Laser welding is a highly precise and efficient welding technology used across various industries including automotive, aerospace, and medical manufacturing.
It offers deep penetration, high welding speeds, and minimal thermal distortion, making it an ideal choice for applications requiring accuracy, speed and repeatability.
However, achieving high-quality welds with a laser welding machine requires careful control of key parameter settings. Even small variations can lead to defects, reducing the strength and reliability of the weld.
This guide will explore the critical laser welding parameters, their impact on weld quality, and best practices to optimize performance.
Table of Contents
Laser welding technology is a fusion process that uses a concentrated laser beam to join materials.
The process can be performed in two ways:
Unlike conventional welding techniques, laser technology requires precise control over multiple factors. Even slight deviations in setup, material properties, or environmental conditions can lead to poor weld quality. Some of the most common challenges include:
When adjusting parameters, you must also understand the different welding methods used and how they impact your settings.
Continuous wave welding provides a steady and uninterrupted laser beam, making it ideal for applications requiring deep penetration and high-speed production. This method is particularly effective for welding thicker materials where consistent energy input is needed to achieve uniform results.
On the other hand, pulsed welding delivers energy in short bursts, which helps minimize heat input. This technique is commonly used for thin materials or applications where heat-sensitive components must be protected from excessive thermal distortion.
High doses can create significant heat, which can cause distortion. Pulsing on and off for microseconds allows the right amount of heat application to avoid negatively impacting the metal, making it ideal for delicate assemblies.
Pulsed laser welding is preferred (in most cases) for applications that require very precise heat input control, such as welding dissimilar metals, thin materials, or components with complex geometries. It's also commonly used for spot welding and tack welding.
Another variation, modulated CW lasers, allows for dynamic power adjustments during welding. By fine-tuning the laser output in real-time, you can optimize energy delivery for different materials and material thickness, improving overall weld quality while minimizing defects.
The quality of the weld is directly related to the process parameters you choose. It’s easy to make mistakes or allow controls to drift without maintaining tight tolerances.
One of the most fundamental aspects of laser welding is ensuring that the workpieces are securely held in place. Proper fixturing eliminates movement during the welding process, ensuring that the laser energy is directed precisely where it is needed. Misalignment or gaps between materials can lead to weak welds, excessive porosity, and even complete failure of the joint.
Lasers are ineffective at welding across air gaps, as they require direct contact between materials to form a strong bond. A widely accepted rule in laser welding states that the gap between 2 components in a lap weld configuration should not exceed 10% to 20% of the thickness of the thinner material being welded. Exceeding this threshold increases the likelihood of incomplete fusion, which results in structurally unsound welds.
Excessive gaps can produce:
The exact tolerance can vary depending on the specific material and applications, but in many applications, the assembly gap must be controlled to less than 0.1mm to ensure proper fusion.
To overcome issues related to fixturing and gaps, manufacturers rely on precision-machined parts from a cutting machine and carefully designed holding fixtures. Additionally, performing pre-weld inspections helps identify and correct potential fit-up issues before welding begins, reducing the risk of defects in the final product.
Shielding gas plays an essential role in maintaining weld quality by preventing oxidation and managing plasma formation.
When laser energy interacts with the metal surface, it can generate a cloud of ionized gas known as plasma. This plasma can interact with the incoming laser beam and act as a negative lens defocusing the beam. This can lead to inconsistent penetration and reduced weld strength. To counteract these effects, manufacturers use shielding gases such as argon or nitrogen.
Argon is the most commonly used gas due to its stability and resistance to ionization, while nitrogen can be used in certain applications where it benefits the metallurgical properties of the weld. Proper shielding gas flow ensures that the weld remains clean and free from oxidation, which is especially important when welding reactive metals such as titanium or aluminum.
Optimizing gas flow requires careful nozzle positioning and appropriate flow rates. Too little shielding gas can allow atmospheric contamination, while excessive gas flow can create turbulence, introducing oxygen leading to defects into the weld. The balance must be carefully maintained to ensure high-quality results.
The size of the laser beam’s focal spot significantly impacts the energy density delivered to the material. A smaller spot size provides a higher intensity, leading to deeper penetration and greater precision. However, small spot sizes require highly accurate positioning which may not be appropriate for some geometries (e.g., butt weld with large gap between components).
Conversely, a larger spot size distributes energy over a wider area, making it useful for applications that require more even heat distribution, such as surface welding or joining materials with different thermal properties. The aspect ratio — the relationship between the spot diameter and weld depth— plays a crucial role in determining the effectiveness of the weld. Generally, a deeper depth of penetration requires higher aspect ratios.
Focal position adjustments can also be used to control weld quality. Most welding applications position the laser focal point at the material surface (focus zero). However, in certain cases, adjusting the focus slightly above or below the surface can help mitigate issues like spatter formation or porosity. While you don’t want molten metal splashing around, this process can slightly change the shape of the weld in the material. These adjustments fine-tune the interaction between the laser and material, improving overall weld consistency and quality.
