Ultrasonic vibration-assisted multi-scale plastic forming of high-entropy alloys in milliseconds

<正>Due to their excellent properties of specific strength,fracture resistance,corrosion and oxidation resistance,the high-entropy alloys have attracted widespread attention as engineering materials.For the sake of industrial applications,one of the essential stages would be the forming of them,especially the construction of multi-sc ale structures from macroscale to nanoscale.     

Fabrication of textured surface with ultrasonic vibration-assisted indentation

An ultrasonic vibration-assisted indentation system/method is proposed and developed to fabricate structured or textured surfaces more precisely and efficiently than the conventional micro-cutting process. Indenters made of single crystalline diamond (SCD) were fabricated by laser fabrication and polishing with diamond abrasives on a cast iron plate. In the experiments, the microarray molds of four-corner cone and semi-sphere shapes were generated precisely on the electroless Ni-P substrate with ultrasonic vibration-assisted indentation using the SCD indenters. From the indentation experiments, it is clear that the microtextured patterns were formed precisely and effectively by using the developed indentation system.     

Investigation on mechanism of metal foil surface finishing with vibration-assisted micro-forging

Vibration-assisted forming is able to reduce forming force and prolong the tools life significantly. Applying vibration-assisted forming in micro-forming is necessary for better form accuracy of micro metal products. In this paper, vibration-assisted micro-forging was proposed for metal foil surface finishing. Different parameters were investigated at different vibration time. It was found that the surface asperity deformation takes place mainly in the initial stage. The surface roughness reduction is closely related to forming work, which is increasing with vibration time. After vibration-assisted micro-forging, the surface roughness could be reduced by 50%.     

A comparative study: polishing characteristics and its mechanisms of three vibration modes in vibration-assisted magnetic abrasive polishing

The automatic precision polishing technique of three-dimensional complicated micro-curved surfaces of components in extremely low surface roughness and high efficiency is greatly demanded by advanced industrial fields. The existing polishing methods have great difficulty in satisfying these demands. Therefore, three modes (horizontal vibration, vertical vibration and compound vibration) of vibration-assisted magnetic abrasive polishing processes have been developed. Previous research focused on each polishing characteristic. The aims of this paper are to characterize effects of vibration of workpiece on magnetic field, polishing pressure, in-process abrasive behavior and polishing performances in three vibration modes and to describe their machining mechanism. Furthermore, a realization of efficient polishing of a 3D micro-curved surface was confirmed to be possible by the process.     

Direct laser assisted machining with a sapphire tool for bulk metallic glass

Bulk metallic glasses (BMGs) are amorphous metallic alloys with high strength and hardness. This paper discusses the machining process of Zr-BMG using a transparent sapphire tool with direct laser assistance. The laser beam passes through the tool and directly heats the workpiece material to improve its machinability. Micro textures were generated on the tool rake face to facilitate chip formation. Reduced cutting forces and improved surface finish were observed with direct laser assistance. The effects of machining speed and laser power on the material deformation mechanism were investigated. A finite element model was developed to investigate the cutting forces.     

Investigation of residual stress by the indentation method with the flat cylindrical indenter

Experiments and numerical simulations have been carried out to study residual stress of copper specimens by the identation method with a flat cylindrical indenter. Copper specimens were annealed at different temperatures for 35 min to obtain different residual stress levels. The experiments carried out on these specimens demonstrated the influence of residual stress on indentation behavior. The influence of annealing temperature on the elastic-plastic transition region is quite obvious. A method has been presented to determine material properties, such as elastic modulus and Poisson ratio. This method can also be applied to determine residual stress with the assumption of knowing the yield stress in advance. The advantage of this method is that it can avoid calculating the contact area. In the finite element modeling (FEM), residual stresses on copper specimens are simulated by preapplying stresses. The influence of residual stress on the indentation load-depth curves has been studied by FEM. There is good agreement between experimental and FEM numerical results. A numerical method has also been presented to determine residual stress. In addition, Mises stress and plastic distribution ahead of the indenter have also been studied to help us further understand the influence of residual stress.     

