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Laser welding has become a widely used welding process in many manufacturing fields. Handheld laser welding is only accelerating this popularity.  

The technology of laser welding is constantly improving, and the process is becoming more sophisticated. 

So, what are the factors that affect the results of laser welding?

Welding Equipment in use

First factor influencing the laser welding results!

Welding Equipment

The performance of various welding equipment and its stability and reliability directly affect the welding quality. The more complex the equipment structure, the higher the degree of mechanization and automation, the welding quality is more dependent on it.

Therefore, such equipment is required to have better performance and stability. Welding equipment must be inspected and tried before use, and a regular inspection system must be implemented for all kinds of welding equipment in service.

For laser welding machines, the following aspects need to be paid attention to:

  • Laser Types: Laser welding machines use either pulsed lasers or continuous lasers. The appropriate laser type should be selected based on the material being used.
  • Beam Mode: A lower beam mode order indicates better focusing performance (i.e., better beam quality), resulting in a smaller spot size and higher laser power density for the same laser power, leading to a larger welding depth-to-width ratio.
  • Single Mode or Multi Mode laser 
  • Output Power Stability: Better stability in the output power of the laser results in better welding consistency.
  • Optical Transmission and Focusing Systems: These optical components may degrade under the influence of high-power lasers, causing a decrease in transmittance and generating a thermal lens effect (where the lens changes focus due to heating). Surface contamination can increase transmission losses or even damage optical components. Therefore, the quality, maintenance, and monitoring of optical components are crucial to ensuring welding quality.

In addition, the use of welding equipment conditions, such as the requirements of water, electricity, environment, etc., the adjustability of welding equipment, the space required for operation, error adjustment, etc. also need to pay full attention, so as to ensure the normal use of welding equipment.

Welding material - Welding Work-pieces

Second factor influencing the laser welding results!

Welding material - Welding Work-pieces

In order to ensure welding quality, the welding quality of raw materials is very important. In the initial stage of production, that is, before feeding materials, it is necessary to check and control the materials and eventual test-weld on some scrap of the material to weld, this in order to stabilize production and stabilize the quality of welded products.

  • Absorption Rate of Material to be Welded: The compatibility of the laser beam with the material depends on important properties such as absorption rate, reflectivity, thermal conductivity, with absorption rate being the most critical. Some materials have excellent absorption rates for lasers, while others have poor or zero absorption.
  • Uniformity of Material for Welding Workpieces: The uniformity of the material directly affects welding quality. For example, when welding aluminum alloys, uneven distribution of alloy elements or varying impurity content can lead to welding defects such as blowholes, undercutting, and craters. Non-uniform material dimensions, especially thickness and height, can result in poor fit with fixtures, deviations from the focal point, and suboptimal welding quality.
  • Accuracy of Welding Workpiece Assembly: Due to the small size of the laser spot and narrow weld seam, welding typically does not involve adding filler metal. If the assembly has excessive gaps due to poor fit, the laser beam may pass through the gap without melting the base material or cause noticeable undercutting and craters.
  • Cleanliness of the Workpiece to be Welded: Insufficient surface cleanliness with impurities can also lead to poor welding quality.
  • Burr-less and straight edges improve drastically the result. Burrs result in an unstable welding speed at hand laser welding and as result an unstable welding bead.

Welding process parameters include laser output power, welding speed, laser waveform, pulse frequency, defocus amount, and pulse width.

Third factor influencing the laser welding results!

Welding Process Parameters

Welding process parameters include laser output power, welding speed, laser waveform, pulse frequency, defocus amount, and pulse width.

