Three-dimensional profile stitching measurement for large aspheric surface during grinding process with sub-micron accuracy

A novel measurement method is proposed to realize three-dimensional (3D) profile stitching for large aspheric surface. The proposed method is based on the multiple sub-regions stitching technology applying a four-axis fixture and a commercial small-range profiler. The partition of sub-regions is due to the effective profiler’s range and the characteristic parameters of aspheric surface, and the measurement for each sub-region within the profiler’s range is achieved through the fixture to translate and rotate the aspheric surface. Then a stitching algorithm including the multi-body theory, the invariability of curvature radiuses and the least square principle is established to reconstruct the full 3D profile. Simulations of multiple sub-regions stitching for different aspheric surfaces are performed to predict the stitching accuracy of proposed method and analyze the influence of alignment errors in Y direction caused by the rotation error along Z direction (Δβ_w,g). The stitching accuracy of proposed method is verified by measuring the 3D profile of an off-axis parabolic surface and an axisymmetric aspheric surface. The experimental standard deviations of stitching errors are 0.16 μm and 0.42 μm, which are less than the form errors of aspheric surface during grinding process. The results show that the proposed method achieves 3D profile stitching for large aspheric surface with sub-micron accuracy.     

不锈钢基板表面粗糙度对水膜吸附夹持的影响

目的从水膜吸附的功能研究出发,对不锈钢基板表面进行不同粗糙度处理,并测量不同基板对蓝宝石晶片的吸附力以及切向摩擦力的影响,从而得出粗糙度对水膜吸附效果的影响规律。方法通过砂纸打磨、研磨、抛光等方法,得到不同平均粗糙度(Sa=633.4、332.6、116.2、64.5、41.4nm)的不锈钢基板。利用接触角计对液滴在基板表面形成的静态接触角进行拍摄,得出不同粗糙度不锈钢表面的润湿性能。开发设计高精度的多维力测量平台,测量蓝宝石晶片在不同粗糙度不锈钢基板上润湿后的吸附力和切向摩擦力,并与未润湿的基板得到的测量结果进行对比研究,得出粗糙度对吸附力和摩擦系数的影响规律。结果5种粗糙度的不锈钢基板的静态接触角均小于90°,属于亲水性材料。水膜吸附条件下,吸附力大小随粗糙度的增加而减小;接触角大小随粗糙度的增加而增大,且吸附力的减小率和接触角的增大率趋势相似;摩擦系数随粗糙度的增大而增大。基板表面粗糙度较大时,水膜提供一定的粘滞力,使水膜吸附条件下比无水膜时的切向摩擦力更大;当粗糙度较小时,水膜更多的是润滑作用,此时比无水膜时的切向摩擦力要小得多。结论基板表面粗糙度较小时,基板能提供较大的吸附力,而摩擦力不如无水膜时的大;基板粗糙度较大时,吸附力相对较弱,但是摩擦力比无水膜的更大。在选择不锈钢基板作为水膜吸附夹持基板时,在保证足够吸附力的条件下,可以适当提高基板的表面粗糙度,抵抗晶片抛光过程中受到抛光垫的摩擦力。     

基于固结磨料盘的钽酸锂高效研磨加工试验研究

目的 实现钽酸锂材料的高效、高质量、低成本加工。方法 选择合适的添加剂作为辅料,利用树脂结合剂将3000#的金刚石磨料通过配混料、固化、压实、修整等步骤,制成金刚石固结磨料盘。以加工过程中钽酸锂工件的材料去除率、表面形貌以及粗糙度等作为评价指标,在相同粒径条件下,用游离磨料、固结磨料磨盘对钽酸锂晶片进行加工,对比加工结果。结果 在压力为4 kPa、研磨盘转速为140 rad/min的条件下,3000#金刚石游离磨料铸铁盘研磨Y-36°钽酸锂晶片10 min后,材料去除率为37.89 μm/h,表面粗糙度Sa由420 nm改善至233.308 nm,但是晶片表面出现深划痕,从而导致易破碎,且有少量磨粒残留在钽酸锂晶片上。而在相同加工条件下,采用3000#金刚石固结磨料盘研磨Y-36°钽酸锂晶片10 min后,材料去除率为66.19 μm/h,表面粗糙度Sa降低至97.004 nm,且晶片表面划痕较浅,无磨粒残留在钽酸锂晶片上。结论 采用固结磨料盘加工后的表面粗糙度比游离磨料加工后的表面粗糙度更低,表面形貌更好,材料去除率更高,达到了钽酸锂晶片精研的加工效率和表面质量。同时固结磨料盘研磨LT晶片时,其表面粗糙度随压力、转速增大而减小,材料去除率随压力、转速增大而增大。     

