Ultrasonic weldingCopyright: © KEmikro
Grooves fabricated, e.g., by ultrasonic hot embossing are closed by ultrasonic welding. This way, sealed cavities or micro channels are generated [65, 24]. Typically so called energy directors are molten by ultrasonic welding and serve as a kind of glue between the joining parts. The energy directors are molten because they are in direct contact to the joining part and heat is generated there by the ultrasonic vibrations. The entire welding process including solidification of the molten material is achieved in approximately one second.
It is possible also welding several layers of micro channels on top of each other. A good example for this is the heat exchanger combining three fluidic levels welded onto each other and onto a connection piece .
If a hose or pipe is laid into a suitable groove, it is sealed in the channel when a lid foil is welded on top and a fluidic connection to a cuvette or a micro fluidic system is generated. A hose acts similar as an energy director and causes melting of the polymer in its vicinity by friction sealing the hose in the channel.
Another possibility providing fluidic connections is welding a connection plate already equipped with threaded holes for standard fittings .
Also metal wires between two polymer layers cause heat by friction and, therefore, are sealed between the layers during ultrasonic welding. This way, electrical connections into a micro system are achieved [7, 32]. An example for this is the anemometric flow sensor.
Not all polymers can be welded with each other. A list of weldable and non-weldable combinations are shown in . If a combination of polymers cannot be welded, joining is achieved by ultrasonic riveting and they possibly can be employed for ultrasonic thermoforming and ultrasonic punching.Copyright: © KEmikro
Instead of an energy director, there can be placed a wire or another part from metal between the joining partners before welding. In the neighboring figure, there is shown the comparison of both methods as cuts through the polymer parts before and after welding. A metal part is not molten by the ultrasound and enables a homogeneous welding under a large sonotrode showing a distribution of vibration amplitudes . Besides this, also polymers such as FEP can be joined which so far have been believed not to be suitable for ultrasonic welding because they are too soft and only pressed flat by a sonotrode resulting in no friction heat generated.
 J. Sackmann, K. Burlage, C. Gerhardy, B. Memering, S. Liao, W.K. Schomburg, “Review on ultrasonic fabrication of polymer micro devices”, Ultrasonics 56 (2015) 189-200, DOI: 10.1016/j.ultras.2014.08.007
 W.K. Schomburg, K. Burlage, C. Gerhardy, ”Ultrasonic hot embossing”, Micromachines 2 (2011) 157 – 166, ISSN 2072-666X, DOI:10.3390/mi2020157.
 K. Burlage, C. Gerhardy, W.K. Schomburg, “PVDF micro heat exchanger manufactured by ultrasonic hot embossing and welding”, Proc. 21st MicroMechanics Europe Workshop, MME 2010 in Enschede, Niederlande, 25. - 27. September (2010) C09, ISBN: 978-9081673716.
 P. Khuntontong, T. Blaser, W.K. Schomburg, ”Ultrasonic micro hot embossing of polymers exemplified by a micro thermal flow sensor”, Proc. Smart Systems Integration 2008, Barcelona, Spain, 9th - 10th April (2008) 327 - 334, ISBN 978-3-8007-3081-0.
 K. Burlage, C. Gerhardy, H. Praefke, M.A. Liauw, W.K. Schomburg, ”Taylor-Flow Monitoring Integrated in a novel PVDF Micro Channel”, Book of Abstracts, IMRET 12, 12th Int. conf. on microreaction technology in Lyon, France, 20th – 22nd February (2012) 75 - 76.
 L. Hoehr, J. Bavendiek, J. Sackmann, W.K. Schomburg, “Ultrasonic welding of polymer micro fluidic devices by inserting metal parts”, Microsystem Technologies 25 (2019) 673-681, doi: 10.1007/s00542-018-3995-y .