Analysis of working principle of gear mold laser phase transformation strengthening technology

Gear mold laser surface strengthening technology refers to the treatment of gear or mold surface with high energy density laser beam and coating or cladding material in the numerical control environment, changing the surface structure or composition to achieve surface phase transformation strengthening or reinforcement. Repaired technology.

Laser phase change strengthened metal materials, the so-called laser phase change enhancement, is to use a laser beam to scan the workpiece, so that the surface of the workpiece quickly rises above the critical point of Ac3. When the spot is removed, the temperature is caused by the heat conduction of the workpiece substrate. When entering the martensite or bainite region, martensite transformation or bainite transformation occurs, and the phase transformation strengthening process is completed.

The phase change strengthening process has the advantages of good surface quality, and the hardness and the depth of the strengthening layer can be controlled according to different materials, heat capacity of the workpiece, and laser processing parameters. The technical factors affecting the strengthening effect in the traditional heat treatment process have changed greatly in the role of laser phase transformation strengthening.

1. Dispersion strengthening and distortion enhancement: The laser phase transformation strengthens the austenite, and when the laser irradiation is stopped, the martensite transformation occurs on the metal surface. Austenite formed in this process environment, whether it is the surface layer or the inner layer, has no chance of growing austenite grains. The diffused austenite grains form a diffuse martensite phase or bainite phase, which gives the structure a lattice strengthening and a dispersion strengthening effect. Moreover, the martensite lattice formed under chilling conditions has a higher defect density than conventional quenching. At the same time, the retained austenite also obtains a very high dislocation density, which makes the metal material have a distortion strengthening effect and the strength is greatly improved.

2. No oxidative decarburization and quenching: In the traditional heat treatment, if there is no protective measure in the heating process, the oxidation and decarburization will occur, which will reduce the hardness, wear resistance, service performance and service life of the workpiece. The light absorbing coating used in laser phase transformation enhancement has the property of protecting the surface of the workpiece from oxidation.

3. Laser-enhanced anti-fatigue mechanism: One of the reasons that affect the fatigue resistance of metal materials is the initiation time of fatigue cracks. Wear and fatigue are promoted in the process of material damage. Wear groove marks can become the starting point of fatigue cracks, accelerate the initiation of fatigue cracks, and after the fatigue crack on the surface of the material, the surface roughness is seriously deteriorated and the wear will be intensified. The laser strengthening layer has strong resistance to plastic deformation and anti-adhesive wear.

4. Equal working layer: The cooling direction of the conventional heat treatment is from the surface to the inside. The surface cooling rate is the fastest, and the cooling rate is gradually decreased from the surface to the inside. Therefore, the gradient distribution from the surface and the hardness value is obtained.

Although the heating direction of laser phase transformation strengthening is the same, the surface temperature is high, and the heating time is relatively long, up to 0.2-0.25 s, while the inner layer austenitizing is completed in the daytime, making the surface austenite It has a higher carbon concentration and a stronger solid solution strengthening effect. The direction of laser quenching and cooling is opposite to that of conventional heat treatment. It is from the inside and the inside. The inner layer temperature is low, but the cooling rate is the fastest. Although the outer layer temperature is high, it has the advantage of solid solution strengthening, but the cooling rate is the slowest, although the inner layer carbon The concentration is slightly lower, but the distortion enhancement and dispersion strengthening are more intense. This results in an almost constant distribution of hardness values ​​within the hardened layer.

The strong working layer such as laser reinforced parts avoids the phenomenon that the wear rate of the conventional heat-treated parts accelerates once the surface wears. Gear laser phase change strengthening technology:

1. Material problem: Medium carbon steel should be used for laser gears, and low carbon steel should not be used. If low carbon steel is used, the base of the gear will have no strength guarantee and reduce the bending fatigue strength.

2. Original state: The optimal original state of the laser gear is the quenching and tempering state, and the specific operation can be combined with the stress relief heat treatment after the gear blank is forged. Forging billet normalizing and high temperature tempering to obtain the desired quenching and tempering state of the laser gear is a low-cost road.

3. Scanning mode: The scanning mode of laser gear mainly includes circumferential continuous scanning and axial tooth scanning.

4. Gear laser-enhanced pretreatment technology: A suitable pretreatment agent is one of the keys to ensure laser beam strengthening treatment, and it has always been a difficult problem in laser processing. Reasonable applicable pretreatment agent and treatment process can prevent the quenching crack on the gear surface, reduce the surface burning sensitivity, ensure the tooth surface precision after laser treatment, and increase the thickness of the hardened layer.

5. No lap joint technology and defocus difference problem: Due to gear working conditions, the hard surface layer of the gear is required to be distributed along the tooth profile, and the shape of the gear is special. In addition, the round face of the gear joint cannot be overlapped by the quenching belt, so it needs special Broadband focusing system. In addition, since the irradiation of the tooth surface by the laser beam cannot ensure the same defocus amount in different parts of the tooth surface, the selection of the focus position is a key link to ensure the reasonable distribution of the tooth surface hardness.

6. Performance of laser gear: The performance of laser gear is mainly three aspects: fatigue performance. If the laser gear and the tempered gear are not found to have broken teeth, it proves that it has high bending fatigue resistance and wear resistance. performance.

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