Fire,electricity,and clouds of gas,fumes,and vapor are the usual image associated with welding.The image of the welder in their self-darkening helmet,working at a welding point that would sear their eyes were they to view it unprotected,is a familiar one and another vivid impression which most people think of when they hear the word “welding.” However, welding can also be carried out using sound waves specifically,ultrasonic vibrations created by a specially designed welding machine.
Ultrasonic welding machines for plastic
Plastic and metal can both be welded using ultrasound, and the machines for these two very different substances have similar,butnot identical,designs.Plastic-welding ultrasonic welders apply the ultrasound vertically,while metal-welding ones apply it horizontally,due to the different effects of the vibration on the materials and the highly divergent ways in which these vibrations cause welding.
The plastic to be welded is placed on the anvil and clamped down by the sonotrode,or “weld horn” the instrument that actually delivers the ultrasonic vibration to the plastic pieces.The sonotrode is part of an assembly called the stack,which includes a converter,a booster,and the sonotrode itself.Interaction between these parts creates the ultrasonic vibration at exactly the frequency needed to weld a certain kind of plastic.
The converter is the source of the vibrations it contains a series of piezoelectric ceramic discs and metal plates which expand and contract rapidly when an electric current is run through them.A titanium cylinder absorbs the vibrations created and passes them to the booster, where the vibration is amplified to a point where it can melt the plastic being welded.The sonotrode then ‘fires’ this vibration into the plastic itself.The vibration is enough to melt the plastic along the contact surfaces between the two pieces,at the point under the sonotrode, producing a strong ‘spot weld.’
Ultrasonic welding machines come with built-in settings suitable for various types of plastic. Care must be taken to adjust the machine properly,however,taking the size of the pieces and the additives in the plastic being used into consideration an incorrect setting can have little or no welding effect, or can even shatter the plastic entirely.
Ultrasonic welding machines for metal
Ultrasonic welding machines built to fuse metal have the same basic components as their plastic-welding counterparts, but arrange them in a very different fashion, and achieve their results not through actual heating, but by mingling at the level of the metal’s atomic structure.
The metal to be welded is clamped together firmly, then placed on the anvil.The ultrasonic stack is activated with a current through the converter’s piezoelectric ceramic discs,and the sonotrode transmits the amplified vibration to the metal horizontally.No melting occurs in this case, however ultrasonic metal welding is a cold-process welding technique.The shear between the parts drives their substance into each other and literally combines them a strange but effective process.
The welds produced by this method are, surprisingly,very strong, and are suitable for use in electronics applications because electrical conductivity still exists through the weld (unlike typical welds, which have a very high resistance and effectively short-circuit any electric circuit passed through them).The molecular bond produced does not damage either piece of metal, and avoids many of the unpleasant side details of other welding methods, such as pollutants, heat, and blinding light.
Ultrasonic welding is a fairly new process compared to other welding types,but it produces excellent results on pieces of a certain shape, with many unique features such as keeping electrical conductivity through the weld and being able to effectively weld plastic.For many applications, it is the best welding choice for these reasons, and despite its apparent strangeness, the ultrasonic welding machine is sure to remain a fixture of metal and plastic fabrication for decades to come.