Laser welding, drilling, heat treatment and cutting

laser cutting

Laser cutting is to use a laser beam to focus to form a high-power density spot to illuminate the workpiece. The material absorbs light energy and the temperature rises sharply. The material is quickly heated to melting or vaporization temperature, and then blown with jet gas to separate the material. In this process, when the laser irradiates the surface of the workpiece, part of the light is absorbed by the workpiece, and the other part of the light is reflected by the workpiece. The absorption part is converted into heat energy, which causes the surface temperature of the workpiece to rise sharply, and the material melts or vaporizes. At the same time, it produces a black hole effect, which improves the material's absorption rate of light, and rapidly heats to melt or vaporize the material in the cutting area. At this time, oxygen blowing can support combustion and provide a lot of heat energy to increase the cutting speed. Continuous output laser should be used for cutting. Features: The laser can cut extremely hard, extremely brittle and extremely soft materials, and difficult-to-process materials with high melting points; the width of the slit is very narrow; the cutting surface is smooth and clean; the heat-affected layer of the cutting surface is shallow, and the surface stress is small; the cutting speed is fast, and the heat-affected zone Small; no mechanical deformation, no tool wear, easy to realize automated production

Laser welding

Laser welding is to focus the laser into a very thin beam of high energy density and irradiate the workpiece to heat and melt the workpiece, and then cool the workpiece to be welded. Laser welding has large penetration depth, high speed and high efficiency; laser welding has a narrow burn area, small heat-affected zone, and small deformation of the workpiece. At the same time, the welding seam is small, which can realize precise welding; the welding structure is uniform and the product size is small , There are few pores, few inclusion defects, and it is better than conventional welding methods in mechanical properties, corrosion resistance and electromagnetic properties.

Laser heat treatment

Laser heat treatment is a method of surface treatment of metals using high-power density laser beams. Ru Dang Pa Jin

When the surface is heated to the critical transformation temperature only lower than the melting point, its surface is rapidly austenitized, and then rapidly self-cooled and quenched, and the metal surface is rapidly strengthened, that is, laser transformation hardening (laser quenching). Laser surface heat treatment technology includes laser phase change hardening technology, laser coating technology, laser alloying technology, laser shock strengthening technology, etc. These technologies play an important role in changing the mechanical properties, heat resistance and corrosion resistance of materials.

(1) Drilling

Early laser drilling used the fixed-point impact method: that is, the pulsed laser beam was used to process the hole continuously at one position until the hole passed. This processing method limits the depth and diameter of the processed hole.

After the high repetition rate YAG laser entered the practical stage, the rotary cutting drilling method (Trepanning) appeared, that is, using a special optical rotating head or a numerical control to automatically generate a circular trajectory for laser nesting processing. This not only eliminates the limitation of the hole diameter, but also because of the auxiliary blowing, the processing area is semi-open, and the molten material is easy to discharge, so the hole surface quality is good.

For parts with a large number of small holes of the same specification, especially the revolving body, the current drilling on the fly method has been developed. That is, after a laser pulses a hole position, the workpiece is used regardless of whether the hole is opened or not. The light pulse gap is quickly moved (moved or rotated) to the next hole position, and the same position is impacted multiple times in multiple cycles until the processing of all holes is completed. The advantage is that the time of the laser pulse gap is used as the displacement of the part hole, which can greatly increase the processing speed. The drilling speed is currently 10 holes per second, and is expected to reach 500 holes per second (sub-millimeter hole diameter). The key to the technology is that the laser arrives, and the workpiece must be moved in place, which is very difficult for non-uniform holes. Controlled by a CNC closed-loop control system, when the hole processing rate is higher, in order to ensure the round hole shape, the laser beam must move synchronously with the part during the laser action time. Laser flight drilling has been used in the processing of aviation parts, and the cooling hole processing of the annular combustion chamber is a typical application example. In addition, the airflow is easily separated from the surface of the wing of the high-speed aircraft wing and engine inlet, resulting in increased turbulence and loss of aerodynamic force. For this reason, a laminar flow wing (nacelle) with suction function is designed. The surface of the sleeve is made of 1mm thick titanium alloy plate, with 12 million to 1 billion cone holes distributed on it, the outer surface diameter is 0.06mm, the inner surface diameter is 0.1mm, the hole spacing is 0.3~1mm, laminar flow wing The small holes of the sleeve are also completed by flying punching method.

For the sieve with a micron-level aperture, fast scanning processing with excimer laser or Q-switched YAG laser (thousands of holes per second can be processed) can obtain satisfactory results.

(2) Cutting

Laser cutting is still dominated by CO 2 lasers in the near future. With the increase of device power, the cutting depth and speed have been greatly improved. In order to improve the processing quality, high-pressure air blowing (pressure up to 1.6-2.0MPa) is used, and a CO 2 laser with a power of 3.4kW can cut aluminum plates with a thickness of 5-6mm. The cut is smooth, and there is no slag left on the front and back. It is worth mentioning that the use of two laser composite cutting materials can achieve lower energy consumption. Figure 1 is a schematic diagram of an experimental device for two kinds of laser composite cutting. Experiments show that the combined cutting of CO (270W) laser and KrF (30W) laser can increase the speed by 30% and increase the cutting thickness by more than 40% compared with a single CO (300W) laser cutting carbon steel.