Written by Mark Boyle, Product Manager
AMADA WELD TECH
Lasers welders produce a beam of high intensity light which, when focused into a single spot, provide a concentrated heat source — providing narrow deep welds and fast welding speeds. The process is frequently used in high-volume applications, such as in the automotive industry.
Here are five commonly asked questions related to how this form of welding is used for automotive components, including its advantages and disadvantages.
1. What are the key automotive applications for laser welding and why is it the best choice for these applications?
Within the automotive industry, there has been an increase in the use of laser welding in manufacturing. It’s now commonplace for many automotive applications, including the large-scale welding of body frames (body-in-white), door frames, trunks, auto hoods, and chassis, and laser plastic welding (for front and back lights, as well as electronic housings).
Laser welding is also widely used for metal welding of many sub-components, including airbag initiators, motor coil windings, battery tab-to-bus bar connections for vehicle electronics, and electrical interconnection within an automobile build.
Previously, welding for these applications have been done through a variety of other technologies, including resistance welding (RW), tungsten inert gas (TIG or GTAW), and metal inert gas (MIG or GMAW).
Lasers are now being used in several mobile welding applications because the process imparts less heat, resulting in more localized heat with a smaller heat-affected zone (HAZ). Additionally, with the industry moving toward lighter and more conductive material, it’s easier to weld with laser welding than, for example, resistance welding (RW). This is because laser welding imparts localized heat, meaning operators can address smaller parts. Better accessibility and fewer restrictions to parts enhance the design flexibility, enabling approaches that may not have been possible with other techniques.
2. What are the biggest impacts on laser welding for the automotive market?
By far the biggest trend today is the electrification of motors, as evidenced by the increasing number of hybrids and all-electric automobiles on the streets. These vehicles require welding of electric-motor components, including powertrain connections and stator hairpins.
Battery welding and connections are additional key applications in vehicle electrification. Welding is required to create the battery cell, join cells to create a module or pack, and sometimes connect the modules to create a complete battery assembly.
The connections in the electric motor and battery pack are, typically, of conductive materials and laser welding is well suited. Weld joints also demand high strength, conductivity, and reliability in adverse conditions, which means welds must meet this criterion and be traceable.
Another trend favoring laser welding is the widespread increase in electronics within vehicles compared to in the past. Today, nearly everything is controlled by a computer and almost the only thing a vehicle operator can do by hand is to refill the windshield wiper fluid.
Laser welding for electronics connections has earned a high safety record. Plus, there’s a high throughput without a great deal of scrap — a factor that ties into improved economics for the laser welding technique. This trend includes the increase in vehicle safety equipment, especially advanced driver-assistance systems (ADAS) and connecting sensor-based safety equipment.
Although some of the connections are made by reflow soldering (such as flex circuit to PCB), often the sensor housings will be sealed via laser welding.
Lastly, laser welding technology is well suited to high-speed production lines — particularly fiber lasers, which have no consumables and no power degradation. These lasers form the backbone of new automotive production lines.
3. What type of laser welding equipment and technology is typically used for automotive applications and what are the advantages and disadvantages?
A variety of laser technologies are currently used, including pulsed neodymium-doped yttrium aluminum garnet for small components, spot welds, and seam welds, as well as blue direct diode lasers, fiber lasers, and pulsed disk lasers.
Recently, fiber lasers have gained more of a foothold and are taking over applications in the automotive industry. A fiber laser is generated within a flexible, doped glass fiber that’s typically 10 to 30 feet long and has a fiber-core diameter between 10 and 50 microns diameter.
Ytterbium is used as the doping element because it provides good conversion efficiency and a near 1-micron output wavelength, which matches well with existing laser delivery components.
It’s available for applications requiring everything from a few watts to tens of kilowatts, fiber offers ease of use, handling, and longevity (if not damaged by mishandling). Fibers are also economical and relatively cheap to operate on the plant floor because they do not draw as much electricity as a YAG or pulsed disk laser.
4. Can you give examples of a recent challenging automotive applications and describe the laser welding process that was developed to meet these challenges?
We have recently seen three interesting automotive industry applications:
- Sealing of airbag initiators
- Tab-to-cell and tab-to-bus bar battery welding
- Copper hairpin welding in an electric motor.
Each of these applications can be achieved with a continuous wave (CW) fiber laser.
Air bag initiator
In this airbag initiator application, a seam weld is used to seal the gunpowder inside the initiator can. If a driver is in an accident, a current is applied across the leads on the can with gunpowder, which heats up and explodes to start the process of opening the airbag.
AMADA WELD TECH has supplied several lasers for airbag initiator welding systems using both pulsed Nd:YAG and fiber laser technology. During the last five to seven years, the industry has transitioned to fiber laser technology, which is a much faster process and increases throughput – the welding process is 10 times faster.
Tab-to-cell and tab-to-bus bar
Another growing market has been connections between battery cells, battery packs, and battery modules. As hybrids and fully electric vehicles continue to increase, the demand for this weld will continue to increase. AMADA WELD TECH has developed several solutions for joining the tab-to-cell and tab-to-bus bar.
As the industry has continued to develop, there has been a transition to more conductive material for the tabs. However, the battery material (if using cylindrical batteries) has not changed. We’re now frequently requested to weld Cu to cold-rolled steel (CRS) can, or even worse, aluminum to CRS.
New laser sources enable this dissimilar metal joining. For example, AMADA WELD TECH has used 500 W-1000 W single-mode continuous wave fiber laser micro welders to concentrate the energy into a small spot to aid energy coupling into the material and resultant penetration.
This new technique shows promise for joining dissimilar metals found in the tab-to-cell application. In one case study, mechanical testing found peel strength to be good – after thermal soak and shock, 50 samples of the weld peeled within ±2 N. This narrow band of peel results shows reproducibility and reliability needed in production. The high power allows for a better connection of thicker tabs to the bus-bar.
It’s now commonplace to use pins to replace traditional copper winding inside the electric motor stator as a way of improving engine performance. However, the pins are made of copper, which is a difficult material to weld. Copper has high reflectivity in the IR, so coupling the material to create a melt pool requires significant energy density.
With the advancement of single-mode fiber lasers and scanning beam delivery systems, AMADA WELD TECH has been able to successfully weld this challenging material and geometry. Depending on the size of the pins, anywhere between 1000 and 4000 W is typically used. The key to success has been in controlling the melt pool while avoiding porosity.
5. What process do you use to consult with customers on their automotive application welding challenges?
Our customers will send or bring in samples of parts for welding to AMADA WELD TECH’s application technical center, which is comprised of 25,000 square feet of lab space situated in an 85,000 square foot manufacturing facility.
The technical center is equipped with application-specific labs that support each of the company’s product lines and various joining technologies.
The experts in the application labs determine the solution that best fits the application and budget. These engineers provide options and develop a report with information showing how to join those two, across all technologies. They also provide information on several different technologies — such as comparing and contrasting laser welding against resistance welding, micro TIG welding, and other platforms.
In addition to flexible technology selection, customers can see equipment options within the technology. On the laser processing side, the application labs have Nd:YAG and fiber welders. Resistance welding choices, for example, include AC, capacitive discharge, high frequency, and linear DC. For cutting and micromachining, customers can see system implementations showing exactly what would be purchased.
We have considerable experience with resistance, micro TIG, and laser welding processes for battery welding. We’ve also noted an interest in a transition to lasers welding, and can help support customers transitioning into this technology.