Influence of coolant conditions in ultrasonic assisted grinding of high performance ceramics

Ultrasonic-assisted grinding finds its main application in the processing of hard, brittle materials. In particular through the superposition of the conventional feed rate and the high velocity with ultrasonic frequency, advantages in drilling processes can be reached. The application of ceramic and glass materials for high performance parts in the aerospace and aeronautical industries, in biomedical components and for parts exposed to wear in the automotive industry is steadily increasing due to their favorable properties. The drilling of these materials in their sintered state with high accuracy and reproducibility presents a significant challenge with respect to the choice of tool and the process parameters implemented. This paper focuses on the influence of the cooling lubricant in combination with different tool specifications on the grinding process. The grain size of the diamond grinding pins was varied in the range of 30 to 126 μm. As bond types, electroplated, sintered bronze and sintered Fe/Co bonds were investigated as well as the pressure of the cooling lubricant and the influence of these factors on the process behavior. In additional to the process behavior, the residual stress profiles of the workpieces were evaluated.     

Analysis of ultrasonic assisted machining (UAM) on regenerative chatter in turning

Ultrasonic assisted machining (UAM) is an advanced technology for improving the machining process, especially for hard materials. This paper presents an experimental and theoretical study toward the effect of UAM on chatter. Theoretical explanation of the effect of UAM on chatter is not fully presented in the available literature yet. In this paper, considering fixed tool geometry, theoretical dynamic equations for UAM are represented. The approach is demonstrated by deriving dynamic formulation of UAM in turning, considering both turning equation and Merchants ultrasonic machining equations. A time domain analysis is fulfilled on each machining condition to verify whether it has a stable vibration or an unstable chatter vibration. Subsequently, an experimental setup is designed and manufactured to investigate UAM effect on regenerative chatter. Special conical shape for workpiece is designed to experimentally generate different points of stability lobe. The generated oscillation by a piezoelectric actuator is transferred, amplified, and concentrated on the tip of the tool by appropriate design of a cutting tool, which is vibrated in its bending mode. The obtained results are encouraging, and indicating good agreement between experimental and theoretical results.     

二维超声磨削纳米复相陶瓷的磨削特性研究(1)

本文通过对二维超声磨削纳米复相陶瓷的磨削特性进行理论分析及试验研究，尤其是磨削力的特性及其影响因素，从而探索磨削加工表面质量的影响因素并提出改善磨削效果的措施。研究结果表明，磨削力随着切深的增大而增大，随着磨削深度的进一步增加，超声振动在磨削加工中所起的作用减弱；二维超声振动磨削大大扩大了复相陶瓷磨削的塑性加工区域，二维超声振动磨削过程的塑性域是磨削深度小于5μm，而普通磨削塑性域是在磨削深度小于2μm；适当增大磨削速度，既可以增强磨削砂轮的自锐能力，获得较高的去除率，又可以增加塑性变形，改善工件的表面质量；砂轮线速度的变化对二维超声振动磨削过程中的磨削力影响比对普通磨削过程中的磨削力的影响小，故二维超声振动磨削可以选用较大的砂轮线速度；工件速度对二维超声振动磨削表面粗糙度影响很大，其值随着工件速度的增加而增大。     

A fundamental study on the mechanism of electrolytic in-process dressing (ELID) grinding

Demands for high quality surface finish, dimensional and form accuracy are required for optical surfaces and it is very difficult to achieve these using conventional grinding methods. Electrolytic in-process dressing (ELID) grinding is one new and efficient method that uses a metal-bonded diamond grinding wheel in order to achieve a mirror surface finish especially on hard and brittle materials. However, studies reported so for have not explained the fundamental mechanism of ELID grinding and so it has been studied here by conducting experiments to establish optimal grinding parameters to obtain better surface finish under various in-process dressing conditions. In this research the results show that the cutting forces are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of the grinding wheel; however, a smoother surface can be obtained using a high dressing current duty ratio at the cost of high tool wear. ELID grinding is efficient for feed rates of less than 400 mm/min, and surface cracks are observed when it exceeds this limit.     

