Improved analytical model for residual stress prediction in orthogonal cutting

The analytical model of residual stress in orthogonal cutting proposed by Jiann is an important tool for residual stress prediction in orthogonal cutting. In application of the model, a problem of low precision of the surface residual stress prediction is found. By theoretical analysis, several shortages of Jiann’s model are picked out, including: inappropriate boundary conditions, unreasonable calculation method of thermal stress, ignorance of stress constraint and cyclic loading algorithm. These shortages may directly lead to the low precision of the surface residual stress prediction. To eliminate these shortages and make the prediction more accurate, an improved model is proposed. In this model, a new contact boundary condition between tool and workpiece is used to make it in accord with the real cutting process; an improved calculation method of thermal stress is adopted; a stress constraint is added according to the volume-constancy of plastic deformation; and the accumulative effect of the stresses during cyclic loading is considered. At last, an experiment for measuring residual stress in cutting AISI 1045 steel is conducted. Also, Jiann’s model and the improved model are simulated under the same conditions with cutting experiment. The comparisons show that the surface residual stresses predicted by the improved model is closer to the experimental results than the results predicted by Jiann’s model.     

Numerical investigation on residual stress in photovoltaic laminates after lamination

A series of simulations were carried out to investigate the residual stress induced in the photovoltaic laminate during the cooling process after lamination with a global model and several submodels. The simulations focus separately on the effects of the cooling rate, the cell layout and anisotropy on the residual stress and deformation of the photovoltaic laminate in a comparative manner with the finite element method. The results have shown that significant stress concentration and twist occurs in the interconnection region in the cell. In addition, different cooling rates, cell layouts and anisotropy only influence the largest stress rather than the stress distribution and deformation. Therefore, the results of a uniform stationary isotropic model with fewer cells can provide enough insight into the stress distribution in real photovoltaic laminates and the modified largest first principal stress can be used for design and verification.     

Characteristics of the residual stress distribution in welded tubular T-joints

Tubular T-joints are structural discontinuities that can be easily involved with stress concentrations. It is therefore necessary to estimate an internal stress distribution of T-joints. However, the complicated residual stresses are unavoidably produced adjacent to the joints by welding. In this paper, the residual stress distributions in welded tubular T-joints were analyzed by using a three-dimensional non-steady heat conduction analysis and a three-dimensional thermal elastic-plastic analysis. Characteristics of the residual stress distribution in welded tubular T-joints are investigated by the thermal-mechanical analysis results.     

Prediction of residual stress distribution after turning in turbine disks

The state of a surface region after machining is definitely affected by cutting parameters, such as cutting speed, feed rate, tool nose radius, tool rake angle and the presence of a cutting fluid, which plays a major role in determining friction at the tool–chip interface. The aim of the present study is to develop a finite element model based on the general-purpose nonlinear finite element code MSC.Marc by MSC.Software Corporation. This software is capable of simulating the cutting process of low-pressure turbine disks of aircraft jet engines from its very beginning to steady-state conditions. Basically, the present analysis is a coupled thermo-mechanical dynamic-transient problem, based on the update Lagrangian formulation; no pre-defined path is given for the separation of the chip from the workpiece, since material deformation occurs as a continuous indentation performed by the rigid tool. In addition to the cutting parameters, the main inputs in this analysis are material constitutive data, the friction coefficient at the toolchip interface and the cutting tool temperature. All the relevant variables, like stresses, strains, temperatures, chip shape and residual stresses, are predicted in a wide range of cutting conditions. The results from the model are compared to some basic theories of metal cutting and to an experimental study, concerning orthogonal cutting of steel AISI 316L. Concerning the specific case of turning process of nickel alloy Inconel 718 low-pressure turbine disks, the calculated residual stress are compared to experimental measurements from real machined disks.     

