Ultrasonic technology is providing Lasko Products with reliable, consistent bonding in the assembly of reservoir jugs for its humidifiers and other household appliances. The company, which had used solvent bonding to fasten the plastic jug to the jug base, experienced a high failure rate due to the glue failing to provide an airtight seal.

The solvent bonding method was replaced with ultrasonic plastic welders from SonobondR Ultrasonics.

"Gluing was sloppy, time-consuming, and involved excess handling of the plastic parts," explains Ralph Zwakenberg, Lasko's industrial design manager. "We needed to speed up the process, so we tried an ultrasonic method."

Sonobond designed a customized unit for Lasko's specific application.

"Because of the size of the finished product, Lasko needed a machine with dual welding heads," notes Kyle Kimbro, vice president of Sonobond. "We adapted the SureWeld 20 integrated welder to accommodate the different jug configurations. We also added soundproofing and a surround enclosure to eliminate noise."

Interface with plastic

Ultrasonic technology utilizes vibrational energy, which is transmitted to the interface of the plastic parts being joined. The plastic material then softens in a fraction of a second. When the material resolidifies, the bond is made.

Sonobond's SureWeld equipment incorporates a high stable bench press with a rectangular support column that minimizes deflection when pressure is applied against the part. These features are critical in the precision welding of rigid plastic assemblies, according to Kumbro. "The SureWeld machine provides Lasko with repeatable accuracy, while at the same time perfectly aligning the welded parts."

By replacing the gluing process with ultrasonic bonding, Lasko eliminated setup time and reduced the testing phase of its assembly process.

"Now," says Zwakenberg, "we no longer need to allow for setup time before the unit can be tested. The jugs can be tested immediately after welding."

Lasko also cut down on the percentage of units that need to be tested. "When we were using glue to assemble the jugs, every unit had to be tested to make sure the seal was airtight," notes Jack Markovich, plant manager at Lasko's Franklin, Tenn., plant. "With the Sonobond equipment, the integrity of the weld condition is terrific, so we've cut back on 100 percent testing."

Lasko Products and Sonobond Ultrasonics are based in West Chester, Pa.