干式切削20Cr表面粗糙度和残余应力研究

针对低渗碳钢20Cr材料制作齿轮轴等零件表面质量要求,如表面粗糙度低于1.6μm,零件表面耐疲劳性能良好。试验采用干式切削20Cr钢材方式,在背吃刀量固定的工序中,研究切削速度和进给量对20Cr材料表面粗糙度的影响,同时结合有限元技术,分析切削速度和进给量对20Cr表面残余应力的影响。干式切削试验采用单因素方法,进行多组干式切削20Cr工件,对比分析各组工件表面粗糙度,结果表明当进给量较小时,切削速度对工件表面粗糙度有显著影响,表现为表面粗糙度随切削速度增加而变大;当切削速度一定时,进给量增加导致表面粗糙度变大,并且进给量对表面粗糙度的影响大于切削速度;对于工件表面残余应力,增加切削速度和进给量均导致残余应力变大,因而较小的切削速度和进给量可以降低工件表面残余应力,改善应力分布状态。     

钛合金切削表面残余应力影响因素及参数优化

钛合金切削过程具有温度高、摩擦力大、刀具严重磨损等缺点。为了减少钛合金表面出现微小裂纹,基于国内外研究现状,以Ti6Al4V切削表面残余应力为研究对象,建立了钛合金切削有限元模型。讨论了切削速度、切削深度、每齿进给量、不同切削用量对切削表面残余应力的影响。建立了切削表面残余应力回归模型,并采用混合遗传退火算法对切削参数进行优化,得到了最优切削参数组合。研究表明:切削速度增加,钛合金表面残余应力增加;切削深度对残余应力的影响较小;残余应力随着每齿进给量增加而减小。     

微织构刀具对工件表面残余应力影响的有限元分析

针对刀具对切削工件表面残余应力的影响,文章利用有限元仿真技术,模拟微凹坑PCBN刀具干式车削AISI 52100试验,通过对有限元结果进行处理分析,得到已加工表面残余应力分布情况,与无织构PCBN刀具对比,分析微凹坑对已加工表面残余应力的影响,并研究不同切削速度对微织构刀具切削后的残余应力产生的影响。有限元仿真结果表明:无织构刀具在较高的切削速度下,可以使工件表层获得残余压应力,从而提高工件的耐疲劳等性能;与无织构刀具相比,微凹坑刀具在较低的切削速度下,可以使工件表层获得残余压应力。有限元仿真得到的残余应力结果对微织构刀具在切削加工领域的应用有实际的推动作用。     

基于Deform-3D的65Mn硬态切削加工仿真研究

以淬硬钢65Mn为原料,采用有限元分析软件Deform?3D构建了硬态切削加工模型。模拟了不同切削速度下淬硬钢65Mn的车削加工过程,对车削加工的切削力、温度随切削速度的提高的变化以及工件表面应力变化的仿真结果给出了分析,为实现工艺参数的优化提供了指导。结果表明：硬态切削加工3个切削力中径向力Fy 最大,第二变形区的切削温度较高,硬态切削加工过程中工件表面应力呈现拉压交替变换且最终表现为压应力。     

Inconel718切削过程的有限元仿真研究

为了研究高速切削Inconel 718的切削机理,应用有限元软件DEFORM-2D模拟了高速切削Inconel 718的切削过程,分析了切削速度对切削温度、切削力和剪切角的影响规律以及切削过程中刀具和工件的应力场分布情况.仿真结果表明:切削力随着刀具的切入先迅速线性增大,然后趋于稳定,切削力随切削速度的增大呈下降趋势.切削温度的最高点总是位于前刀面上距离刀刃不远的地方.最高切削温度随着切削速度的增大而增高.最大刀具等效应力出现在前刀面上切削刃的周围,工件上最大等效应力出现在第一变形区.切削过程中,剪切角随切削速度的增加而增大.     

