Wiring Harness News Sep-Oct 2022 - Page 56


Innovation Advances Ultrasonic Metal Welding of Large EV Battery Cables

By Craig Birrittella , Business Development Manager , Automotive , Branson Welding and Assembly at Emerson ___________________________

The amount of time required to charge electric vehicle ( EV ) batteries — compared to the quick fill-ups available to gas or diesel-powered vehicles — are a significant drawback to their acceptance . In their desire to overcome this obstacle , OEMs have attempted to deploy much faster charging systems that have peak charging power of 250kW or more . While these charging systems need only about 20 minutes to produce enough charging capacity for roughly 160 miles of driving range ( depending on the car or truck ), they also create a variety of problems .

To improve charging speed and capacity , EV batteries needed highercapacity wire harnesses and much thicker power cables . Today , typical EV batteries and charging stations use copper cabling of up to 95 mm2 , but to satisfy the demand for faster charging speed , these cables will likely soon exceed 120 mm2 . In fact , until recently , manufacturers have
had problems welding cables in the 60 mm2 , 90 mm2 or 120 mm2 cables needed today . The problems are caused by the increased power and amplitude requirements needed to weld the thicker charging cables , including :
• The increased bending and stretching of the cable strands during welding often led to greater strand fatigue and increased risk of failure .
• The greater weld forces that were needed produced excess friction and heat in the weld zone that not only spread to nonweld areas but also demonstrated the inefficiency and waste of electrical power needed to create the heat for welding .
• The increased cable diameters caused the tooling to lose its grip and allow cables strands to slide across the tooling surfaces , rather than gripping and holding the strands in place . This caused faster tool wear , more frequent tool replacement , greater energy consumption and unnecessary stress on the welding equipment .
These are formidable challenges to an industry experiencing rapidly growing demand for faster , more
efficient EV charging systems . Emerson engineers studied the problem and found that the increased weld forces needed to weld thicker cables pushed the cantilever-type actuator arms used on typical ultrasonic welders to their mechanical limits . It caused vibration , decreased clamp stability and greater inefficiency . The current ultrasonic welding technology needed to be re-engineered .
To address the problem , Emerson engineers developed an innovation technology included in the “ direct press ” ultrasonic welder , the BransonTM GMX-20-DP .
The GMX-20-DP welder ( Figure 1 ) employs a new vertical actuator motion that is able to apply a much greater clamp force ( as high as 6100 N ) than was practical using a cantilevered actuator arm . The more-controlled motion and increased downforce available with the new vertical actuator eliminate the stress and vibration caused by cantilevered actuator arms .
In addition , Emerson engineers addressed the problem of cable slippage by redesigning the tooling on the GMX-20-DP ultrasonic welder in two important ways . The horn and anvil both have a specialized coating that increases their hardness and durability , and the welding surfaces on each component incorporate knurling to significantly improve the gripping strength of each component .
The result is more consistent , repeatable large-cable welding than cantilevered tooling can deliver .
The GMX-20-DP ’ s increased downforce , combined with the redesign of the gripping surface of the horn and anvil eliminates the slippage that occurs with cantilevered actuator arms . The parts are held firm while the weld energy is delivered much more efficiently — all resulting in the stability required to successfully weld cable cross sections of 20 , 30 , 50 , 60 , 70 and 95 sq . mm as well as other large parts . The new technology also provides a “ gentler ,” higherquality , low-stress cable weld that requires typically 30 % to 40 % lower amplitude than previous ultrasonic technology used for welding EV battery cables .
The new tool design , combined with the vertical weld motion of the direct-press welder , also eliminates the rapid tool wear caused by slippage on cantilevered actuators . This decrease in tool wear not only ensures more consistent tool performance but also measurably increases the interval between tooling changes ( see Figure 2 ).
Overall , the remarkable improvement in large-cable metal welding available with the GMX-20-DP welder is the result of a unique combination of innovative tool design , enhanced
Figure 1 . Branson GMX-20-DP “ Direct Press ” Ultrasonic Metal Welder from Emerson ( left ) represents a new generation of Metal welding technology . ( photo courtesy of Emerson )
Figure 2 . Conventional , cantilever-type ultrasonic metal welders can be stressed when welding thicker materials , resulting in “ slippage ” marks ( left ) from high amplitude and limited tooling grip on the part .
( photo courtesy of Emerson )
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