Contact force modeling and analysis for robotic tilted-disc polishing of freeform workpieces

This paper investigates the tool-workpiece contact mechanism in the disc polishing process, where the soft polishing disc touches the rigid freeform workpiece with a small tilt angle. The developed contact force model can explain how the contact parameters, including the disc contact depth, the disc tilt angle, the radii of curvature of the disc and the workpiece, affect the normal contact force. Under some reasonable geometric and mechanical assumptions of the disc and the workpiece, an approximated contact force equation is derived in a simple power-law form similar to the Hertzian contact model. The contact force is found to be positively related to the disc contact depth and the disc radius, while negatively related to the disc tilt angle and the workpiece normal curvature that is orthogonal to the feed direction. Both finite element simulations and experiments verify the effectiveness of the proposed contact force model. Furthermore, the material removal process is analyzed and a model-based process parameter planning method is developed to achieve uniform material removal considering the variation of workpiece curvatures.     

微织构刀具对工件表面残余应力影响有限元分析

针对微织构刀具对切削工件表面残余应力的影响,设计不同尺寸的垂直槽和平行槽微织构,利用有限元仿真技术,模拟不同类型、不同尺寸微织构PCBN刀具干式车削GCr15试验。通过对有限元结果进行研究分析,得到已加工表面残余应力分布情况,并与无织构PCBN刀具对比,分析微织构对已加工表面残余应力的影响。有限元仿真结果表明:与无织构刀具切削工件表面获得拉应力相比,槽型织构刀具切削后的工件已加工表面呈现压应力,提高工件表层的耐磨损和耐疲劳性能;宽度50μm垂直槽和宽度40μm平行槽刀具切削得到的工件表面压应力最大,对工件表面应力分布影响最显著。     

Simulation of media behaviour in vibration assisted abrasive flow machining

Abrasive flow machining (AFM) is an abrasive-based precision finishing process used for achieving surface finish in micro and nano-level. The AFM polishes surfaces by extruding a visco-elastic media in contact with the workpiece. The media, also called a ‘flexible tool’, plays a key role in the performance of the process. Ultrasonic assisted abrasive flow machining (UAAFM) is a new variant of the AFM process in which the workpiece is subjected to mechanical vibration orthogonal to the media flow direction. In this process a high frequency, in the range of about 5–20 kHz, is given to the workpiece with the help of a piezo actuator and a specially designed fixture. The present work highlights on the possible behaviour of the tool (media) during UAAFM and its effect on the machining process through a computation based approach. Commercially available simulation tool was used to study the effect of the media in response to different set of machining conditions. The responses were evaluated in terms of changes in the fluid pressure, velocity profile of the fluid, temperature distribution in the working fluid and the possible wall shear on the work surface. A three-dimensional model was constructed for simulating the UAAFM process. The simulation shows that the abrasive particles tend to hit the target surface at an angle ‘θ’ which significantly affects the basic mechanisms involved and enhances the effectiveness of the process. The computed wall shear explains that the process will have higher finishing rate and hence the performance. The enhanced interaction of abrasive media in UAAFM while compared to simple AFM could be explained by the resultant pressure–velocity phenomena. Results show that while changes in the amplitude of applied vibration (10 μm and 50 μm) significantly affect the wall shear, the media velocity and pressure profiles are only marginally sensitive to this parameter. The simulation results also confirm that the rise in temperature during the process will not affect the media stability. Results have been discussed vis-a-vis the basic mechanism of the process through suitable illustrations.     

铼钠克G-SPEED数控系统在当代模具及零部件加工中的应用

本文介绍了铼钠克G—SPEED开放式数控系统的功能、特点以及G—SPEED数控系统往现代模具及零部件加工中的应用方法与技巧。包括在CNC自动车床上的应用、在加工小心及磨床上的应用、在鞋揎机上的应用、在四轴及五轴加工、在高光加工上的应用。     

磁性磨粒辅助磁针磁力研磨的应用研究

目的解决磁针磁力研磨工艺中磁针对工件表面碰撞损伤及存在研磨盲区的问题。方法在磁针中加入磁性磨粒增加磁针束的柔性,同时磁针为磁性磨粒提供研磨压力和切削力。将三相正弦交流电接入定子线圈,利用交流电的相位差产生旋转磁场,驱动混合磨料对微小复杂工件进行研磨。在混合磨料总质量不变的条件下,依次采用磁针、磁性磨粒和不同质量混合比的混合磨料进行对比试验。结果相较于单一磨料,使用混合磨料加工40 min后的工件表面形貌较好,表面粗糙度值下降幅度大,且有较大的材料去除量。当磁针与磁性磨粒的质量混合比为1∶2时,加工后的工件表面形貌最佳,无明显加工纹理和磁针碰撞痕迹,工件表面粗糙度值由原始的1.0μm下降到0.54μm左右,材料去除量为2.8 mg左右,微小沟槽内无研磨盲区。结论在电磁研磨工艺中,使用磁针和磁性磨粒质量比为1∶2的混合磨料可提高研磨效果,避免磁针的碰撞对工件表面造成损伤,磁针可将磁性磨粒挤入工件微小沟槽,无研磨盲区。     

