Wiring Harness News Sep-Oct 2022 - Page 57

Figure 3 . Diagram of the ultrasonic metal welding process .
direct-press downforce , and a more controllable weld process than has been possible with previous cantilevered actuator technology .
SIDEBAR : Understanding the ultrasonic metal welding process
The soft , nonferrous metal foils used in EV batteries cannot be successfully joined using resistance or laser welding ( processes that are excellent for bonding high-strength ferrous metals ) because they can melt the delicate foil surfaces during welding . The thin , fragile metal foils typically used in batteries require ultrasonic welding , which uses the heat from friction to join surfaces , rather than melting the metal . The problem is melting the surface of these softer , nonferrous metals can form intermetallic compounds and galvanic corrosion that cause material deterioration , as well as connection and
( photo courtesy of Emerson ) battery failure . In addition , because EV batteries require as many as 90 or more thin foils , it would be complicated to assemble because the foils are so fragile .
Ultrasonic welds are created by applying high-frequency vibration to two metal components held tightly between an upper sonotrobe ( or horn ) and a lower anvil ( Figure 3 ). One component part is placed on the lower , stationary anvil and held there by a knurled pattern on the tool surface . The welder ’ s actuator brings the horn down to hold the metal components together under a specified pressure . Vibration is then applied , and welding occurs as the horn vibrates horizontally across the stationery anvil , first “ scrubbing ” away surface oxides and other potential contaminants . The oscillation continues , generating the heat that joins the clean bonding surfaces .
The heat generated by the oscillation is generally about one-third to one-half the melting point of the materials being used . That allows for joining the materials with strong bonds without melting , burning through the thin foils , or creating unwanted intermetallic compounds that could degrade the quality of the bond between the component parts . Rather than melting the material surfaces , it breaks down surface asperities and creates a continuous weld bond characterized by atomic diffusion across the interface that crystallizes into finely grained structures when the vibration stops . The process , which happens in a fraction-of-a-second weld cycle , creates a bond similar in structure to cold-worked metals .
Ultrasonic welders are also uniquely versatile in that they are capable of operating gently enough to join multiple layers of thin , delicate metal foils or , using different parameters , powerful enough to generate strong bonds between large metal parts and conductors ( Figure 4 ).
Figure 4 . Strong highly conductive ultrasonic welds splice not only small wires and large conductors but also wire terminations .
( photo courtesy of Emerson )
Ultrasonic metal welding and splicing : Process benefits
• Works with many types of nonferrous metals , from thin films to large conductors
• Creates permanent , metallurgical bond between dissimilar metals
• No melting required — no change to chemistry or metallurgy of materials
• Ideal for joining highly conductive alloys : Reactivity of materials does not matter
• Creates no intermetallic compounds , particulates , or corrosioncausing reactions
• Connections offer maximum conductance , minimum resistance
• Multiple methods of control enable process customization , repeatability and SPC
• Low energy input ( 30x lower energy use than fusion or resistance welding ), no consumables
• Lowest total cost per weld of any welding technology
About the author
Craig Birrittella is the Business Development Manager , Automotive , Branson Welding and Assembly at Emerson . During his 25-plus year career at Emerson , Craig has received a U . S . patent for lens adaptation to improve laser energy and has focused on a variety of additional technical areas , from vibration , clean vibration , and infrared welding . Birrittella has a BS in mechanical engineering from the State University of New York , Buffalo .