组合型微织构化铝合金表面的摩擦学性能研究

为改善铝合金的摩擦学性能,运用有限元方法对单一方形凹坑、条形凹槽、方形凹坑和条形凹槽组合3种不同形貌织构摩擦副间润滑油膜承载能力进行仿真分析,并探究不同织构尺寸对油膜承载能力的影响。仿真结果表明：方形凹坑和条形凹槽组合织构润滑油膜承载能力最佳。采用脉冲Nd:YAG激光器在铝合金试件表面加工出具有规则形貌的方形凹坑和条形凹槽组合的织构阵列,借助CFT-I型高速往复摩擦磨损试验机进行摩擦试验,研究织构几何尺寸对摩擦副接触面间摩擦学性能的影响规律,并利用超景深显微系统对试件磨损表面的形貌进行观测。试验结果表明：组合织构化表面的平均摩擦因数与无织构表面相比明显减小,且波动幅度较小;当织构尺寸为80μm时,织构表面的摩擦因数最小,且试验得到的基体表面磨痕深度随织构尺寸的变化规律,与仿真计算得到的润滑油膜升力系数的变化规律相吻合,为微织构参数设计提供了一定的理论依据。     

粗糙度对微凹坑织构化表面摩擦学性能的影响

为了研究表面初始粗糙度和微凹坑织构共存时的表面摩擦性能,采用激光微织构加工技术在不同粗糙度的试样表面上加工出不同几何形貌的微凹坑织构,在MMW-1A摩擦试验机上进行正交摩擦学性能试验。结果表明:在混合润滑区域,表面粗糙度对摩擦性能的影响最为明显,未织构表面越粗糙,摩擦因数越小;存在合适的微凹坑几何参数与表面初始粗糙度值组合,使得织构化粗糙表面的摩擦性能达到最优;表面初始粗糙度对织构化粗糙表面摩擦性能的影响最为重要,其次为微凹坑的面积占有率,最后为凹坑深度,并且织构几何参数与粗糙度之间的交互作用对摩擦性能的影响也是不能忽视的。     

微织构车刀椭圆超声辅助切削加工性能研究

为了进一步改善切削性能,将微织构刀具应用于椭圆超声辅助切削过程中,分析其对切削力、刀具磨损及表面质量的影响,然后分析刀具表面微织构角度与尺寸对刀具磨损的影响规律。研究结果表明：微织构刀具可以在保留椭圆超声辅助切削优异性能的基础上进一步改善切削性能,而且根据实验结果,微织构角度与尺寸变化会影响刀具抗磨损效果,当微织构与主切削刃平行、宽度为70μm、间距为70μm时,刀具黏结磨损最小。     

织构化表面空化效应影响润滑性能的CFD分析

考虑织构化表面润滑介质流场的空化效应,建立具有不同截面微结构特征的有限元计算模型,利用Fluent14.0软件进行计算,研究表面织构几何形状及尺寸对流体润滑性能的影响。结果表明:考虑惯性项作用时,表面微织构会产生额外的承载力,而且随着速度提高,承载力会进一步增大;考虑空化效应时,承载能力增大近一个数量级,更符合文献中的试验结果;与三角形、矩形及椭圆织构截面相比,球缺截面的织构空化面积更小,更有利于提高承载;微结构深度和宽度尺寸影响摩擦和承载性能,研究表明,减小织构深度、增大织构宽度有利于改善润滑性能。     

表面凹槽织构微机械加工及其摩擦学性能研究

作为新兴的表面改性技术,表面织构化可以有效减少摩擦,在摩擦表面应用较为广泛.本文介绍了0Crl7Ni7Al表面织构微机械加工技术,研究了相同载荷及转速工况条件下的光滑表面与凹槽织构表面在摩擦过程中的摩擦性能及磨损机理.研究发现,精雕JDGR200T高速加工中心可以加工0.8mm宽度0Cr17Ni7Al表面凹槽织构,且凹槽槽底圆滑平整,光滑表面的摩擦系数高于凹槽织构表面,但二者的磨损量差别不大.     

