Laser welding has become more popular in automotive body-in-white and component production because it is highly productive—a single laser welding robot can replace up to five conventional spot welding robots. High-power disk or fiber lasers, combined with a scanner welding head and an industrial robot for on-the-fly laser welding, can produce more than one hundred welds per minute.
This causes a challenge: if the production is so high, how can one ensure that stable, good-quality welds are produced? Often, crash safety-relevant parts are produced in the automotive industry, making weld quality even more important. AWL-Techniek, as a specialized machine builder, supports its customers in tackling this challenge (FIGURE 1).
FIGURE 1. AWL-Techniek's laser welding machine. (Courtesy: AWL-Techniek)
This article will discuss the three aspects of a stable production machine: the machine itself, the limits of quality control by a human inspector, and automatic quality inspection.
Quality starts in the welding machine. The laser welding fixture must be able to clamp the parts in a stable manner even if the tolerances are rough, as is often the case in stamped metal parts.
The fixture must also be able to prevent errors by the operator. A good laser welding fixture detects if all single parts are loaded correctly before the laser welding process can be started. Poka yoke systems (a Japanese development of any mechanism in a lean manufacturing process that helps an equipment operator avoid [yokeru] mistakes [poka]), product detection sensors, and a well-designed tolerance chain are needed. Attention must be paid to clean air supply and fume exhaust, and the fixture must be easy to clean and to service (FIGURE 2).
FIGURE 5. This schematic illustrates the principle of photodiode-based laser quality monitoring [2].
Diode-based systems have the advantage of being quick and automatic. They evaluate weld quality during the actual welding, so no extra inspection station is needed in the production line. Of course, this is only valid if the system is reliable.
However, a disadvantage of diode-based systems is that they measure indirectly. The diode measures the process light, which is correlated to the weld quality—but is not the actual weld quality. This leads to errors that are not detected (false-negatives) and to good welds that are detected as errors (false-positives). AWL-Techniek experiments showed that the reliability of the diode-based automatic systems was not perfect, but when the error rate of automatic quality monitoring systems was compared to human visual inspection, it was clear that a well-adjusted automatic system performs significantly better.
It is important to realize that quality monitoring systems will need adjusting and fine-tuning not just at installation, but especially during full-scale production. A fine balance between sensitivity (no true errors missed) and no false-positive errors must be found. It is important to educate the maintenance team working with the installation so that they feel comfortable in performing these optimizations. Therefore, strong support and understanding by the factory management is needed.
A challenge is to design a good error handling strategy that includes how to handle false-positives. A typical part can have several hundreds of welds. Therefore, even a low percentage of false-positives for a single weld can lead to a considerable number of positives for a complete part.
It is important to make rules for the part quality—for example, a rule that a defined percentage of welds can be defective before the part must be sorted out. A statistical analysis of the results, during production and fine-tuning the system, can be helpful. If the error handling strategy is not sufficiently robust, the user will not be satisfied with the quality control system.
For the future, more reliable systems are expected on the market. An emerging trend—with several systems being brought to market—is optical coherence tomography (OCT), where the actual depth of a laser weld, as well as the profile of the surface, is measured. This enables direct evaluation of the features of a laser weld and thus promises more reliability. An ultimate step would be to use this measurement signal as an input for feedback control of the laser welding process. A further possibility is to use a laser triangulation-based system, which checks the quality of the surface of the weld. These systems are especially appropriate for edge welds.
Clearly, quality monitoring in laser welding is a theme that has grown more important over recent years, as output from laser welding machines has increased. Quality monitoring is not without challenges, but commercially available monitoring systems can be a great help.
Popular systems that are available are not plug-and-play. Optimization and fine-tuning during production are necessary, as well as training for the maintenance staff in doing this optimization. A robust quality strategy must be designed, which does take into account the reliability of the monitoring system as well as the danger of false-positive errors.
1. C. G. Drury and J. Watson, "Good practices in visual inspection," FAA/Human Factors in Aviation Maintenance (); see https://goo.gl/w2X5qN.
2. M. Schmidt, "Process monitoring for laser materials processing - standstill or progress," Proc. EALA, Bad Nauheim, Germany ().
3. W. M. Zweers, "Process control in industrial applications," Proc. AKL'16, Aachen, Germany ().
WOUTER M. ZWEERS ([ protected]) is technology manager for AWL-Techniek, Harderwijk, Netherlands; www.awl.nl.
Laser welding is not as prevalent as technologies like MIG, TIG and arc welding. That’s mainly because until recently, it required major investments.
Around the year however, fiber laser technology made important advances, drastically bringing down costs. And for the last 18 years, further advances have continued to drive down production costs and the cost of ownership of laser welding machines.
We’ve reached a time where laser welding is not only viable for high-volume production lines, but also for all types of manufacturers. We’re even seeing a rise in handheld devices.
With laser welding being so accessible, now is a good time to explore this proven process that promises precision, speed, and cost effectiveness.
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Laser welding is a precise process that produces very little deformation compared to traditional welding methods. It uses a high-energy laser beam to fuse metals together, creating a strong metallurgical bond. As the energy from the laser beam is absorbed by the surface, the heat causes the surface to melt, forming a molten pool that resolidifies in a few milliseconds.