薄壁Ti6Al4V管件采用不同车削参数加工引起的表面残余应力的测量（英文）

同时考虑测量精度、测量可行性以及节约材料诸多方面的问题,运用有限元验证的方法确定零件合适的长度。同时运用精度较高的基于有限元分析的修正方法结合X射线法测量Ti6Al4V管件车削加工引起的表面残余应力,分析不同切削参数以及退火处理对表面残余应力的影响。结果显示:切削速度、进给量以及切削深度在指定范围内增大时会导致表面切削和进给方向的压应力增大,退火处理会使得表面2个方向的残余应力减小将近85%。     

新型微坑车刀切削AISI4140残余应力影响因素分析研究

为了探究切削用量对新型微坑车刀切削工件表面残余应力的影响规律,应用AdvantEdge切削仿真软件,结合单因素和正交实验,通过微坑车刀和原车刀切削AISI_4140仿真及实验验证。结果表明,原车刀和微坑车刀残余拉应力随切削速度增大,先增大后减小,随进给量的增大而减小,总体上,微坑车刀切削工件残余拉应力更小。残余压应力随切削速度增大,微坑车刀切削工件先增大后减小,随进给量增大先增大后减小。原车刀几乎不变。切削用量对微坑车刀切削工件残余应力影响,进给量最大,切削速度次之,切削深度最小。通过实验验证,相同切削条件下,微坑车刀降低了加工工件表面残余拉应力,提高了加工工件表面质量,一定程度提高了工件的服役寿命。     

2024铝合金铣削加工表面残余应力仿真研究

为了研究不同的铣削参数对2024铝合金铣削过程中铣削加工表面残余应力的影响,采用有限元仿真与试验验证结合的方法,利用有限元建立2D铣削仿真模型,研究铣削过程中切削表面残余应力随切削参数的变化,并在相同的切削参数下进行铣削试验测量切削表面残余应力,采用正交试验和单因素试验对铣削参数进行优化。结果表明,有限元仿真的结果与试验的结果数据相近,验证了有限元模型的准确性,通过正交试验选出最优的铣削工艺参数为切削速度500m/min、每齿进给量0.05mm/z、铣削宽度10mm、铣削深度0.5mm;在切削2024铝合金时,在不影响生产的条件下,采用较低的切削速度,较低的进给量、铣削深度和铣削宽度,得到的表面残余应力值较小。     

硬质合金微坑车刀切削304不锈钢残余应力有限元仿真

为了研究硬质合金微坑车刀对304不锈钢表面残余应力的影响规律,采用有限元仿真平台建立二维切削模型,用不同切削参数车削304不锈钢,得到切削参数对切削力、切削温度及残余应力分布的影响规律。研究结果表明:表面残余拉应力和里层残余压应力随切削速度的增大均先增大后减小,而随着进给量的增大,表面残余拉应力逐渐减小,里层残余压应力逐渐增大。     

微槽刀具切削GH4169的工件表面完整性研究

针对如何改善零件的已加工表面完整性,提高零件的服役能力,文章基于温度场形状开展切削GH4169的刀具前刀面微槽设计研究,设计并制备了新型微槽刀具,并将原刀具和微槽刀具加工后的工件表面完整性进行对比试验研究,结果表明:微槽结构改变了刀具的平衡力系,使其切削力和切削温度降低,进而使得在推荐切削参数下,使用微槽刀具切削的表面质量优于原刀具,粗糙度降低了22.96%,残余拉应力降低了30.7%,工件表面显微硬度随切削速度的增加而加剧,且微槽刀具切削后的工件硬化程度和深度均有所降低。     

Improving the shape quality of bearing rings in soft turning by using a Fast Tool Servo

In machining of ring shaped components, the workpiece is deformed by the clamping forces of the chuck. This elastic deformation generates shape deviations in soft turning. Moreover, the machining process generates locally varying residual stresses which contribute to shape deviation of the workpiece. Hence, in machining of thin-walled bearing rings hexagonal out‐of‐roundness up to 200 μm occur. In order to minimize the shape deviations, a long stroke Fast Tool Servo (FTS) for controlling the depth of cut was developed. The applied FTS differs from other published FTS systems in the guidance design. The moving tool holder is suspended to the FTS frame by flexure joints instead of using a linear guidance. The flexure joints provide a low stiffness in moving direction and high stiffness in orthogonal directions. The high stiffness in cutting force direction is essential for a real time reduction of shape deviations in soft turning. In this paper, results of an experimental investigation for the reduction of the shape deviation by adapted non circular machining are presented, using the developed FTS. Based on the results, the influence of the cutting forces on part accuracy is discussed.     