Wobbling is an advanced technique that enhances the effectiveness of laser welding by oscillating the laser beam in a controlled pattern. Instead of a fixed beam path, the laser moves in a defined path, increasing the effective weld width and improving fusion between materials.
Circular patterns are common. Circular wobble patterns can bridge gaps between parts and widen welds. Figure-eight patterns improve penetration and reduce porosity in some specific cases.
This method is particularly useful when dealing with parts that have small gaps or varying thicknesses. Wobbling allows you to go wider, using a smaller spot whilevarying the path. This can bring more molten metal into the area of the weld to provide a better joint.
The wobble frequency determines the speed at which the laser beam oscillates, while the amplitude controls the width of the wobble pattern. Higher frequencies can improve weld mixing and reduce porosity, while larger amplitudes can increase weld width and penetration. The relationship between wobble speed and travel speed must also be considered to prevent issues such as undercutting. Note that commercial scanning optics also have frequency limits so it is important to understand its limitations to ensure best results and extended lifetime of your equipment.
Different beam motion control techniques further optimize weld quality. Fixed optic heads direct the laser at a stationary position, while galvo scanner heads use rapid mirror movement to dynamically adjust beam placement. Hybrid systems combine fixed optics with controlled beam movement to create simple 1-D or 2D weld patterns. For example, moving in a sine-wave pattern can overlap the beam and allow you to move faster while filling in gaps.
When the beam goes through the focusing lens, the motion of the mirrors is automatically adjusted based on the patterns you draw in the software for the plan of focus. You can set speed and superimpose wobbling if you desire.
The weldability of a material is significantly impacted by its properties. You need to tailor your laser welding parameters to specific materials.
The presence and concentration of specific alloying elements profoundly affect weldability. For example, in carbon steel, high carbon content (>0.3%) can lead to the formation of martensite during rapid cooling, resulting in a hard, brittle weld susceptible to cracking. Similarly, sulfur and phosphorus can promote hot cracking.
On the other hand, elements like manganese can improve weldability by scavenging sulfur and promoting a more ductile microstructure. In aluminum alloys, magnesium and silicon content influence the alloy's response to heat treatment and its susceptibility to solidification cracking.
Surface contaminants such as oxides, scale, paint, or oil interfere with laser beam absorption and weld penetration. Oxide layers, particularly on aluminum and stainless steel, can significantly increase weld defects and benefit from pre-weld cleaning for best results.
The type of coating can drastically change the absorption rate of the material. For example, a coated steel will absorb energy at a greater rate than a non-coated steel.
Laser welding involves rapid heating and cooling cycles that can induce phase transformations in the material's microstructure. These transformations can affect the weld's mechanical properties, such as hardness, strength, and ductility.
For example, in steel, austenite can transform into martensite, bainite, or pearlite, depending on the cooling rate. Controlling the cooling rate through techniques like preheating or post-weld heat treatment is essential for achieving the desired microstructure and properties. Some lasers such as core/ring fiber lasers can provide pre/post heat treatment benefits.
Here are some of the issues we see, along with best practices to minimize them.
One of the most common issues in laser welding is the formation of crater cracks at the end of a weld. This occurs when the laser power is abruptly terminated, causing a rapid shrinkage of the molten pool, which can lead to cracking. These defects compromise the structural integrity of the weld and are especially prevalent in steel welding but also seen frequently in some aluminum alloys.
To mitigate crater cracks, a common approach is to implement a controlled ramp-down of the laser power density at the end of the weld. This gradual reduction in energy allows the molten pool to solidify evenly while controlling the temperature gradient across the weld, reducing stress and the likelihood of cracking. Post-weld heat treatment can also be added to relieve residual stresses and enhance weld durability.
Spatter is another undesirable effect in laser welding, where molten metal droplets are ejected from the weld pool. This issue typically arises due to excessive power input, improper shielding gas flow, or misalignment of the laser beam — producing burn-through and spatter formation, where molten metal droplets are ejected. Spatter affects weld aesthetics and can lead to defects such as porosity and weak joints.
There are many approaches to reducing spatter. Adjusting the laser focus position can help control the energy density at the weld site, thereby reducing spatter formation. Optimizing shielding gas type, flow rate, and delivery method are also important. For example, using argon as a shielding gas can minimize plasma interference and improve weld quality and consistency.
Proper fixturing is just as important to ensure the parts fit-up does not create any gaps in the weld zone as the latter typically cause a collapse of the keyhole which is often accompanied with ejection of molten metal from the weld.
Porosity in laser welding is primarily caused by trapping gas within the molten metal. This issue can result from contamination, inadequate shielding gas coverage, or rapid solidification that traps gases inside the weld.
Pre-cleaning materials before welding remove contaminants that contribute to gas entrapment. Using an appropriate shielding gas, such as argon, minimizes oxidation and helps produce defect-free welds. Adjusting welding speed and power can also prevent overheating to help reduce the likelihood of porosity.
Not all materials weld easily. For example, welding certain steel alloys might introduce cracks or unstable states, causing them to become more brittle. Materials might crack during the cooling period or under stress after welding.
