Cellular Manufacturing: Part 1 - What's it to You?
Implementing work cells can reduce inventory, rejects, material handling and delivery times.
By Tom Dossenbach
Most small manufacturers conjure up visions of CNC routers and other sophisticated machines when- ever the term "cell" is used. They think of a work cell as a complicated machine or a group of machines that requires highly skilled industrial en- gineers to design. If you are mystified by the reference to cells, this article is for you. More than five years have passed since I last wrote about this subject; so, let me start with the basics.
The Way It Was
Thirty to 40 years ago the focus in manufacturing was to maximize the output of machinery. This was the engine that drove industrial output and growth. A plant that made furniture or other products would accumulate orders and forecast future demand in order to produce a quantity of products that would justify setting up the various pieces of machinery required to manufacture that product. Because each machining operation did not take the same amount of time to perform its required task - which is still the case today - the quantity was calculated not only to minimize the downtime of the machinery, but also to serve as a buffer as the parts moved from machine to machine.
The woodworking plants then, and many now, had machinery grouped by type or function. A typical small shop would group saws together in one area and tightly cluster shapers in another. Likewise, routers and sanding machines would be grouped in separate areas. Thus was born the reference to "cutting rooms," "machining rooms" and "sanding rooms." Typically there would also be an assembly area that would include designated areas for sub-assemblies and final assembly.
Machines were most often lined up in what I call the Roman legion formation - much like the charging lancers and bowmen of Roman history with lines of legions appearing to stretch on forever. The above photo shows a new Asian woodworking plant with a bad case of this Roman legion mentality. Note that there are nine sanders lined up in this one machine location. The plant is filled with similar rows of machines designed to do the same kind of processing.
You can picture these machines as one of the lines of sanders represented in Figure 1 on page 30. This drawing illustrates the diverse routes parts and sub-assemblies took as they worked their way through a factory of the 1960s.
Inefficiency and Waste
Many of the woodworking plants in this country are still doing it the Roman legion way. Let's look at the results of this mode of operation. Read carefully to see if your plant has some of the symptoms of the Roman legionnaires' disease.
First, any part or product that moves from machine to machine in batches would take a lot of time to work its way through the maze of machines. As Figure 1 illustrates, the part's path would include a lot of backtracking because all of the machines were not grouped to accommodate the many product flow variations. Instead, they were arranged in a loose order of machine sequence such as cut, surface, machine, sand, assemble, finish and pack. When a manufacturer has a pallet of parts that needs to be processed, the biggest challenge is to get them completed on time to meet the customer's delivery schedule.
Unfortunately, meeting the shipping deadline requires scheduling six or eight machines to process each part. First, the parts are cut and stacked on a pallet. Next, they are sent to a moulder for surfacing on all four sides. If the moulder is busy, the pallet of parts sits in a queue waiting its turn. After being processed on the moulder, the part must go to a shaper, then a boring machine, a router, and so on.
Because this process is repeated for hundreds of different parts, there is a queue at each machine. This represents a lot of inventory on the floor waiting to be processed. Manufacturers who have set up their plants as Roman legions justify this type of batch production because it guarantees work for the machines as soon as the next changeover is completed. Invariably, though, the Roman legion method leads to a scarcity of floor space and a cadre of supervisors screaming for a factory addition to gain more floor space.
Meanwhile, the clock is ticking. In fact, not only does the hour hand of the clock fly by, but also the pages of the calendar. It is not uncommon for this type of woodworking factory to take a week or more to do two hours of value-added work. Every time the parts go to a machine, one or more persons also must handle them in transit. The rest of the time these parts just sit around taking up precious space and tying up inventory dollars.
The result is a crowded plant with a huge inventory of work in progress and excessive material handling to move hundreds of batches of parts through the plant over a long period of time. Typically, only 5 to 7 percent of the total process time (handling + waiting + machining) is actually adding value to the product - such as cutting a shape into the wood part. I assume you can see the waste that accompanies any large batch scheduling and processing in your plant; these batches do not necessarily have to be hundreds or thousands of parts.
The Alternative - Cellular Manufacturing
It might be a good idea at this juncture to explain what a manufacturing cell is for the benefit of those who are not sure. First of all, there is no one kind of machinery or other operations that make up a cell. A manufacturing cell is illustrated in Figure 2, shown on this page. Each cell is designed to produce a family of parts or products that share common processes; the machines within the cell facilitate those processes. While an attempt is made to attain one-piece flow through the cell, the main focus is to have a part or product continuously moving from machine to machine until it is completed.
The typical process time in a cell will be minutes instead of the days required in the typical plant of yesteryear.
The manufacturing cell offers a way to simplify production control and scheduling and shorten the total manufacturing cycle time from days to minutes. In addition it eliminates virtually all inventory between each cell operation. This results in less work in progress and frees valuable floor space taken up by carts of parts.
As a bonus, cellular manufacturing enables much better quality control.
Typically, defects are not discovered until a downstream operation occurs. For example, an improper shaper cut may not be noticed until a boring machine operator looks at that piece as he loads his machine. Hundreds of pieces may have been machined wrong in this scenario. However, in a cell, one or two pieces are all that exists between the shaper and the next machine. In fact, the same operator may be doing both jobs and has a good chance of catching the defect immediately after it leaves the shaper.
The Competitive Advantage
It remains a mystery why more small wood products manufacturers do not embrace cellular manufacturing. It is not necessary to incorporate cells throughout a factory to reap the benefits of this manufacturing methodology. To the contrary, any small step that can be taken to eliminate non-value-added activities and shorten process time will only make a manufacturer more competitive.
Getting back to the photograph of the Asian factory, while it may enjoy the competitive advantage of cheap labor, it is not deploying its workforce as efficiently as it could. To the contrary, this company is going to have a difficult time scheduling and moving five containers a day through the factory. In fact, it will approach a nightmare for all concerned. Can you imagine all the parts that need pump sanding converging down this factory aisle? Where will these parts come from? Where will they go from here? How long will it take these and other parts to flow through this Roman legion factory? One week? Two weeks? Four weeks?
Maybe now, you have a clearer picture of why some U.S. furniture retailers are fed up with long delivery times from China and other low-cost producing countries. No matter what woodworking business you are in or where you are located within the United States, you should be able to beat the Chinese on delivery times to your customers. This gives you a competitive advantage that you can and must exploit. The shorter your lead times, the more opportunities are open to you.
That is the good news. Now, the bad news. There are factories all over the world trying to figure out how to compete with the Chinese. When they find a solution, they also will compete for your customers. With the advent of lean manufacturing in developing countries, industry competitiveness is truly in jeopardy.
So, what's it to you if you go to cellular manufacturing? For starters, you will be able to get your products to your customers quicker and at a lower cost.
Next month, in part 2, I will delve into the makeup of a cell in more detail and how to set up one in your factory or shop, with your people (not an industrial engineer) doing the design work.
Tom Dossenbach is managing director of Dossenbach Associates LLC, a Sanford, NC-based international consulting and research firm. Contact him at (919) 775-5017 or at www.dossenbach.com.
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