Prediction model of surface residual stress within a machined surface by combining two orthogonal plane models

The variation of surface residual stress within a machined surface layer caused by face turning was studied. The size of the tool’s corner radius and the feed rate affect residual stress. A process model using the finite element method is proposed and the mechanical effects of the corner radius and feed rate on a machined surface were discussed. When a tool with a small corner radius is used, surface residual stress perpendicular to the cutting direction becomes compression stress. As well, surface residual stress changes from tension to compression as the feed rate decreases. The process model consists of an orthogonal cutting simulation and an indentation-like simulation of a corner radius into a work piece surface. The simulated results show quantitative agreement with the residual stress measured experimentally. The integrity of the machined surface will be controlled more efficiently if the cutting conditions during finishing are determined with the proper consideration of the surface generating process.     

Experimental and numerical modelling of the residual stresses induced in orthogonal cutting of AISI 316L steel

Residual stresses in the machined surface layers are affected by the cutting tool, work material, cutting regime parameters (cutting speed, feed and depth of cut) and contact conditions at the tool/chip and tool/workpiece interfaces. In this paper, the effects of tool geometry, tool coating and cutting regime parameters on residual stress distribution in the machined surface and subsurface of AISI 316L steel are experimentally and numerically investigated. In the former case, the X-ray diffraction technique is applied, while in the latter an elastic–viscoplastic FEM formulation is implemented. The results show that residual stresses increase with most of the cutting parameters, including cutting speed, uncut chip thickness and tool cutting edge radius. However, from the range of cutting parameters investigated, uncut chip thickness seems to be the parameter that has the strongest influence on residual stresses. The results also show that sequential cuts tend to increase superficial residual stresses.     

Influence of tool edge preparation on performance of ceramic tool inserts when hard turning

Coating, as a form of tool edge preparation, changes the properties, geometry and roughness of the active parts of tool inserts. The performance of both uncoated and coated ceramics was tested in machining tests and the results were related to the tool edge and the machined surface as well as cost indices. The presented results show that tool edge preparation by coating does affect forces, tool wear and the machined surface, while friction force from scratch tests and the coating thickness and its hardness have been identified as being relevant to the results of machining tests. The relationship between the thickness of the surface layer and residual stress at the surface due to coating has been evaluated. Though the tool life of coated ceramics is shorter than that of cubic boron nitride, tool edge preparation by coating contributes to the reduction in machining costs due to the application of higher cutting speeds.     

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。     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响，采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试，通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试，机加工对试样表面造成残余应力层深度小于0.01 mm，内部残余拉应力减小；根据疲劳试验结果，GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响,采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试,通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试,机加工对试样表面造成残余应力层深度小于0.01 mm,内部残余拉应力减小;根据疲劳试验结果,GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

Modelling the effects of tool-edge radius on residual stresses when orthogonal cutting AISI 316L

Tool-edge geometry has significant effects on the cutting process, as it affects cutting forces, stresses, temperatures, deformation zone, and surface integrity. An Arbitrary-Lagrangian–Eulerian (A.L.E.) finite element model is presented here to simulate the effects of cutting-edge radius on residual stresses (R.S.) when orthogonal dry cutting austenitic stainless steel AISI 316L with continuous chip formation. Four radii were simulated starting with a sharp edge, with a finite radius, and up to a value equal to the uncut chip thickness. Residual stress profiles started with surface tensile stresses then turned to be compressive at about 140 μm from the surface; the same trend was found experimentally. Larger edge radius induced higher R.S. in both the tensile and compressive regions, while it had almost no effect on the thickness of tensile layer and pushed the maximum compressive stresses deeper into the workpiece. A stagnation zone was clearly observed when using non-sharp tools and its size increased with edge radius. The distance between the stagnation-zone tip and the machined surface increased with edge radius, which explained the increase in material plastic deformation, and compressive R.S. when using larger edge radius. Workpiece temperatures increased with edge radius; this is attributed to the increase in friction heat generation as the contact area between the tool edge and workpiece increases. Consequently, higher tensile R.S. were induced in the near-surface layer. The low thermal conductivity of AISI 316L restricted the effect of friction heat to the near-surface layer; therefore, the thickness of tensile layer was not affected.     

300 M超高强钢车削加工表面质量

目的研究切削参数对300M超高强度钢加工表面质量的影响。方法选用硬质合金刀具车削加工300M超高强度钢,研究切削参数对表面加工硬化、残余应力及表面粗糙度的影响。通过HXD-1000显微硬度检测仪、X-350A型X射线应力测试系统、TR240表面粗糙度测量仪对实验过程进行检测分析。通过单因素试验研究影响表面粗糙度的主次因素,并通过正交试验,以进给量f、切削速度v、刀尖圆弧半径rε、背吃刀量a_p为变量建立表面粗糙度的预测模型。结果背吃刀量a_p=0.2 mm,切削速度v为60~120 m/min,进给量f为0.1~0.25 mm/r时,300M钢经切削加工后,维氏硬度在467~550HV范围内变化。切削速度从60 m/min增大至200 m/min时,表面残余应力从压应力-59.13 MPa变为拉应力257.33 MPa,次表层残余应力的最大残余压应力从-147.46 MPa增大到-422.65 MPa,并且层深至50μm左右处,工件材料的加工变质层结束。结论表面硬度随着进给量和切削速度的增大而减小,并且越往里层,硬度越低,直至达到基体的硬度。影响表面粗糙度的最主要因素为进给量,其次是刀尖圆弧半径,再次为切削速度,背吃刀量对表面粗糙度的影响最小。建立的表面粗糙度预测模型通过了试验验证,具有很高的加工精度。     

