激光冲击成形对表面光洁度的影响

Effect of laser shock forming on surface roughness of targets

为了研究激光冲击成形对板料表面光洁度的影响,采用0.5mm厚铝板和304不锈钢板料作为试样,选择光斑直径8mm、波长1054nm、脉冲宽度23ns的激光脉冲进行冲击成形实验,铝板冲击成形的激光能量为15.4 J,304不锈钢的激光能量为18.92 J。冲击成形后对板料表面光洁度进行检测,结果表明,激光冲击成形可使板料表面光洁度提高接近两个精度等级。通过理论分析可知,板料背面光洁度的提高有两个方面的原因,一方面由于应力波在板料背面的微尖峰中传播时产生一系列的反射波,当反射波强度超过材料抗拉强度极限时将引起微尖峰的断裂;另一方面由于板料的高速运动在板料背面的空气中形成高压区,当作用在板料表面的空气压力大于动态屈服强度时微尖峰发生塑性变形,因微尖峰断裂和塑性变形使板料背面光洁度提高。

In order to study the effects of laser shock forming on the surface roughness, metal sheet of aluminum and 304 stainless steel of 0.5mm thickness are used as samples of laser shock forming, and laser beams with radius of 0.4mm, wavelength of 1054nm and pulse width of 23ns was applied in laser shock forming, while the energy for aluminum sheet was 15.4J and for 304 stainless steel was 18.92J. The measurement results after laser shock forming show that laser shock forming may improve the surface roughness to two roughness rank. There are two reasons for surface roughness improvement. On the one hand, it will generate a series of trasmission wasves and reflection waves when the stress wave spreads in tiny peak of sheet surface, and the tiny peak would rupture if the strength of reflection tensile wave is beyond the tensile strength of targets. On the other hand, a high pressure zone is formed in the air because of high speed motion of sheet, and plastic deformation of tiny peak would take place if the pressure of air acted on the back of sheet is greater than the dynamic bend intensity. So the altitude of tiny peak is decreased by the rupture and plastic deformation of tiny peak and it results in improvement of the surface roughness.