超声滚压装置设计及试验研究

设计了一种新的超声滚压装置,并利用该装置研究了超声滚压加工对18CrNiMo7-6齿轮钢表面性能的影响。首先对滚压装置进行了结构设计,应用ANSYS Workbench对装置进行了模态分析和谐响应分析,通过调整滚压装置结构,使该装置能够正常高效地工作;然后综合利用NPFLEX型三维表面形貌测量系统、Proto高速大功率X射线残余应力分析仪、HV-1000型显微硬度计及VHX-2000E型超景深三维显微系统观察分析了超声滚压加工前后试样的表面粗糙度、表面二维形貌、表层显微硬度及残余应力。经超声滚压加工后试样的表面粗糙度从3.003μm降低至0.419μm,最大残余压应力出现在距离表面80μm处,大小约为-672.04MPa,高硬度层达到了200μm。结果表明,利用该装置能够有效的改善材料的表面性能。     

不同加工工艺对EA4T车轴表面性能的影响

对车削加工后的EA4T车轴进行打磨、滚压和超声滚压等工艺的表面强化处理,测量了经过不同工艺处理后车轴圆弧处的表面粗糙度、表面残余应力和表层硬度,对比观察了不同工艺处理后车轴的表面形貌和表层微观组织。结果表明:超声滚压处理的车轴圆弧表面光洁度最好,粗糙度值低至0.074μm;车轴圆弧处车削加工后表面轴向和周向残余应力都为拉应力,经过打磨、滚压和超声滚压处理后都转变为压应力,超声滚压处理后轴向残余压应力达到-770MPa;超声滚压处理车轴的表面硬度值最大,硬化层深度也最深;超声滚压处理后车轴表层微观组织最均匀,且细晶层的厚度最大。     

表面滚压处理对EA4T车轴钢疲劳性能的影响

表面强化可提高高速列车车轴疲劳性能，延长使用寿命。对广泛应用于高速列车的EA4T车轴钢表面进行滚压处理，使用激光共聚焦显微镜表征表面形貌和粗糙度；借助光学显微镜分析滚压处理前后试样的显微组织，并采用EBSD测试滚压试样表层晶粒尺寸；采用显微硬度计测试强化层显微硬度分布并与未处理试样进行对比，采用X射线衍射残余应力分析仪分析其残余应力分布；基于旋转弯曲疲劳试验和扫描电子显微镜下的断口观测分析试样的疲劳性能。研究结果显示：滚压强化后，试样表层发生塑性变形，表面质量得到改善，且形成厚度约为400μm的硬化层，表层产生纳米晶；显微硬度提高了29%,表面最大残余应力为-576MPa,试样显微硬度和残余应力变化趋势一致，均为从表面向心部减小；滚压试样疲劳强度增幅为28%。试验结果表明，滚压是车轴延长寿命的一种有效方式。     

超声滚压载荷对25CrMo4车轴钢表面强化特征的影响规律

为了提高列车车轴的使用寿命,研究分析了不同强化处理后试样的表面形貌及其粗糙度、表层组织结构、表面硬度及其深度和表面残余应力,探索了滚压处理和不同载荷超声滚压处理对25CrMo4车轴钢表面强化特征的影响规律。结果表明：与磨削试样相比,滚压和超声滚压处理均改善了试样的表面粗糙度,其中低载荷超声滚压试样的表面粗糙度最低,达到了0.2μm;高载荷超声滚压试样的表层获得的塑性变形层最深;高载荷超声滚压试样的表面硬度值最大,达到了370 HV0.1,并形成了深度为150μm左右的硬化层;滚压试样和超声滚压试样表面均产生了较高的残余压应力。滚压和超声滚压处理使25CrMo4车轴钢表面硬度及硬化层深度的增加、产生较高的残余压应力和表面粗糙度的降低均会对其疲劳性能的提高产生有利的影响,特别是超声滚压处理的效果更佳。但过高的载荷会使车轴钢的表面粗糙度升高,从而对其疲劳性能的提高产生不利的影响。     

