Experimental study of the temperature field generated during orthogonal machining of an aluminum alloy

During the machining of metals, plastic deformation and friction lead to the generation of heat in the workpiece, which results in thermomechanically coupled deformation. Recently, several numerical models of this highly coupled process have been produced in response to increased interest in high speed machining. It is important to characterize the thermal field in the cutting zone in order to completely verify these models of high speed machining and to direct further advancement in this area. In this work, HgCdTe infrared detectors are used to experimentally measure the temperature distribution at the surface of a workpiece during orthogonal cutting. From these temperature measurements, the heat generated in the primary shear zone and the friction zone can be examined and characterized. A modified Hopkinson bar technique has been developed to perform orthogonal machining at speeds ranging from 10 to 100 m/s. In the present work, a cutting velocity of 15 m/s is employed in all the tests in order to demonstrate the capability of the apparatus and characterize thermal fields during low speed machining. Temperature fields are obtained during the orthogonal cutting of aluminum as a function of depth of cut. It is seen that depth of cut can vary both the maximum temperature as well as the distribution of the temperature field in the aluminum workpiece. the maximum temperature increased with depth of cut (238°C for 1.5 mm cut, 207°C for 1.0 mm cut and 138°C for 0.5 mm cut) and the temperature field extended further beneath the cut surface with decreasing depth of cut.     

Design and Modeling for Chatter Control

Boring bars for single-point turning on a lathe are particularly susceptible to chatter and have been the subject of numerous studies. Chatter is, in general, caused by instability. Clearly, the cutting process can be limited to regions of known stable operation. However, this severely constrains the machine-tool operation and causes a decrease in productivity. The more aggressive approach is to attack the stability problem directly through application of vibration control. Here, we demonstrate a new biaxial vibration control system (VPI Smart Tool) for boring bars. We present the experimentally determined modal properties of the VPI Smart Tool and demonstrate how these properties may be used to develop models suitable for chatter stability analysis, simulation, and development of feedback compensation. A phenomenological chatter model that captures much of the rich dynamic character observed during experiments is presented. We introduce the notion that the mean cutting force changes direction as the width of cut increases due to the finite nose radius of the tool. This phenomenon is used to explain the progression from chatter that is dominated by motions normal to the machined surface at small widths of cut to chatter that is dominated by motions tangential to the machined surface at large widths of cut. We show experimental evidence to support our assertion that a biaxial actuation scheme is necessary to combat the tendency of the tool to chatter in both directions. We then present some preliminary theoretical results concerning the persistence of subcritical instability as we expand consideration to high-speed machining.     

轨迹成型法精密磨削加工机床的精度分析

为了保证用轨迹成型法加工光学零件的面形精度,对精密磨削机床影响工件面形误差的因素进行了理论分析。推导出机床调整机构可消除误差的公式。并以误差公式计算出的误差值来调整机床的微调机构,可达到减少面形误差,进而保证面形精度的目的。     

微池润滑刀具干切削过程中的减摩机理

通过在前刀面月牙洼磨损区域加工装填MoS2固体润滑剂的微孔产生"微池效应"来改善刀具的摩擦学特性,制备了YG8微池润滑刀具.以该微池刀具对45#钢进行干切削试验,结果表明:微池刀具与普通的YG8刀具相比具有良好的摩擦磨损特性,切削力明显减小,前刀面摩擦系数显著降低.通过扫描电子显微镜(SEM)和能谱分析(EDX)对微池刀具前刀面观察研究,分析了刀具自润滑机理:微池刀具前刀面小孔中的润滑剂受热膨胀及切屑摩擦挤压作用析出,在前刀面表面拖覆形成固体润滑层,直接渗入到刀屑接触区域,从而起到减摩润滑作用,改善刀具基体减摩抗磨性能.润滑膜层在切削加工中是一个润滑膜形成、磨损、再形成的循环过程,微池润滑刀具在微孔完全磨损的整个生命周期内始终具有自润滑效果.     

