超声振动切削刀具设计

介绍频率40kHz,振幅在(10～35)μm范围可调的振动刀具的设计过程,该刀具选用通用信号发生器作为超声波信号源,对其(0～5)V正弦电压信号进行放大,输出幅值(0～350)V用于激励压电换能器,将超声电振荡转换成机械振动,对振动信号再经变幅杆机械放大,使刀具振动幅值达到(10～25)μm以上进行切削。利用该刀具切削工件的精度和表面粗糙度达到精密切削的效果,并且已进行了天然金刚石精细切削不锈钢零件的实验,切削后的刀具磨损量明显降低。     

Integration of cutting force control and chatter suppression control into automatic cutting feed adjustment system design

Abstract

This study designed an automatic cutting feed adjustment system for computer numerical control (CNC) turning machine tools, which integrate the operational characteristics of cutting force control and chatter suppression control to shorten the machining time and maintain the quality of workpieces. The setting of appropriate machining conditions (such as cutting feed, spindle speed and depth of cut) to consider both machining quality and efficiency often causes difficulties for machine tool operators. Therefore, this study uses cutting force control to design an automatic cutting feed adjustment method for cutting tools, and then, the chatter suppression control design is used to modify the cutting force command to suppress cutting chatter. The experimental results of the CNC turning machine tool show that the use of the cutting force control to adjust the cutting feed can shorten the machining time; however, the cutting chatter results in larger surface waviness on the workpiece surface. When the cutting force command is properly modified by actuating the chatter suppression control, the workpiece shows better surface roughness with prolonged machining time. Therefore, the cutting tests demonstrate that the proposed system is feasible for satisfying the machining requirements of the manufacturing processes of mechanical parts for high speed and high accuracy.     

Self-tuned ultrasonic elliptical vibration cutting for high-efficient machining of micro-optics arrays on brittle materials

Ultrasonic elliptical vibration cutting is a very promising technique for the machining of brittle materials. However, its machining performance is currently limited by the ductile machining model and the machining strategy with a constant feed rate, leading to low machining efficiency. To overcome this defect, this paper presents a novel self-tuned ultrasonic elliptical vibration cutting (SUEVC) technique to achieve high-efficient ductile-regime machining of the micro-optics array on brittle materials. The proposed SUEVC includes a ductile-regime machining model and a tool path generation method. In SUEVC, the feed rate adaptively changes with respect to the local shape variation of the desired surface along the feeding direction to ensure both crack-free surface and high machining efficiency. Finally, two 1 × 3 spherical micro-optics arrays were successfully fabricated on single-crystal MgF₂ by SUEVC and the traditional machining strategy respectively. Results demonstrated that the SUEVC could enhance the machining efficiency by 30% relative to the traditional machining strategy, while maintaining similar surface roughness and a crack-free surface.     

超声振动切削超薄壁精密零件的粗糙度试验研究

对直径为 47.75mm壁厚为 0 .8～ 1 .5mm的照相机导向镜筒零件进行普通和超声车削试验 ,研究了各切削参数对此类超薄壁零件表面粗糙度的影响规律 ,也试验研究了超声振动切削时切削液及车刀对表面粗糙度的影响     

Automatic selection of spindle speed for suppression of regenerative chatter in turning

The paper presents a new spindle speed regulation method to avoid regenerative chatter in turning operations. It is not necessary to analyse complex cutting dynamics to search for stable spindle speeds to eliminate regenerative chatter. The metal removal rate is also greatly improved by using this method. The stability lobe diagram for the stability limit of chip width and chatter frequency versus spindle speed is derived by using the Nyquist stability criterion. It is shown that stable spindle speeds can be automatically obtained when the chatter frequency is found. Computational simulations and experimental cutting tests are performed to illustrate the proposed method.     

