STUDY ON REDUCTION OF POLISHING TIME OF METAL MOLD USING LASER IRRADIATION

目前，冷作模具钢SKD11因其优异的耐磨性和耐腐蚀性而被广泛用作金属模具。在模具钢的电火花加工中，金属模具表面会形成一层不同于母材的硬白层，从而引起快速的加热和冷却。根据加工条件的不同，白层表面会出现裂纹和微凹坑。这种热影响区(HAZ)会大大缩短金属模具的寿命。因此，电火花加工后去除这一层是必要的。在目前的情况下，热影响区的去除是通过手工完成的。但这一工艺延长了金属模具的加工时间，提高了金属模具的制造成本，因此，激光熔融表面改性被提出作为一种新的表面改性方法来代替机械去除方法。该方法利用US…熔化和凝固热影响区来释放裂纹和微凹坑等缺陷，并改善表面粗糙度。更多的是用激光束作为热源。在本研究中，激光束被照射在面积为50×50 mm^2的三维金属模具中。表面改性采用1kW连续二氧化碳激光器。为了避免表面氧化，在金属模具上使用了与激光同轴的气体。激光照射到电火花加工表面，激光输出功率800W，进给速度200 mm/min，离焦条件5 mm，台阶宽度1 mm。研究结果表明：(1)电火花加工产生的裂纹、微凹坑等表面缺陷可以通过表面层的熔化得到释放。随后，在辐照后可以得到均匀分布的熔融层。结果表明，新的表面改性方法改善了金属模具的电火花加工表面。(2)金属模具电火花加工表面经激光处理后，表面粗糙度由原来的25μ左右降低到2~5μ。在激光处理表面重叠的情况下，可以观察到表面粗糙度的增加。较少

At present, the cold working die steel, SKD11 is commonly being used as the metal molds due to its superior wear and corrosion resistance. In electrical discharge machining(EDM) of die steel, a hard white layer, that is different from the base metal, is formed on the metal mold surface causing rapid heating and cooling. Cracks and micro-craters appear on the surface of white layer depending machining conditions used. Such heat-affected zones(HAZ) can greatly shorten the life of metal molds. Therefore, the removal of this layer after EDM is necessary. Under the present situation, HAZ is removed by hand finishing. However, this process extends the machining time and raises the price of metal mold manufacturing.Therefore, a laser surface modification with melting has been proposed as a new surface modification method instead of the mechanical removal method. This method releases defects such as cracks and micro-craters and improves surface roughness using melting and solidifying HAZ by us … More ing a laser beam as the heat source. In this study, the laser beam was irradiated in three-dimensional metal mold with a area of 50 x 50mm^2. The surface modification was conducted using a 1kW CW carbon-dioxide laser. Argon gas was used on the metal mold coaxial with the laser beam in order to avoid oxidation of the surface. The laser beam was irradiated onto the electrical discharge machined surface with a laser output power of 800W, a feed speed of200 mm/min, a defocused condition of 5mm and step width of 1mm. As the result, the following conclusions are obtained.(1)Surface defects such as cracks and micro-craters generated by EDM could be released due to melting of surface layer. Subsequently, a melting layer could be obtained which is distributed uniformly after irradiation. It could be therefore shown that the new surface modification method improved the electrical discharge machined surface.(2)The surface roughness of about 25μmRy in the electrical discharge machined surface of metal mold could be decreased to 2〜5μmRy due to the overlapped laser treatment. The increase in surface roughness could be observed in the case of overlapped laser treatment surfaces. Less