青铜结合剂金刚石砂轮胎体性能评价的研究(2)——评价方法

在金相组织测试结果的基础上,分别对四种不同工艺条件下制备的青铜胎体试样的金相形貌进行了观测,并分别测试了其密度、硬度和抗弯强度.综合考虑金刚石砂轮对金属结合剂性能的要求,结合其微观组织形貌和宏观物理力学性能差异,评价了各工艺条件下制备的胎体试样性能的优缺点,并为砂轮制备工艺优化提出了参考意见.     

提高电火花磨削加工一致性性的新方法

采用块状工具电极的精密电火花磨削加工法是低刚度轴和微细轴类零件电火花加工的主要方法之一，该方法过去采用的径 给方式。由于是损耗的因素，使得工件的形状和尺寸的一致性不好，且对生产率也有影响。本文采用一种新的块状工具电极的进给方式－切向进给方式，利用伺服进给自动补偿电极损耗，大大地提高了成批加工工件的一致性和生产率。     

新型切削加工机器人及运动分析

根据机械加工的要求，提出了切削加工机器人的结构方案，对切削加工机器人的加工运动进行了分析。     

A new method for the identification of stability lobes in machining

This paper introduces a new method for identifying the stability lobes in milling. The method depends on ramping the spindle speed while monitoring the behaviour of a chatter indicator. Based on the pattern of this indicator, the stability lobes are located accurately. The lobes are identified on-line without stopping the machine. It is not necessary to calculate the frequency spectrum of any vibration signal. The method was tested successfully in immersion down-milling and was shown to be applicable to slotting. Experimental results showed that the frequency characteristics of the stability lobes identified using the developed method are the same as those of the lobes established using constant speed cutting.     

Investigation of machining performance in high pressure jet assisted turning of Inconel 718: A numerical model

This study aims at investigating the effects of high-pressure jet assistance (HPJA) in rough turning of Inconel 718. A finite element (FE) model for orthogonal machining has been developed in order to reach additional data, compare trends to the experimental ones and understand the influence of the jet on the cutting process. Mechanical and thermal loads induced by the jet are considered. Consequences on the primary and secondary shear zones, chip formation and tool rake face have been studied on a whole pressure range (30-130 MPa) and compared to dry cutting. It is shown that the jet is able to decrease the cutting forces, chip radius and tool-chip contact length. Contact pressure and temperature fields on the cutting tool are also reduced as well as the sticking part of the contact zone. Authors confirmed that the effects of convection are able to change and even amplify the influence of the pure mechanical load induced by the jet.     

变参数激光三维加工方法及试验

介绍了在一次走刀中连续改变加工参数的激光加工新方法，研究变加工条件对切口几何尺寸的影响。在试验切割过程中，调整激光移动速度、输入功率和相对试件表面的焦点位置，来模拟激光三维切割实际状态，进一步分析得出变参数激光加工材料的去除规律。试验参数设计分为线性和二次方两种输入方式，证明了该方法的有效性。     

超声振动辅助ELID复合内圆磨削系统中大负载变幅器的设计及应用

为解决超声振动辅助ELID复合内圆(UAEI)磨削陶瓷等硬脆材料的声学系统设计难题,对驱动几何尺寸大、质量重的金属结合剂金刚石砂轮用的小端较长的变幅器进行理论设计及优化。基于弹性波在介质中的传播规律,利用MATLAB确定变幅器取值方案,再根据加工要求并结合ANSYS模态分析筛选出符合要求的方案,然后采用零阶算法进一步优化处理,得到满足几何尺寸、应力及振动频率要求的变幅器尺寸。对设计出的变幅器进行振动特性测试,其谐振频率理论误差为0.192%～1.824%,符合预期设计要求。采用研制出的UAEI磨削系统进行加工特性测试,与在线电解修整砂轮(ELID)内圆磨削比较,其工件的表面粗糙度降低了44.2%,且工件三维形貌更加平整,砂轮表面状况获得改善。      

