【作者】 郭海涛；

【导师】 韩雪松； 王利峰；

【作者基本信息】 天津大学 ， 机械工程， 2018， 硕士

【摘要】 KDP晶体是上世纪四十年代随着大功率激光器的发明和发展而逐步被广泛应用起来的一种具有优良性能的非线性光学材料,由于其在光学应用领域具备巨大的发展前景,使其成为了各国争相投入巨大人力物力的一个研究热点。但是KDP晶体质地软、脆性高、易潮解、材料各向异性、对温度变化敏感等物理属性使其在单点金刚石切削加工过程中非常容易产生凹坑和裂纹等表面缺陷,进而导致KDP晶体零件易在表面缺陷处出发生激光损伤现象,严重影响激光器的使用寿命,因此针对KDP晶体单点金刚石切削表面质量分析与工艺参数优化研究具有十分重要的意义。为了提高KDP晶体单点金刚石切削表面质量,本文首先从KDP晶体的微观结构出发,明确KDP晶体的基本组成单元和理想构型,推导出常用晶面各晶向弹性模量和剪切模量各向异性分布情况,为之后探索材料最优加工晶向与材料力学特性分布规律之间的内在联系奠定理论基础。其次,通过ABAQUS有限元软件对KDP晶体切削仿真模型中的物理模型,特别是材料各向异性属性建立及赋予方法作出了详细介绍,并针对KDP晶体加工过程,分别建立了直角切削模型、端面切削模型和飞刀切削模型。通过以上有限元模型探索刀具几何角度和切削工艺参数对切屑形成过程、切削力以及最终创成表面质量的影响。最后,通过采用正交试验方法进行KDP晶体超精密切削实验设计,然后对实验结果进行相关分析,探究随机性背后隐藏的数学统计规律,建立影响因素对单点金刚石切削KDP晶体加工表面粗糙度值和质量优劣分布的预测模型。并通过设计专用夹具装置实现在通用单点金刚石车床中模拟飞刀断续切削加工方式,实现KDP晶体在某一确定晶面近似沿着某一确定晶向切削加工过程,通过实验数据分析得出材料加工获得最高表面质量的最优加工晶向。通过有限元仿真和工艺实验研究表明:在单点金刚石切削中采用负前角切削虽然存在切削力大、排屑困难等缺点,但其有利于脆性KDP晶体的塑性加工能力增强。通过工艺实验优化端面车削KDP晶体加工工艺参数,其最优组合为主轴转速1000 r/min、进给速度5 r/min、切削深度2μm、刀具前角-25°,此时获得表面粗糙度为5.0 nm。通过飞刀切削实验、端面车削实验和KDP晶体材料力学各向异性综合对比研究表明,切削KDP晶体沿着弹性模量较小、剪切模量较大方向可以获得更高的表面加工质量。更多还原

【Abstract】 KDP crystal is a kind of non-linear optical material with excellent properties,which has been widely used with the invention and development of high power lasers in the 1940 s.Because of its great development prospects in the field of optical application,it has become a research hotspot that countries are competing to invest tremendous human and material resources.However,the physical properties of KDP crystal,such as soft texture,high brittleness,easy deliquescence,material anisotropy and sensitivity to temperature change,make it very easy to produce surface defects such as pits and cracks during single point diamond cutting.As a result,KDP crystal parts are easily damaged by laser at surface defects,which seriously affects the service life of the laser.Therefore,it is of great significance to study the surface quality analysis and process parameters optimization of KDP single point diamond cutting.In order to improve the surface quality of single point diamond cutting of KDP crystal,the basic unit and ideal configuration of KDP crystal are defined from the microscopic structure of KDP crystal,and the anisotropic distribution of anisotropic elastic modulus and shear modulus of common crystal plane are deduced.It lays a theoretical foundation for exploring the internal relationship between the optimal processing orientation of materials and the distribution law of mechanical properties of materials.Secondly,through ABAQUS finite element software,the physical model of KDP crystal cutting simulation model,especially the method of establishing and assigning anisotropic properties of materials,is introduced in detail.Aiming at the KDP crystal processing process,the right angle cutting model,the end cutting model and the flying cutter cutting model are established respectively.Through the above finite element model,the effects of tool geometry angle and cutting parameters on chip formation process,cutting force and final surface quality are explored.Finally,through the orthogonal test method,the experimental design of ultra-precision cutting of KDP crystal is carried out,and then the experimental results are correlated and analyzed to explore the mathematical statistical law hidden behind the randomness,and the prediction model of the influence factors on the surface roughness and quality distribution of single-point diamond cutting KDP crystal is established.Through the design of special fixture device,the intermittent cutting mode of flying cutter is simulated in general single point diamond lathe,and the cutting process of KDP crystal along a certain orientation is realized.The optimum processing orientation of the highest surface quality is obtained by the analysis of experimental data.The results of FEM simulation and technological experiments show that negativerake angle cutting in single-point diamond cutting has some shortcomings,such as large cutting force and difficult chip removal,but it is beneficial to enhance the plastic processing ability of brittle KDP crystal.The processing parameters of KDP crystal were optimized by technological experiments.The optimal combination was spindle speed 1000 r/min,feed speed 5 r/min,cutting depth 2 um,tool rake angle-25o,and the surface roughness was 5.0 nm.The results of flying cutting experiment,end turning experiment and mechanical anisotropy of KDP crystal show that cutting KDP crystal along the direction of smaller elastic modulus and larger shear modulus can obtain higher surface processing quality.更多还原