Plastic deformation of magnesium alloy with different forming parameters during ultrasonic vibration-assisted single-point incremental forming

The research of forming parameters on the ultrasonic vibration single-point incremental forming of magnesium alloy plastic deformation can provide a theoretical basis for the establishment of the forming parameters.According to the forming characteristics of magnesium alloy sheet,a new method of ultrasonic vibration-as sis ted single-point incremental forming was proposed.The influence of forming parameters on the plastic deformation of magnesium alloy was studied by finite element simulation an...     

An investigation on wear mechanism of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire

An investigation is carried out to analyze and quantify the wear mechanisms of resin-bonded diamond wheel in Elliptical Ultrasonic Assisted Grinding (EUAG) of monocrystal sapphire. The EUAG is a new grinding method proposed by the present authors in which an elliptical ultrasonic vibration is imposed on the workpiece by using an elliptical ultrasonic vibrator. In this paper, a series of grinding experiments under the presence/absence of ultrasonic vibration assistance are performed. The grinding forces and work-surface roughness are measured, and the wheel surface is examined too. The experimental results indicate that during grinding, the steady process region performed in EUAG is longer than that in Conventional Grinding (CG) by 20%, meaning that the grinding wheel has a longer sharp cutting period in EUAG. It is validated that the main wear mechanisms in EUAG is micro-fracture and cleavage of abrasive grains, which has a positive effect on the better grinding performance, such as lower grinding forces, force ratio F_n/F_t, wheel loading, and smoother work-surface. This study demonstrates that the improved grinding performance of diamond wheel can be realized by using EUAG method.     

Ultrasonic evaluation of spot welds with a focused probe

Summary

High current density spot welding develops a large electromagnetic force between the electrodes. This electromagnetic force causes fluctuation of the load, which in turn adversely affects the weldability. The load fluctuation varies depending on the loading system stiffness, friction, or response. This paper describes the design of a loading system able to control the electrode movement together with an investigation of its dynamic properties at energising. The load is affected by the electromagnetic force and thermal expansion. The electromagnetic force increases proportionally to the square of the peak current in the opposite direction of loading, which consequently reduces the actual loading of the work. The electrode movement is controlled by a stopper and spring assembled in the loading system. In a rigid loading system with a large spring constant, the electrode movement due to the electromagnetic force is restrained, so that the load is increased by the thermal expansion. On the other hand, in a loading system with a small spring constant, the load is decreased, because the electrode movement due to the electromagnetic force is greater than the thermal expansion.     

FBG超声波焊接封装及其弯曲传感特性

为获得金属层片封装的光纤布拉格光栅（FBG）片状传感头,预先对裸光栅表面化学镀加电镀镍,然后对金属化FBG进行超声波焊6061铝合金薄片封装.采用拉伸试验测试超声波焊接结合强度和金属化FBG的嵌入强度,文中还研究了FBG的光谱特性、温度传感特性和三点弯曲应变传感特性.结果表明,当焊接压力为5.4 MPa,焊接时间为45 ms,镀层厚度为45 μm时,焊接封装效果较好;超声波焊接封装后铝箔的平均撕裂强度可达58.96 N,金属化FBG嵌入铝箔的拉断力可达8.89 N;封装后的FBG仍保持了良好的波形,平均温度灵敏度系数为29.07 pm/℃,平均三点弯曲应变灵敏度系数为0.096 7 pm/με.     

固结磨料研磨蓝宝石晶片的工艺优化

为了满足蓝宝石晶片高效低损伤的加工要求,采用亲水性固结磨料研磨垫研磨蓝宝石晶片的工艺,研究基体中碳化硅粒度尺寸、基体类型、金刚石粒度尺寸及研磨液中磨料4个因素对材料去除率和表面粗糙度的影响,并综合优化获得高加工效率和优表面质量的工艺参数。实验结果表明:基体中碳化硅粒度尺寸为10 μm、基体类型为Ⅱ、研磨垫采用F公司粒度尺寸为35~45 μm的金刚石、研磨液中磨料的粒度尺寸为5 μm的碳化硅为最优工艺组合,亲水性固结磨料研磨蓝宝石的材料去除率为431.2 nm/min,表面粗糙度值为R_a 0.140 2 μm。      

Multi-wire sawing of sapphire crystals with reciprocating motion of electroplated diamond wires

This study examined the multi-wire sawing of C-plane sapphire ingots using diamond wires. Feeding new wire during the reciprocating motion of the wire was found to vary the cutting force, wafer shape, and roughness as a result of the break-in effect. The break-in and wire wear seemed to cause a gradual change in the cutting performance along the ingot position. The cutting force results indicated that an inappropriate supply of wire yielded an unbalanced force between the front and back sides of the ingot, which was caused by a difference in the cutting depth along the ingot. The results showed that controlling the wire consumption resulted in an average flatness of 16 μm, with a maximum value of 26 μm.     