A new process to develop (100) texture in silicon steel sheets

A process for developing (100) texture in silicon steel sheets by manganese removal and decarburization is described. The process consists of annealing in vacuum and subsequent decarburization of conventionally hot-and cold-rolled steel sheets that contain silicon, manganese, and carbon. During the vacuum annealing at α/β duplex or γ-phase temperatures around 1000 °, manganese removal occurs and a thin layer near the sheet surface transforms to a. The (100) texture markedly develops in the surface layer. Various types of (100) texture—for example, (100)[021], (100)[001], and (100)[011]—appear at this stage of annealing, depending on processing conditions. During the subsequent decarburization, the grains at the surface layer grow inward as columnar grains retaining the (100) texture. The decarburized steels with a grain size of a few hundred micrometers exhibit excellent soft-magnetic properties.     

Mechanisms involved in the improvement of Inconel 718 machinability by laser assisted machining (LAM)

The aim of the present research work has been to gain a broader understanding of how or why laser assisted machining (LAM) improves machinability of Inconel 718, a hard-to-machine material of interest in the aeronautic industry. This has been accomplished by, first, running short run tests to determine the laser parameters and configuration for which highest force reductions are obtained and also to determine the effect of cutting parameters (feed, cutting speed and depth of cut) on force reduction. Secondly, long run tests have been performed in order to analyze process variables such as cutting forces, tool wear and surface roughness. Temperatures and hardness have been also measured in order to gain a broader perspective of the process.Experimental results have demonstrated that LAM improves machinability of Inconel 718 since machining forces and final surface roughness are reduced. The novelty reached with the present research work is the identification of three mechanisms associated to the laser heating as the responsible of this machinability improvement: material yield strength reduction, material base hardness reduction (only in precipitation hardened Inconel 718) and elimination of the work hardening generated in previous machining passes. The reduction of the work hardening leads also to a lower notch wear that limits the risk of sudden failure of the cutting tool and thus the wear mode is changed to flank wear, which leads to a controllable tool life and better surface roughness.     

超声磨削氧化锆陶瓷表面相变与残余应力特征实验研究

针对氧化锆陶瓷的易相变特点,通过对ZTA陶瓷和纳米氧化锆陶瓷进行对比实验,研究了氧化锆陶瓷磨削表面相变特性,分析了磨削表面的残余应力特征.实验结果表明,亚稳态四方相氧化锆的含量以及磨削应力是诱发氧化锆陶瓷产生马氏体相变的主要因素;陶瓷磨削过程中,砂轮的磨削深度越大、磨粒粒径越大,在材料基体中产生的磨削应力越大,从而马氏体相变率增大;纳米氧化锆陶瓷磨削表面产生的残余压应力值大于ZrO2增韧Al2O3(ZTA)陶瓷.通过分析磨削参数对残余应力的影响,验证了马氏体相变可在一定程度上促进残余压应力的产生,从而提高磨削表面的质量.     

新一代SiC功率器件及其在逆变焊机中的应用

目前逆变焊机普遍采用的Si基功率器件的性能已接近由其材料特性决定的理论极限,依靠Si基功率器件继续完善和提高逆变焊机性能的潜力已十分有限。SiC是一种革命性的宽禁带半导体材料,是下一代功率半导体材料的重点发展方向。介绍了新型SiC材料的特性及其功率器件的类型、原理和特点;对比分析SiC和普通Si基功率器件的性能;在此基础上探讨将SiC功率器件应用于逆变焊机的优势;分析和展望SiC功率器件在新一代逆变焊机中的应用前景。     

Progress in fluidized bed assisted abrasive jet machining (FB-AJM): Internal polishing of aluminium tubes