用水蒸气作冷却润滑剂的切削试验研究

研制水蒸气发生器 ,并用水蒸气作为冷却润滑剂进行切削试验时发现 ,切削力可比干切减少 10 %左右 ,比用乳化液减少 6%左右 ,并初步分析水蒸气作冷却润滑剂的作用机理     

碳化硅晶须增强铝基复合材料的切削力实验研究

采用三种不同种类的刀具对碳化硅晶须增强铝基复合材料(SiCw/2024)进行车削试验,用Kistler三向测力系统检测切削力波形和三向切削分力Fc、Fp、Ff。试验结果表明,对增强相体积分数超过某一阈值(如17～18%)的碳化硅晶须增强铝基复合材料,用K类硬质合金(K10TiAlN)固定式刀具切削,会出现背吃刀抗力Fp、进给分力Ff大于主切削力Fc的现象,三者大小的关系为Fp>Ff>Fc,且随着SiCw含量的增高切削力差值越大;用硬质合金圆形自回转刀具切削,平均背吃刀抗力Fp减少(30～60)%;用PCD刀具切削,三向切削力都最小。     

The residual stress distribution in a plastically deformed model asperity

When rough metallic surfaces come into contact, plastic deformation may occur locally, even at the lightest loads. This plastic deformation is thought to be an important element in a wide range of contact failure mechanisms, including fatigue and nearly all forms of wear.In this paper a simple model of asperity plastic deformation is presented. The model is based on slip line field theory and is used to calculate residual and full-load stress distributions at fully plastic asperity contacts for normal and moderate tangential loads.Measurements of surface residual stress were carried out using two different techniques on a range of plastic contacts of various materials and geometries. The results show agreement with the main predictions of the theory.     

Formation of tangential pre-stress as a residual stress and its influence on the tribological performance of nodular cast irons

Since any state of residual stress influences the service behavior of a material, it is of particular interest for engineers and designers to know its benefits to machine parts, and where it can be utilized successfully. From this point of view, mechanical tangential pre-stress as circumferential compressive residual stress has been investigated for wear performance. For this purpose, a thick walled cylinder specimen model was established as a tribo-element, and the force, which will form the desired tangential pre-stress representing residual stress, has been calculated by the rules of elasticity theory. In order to compare the effect of residual stress on the wear performance under dry and lubricated conditions, 0.8 R_e (R_e: unidirectional yield strength) were applied to the nodular cast iron (DDK-40, DDK-60) specimens. Wear test results have been evaluated in terms of two different stress levels, 0 R_e and 0.8 R_e, formed on the specimen.     

Experimental and numerical investigation of cutting forces in micro-milling of polycarbonate glass

Abstract

Polycarbonates have found important applications in various types of industries including optical, automotive, aerospace, biomedical, and defense manufacturing industries. Conventional mechanical machining has the capability to create complex multi-scale parts and components for various materials including polymeric materials. This study investigates the cutting forces generated during the machining of polycarbonate glass using the micro-milling process. The goal of this research is to machine high quality micro-channels in polycarbonates for microfluidic applications. Both experimental investigation and numerical simulations using the Finite Element Method (FEM) have been carried out to assess the cutting forces generated in three directions during machining of polycarbonate. The effectiveness of tool coating on the reduction of cutting forces has been investigated. It was found that with the careful combination of depth of cut and feed rate, the ductile mode machining of polycarbonate can be achieved, which produces lower cutting forces, that could result in improved surface finish and low tool wear. Both lower and higher of depths of cut were found to generate higher cutting forces due to dragging action and higher tool-workpiece contact area respectively. The Finite Element Method (FEM) was found to be effective in simulating the cutting forces with acceptable range of errors, and thus, could be used to predict cutting forces at the parametric combinations beyond the capacity of the machine or without carrying out further expensive experimentation, for which the chances of tool failure are higher.     

