best use of our critical resources – in particular to avoid capacity losses on our bottlenecks
  • To give our production teams clear priorities so they can make the right decisions in real time
  • To facilitate flow, lead time reduction, and continuous improvement

Taking variability into account

Do not worry: Murphy’s Law will strike, there will be variability. So, we have to integrate it into the plan – and into the execution as it happens. In the DDOM (Demand Driven Operating Model) this is ensured by considering capacity buffers and time buffers when establishing the plan.

Demand Driven buffers include degrees of freedom: as long as the execution reality does not go beyond the operating ranges defined by these buffers, our schedule will be protected. This also means that in our control routines in the workshop we must make our decisions based on the status of these buffers. If some orders drift into the red there is no ambiguity: they must be prioritized.

Optimization by exception

A relevant production schedule does not define everything on all workstations. It is fine-tuned, optimized only on critical resources. The constraints. The dispatch plans. The start of the WOs.

It is important that a constraint is optimized, that no more changes of series are made than necessary, that this constraint is not stopped because of lack of material.

For all other workstations, we just must follow the status of the buffers from time to time: as long as we don’t risk starving them, everything is fine!

When the plane takes off, we take it to its destination

Real-time replanning is not a great idea… The more a plan changes, the less plan there is.

So as much as possible, when it comes to the key points of the process – the control points – your schedule must remain unchanged when a WO starts. Buffers are there to protect these points.

When a plane takes off, it follows its flight plan as much as possible. There may be thunderstorms on the way, but the pilot must adjust by exception, respecting as much as possible the arrival time…

An imperfect plan for excellent service

Our production plan must therefore allow us to promise realistic dates – compatible with our capacities and protected from variability. It must also allow the teams on the ground to make the best possible decisions as they go along – for example, through the DBR+ time buffer boards, displayed on the LCD touch screens of your workshop 4.0!  

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