This issue is common in some areas of automotive manufacturing, such as welding trunk parts or rooflines.
Brazing can help by adding additional material into the melt pool that slightly alters the elemental properties of the molten pool to reduce cracking. The filler material creates a more stable joint.
Highly reflective materials, such as aluminum and copper, present unique challenges in laser welding. These materials reflect over 85% of incident laser energy, making it difficult to initiate and maintain a stable weld. High thermal conductivity results in rapid heat dissipation, requiring precise energy management.
Steel retains heat. However, with copper or aluminum, the heat runs away. If you hit it with less-than-optimal intensity, nothing happens. You have to have high intensity for reflective materials to melt at a rate that adds more than escapes. Otherwise, it can just resolidify.
Fiber laser welding with wavelengths in the 1070-1080 nm range is commonly used in the industry to weld these materials. Using a smaller spot size and high power helps to increase initial energy coupling, allowing for more efficient melting. High-intensity laser pulses can also help overcome reflectivity challenges by ensuring a rapid temperature increase at the surface, facilitating better energy absorption.
Back-reflected light from highly reflective materials can also damage the laser and/or delivery components, leading to system failures and inconsistent weld quality. Depending on the condition of your lens cover and the quality of your glass, it can absorb light and slightly deform the optics which leads in turn to thermal lensing. Thermal lensing can impact the focusability of the laser beam by moving the focus of the laser above the part. This leads to a reduction in power density and loss of penetration into the material.
Protective coatings on optics, such as anti-reflective and high-durability coatings, help to minimize damage. High grade glass designed for the wavelength and power level of your laser system is also key in preventing laser absorption into the optcs. Implementing back-reflection sensors and beam dumps can further protect the laser system by detecting and redirecting stray light away from sensitive components. Regular inspections are also necessary to ensure consistent delivery.
During production runs, ensuring consistent quality is crucial. Every weld needs to hold up under stress and perform under the tolerances you need.
Ensuring Weld Consistency
To maintain high-quality welds, in-process monitoring systems are used to track key parameters such as plasma emissions and surface temperature. These sensors provide real-time feedback, allowing welders to make necessary adjustments to maintain process stability.
Cross-sectional analysis and CT scanning can detect internal defects and verify weld penetration depth. In the case of CT scanners, the inspection can be done without destroying the part. Furthermore, other Non-Destructive Testing (NDT) methods offer valuable insights without compromising the integrity of the welded parts. For example:
The choice of NDT method depends on the specific application, material, and the type of defects being investigated.
Dialing in your parameters and welding recipe upfront is the key to consistency. This allows you to evaluate the welds, make adjustments as necessary, and ensure your receipt is dialed in before major production runs.
Today’s laser welding systems incorporate automation, data logging, and analysis capabilities. By continuously recording key welding parameters, such as laser power, welding speed, shielding gas flow, and temperature, you can establish a comprehensive database of process data.
Statistical analysis of this data can reveal trends, identify potential issues, and optimize welding parameters for improved consistency and quality.
Implementing statistical process control (SPC) charts can help monitor process stability and detect deviations from baselines to identify degradation or anomalies that require further investigation and proactive interventions.
The data can also be used for traceability, allowing you to track the welding history of individual components and ensure accountability.
Routine laser maintenance is critical to ensuring long-term laser stability and weld quality.
Checking and replacing protective cover slides or optics prevents contamination that can lead to power fluctuations and thermal lensing.
Measuring laser power output daily helps detect gradual degradation, allowing for corrective actions before it impacts weld performance. High-quality lasers typically exhibit minimal power drift, but regular calibration ensures consistency in production environments.
Achieving optimal laser welding results requires more than just setting the right parameters. It demands a holistic approach that includes rigorous preparation, real-time monitoring, and ongoing refinement. Ultimately, the key lies in continuous learning and adaptation.
Every material, application, and environment presents unique challenges, requiring operators to understand the key principles of each aspect and manage parameters appropriately.
By embracing a mindset of precision, experimentation, and proactive problem-solving, you can optimize your laser welding processes and achieve consistent, superior results.
Jean-Philippe (JP) Lavoie, Senior Director of Laser Process Innovation, graduated from Laval University with a Ph.D in Physics Engineering. JP brings over 20 years of experience in the laser industry working with a broad range of laser technologies. JP joined Laserax after spending 15 years at Coherent Corp. as North America Applications Labs Manager.
The integrity of a weld is highly dependent on surface preparation. Aluminum has a natural tendency to form oxide and even a thin layer can lead to weld defects. Oxide and potential contamination from oils, lubricants, paints, and particulate matter can create bubbles of air trapped inside the materials, impacting the bonding process.
Laser beam welding (LBW) is a precise and efficient method used to join materials through the use of a laser beam. It is known for its accuracy, speed, and ability to work on small, delicate components, making it ideal for industries like electronics, batteries, automotive, and aerospace.
Laser welding is a technology that has applications in a wide variety of industries. It is chosen for its ability to generate high-quality welds at high speed. It is also chosen for precision welds that do no cause damage to delicate components.
