Making mass customization work
By Ken Susnjara, chairman and CEO, Thermwood
October 15, 2009 | 7:00 pm CDT

Thermwood, one of the major sources of the technology and equipment needed, conducted a six month program last summer to see if it really works and to uncover any missing elements.

For a product line they decided to complete the remaining open orders for a Canadian line of contemporary furniture that closed down. The primary focus of this experiment was to verify that a highly variable product line could be efficiently machined and assembled using modern technology.

Product design was electronically reproduced using Thermwood's  eCabinet Systems design software. This software, a highly sophisticated design tool that can literally create any piece of wood furniture regardless of its shape or complexity, is available to any cabinet or furniture company for free.

The only catch is that if you want to automatically machine the parts from the software it only outputs to Thermwood's CNC control, so machine sales actually pay for the software.

On the plus side, this approach supports an unprecedented integration between the design software and machine control. For example, actual nesting and CNC program generation is done automatically at the machine, not in the design software. This allows you to easily react to situations at the machine, such as reusing partial sheets of material from old jobs, nesting around defects or replacing damaged parts.

If the design calls for a custom profile shape and the machine doesn't have the custom tool, it can automatically generate a modeling program using standard tools and in a few minutes reproduce the shape, even without the custom tool. This integration between the design effort and machine control is critical to efficient mass customization.

The product line that Thermwood tackled has more than 95 million possible variations. This is about as close to full mass customization as you can get but if you examine it carefully, it is not as bad as it first looks.

The product consists of a series of individual modules that are connected and combined in various ways. When you add a wide selection of finishes, it is not difficult to get 95 million unique products. This wide variety of products, however, presents several special challenges.

The first challenge is how to specify and communicate the precise product the customer wants. To address this Thermwood developed a web-based system to configure the product and then view a three-dimensional image of the exact configuration selected. This software could then submit an order directly to the company.

Thermwood envisioned the retail store using this type of system, working with their customers to develop and sell the product. The software also offers a perfect interface between the manufacturer and retailer.

Within the manufacturing facility, each of the component modules were first designed using the design software. When an order was processed, modules were combined into a complete piece of furniture using the same software. This is a fairly quick process. The resulting job file was placed on a server where it could be accessed by any of the CNC routers.

Since this is a design file and not individual CNC programs, it is not necessary to post them for a specific machine. Any machine can access the file and then nest, program and post right at the machine. This approach preserves maximum flexibility and insulates against sending programs to the wrong machine.

Nested-based techniques  

The products were made primarily from veneered MDF. They were processed using nested based techniques borrowed from the custom cabinet industry, but there were a few twists that were unique to furniture.

The first problem encountered was that, unlike cabinets where all parts are relatively large size, many parts of the furniture were small. The high flow vacuum table commonly used to hold parts during machining would not adequately hold these small parts.

The solution was to not cut all the way through but to leave the thin back veneer skin to hold the small parts together and then use a small router table with a bearing tipped bit to remove the skin after machining. This proved to be quick and easy enough that the machine operator could do it in a couple of minutes while the next cycle was being cut.

The furniture designs also spawned a series of new joints that made assembly easier by taking advantage of the speed and accuracy of the router. When you are mass customizing furniture, you cannot rely on alignment fixtures or jigs because there are so many possible variations, so special techniques and joints must substitute for the fixtures.

Most joints between panels were blind dados, which have become very popular in custom cabinet design. These joints interlock panels much like long mortise and tenon joints and make assembly and alignment quick and easy. They also offer superior rigidity and strength. The high accuracy of the CNC router make sure that the joints fit together smoothly and precisely every time.

One serious problem with mass customized furniture that doesn't exist in batch produced furniture is trying to determine how various pieces fit together in the final design. The CNC router machines all the parts for a piece of furniture which are then labeled and stacked on a cart. These parts could be virtually anything. Some method was needed to communicate to the assemblers exactly how to assemble the parts.

The machine control prints labels for each part, so the first approach was to create assembly drawings that detailed how the labeled parts fit together. Although this sounds simple enough, in practice it really didn't work very well. Some of the more complex assemblies took a lot of time and effort to sort out and because some parts can be assembled upside down, assembly errors were common. A new approach was needed.

Assembly and joints  

The solution required that a new set of capabilities be added to the design software and these additions addressed the issue very effectively. Small hole patterns, called "assembly marks," were added to both parts of each joint. Then assembly consisted of simply mating parts with the identical assembly marks. In many cases assembly time was reduced by 75 percent or more, solving this sticky problem. The marks are positioned so that they are hidden once the parts are mated together.

