The laser-treated surface makes the workpiece more load-resistant. Laser quenching, melting and coating make the workpiece more resistant to load: increased hardness and toughness, altered surface texture, pressure build-up on the surface or protective coating. Laser marking and laser micromachining can also change the surface of the workpiece.
[laser quenching]
Principle of laser quenching: The laser beam heats the surface layer of the metal and rapidly cools it to increase its hardness. The advantage of laser quenching technology is that it requires very little subsequent processing and can process irregular three-dimensional workpieces. Due to the small amount of heat input, the deformation of the workpiece is small, reducing or even eliminating the need for subsequent processing.
Laser quenching is a surface layer hardening process. Can only be used on iron-based materials that can be hardened. That is, steel and cast iron with a carbon content of more than 0.2%.
In order to harden the workpiece, the laser beam in most cases heats the metal surface layer to near the melting point, i.e., about 900 to 1400 °C. When the surface reaches the desired temperature, the laser beam leaves this position and continues to advance, continuing to heat the surface of the workpiece in the new direction. Under the action of high temperature, the carbon atoms in the metal lattice change their position (austenization). Once the laser beam leaves a location, the material around the location cools the hot surface layer very quickly. This phenomenon is called "self-quenching." Due to rapid cooling, the metal lattice does not return to its original shape, but instead produces martensite. Martensite is a very hard metal structure. Conversion to martensite increases the hardness of the material.
The laser beam heats the surface layer of the workpiece. Typical surface hardening depths range from 0.1 to 1.5 mm, and some materials reach 2.5 mm or higher. If the depth of surface hardening is to be greater, the surrounding volume must be larger so that heat can be quickly led out so that the hardened zone can be cooled quickly enough. The laser quenching process requires relatively little power density. At the same time, the workpiece should be machined on the same plane. Therefore, the laser beam can be irradiated onto the largest possible plane. Currently used is a square illuminated surface. Similarly, the scanning mirror set is also used in the laser quenching process to cause the laser beam of a circular spot to move back and forth very quickly. A line of substantially uniform power density is formed on the surface of the workpiece. A hardened trajectory with a width of up to 60 mm can be generated. The bearing portion of the shaft close to the turbocharger as shown above has been laser-quenched.
[laser cladding]
In order to improve the wear resistance of the material or to modify the surface, a laser surfacing process is employed. With the laser cladding system, the surface of the existing workpiece can be coated with a metal coating, the quality is the same as casting. No mass loss, seals, no porosity and cracks.
The laser cladding system makes the laser surfacing process very simple: using a laser to create a molten pool on the surface to be treated. The powdered material is sprayed onto the surface through the nozzle, and when the new material solidifies, the next layer of welding is started, or subsequent processing is performed.
A typical laser cladding system consists of three main functional units: a powder conveyor, a powder conveyor line, and a processing mirror set with a powder nozzle. The powder conveyor is a movable unit that sits next to the laser processing machine. The powder gas mixture from several vessels is mixed in a powder conveyor into a powder stream that is introduced into the powder nozzle at a precisely set flow rate. The integrated sensor system ensures high quality coatings at all times.