Fluctuations can also originate within your area of responsibility. In my previous post, I looked at how to reduce fluctuations coming from upstream. In this post I look at your shop floor. Using the source-make-deliver structure, this post is about reducing fluctuations at “make.”
There are a lot of possibilities for reducing fluctuations in the “make.” Some are of technical nature, like line balancing and preventive maintenance. Others are organizational, like flow shops and pull production. Please note that besides the methods listed in this post, there is also leveling and lot size one, as explained in my last post.
Line balancing is having all your stations produce at roughly the same speed, ideally the customer takt. This reduces fluctuations in the work content. While it may not be obvious, this is also a source of fluctuation: it fluctuates the workload of your workers. Alternating between idle and working are fluctuations (mura), which in turn can create both waste (muda) and overburden (muri). Balancing your line reduces such fluctuations, and improves your system performance. For more details I have a six-post series only on Line Balancing.
Preventive maintenance, or even maintenance in general, can reduce the tricky fluctuations of machine breakdowns. However, this is often tough, since you may not know why the machine broke down in the first place. Even if you do, there may be many different reasons why a machine breaks down. Identifying the main reason for the breakdowns is tricky and may take some time. However, it is worth it. The solution is often surprisingly simple.
I have many examples of such problems. For example, one machine that tested some tubing had an O-ring wear out every two weeks. The number of defects increased, not because the product was faulty but because the testing machine was. This led to a loss of a couple thousand euros worth of products every two weeks until the O-ring was fixed. The simple solution was to replace the O-ring not after it wore out but before. Instead of fixing it every two and a half weeks when defects increased, it was automatically replaced every one and a half weeks, before it wore out. The O-ring cost around 0.03€.
Another example is a machine component that counted sheets. Unfortunately, there were frequent miscounts, and maintenance could not find out why. Eventually someone figured out that the screws attaching the component to the machine were loose. The component was simply wobbling and hence miscounted. The fix was easy: just tighten the screws, and maybe add some adhesive so the screws didn’t come loose by themselves again.
There are plenty of other examples where something broke and the problem went away after it was fixed. A shaft bearing was broken, creating more faulty products. An air ventilator was clogged, causing the machine to stop due to overheating. A cable was not plugged in, leading to wrong data. Once you find it, the fix is not that difficult.
Let’s start with the fact that I love flow shops! They make a lot of things so much easier. Efficiency, visual management, control, productivity – almost every important KPI improves in a flow shop compared to a job shop. And this of course includes fluctuations!
Job shops usually have an irregular material flow, which sometimes put loads on one process, sometimes on others. It is hard to balance the workload, it is hard to keep a steady flow, and it is hard to keep the inventories under control. All of this is much simpler in a flow shop, where you can balance the workload more easily, define clear inventory buffers, keep all processes working at the same time, and have a steady and stable stream of material coming out. If it is in any way possible, try to convert a job shop into a flow shop. For more info, see my posts Why Are Job Shops Always Such a Chaotic Mess? and How to Convert a Job Shop into a Flow Shop.
Pull production is another way to reduce fluctuations. The basic concept behind pull is to have an upper limit on your inventory. Whenever an item leaves the system, another job is started. This avoids the clumping together of jobs and makes production much more smooth. It also avoids the dreadful bullwhip effect, where fluctuations can increase along the supply chain.
The best known approach to implement pull is kanban, but there are many others like CONWIP, POLCA, or reorder point methods. I have written many post on kanban, so look at my list of post for kanban-related topics. A book on pull production is currently on the final stages of editing. Of my many posts on pull, I especially recommend The (True) Difference Between Push and Pull and Why Pull Is So Great!
Just in Time, Just in Sequence, and Ship to Line
Just in Time (JIT), Just in Sequence (JIS) and Ship to Line (STL) are a few related tools that streamline the material flow both inside and outside of the plant. Toyota even considers Just in Time as one of the two main pillars of their Toyota Production System (along with Jidoka; see next heading).
The underlying concept of Just in Time is that material arrives when it is needed, where it is needed, in the right amount and in good quality. Too much, too little, too early, and too late should be avoided. But be warned, Just in Time is not easy and requires already a system with few fluctuations. I have seen plenty of plants that showed me their Just in Time inventories … worth 3 days of production or more …
Just in Sequence is the idea of having parts arrive in the right sequence as they are needed at the assembly line. This makes sense only for expensive or big parts. It is often used for seats in automotive. Finally, Ship to Line is the idea of moving material directly from the loading docks to the line, without any warehousing in between (but possibly with a shuffling area). Any Ship to Line system is also Just in Time, as you can’t have any inbound warehousing for your goods. Therefore it also requires an already pretty stable system with few fluctuations.
Finally, the second pillar of the Toyota production system is Jidoka, also known as Autonomation. The idea is that a machine detects abnormalities by itself. Such abnormalities could be quality issues, process issues, or lack of material. If such an abnormality is detected, the machine stops automatically.
This may sound counterintuitive. If you want to reduce fluctuations, why do you stop your machine? Well, because if you don’t, the fluctuation later on to fix the mess will be much larger than if you did not stop your machine!
There are probably even more methods or tools to reduce fluctuations on your shop floor. Most lean tools are connected to reduction of fluctuations. But for now, these should suffice. In the next post I will talk about how to reduce fluctuations on the customer side of your value stream. Now, go out, get those pesky fluctuations under control, and organize your industry!
- Why Are Fluctuations So Bad?
- Structure for Reducing Fluctuations
- Reducing Fluctuations Upstream
- Reducing Fluctuations on Your Shop Floor
- Reducing Fluctuations Downstream