Laser cutting is the use of high-power-density laser beams to focus on and illuminate the workpiece, so that the irradiated material quickly melts, vaporizes, ablates or reaches the ignition point. At the same time, the molten material is blown away by means of a high-speed air flow coaxial with the beam, so that the workpiece can be cut. Laser cutting is one of the thermal cutting methods.

Classification

Laser cutting can be divided into four categories: laser vaporization cutting, laser melting cutting, laser oxygen cutting, and laser scribing and controlled fracture.

1) Laser vaporization cutting

The high-energy-density laser beam is used to heat the workpiece,leading to a rapid increase in temperature and reaching the boiling point of the material in a very short period of time. The material begins to vaporize and form vapor. The ejection speed of these vapors is very fast. While the vapors are ejected, incisions are formed on the material. The heat of vaporization of materials is generally very large, so the laser vaporization cutting method requires a lot of power and a high power density.

Laser vaporization cutting is mostly used for cutting extremely thin metals and non-metallic materials (such as paper, cloth, wood, plastic, rubber, etc.).

2) Laser melting cutting

In laser melting cutting, the metal is melted by heating with laser beams. Then the non-oxidizing gas (Ar, He, N, etc.) is sprayed through a nozzle coaxial with the beam which makes use of the strong pressure of the gas to discharge the liquid metal to form an incision. Laser melting cutting does not need to completely vaporize the metal, and the energy required is only 1/10 of laser vaporization cutting.

Laser melting cutting is mainly used for cutting the materials or active metals that are not easy to oxidize, such as stainless steel, titanium, aluminum and their alloys.

3) Laser oxygen cutting

The principle of laser oxygen cutting is similar to that of oxygen acetylene cutting. It uses a laser beam as the preheating heat source and an active gas such as oxygen as the cutting gas. On the one hand, the ejected gas acts with the metal cut, oxidizes, and releases a lot of oxidizing heat; on the other hand, the molten oxide and molten materials are blown out of the reaction zone, forming an incision in the metal. Since the oxidation reaction in the cutting process is exothermic, the energy required for laser oxygen cutting is only 1/2 of that for laser melting cutting. Apart from that, the cutting speed is much greater than that of laser vaporization cutting and laser melting cutting. Laser oxygen cutting is mainly used for easily oxidized metal materials such as carbon steel, titanium steel, and heat-treated steel.

4) Laser scribing and fracture control

Laser scribing uses a high-energy-density laser to scan the surface of brittle materials, so that the materials are heated up and evaporates to form a small groove. After that a certain pressure is applied, and the brittle materials will crack along the small groove. The lasers used for laser scribing are generally Q-switched lasers and CO2 lasers.

Fracture control is based on the steep temperature distribution generated by laser grooving which generates local thermal stress in the brittle material, causing the material to be disconnected along small groove.

Features

Compared with other thermal cutting methods, laser cutting is generally characterized by its fast cutting speed and high quality. The specific aspects can be summarized as follows.

(1) Good cutting quality

Due to its small laser spot, high energy density and fast cutting speed, laser cutting can obtain better cutting quality.

①The laser cutting incision is narrow and the two sides of the incision are parallel and perpendicular to the surface, with the accuracy in the dimension of the cuts can be limited to ±0.05mm.

②The cutting surface is smooth and beautiful, with a surface roughness of only tens of microns. Laser cutting can be used as the last process in production. There is no need for machining and the parts can be used directly.

③ After the material is laser cut, the width of the heat-affected zone is very small. The performance of the material near the seam is almost unaffected, and the workpiece deformation is small. With a high cutting accuracy, the geometry of the seam is good and the cross-sectional shape of the seam presents a more regular rectangle. The comparison of laser cutting, oxygen acetylene cutting and plasma cutting methods is shown in Table 1. The material cut is 6.2mm thick low-carbon steel plate.

(2) High cutting efficiency

Due to the transmission characteristics of lasers, laser cutting machines are generally equipped with multiple CNC workstations, and the entire cutting process can be fully CNC controlled. During operation, operators only need to change the CNC program, which can be applied to the cutting of parts of different shapes. Both two-dimensional cutting and three-dimensional cutting can be realized.

(3) Fast cutting speed

Using lasers with a power of 1200W to cut low-carbon steel plates of 2mm thick can reach a cutting speed up to 600cm/min; to cut polypropylene resin plates of 5mm thick can reach a cutting speed up to 1200cm/min. The material does not need to be clamped and fixed when laser cutting, which not only saves tooling and fixtures, but also saves auxiliary time for loading and unloading.

(4) Non-contact cutting

During laser cutting, since the torch has no contact with the workpiece, there is no tool wear. For machining parts of different shapes, there is no need to replace the “tool”. Only changing the output parameters of the laser is sufficient. The laser cutting process has low noise, low vibration and no pollution.

(5) There are many types of cutting materials

Compared with oxygen-acetylene cutting and plasma cutting, there are many types of materials that can be laser-cut, including metals, non-metals, metal-based and non-metal-based composite materials, leather, wood and fiber. However, for different materials, due to their different thermophysical properties and absorption rates of lasers, they show different adaptability to laser cutting.