Laser Welding Head Collimator: Differences Between 100 mm and 150 mm Focal Lengths

        The collimator is a crucial component of a laser welding head. What is the focal length of the collimator? How does the collimating focal length affect the actual production process? Let's explore this further.

        Different Focal Lengths

        The collimators with 100 mm and 150 mm focal lengths exhibit significant differences in their collimation effects on laser beams. The 100 mm collimator, having a shorter focal length, allows the laser beam to be collimated over a shorter distance. For instance, when a diverging laser beam emitted from an optical fiber passes through a 100 mm focal length collimator, the point at which the beam becomes parallel is relatively close to the collimator. In contrast, with a 150 mm focal length collimator, the longer focal length necessitates that the laser beam travels a greater distance before it becomes parallel.

         This is similar to using two magnifying glasses with different focal lengths to concentrate sunlight. The magnifying glass with a shorter focal length, positioned closer to the ground, can effectively focus the light. In contrast, the magnifying glass with a longer focal length must be placed further away from the ground to achieve the same convergence effect. The inverse process of convergence in this context is analogous to collimation.

        Different Working Distances

        Working distance refers to the optimal distance range from the welding head, where the collimator is located, to the surface of the workpiece. For a collimator with a focal length of 100 mm, the corresponding working distance is generally shorter than that of a collimator with a focal length of 150 mm. In practical laser welding operations, the 100 mm collimator may be more suitable for scenarios with limited space or when close-range welding is necessary. Conversely, the 150 mm collimator is more advantageous in situations that require larger working distances, such as welding large workpieces or when it is essential to maintain a specific distance between the welding head and the workpiece surface to prevent damage to the welded joint, such as spatter.

        Beam diameter control varies.

        The collimator with varying focal lengths exerts different effects on the diameter of the laser beam. Under identical laser input conditions (such as consistent laser power and initial divergence angle), a collimator with a focal length of 150 mm typically produces a larger beam diameter after collimation compared to a collimator with a focal length of 100 mm. This occurs because, during the collimation process, a collimator with a longer focal length has a longer light propagation path, resulting in a greater degree of beam expansion.

        For instance, if the divergence angle of the initial laser beam is assigned a specific value, the principles of geometric optics indicate that the diameter of the beam after passing through a 150 mm focal length collimator will be closer to the theoretically larger value calculated from the divergence angle and focal length than the diameter of the beam after passing through a 100 mm focal length collimator. This distinction is crucial for controlling spot size according to various welding process requirements. For example, a larger spot size may be necessary for extensive preheating, while a smaller spot size is preferable for precision welding. This can be achieved by selecting collimators with different focal lengths.

        The influence on the distribution of laser energy varies.

        Due to their varying effects on beam diameter and working distance, 100mm and 150mm focal length collimators will also influence laser energy distribution differently. The 150mm focal length collimator, with its larger beam diameter after collimation, may result in a relatively more dispersed laser energy distribution. In contrast, the 100mm focal length collimator produces a smaller beam diameter after collimation, leading to a more concentrated energy distribution.

        In the welding process, the distribution of laser energy significantly impacts the quality of the weld. For instance, when welding thin materials, a small-diameter beam with concentrated energy is often preferred, making a 100 mm focal length collimator more suitable. Conversely, for welding thick materials or when a larger area of material needs to be melted, a relatively dispersed energy distribution—potentially achieved with a 150 mm focal length collimator—can be more beneficial for effective welding.