1. Causes and initial distribution of stress
During the process of carbon steel cold bending laser cutting, the generation of stress mainly comes from the uneven local heating and cooling of the material. During laser cutting, the laser beam is focused on the surface of carbon steel, causing the material to melt and vaporize rapidly. The temperature of this area rises sharply, while the temperature of the surrounding materials is relatively low. Due to the difference in thermal expansion and contraction, the heated area produces a large thermal expansion, which is constrained by the surrounding cold materials, thus forming thermal stress inside. At the beginning of cutting, the stress is mainly concentrated near the laser action point, showing an uneven distribution centered on the cutting line.
For example, for thicker carbon steel materials, at the beginning of laser cutting, the stress value at the cutting front can quickly reach 50%-70% of the material yield strength. This initial stress distribution lays the foundation for subsequent deformation and stress evolution.
2. Stress evolution during cutting
With the advancement of laser cutting, the stress distribution continues to change. On the one hand, the heat conduction during the cutting process causes the heat to gradually diffuse to the surrounding area, and the stress originally concentrated at the cutting front also expands outward. On the other hand, new melting and vaporization areas continue to generate new stresses, which are superimposed and influenced by existing stresses. When cutting a straight line segment, the stress is distributed in a certain gradient along the cutting direction. The stress is larger near the cutting line and gradually decreases away from the cutting line. When cutting corners or curved parts, the stress distribution becomes more complicated due to the change in cutting direction.
For example, when cutting a 90-degree corner, the material inside the corner is pulled by the different cutting directions on both sides, and the stress concentration phenomenon is significantly aggravated, which is easy to cause local deformation or even cracking. The stress value here may be 2-3 times higher than that when cutting a straight line.
3. The correlation between deformation law and stress
The deformation law after carbon steel cold bending laser cutting is closely related to the stress distribution. When the internal stress exceeds the yield strength of the material, the material will undergo plastic deformation. When cutting thin carbon steel, if the stress is unevenly distributed in the width direction of the plate, it may cause the plate to bend and deform.
For example, if the stress on one side of the cutting line is greater than the other side, the plate will bend to the side with greater stress. For carbon steel products with cold bending shape requirements, such as bending into a U-shaped or V-shaped structure, uneven stress may also affect the accuracy of the bending angle. During the bending process, the residual stress originally generated by cutting will be redistributed and interact with the bending stress. If handled improperly, the product after bending may rebound, that is, the bending angle cannot meet the design requirements, and the amount of rebound is directly related to the size and distribution of the residual stress during the cutting process.
IV. Measures to control stress and deformation
In order to control the stress and deformation during the carbon steel cold bending laser cutting process, a variety of measures can be taken. In terms of laser cutting parameters, optimize parameters such as laser power, cutting speed and spot diameter to make the heat input more uniform and reduce the generation of thermal stress.
For example, appropriately reducing the laser power and increasing the cutting speed can reduce the thermal impact while ensuring the cutting quality. In terms of process sequence, pre-deformation treatment can be performed first to offset part of the deformation trend caused by cutting. In addition, the use of appropriate cooling methods, such as simultaneous gas cooling or water cooling during the cutting process, can accelerate the cooling process of the material and make the stress distribution more uniform. For products that have already deformed, they can be corrected through subsequent shaping processes, but this requires precise control of the shaping force to avoid introducing new stress problems. By comprehensively applying these measures, the quality and precision of carbon steel cold bending laser cutting products can be effectively improved.