微凹槽织构化表面在往复运动条件下的摩擦学特性

采用自主研制的激光微织构加工设备在45#钢试样表面制备出具有不同间距和夹角的微凹槽织构,在UMT-Ⅱ摩擦试验机上进行往复运动摩擦学性能试验。结果发现:在富油润滑条件下,当载荷较低、速度较大时,微凹槽织构具有较好的润滑减摩效果,织构面的平均摩擦因数最大比未织构面下降超过60%;凹槽夹角对摩擦因数的影响受载荷大小的影响,在给定的在载荷下,存在最优的夹角使摩擦因数最小;在其他几何参数相同的情况下,存在最优的槽间距使得平均摩擦因数达到最小,且最优的槽间距基本不受载荷大小的影响。     

计入粗糙度的液压缸仿生微织构耦合效应研究

在间隙密封液压缸缸筒的内表面构造仿生菱形微织构,研究计入液压缸摩擦副表面粗糙度与表面微织构对液压缸缸筒内表面摩擦润滑性能的耦合影响。利用等效流量法求解表面微织构与表面粗糙度的耦合效应,同时以液压缸常用材料45钢为试件开展摩擦学试验,并对试验结果和仿真结果进行比较。研究结果表明:液压缸摩擦副的表面粗糙度与表面微织构耦合作用非常明显,合适的表面粗糙度和表面微织构尺寸,可使液压缸缸筒内表面从混合润滑状态转变为流体润滑状态,从而增大缸筒内表面的动压润滑效应;缸筒内表面的菱形微织构形貌存在最优组合,使得液压缸缸筒内表面的摩擦因数最小、润滑性能最好。     

45号 钢表面微凹槽织构激光加工工艺

为优化激光表面织构技术加工微凹槽的工艺参数,采用声光调Q二极管泵浦Nd:YAG激光器在45#钢表面开展工艺试验研究。通过WKYO NT1100三维形貌测量仪获得织构形貌,应用单因素法分析泵浦电流、脉冲重复频率、扫描速度工艺参数对织构形貌的影响。结果表明,随着泵浦电流的增加,微凹槽织构的宽度和深度均随之增大;随着重复频率的增加,微凹槽织构的宽度逐渐变小,而深度先变大后变小;随着扫描速度的增加,微凹槽织构的宽度逐渐增大,而深度逐渐减小。通过对上述参数的优化可以获得较为理想的微凹槽形貌,较佳工艺参数范围为：泵浦电流15～17 A,重复频率1 500～2 500 Hz,扫描速度10～20 mm/s。     

摩擦副表面气膜屏蔽微细电解加工微织构及摩擦性能分析

采用气膜屏蔽微细电解加工方法在金属平面副、圆柱副表面加工不同阵列形貌微织构。通过试验将该方法与微细电解加工的微织构尺寸精度、表面质量、摩擦性能进行对比，研究结果表明，气膜屏蔽微细电解加工的微织构相比微细电解加工方法加工的微织构平面副及圆柱副凹槽深径比分别提高了约45.6%和25.8%，改善了加工的定域性，提高了加工精度。进一步的摩擦磨损试验结果表明，相较于微细电解加工方法，气膜屏蔽微细电解加工出的平面副及圆柱副微凹槽的表面摩擦因数分别减小了13.6%与16.2%，表面摩擦性能得到了提高。     

刀具表面微织构激光加工方法研究与分析

在刀具的表面加工微织构,可显著提升刀具的切削性能,大幅提高刀具耐用度并延长刀具的使用寿命。本文利用脉冲激光在硬质合金(WC-Co,YG8)刀具的表面加工微织构,重点对激光功率、频率、脉冲个数和光斑直径对微坑织构的尺寸、形貌以及激光加工中产生微裂纹的影响进行了系列试验研究。采用波长λ=1064nm、激光功率W=90W、频率f=20Hz、脉冲个数n=20、光斑直径d=500μm的激光参数,在硬质合金刀片300℃预热处理后,用带有4个档位的超声振动辅助手段在刀具表面加工微坑织构。并选用原始激光加工后的硬质合金片和热处理超声振动辅助激光加工后的硬质合金刀片进行比较,试验结果表明,当刀具采用预热处理后,辅以超声振动进行激光加工的方法对控制刀具表面织构尺寸精度、刀具表面形貌的均一稳定和抑制表面微裂纹的产生具有重要意义。     

镍基高温合金珩磨表面粗糙度研究

为探索镍基高温合金的珩磨加工性,进而实现镍基高温合金精密孔的高效加工,进行了GH4169定量进给珩磨试验,并对珩磨加工表面粗糙度进行了分析。结果表明：油石平均粒径及每往复进给量是影响珩磨表面粗糙度的显著因素（置信水平分别为99.5%及95%）,切向珩磨速度、轴向往复速度对珩磨表面粗糙度的影响不显著;减小油石平均粒径与每往复进给量后,单颗磨粒的平均切厚、珩磨表面粗糙度和工件表面的划痕沟槽宽度减小。     