Roughness and texture generation on end milled surfaces

Plane surface generation mechanism in flat end milling is studied in this research. The bottom of a flat end mill has an end cutting edge angle that plays an important role in surface texture. Surface texture is produced by superposition of conical surfaces generated by the end cutting edge rotation. The machined surface is cut once again by the trailing cutting edge. This back cutting phenomenon is frequently observed on surfaces after finishing. Tool run-out and tool setting error including tool tilting and eccentricity between tool center and spindle rotation center are considered together with tool deflection caused by cutting forces. Tool deflection affects magnitude of back cutting and the surface form accuracy. As a result, the finished surface possesses peaks and valleys with form waviness. Surface topography parameters such as RMS deviation, skewness and kurtosis are used for evaluating the generated surface texture characteristics. Through a set of cutting tests, it is confirmed that the presented model predicts the surface texture and roughness parameters precisely including back cutting effect.     

Mechanism of Micro Chip Formation in Diamond Turning of Al-Mg Alloy

This paper deals with diamond turning experiments of Al-Mg alloy. Variation in tool setting angles using straight tools with sharp cutting edges was performed to study the difference between the machined surface roughness and the theoretical surface roughness estimated with a steady vibration model. Tears with 0.1 μm depth which are generated on the side cutting edge deteriorates the machined surface roughness. The tears are cut off by the trailing end cutting edge at a negative tool setting angle. Burrs generated at the tool setting angle less than -0.1° are another cause for the deteriorating the machined surface roughness.     

Effect of tool nose radius and tool wear on residual stress distribution in hard turning of bearing steel

This study presents a experimental investigation to clarify the effects of tool nose radius and tool wear on residual stress distribution in hard turning of bearing steel JIS SUJ2. Three types of CBN tools with different nose radius (0.4, 0.8 and 1.2 mm) were used in this study. The residual stresses beneath the machined surface were measured using X-ray diffraction technique and electro-polishing technique. The results obtained in this study show that the tool nose radius affects the residual stress distribution significantly. Especially the effect on the residual stresses at the machined surface at early stage of cutting process is remarkable. For the tool wear, as the tool wear increases, the residual stress at the machined surface shifts to tensile stress range and the residual compressive stress beneath the machined surface increases greatly.     

Performance of nano/micro CBN particle coated tools in superfinish hard machining

A two-stage composite coating method has been developed for coating of nano/micro cubic boron nitride (CBN) particles on cutting tools. Since nano/micro CBN particle coated tools are more cost-effective than solid polycrystalline CBN (PCBN) tools, a comprehensive study on the coated tools is required. This paper studies the performance of these tools in superfinish hard machining. Specimens were machined by a solid PCBN tool and CBN particle coated tools with two different CBN particle size distributions: less than 0.5 and 2 μm. The specimen machined by a tool with small CBN particle coating (less than 0.5 μm) showed more compressive residual stresses and less thermal damage below the machined surface than other specimens. Furthermore, the specimen machined by a tool with small CBN particle showed less residual stress scatter than other specimens. The rolling contact fatigue life was predicted by using a rolling contact fatigue life model. The rolling contact fatigue life predictions indicate that the predicted life of the specimen machined by a tool with small CBN particle coating is longer than that of other specimens. The results thus indicate that a tool with small CBN particle coating provides better performance than other tools in superfinish hard machining.     

Statistical analysis of the effects of machining parameters and workpiece hardness on the surface finish of machined medium carbon steel

The objective of this study is to ascertain the effect of machining parameters and workpiece hardness on surface roughness of machined components and to develop a better understanding of the effect of process parameters on the machined surface. Such an understanding can provide insight into the problems of controlling the finish of machined surfaces when the process parameters are adjusted to obtain a certain surface finish. The collected data were analyzed using parametric analyses of variance (ANOVA) with surface finish as the dependent variable and hardness of the workpiece material, cutting tool position from the surface of the clamping device (chuck), depth of cut, cutting velocity, and cutting feed as independent variables. The results showed that surface roughness is significantly affected by the workpiece hardness, cutting feed, cutting speed, depth of cut, cutting tool position from the chuck, and their interactions with each other. The results suggest that feed rate and cutting speed can be adjusted to produce a certain surface finish when the position of the cutting tool from the surface of a clamping device or the hardness of the workpiece is changed.     

