不同切削参数的镍基合金直角切削有限元模拟

利用非线性有限元方法研究镍基合金高速切削过程。在平面应变状态下,通过对材料本构模型、边界条件与接触摩擦模型,以及网格划分环节进行处理,建立有限元直角正交二维切削模型。采用不同刀具前角、切削深度条件对镍基合金直角切削过程进行模拟和试验,分析得出直角切削过程中不同刀具前角和切削深度时切削力、剪切角变化情况,为选择合适的切削参数、提高切削质量提供理论依据。     

Effect of polar organic substance on burr formation in orthogonal cutting

The initiation of burr formation is characterized by the initial negative shear angle and the initial tool distance which are obtained from the minimum energy principle and energy conservation at the chip/burr transition point. Specially in this report the rollover burr is dealt as a specific case of the chip formation process in the final stage of cut, which the tool moves toward the end of workpiece. The purpose of this paper is to experimentally invesigate the burr formation mechanism near the end of cut by using a copper with various cutting conditions and tool geometries, and the influence of the surface active medium, that was used to reduce the burr size and improve the machinability, upon the mechanism of burr formation in the orthogonal cutting using the milling machine.     

正交切削加工温度场的有限元仿真分析

本文简述了切削加工切削热的产生于传导,基于有限元仿真技术分析了正交切削加工过程的温度场分布,并对结果进行了后置处理与分析,结果表明有限元仿真技术的分析结果对研究切削加工过程有较好的辅助作用。     

Finite element modeling and simulation in dry hard orthogonal cutting AISI D2 tool steel with CBN cutting tool

The influences of cutting parameters on temperature, stress, and shear angle during dry hard orthogonal cutting (DHOC) of D2 tool steel (62?±?1 HRC) are investigated in this paper. Temperature and stress are considered the most important aspects to be taken into account in dry hard machining; however, dry hard machining is a complex process, and the temperature fields and residual stress are the most difficult to be measured. Up to now, only very few studies have been reported on influences of cutting parameters on shear angle, temperature, and stress of AISI D2 tool steel (62?±?1 HRC). In this paper, the Johnson–Cook model is utilized to propose a finite element (FE) model. The FE model is properly calibrated by means of an iterative procedure based on the comparison between experimental resultant forces obtained from literatures and simulated resultant forces. At last, this FE model is utilized to predict the influences of cutting speed and depth of cut on temperature fields and residual stress within a workpiece, cutting tool edge temperature, and shear angle during DHOC hardened AISI D2 tool steel (62?±?1 HRC) and validated by experimental results. As shown in this investigation, it is also possible to properly analyze the influences of cutting parameters on the cutting mechanism for industrial application.     

Finite element analysis of the rake angle effects in orthogonal metal cutting

The plane-strain finite element method is developed and applied to model the orthogonal metal cutting of annealed low carbon steel with continuous chip formation. Four sets of simulation results for cutting with −2°, 0°, 5°, and 15° rake angle are summarized and compared to analyze the effects of rake angle in the cutting processes. The initial and deformed finite element meshes, as the cutting reaches steady-state condition, are first presented. Simulation results of the cutting forces and residual stresses, along with the X-ray diffraction measurements of the residual stresses generated using a worn cutting tool with 5° rake angle, are used to identify the influences of the rake angle and tool sharpness. Elements are selected to represent three sections along the shear and contact zones and under the cut surface. The normal and shear stresses, distributions of parameters along these three sections, and contours of temperature, plastic strain, and effective stress are then presented. Limitations of the finite element method for metal cutting simulation are discussed.     

Finite element simulation of high-pressure water-jet assisted metal cutting

Experimental studies have shown that improved metal cutting efficiency can be obtained when a high-pressure water/coolant jet is injected at the tool–chip interface. The pressure exerted on the chip face by the jet is expected to reduce, for example, friction along the tool–chip interface, temperature rise in the chip and the workpiece, the cutting force, and residual stress in the finished workpiece, leading to a longer tool life and a better surface integrity for the finished workpiece. This paper presents the results of finite element simulations of high-pressure water-jet assisted orthogonal metal cutting, in which the water jet is injected directly into the tool–chip interface through a small hole on the rake face of the tool. The mechanical effect of the high-pressure water jet is approximated as a pressure loading at the tool–chip interface. The frictional interaction along the tool–chip interface is modeled by using a modified Coulomb friction law. Chip separation is modeled by a nodal release technique and is based on a critical stress criterion. The effect of temperature, strain rate and large strain is considered. Cooling effect of the high-pressure jet on the temperature distribution is modeled with a convective heat-transfer coefficient. The effect of water jet hole position and pressure is studied. Contour plots showing the distributions of steady-state temperature and stress and the residual stress are presented. The simulation results show a reduction in temperature, the cutting force and residual stresses for water-jet assisted cutting conditions. The mechanical effect of the water jet is found to reduce the contact pressure and shear stress along the tool–chip interface and also the contact zone length for certain water jet hole locations.     