Study on removal mechanism and removal characters for SiC and fused silica by fixed abrasive diamond pellets

Fixed abrasive is known as a high-efficient and stable technique for fabricating various materials. This work studies the removal mechanism and removal characters of fixed abrasive diamond pellets (FADPs) for lapping SiC and fused silica. The critical sizes of diamond particles changing brittle fracture to ductile removal (with better surface roughness and less damages) are figured out for SiC (9.56 μm) and fused silica (0.53 μm). Multi-distribution models are presented and a mathematical removal model is built based on Preston law. Then, removal characters of FADPs are investigated, including removal profile, removal rate, linear removal, removal stability, surface roughness, subsurface damage etc. Results show that (i) the removal shape is predictable and the removal rate is highly correlative with diamond size, velocity and pressure; (ii) the cumulative removal is temporally linear and removal stability is within ±10%; (iii) SiC can be ductilely lapped by 1.5, 3, 5 μm pellets, with best roughness Ra=4.8 nm and a specular surface for optical metrology; (iv) removal of fused silica is mostly brittle fracture and it can change as semi-ductile by 1.5 μm pellets, with a non-specular or semi-specular surface which is hard for optical metrology; (v) subsurface damage is highly dependent on diamond size, but free to pressure and velocity. Finally, two engineering applications validated its feasibility in uniform or deterministic lapping/polishing of optical mirrors.     

喷嘴结构对气雾化激光熔覆专用合金粉末的影响

针对气雾化制备激光熔覆专用粉末的问题,调整粉末材料配比,采用改进后的超音速气雾化喷嘴,对比原喷嘴进行气雾化制取激光熔覆专用镍基合金粉末的实验。结果表明,喷嘴是影响雾化粉末的重要因素。随着喷嘴结构的改进,粉末的平均粒度dm越小、体积四次矩平均径dVm和Sauter平均直径dVs越小,即颗粒越细。与此同时,粉末的流动性更好,松装比更大,粉末的有效雾化率高,符合激光熔覆的要求。     

新型旋转比例电-机械转换器静态特性研究

针对传统旋转电-机械转换器静态特性线性度不高、工作范围小的问题,设计了一种新型旋转比例电-机械转换器,采用磁路解析、Maxwell 3D静磁场有限元分析和实验测试等方法研究了旋转比例电-机械转换器的静态特性,并加工了样机,进行了相关实验研究。实验结果表明,电-机械转换器工作范围为-5～5°,最大输出力矩约为±252 m N·m,具有正的磁弹簧刚度,实验与仿真的差值集中在9. 6 m N·m以内,相对误差基本小于6%;电-机械转换器具有良好的重复精度,转角-力矩特性曲线非线性误差小于1. 5%,滞环小于3. 5%,电流-力矩特性曲线具有很好的线性度及较小的滞环,测试结果与仿真结果基本一致。     

High speed titanium coatings by supersonic laser deposition

The importance of metal coating technologies drives the continuous improvement of metal deposition techniques for application in a wide range of industrial sectors. This work presents the foundations of a new process technology for the deposition of titanium coatings on steel tube substrates using supersonic powder streams and impact site laser heating, known as Supersonic Laser Deposition (SLD). Metallic deposits are obtained under appropriate impact conditions without the need for exceeding the melting point of the deposited material or substrate leading to improved coating quality. Details of the experimental approach are presented along with the general characteristics of the titanium coating produced using this novel coatings method.     

牛血清环境下等离子喷涂ZrO_2增强羟基磷灰石涂层的摩擦磨损性能

为了研究ZrO_2增强羟基磷灰石(HA)复合涂层在牛血清润滑环境下的摩擦磨损性能,首先,采用等离子喷涂技术在钛合金基体上制备了ZrO_2含量分别为0、15wt%和30wt%的HA生物陶瓷涂层;然后,分析了ZrO_2/HA复合涂层的物相成分和结合强度;最后,采用UMT-3销盘摩擦试验机研究了ZrO_2/HA复合涂层在牛血清润滑环境下的摩擦磨损性能,观察涂层磨损表面微观形貌并分析了磨损机制。结果表明:HA涂层的主要物相为HA,15wt%ZrO_2/HA复合涂层和30wt%ZrO_2/HA复合涂层中的ZrO_2以立方相形式存在,并且衍射峰强度高于HA的。随着ZrO_2含量增大,涂层的结合强度明显增大。ZrO_2/HA复合涂层与纯HA涂层相比,有更好的耐磨性和更低的摩擦系数。纯HA涂层的磨损机制以犁沟效应和磨粒磨损为主,而15wt%ZrO_2/HA复合涂层和30wt%ZrO_2/HA复合涂层的磨损机制为脆性剥落磨损。