“We definitely see increased use of biodegradable thermoplastics and more manufacturers needing to weld ergonomically shaped parts, rather than always welding flat parts with a single horn,” explains Steve Potpan, onsite manager at Rinco Ultrasonics USA. “One medical-device company we serve regularly uses a composite horn to weld handles with 3D contours onto surgical instruments. The many extenders are in a circular pattern to reach the exact spot where the weld needs to be made.”
Each part design requires a different ultrasonic horn, and the horn’s mechanical path length must be tuned exactly to the part. Correct tuning ensures maximum energy absorption at the joint interface and minimum energy reflection back to the power supply, resulting in longer equipment life.
Ultrasonic robotic welding presents a few challenges as well. Stacks for welding large parts are heavy and can significantly slow down the robot arm. As a result, manufacturers sometimes prefer using robots with lighter stacks for 35- or 40-kilohertz systems, instead of dedicated machines integrated with 15- or 20-kilohertz systems.
Robots also often produce backlash or deflection, and have difficulty producing the dynamic follow-through necessary for a high-quality ultrasonic weld. For these reasons, an air cylinder can be added—located between the robot arm and the ultrasonic stack—for ultrasonic spot welding or staking on the B side of a part, or for large parts that require several welds, like door panels. Such robotic systems incorporate multiple welding horns that can be easily programmed and changed.
Last March, Rinco brought to market the Ecoline generator, designed for use with the company’s Ecoline hand gun (HG35-4), welder (HW35-4) and tacker (HT35-3) to join thermoplastic parts. Potpan says the compact generator is a cost-effective alternative to tabletop machines for end-of-line or station-to-station spot welding corrective work. One consumer products manufacturer uses several of the generators to accurately weld four brass inserts into hundreds of plastic housings per day.
The generator has an operating frequency of 35 kilohertz and allows for 110VAC or 220VAC input voltage. Amplitude is adjustable from 40 to 100 percent, in 10 percent increments. Maximum power output is 480 watts.
Sonics & Materials Inc. makes the GXP Series of ultrasonic welding presses, which are driven by a stepper motor and come in frequencies of 15, 20, 30, 35 and 40 kilohertz. The presses ensure high repeatability, according to Brian Gourley, sales manager of the welding group at Sonics & Materials, and offer Ethernet/IP capability, and remote weld monitoring on a tablet or cell phone.
One Tier 1 automotive supplier customer makes sealed batteries with six small pressure relief valves, and each valve consists of three parts welded together. When battery pressure exceeds a nominal set value, the valves open to vent the pressure.
“Originally, the valves were welded with a pneumatic press,” explains Gourley. “But, to improve repeatability and lower scrap rate, we suggested a switch to the GXP 800 at a frequency of 40 kilohertz. The unit’s optical linear encoder provides excellent control, with a weld-depth tolerance of ±0.0003 inch.”
Since being integrated into the customer’s 10 automated assembly lines, the GXP press has lessened the scrap rate, and improved repeatability and throughput, which is now at 20 parts per minute for each machine.
Sonics & Materials also offers a high-throughput rotary index table for use with the company’s pneumatic and stepper motor welding systems. The table features a built-in HMI and a safety guard with hinged door. An LED light tower provides visual process indicators of green, yellow and red.
When used with the 15- kilohertz pneumatic welder, the table can increase throughput for medium to large-size parts at higher amplitudes, as well as softer-plastic parts with a joint that’s more than 0.25 inch from the horn.