Kinetic welding: New efficiencies in product assembly

A welding process developed and patented by Lucent Technologies, and used for five years to manufacture more than 15 million telephone handsets, is now being licensed by the telecommunications company. Dubbed kinetic welding, or k-welding, the process uses heat of friction to permanently bond two thermoplastic parts.

The concept and practice of k-welding is relatively simple. Two parts with an interference fit of mating bosses (Figure 1) are pressed together at a high velocity. The heat generated by the friction of the interference melts and fuses the two thermoplastic parts together. The machine can force together parts at velocities up to 70 inches/second and is powered by an air cylinder.

This is the key difference between kinetic welding and traditional vibration or spin welding. With vibration or spin welding, two plastic parts are rubbed together in either linear or angular displacement to produce friction to melt the surfaces at the interference. In k-welding, the heat required to melt the plastic is generated by forcing two mating surfaces directly against each other at a high rate of speed (Figure 2).

Machine users can control pressure and stop locations on the device, depending on the shape and configuration of the part being welded. The machine uses nests to cradle parts and secure them for welding, with particular attention paid to protecting part surface aesthetics. For short runs, a cast of the part itself can be used as a cradle.

"This process could be used in lieu of other assembly techniques, such as spin welding, ultrasonic welding, or solvent or glue assembly," says John Simone, licensing manager at Lucent Technologies at the company's Miami Lakes, FL facility. The pins on the Lucent handsets, says Simone, are about .25 inch in diameter, but he admits they "don't know what an upper and lower limit of diameter would be for this process."

Another unknown is material compatibility, although it's probably fair to assume that the guidelines governing other welding methods would apply to k-welding as well. Simone says that most of the work Lucent did with the kinetic welding device was with ABS, with a smattering of styrene.

Also, Lucent welded only two parts molded of the same material. Simone has no data or information about how well the process works with other thermoplastics, or thermoplastics of dissimilar material type.

In application, Simone says k-welding is best suited for high-volume assembly at injection molding facilities, especially for toys, electronic equipment, automotive parts, and disposable medical equipment. Also, because the process is solventless, environmental concerns are virtually eliminated.

For Lucent, k-welding saved the company approximately 5 to 8 cents per handset as the process eliminated the cost of screws and the labor to install them. For 15 million ABS handsets, that represents almost $1 million in total savings to Lucent.

The machine itself, Simone reports, is simple and reportedly can be constructed with off-the-shelf parts, which means a molder could license the process and build the machine to do the job. Lucent, however, ideally would like to license the process to a manufacturer who would then build and sell the machine itself.

The cost of the license is flexible and will vary depending on the needs of the licensee and the volume of welding work required. Licensing of this process is part of a wide-scale effort by Lucent to release a series of intellectual properties and processes from its noncore business systems.