Continuous Flow

Continuous Flow is Key to Lean Manufacturing


What is continuous flow?

Continuous flow is a way of moving products through the manufacturing process so that each product is being made one at a time.

Continuous flow vs. batch manufacturing

Batching products in a manufacturing process means a group of products go through the process together, along with any defects that may exist. The whole group makes it to the final stage of the process at the same time. If a defect occurred at step two and it wasn’t discovered until step five, the whole batch would have that same defect and would require the same rework.

In a continuous flow system, the products go through the process individually and defects are found in time so that subsequent products can be corrected earlier in the process. Fewer products would require the rework, because the defect would be corrected before it was put into the remaining products.

At the very least, finding the defect sooner can reduce the time it takes to fix it because the product hasn’t been finished. Think of fixing a part in a machine before the rest of the machine is put together and many other parts are blocking that part.

How does continuous flow expose defects and other problems?

In a continuous flow system, as a product moves through the manufacturing process it tests each step in the process and finds the problems in the process. Only some of the products will go through the defective step before it is discovered and fixed. This allows the team members to take quick action and make improvements for the next products that will come through.

Takt time and continuous flow

Continuous flow is also helpful in creating predictability in the process, which makes the process easier to follow and react to. It reduces time spent waiting, overproduction, underproduction, and rework – four of the major forms of waste (aka muda) – because the products move through the process at a steady pace.

Establishing a steady pace is where takt time enters the process, including the process of planning the production schedule.

Takt time looks at how often a customer is buying the product and how much time is available to make the product. The result is the frequency at which the final product needs to be rolling off the line. From there, the production schedule is created and process steps can be organized to meet the takt time, i.e. the customer demands.

You’re selling 10 widgets per day and the plant runs for 10 hours per day. That means, the production team needs to produce an average of 1 widget per hour. This is obviously an oversimplified example, but you get the idea.

Knowing and following the necessary takt time, or pace, ensures the production of the right number of products to meet customer demand. No more and no less. There are no delays in delivering the final product to the customer and there are no extra products to store in a warehouse somewhere.

Lean Manufacturing and Continuous Flow

Continuous flow also allows your organization to utilize some other key Lean tools more effectively, especially the idea that everyone is allowed to identify a problem and stop the line. Of course, everyone is supposed to be looking for defects and nothing is supposed to leave a work cell before it is inspected and its quality has been verified. This process is much easier when a single product is going through the work cell. Fixing that defect is also much easier when a smaller number of products have it.

Flow is good for your mind and productivity

A close relative of continuous flow is the idea of the flow we achieve when our minds are “in the zone” and we’re flying through our work. Whether it’s a favorite hobby or a smooth work process, we’ve all been there. Think back to the last afternoon when you were so focused and you were accomplishing things you thought would have taken much longer.

Benefits of continuous flow:

  • Creates a work environment where team members can get into the zone, find their mental flow, and achieve work goals more easily. They aren’t stalled by needing to wait around for more parts to arrive or to work at a frenzied pace to get the latest batch through their work cell.
  • Allows the parts and products to move through the manufacturing process smoothly
  • Allows your team members to identify small problems before they become larger problems that affect more people and more products. That’s good for everyone, including your customer.

If your work environment needs some help with finding or improving its continuous flow, here are some steps you could take to get the ball rolling.

  1. Calculate (or recalculate) your takt time
  2. Review products and parts to be reworked and figure out what caused the problems
  3. Take a Gemba walk and learn about what your team members are seeing

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