This paper deals with the internal finishing of tubular components made from a high strength aluminium alloy (AA 6082 T6) using a fluidized bed assisted abrasive jet machining (FB-AJM) system.Firstly, a Taguchi's experimental plan was used to investigate the influence of abrasive jet speed, machining cycle, and abrasive mesh size on surface roughness and material removal trends. Secondly, the leading finishing mechanisms were studied using combined 3d profilometer-SEM analysis to monitor the evolution of the surface morphology of machined workpieces. Finally, the circumferential uniformity and precision machining of the inner surface of workpieces were tested by evaluating the values of the more significant roughness parameters in different circumferential locations.Consistent trends of surface roughness vs. operational parameters were measured, and significant material removal was found to affect the workpieces during machining. As a result, FB-AJM was found to preferentially machine the asperities and irregularities of the surface, thereby altering the overall surface morphology producing more regular and smoother finishing. Moreover, the good circumferential uniformity and machining accuracy FB-AJM guarantees even on ductile aluminium alloy workpieces ensure that this technology can be applied to a diverse set of industrial components.     

High performance grinding of zirconium oxide (ZrO2) using hybrid bond diamond tools

Hybrid bond (metal–ceramic) diamond tools are proposed for grinding zirconium oxide used in medical implants. Compared to conventional grinding tools, material removal rates and tool life time are drastically increased without deterioration in mechanical properties of the workpiece. This is achieved within a selected process window in combination with an elaborate oil cooling system, where material removal is mainly occurring within the ductile cutting mode. Self-sharpening effect of the tool can be observed and the dressability of the tool further improves the grinding performance.     

Microstructural investigation and machining performance of NbC-Ti(C0.5N0.5) matrix cermets

In this study, Ni or Co + Ni bonded NbC matrix cermets with secondary carbides (Mo₂C and WC) as well as Ti(C_0.5N_0.5) were prepared by liquid phase sintering at 1450 °C in vacuum. Detailed microstructural investigation was performed by SEM, EPMA and XRD analysis. The microstructure, mechanical properties as well as the C45 (HB140) steel turning performance of the cermets were investigated, and compared with a commercial Ti(C_0.5N_0.5) based cutting insert. The sintering results indicated that the partial substitution of NbC by Ti(C_0.5N_0.5) had a significant effect on the core-rim microstructure and refinement of NbC solution grains, as well as improved mechanical properties of the NbC-Ti(C_0.5N_0.5) cermets. The phase constitution and composition of the cermets were supported by thermodynamic equilibrium calculations. All sintered cermets were composed of a fcc solid solution metal binder and a cubic core-rim NbC based solution phase, as well as an independent N-rich Ti(C,N) phase. The NbC-Ti(C_0.5N_0.5) and Ti(C_0.5N_0.5) matrix cermets had a comparable HV₃₀ of 1500–1600 kg/mm² and a similar fracture toughness of 8.0 MPa m^1/2.     

A comprehensive tool-wear/tool-life performance model in the evaluation of NDM (near dry machining) for sustainable manufacturing

Traditionally, metal working fluids (MWF) are known to improve machining performance despite poor ecological and health side effects. A new sustainable process that has minimized the use and application of MWFs is NDM (near dry machining). Although there is much controversy on the effectiveness of NDM, it is agreed that a lack of science-based modeling prevents its widespread use. This paper presents a new method to predict tool-wear/tool-life performance in NDM by extending a Taylor speed-based dry machining equation. Experimental work and validation of the model was performed in an automotive production environment in the machining of steel wheel rims. Machining experiments and validation of the new equation reveal that tool-wear can be predicted within 10% when the effect of NDM is statistically different than dry machining. Tool-wear measurements obtained during the validation of the model showed that NDM can improve tool-wear/tool-life over four times compared to dry machining which underlines the need to develop sustainable models to match current practices.     

A technique and its application for evaluation of material removal contributions of pulses in electric discharge machining (EDM)

A technique and related software is developed to determine material removal quantities of pulses in pulse trains by using results of pulse train analysis and material removal rates. Erosive pulses are classified into groups as short circuit pulses, arcs and discharges with time-lags not more than 15% of pulse time, and discharges with time lags longer than 15% of pulse time considering their resembling material removal rates. It is experimentally verified that this grouping of pulses is the best combination considering the minimum loss of information about performance of machining.