June 2005

Ultrasonic Energy Drives New Dowel Construction Process

New development is said to dramatically speed up cabinet and drawer box assembly.

By Rich Christianson
The specially designed dowels used in the ultrasonic process are manufactured from ABS.
A 5-second burst of ultrasonic energy liquifies a plastic dowel. Under the pressure exerted by a clamp, the melted dowel fuses to the porous particleboard parts.

A new process using ultrasonic energy to quickly weld plastic dowels to wood for cabinet and drawer box assembly was demonstrated last month at Ligna-Plus in Hannover, Germany.

The ultrasonic process, marketed jointly by Titusonic and Ligmatech, was shown in a Ligmatech drawer clamp at the Homag Group's booth. The two companies hail it as a "revolutionary" alternative to traditional glue and dowel construction methods.

Peter Cove, chief operating officer of the Titusonic Div. of Titus Tool International based in the United Kingdom, says, "The combination of speed with quality is probably the key. This is a 100 percent controlled process, with no human intervention, providing consistent strength and quality. It has more in common with the steel welding process in the automotive industry than with glue and dowels."

Joe Keilen, material handling product manager for Stiles Machinery Inc., which represents the Homag Group in the United States, agrees with Cove's assessment of the new process' key advantages. "The two things that stand out with the process is that the connection points are approximately 30 percent stronger and the process is approximately six times faster," he says.

Birth of the Process

The ultrasonic process was developed during 2003 and 2004 in a collaborative effort between WoodWelding Technology SA and Titus International PLC. Cove describes WoodWelding as "a Swiss technology research company with the basic technology for welding plastic to porous material, bone, building blocks and particleboard."

Cove says Titus funded the research project. It involved testing various combinations of different materials and dowel shapes "before we alighted on the current design."

The dowels, manufactured from ABS, are "asymmetric and designed to melt in a special way to ensure that when they cool, they shrink in their length to ensure a very tight joint," Cove says. "The principle product for furniture assembly and bonding is 8mm diameter by 40mm length. This utilizes a standard size of hole in both panels (to be joined), 8mm diameter by 15mm deep. The Titusonic process requires a 10mm gap for this dowel, hence the dowel length of 40mm."

How It Works

Cove notes that ultrasonic energy has been used to bond plastic to plastic for many years.

"This process requires a purpose-designed frame fitted with ultrasonic equipment, some of which is standard and some special and innovative software," Cove explains. "The ultrasonic energy in the Titusonic process is delivered in a conventional way from an electronic generator, through a converter to the head at 20,000 Hz."

In its joint marketing venture, the ultrasonic equipment is mounted on the frame of a specially designed Ligmatech drawer clamp. After the special plastic dowels are inserted without glue into the construction holes, the sides, front and back of a drawer are assembled. The assembled unit is placed into the drawer clamp. A 5-second burst of ultrasonic energy liquifies the dowel, fusing it with the porous particleboard parts.

Key Benefits & Limitations Cove rattles off four major advantages of the ultrasonic process.

"First, it's quicker. The complete cycle time through a press can be improved by between three and six times. The dwell time in a traditional press can be between 20 and 60 seconds waiting for the glue to go off sufficiently. The dwell time for the new Titusonic dowel is 1.2 seconds. The difference is made up of delivery and exit times from the press, which are altered by the process.

"Second, the process is approximately 30 percent stronger than its traditional wooden dowel rival.

"Third, it's cleaner because the new product takes glue out of the process. This simplifies machinery and eliminates clean up at the end of a shift and removal of glue squeeze-out on furniture.

"Finally, this is an engineered process. The old process is wood and glue, which varies according to a number of factors. The new process is more reliable and repeatable, with performance that is more recordable and traceable for quality assurance purposes."

Cove and Keilen each say there are limitations to the ultrasonic process, all of which are addressed by ongoing research and development.

"Miter joints are a problem right now due to the dowel hole being at 45 degrees to the frame because we need to direct the pressure and power in exactly the right direction," Cove says. "If the hole was drilled before the frame was mitered, this could eliminate our problems with this kind of joint.

"Also, there is currently a limit to the thickness of the panel or frame we can bond. We can certainly cope with sizes up to 25mm right now and are developing the process so we can bond frame doors up to 50mm thick."

Keilen says, "There are no real long-term drawbacks or limitations to the ultrasonic process...The technology is so new that it seems any limitation we run into is not a limitation, but rather an opportunity for a modification to a machine design, etc. Currently, the largest limitation is designing assembly equipment to incorporate ultrasonic technology, as many of the current machine designs do not easily accommodate for adding it."

Initial Reaction

Cove says the response at Ligna "has been superb. I have spent 35 years in furniture fastening and have waited all my life for a process and project as exciting as this." He adds that in addition to particleboard, the ultrasonic process has been successfully tested with MDF, plywood and some solid woods. Other potential markets include windows, picture frames and furniture-door frames.

"Any industry that requires a solid construction of wood components is a prime target for this technology," Keilen says. He adds that American customers who witnessed an ultrasonic doweling demonstration at Ligna were "extremely interested in the process and how it can apply to their business to help them increase production with a lower labor content per unit."

The process will make its North American debut at Stiles Machinery's booth 7029 during the AWFS Fair in Las Vegas, July 27-30.

                                                                                                                                                                                           

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