工件表面缺陷图像检测中的自适应聚类

目的 针对工件表面形态复杂、干涉交叠缺陷难以实现自动分离、分类图像检测的情况,提出一种工件表面交叠缺陷自适应图像聚类方法。方法 首先提取工件表面缺陷二值图像,采用混合概率主成分分析器估计缺陷位置各像素点局部切空间信息,并改进局部切空间之间的相似性矩阵;然后通过改进局部密度峰值自适应方法,基于相似性矩阵确定聚类中心点和数目;最后通过谱多流形聚类,将各分析器所包含的像素点分配至不同缺陷流形结构中,实现多个交叠缺陷分离、检测。结果 首先通过比较计算与实际测量的长度、宽度来验证该方法对相互交叠结构缺陷良好、准确的分离效果,平均相对误差分别为0.957%和0.650%。其次为了体现该方法对于分离工件表面相互交叠缺陷的有效性及优越性,使用k-means聚类、谱聚类与该方法进行对比实验,证明了该方法良好的聚类效果。最后对所设计方法的稳定性进行测试,统计检测结果的平均ME值均在6%以下,正确聚类数目率高达99%~100%。结论 该方法能够较为准确地自动识别工件表面图像中存在相互干涉的不同缺陷,并进行分离。     

发电厂内强迫共振型低频振荡源的定位方法

强迫共振型低频振荡严重危害了电网的安全稳定运行,快速查找并切除扰动源对消除振荡恢复系统稳定意义重大。利用低频扰动电压的衰减特性,提出一种发电厂内强迫共振型低频振荡源定位的新方法。首先利用三次Hermite插值函数提取各个测点的低频振荡扰动变量;然后通过比较各个测点扰动电压的幅值大小定位低频振荡源机组;最后通过理论分析、六机无穷大系统的仿真分析以及某发电厂的实际相量测量单元测量数据的分析,对该方法的正确性进行了验证。     

面向大型工件现场测量的光笔式视觉测量系统

研制了一种面向大型工件现场测量的光笔式视觉测量系统,对其中的关键技术进行了深入研究。该系统主要由带有红外LED光点的光笔、1台CCD摄像机、靶点亮度控制器、一维标定尺以及安装有测量软件的计算机组成。在对LED点光源光强控制方式及成像系统工作原理进行分析的基础上,设计并实现了以多靶点亮度自适应控制技术和主动离焦模糊技术相结合的靶点光斑图像生成技术。该技术保证了在大跨度测量范围内均能获得高质量的靶点光斑图像,解决了对焦成像中摄像机视场范围与景深有限的问题;针对光笔标定问题,提出了一种简便易行的现场标定方法,此方法只需要若干个辅助靶点和2个以上间距已知的圆锥孔,就可以同时确定光笔上各靶点及光笔测头在光笔坐标系下的坐标。实验结果显示:该测量系统在2~10 m空间长度测量标准差不大于0.095 mm,能够满足中等精度的大型工件现场测量要求。     

振动式滚磨光整加工过程中的受力测试与分析

目的测试不同加工参数对振动式滚磨光整加工过程中作用力的影响,对实际加工过程中加工参数的选择提供一定的数值指导。方法通过改变偏心块夹角、固定工件埋入深度及固定工件装夹角度,应用动态式压力传感器测试每种加工参数对加工作用力的影响。结果偏心块夹角不同时,磨料的运动形态及运动轨迹差异明显,且偏心块夹角大小对工件的作用力影响显著,偏心块夹角为90°时磨料螺旋运动显著,加工效果好。固定工件埋入深度越深,其所受作用力越大;超过一定范围时,作用力陡增。通过改变固定工件装夹角度,观察磨料流态并测试工件不同装夹角下所受作用力,分析得到在装夹角为20°时磨料会以工件为中心聚集,工件所受作用力最大。结论偏心块夹角不同,磨料的运动流态及对工件的作用力不同,偏心块夹角为90°时光整加工效果最好。埋入深度对工件作用力影响显著,加工过程中应根据工件的加工要求确定合适的埋入深度。固定工件装夹角度不同,磨料流态变化明显,固定工件装夹角为20°时工件所受作用力最大,需根据实际加工要求确定装夹的具体角度。     

镜面电火花加工技术的研究与应用

目前镜面电火花加工技术在精密型腔模具制造中逐步得以推广。文章就企业中镜面电火花加工应用的关键环节,结合实践分析了影响镜面加工性能的因素。通过控制各个工艺环节,可有效实现高质量、高效率的镜面电火花加工。对模具制造企业吸收与消化当前先进的电火花加工工艺具有实际的应用价值。