Another interesting feature added at the same time was placing a color box on each part label to identify which item the part was for. This allowed more than one piece of furniture to be machined in the same job, many times improving yield. The color boxes made sorting parts into individual pieces of furniture much easier than trying to read text on each label. This made the process practical in the real world.

A joint that Thermwood calls a "puzzle joint" was used to assemble frames. This joint looks much like the joints used to hold parts of a jigsaw puzzle together. It is machined about three-quarters of the way through the parts so the front looks like a simple butt joint.

This joint has many valuable features. First, it is extremely easy to assemble and can only fit together one way. It does not require fixtures, pocket drills, alignment jigs or anything else. It is simply pushed together by hand and once together, is locked in place. The joint can't separate or loosen and can't be assembled out of square or out of alignment.

A type of dovetail can be used on drawer boxes, which are also machined directly from sheet stock. This increases quality, speeds drawer production while allowing virtually any size drawer to be machined with no setup or adjustments.

Another special joint is what  Thermwood calls a "box miter." This joint produces a miter look in the front but works well in a case clamp. It consists of a miter joint that extends a couple of inches into the joint and then transitions into a box joint with a veneer ledge.

This joint assembles easily, aligns perfectly and allows some potentially difficult to assemble components, such as box rails for beds, to be assembled and aligned quickly and easily.

CNC machining accuracy was used in other areas to address common assembly problems. Whenever two panels were to be laminated together, matching dowel holes were drilled into each panel. Then, short dowels were used with hand assembly to achieve and assure perfect alignment without fences, clamps or alignment fixtures.

It is interesting that when building mass customized furniture, you must use design features within the furniture parts themselves to achieve alignment instead of relying on external fixtures or alignment tools that are typically used in batch manufacturing. After all, you may only build one copy of a particular configuration so it is impractical to build a fixture for that one product. The joints and techniques described here were designed to address this and they worked rather well.

Once machining was complete, parts were sent to edgebanding. Edgebanders are typically designed to band solid panels but in the Thermwood program many parts were deep wall panels that were essentially two-inch-deep trays. In many cases the two-inch-edge needed to be banded.

Thermwood used two different edgebanders in this program. Both were made by Fravol, a line that Thermwood distributes in the U.S. The SX8 is an automatic straight line machine that allows quick changeover for different widths, had a pre-milling unit and worked well for this application.

Thermwood modified the machine so that all joints could process through without requiring adjustment to avoid machined slots or holes. The large tray panels did require a plug frame to keep the sides from flexing during the banding process since the wide edge was first machined and then banded.

Curved pieces were banded using a Fravol VSV manual bander. This machine does require that the length of banding in metric be input for each part. To make this easy, Thermwood added this information to the label for each part that needed manual banding so no calculations were needed at the edgebander. A Fravol VSR manual edge trim machine was then used to trim the curved panels.

Although the final operation looks pretty simple, smooth and straightforward, a lot of technical development was necessary to achieve that result. This technology has been added to Thermwood's product offering and they believe that the process is viable for full scale production.

Cost tracking system  

As a final note, Thermwood's engineers envisioned and designed a real time cost tracking system which they believe would be a major addition to the system. All material, hardware and component information is contained in the job file that comes from the  eCabinet Systems software.

When the machine runs the job, it first relieves inventory from the factory system for the hardware used, then it keeps track of how much material was used in machining, including any replacement parts. It also tracks the amount of time that the machining required.

A barcode is placed on each cart and each production person has a wireless barcode reader. They scan the barcode when they begin working on a job and the system keeps track of actual cost of each piece of furniture. A large flat screen color monitor was planned to show, real time, the exact status of every job flowing through the plant. Although not fully implemented, enough work was completed to validate that the system would work.

Overall, it required about three days from the beginning of a job until it was ready for shipment. Also, all the items for a particular order were run sequentially so that the entire order could be built and shipped together.

Based on these efforts,  Thermwood believes that this approach could work for mass-customized higher end furniture. Additional equipment and techniques would be needed if the designs incorporated carvings, large mouldings, legs or similar products, but systems to handle these items also currently exist.

While Thermwood is not interested in manufacturing furniture on a full-time basis, it is interested in supplying the technology and equipment needed to other furniture companies. It is also interested in offering the capabilities of the sales and configuration software it developed.

Mass-customized furniture is one step closer to reality.

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