Definition of laser quenching
Laser quenching is the use of a laser to heat the surface of a material above the phase transition point.
As the material cools itself, the austenite transforms into martensite, which hardens the surface of the material.
It has the unique advantages of small deformation of the workpiece, clean working environment, no need for finishing after grinding, and the size of the treated gear is not limited by the size of the heat treatment equipment.
1) Quality advantage
Laser quenching has a high power density, a fast cooling rate, and does not require a cooling medium such as water or oil.
It is a clean and fast quenching process.
Compared with induction quenching, flame quenching and carburizing quenching, the laser quenching hardened layer is uniform, the hardness is high (generally 1-3HRC higher than induction quenching), the workpiece deformation is small, the heating layer depth and heating trajectory are easy to control, and it is easy to automate.
It is not necessary to design corresponding induction coils according to different part sizes like induction quenching.
The processing of large parts does not need to be limited by the size of the furnace during chemical heat treatment such as carburizing and quenching.
Therefore, traditional processes such as induction hardening and chemical heat treatment are gradually being replaced in many industrial fields.
Especially important is that the deformation of the workpiece before and after laser quenching is almost negligible.
Therefore, it is especially suitable for surface treatment of parts with high precision requirements.
- Technical features
The depth of the laser hardened layer depends on the composition, size and shape of the part and the laser process parameters.
Generally in the range of 0.3~2.0mm.
The tooth surface of large gears and the journal of large shaft parts are quenched, the surface roughness is basically unchanged, and the need of subsequent machining can meet the requirements of actual working conditions.
Laser fused quenching technology is a process in which the surface of the substrate is heated to a melting temperature by using a laser beam, and the surface of the molten layer is rapidly cooled and solidified by the heat conduction cooling inside the substrate.
The obtained fused and quenched structure is very dense, and the microstructure in the depth direction is a melt-solidified layer, a phase change hardened layer, a heat affected zone, and a substrate.
The laser fused layer has a deeper depth of hardening than the laser quenched layer, higher hardness, and better wear resistance.
The shortcoming of this technology is that the roughness of the surface of the workpiece is damaged to a certain extent, and generally requires subsequent machining to recover.
In order to reduce the roughness of the surface of the parts after laser fusing treatment and reduce the subsequent processing amount, the special laser fused quenching coating can greatly reduce the surface roughness of the fused layer.
Now the laser melting treatment of the metallurgical industry of various materials such as rolls, guides and other workpieces. Its surface roughness is close to the level of laser quenching.
- Applicable material
Laser quenching has been successfully applied to the surface strengthening of consumable parts in the metallurgical industry, machinery industry and petrochemical industry.
In particular, in terms of improving the service life of wearing parts such as rolls, guides, gears, and cutting edges, the effect is remarkable, and great economic and social benefits have been achieved.
In recent years, it has become more and more widely used in the surface strengthening of parts such as molds and gears.
Laser quenching history and development
As early as 1980, the Applied Technology Laboratory of the US Military Technology Research Laboratory reported on the results of the laser hardening investigation of gears, and the laser hardening research project of gears was undertaken by the Illinois Institute of Technology in Chicago.
The company’s Altegott collaborated with Patel of the Bell Aircraft Manufacturing Company to publish a paper entitled “Spindle Gear Laser Surface Hardening MM&T”, which published the results of the experiment:
Comparison of the anti-gluing life of the AMS (American Aerospace Materials Specification) 6265 spur gear and the flexural strength of the gear after laser surface hardening treatment shows that the laser hardening replaces the AMS6265 gear energy of the carburizing treatment in the aerospace device will get significant economic results.
The effective hardening depth is 0.66~0.86mm, and the cost per piece is reduced by 37%~78%.
At the end of the 1980s, James F Lewis of the California Institute of Mechanical and Electrical Engineering used a 5 kW laser to laser quench a large spline shaft. At a scanning speed of 4.32 to 7.62 mm/s and a spot diameter of 6.35 to 7.62 mm, the quenching hardness HRC59 and a hardened layer with a depth of 0.762 ~ 0.864mm were obtained.
The US Military Research Institute uses laser-quenched heavy-duty large gears such as submarines and airplanes to solve the problem of excessive gear deformation and noise caused by conventional heat treatment.
The laser-hardened gears include the planetary gears of the AH-64 helicopter auxiliary power unit and the transmission gears of the main drive of the aircraft.
Since laser grinding does not require grinding, it can greatly reduce production costs and increase productivity.
Laser quenching characteristics
- The quenched parts are not deformed, and the thermal cycle of laser quenching is fast
- Almost no damage to surface roughness, thin coating with oxidation protection
- Laser quenching without cracking, precise quantitative CNC quenching
- Quenching of local, groove, accurate numerical control quenching
- Laser quenching is clean and efficient, eliminating the need for cooling media such as water or oil
- The quenching hardness is higher than the conventional method, and the quenched layer has fine structure and good toughness.
- Laser quenching is rapid heating, self-excited cooling, no need for furnace insulation and coolant quenching. It is a pollution-free green heat treatment process, which can easily perform uniform quenching on large mold surfaces.
- Due to the fast heating speed of the laser, the heat affected zone is small, and the surface scanning is heated and quenched, that is, the local heating and quenching, so the deformed mold is small.
- Due to the small divergence angle of the laser beam and good directivity, the surface of the mold can be accurately quenched by the light guiding system.
- The depth of the hardened layer of the laser surface hardening is generally 0.3 to 1.5 mm.
Laser quenching equipment
1) The laser
Currently, the equipment used for laser quenching is mainly a cross-flow CO2 laser.
The working gas of the laser rapidly flows through the discharge region in a direction perpendicular to the optical axis to maintain a lower gas temperature in the cavity, thereby ensuring high power output.
The beam mode is a multimode output.
The selection of lasers should consider the following aspects:
- The laser outputs good beam quality, including mode and mode stability.
- Laser output power stability.
- The laser should have high reliability and should be able to meet continuous operation in industrial processing environments.
- The laser itself should have good maintenance, fault diagnosis and chain function;
- The operation is simple and convenient.
- The economic and technical capabilities and credibility of equipment vendors.
- Whether the source of the wearing parts of the equipment is protected and whether the supply channels are unblocked.
2) The machine tool
The basic dimensions of laser machining machines are: 5.5 m long and Φ 2.6 m in diameter.
Special workpieces with a wider range of sizes.
The laser processing machine is a double cantilever machining system that can perform multi-station laser processing.