Process
For joining complex injection molded thermoplastic parts, ultrasonic welding equipment can be easily customized to fit the exact specifications of the parts being welded. The parts are sandwiched between a fixed shaped nest (anvil) and a sonotrode (horn) connected to a transducer, and a ~20 kHz low-amplitude acoustic vibration is emitted. (Note: Common frequencies used in ultrasonic welding of thermoplastics are 15 kHz, 20 kHz, 30 kHz, 35 kHz, 40 kHz and 70 kHz). When welding plastics, the interface of the two parts is specially designed to concentrate the melting process. One of the materials usually has a spiked energy director which contacts the second plastic part. The ultrasonic energy melts the point contact between the parts, creating a joint. This process is a good automated alternative to glue, screws or snap-fit designs. It is typically used with small parts (e.g. cell phones, consumer electronics, disposable medical tools, toys, etc.) but it can be used on parts as large as a small automotive instrument cluster. Ultrasonics can also be used to weld metals, but are typically limited to small welds of thin, malleable metals, e.g. aluminum, copper, nickel. Ultrasonics would not be used in welding the chassis of an automobile or in welding pieces of a bicycle together, due to the power levels required.
Ultrasonic welding of thermoplastics causes local melting of the plastic due to absorption of vibration energy. The vibrations are introduced across the joint to be welded. In metals, Ultrasonic welding occurs due to high-pressure dispersion of surface oxides and local motion of the materials. Although there is heating, it is not enough to melt the base materials. Vibrations are introduced along the joint being welded.
Practical application of ultrasonic welding for rigid plastics was completed in the 1960s. At this point only hard plastics could be welded. The patent for the ultrasonic method for welding rigid thermoplastic parts was awarded to Robert Soloff and Seymour Linsley in 1965. Soloff, the founder of Sonics & Materials Inc., was a lab manager at Branson Instruments where thin plastic films were welded into bags and tubes using ultrasonic probes. He unintentionally moved the probe close to a plastic tape dispenser and the halves of the dispenser welded together. He realized that the probe did not need to be manually moved around the part but that the ultrasonic energy could travel through and around rigid plastics and weld an entire joint. He went on to develop the first ultrasonic press. The first application of this new technology was in the toy industry.
The first car made entirely out of plastic was assembled using ultrasonic welding in 1969. Even though plastic cars did not catch on, ultrasonic welding did. The automotive industry has used it regularly since the 1980s. It is now used for a multitude of applications.
Ultrasonic welding can be used for both hard and soft plastics, such as semicrystalline plastics, and metals. Ultrasonic welding machines also have much more power now. The understanding of ultrasonic welding has increased with research and testing. The invention of more sophisticated and inexpensive equipment and increased demand for plastic and electronic components has led to a growing knowledge of the fundamental process. However, many aspects of ultrasonic welding still require more study, such as relating weld quality to process parameters. Ultrasonic welding continues to be a rapidly developing field.
Scientists from the Institute of Materials Science and Engineering (WKK) of University of Kaiserslautern, with the support from the German Research Foundation (Deutsche Forschungsgemeinschaft), have succeeded in proving that using ultrasonic welding processes can lead to highly durable bonds between light metals and Carbon-fiber-reinforced polymer (CFRP) sheets.
The benefits of ultrasonic welding are that it is much faster than conventional adhesives or solvents. The drying time is very quick, and the pieces do not need to remain in a jig for long periods of time waiting for the joint to dry or cure. The welding can easily be automated, making clean and precise joints; the site of the weld is very clean and rarely requires any touch-up work. The low thermal impact on the materials involved enables a greater number of materials to be welded together.
Read more about this topic: Ultrasonic Welding
Famous quotes containing the word process:
“The practice of S/M is the creation of pleasure.... And that’s why S/M is really a subculture. It’s a process of invention. S/M is the use of a strategic relationship as a source of pleasure.”
—Michel Foucault (1926–1984)
“If thinking is like perceiving, it must be either a process in which the soul is acted upon by what is capable of being thought, or a process different from but analogous to that. The thinking part of the soul must therefore be, while impassable, capable of receiving the form of an object; that is, must be potentially identical in character with its object without being the object. Mind must be related to what is thinkable, as sense is to what is sensible.”
—Aristotle (384–322 B.C.)
“You can read the best experts on child care. You can listen to those who have been there. You can take a whole childbirth and child-care course without missing a lesson. But you won’t really know a thing about yourselves and each other as parents, or your baby as a child, until you have her in your arms. That’s the moment when the lifelong process of bringing up a child into the fold of the family begins.”
—Stella Chess (20th century)