Although milling and planing are used in traditional machining of V-grooves, tool wear and passivation affect the machining efficiency and quality. Laser subtractive forming technology exhibits the characteristics of no tool wear, high processing efficiency, and flexible forming, and uses a high-power laser beam as a heat source to realize non-contact processing. Nevertheless, there are some limitations in traditional laser subtractive forming technology. For example, laser drilling and laser ablation technologies generally use a pulsed laser, whose aperture size is of a micron level. As a result, the processing efficiency is considerably reduced when the processing amount is large. Furthermore, it is difficult for traditional laser subtractive forming technology to process millimeter-deep V-grooves at one time. In this paper, a new method of laser subtractive forming of V-grooves is proposed. The Lorentz force is generated inside the molten pool by applying an electromagnetic composite field to drive the melt discharge and achieve the purpose of V-groove machining. Based on a certain machining accuracy, this method can process V-grooves with different angles and depths. Moreover, this method can avoid the problem of tool wear in traditional machining, and its material removal efficiency is much higher compared to traditional laser material removal technology. Therefore, this technology is expected to become a new high-efficiency and high-quality material subtractive forming method.
316L stainless steel is employed as the substrate in the present study. First, a 2 kW semiconductor laser is used to irradiate the surface of the substrate, and the Lorentz force formed by the steady electric and magnetic fields drives the melt to overflow upwards. Simultaneously, a gas nozzle is applied at the tail of the molten pool to separate the metal melt from the substrate. The spatters are collected by a device to ensure that the V-groove forming is safe for operation environment. Second, the three-dimensional profile of the V-groove is captured by VHX-5000 three-dimensional microscope and the groove's wall surface is analyzed by VK-X 1000 shape-measuring instrument to calculate the roughness of processed area. Furthermore, the influence of the magnetic induction intensity on the thickness of the remelting layer in the processed area is analyzed. The influence of laser parameters and electromagnetic field parameters on the morphology of the V-groove is evaluated. Finally, the flow behavior of the molten pool is observed using a high-speed camera, and the mechanism of the Lorentz force in the machining of the V-groove is discussed.
A high-quality and efficient V-groove processing method is established through comparative experiments (Fig. 2), which verifies the feasibility of the new laser subtractive forming technology. Owing to the increase in the Lorentz force, the melt is accelerated to overflow upward, resulting in an increase in the depth of the V-groove and decrease in the remelted layer thickness (Fig. 5, Fig. 6). Owing to the change in the heat input, a V-groove with an angle of 34.82-65.20° and depth of 1719-5667 μm is prepared (Fig. 8). It is found that the material removal efficiency increases with an increase in the laser power, and the material removal efficiency is 67.58 mm3/s at a laser power of 2000 W (Fig. 9). The target V-groove is processed, and according to the national standard, the angle tolerance level is precision f and the depth linear tolerance level is medium m (Fig. 10). The videos captured by the high-speed camera show that the applied Lorentz force causes the melt to overflow (Fig.12), and the material removal efficiency is significantly increased.
In V-groove forming with electromagnetic composite field, the Lorentz force drives the melt to flow upward under different laser heat inputs, a V-groove with an angle of 34.82°-65.20° and a depth of 1719-5667 μm is obtained on the basis of ensuring a certain machining accuracy. The increase in the Lorentz force further promotes the overflow of the molten pool, and the metal melt adhering to the side wall is reduced; the thickness of the remelting layer at the bottom of the V-groove is 42 μm. Based on the video captured by the high-speed camera, the material removal efficiency is found to increase significantly when the electromagnetic composite field is applied, and the center forms obvious pits and grooves. Moreover, the material removal efficiency is mainly related to the laser power and reaches 67.58 mm3/s at laser power of 2000 W. A molten pool is formed by irradiating the substrate with a laser heat source. When an electromagnetic compound field is applied, the Lorentz force causes the melt to overcome the surface tension and gravity, flow upward, and eventually escape from the substrate with multiple spatters, completing the processing of the V-groove in the area to be processed.