硬质合金刀具车削Cr12Mn5Ni4Mo3Al不锈钢的试验研究

使用硬质合金刀具YW2进行Cr12Mn5Ni4Mo3Al不锈钢的干车削试验。分析了切削速度对车削力及表面粗糙度的影响,并采用扫描电子显微镜(SEM)观察刀具的磨损形貌。研究结果表明:使用硬质合金刀具YW2干车削Cr12Mn5Ni4Mo3Al不锈钢时,在小进给量和小背吃刀量切削的条件下,车削三向力的大小顺序为:径向力轴向力切向力;受积屑瘤的影响,表面粗糙度呈现出随车削速度的变化先减小后增大的变化趋势;硬质合金刀具后刀面磨损较轻微,而沿刀尖周围出现了较严重的粘结现象,前刀面上出现了较严重的划痕现象,低速时,前刀面还出现了贝壳状的剥落现象。     

A Study on the Mechanism of Generating Wear Track Grooves

The mechanism of generating wear track grooves on metallic materials was investigated to elucidate the cause of similar wear track appearance based on pin-on-disk wear test results. As previously shown, most wear tracks on metallic materials appear similar in appearance irrespective of test conditions and materials. This phenomenon is attributed to the similar scales of prominent grooves in wear tracks, as wear tracks have common characteristic groove sizes in terms of width and depth. The ploughing by transfer particles adhering to counter surface initially generates these grooves, which become larger along with the growth of transfer particles. Pin-on-disk wear tests revealed that transfer particles adhering to the pin surface stopped growing at a certain size upon being enclosed by ridges forming along the sides of grooves on the disk and penetrating the pin surface. This final transfer particle size determines the characteristic scales of wear track grooves. We supposed that this enclosure by ridges terminated particle growth. Based on this supposition, the formation of ridges had a key effect on determining the sizes of grooves. Ridges form when the grooves grow to a certain size; thus, characteristic grooves could be expected to be a bit larger than this size. Therefore, these processes generate the characteristic scales of wear track grooves which lead to similar wear track appearance.     

Experimental investigation of surface roughness and cutting ratio in a spraying cryogenic turning process

Abstract

Surface roughness is one of the most common criteria indicating the surface finish of the part, which depends on various factors including cutting parameters, geometry of the tool, and cutting fluid. One of the goals of using cutting fluids in machining processes is to achieve improved surface finish. In addition to high costs, commonly used cutting fluids cause dermal and respiratory problems to the operators as well as environmental pollution. The present article aims at investigating the effect of spray cryogenic cooling via liquid nitrogen on surface roughness and cutting ratio in turning process of AISI 304 stainless steel. Through conducting experimental tests, the effects of cutting speed, feed rate, and depth of cut on surface roughness and cutting ratio have been compared in dry and cryogenic turning. A total number of 72 tests have been carried out. Results show that cryogenic turning of AISI 304 stainless steel reduces surface roughness 1%–27% (13% on the average), compared to dry turning. The obtained results showed that the cutting ratio in cryogenic turning is averagely increased by 32% in comparison with dry turning, also that chip breakage is improved in cryogenic turning.     

The use of D-optimal design for modeling and analyzing the vibration and surface roughness in the precision turning with a diamond cutting tool

Using a diamond cutting tool in the precision turning process, the vibration of tool-tip has an undesirable effect on the machined surface??s quality. The objective of this paper is to present the mathematical models for modeling and analyzing the vibration and surface roughness in the precision turning with a diamond cutting tool. Machining parameters including the spindle speed, feed rate and cutting depth were chosen as numerical factor, and the status of lubrication was regarded as the categorical factor. An experimental plan of a four-factor??s (three numerical plus one categorical) D-optimal design based on the response surface methodology was employed to carry out the experimental study. A micro-cutting test is conducted to visualize the effect of vibration of tool-tip on the performance of surface roughness. With the experimental values up to a 95% confidence interval, it is fairly well for the experimental results to present the mathematical models of the vibration and surface roughness. Results show that the spindle speed and the feed rate have the greatest influence on the longitudinal vibration amplitude, and the feed rate and the cutting depth play major roles for the transverse vibration amplitude. As the spindle speed increases, the overall vibration of tool-tip tends to more stable condition which leads to the results of the best machined surface. The effects of the feed rate and cutting depth provide the reinforcement on the overall vibration to cause the unstability of cutting process and exhibit the result of the worst machined surface.     