  • Output Power:  The power required for laser #welding depends on the thickness of the material being welded. During laser welding, both excessive and insufficient power output can affect the depth of fusion. Laser welding involves a threshold energy density. Below this value, the melt depth is shallow. Once this value is reached or exceeded, the melt depth increases significantly. Plasma is generated only when the laser power density on the workpiece surface exceeds the threshold (related to the material), indicating the onset of stable deep penetration welding. If the laser power is below this threshold, only surface melting occurs, resulting in stable heat conduction welding. When the laser power density is close to the critical conditions for pore formation, the welding process becomes unstable, leading to significant fluctuation in melt depth. Laser power controls both the melt depth and welding speed during deep penetration welding. The melt depth is directly related to the power density of the incident beam and the focal spot size. In general, higher laser power leads to faster welding speeds, but excessively high power can cause the melt pool to be too deep, resulting in defects such as cracks. Therefore, it is recommended to prioritize determining the effective power range for better parameter adjustment during the tuning process.
  • Output Power Stability: Better stability in the output power of the laser results in better welding consistency. Output Power stability is depending mostly on the quality of the laser.
  • Controlling Heat Input:  Controlling heat input during laser welding is essential to prevent undesirable outcomes such as excessive distortion or damage to the workpiece surface. Various parameters contribute to regulating heat input effectively:
    • Focal length: Adjusting the focal length of the laser source enables precise control over energy concentration.
    • Focus position: Properly positioning the focus point ensures optimal energy delivery at desired locations.
    • Plate thickness: The thickness of the workpiece affects heat dissipation, penetration depth, and the welding process.
    • Spot size: Modifying spot size allows for flexibility in managing power density.
    • Melt depth: Monitoring melt depth is crucial in the laser deep fusion welding process to ensure consistent weld quality. This can be achieved by controlling the welding speed using advanced laser welding machines.
  • welding density: In the same format, the same spot and the same depth, the higher the density of the weld, the faster the corresponding welding speed.
  • Welding Speed: Welding speed affects fusion depth, and the choice between high or low speed depends on the material's thickness and desired welding quality. High-speed welding is suitable for thin sheets or materials with good performance, while low-speed welding may be prone to sagging or uneven weld seams.  Higher welding speeds result in shallower melt depths. A large and wide melt pool is formed at low speeds, making it prone to collapse. When welding at high speed, the intense flow of liquid metal in the center of the weld pool solidifies on both sides of the weld before having a chance to redistribute, resulting in an uneven weld seam. Therefore, Lasermach Laser recommends using high-speed welding for thin plates or materials with good weldability and lower speeds for thick plates and challenging materials.
  • Laser Waveform: Laser waveforms include pulse waveforms commonly used for pulsed lasers and seam welding waveforms for continuous welding. For example, when welding high-reflectivity materials such as copper, aluminum, gold, or silver, a trapezoidal laser waveform can be used to overcome the barrier of high reflectivity. For black metals like iron and nickel with low surface reflectivity, rectangular waves or gradually attenuating waveforms are preferable.
  • Wobble frequency:  Frequency plays a crucial role in determining the appearance and quality of the weld seam. Lower frequencies result in lower overlap rates and coarser weld seam surfaces, while excessively high frequencies can lead to issues like welding slag or penetration. Selecting an appropriate welding frequency is essential to maintain a smooth and clean weld seam.
  • Pulse Frequency: Pulse frequency, beam size, and welding speed must be matched to achieve the desired overlap rate. In general, a larger overlap rate results in a smoother weld, but the welding speed also decreases accordingly. When the laser pulse frequency exceeds a certain value, the overlap rate becomes too high, surpassing the material’s welding limit and leading to penetration or weld spatter.
  • Defocus Amount: Focus, in laser welding, refers to the minimum distance from the material surface to the focused laser beam's smallest spot. It affects the welding quality since altering the focus-to-material surface distance (known as the focal distance) can influence the welding result. This distance can be either positive or negative, each affecting aspects like penetration and spattering.  There are two types of defocusing: positive defocusing and negative defocusing. Positive defocusing places the focal plane above the workpiece, while negative defocusing places it below. With negative defocusing, the internal power density of the material is higher than on the surface, making it prone to stronger melting and vaporization, allowing the light to penetrate deeper into the material. In practical applications, negative defocusing is used when a large melt depth is required, while positive defocusing is suitable for welding thin materials.
  • Pulse Width: This parameter mainly applies to pulse laser welding machines. Pulse width is one of the important parameters of pulse laser welding machines. It distinguishes between material removal and material melting and is a key parameter that determines the cost and volume of processing equipment. A longer pulse width results in a larger weld diameter, and for the same working distance, a deeper melt depth.
  • Width of welding seam:  The width refers to the width of the laser beam formed by the reflection of the laser beam on specific rotating mirrors. Narrow widths provide concentrated high-density laser energy, while wider widths distribute the energy over a larger area. This parameter directly impacts weld seam performance, affecting the depth-to-width ratio and overall quality.

It's important to note that several other factors, such as gas type, material absorption, temperature of work-piece, … etc can also influence the effectiveness of laser welding.  In practice, adjusting the main laser welding parameters to meet specific processing needs and conducting multiple trials can lead to improved #welding results.

Worktable

Fourth factor influencing the laser welding results!

Worktable

The worktable directly influences the welding effect and processing efficiency. If the welding platform is not level or not vertical, the quality of the weld seam will be affected. Additionally, if the welding platform surface contains impurities such as oil and dust, these impurities can mix into the weld seam during the welding process, affecting the density and strength of the weld. In large-scale production, fully automatic laser welding machines often use automatic worktables to improve production efficiency, so the difference in worktables can have a significant impact on welding results.

Welding Fixtures

Fifth factor influencing the laser welding results!