纵-扭复合振动超声深滚加工残余应力场数值分析

为研究平面试件在纵-扭复合振动超声深滚加工后材料应力分布及变化规律,采用有限元方法对Q345钢进行了纵-扭复合振动超声深滚加工残余应力场数值模拟。首先分析了加工后试件材料各应力分量沿深度方向的分布情况,然后研究了静压力、滚压速度、振幅和相位差对加工后材料残余应力的影响规律。结果表明:经纵-扭复合振动超声深滚加工后材料表层残余应力分布较均匀,表面为压应力,压应力沿试件深度方向先增后减;试件最大残余压应力及最大横向残余压应力深度和残余压应力层深度随静压力的增大而增大,随滚压速度的增大而减小,而表面残余压应力和最大纵向残余压应力深度无显著变化;试件横向残余压应力层深度随振幅的增加小幅度地增大,但最大残余压应力幅值和深度和纵向残余压应力层深度几无变化;相位差对残余应力影响可忽略不计。     

AZ31B镁合金超声滚压表层力学性能的纳米压痕测试

超声滚压可以使镁合金表面纳米化,从而影响表层的力学性能。研究多道次超声滚压AZ31B镁合金表层力学性能,可以为镁合金超声滚压仿真分析提供依据。本文通过车削和多道次超声滚压对AZ31B镁合金棒进行表面处理,采用白光干涉ZeGageTM Plus光学轮廓仪对车削和超声滚压后试样的表面形貌进行观测,通过纳米压痕仪测定试样表层的纳米硬度和弹性模量,并获得载荷-位移曲线。结果表明,经3道次超声滚压加工后,AZ31B镁合金表面粗糙度由车削后的0.568um降低至0.192um,下降了66.2%;相同的加载方式下,越接近超声滚压表面,纳米压痕深度越浅;在距离表面300μm深度内,纳米硬度得到明显提升,且越接近超声滚压表面,纳米硬度越大;在距离表面200μm深度内,弹性模量明显增大,说明3道次超声滚压对AZ31B镁合金表层纳米力学性能的显著影响层深度达到200μm。多道次超声滚压提高了材料表层的纳米硬度和弹性模量,起到了表面强化的作用。     

GCr15SiMn轴承钢表面超声滚压处理改性分析

使用HK30数控车床对GCr15SiMn轴承钢进行表面超声滚压处理,利用金相显微镜和扫描电镜观察试样超声滚压前后表面形貌和截面组织,并对比分析了超声滚压处理前后试样的硬度、表面粗糙度和残余应力。研究结果表明:超声滚压处理后,试样表面显微组织发生明显的塑性变形,形成约1μm的塑性变形层;试样平均表面粗糙度Ra值降低,表面更加平整,表面硬度和表面残余压应力升高;超声滚压处理改变了表面压应力的分布规律,即试样的残余压应力最大值都不在表面,而在次表面,残余压应力作用层由100μm增加至700μm。     

超声滚压处理提高30CrNiMo8钢疲劳性能可行性的研究

为了提高机车牵引电机轴的疲劳性能,对30CrNiMo8电机轴用钢进行了超声滚压强化处理。采用金相组织和表面形貌观察、表层硬度和残余应力以及疲劳极限测试等实验手段研究了精车加工试样分别经磨削和超声滚压处理后的表层组织、表面粗糙度、硬度和残余应力以及疲劳性能的变化规律。结果表明,超声滚压后试样表层产生了约300μm厚的变形层,距表面越近塑性变形程度越大,并在最表面产生了2～3μm厚的白亮层。与磨削处理相比,经超声滚压处理后试样的表面粗糙度Ra由精车的1. 886μm减小到1. 303μm,与磨削的1. 404μm相当;而表面硬度由350 HV增加到446HV,且随着距表面的距离增加而逐渐减小,其硬化层厚度约为300μm;而表层残余压应力由-249MPa大幅度提高到-838 MPa。超声滚压试样的疲劳极限比磨削试样的提高了约为33. 5%。此外,根据表面的粗糙度值,可以用超声滚压替代磨削这一工序。     

GH4169高速车削参数对加工表面完整性影响研究

使用PVD-TiAlN涂层硬质合金刀片进行高温合金GH4169的高速车削正交试验,建立了表面完整性特征中表面粗糙度、表面残余应力、显微硬度的经验公式,分析了车削参数对表面完整性各特征量的影响规律,并观测了高速车削加工的表面形貌。结果表明:表面粗糙度随车削速度的增加而减小,随进给量和切削深度的增加而增大,进给量是影响表面粗糙度的最主要因素;随着进给量的增加,表面形貌变差;轴向残余应力表现为压应力,切向残余应力表现为拉应力,减小进给量,降低车削速度可减小车削加工的残余应力,轴向残余应力对进给量最敏感,切向残余应力对切削深度最敏感;显微硬度随车削速度的增大而增加,车削速度是影响显微硬度的主要因素。     

