Laser surface cleaning technology is no longer a novelty, and there are already many applications being used across industries. Very similar to this technology is laser roughening, or laser texturing, of surfaces, which, to a large extent, can even use the same hardware, with only minor changes and modifications. In laser surface treatment, the term texturing is more common, since the beam forms a certain ordered pattern. Airblasting, electroerosion and other "conventional" technologies became the ways to achieve the desired surface roughness recently. With the development of laser surface treatment technology, the technology of laser surface texturing is seeing rapid development as well.In airblasting technology, the desired roughness is achieved by adding abrasive grains to a jet of compressed air, which fly against the surface of the workpiece at a certain speed. The roughness to be achieved is determined by setting the parameters affecting it. In most cases, the roughness is influenced by the following parameters: 1.) compressed air pressure, which determines the speed of the abrasive grain hitting the surface of the workpiece; 2.) properties of the abrasive grain such as size, shape and hardness. In addition to the above, the selection of the right parameters to achieve the desired roughness also depends on the properties of the product to be texturized. Applying the abrasive to the surface of the workpiece requires the use of suitable hardware such as airblasting machines. Modern airblasting machines must allow safe work in an enclosed space with good dust extraction for good visibility, and must also have a device for collecting and recycling abrasives for smooth and productive work. For the operation of the processes in an airblasting machine, compressed air is needed, which today is considered a relatively expensive medium, since the compressors that drive airblasting machines consume a lot of energy. For example, a manual airblasting machine that uses one nozzle with a diameter of D8 mm at a pressure of 6 bar consumes 4 Nm3/min of compressed air. To ensure such a flow, we need a 20–25 kW compressor. In addition to the above, regular equipment maintenance is also important for smooth operation of airblasting machines, which consequently also requires money.
When texturing a surface with laser technology, the roughness is achieved by removing the material from the workpiece with the pulse action of the laser beam, thereby creating a crater and thus generating roughness. For these purposes, pulsed fiber lasers are used, which are the most suitable for this task. Surface roughening with laser technology also requires the setting of certain parameters that achieve different degrees of roughness. The parameters that affect roughness include laser power, PRR (pulse repetition rate), scanner speed, and focal length of the lens. Changing these parameters and the ratio between them has the greatest impact on the roughness. The material and hardness of the workpiece also play an important role, just as in the case of roughening with airblasting technology.
To explain in more detail the significance of the parameters that are important in laser texturing, the power of the laser, PRR and speed have influences on the depth of the profile and the distances between individual craters. When a higher degree of roughness is to be achieved, the same surface can be roughened several times using the same parameters. Precise laser technology allows us to do just that, as the laser beam repeatedly hits the same spot and thereby increases its depth. The result of this is manifested in greater roughness.
The two images below show the difference in the distances between the craters depending on the different values for PRR and scanner speed. The first image shows the distances between craters with a higher PRR and a lower velocity, and the second one with a lower PRR and a higher velocity. It is noticeable that the raw surface changes between individual lines.
The distance between individual crater lines can be changed by adjusting the hatch spacing. This parameter determines the distance between individual lines of craters. For example, if we take a crater diameter of 0.1 mm (which is the size of the spot of the laser beam on the surface) and a hatch spacing of 0.15 mm, it means that there will be 0.05 mm of profile left between the craters, which determines the roughness profile along with the crater depth.
To summarize, with laser technology, it is also possible to perform quality texturing of the surface of workpieces and achieve different degrees of roughness by setting the parameters. Customizable parameter sets offer many possibilities for achieving different levels of roughness and complete control of the process.
The main advantages of laser texturing over airblasting include much more precise processing, no need to mask off other surfaces, the repeatability of the process, no need for an abrasive medium, the possibility of producing different textures in one step, and low operating and maintenance costs.
It is also necessary to mention the limitations of laser texturing or areas where conventional technology should not be replaced by laser technology. Productivity can be much higher with airblasting, depending on what kind of surface one wants to achieve. It is therefore not to be expected that in the near future, laser will replace airblasting in the uniform treatment of larger surfaces.
It is believed that the observed differences will decrease with the development and progress of laser technology, which is commonly seen in development.
For Information: FerroČrtalič d.o.o.
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