Determination of surface and in-depth residual stress distributions induced by hard milling of H13 steel

In the present study, an experimental investigation was conducted to determine the effects of surface texture, cutting parameters and phase transformation on the surface and in-depth residual stress distributions induced by hard milling of AISI H13 steel (50?±?1HRc) with the coated carbide tools. The results show that the surface residual stress distribution between two adjacent machined lays has the same periodic variational regularity as the surface profiles, which means that the surface residual stress distribution has a high correlation with the machined surface texture. Surface residual stresses in the pick direction are much more compressive than that in the feed direction; at the same time, radial depth of cut and feed are the main cutting parameters affecting surface residual stresses. Very thin white layer forms or even no obvious microstructural alteration appears in the subsurface. Phase transformations of the subsurface material deeply affect the in-depth residual stress distribution, a ??hook?? shaped residual stress profile beneath the machined surface is generated in which the maximum compressive stresses occur at the depth of 3?C18???m below the surface.     

Development of a new tool to generate compressive residual stress within a machined surface

Generally, critical machined parts such as aircraft parts require high fatigue strength and resistance to stress corrosion cracking. These machined parts almost all usually have tensile residual stress within the machined surface after milling. However, if the compressive residual stress within the machined surface can be obtained by a milling process alone, it is expected that fatigue strength and resistance to stress corrosion cracking of the machined components will be improved. The purpose of this study is to develop a new tool that can generate compressive residual stress within the machined surface concurrently with the milling process. This tool has cutting edges for material removal and a projection pin for a burnishing-like process. It was shown that the proposed cutter could generate effective compressive residual stress within the machined surface during the milling process. Residual stress levels were in the region of −100 to −200 MPa on the machined surface, and −300 to −400 MPa at 0.05 mm beneath the surface. These levels are almost comparable with those obtained by the shot peening process.     

Study on surface damages caused by turning NiCr20TiAl nickel-based alloy

The machined surface damages were investigated after NiCr20TiAl nickel-based alloy was turned in the various cutting conditions. It is found that the plastic deformation and carbide particles of NiCr20TiAl alloy are responsible for the machined surface damages during turning. When the carbide particles are removed from the machined surface during machining, the residual cracks inside surfaces are linked together due to a steep rise in the shear stress, which results in the surface cavities and plucking. The slip zones are formed inside the machined surfaces because the dislocation movement is inhibited by many grain boundaries of NiCr20TiAl alloy during machining, and a work-hardening layer with a non-uniform depth is produced. At the cutting speed of 100 m/min, feed of 0.15 mm/r and depth of cut of 1 mm, a relatively smooth surface with the thinner work-hardening layer is generated owning to the reduced cutting force.     

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.     

Effects of process parameters on material side flow during hard turning

The phenomenon of material side flow represents an important aspect of machined surface quality during hard turning. In this paper, an experimental study was performed to investigate the main features of this phenomenon. The effects of process parameters including edge preparation, nose radius, feed and tool wear on material side flow were examined. Two possible mechanisms for material side flow were investigated. In the first one, the material is squeezed between the tool flank face and the machined surface when chip thickness is less than a minimum value. In the second mechanism, the plastified material in the cutting zone flows through the worn trailing edge to the side of the tool. Both of these mechanisms can exist simultaneously. The results obtained from surface examination showed a strong correlation between edge preparation and material side flow. An increase in the tool nose radius resulted in a remarkable increase of material side flow. Feed had an indirect effect on material side flow. In addition, tool wear significantly affected the existence of material side flow on the machined surface. An increase in tool wear promoted the occurrence of material side flow.     

钛合金侧铣加工残余应力与变形研究北大核心

为研究加工残余应力对钛合金薄壁结构变形的影响,利用有限元软件建立2D切削模型,分析每齿进给量与刀具刃口半径对加工表面残余应力的影响。利用切削仿真得到的残余应力对薄壁件进行变形仿真分析;分别以每齿进给量0.06、0.08 mm进行闭腔侧铣试验。结果表明:与实测值相比,仿真表面残余应力误差约为20%、最大变形量误差约为12%。所提方法具有一定的可靠性与可行性。     

Characteristics of high speed micro-cutting of tungsten carbide

In this study, experiments are carried out to evaluate the characteristics of high speed cutting of tungsten carbide material using a Makino V55 high speed machine tool with cubic boron nitride (CBN) tool inserts. The cutting forces were measured using a three-component dynamometer, the surface roughness of the machined workpiece was measured using a Mitutoyo SURFTEST 301, and the machined workpiece surfaces and the chip formation were examined using a scanning electron microscope (SEM). Experimental results indicate that the radial force F_x is much larger than the tangential force F_z and the axial force F_y. Two types of surfaces of the machined workpiece are achieved: ductile cutting surface and fracture surface. Continuous chips and discontinuous chips are formed under different cutting conditions. Depth of cut and feed rate almost have no significant effect on the surface roughness of the machined workpiece. The SEM observations on the machined workpiece surfaces and chip formation indicate that the ductile mode cutting is mainly determined by the undeformed chip thickness when the tool cutting edge radius is fixed. Ductile cutting can be achieved when the undeformed chip thickness is less than a critical value.