Welding Fixtures

Welding fixtures ensure the precise positioning and secure clamping of welded components, facilitating the installation and welding of components and meeting the process requirements for structural accuracy. Actively promoting and applying fixtures that are compatible with product structures in modern welding production plays a crucial role in enhancing product quality, reducing labor intensity for workers, and accelerating the mechanization and automation of the welding process.

Welding Gas - Protective Gas

Sixth factor influencing the laser welding results!

Protective Gas

Protective gas, or shielding gas, is also one of the important factors affecting welding quality. Protective gas is an inert gas used to protect the molten pool during the laser welding process. Some materials may not require protective gas if surface oxidation is not a concern, but it is generally needed for most applications. 

Choosing appropriate shielding gases in the welding process helps minimize spatter formation and maintain arc stability with laser welding equipment. Handheld laser welding machines can also benefit from the use of shielding gases.

Protective gas serves various purposes, such as expelling or weakening plasma (which is easily generated during laser welding and has effects on laser absorption, refraction, and reflection), increasing the cooling rate of the weld seam, reducing the degree of surface oxidation in the weld seam, and improving the surface appearance of the weld. Commonly employed protective gases include nitrogen, argon, helium, as well as mixtures of argon and helium. 

For more information about shielding gas in laser welding, you can see here.

Additional Considerations

In addition to material selection, heat control, …. ,  several other factors influence laser welding parameters:

  • Filler metal: Depending on the application requirements, filler metals can enhance strength or improve corrosion resistance.
  • joint design: 
  • Machine labor cost:  Optimizing laser welding machine parameters can reduce labor costs by improving efficiency and minimizing rework on the equipment.
  • Surface cleanness
  •  

By considering these key factors, welders can determine the optimal laser welding parameters for each specific application. This ensures high-quality welds with minimal distortion and reliable performance.

The Interplay of Parameters

The Laser welding parameters play a crucial role in the overall laser welding process. Understanding how different parameters interact with each other is essential for achieving optimal results.  During laser welding, various process parameters come into play, affecting the stability, deformation, penetration, power, temperature, and properties of the weld. Let’s delve into some key aspects:

Parameter Combinations

Different parameter combinations yield varying outcomes in specific applications. For example:

  • Higher power settings on a laser welding machine increase weld penetration but may also lead to increased heat input.
  • Adjusting the focal point of a laser welding machine can significantly impact surface quality and allow for precise control of heat distribution.

An increase in laser power might demand a corresponding adjustment in welding speed to maintain the desired weld depth and quality. Similarly, modifying the pulse duration can impact the heat affected zone and require alterations in shielding gas flow rate or type.

  • Consider another example: If the beam diameter is decreased (resulting in a more concentrated focus), the laser’s intensity increases. This may necessitate a reduction in laser power or an increase in welding speed to prevent burn-through or excessive weld width.

Balancing Trade-offs

When selecting parameters, it’s crucial to strike a balance between speed, quality, and cost. This involves considering factors such as:

  • Welding speed: Faster speeds may compromise weld quality.
  • Heat input: High heat input can affect material properties.
  • Surface preparation: Proper cleaning and preparation contribute to better results.

Material Considerations

While machines and lasers function based on set parameters, the materials being welded have their own intrinsic properties, like melting point, reflectivity, and thermal conductivity. These can introduce another layer of variability into the laser welding process. Thus, understanding material responses and adjusting parameters holistically becomes paramount.  Different materials require specific parameter adjustments due to variations in their thermal conductivity and melting points. Factors to consider include:

  • Material surface condition: Surface roughness affects laser absorption.
  • Composite materials: Welding dissimilar materials requires careful parameter selection.

Understanding how these parameters interact enables welders to optimize their laser welding processes for desired outcomes while minimizing defects or issues that may arise during laser welding.

Conclusion

In conclusion, the effectiveness of laser welding is influenced by a big mix of factors, ranging from the characteristics of the welding equipment to the intricacies of the welding process and the quality of the workpieces involved.

Selecting the appropriate laser type, ensuring stability in output power, and maintaining the integrity of optical components are critical considerations in welding equipment. The properties of the materials being welded, such as absorption rate, uniformity, and cleanliness, play a pivotal role in determining the overall welding quality.

Fine-tuning welding process parameters, including output power, welding speed, laser waveform, pulse frequency, defocus amount, and pulse width, is essential for achieving the desired welding results. Moreover, the condition of the worktable, the use of suitable welding fixtures, and the application of protective gas further contribute to the overall success of the laser welding process.

As laser welding technology continues to advance, understanding and optimizing these factors will be key to pushing the boundaries of precision, efficiency, and quality in various manufacturing applications. 

The intricate interplay of these elements underscores the importance of a holistic approach to laser welding, where careful consideration of each factor collectively contributes to the success of the welding process and the quality of the final product.