薄壁Ti6Al4V管件采用不同车削参数加工引起的表面残余应力的测量

切削加工引起的金属零件的表面残余应力,其性质和大小对零件的服役性能产生很重要的影响。在测量车削加工Ti6Al4V薄壁管件引起的表面残余过程中,由于边缘效应的存在,使得零件的长度对测量精度有严重的影响。由于管件的壁厚很薄,当去除一应力层时会对剩余部分的残余应力的重新分布产生重要的影响,因此必须对剥层后X射线法测得的应力值进行修正补偿才能得到其初始应力值。传统的修正方法其计算比较复杂,对零件和应力都有特别的要求,而且在某些情况下其修正精度还达不到要求。同时考虑测量精度、测量可行性以及节约材料诸多方面的问题,本文运用有限元验证的方法确定零件合适的长度。同时本文运用精度较高的基于有限元分析的修正方法结合X射线法测量Ti6Al4V管件车削加工引起的表面残余应力,分析不同切削参数以及退火处理对表面残余应力的影响。结果显示：切削速度、进给量以及切削深度在指定范围内增大时会导致表面切削和进给方向的压应力增大,退火处理会使得表面两个方向的残余应力减小将近85%。     

The influence of tool flank wear on residual stresses induced by milling aluminum alloy

The machining processes could induce residual stresses that enhance or impair greatly the performance of the machined component. Machining residual stresses correlate very closely with the cutting parameters and the tool geometries. In this paper, the effect of the tool flank wear on residual stresses profiles in milling of aluminum alloy 7050-T7451 was investigated. In the experiments, the residual stresses on the surface of the workpiece and in-depth were measured by using X-ray diffraction technique in combination with electro-polishing technique. In order to correlate the residual stresses with the thermal and mechanical phenomena developed during milling, the orthogonal components of the cutting forces were measured using a Kistler 9257A type three-component piezoelectric dynamometer. The temperature field of the machined workpiece surface was obtained with the combination of infrared thermal imaging system and finite element method. The results show that the tool flank wear has a significant effect on residual stresses profiles, especially superficial residual stress. As the tool flank wear length increases, the residual stress on the machined surface shifts obviously to tensile range, the residual compressive stress beneath the machined surface increases and the thickness of the residual stresses layer also increases. The magnitude and distributions of the residual stresses are closely correlated with cutting forces and temperature field. The three orthogonal components of the peak cutting forces increase and the highest temperature of the machined workpiece surface also increases significantly with an increase in the flank wear. The results reveal that the thermal load plays a significant role in the formation of the superficial residual stress, while the dominative factor that affects thickness of residual stresses layer is the mechanical load in high-speed milling aluminum alloy using worn tool.     

Distortion Engineering - Identification of Causes for Dimensional and Form Deviations of Bearing Rings

Distortion of power transmission parts after heat treatment is influenced by each step of the process chain, ranging from material production to hard-machining. However, an experimental analysis for each production step in the manufacture of bearing rings has shown that distortion is significantly influenced by turning before heat treatment. Elastic ring deformation caused by fixing the workpiece in the chuck leads to a variation of the depth of cut and polygonal form deviations occur after machining. In addition the cutting process induces locally varying residual stresses which also contribute to dimensional and form deviations of machined rings. In this paper results from experimental investigations of the principle physical causes for the distortion of bearing rings are presented and discussed. Finally, strategies for the minimization of distortion are derived.     

Predictive modeling of machining residual stresses considering tool edge effects

The surface integrity of machined components is defined by several characteristics, of which residual stress is extremely important. Residual stress is known to have an effect on critical mechanical properties such as fatigue life, corrosion cracking resistance, and dimensional tolerance of machined components. Among the factors that affect residual stress in machined parts are cutting parameters and tool geometry. This paper presents a method of modeling residual stress for hone-edge cutting tools in turning. The model utilizes analytical cutting force models in conjunction with an approximate algorithm for elastic–plastic rolling/sliding contact. Oxley’s cutting force model is coupled with a slip line model proposed by Waldorf to estimate the cutting forces, which are in turn used to estimate the stress distribution between the tool and the workpiece. A rolling/sliding contact model, which captures kinematic hardening, is used to predict the machining residual stresses. Additionally, a moving heat source model is applied to determine the temperature rise in the workpiece due to the cutting forces. The model predictions are compared with experimental data for the turning of AISI 52100. Force predictions compare well with experimental results. Similarly, the predicted residual stress distributions correlate well with the measured residual stresses in terms of magnitude of stresses and depth of penetration.     