Experimental investigation on cutting mechanisms in fixed diamond wire sawing of bone

Bone sawing has been widely used in performing bone surgery. However, thermal necrosis, loss of cutting precision and surface damage may occur in cutting process. The primary objective of this research is to improve cutting performance of bone by advantages of diamond wire sawing. Mechanism of material removal, cutting force, temperature and surface quality are analyzed based on experimental results. It is indicated that wire sawing provides small depth of cut, which is effective to obtain ductile material removal mode. Due to small material removal rate per abrasive, thermal energy is low and most of the heat can be taken away by the cyclic wire and bone chips. Consequently, cutting force and temperature in cutting zone are lower than that of traditional sawing. Due to the high efficiency of chip ejection, burrs and fracture are reduced and a significant improvement in surface quality is achieved. Based on cutting experiments with various values of cutting parameters, it is observed that better performance is achievable at higher wire speeds. These results provide a valuable basis for application of wire sawing and understanding of bone cutting mechanisms.     

Experimental investigation on the CO2 laser cutting of soda-lime glass

Journal of Mechanical Science and Technology - This study reports on complete glass cutting using a single CO2 laser beam with a low power of several tens of watts. In this study, the morphological...     

Understanding the residual stress distribution in brazed polycrystalline CBN abrasive grains

This article investigates the brazing-induced residual stresses in the polycrystalline cubic boron nitride (PCBN) abrasive grains based on finite element simulation. The effects of embedding depth and gap thickness on the residual stress distribution in brazed PCBN grains are discussed. Results obtained show that, compared with the Ag-Cu-Ti alloy joining CBN grains and AISI 1045 steel substrate, the AlN binder materials in the polycrystalline CBN grains always have a greater effect on the brazing-induced residual stresses; meanwhile, large residual tensile stresses usually exist at the interface between the microcrystalline CBN particles and AlN binders. In comparison to the embedding depth, the gap thickness has little influence on the brazing-induced residual stresses. Furthermore, compared with the other embedding depth, in the case of the embedding depth of 40 %, the residual stresses in the brazed PCBN grain are generally the lowest in the grain bottom and the largest in the grain top surface. Finally, the finite element model applied in the current simulation work is validated through measurement experiments of the brazing-induced residual stresses in the monocrystalline CBN grain.     

椭圆振动切削的表面残余应力有限元模拟研究

基于ALE(Arbitrary Lagrange-Euler)网格划分方法建立了椭圆振动切削有限元仿真模型,模拟了椭圆振动切削过程中切削力的变化规律,并将模拟获得的切削力平均值与相同工艺参数下Kim等人[1]所做的超声椭圆振动切削V型槽实验获得的切削力平均值比较,验证了有限元模型的正确性。利用建立的二维有限元模型模拟了椭圆振动切削和普通切削表面残余应力的分布情况,对比结果表明,采用椭圆振动切削的工件已加工表面在一定深度内形成了分布均匀的表面残余压应力,而普通切削情况下工件已加工表面并没有形成有效的残余压应力,从而预测了椭圆振动切削不仅能够降低切削力、延长刀具使用寿命,还对提高工件表面完整性、增强疲劳寿命和抗腐蚀能力等具有显著的作用。     

难加工材料硬态干车削中切削参数对残余应力的影响

本文对切削参数和残余应力之间的关系的进行研究.针对某型号高强高硬钢在硬态干车削过程,研究了各切削参数对已加工表面残余应力及残余应力层深分布的影响.结果发现,不同的切削参数条件下,工件已加工表面残余应力可以为拉应力也可以为压应力,残余应力作用层深度为300μm左右.对残余应力影响较大的切削因素为切削速度和进给量,切深对残余应力影响较小,切削参数选择低速低进给时,容易得到有利于提高工件疲劳寿命的表面残余压应力.     