Unique regenerative chatter in wiper-turning operation with burnishing process Part 2: Experimental verification of predicted generation mechanism,critical stability,and characteristics

In this paper, the predicted generation mechanism, chatter stability, and characteristics of the unique regenerative chatter with the burnishing process in wiper-turning operations are verified experimentally. It was found in the first part of the paper that the vibration regenerates in the burnishing process by the wiper part of the insert causing a novel type of chatter. In this second part, this chatter phenomenon is investigated in an experimental manner to verify its mechanism. The specific burnishing force, which is a gain factor characterizing the burnishing process, is determined by the Hertzian contact law. In addition, the specific cutting force is measured by a cutting test, the compliance of the flexible structure is measured by a hammering test, and the residual compliance is measured by a static indentation test. Then, experiments are conducted where the tilt angle and the feed rate are varied to find the critical stability. The conducted chatter experiments prove that the predicted generation mechanism, critical stability, and characteristics are true.     

PCD刀具超声振动切削金属基复合材料SiCp/Al的特性研究

试验研究了普通和超声切削新型颗粒增强金属基复合材料SiCp/Al的切削特性 ,得到超声振动切削该材料的切屑形态、切削力变化规律     

Unique regenerative chatter in wiper-turning operation with burnishing process Part 1: Prediction and analytical investigation of generation mechanism,critical stability,and characteristics

The purpose of this paper is to understand the generation mechanism and to propose an analytical model of a unique regenerative chatter with the burnishing process in wiper-turning operations. The authors have found a unique chatter when using wiper inserts, which cannot be explained by the existing chatter theory found in the literature. The authors believe that this occurs because of the burnishing process of the wiper insert, which is the only difference from ordinary turning. At first, the burnishing process, which accompanies wiper inserts, is explained, and the turning operation with this process and the well-known regenerative effect in the cutting process is discussed. Then, the stability of the turning process with the regenerative effects in the cutting and burnishing processes are investigated, and an analytical model is proposed to evaluate the critical stability. Finally, the stability analysis of this unique chatter is conducted, and its generation mechanism and characteristics are examined clearly.     

超声振动切割细胞系统的设计

根据细胞微切割实验对超声振动切割系统的要求,对夹心式超声换能器和超声变幅杆组成的振动系统进行了设计,超声换能器采用夹心式压电换能器,变幅杆是一种将等截面圆柱形阶梯变幅杆的一端替换成圆锥形变幅杆构成的新型复合圆锥阶梯形变幅杆,设计了超声换能器和变幅杆的基本结构,并给出其制造尺寸.     

Design of ultrasonic elliptical vibration cutting system for tungsten heavy alloy

Nanoscale surface roughness of tungsten heavy alloy components is required in the nuclear industry and precision instruments. In this study, a high-performance ultrasonic elliptical vibration cutting (UEVC) system is developed to solve the precision machining problem of tungsten heavy alloy. A new design method of stepped bending vibration horn based on Timoshenko’s theory is first proposed, and its design process is greatly simplified. The arrangement and working principle of piezoelectric transducers on the ultrasonic vibrator using the fifth resonant mode of bending are analyzed to realize the dual-bending vibration modes. A cutting tool is installed at the end of the ultrasonic vibration unit to output the ultrasonic elliptical vibration locus, which is verified by finite element method. The vibration unit can display different three-degree-of-freedom (3-DOF) UEVC characteristics by adjusting the corresponding position of the unit and workpiece. A dual-channel ultrasonic power supply is developed to excite the ultrasonic vibration unit, which makes the UEVC system present the resonant frequency of 41 kHz and the maximum amplitude of 14.2 μm. Different microtopography and surface roughness are obtained by the cutting experiments of tungsten heavy alloy hemispherical workpiece with the UEVC system, which validates the proposed design’s technical capability and provides optimization basis for further improving the machining quality of the curved surface components of tungsten heavy alloy.     

Vibration analysis and development of an ultrasonic elliptical vibration tool based on a portal frame structure

An ultrasonic elliptical vibration tool utilizing the coupled resonant vibration modes is the key component in the elliptical vibration cutting/texturing process, which has been successfully applied to ultra-precision machining and surface texturing. In this paper, an analytical approach is proposed to analyze the resonant frequency and mode shapes of the ultrasonic elliptical vibration tool. A new design of ultrasonic elliptical vibration tool based on a portal frame structure is presented and analyzed using the proposed model. The model assumes Euler-Bernoulli beams and utilizes the transfer matrix technique to reduce the order of the system to only six variables. The model can be utilized to provide a systematic approach for an optimal design and be extended to dynamic analysis of the tool for study of machine-tool dynamics. Finite element simulation results as well as experimental data based on the prototype design are presented to verify the model. An application of the proposed tool is also demonstrated in machining micro/nano-structured surfaces for structural coloration.     

