Introduction
The worldwide demand for lithium-ion batteries is at an all-time high due to the growing popularity of electric vehicles (EVs) / energy storage systems. Although the majority of battery development efforts focus on battery cells, the quality and reliability of the aluminum busbar welds that connect the individual cells are equally important. Poor welds increase electrical resistance (heat generation), impede battery efficiency, and lower the overall life of the battery.
Laser welding has emerged as the most popular method of joining aluminum busbars due to its ability to create clean and repeatable welds with minimal heat distortion. However, achieving strong welds is dependent not only upon the power of the laser but also upon proper optimization of multiple variables.
This guide identifies key factors affecting the quality of the welds, defects commonly found in laser-welded connections, methods of inspecting the weld quality, and practical tips for improving manufacturing consistency.
In laser welding, parameters are defined as the machine settings used for connecting aluminum busbars.
Common types of parameters for laser welding include:
Laser power
Welding speed
Focus position
Beam spot size
Shielding gas type/flow
Joint fit-up
By properly optimizing the above parameters for laser weld type aluminum busbars, it is possible to manufacture strong welds with low electrical resistance while simultaneously minimizing defects (e.g., porosity, cracking, and/or incomplete fusion).
Aluminum busbars link individual prismatic cell lithium battery cells together and transport a large amount of electrical current throughout a battery pack. Because typical battery modules have many welded connections, each connection’s performance must have low electrical resistance and consistent mechanical strength over time.
Compared to other conventional welding methods, there are many benefits that laser welding provides:
High level of accuracy and consistency
Low levels of heat are introduced into the battery module (minimal distortion).
High-speed processing delivered through automated production methods
A clean and consistent-looking weld
A reliable electrical and mechanical performance level
Laser welding is an ideal method for welding battery busbars for use in EV battery packs, battery energy storage systems (BESS), telecom batteries, UPS systems, and any other application where high currents are used.
Laser power or energy delivery at the joint controls insufficient energy may cause failure incomplete penetration and excessive output energy may burn through too much with an inappropriate amount of input energy.
Travel speed controls input heat. Narrow speeds are beneficial to increased productivity and better control over thermal distortion, but they may cause incomplete penetration. Conversely, too slow a travel speed increases fusion but provides additional heat into the fuse joint area.
The focus setting determines where the energy of the laser is focused, and even slight changes to this focal point have a major effect on the depth of penetration, bead contour (geometric shape of the bead), and the consistency of the weld. Good calibration of the laser focus will promote more stable production and lower the incidence of defects.
A small spot creates greater penetration depths, whereas a larger beam allows for better fitting of welded members. Each of these systems should provide ideal sizes of beams depending on the application and desired geometry of the finished weld.
Shielding gas plays an important role in preventing the oxidation and contamination of the molten weld pool. Though argon is the most popular, which means that it is generally chosen, it is possible to utilize helium or another mixed gas for particular applications. Furthermore, proper gas flow will contribute to minimizing porosity and creating a better surface finish.
Proper alignment of the busbar to the battery terminal is essential in order to have adequate joint penetration; poor fitting will diminish the joint’s overall strength and add to the electrical resistance that exists in the joint. Precision devices will assist in maintaining consistent quality during production.
Although optimizing parameters is only a portion of the overall process, manufacturers need to inspect every weld. Welds can be inspected visually and electrically (through use of resistance), as well as through the use of pull or peel tests and cross-sectioning (when necessary).
Some common welding defects include:
The process of routinely inspecting parts aids companies with discovering potential issues earlier and improving their production’s consistency.
To achieve dependable weld quality, both process control and preparation of the base material must be done properly. The best ways to do this are through the following points:
Clean the aluminum surfaces prior to welding to eliminate oil and/or dirt from the material as well as the oxide layer on the surface.
Utilize precision fixtures to keep everything aligned properly.
Regularly calibrate your laser equipment (and check for focus).
Perform trial runs with various combinations of welding parameters prior to making an adjustment to the welding parameters.
Save the process data on file for the purpose of quality controls.
Perform routine inspections while manufacturing.
By utilizing every one of these procedures, you will reduce rework, improve repeatability, and improve battery reliability.
The overall quality of the weld starts with the quality of the busbar itself. A reliable aluminum busbar manufacturer will produce the following:
High-conductivity aluminum suitable for battery applications.
Precision manufactured, including CNC punched, bent, hole punched, slot punched, sleeved, or plated.
Tight dimensional tolerances necessary for successful automation of assembly.
Clean burr-free surfaces that allow good weld quality.
Documentation of material traceability and quality controls.
Using the services of an experienced manufacturer will provide you with the reliability and consistent welding performance required for long-term reliability.
Manufacturers should adhere to internationally accepted good practices as required under a system such as ISO 9001:2015, be sure to keep documented evidence of processes for quality assurance purposes, calibrate all equipment on a regular basis, and sample inspect every production run for quality. In addition to complying with the above, other testing may be necessary depending on the intended application, including electrical resistance, tensile strength, thermal cycling, vibration, etc.
Battery making continues to advance due to AI-based weld monitoring, robotic laser systems, digital traceability, and advancements in the fiber laser technology all of which allow manufacturers to increase production levels while still maintaining consistent weld quality.
1. What is so great about laser welding as the chosen method to manufacture aluminum busbars?
With laser welding being capable of producing welds that are highly precise/accurate with low resistance and very little thermally distorted, they make it easy for automated assembly lines to manufacture batteries out of aluminum busbars.
2. What welding parameters matter most when creating strong welds?
The strength/consistency of a weld will be affected by the amount of laser power used, the welding speed, how well the laser is focused (beam focus), the spot size, the type of shielding gas used (when applicable), and how well the welded pieces fit together prior to welding.
3. Should I clean the surface of the part before welding?
Yes! When a surface has oxidation or contamination present, they can inhibit laser penetration into the surface, therefore creating strong welds free from defects.
4. What do welders do to verify their workmanship?
To ensure their work meets the specified requirements, welders will use a combination of inspection methods such as visual inspection, resistance testing (to the current flowing through the weld), pull/peel testing, measuring the dimensions of the welded parts, and analyzing cross-sections of the welded parts.
The performance of lithium prismatic battery packs and their ability to provide safety depend on the quality of the laser welding that is used to assemble them. In order to produce quality laser welds, it is critical that the manufacturer has the proper balance of laser power vs. welding speed, focal location of the beam, proper shield gas, and proper joint alignment. When combined with adequate inspection procedures and a quality assurance program, these elements allow the manufacturer to produce high-quality, low-resistance connections that will provide the battery with a long service life as well as reliable performance.
If you are designing a battery in an electric vehicle, creating lithium battery modules or energy storage systems (BESS), or other types of high-current electrical assemblies, you need to select the correct busbar manufacturer.
Adinath Enterprises delivers exceptional quality custom-manufactured aluminum and copper busbars using state-of-the-art CNC-based fabrication methods that include bending, punching, sleeving, plating, and an extensive quality control program. Our engineering knowledge and manufacturing capabilities provide the customer with reliably, efficiently, and dependably produced busbars to allow them to create dependable laser welds and to have a smooth assembly process with dependable electrical performance for high-current battery applications.
Do you need to manufacture custom aluminum busbars for your next project? Kindly contact Adinath Enterprises so we can help you create an aluminum busbar that meets your design specifications and manufacturing requirements.
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