Cellular manufacturing is the primary model for Lean Manufacturing. The idea is to build an entire unit in a single process rather than making piles of parts and then assembling them into finished units. For a custom cabinet shop, this means building each individual cabinet as a complete unit from start to finish rather than cutting all the parts, then edgebanding all the parts, then drilling all the parts, etc. I touched on this before in earlier blog posts. Now that we have cleaned and organized the shop, and have gotten control back of our parts and materials, it is time to work out the details of One Unit Flow.
Recently, in working with a client building a fairly small job, I took the time to record how the parts were handled. The job was a small kitchen, and three small vanity bath units, a total of 50 cabinets. Interiors were prefinished maple, with beech exposed edges, and one of the vanities was paintgrade.
The parts were all precut on the CNC as a batch, and stacked on racks and carts as they came off the machine. In order to edgeband, they needed to be sorted out. Adjustable shelves get maple edgeband, cabinets get beech edgband, and the paint grade cabinets get unfinished maple. Then all the parts need to get resorted into individual cabinets for assembly. By my count, from CNC to assembly, this pile of parts was stacked, sorted and restacked four times.
Now let’s look at working this job in a cellular operation: The CNC nest is outputted to cut parts for individual cabinets as a group. Each set of parts is moved to the edgebander, where appropriate banding is applied. (the adjustable shelves could be milled and processed as a group since they are, in this shop, stacked and shipped to the jobsite separately) The stack of parts equaling one complete cabinet is taken from the edgebander directly to an assembly bench where it is assembled.
At this point, we can begin applying another Lean Manufacturing technique, that of Cycle Timing. The time needed to machine the part set, and edgeband them, and or dowel them, should be recorded and tracked. The time needed for assembly can be recorded as well. These times are compared to determine the distribution of human resources. If it takes a total of 10 minutes to process the parts for assembly, and takes 20 minutes to add slides, hinges and assemble, then we know that you’ll need two assembly tables working to match the flow from the CNC and edgebander.
Working this way, you can begin getting very accurate times for processing your cabinets. This means that you can now determine how much it actually costs you. You got control of your materials, so you know what is going in there, and now you know exactly how much each cabinet is using in manpower and shop time.
There are several other advantages to One Unit Flow. Since the parts get handled fewer times, there is far less chance of scratching and other surface damage. Floorspace is maximized since there are not parts stacked all over as they are sorted and processed. If your machining is not correct for some reason, you will know it right away, rather than finding out after all the parts have been cut. You will be able, once you are familiar with the process, to establish ahead of time very accurate estimates of shop time, allowing for much more accurate proposals, and reducing the opportunity of costly estimating mistakes.
The time issues bring me to the subject of my next blog posting, understanding what your jobs actually cost you to make.
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rbagnall@consultingwoodworker.com