A novel method for effecting flexible guided wave propagation in elliptical vibration cutting

As a key part of elliptical vibration cutting (EVC) technology, a two-dimensional ultrasonic elliptical vibration cutting (UEVC) device has become a prevalent area of importance and research interest. This paper dissects through the conventional structural design and creatively proposes the UEVC device with flexible guided wave propagation. The device resolves the problems of poor coupling efficiency of two-way excitation signal, complex structure design, non-orthogonal, and the difficulty in controlling the ellipse trajectories of the tool tip. It has been confirmed that a flexible guided wave exhibits an effective unidirectional propagation and lateral load decoupling ability via establishing its system dynamic response and frequency impedance characteristics. Here, we explain the coupling mechanism of the two-way flexible guided wave in the UEVC device. Results suggested that the experimental measurement of the impedance for the cutting device and the individual transducer shows that the cutting device with the transducer and the tool bar connected by the flexible guided wave has a lower impedance increase ratio compared to the individual transducer, and hardly influence the tool bar mode of the cutting device. At the same time, the tool tip trajectory of the cutting device having a phase difference of 90° showed a satisfactory “elliptical” shape, while the microstructure processed by the tool tip ellipse trajectory with a phase difference of 60° reached a burr-free state. Theoretical and experimental findings reveal that the flexible guided waves exhibit excellent weak coupling characteristics in the non-transmitting direction. This is convenient to the independent, orthogonal and stable propagation of signals in the two directions. Based on flexible guided wave propagation technology, our findings provide theoretical foundation and application value for the design of a two-dimensional UEVC device.     

Characteristics of chip generation by ultrasonic vibration cutting with extremely low cutting velocity

Recently, mirror-surface machining of brittle materials such as ferrite, glass, and optical plastics has become more important, as these materials are used in optical communications and precision devices. Non-ferrous metals such as aluminium and copper were readily turned with diamond tools, but as the need for both infra-red and reflective optics escalated, the need to machine brittle materials arose. In this paper, ultrasonic vibration cutting at 20 kHz at extremely low cutting velocity for the precision machining of brittle plastics used for optical lenses is suggested and tested. The mechanism of chip generation, and characteristics of surfaces in the ductile mode, machined by ultrasonic vibration cutting are investigated. As a result, when micro cutting by ultrasonic vibration, it was confirmed that the chips generated by ductile mode cutting are obtained at 1/40 of the critical cutting velocity of the ultrasonic vibration cutting system, which is an extremely low cutting velocity.     

A study of ultrasonic vibration cutting of carbon fibre reinforced plastics

In the use of carbon fibre reinforced plastics (CFRP) it is often necessary to cut the components, but cutting CFRP is often made difficult by delamination of the composites and by the short tool life. In this paper, the machinability of CFRP by means of ultrasonic vibration cutting was experimentally investigated. The experimental results have led to a trial application of ultrasonic vibration cutting, which has been verified experimentally to be highly effective in view of cutting force and surface quality.     

Proposal of novel spindle speed variation profile with constant acceleration rate for improvement of chatter stability

Spindle speed variation (SSV) is one of the effective methods which suppresses regenerative chatter. However, regenerative chatter can grow even if SSV is applied. In the previous work, the chatter growth characteristics in SSV were clarified. The chatter frequency changes proportionally to the varying spindle speed, and it causes the change of the magnitude of the dynamic compliance. Hence, chatter can be suppressed through SSV since the dynamic compliance usually reduces as the chatter frequency changes. A greater compliance reduction can be obtained by a higher rate of spindle speeds in two consecutive revolutions at the same angular position, i.e., acceleration rate. From the investigations in the previous work, limitation of the conventionally utilized SSV profiles is found as follows: the acceleration rate always fluctuates with speed variation and the chatter vibration grows where the acceleration rate is insufficient for suppression, and hence suppressing chatter in all sections of SSV is difficult. In this paper, a new SSV profile with a constant acceleration rate, namely CAR-SSV, is proposed to overcome the limitation of chatter stability improvement by utilizing conventional SSV profiles. The magnitude of the acceleration rate is kept constant to realize the chatter suppression effect throughout the cutting process. Through time-domain simulation and cutting experiments, the chatter stability of CAR-SSV is investigated based on the previously introduced chatter stability evaluation indices. Influence of the parameters of CAR-SSV on the stability is investigated, and an appropriate strategy for setting SSV parameters to achieve higher stability is discussed. In addition, in order to verify the effectiveness of the proposed profile, the stabilities of conventional SSV profiles and CAR-SSV are compared through time-domain simulations and cutting experiments.     