深冷处理对PCBN刀具切削性能的影响研究

针对PCBN刀具在硬切削加工中磨损严重、切削寿命短的问题,开展了PCBN刀具深冷处理试验和经深冷处理的PCBN刀具高速硬车削AISI 4340钢的试验,研究深冷处理对PCBN刀具表面完整性（包括微观形貌、粗糙度、显微硬度和残余应力）及切削性能的影响规律,探究提高PCBN刀具耐磨性和刀具寿命的方法。研究结果表明,经过深冷处理之后,刀具表面缩松缩孔等缺陷明显减少甚至消失,表面形貌得到改善,但刀具表面粗糙度增大;刀具表面显微硬度、残余应力均得到提高;表面形貌和表面残余应力对刀具寿命影响较大,其次是表面显微硬度,表面粗糙度对刀具寿命影响较小。深冷处理后,刀具黏结、氧化磨损减少,刀具寿命较未处理刀具提高24.78%,可见,深冷处理可有效改善PCBN刀具表面完整性,从而提高刀具寿命。     

Influence of thermal mechanical coupling on surface integrity in disc milling grooving of titanium alloy

Disc milling strategy has been applied in grooving for decades for its capacity to provide huge milling force on the difficult-to-cut material. The processing efficiency of machined components thus can be tremendously improved with the application of disc milling. However, the fundamental research of the mechanisms of disc milling on cutting metal materials, especially on titanium alloys, is lacking in the literature. In this study, the milling force and temperature were inspected in disc milling grooving experiment, and the effect of thermal-mechanical coupling on surface integrity of titanium alloy, including surface roughness, surface topography, surface and subsurface residual stress, microstructure, and microhardness, was analyzed. The results showed that a better surface quality can be obtained at the center of the surfaces compared to the marginal regions on the same machined surface. Residual compressive stress was generated on the machined surface and subsurface and gradually reduced to zero with an increase in depth. The microstructure of lattice tensile deformation was emerged along feed direction, while the phase transition was not produced. A hardened layer was found on the machined surface and subsurface, mostly causing by the mechanical loads and oxidation reaction.     

车削参数和滚挤压参数对滚轮滚挤压表面质量影响分析

滚挤压是一种金属表面微塑性连续变形精加工工艺,现在日益被用作切削加工后的表面强化终处理工艺以获得具有压缩残余应力的高性能低粗糙度的镜面零件表面。本文分析了车削前处理工艺对后续滚挤压加工效果的影响,采用考虑交互作用的L27(313)正交试验设计与分析方法研究了车削滚挤压复合工艺中车削三要素(即车削速度v、车削进给量f、车削深度ap)和滚挤压三要素(即滚挤压速度vb、滚挤压进给量fb、滚挤压深度ab)对滚轮滚挤压45号钢的滚挤压效果(即表面粗糙度Ra、小负荷维氏硬度Hv的影响规律),其中考虑了对滚挤压效果影响最显著的车削进给量f、滚挤压深度ab与滚挤压进给量fb两两之间的交互作用,分析得出了对滚挤压效果影响最显著的主要因素及其规律。从试验的角度发现车削进给量对滚挤压效果有显著影响,与理论分析和预测相吻合。     

Developing and investigating of elastic ball burnishing tool

Burnishing, a plastic deformation process, is becoming more popular in satisfying the increasing demands of machine component performance and reliability. Thus, investigating the burnishing parameters in order to improve the product quality is especially crucial. The objective of this research is to evaluate the effect of different burnishing conditions on surface microhardness, surface roughness, and form accuracy. Orthogonal central composite experiment design was used to select the input parameters making them into the right order. Optimum burnishing parameters were established to minimize roughness and/or maximize surface hardening. Emperical formulas were developed to predict the surface microhardness and roughness of leaded brass obtained by burnishing under lubricated conditions.     

EXPERIMENTAL INVESTIGATION ON SURFACE INTEGRITY OF END MILLING NICKEL-BASED ALLOY— INCONEL 718

Inconel 718 is a typical difficult-to-machine material, and its high speed end milling process has wide applications in manufacturing parts from aerospace and power industry. Surface integrity of these parts greatly influences the final characteristics. This paper presents an experimental investigation to evaluate surface integrity behaviors in high speed end milling of Inconel 718 with finishing cutting parameters in terms of surface topography, surface roughness Ra, residual stresses, subsurface microstructure, and microhardness. The results show that abraded marks can be observed on the machined surfaces, and high cutting speed is advisable to get better surface topography and roughness quality. Due to high cutting temperature, residual stress is mainly high tensile stress. After increasing the cutting speed beyond 80m/min, the cutting forces hardly increased and the chips take away more cutting heat, which leads to that the residual stress barely increases. Microstructures in subsurface layers have only slight deformations after high speed milling, and there was also no obvious difference when the cutting speed increased beyond 80m/min against the microhardness in subsurface increases together with the cutting speed.     