火花放电电极结构及其等离子体反应器

在阐述火花放电机制与等离子体特性基础上,着重探讨了火花放电的电极结构与等离子体反应器。新研制的电极旋转的新型 kHz 交流火花放电反应器,在甲烷裂解制乙炔和甲烷与二氧化碳重整制合成气应用研究中,其放电稳定性、反应物转化率、产物浓度和能量效率等指标,均明显优于其它放电反应器。     

An approach for the coupled simulation of machining processes using multibody system and smoothed particle hydrodynamics algorithms

The prediction accuracy of a simulation method is limited by its theoretical background. This fact can lead to disadvantages regarding the simulation quality when investigating systems of high complexity, e.g. containing components showing a fairly different behavior. To overcome this limitation, co-simulation approaches are used more and more, combining the advantages of different simulation disciplines. That is why we propose a new strategy for the dynamic simulation of cutting processes. The method couples Lagrangian particle methods, such as the smoothed particle hydrodynamics (SPH) method, and multibody system (MBS) tools using co-simulations. We demonstrate the capability of the new approach by providing simulation results of an orthogonal cutting process and comparing them with experimental data.     

铝基复合材料超精密加工中的刀-屑摩擦磨损性能及模型研究

通过金刚石PCD刀具对非连续SiC增强铝基复合材料的超精密车削加工试验,考察了刀具第二切削变形区(刀具前刀面-切屑间)的摩擦磨损性能,并提出了相应的模型;采用爆炸式快速落刀装置制备出切屑根并分析了积屑瘤的影响因素;采用原子力显微镜对PCD刀具的刃口磨损形貌进行观察,并分析其磨损机理.结果表明:在超精密切削加工非连续增强铝基复合材料的过程中,前刀面仍然有极小的楔型积屑瘤产生;铝基复合材料的摩擦磨损性能明显优于铝合金,且当SiC增强相达到最佳体积分数(20%～25%)时,其摩擦磨损性能最佳;从刀具的耐磨性角度考虑,在超精密加工非连续增强铝基复合材料时适宜采用金刚石刀具.     

The Existence and Uniqueness of the Weak Solution for the Evolutionary Electrochemical Machining Problem

A time dependent electrochemical machining problem, in which the cathode is fed towards the anode with a constant velocity, is studied. We prove the existence and uniqueness of the weak solution for the problem under the assumption that the cathode is C^{1+β} for some β ∈ (0,1).     

分散液-液微萃取-气相色谱/质谱联用法测定机械加工水基切削液及其废水中的三氯苯

建立了以丙酮为分散剂、氯苯为萃取剂,采用分散液-液微萃取、气相色谱/选择离子质谱联用测定机械加工水基切削液及其废水中三氯苯的方法。该方法与顶空萃取、液-液萃取和固相萃取结合气相色谱/电子捕获检测法相比,具有线性范围广、富集倍数高、重现性好、操作简便、干扰小等优点。样品中三氯苯的加标回收率为94.7％~104.3％,相对标准偏差为2.3％～7.8％。三氯苯的3种同分异构体1,3,5-,1,2,4-和1,2,3-三氯苯的检出限分别为2.0,6.0和3.0 μg/L。重点探讨了萃取剂和分散剂的种类、体积、萃取时间和盐效应等对三氯苯萃取效率的影响,优化了萃取条件。考察了机械加工水基切削液中常用的添加剂对检测结果的影响,结果表明1.0％的亚硝酸钠和聚乙二醇对三氯苯的检测基本无影响。采用该方法对4种实际样品中的三氯苯进行了测定,其中两个样品中含有三氯苯,质量浓度范围为0.15～1.67 mg/L。     

高准确度多功能激光直写装置

采用高数值孔径物镜和高准确度纳米平台搭建了一台激光直写装置,可以在光敏感薄膜材料上进行打点、刻画矢量和标量图形等多种操作,其最小特征尺寸小于300 nm,重复性5 nm.在刻写前准确标定刻写激光功率,刻写过程中采用象散法精确自动聚焦,刻写完成后采用两种不同波长的激光束探测样品的透过率和反射率的细微变化,最终实现了高准确度亚微米图形的刻写和检测.