不同球心距对连续挤压异型材成形流动特征的影响

针对异型材形状特殊,引起连续挤压成形不稳定的问题,利用球形卸压的方法,将模具成形平面改为圆弧面。模拟半径为6. 5 mm的球心分别与模具入口表面距离为1. 5、2. 5和3. 5 mm时,横截面球形卸压区域的温度场和速度场,研究了纵截面某一稳态时刻,对称面直角变形区从上向下5个层面的速度和温度;讨论了模具不同球心距定径带处边缘和中间的流速均方差。研究结果表明,当半径为6. 5 mm的球心与模具入口表面距离为2. 5 mm时,坯料在球形卸压区域的温度分布均匀且温度较低,为575℃;坯料纵截面定径带处的速度为30～70 mm·s~(-1),且整体速度的极差最小为0～70 mm·s~(-1);定径带处边缘和中间的流速均方差差值最小为0. 324 mm·s~(-1)。经连续挤压得到的细化晶粒,不仅有利于提高金属强度和塑性,还可提高材料的表面质量。     

Ultrasonic fast identification of automotive body spot weld defect based on echo characteristics qualitative analysis

Abstract

Spot welds are used extensively by automobile manufacturers as an efficient method for joining sheet steel. The quality of them can be tested non-destructively by using ultrasound. But when spot weld defect happens, the current ultrasonic inspection methods of weld quality are difficult to achieve an ideal result especially for the stick weld defect which is one of the most important types of spot weld defects in the automotive body. At first, this paper detailedly analyses the echo characteristics of ultrasonic curves which can reflect different spot welding joint defects. After echo characteristics qualitative analysis of different spot weld defects, a peak value marking algorithm is developed to identify the joint defects especially the stick weld defect rapidly and efficiently through selecting and confirming many optimal characteristic parameters. Finally, a lot of experiments are performed to verify the proposed methods. The results indicate that this fast identification method is credible and the identification rate can reach 95% in total test samples.     

Ultrasonic evaluation of TiAl and 40Cr diffusion bonding quality based on time-scale characteristics extraction

To solve the problem of ultrasonic pulse-echo method in the evaluation of kissing bond and unbond in TiAl and ⁴⁰Cr diffusion bonding, a characteristics extraction algorithm was proposed. The algorithm was based on continuous wavelet transform to convert ultrasonic TiAl and ⁴⁰Cr diffusion bonding interface signals into time-scale domain. The ultrasonic tests were performed by an ultrasonic C-scan imaging system using a 10 MHz focused transducer. The time-scale amplitude and phase of the interface signals were calculated and analyzed to distinguish the kissing bond and the unbond from the perfectly bonded interface. The kissing bond can be detected by the scale-dependent amplitude combined with phase variation and the unbond can be measured by the opposite phase. The amplitude and phase characteristics were extracted to reconstruct the amplitude and phase characteristics images for TiAl and ⁴⁰Cr diffusion bonding specimens evaluation. The amplitude and phase characteristics images are effective in the evaluation of bonding quality.     

焊缝超声相控阵扇形扫查的覆盖范围

介绍用超声波相控阵对焊接接头作编码线扫查时,以声线示踪表示声束覆盖范围的建模原理。模拟了多种壁厚的多种焊接结构,包括V型坡口单面焊、X型坡口双面焊和T型接头组合焊等。对壁厚在10mm以下的薄壁对接焊缝,单次扇形（S）扫查,声束即能覆盖整个被检焊缝;但对中厚壁和厚壁焊缝以及更为复杂的结构,则需要作多次扇形扫查。因焊接结构很多,相控阵UT并无单一定规,这里给出一些建模施探导则。     

Ultrasonic cutting with simultaneous welding of plastic components

A method of ultrasonic cutting with simultaneous welding of plastic components is described. It is shown that filter components can be produced by ultrasonic cutting with simultaneous welding.