Laser Welding

Understanding the Impact of Defocus Amount in Laser Welding Processes

Understanding The Impact Of Defocus Amount In Laser Welding Processes | Laserchina

In the realm of advanced manufacturing, laser welding stands out for its precision and efficiency. A critical parameter that significantly influences the quality of welds in laser welding is the defocus amount. This article, curated by LASERCHINA engineers, delves into how the defocus amount affects the welding process, especially concerning the energy distribution and its implications on materials like stainless steel and aluminum alloys. Let’s explore the nuances of defocus in laser welding and how it can be optimized for better outcomes.

The Role of Defocus Amount in Energy Distribution

The defocus amount in laser welding is pivotal in determining the energy distribution across the weld. In a standard laser energy distribution, the focus is symmetrically distributed around the focal point, where the laser spot is smallest and the unit energy at its peak. As the defocus amount increases, the laser energy disperses, enlarging the laser spot. LASERCHINA engineers emphasize that the defocus amount is crucial for materials with high reflectivity surfaces, such as stainless steel and aluminum alloys. Excessive defocus can lower the unit energy too much, hindering the rapid melting of the material’s surface and potentially causing laser energy to reflect back, damaging the welding head lenses and fiber ends.

Understanding The Impact Of Defocus Amount In Laser Welding Processes | Laserchina

Positive vs. Negative Defocus

In the context of laser welding, defocus can be categorized into positive defocus, where the focal point is above the workpiece, and negative defocus, with the focal point inside the workpiece, below the welding surface. Generally, a specific defocus amount range is maintained to accommodate workpieces with large gaps, preventing laser leakage through the weld seam. Positive defocus is often preferred over focal point alignment and negative defocus because it prevents the laser energy from concentrating too intensely within the melt pool, which could lead to welding spatter, rough weld surfaces, and unevenness.

The Relationship Between Defocus Amount and Melt Depth and Width

The defocus amount directly influences the melt depth and width in laser welding, a relationship that LASERCHINA engineers highlight for optimizing welding processes. Typically, the same defocus amount results in a greater melt depth with negative defocus compared to positive defocus due to the focal point’s position inside the workpiece, allowing for greater energy absorption. As defocus amount increases, the melt depth gradually decreases, while the melt width initially increases before decreasing.


The defocus amount is a critical parameter in laser welding processes, significantly affecting energy distribution, weld quality, and material adaptability. By understanding and strategically adjusting the defocus amount, manufacturers can enhance the precision and efficiency of their laser welding operations. LASERCHINA engineers continue to pioneer in optimizing laser welding techniques, including the judicious application of defocus, to meet the evolving demands of advanced manufacturing. Whether working with reflective materials or aiming for specific weld dimensions, the insights provided here serve as a foundation for achieving superior welding outcomes with laser welding machines.


With over two decades of laser expertise and a comprehensive product range encompassing individual components to complete machines, LASERCHINA is your ultimate partner for addressing all your laser-related requirements.

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