Author: Paul Van Metre
When our shop was about 6 years old, we went through a massive Lean Manufacturing transformation. We went all in - Kaizen events, 5S, Kaizen Newspapers, Value Stream Mapping events, and more. One of the most impactful things we did was the change to one-piece-flow for nearly all our jobs for the subsequent 11 years (and still to this day with the new owner). In a low volume, high mix CNC job shop like we were, the process is perhaps a bit different than what is traditionally thought of. However, the impacts were huge and it worked really well for our shop.
It eliminates a ton of different wastes:
Wait a minute... is that all 7 of them as defined by the Toyota Production System?? You bet! Flow processes can reduce or eliminate all 7 wastes.
We called the process Bar-to-Box. Here is how it worked:
That’s the process. Bar-to-Box during the machine cycle. We designed the process to make sure it can fit in the machine cycle. Sometimes that means machining multiple parts at once, which can make sense if it’s a small part and we can machine a strip of them to optimize cycle time and tool changes as well. It’s also more fun for the machinist who gets to see finished parts every cycle, stay more engaged in a variety of tasks, and feel more ownership of the parts they are making.
Here are 5 key benefits of doing a one-piece-flow. (There are many others as well):
A few other thoughts to help this work.
How can ProShop help?
In the part module where the routings are defined, it’s possible to outline a flow process by linking operations together so ProShop understands that the operations are part of a flow process. When this is done, ProShop will schedule those operations and resources together at the same time and will understand that completely finished parts are being created with each “takt” time. This makes it much easier to schedule this and have everyone understand what is going on.
In this example below, we can see that all the operations are being flowed with Operation 65 and it takes 26 minutes to complete that full flow including the bandsaw, 2 CNC machines, and the assembly bench. Astute viewers will also notice that we’re doing this flow at a 25% labor target, or about 6.5 minutes of labor which is the longest manual segment of time in this flow process. This enables nearly 20 minutes of free time per cycle for the operator to run some other machines or do other value-added activities somewhere else. So essentially, we’re making a part every 26 minutes even though it has 46 minutes of cutting time, and only using 6.5 minutes of labor. Also, we get finished and inspected parts off each time, that can start shipping to the customer or to an outside process right away.
There are certain situations where a flow like this is more difficult or impossible. However, with a bit of creativity and brainstorming it’s remarkable how many parts can be made into a flow process with an amazing amount of upside in terms of cost, quality, and lead time improvements, and waste reduction.