How to implement lean manufacturing in door assembly
I am going to share some pictures with you from Hodges Millwork of Royce City, Texas, in this article to demonstrate just how common sense lean is for anyone who may still doubt the simplistic, yet dynamic, process of implementing lean thinking.
One of the observations that I incorporated into my training session in the first week at Hodges was an example of a few of the Seven Deadly Wastes all captured in one process: manufacturing doors. The first picture shows several door fronts staged on the floor next to the assembly station. At first glance you may not see an opportunity for improvement, but when you become more familiar with lean, especially the technique of going to gemba (Japanese word for where the work is done or the shop floor), the sequence of events will reveal several opportunities.

Making doors

As you likely know, doors flow through several steps including ripping parts to width, gluing blanks as necessary, cross-cutting to length, machining, sanding, assembly, sanding, and hinging. Doors are generally run in a batch so even though the first door through each process step is ready to move to the next step it can’t because it has to wait for the rest of the batch. The larger the batch, the longer the entire process takes. Likewise, the smaller the batch, the more velocity is created and the quicker completed doors move to the internal customer at cabinet assembly.
After each process step the employee sets parts and completed doors aside, as you see in Picture 1. The next process owner picks up the parts and performs another step. The most productive way to complete a series of tasks is for each task to be synchronized with the next so there is no accumulation of parts between processes. That is the basic theory of continuous flow.
If it isn’t possible to pass one piece at a time between process steps then a batch size that accommodates continuous flow needs to be determined. In the case I am describing here, there is no flow, so parts are accumulating between steps. Picture 2 shows the location of a cart that the doors are eventually going to be placed on to go to the next step. You may ask, “What’s wrong with the process?” I want to turn that question around and ask you the same thing. Can you identify a waste in the picture?


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Identifying waste

Here is a hint: The assembly person already had the door in his hands when he walked two paces to the end of the assembly station and placed the door on the floor. Now another person is going to pick the door up, turn to the cart, take a step or two, and stack the doors on the cart, as shown in Picture 3.
The carts have wheels. That means the cart can be placed anywhere in the layout. If the assembly person moved the cart closer to him, he wouldn’t have to carry the door to the end of the station, stack it on the floor, and walk back to the assembly position. The other person wouldn’t have to walk to the stack, pick up a door, or multiple doors, walk to the cart, and then place them where they should already be. There are examples of the Waste of Processing, Waste of Transportation, and Waste of Movement all embedded in these three pictures.

Making face frames

I will come back to the door process in a minute, but let’s take a look at another process that also lacks flow and is disconnected from the internal customer. The face frames in Picture 4 were fabricated in a building adjacent to the building that houses the rest of the processes. As you can see, face frames are made in a batch as well. However, the face frames are not sequenced in the same order that the doors are being made, so there won’t necessarily be a match of parts at the assembly station.
Sequencing parts to ensure continuous flow will be the subject of another article as the transformation progresses at Hodges. The batch of face frames will now have to be carried from one temporary staging location to another temporary staging location in the next building before they make their way to assembly. By the time the face frames get to assembly they will have been handled multiple times rather than just one time between the face frame builder and the assembly person. Again, just as in the door process, there are multiple Wastes of Transportation, Processing, and Movement in the face frame process.

Chaos and confusion

Now back to the door operation. The chaos and confusion depicted in Picture 5 of the assembly building gives you an idea of why face frames are fabricated in a separate building, and you should also be able to get an appreciation for additional waste in the door process when I tell you that the hinging operation is at the opposite end of the building from the door assembly station. Because of all of the work-in-process scattered around the building it isn’t possible for door carts to be moved to the hinging operation so the employee has to carry them there a few at a time. More waste!
Does all of this matter in the larger scheme of trying to get product out the door to your customer? It certainly does, that is if you are interested in delivering a quality product; on time, every time; at the lowest cost possible. Seconds and minutes cost money. The seconds and minutes that are wasted doing unnecessary tasks are forever lost. You can never regain them. The best you can do is work overtime to make up for the loss, which will cost even more money.

Taking action

All of these points matter to Chris, Joan, Jesse, and every other employee at Hodges. Immediately following the training, Jesse pursued the examples with several of the employees to see what measures they could put in place to eliminate the wastes.
Carts were moved closer to door assembly, and the cart design is being changed so they can get even closer to the assembly station. Sequencing of doors was changed so they will be available for the assembly person to install as the cabinet is being built, which wasn’t being done before. That was one of the reasons why so much work in progress was accumulating. Finally, they developed a plan to move the hinging operation closer to door assembly, and to move the face frame process to the main building. They were able to accomplish these things by applying lean thinking to their daily routine.
On my second visit I witnessed some of the changes that were already well under way. The employees are continuing to do Workplace Organization to eliminate physical waste as well as interference waste. Have they experienced a quantum leap change on the bottom line yet? Not yet, but Chris and Joan are encouraged by what they see and are confident that bottom line improvements will be realized very soon. I will keep you posted.

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About the author
Jim Lewis

Jim Lewis has worked in the furniture industry for 40 years with a special emphasis on facilitating the transformation process for businesses embracing the Lean Business Model.  Jim’s company, The Center for Lean Learning, is headquartered in Grand Rapids, MI, with an office in St. Thomas, ON, Canada.  He is a consultant, author, and writer.  Jim’s books include, “The Journey to Excellence – Successfully Applying Lean Thinking in Your Business,” “A Testament to Lean Thinking – Cases for Change,” and a series of ebooklets under the main title “Applying Lean Thinking.”  The books are in ebook format and are available through all major ebook retailers and through