Prediction of surface characteristics obtained by burnishing

To reduce the irregularities of machined surface, burnishing is used as a finishing process by plastic deformation. This process does not only improve surface finish but also generates compressive residual stresses throughout the surface. In this work, an analytical study and a finite element modelling were performed to provide a fundamental understanding of the burnishing on an AISI 1042 workpiece. The analytical results were concentrated on the surface roughness and on some burnishing parameter effects. The simulations were devoted to the study of the surface profile, the residual stresses and the influence of burnishing parameters (penetration depth, feed rates, diameter of the ball of burnishing tool and initial surface quality) on surface roughness and the residual stress distribution. It has been noted that burnishing improves surface quality and introduces compressive residual stresses. These results were successfully compared to experimental data obtained in previous works.     

Investigations on surface integrity of AISI 1045 using LPB tool

Low plasticity burnishing (LPB) is relatively a new method of surface enhancement, which raises the burnishing to the next level of sophistication. LPB can provide deep stable surface compression for improved surface integrity characteristics. The present study focuses on the surface roughness, microhardness, surface integrity and fatigue life aspects of AISI 1045 work material, using full factorial design of experiments. The assessment of the surface integrity aspects on work material was done, in terms of evaluating the interaction effects of parameters, identifying the predominant factor amongst the selected parameters, their order of significance and setting the levels of the factors for minimizing surface roughness and/or maximizing surface hardness and fatigue life. Mathematical expressions were developed for surface characteristics of importance as response variables. Subsurface microhardness studies were also done to assess the depth of compression, altered material zone and correlate fatigue life with surface roughness and surface hardness. The process can be applied to critical components effectively, as the LPB process today has significant process cycle time advantages, and lower capital cost. Additional cost reduction will be realized by introducing proven high speed machining concepts into the LPB process.     

Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a_p increases enough to cause grinding burn, the strengthening effect of particles ?′ in ? base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

AlTiN涂层刀具精铣TC4钛合金工艺参数的影响与优化

采用AlTiN涂层4刃?10 mm硬质合金立铣刀,在VMC850立式加工中心上对TC4钛合金进行铣削精加工试验。利用高精密数字化检测设备,对加工成形的TC4钛合金试件表面粗糙度、平面度、平行度、表面形貌、残余应力及显微硬度测量。分析AlTiN涂层刀具在设定不同工艺参数条件下TC4钛合金的整体加工质量和表面形貌变化规律。结果表明:在主轴转速n=8000 r/min、每齿进给量f z=0.04 mm/z、切削深度Δd=0.5 mm的最优精铣工艺参数下,TC4钛合金工件的加工质量和表面形貌好,刀具寿命长,其平面度为0.39μm,平行度为0.33μm,表面粗糙度为0.70μm,表面残余应力为-175 MPa,表面显微硬度为269 HV 0.2,实现了TC4钛合金的高质量高效率的精铣加工。     

THE EFFECT OF DIAMOND PRESSING AND ROLLER BURNISHING OF UNHEAT TREATED CARBON STEEL SURFACES

Diamond pressing (DP) and roller burnishing (RB) processes are surface plastic deformation methods used to improve surface quality (microhardness and surface roughness). In the present work DP and RB tools with a special holder were used to study the effect of DP and RB on the surface texture of three different carbon steels (low, medium, and high) and to compare the both methods. The results show that the RB in the case of low carbon steel is better than the DP in terms of its effect on the microhardness and surface roughness, but in the case of the medium and high carbon steel the results depicts that the DP is better than RB in terms of its effect on the microhardness, but the RB is better than DP in terms of its effect on the surface roughness. As a result of this study it was found that DP and RB have a great effect on surface texture and RB was found to be better in surface roughness, but DP has better results in surface microhardness relative to ground surfaces. Also in this paper micrographs of the processed surfaces of low, medium and high carbon steel are given and it is shown that the depth of plastic deformed surfaces by diamond pressing was about (330, 345, 390) µm and by roller burnishing about (270, 245, 230) µm for the three steels, respectively.