The 4.0 shop floor — so talked about of late — is not only about incorporating real-time technology and digital tools. The 4.0 shop floor must be agile and respond to real customer demand. Lead times must be short, priorities must be visible, and decisions must be intuitive for all.
In this series of articles, we look back at the key principles of a demand-driven operating model for Industry 4.0.
Starting Production Orders at the Right Time
In the 17th century, the French author La Fontaine wrote a collection of fables, one of the most famous of which is The Hare and the Tortoise. The hare and the tortoise run a race, and it is the tortoise who wins despite its slowness, because it progresses steadily, while the hare rambles and leaves too late. The moral of the story is that there is no point in running; you must leave in time.
You don’t see the connection between a 17th century fable and Industry 4.0? And yet…
This moral also applies to our manufacturing shop floors. The moment we start working on an order, the moment we start the flow is decisive. How do you start the production orders at the right time? What is this right moment? How to respect it? How can we improve?
What happens if we release too early? If we release too late?
Understanding Rhythm and Flow
First of all, a production flow needs to be paced. We mentioned this in a previous article and described some of the mechanisms at work, such as heijunka.
The most important rhythm is, of course, the actual demand of your customers. The entire Demand Driven model is based on this: to pace production and supply as closely as possible to the market demand — while regulating the load to make profitable use of our industrial resources.
In practice, this will consist of pacing your production flow on a key transformation step, for example a constrained workstation. We will come back to this in our series of articles.
When You Can’t Start Too Late
Depending on the nature of your production flow, the starting point is more or less easy to determine.
If you have been able to put your processes in line, and you carry out all of your steps in a sequenced manner, for example on a conveyor, things can be relatively simple: you need to supply the line side so that you have all of the required components at the right time, based on the “film” of the line.
This is, for example, what happens on a beverage bottling line, or on a car assembly line.
OK, I said “things can be relatively simple,” but if you’ve worked in the automotive industry you know that it involves rigorous sizing of Kanban loops, synchronous logics that incorporate properly sized and controlled safety times, etc.
The determination of when to start is quite basic: it is, according to the dimensioned safety times, based on the production schedule of the coming hours, with the “right advance” to ensure availability despite the usual supply and process variability.
When you are working on more or less complex operating routings that involve multiple industrial resources that are not in line, it is a different matter. What is the right time to launch a work order that will be subject to cutting, machining, subcontracted surface treatment, new machining in three passes on two work centers, adjusting followed by welding with another machined sub-assembly, a three-dimensional control, followed by a possible rework, and a final assembly within a wider system?
In order to efficiently control this type of flow, we will have to determine the “right advance” to be applied in relation to the critical transformation stage (our primary constraint, or pacesetter workstation).
We call this the upstream “rope length.” This is a concept defined by the DBR (Drum Buffer Rope) methodology of Theory of Constraints.
This duration includes the operating times of the transformation steps to be carried out up to the primary constraint, to which are added the time buffers which are controlled queues allowing you to dampen the randomness of upstream processes and to synchronize the sequences.
In other words, work is started at the right time to ensure that the upstream processing steps are completed so that the work reaches the queue for the key processing step always early enough.
If you start too late, you risk disrupting the key transformation step that sets the tempo, or forcing it to be rescheduled, which will result in productivity losses.
Why Not Start Earlier?
The temptation is great, in order to avoid disrupting the key manufacturing steps, to release work to the floor as soon as possible, to “feed” the shop floor. Releasing too early is a common (bad) practice. The more WIP you have on the shop floor, the longer it will take for a newly released WO to go through the transformation steps. The more WIP you have, the longer the lead times. The more WIP you have, the more conflicting priorities you have to deal with. The more work in process you have, the more people you will need to sort out the orders that need to be passed before the others, the more impact quality problems will have, etc. Ever seen a stuffed shop floor ?
Piloting On-Time Releases
In a simple and inline environment, specific or generic kanban loops allow you to determine the right time to start. In the Industry 4.0 era, these loops must be digitized to ensure integration with the company’s management system and deliver end-to-end visibility.
In a more complex environment, with multiple routing steps, shared resources, a mix of make-to-stock and make-to-order manufacturing, you need a computerized way to determine the rope lengths in accordance with the industrial model. Does your favorite ERP provide this? Probably not: its logic is not based on a level loaded pull flow paced by customer demand on finite capacity scheduled key manufacturing steps protected by time buffers.
Whether you are in a simple or complex pull model, our Intuiflow suite will tell you when to release on time and will give you complete, collaborative visibility throughout your relay race!
Securing Multi-Skills Availability
Don’t forget that adapting to customer demand via a smooth flow of work requires the right degree of versatility. How many WOs are launched to “occupy” the available skills, while work is accumulating upstream of a stage where there is a lack of skills? The development of multi-skilling, described by the “skills buffers” is an essential step in your 4.0 deployment! There’s no point in running…