脉冲光纤激光修整青铜金刚石砂轮相爆炸及磨粒热损伤控制研究

During the process of pulse fiber laser truing and dressing of bronze bond diamond grinding wheel, the existence of a super-hot layer will lead to the occurrence of the phase explosion, and result in the grits fall off in the finishing area, reducing chip space around the diamond, causing an insufficient diamond protrusion height over the bond; moreover the temperature is high in the finishing area and the graphitization is formed on the diamond grits surface, associating with hot cracking. Those phenomenon affect the grinding performance and should be control. Firstly, this project based on the fourier heat conduction equation, considering the evaporation, plasma shielding, dynamic absorption and energy accumulation under the pulse interval etc, and built the three-dimensional dynamic energy complex coupling heat transfer model of pulse fiber laser truing and dressing of bronze bond diamond grinding wheel. Secondly, according to the theory research of phase explosion control, the laser power density accurate range of occurring phase explosion for laser truing and dressing of bronze bond diamond grinding wheel is obtained under the relevant conditions. Then Put forward the method of the single tangential flow of liquid column auxiliary the laser truing and dressing of grinding wheel, its can control phase explosion, avoiding the graphitization and hot cracking of the diamond grits surface and providing theoretical guidance for optimization of process parameters. The research results of this project provide a theoretical basis for the study of heat transfer property of nanosecond pulse laser ablation of metal material, can also have important application value for improving the quality of the metal surface after laser ablation.

脉冲光纤激光修整青铜金刚石砂轮过程中，由于存在液相超热层，导致相爆炸发生，致使修整区域内磨粒易脱落,修整区域周边磨粒容屑空间减少且突出结合剂高度不够；并且修整区域内温度高，金刚石磨粒表面会石墨化，伴随产生热裂纹，从而降低其磨削使用性能，需要对其进行控制。本项目首先以傅里叶传热模型为基础，考虑纳秒脉冲激光修整青铜金刚石砂轮过程中出现的蒸发、等离子体屏蔽、动态吸收以及脉冲能量累积等效应，建立三维动能量复耦合热模型；其次，应用相爆炸控制理论研究，得出相关条件下发生相爆炸的激光功率密度精确范围；最后，提出单切向水柱流辅助激光精修整青铜金刚石砂轮工艺方法，为控制相爆炸发生，避免金刚石磨粒表面石墨化与热裂纹，提升其磨削使用性能，提供理论指导并优化工艺。本项目的研究成果可为激光烧蚀金属材料传热属性的研究提供理论依据，也可改善激光烧蚀后金属材料的表面质量，具有重要的应用价值。

脉冲光纤激光修整青铜金刚石砂轮过程中，由于存在液相超热层，导致相爆炸发生，致使修整区域内磨粒易脱落,修整区域周边磨粒容屑空间减少且突出结合剂高度不够；并且修整区域内温度高，金刚石磨粒表面会石墨化，伴随产生热裂纹，从而降低其磨削使用性能，需要对其进行控制。本项目首先以傅里叶传热模型为基础，考虑纳秒脉冲激光修整青铜金刚石砂轮过程中出现的蒸发、等离子体屏蔽、动态吸收以及脉冲能量累积等效应，建立动能量复耦合热模型；其次，应用相爆炸控制理论研究，得出相关条件下发生相爆炸的激光功率密度精确范围；通过数值仿真与实验研究新发现烧蚀青铜的飞溅主要由相爆炸效应引起，与等离子体膨胀压力无关；约在25 ns后，距离材料表面约0.05 mm，达到等离子体最高浓度，相关条件发现，激光功率密度值在18.37×107 W/cm2-20.99×107 W/cm2范围时，激光修锐后青铜轮表面质量高，可抑制相爆炸效应发生。激光功率为小于25W时，只能对青铜金刚石砂轮进行修锐；激光功率大于25W小于30W时，可以实现修锐和整形合二为一；激光功率大于30W时，可以实现大深度修锐并会严重影响金刚石磨粒突出结合剂的高度和磨削性能，实际中应该避免出现这种现象。脉冲光纤激光修整金刚石数值分析表明相关条件下，随激光功率密度的增加从1.68×108 W/cm2-3.36×108 W/cm2时，修整后的金刚石温度逐渐增高，超过金刚石石墨化温度，此时金刚石将石墨化转变形成变质层，并且激光功率密度越大，达到石墨化温度所需的时间越短。最后，提出单切向水柱流辅助激光修整青铜金刚石砂轮工艺方法、双切向水柱流并联吹气辅助激光精修整工艺与带有气液并联管式的砂轮双激光精修整工艺，为控制相爆炸发生，避免金刚石磨粒表面石墨化与热裂纹，提升其磨削使用性能，提供理论指导并优化工艺。本项目的研究成果可为激光烧蚀金属材料传热属性的研究提供理论依据，也可改善激光烧蚀后金属材料的表面质量，具有重要的应用价值。