The laser cutting machine is to focus the laser emitted from the laser into a high power density laser beam through the optical path system. The laser beam is irradiated on the surface of the workpiece, making the workpiece reach the melting point or boiling point, while the high-pressure gas coaxial with the beam blows the molten or vaporized metal away. With the movement of the relative position of the beam and the workpiece, the material is finally formed into a slit, so as to achieve the purpose of cutting. Laser cutting process replaces the traditional mechanical knife with invisible beam, which has the characteristics of high precision, fast cutting, not limited to cutting pattern, automatic typesetting to save materials, smooth incision, and low processing cost. Learn more about it in the next installment.

First, the principle of laser cutting machine

A laser is a kind of light that, like other natural light, is produced by the transition of atoms (molecules or ions, etc.). But it is different from ordinary light in that laser only relies on spontaneous emission for a very short period of time at first, and the subsequent process is completely determined by stimulated emission, so laser has a very pure color, almost no divergent directionality, and extremely high luminous intensity. and high coherence.

Laser cutting is achieved by applying high power density energy generated by laser focusing. Under the control of the computer, the laser is discharged through pulses, thereby outputting a controlled repetitive high-frequency pulsed laser to form a beam with a certain frequency and a certain pulse width. The pulsed laser beam is transmitted and reflected through the optical path and focused on the On the surface of the processed object, tiny, high-energy-density light spots are formed, and the focal spots are located near the surface to be processed, melting or vaporizing the processed material at an instant high temperature. Each high-energy laser pulse instantly sputters a small hole on the surface of the object. Under the control of the computer, the laser processing head and the material to be processed perform continuous relative motion and dot according to the pre-drawn pattern, so that the object will be processed into desired shape.

The process parameters (cutting speed, laser power, gas pressure, etc.) and movement trajectory during slitting are controlled by the numerical control system, and the slag at the slit is blown off by a certain pressure of auxiliary gas.

Second, the main process of laser cutting machine

1. Vaporization cutting

During the laser vaporization cutting process, the surface temperature of the material rises to the boiling point temperature so fast that it can avoid melting caused by heat conduction, so part of the material vaporizes into steam and disappears, and part of the material is ejected from the bottom of the slit by the auxiliary gas Flow blows away. Very high laser powers are required in this case.

To prevent material vapor from condensing on the kerf wall, the thickness of the material must not greatly exceed the diameter of the laser beam. This process is therefore only suitable for applications where the exclusion of molten material must be avoided. This machining is really only used in very small areas of use for iron-based alloys.

This process cannot be used, such as wood and certain ceramics, which are not in a molten state and therefore less likely to recondense the material's vapors. In addition, these materials typically achieve thicker cuts. In laser gasification cutting, optimal beam focusing depends on material thickness and beam quality. The laser power and the heat of vaporization have only a certain influence on the optimal focus position. In the case of a certain thickness of the plate, the maximum cutting speed is inversely proportional to the gasification temperature of the material. The required laser power density is greater than 108W/cm2 and depends on the material, depth of cut and beam focus position. In the case of a certain thickness of the sheet, assuming sufficient laser power, the maximum cutting speed is limited by the velocity of the gas jet.

2. Melting and cutting

In laser melting cutting, the workpiece is partially melted and then the melted material is ejected by means of an air flow. Because the transfer of the material occurs only in its liquid state, the process is called laser melting cutting.

The laser beam coupled with a high-purity inert cutting gas pushes the molten material out of the kerf without the gas itself cutting. Laser fusion cutting can achieve higher cutting speeds than gaseous cutting. The energy required for gasification is usually higher than the energy required to melt the material. In laser melting cutting, the laser beam is only partially absorbed. The maximum cutting speed increases with increasing laser power and decreases almost inversely with increasing sheet thickness and material melting temperature. In the case of a certain laser power, the limiting factor is the gas pressure at the kerf and the thermal conductivity of the material. Laser fusion cutting can produce oxide-free cuts for iron and titanium. The laser power density that produces melting but not gasification is between 104W/cm2 and 105 W/cm2 for steel materials.

3. Oxidation melting cutting

Fusion cutting generally uses inert gas. If oxygen or other active gas is used instead, the material will be ignited under the irradiation of the laser beam, and a violent chemical reaction with oxygen will generate another heat source to further heat the material, which is called oxidative melting cutting. .

Due to this effect, for the same thickness of structural steel, higher cutting rates can be obtained with this method than fusion cutting. On the other hand, this method may have a poorer cut quality than fusion cutting. In practice it produces wider kerfs, noticeable roughness, increased heat affected zone and poorer edge quality. Laser flame cutting is not good for precision models and sharp corners (risk of burning the sharp corners). Thermal effects can be limited using a pulsed-mode laser, where the power of the laser determines the cutting speed. At a given laser power, the limiting factors are the supply of oxygen and the thermal conductivity of the material.

4. Control fracture cutting

For brittle materials that are easily damaged by heat, high-speed and controllable cutting by laser beam heating is called controlled fracture cutting. The main content of this cutting process is that the laser beam heats a small area of brittle material, causing large thermal gradients and severe mechanical deformation in this area, resulting in the formation of cracks in the material. The laser beam can direct cracks in any desired direction as long as a uniform heating gradient is maintained.