Visualization of fluctuations in internal stress distribution of workpiece during ultrasonic vibration-assisted cutting

The aim of this study is to construct visualization system of stress distribution under ultrasonic vibration-assisted cutting condition in order to investigate the cutting phenomenon. The vibrating cutting edge is considered to be cause of dynamic change of cutting force at ultrasonic frequency. However, many researchers have explained the effect of ultrasonic vibration-assisted cutting by evaluating the time-averaged cutting force, because it is difficult to measure the dynamic cutting force by using dynamometers. In this study, the instantaneous stress distribution on workpiece was visualized by photoelastic method in combination of pulse laser emission synchronized with vibration of cutting edge. Orthogonal cutting test was carried out at low cutting speed relative to vibration speed of insert. A constructed photographic system divided the ultrasonic vibration period of 36.2 μs into 360 points and took one photograph frame at each point. By counting the number of criteria pixels which images the cutting stress, the intermittent cutting condition was evaluated. It was experimentally confirmed that the stress distribution under vibration-assisted condition showed the periodical change synchronized with insert vibration. Because these results are compatible with well-known vibration cutting theories, the imaging system is able to show the periodic change of stress distribution in ultrasonic frequency band. The intermittent cutting condition was affected not only feed speed but also depth of cut. The theory of relative motion between tool and workpiece is insufficient to explain these results. Therefore, remnants formed due to elastic deformation of the workpiece were examined. The vibration cutting dramatically reduced the elastic deformation and the vibration amplitude had effect on the amount of remnant thickness.     

Experimental study on grinding-induced residual stress in C-250 maraging steel

Residual stress plays a significant role in the performance of a part, while the residual stress in the ground maraging steel, which is often used in the manufacture of precision parts, is rarely mentioned. In order to understand the variations of residual stress in ground maraging steel and provide insight into the controlled-stress grinding process of the steel, the surface and subsurface residual stress distributions in ground C-250 maraging steel (3J33) were studied. The results show that the mechanical effects dominate the thermal effects in the dry grinding process, indicated by only compressive residual stress generated in the ground workpiece. Furthermore, more insights into the residual stress distribution were provided by proposing four residual stress distribution parameters including surface residual stress, peak compressive residual stress, the depth of peak compressive residual stress, and residual stress penetration depth. The variations of these parameters were comprehensively studied. Results show that the surface residual stress and peak compressive residual stress depend greatly on the grinding speed and higher grinding speed generates larger compressive residual stress, while the depth of peak compressive residual stress varies slightly with the grinding parameters. The residual stress penetration depth increases with the increase of the grinding speed and grinding depth, and decreases with the increase of the workpiece speed. The results in this study can be used to assist in controlled-stress grinding applications for high performance critical parts of maraging steel.     

Comprehensive investigation on the residual stress of large screws by whirlwind milling

This study investigated the influence of cutting parameters on the residual stress obtained in whirlwind milling of AISI 52100 steel. Single-factor and Box-Behnken experiments were separately carried out. A prediction model of residual stress was developed on the basis of response surface methodology using experimental data. Results indicated that the cutting depth was the dominant factor, and the interaction between cutting speed and tool number was significant. The developed model could be effectively used to predict surface residual stress within high confidence. The optimum value and cutting condition were validated by confirmation experiments.     

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.     

Establishment of a cutting force model and study of the stress–strain distribution in nano-scale copper material orthogonal cutting

This article focuses on the establishment of a cutting force calculation model in terms of nano-scale orthogonal cutting, and investigates the stress–strain distribution of single-crystal copper that occurs in terms of nano cutting. The cutting force that occurs during the nano-scale cutting of single-crystal copper, and also its changes under different situations, can be found in this study. The molecular dynamics (MD) model was proposed to evaluate the displacement components of the atom in any temporary situation on the nano-scale cutting. The atom and lattice were regarded as the node and element, respectively. The shape function concept of the finite element method (FEM) is used to calculate the equivalent strain of the nodal atom and element. The equivalent stress–strain relationship equation was acquired by nano-scale thin-film tensile simulation in this study, and was used to further calculate the equivalent stress that occurs under the equivalent strain. Subsequently, a stress–strain distribution during nano-scale orthogonal cutting can be acquired.