Introduction to laser drilling technology

Laser drilling is a laser processing technology that uses a pulsed heat source with high power density and a short stay (lower than laser cutting) for drilling. The formation of the aperture can be achieved by a single pulse or multiple pulses. Compared with traditional drilling technologies such as mechanical drilling, electrochemistry and electric spark discharge, laser drilling is a more economical drilling technology when processing shallow holes. Although the laser heat source based on the cutting design can also be used for drilling, it is more effective to use the laser heat source based on the drilling design. At the same time, this high-power, repeatable pulsed laser can realize laser cutting by processing a series of closely connected small holes. Generally speaking, the diameter of laser drilling is generally between 0.075 and 1.5 mm. (0.003～0.060 inches).

The small holes prepared by the laser are clean and accompanied by a small amount of recast layer, which means that the molten metal may adhere to the inner wall of the small holes during the drilling process. When a larger aperture is required, laser beam drilling technology in cutting mode is needed to obtain the required aperture. In the punching process, first use the punching mode to prepare small holes of sufficient size, so that the subsequent cutting process starts from here. The drilling or penetration process requires a repetitive pulsed laser beam with high peak power and high air pressure. After the workpiece penetrates, the laser beam reduces the peak power or even transforms into a pulseless mode to achieve cutting.

The solid-state laser has a short wavelength and can achieve high-intensity pulse output, so it is more suitable for laser drilling, such as Nd:YAG laser, Nd:glass laser and Nd:ruby laser. In engineering applications, Nd:YAG lasers are often used for laser drilling of metal materials (as shown in Figure 1). CO2 lasers are commonly used to open holes in non-metallic materials, such as ceramics, composites, plastics or rubber.

Laser drilling of metal materials requires a pulsed laser, and the beam focus power density must be above 10^5 W/mm^2 (6.5 W/in.^2 × 10^7 W/in.^2). During the cutting process, the focused beam hits the surface of the material, the material is melted and volatilized, and the molten and vaporized metal will be ejected, thereby forming a hole in the workpiece. Generally speaking, the depth of the laser opening is generally 6 times the aperture. For laser drilling of thick-walled parts, multiple pulses may be required to achieve complete penetration of the material. The laser drilling technology can reach up to 25mm thick material drilling.

Focusing of the laser beam

In the laser drilling mode, it is necessary to use a short focal length lens to focus the high peak power beam of the pulsed laser onto a spot of the order of 0.6 mm in diameter to achieve the power density level required for drilling.

The low divergence of the laser beam can be achieved by a specific laser resonator. During the drilling process, the laser beam with low divergence changes the reflection and propagation of the beam during work, thereby improving the quality and depth of the drilling. The beam diameter can be controlled by changing the aperture of the focusing device. Therefore, the aperture can be used to increase the energy density of the focused beam and increase the intensity distribution of the beam. These principles have certain reference significance for the application of laser drilling.

        Figure 1: Using Nd:YAG laser to open lubricating holes on the piston rod of the engine

Advantages of laser drilling technology

Laser drilling has most of the advantages of laser cutting. When the required hole diameter is less than 0.5 mm (0.020 inch), laser drilling is particularly advantageous, and when opening a hole in an area that cannot be accessed by conventional tools, the laser beam can be achieved by only forming a certain angle between the beam and the surface of the material. Intake and punching can effectively avoid the occurrence of crushing incidents caused by structural interference during mechanical processing.

The advantages of other laser drilling are as follows:

Short hole opening time

Strong automation adaptability

Can be used for penetration processing of difficult-to-open materials

Compared with mechanical drilling, there is no mechanical abrasion between the workpiece and the workpiece during the drilling process