Briefly describe the laser treatment of the surface of the car body cover mold

The laser surface hardening process is one of the effective ways to solve the defect of bumper drawing die bonding buildup. Compared with conventional flame quenching, laser treatment can further improve the surface hardness of the mold and enhance the surface anti-bonding ability.

Laser surface strengthening technology is currently mainly applied in two ways: one is laser quenching and hardening of the mold surface, and the other is laser welding repair of local damaged parts on the mold surface. This technology is suitable for most automobile drawing dies, both for newly-made dies and for in-service dies. The mold materials include all kinds of gray cast iron, chromium-molybdenum alloy cast iron and air-cooled steel. It also has a significant improvement effect on repeated repair welding or flame quenching molds.

1. Principle of laser processing

Laser phase change hardening is a high-energy (104～105W/cm2) beam that scans the workpiece quickly, so that the irradiated metal surface rises extremely quickly to higher than the phase change point and lower than the melting temperature (the heating rate can be Up to 105～106℃/s). When the laser beam leaves the irradiated part, due to the effect of heat conduction, the cold substrate quickly cools it and performs self-cooling quenching (cooling rate can reach 105℃/s), and then realizes the surface transformation hardening of the workpiece. This process is completed under rapid heating and rapid cooling, so the hardened layer structure with ultra-fine grain size is obtained. The microstructure is very fine lath martensite and twin martensite, and the hardness is significantly higher than conventional Heat treatment hardness. 2. Laser phase transformation hardened structure (Guide: The main problems that occur during the processing of high-strength fastener products)

The microstructure after laser transformation hardening is obviously refined, it is very fine dislocation martensite and twin martensite structure, lath martensite dislocation density is very high, and contains more retained austenite Body. With the grain refinement, the number of grain boundaries increases, fatigue crack growth is hindered, while the grain refinement, the carbide is dispersed and distributed, so that the degree of uneven slippage under alternating stress is reduced, and the generation of fatigue crack cores is delayed. ; While the retained austenite located between the martensite laths is a ductile phase. When the propagating crack meets the ductile phase, the propagation is hindered, which delays the nucleation and propagation rate of the crack; and the laser transformation hardens the surface It can generate hundreds of megapascals of residual compressive stress and improve the fatigue strength of the material. Therefore, laser phase transformation hardening can effectively solve the problems of mold wear failure, fatigue failure, and local plastic deformation, and extend the service life of the mold.

The advantage of laser surface strengthening of the mold is not only to improve the performance of the working surface of the mold, but also to keep the performance of the matrix material unchanged. More importantly, the hardness of the hardened layer is uniform and the layer is deep; the mechanical performance parameters of the strengthened part can be controlled more accurately, and it is easier to implement for some parts that are difficult to handle with traditional processes.

3. Laser processing mold usage

The mold surface treatment process has achieved very significant results. Then we processed the truck side outer panel, door inner panel mold, commercial vehicle side wall, front wall and back door outer panel molds in phases and batches.

Laser processing technology can also be applied to molds that have been debugged and finalized without any surface treatment. For example, the imported German BMW new five-series car side panel, door inner panel, trunk cover and hair cover outer panel and other molds. German molds have a feature that they are put into small batch production without any heat treatment on the surface of the delivered mold. The surface of the drawing die for large-scale covering parts is flame-quenched, and the temperature field effect is large, and it is easy to produce local uplift and deformation of the profile. It is not suitable for car molds.

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