Simultaneous double-sided milling of flexible plates with high accuracy and high efficiency—Suppression of forced chatter vibration with synchronized single-tooth cutters

This paper presents a new method to finish flexible plates with high accuracy and high productivity. Precision steel plates are finished conventionally by face milling with electro-magnetic chucks. It is difficult to improve flatness of the flexible plates, because they deform to fit the chuck surfaces while clamped. The authors have applied simultaneous double-sided milling to solve this problem, but it causes forced chatter vibration which is not allowed in precision finishing. Thus, the new method is proposed and verified to suppress the forced chatter vibration, in which the both surfaces are finished simultaneously with single tooth milling cutters with synchronization so that the thrust forces are cancelled out on the both sides.     

椭圆振动切削的表面残余应力有限元模拟研究

基于ALE(Arbitrary Lagrange-Euler)网格划分方法建立了椭圆振动切削有限元仿真模型,模拟了椭圆振动切削过程中切削力的变化规律,并将模拟获得的切削力平均值与相同工艺参数下Kim等人[1]所做的超声椭圆振动切削V型槽实验获得的切削力平均值比较,验证了有限元模型的正确性。利用建立的二维有限元模型模拟了椭圆振动切削和普通切削表面残余应力的分布情况,对比结果表明,采用椭圆振动切削的工件已加工表面在一定深度内形成了分布均匀的表面残余压应力,而普通切削情况下工件已加工表面并没有形成有效的残余压应力,从而预测了椭圆振动切削不仅能够降低切削力、延长刀具使用寿命,还对提高工件表面完整性、增强疲劳寿命和抗腐蚀能力等具有显著的作用。     

超声振动切削超薄壁精密零件的圆度误差试验研究

试验研究了超声振动车削直径为47.75mm壁厚为0.8-1.5mm的照相机导向筒超薄壁精密零件的圆度形成规律及切削参数对圆度误差的影响。研究表明:超声车削精密超薄壁零件,圆度误差最小是普通精密切削的1/3。     

Micro ECM with ultrasonic vibrations using a semi-cylindrical tool

In recent years, there has been a growing demand for micro holes. However, electrochemical machining has rarely been employed in drilling these holes because of problems with electrolyte diffusion. In this research, a semi-cylindrical tool was used as a tool electrode to increase the flow space of the electrolyte, and electrolyte diffusion was improved via the application of ultrasonic vibrations. Micro holes with a specified diameter of 76 μm were drilled on a 304 stainless steel plate of 300μm thickness. The proposed technique reduced both the machining time and the machining gap.     

Simulation of elliptical patterns based on grinding with wheel dressed by elliptical tool

Dressing is a sharpening operation aimed to produce a specific groove shape on the active surface of the wheel. The preparation of grinding tools in special way is the most important enabling factor in the grinding process. It greatly influences the subsequent geometry of the workpiece. As the groove shape of the wheel surface determines the shape of the surface patterns, therefore, it is essential to produce desired groove on the wheel cutting surface before grinding. Therefore, an elliptical groove surface pattern model is proposed based on grinding with dressed wheel. An elliptical tip tool is used for the dressing process to make grooves on the wheel instead of sharp tip tool or rounded tip tool in the previous work. The dressing tool passes helically over the surface of the grinding wheel for making grooves. After that, the grooved wheel passes over the flat surface to generate elliptical patterns. The results showed the three-dimensional geometry of the surface patterns with elliptical groove which are uniformly distributed on the workpiece. An experiment is carried out for the verification of the simulation results and it is revealed that the simulation results agreed well with the experiment.