Ultrasonic-welding,Low Power, Big Results.SOLUTIONS with Effective, Practical AdviceUltrasonic-welding is a solid state process that achieves the joining of metals by locally applying vibratory energy to workpieces pressed together. The energy of vibration produces a local relative parallel displacement at the interface between the two abutting surfaces. The motion breaks and disperses surface oxides and causes intimate metal to metal contact that results in a weld. A similar process is used to weld plastic materials but with two essential differences: in the case of plastics the direction of vibration is normal to the surfaces, and the vibrational energy is transformed in actual local heating that causes fusion. See Welding of Plastics (Opens a new Page). A short introduction to Ultrasonic-welding was published (2) in Issue #008 of Practical Welding Letter for March 2004. Ultrasonic-welding was originally developed for applications requiring the avoidance of heating, like those involving explosives, combustible gases or liquids, but was later used for overlapping joints of sheets, strips or foils and wires in diverse industries as electronics, automotive, aerospace. Ultrasonic-welding, like most of other solid state processes, permits joining of dissimilar metals that cannot be successfully fusion welded together. An Ultrasonic-welding system includes an electronic power supply which elevates the frequency of the electrical current from that of the grid to the one required by the process, typically from 15 to 40 kHz (kilo Hertz), a piezoelectric transducer that transforms electrical into mechanical energy, an acoustic coupling device or booster that modifies the shape and magnitude of the vibrations and a weld tool called horn or sonotrode that transmits the oscillations to the materials to be welded, clamped together by pressure unto the stationary anvil. The vibration amplitude is around 20 microns, the weld time is usually less than one second. Best results are obtained by applying sufficient power for short durations. Longer times at insufficient power fail to produce acceptable welds. Shape, thickness and cleanliness are most important for acceptable results. The most usual implementation introduces spot welds of shape and size depending on the tool used. The spot spacing may vary with the application, from as wide as possible to satisfy strength requirement, to overlapping if sealing is needed. The Benefits of Ultrasonic-welding are:
Limitations:
If welded material sticks to the sonotrode (weld tool), a low power ultrasonic pulse will release it. In some cases repeating the full welding cycle on a thick piece of brass may be helpful. Most metals are easily joined by Ultrasonic-welding. If the metal oxide is much harder than the metal (as for Aluminum) it breaks easily and does not interfere. Copper oxide which is more soft and ductile is not removed by the process, so that it has to be taken away by thorough cleaning beforehand. Different materials display different ultrasonic weldability, so that the practical thickness limits must be established for each material to be used in real applications. The economic benefits of the process are generally favorable to its applications when the performed welds meet requirements. Energy expense is much lower than for comparable joining with alternative methods and equipment (resistance- or laser spot-welding). A derivative process, called ultrasonic microwelding, was adapted to the requirements of microelectronic industry to deal with extremely thin wire and ribbon leads, generally with soft and conductive materials. The differences are not in the physical process, but in parameters like frequency (higher), power, static load and dimensions (much lower). This kind of equipment is generally automated for mass production. See also the following Article.
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