Part 2:  Ultrasonic Welding—The Solid-state Welding of Plastics 

While available commercially on a global scale, electrical components such as plugs and sockets are so common in most retail stores that unless purchased, it’s unlikely most people give them a second thought—especially about their manufacturing processes from beginning to end: the raw materials such as resins and metal alloys, or the molds and designs that have met precise specifications and testing agency criteria, the skilled labor and expensive machinery being used, and the factory space and overhead costs to make it all happen. One lesser known hero in the world of manufacturing of electrical products containing plastics is ultrasonic welding, despite its popularity in manufacturing for nearly 70 years.

Jon Zobel, Molding Supervisor for Interpower, discusses why some countries use multiple plug patterns.

Solid-state Welding and the Power of Piezo

In a perfect ultrasonic welding world, two thermoplastics of similar compositions should provide strong candidates for a smooth and consistent weld provided each material has a melting point within 50°F of the other.

However, despite compatible material and melting points, inconsistencies in welds may occur due to factors such as moisture, dyes, oils, and foreign matter such as dust and dirt. Or improper alignment of the materials in the machine’s jointing zone or “nest” can affect the weld. Typically, ultrasonic welders have base plates with drilled and tapped holes for leveling screws for secure fixturing of the materials. Still, no matter how secure materials are in the nest, the surface of the materials must be thoroughly cleaned. Otherwise, marring, flashing formations, or other imperfections may occur. Vital, too, is that the welder is properly grounded to reduce radio frequency interference (RFI). The Dynamic Process Controller (DPC)—in certain long established vertical welders such as Dukane’s 220 and 340 models—contains an RFI filter, but additional grounding may be needed to prevent RFI from entering the AC line. A 14 AWG wire is the minimum recommended size for the ground.

Welding Interpower^® Thermoplastic NEMA 5-15 Faceplates onto NEMA Receptacles 

An Interpower molder or Made-to-order (MTO) technician has likely already determined in advance whether the NEMA 5-15 faceplate and its mated plastic receptacle (socket) housing are compatible thermoplastics, and likely what frequency to use for a successful weld, i.e., electricity converted to kHz frequencies (20-90kHz) and acoustic vibrations via expanding and contracting piezoelectric ceramics in the stack’s converter. As is the case for the faceplate and the plastic socket housing, 20kHz is used for a wide range of products in multiple industries. These high-frequency vibrations are intensified in the welder’s booster, which is connected to the horn toward the bottom of the stack. The vibrations travel vertically down the horn to the tip where pressure is applied pneumatically to the material to form the weld.

Fixture of the Welder

The Fixture of the Welder Holding NEMA 5-15 Faceplate

Friction from the horn melts the thermoplastic surface in fractions of a second and creates a molecular bond without the plastic materials liquifying and losing their shapes. There’s always the possibility of the welder’s horn marring the thermoplastic surface—or it may remove part of a textured surface. To prevent tool marks, flashes, or blemishes on the NEMA 5-15 faceplate in our example, Interpower automatically feeds see-through film over the surface of the faceplate residing in the welder’s fixture to prevent marring.

Ultrasonic Welder Horn Welding NEMA 5-15 Faceplate

Settings and Adjustments

The controller can be preset or adjusted with settings such as amplitude, pressure, weld time, and hold time. It is also recommended to shorten the distance between the horn tip and the materials being welded to shorten cycle times and thus increase production. Whatever polymer or resin you choose to weld, the material is placed in the fixture where it is secured to be welded.

Ultrasonic Plastic Welders

After growing exponentially in the auto industry in the 1960s, ultrasonic welding has kept stride with computer technology, its microprocessors offering a wide range of weld settings while storing a vast amount of data such as numerous plastic “recipes.” They contain sensors and real-time graphing. The result is a more consistent quality control through exact presets for various resins. As briefly mentioned earlier, older Dukane 220 and 340 models still provide enough programmable features to do many of today’s ultrasonic welds.

Ultrasonic Welder Stack with Protective Film Below the Horn

Various industries, including automotive, electronics, medical, and packaging rely on ultrasonic welding for a wide range of applications. Ultrasonic welding is compatible with different types of thermoplastics, providing flexibility in material selection. When choosing ultrasonic welding equipment, factors such as frequency, power output, and horn design should be considered. From toys to cars, to computers to medical equipment and supplies, the ultrasonic welding of plastics is still a very essential process in the manufacture of products worldwide.