Think of laser welding like a magnifying glass and the sun. If you focus enough energy on a metal surface, you can melt it—and even vaporize it in some cases.
The power density is very high, resulting in a concentrated heat source of millions of watts per cm2. For a fast laser welding speed or a deep penetration, more laser power is needed. Laser power is the main factor that drives up the cost of a machine.
Laser welding can be used on any material that can melt and resolidify. This means that it is not only used to weld metals like aluminum, copper, and stainless steel, but also other types of materials, including certain types of thermoplastics, glasses, and composites.
The two main types of laser welding processes—conduction welding and keyhole welding—work differently.
Conduction welding is a soft process where the laser beam slowly melts the metal. During this type of welding, the metal’s temperature goes beyond its fusion point and achieves the liquid state but never goes into the gaseous state. Heat transfer within the metal is similar in all directions.
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Conduction welding is slower but generates higher-quality results with little or no spatter and low fumes.
Keyhole welding is a fast but aggressive process that melts and vaporizes the metal, digging deeper into the material. The metal reaches its fusion temperature and even its vaporization temperature in some areas. As a result, part of the melting pool is in the gaseous state and can cause spatter. Heat transfer within the metal is mostly perpendicular to the laser beam.
Keyhole welding is ideal for high-volume production lines because it is faster, but it can lead to porosity and a higher heat affected zone (HAZ).
Laser welding of dissimilar metals is possible, but it is not always easy or feasible. Different metals have different fusion temperatures, absorb a different percentage of light, and conduct heat at different rates.
At Laserax, we have previously laser welded dissimilar metals when we welded cylindrical and prismatic cells to busbars for EV batteries. In those cases, we laser welded aluminum to nickel-plated copper and aluminum to nickel-plated steel.When laser welding dissimilar metals, the two metals do not merge into a homogeneous mixture but rather join at the interface between the two metals. This creates a joint that is not as structurally strong as when welding the same metal.
To address this issue, two strategies are available:
One of the best strategies to diminish spatter is to use what we call adjustable ring modes.
While energy is typically focused in a very small point when laser welding, ring modes offer advanced control on how energy is distributed.
A ring surrounding the laser’s spot can be used to preheat the part. This offers better control over the melt pool and, ultimately, diminishes spatter.
To be able to use different ring modes, a fiber optic cable with an outer core is needed to project an “outer” beam (see image).
The first experiments with laser welding go back to the s—shortly after Ted Maiman built the first laser. But it wasn’t until , after researchers at the Battelle Memorial Institute did a demonstration of laser welding, that manufacturers began to see real potential for industrial applications.
To understand how this process has come to hold such an important place in manufacturing, we need to go back to the invention of the laser itself. Here are key technological advancements that have shaped the development and adoption of laser welding as we know it today.
Laser welding technology continues to evolve on a wide range of aspects, including in terms of laser power, optical components, beam quality, scanning heads, and computer control systems.
Fiber lasers are the most prevalent types of lasers used for welding, but other types of lasers can be used as well, including blue lasers, green lasers, CO2 lasers, Nd:YAG lasers, and diode lasers.
Let’s look at each type of laser to understand how they can be used for welding.
Type of LaserCharacteristicsFiber LaserWhen choosing a type of laser, one of the important factors to consider is its wavelength. Each type of metal absorbs and reflects wavelengths at varying percentages. If a wavelength is absorbed well, less laser power is needed.
The graph below provides an overview of common types of metals and their absorption spectrum for different wavelengths.
Laser welding offers a wide range of advantages compared to other methods like MIG, TIG, and arc welding. Let’s look at the most important ones.
There are not many disadvantages to laser welding, but they are still important to consider and address. Let’s look at them more closely.
Laser safety is a serious issue during welding. The laser beam and its reflection can cause eye injuries, skin burns, and fire hazards. Ideally, the laser is enclosed in a class-1 laser safety enclosure that contains the laser beam and its reflections.
For some applications, this can cause headaches. Large parts and structures such as ships can be difficult to contain in an enclosure. Other solutions than enclosures can be explored to contain the beam (for example, some solutions use clamping tools to block the beam).
Handheld devices can be dangerous for operators who need to wear PPE and follow laser safety control measures.
The initial investment can be pretty high too. Even if their cost keeps going down, lasers are still more expensive to acquire than alternatives. Add to this that most manufacturers are seeking automated solutions, and you’re looking at a serious investment.
This battery laser machine is a fully enclosed solution that overcomes the challenges of welding batteries such as clamping adaptability, quality, and speed. It uses SCARA robots to perform clamping with high speed and precision.
This handheld system is an example of how laser welding products are becoming more accessible to a wider range of manufacturers.
This machine demonstrates the ease of automation of laser welding, featuring remote welding, rotating fixtures, and robot handling of the laser head.
For large parts like car frames, enclosing the welding process can be problematic in terms of space usage and cost. This machine addresses this problem by enclosing the beam and its reflections with a well-designed clamping tool. This provides complete laser safety without the need for an enclosure.
With its precision, speed, and high level of control, laser welding offers amazing possibilities. For manufacturers new to this technology, it’s important to discuss your application with an expert who can help you:
If you have a laser welding application for batteries, contact a Laserax expert to discuss your needs.
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