单点金刚石切削加工表面粗糙度的影响因素分析

本文研究了单点金刚石切削加工表面微观形貌形成机理,建立了圆弧刃金刚石刀具超精密加工表面微观形貌的理论模型,重点分析了主轴转速、进给量、刀尖圆弧半径和振动等因素对超精密加工表面粗糙度的影响。     

超声波振动精密切削GFRP的实验研究

为改善玻璃纤维增强塑料(Glass Fibre Reinforced Plastics)的切削加工性,提高加工精度和质量,采用超声波振动切削的方式对GFRP进行了精密切削加工.介绍了超声波振动切削的特性和GFRP的纤维束与切削速度方向的相位参数,相位参数沿圆周方向成周期性变化,变化周期为π.通过实验获得了不同切削条件下表面粗糙度的变化规律,粗糙度随相位角变化基本呈正弦规律,但在45°时粗糙度最大.振幅增大导致粗糙度明显下降.切削速度对粗糙度的变化曲线呈极值状态,在速度为100 m/min时粗糙度最小.进给量小于0.06 mm时,粗糙度呈下降趋势;大于0.06 mm时,粗糙度增加较快;而大于0.09 mm后粗糙度上升趋缓.切削深度对粗糙度的影响呈单调上升趋势.实验结果表明超声波振动切削可以使GFRP的加工表面粗糙度减少1倍,使加工质量得以提高.     

A multi-spectrum analysis of surface roughness formation in ultra-precision machining

The formation of surface roughness in ultra-precision diamond turning is investigated using a multi-spectrum analysis method. The features on a diamond turned surface are extracted and analyzed by the spectrum analysis of its surface roughness profiles measured at a finite number of radial sections of the turned surface. It is found that the tool feed rate, the spindle rotational speed, the tool geometry, the material properties, as well as the relative tool-work vibration are not the only dominant components contributing to the generation of surface roughness. The material induced vibration caused by the variation of material crystallography is another major factor. The vibration causes a significant variation of the frequency of the surface modulation of the machined surface. With the use of the multi-spectrum analysis method, it is possible to conjecture the patterns of this vibration as well as to evaluate the properties of the workpiece materials.     

Image processing for chatter identification in machining processes

Identifying chatter or intensive self-excited relative tool–workpiece vibration is one of the main challenges in the realization of automatic machining processes. Chatter is undesirable because it causes poor surface finish and machining accuracy, as well as reducing tool life. The identification of chatter is performed by evaluating the surface roughness of a turned workpiece undergoing chatter and chatter-free processes. In this paper, an image-processing approach for the identification of chatter vibration in a turning process was investigated. Chatter is identified by first establishing the correlation between the surface roughness and the level of vibration or chatter in the turning process. Images from chatter-free and chatter-rich turning processes are analyzed. Several quantification parameters are utilized to differentiate between chatter and chatter-free processes. The arithmetic average of gray level G _a is computed. Intensity histograms are constructed and then the variance, mean, and optical roughness parameter of the intensity distributions are calculated. The surface texture analysis is carried out on the images using a second-order histogram or co-occurrence matrix of the images. Analysis is performed to investigate the ability of each technique to differentiate between a chatter-rich and a chatter-free process. Finally, a machine vision system is proposed to identify the presence of chatter vibration in a turning process.     

Elliptical vibration cutting of hardened die steel with coated carbide tools

Elliptical vibration cutting of hardened die steel with coated carbide tools is examined in this research in order to achieve low-cost high-precision machining. Diamond coated tools are applied because of superior hardness of their polycrystalline diamond coating and its low manufacturing cost. TiN coated tools are also tested, since they are widely used for conventional machining of steels. Machinability of hardened die steel by the elliptical vibration cutting with coated carbide tools is discussed in three aspects in this study, i.e. transferability of cutting edge profile to cut surface, cutting force, and tool life. The transferability is evaluated quantitatively by calculating correlation coefficients of measured roughness profiles. It is clarified that the diamond coated tools have high transferability which leads to diffraction of light on the surface machined at micro-scale pick feed. Total cutting forces including ploughing components are measured at various feed rates, and then shearing components and ploughing components are separated utilizing linear regression. The measured results indicate, for example, that the all forces become considerably smaller only when elliptical vibration is applied to the TiN coated tool without cutting fluid. It is also found that this considerable reduction of forces interestingly corresponds to higher friction coefficient, which is identified from the ploughing components. Tool life tests are carried out by various machining methods, i.e. elliptical vibration/ordinary wet/dry cutting with diamond/TiN coated tools. The result shows, for example, that the flank wear is smallest in the wet elliptical vibration cutting with the diamond coated tool.