Residual stresses in surface layer after dry and MQL turning of AISI 316L steel

Residual stresses in the surface layer exert a significant impact on functional aspects of machined parts. Their type and value depend on the workpiece and tool material properties, cutting parameters and cooling and lubrication conditions in the tool-chip-machined surface interface. As the effects of material properties and cutting parameters have been widely studied, the influence of cooling and lubrication conditions, especially minimum quantity lubrication (MQL) on the surface layer residual stresses and the relationships between them have not been investigated. In this paper the effects of dry, MQL cutting and cutting with emulsion conditions together with cutting parameters on residual stresses after turning AISI 316L steel were investigated. X-ray diffraction method was used for measuring superficial residual stresses in the cutting (hoop) and feed (axial) directions. Tensile residual stresses were detected in both directions and the values in the cutting direction turned out to be higher than in the feed direction. The effects of cooling and lubrication conditions largely depend on the selected cutting parameters, whose influence is linked to the cutting zone cooling and lubrication mode. Elaborated regression functions allow calculation and optimization of residual stresses in turning AISI 316L steel, depending on cooling and lubrication conditions as well as cutting parameters.     

Process simulation using finite element method — prediction of cutting forces, tool stresses and temperatures in high-speed flat end milling

End milling of die/mold steels is a highly demanding operation because of the temperatures and stresses generated on the cutting tool due to high workpiece hardness. Modeling and simulation of cutting processes have the potential for improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. The main objective of this study was to develop a methodology for simulating the cutting process in flat end milling operation and predicting chip flow, cutting forces, tool stresses and temperatures using finite element analysis (FEA). As an application, machining of P-20 mold steel at 30 HRC hardness using uncoated carbide tooling was investigated. Using the commercially available software DEFORM-2D™, previously developed flow stress data of the workpiece material and friction at the chip–tool contact at high deformation rates and temperatures were used. A modular representation of undeformed chip geometry was used by utilizing plane strain and axisymmetric workpiece deformation models in order to predict chip formation at the primary and secondary cutting edges of the flat end milling insert. Dry machining experiments for slot milling were conducted using single insert flat end mills with a straight cutting edge (i.e. null helix angle). Comparisons of predicted cutting forces with the measured forces showed reasonable agreement and indicate that the tool stresses and temperatures are also predicted with acceptable accuracy. The highest tool temperatures were predicted at the primary cutting edge of the flat end mill insert regardless of cutting conditions. These temperatures increase wear development at the primary cutting edge. However, the highest tool stresses were predicted at the secondary (around corner radius) cutting edge.     

Influence of turning parameters on distortion of bearing rings

The turning of bearing rings often leads to undesired form and dimensional changes after heat treatment which are referred to as distortion. In order to investigate the influence of cutting parameters on distortion, external longitudinal turning experiments were conducted. After machining the ring geometry and the residual stresses around the rings’ circumference were measured. The residual stresses were then released by a subsequent heat treatment. After the heat treatment the ring geometry was measured again. The results show that the residual stresses induced by the machining process correlate well with the dimensional changes after heat treatment. The cutting parameters that have the highest influence on the dimensional changes are the feed rate and the depth of cut. Residual stresses induced by soft-machining lead to an increase of the ring diameter, depending on the machining parameters.     

Characterization of the transition from ploughing to cutting in micro machining and evaluation of the minimum thickness of cut

When the machining process is miniaturized two process mechanisms, ploughing and chip formation, are essential and a critical cutting thickness needs to be exceeded so that not only ploughing will occur but chips will also be formed. The ploughing effect thereby influences the chip formation process, workpiece surface roughness, burr formation and residual stress state after processing and is therefore of great interest. In order to optimize the machining process a better understanding of the minimum thickness of cut is crucial.The changes in surface topography along the cutting track occurring during machining with a constant feed rate of the cutting tool were analyzed. The influence of the built-up edge phenomena on the micro machining process was investigated for normalized AISI 1045 using confocal white light microscopy and scanning electron microscopy. Furthermore the sin²ψ-method was applied in order to study the residual stress state in the workpiece surface induced by the machining process. Both surface layer properties investigated, surface roughness and residual stresses, show a characteristic transition indicating a change in the dominating process mechanisms. Based on these results a model is developed to determine the minimum thickness of cut. The minimum thickness of cut is found to significantly decrease with higher cutting velocities and to moderately increase with higher cutting edge radii. In addition a propagation of error for the values obtained with the model was performed, proving the quality of the model developed.