Investigation on the burr formation mechanism in micro cutting

It is desirable to minimize burr formation for improving part quality. This paper presents an investigation on the burr formation mechanism in micro cutting by taking into consideration the stress distribution around the cutting edge arc. The influences of the uncut chip thickness and the cutting edge radius on burr formation were investigated. Poisson burr is attributed to the side flow of the stagnation material at the bottom of the cutting edge arc. The stress distribution at the cutting edge arc has great influence on Poisson burr formation. The burr height decreases to the minimum value and then increases with reducing the uncut chip thickness due to the change of the maximum stress distribution. An optimum machining strategy also is suggested in micro milling of snake-shaped groove microstructure.     

盾构刀盘振动切削性能有限元仿真研究

针对盾构机刀盘的掘进效率问题,对振动切削原理、刀具运动轨迹与破岩机理、盾构刀盘建模、切削力学模型等方面进行了研究,将振动切削技术运用到盾构刀盘的开挖过程中,对刀盘振动切削过程中各项性能参数进行了分析与对比,提出了在刀盘圆周添加正弦激励改变转速实现振动切削的方法,利用LS-DYNA仿真软件分别进行了单把刀具的振动切削及盾构刀盘振动切削过程的数值模拟仿真。研究结果表明,切刀振动切削减阻效果优于滚刀,刀盘在振动切削条件下受力减小,产生的内能增加。     

基于热力耦合模型的金属切削过程有限元分析

基于有限元理论和热力耦合模型的研究,通过讨论切削过程中的关键技术,主要包括切削加工有限元方程的建立：构件材料的Johnson-Cook本构模型;切屑分离准则;材料断裂准则;接触摩擦模型;切削热的产生和分布;残余应力的分析和切削力的比较分析等,建立了二位金属切削过程模型,通过采用粘结．滑移摩擦模型,有效地模拟了航空钛合金的切削加工过程,对此类材料加工的切削力、切屑温度以及应力场和应变的分布进行了分析。     

Finite element models of orthogonal cutting with application to single point diamond turning

Two computer models are described that treat the special case of orthogonal cutting. The models are based on the finite element method, which is used to discretize a portion of the workpiece in the vicinity of the cutting tool. From the models, the detailed stress and strain fields in the chip and workpiece, chip geometry and tool forces can be determined.

The first model is based on a specially modified version of a large deformation updated Lagrangian code developed at Lawrence Livermore National Laboratory called NIKE2D, which employs an elastic-plastic material model. The second model treats the region in the vicinity of the cutting tool as an Eulerian flow field. Material passing through the field is modeled as viscoplastic. Results obtained from both models show excellent agreement when compared with measured tool forces for slow speed cutting of aluminium 2024-T361.     

Influence of size effect on burr formation in micro cutting

Burr is an important character of the surface quality for machined parts, and it is even more severe in micro cutting. Due to the uncut chip thickness and the cutting edge radius at the same range in micro cutting process, the tool extrudes the workpiece with negative rake angle. The workpiece flows along the direction of minimum resistance, and Poisson burr is formed. Based on the deformation analysis and experiment observations of micro cutting process, the factor for Poisson burr formation is analyzed. It is demonstrated that the ratio of the uncut chip thickness to the cutting edge radius plays an important role on the height of Poisson burr. Increasing the uncut chip thickness or decreasing the cutting edge radius makes the height of exit burr reduce. A new model of micro exit burr is established in this paper. Due to the size effect of specific cutting energy, the exit burr height increases. The minimum exit burr height will be obtained when the ratio of uncut the chip thickness to the cutting edge radius reaches 1. It is found that the curled radius of the exit burr plays an important role on the burr height.     

切削参数对弯曲薄壁件变形规律的有限元仿真

钛合金薄壁件在切削加工时易产生弹性变形,降低薄壁件的加工质量。针对钛合金弯曲薄壁零件加工易变形的问题,建立了薄壁零件的有限元模型,研究了刀具在加工零件时不同位置和不同切削参数下对薄壁零件铣削变形的影响,确定了零件的最大变形点,并运用多指标正交试验确立了最优的刀具切削参数。     

刀具温度场的有限元分析

建立了正交切削的热传导分析模型,采用有限元法中的Lagrange法研究刀具的温度场,并分析刀具前角、进给量 对切削温度的影响规律,为研究刀具磨损机理、提高刀具寿命提供有用的参考数据。     

Investigations on exit burr formation mechanisms based on digital image correlation and numerical modeling

Abstract

Requirements on burr height and burr amount on machined parts are getting stricter. This leads to method development from manufacturing companies to predict burr distribution and its size along part edges. A deeper understanding of burr formation mechanisms will assist to more accurate model development. This study aims to analyze the exit burr formation, which is formed during orthogonal cutting of a brittle cast aluminum alloy. A customized digital image correlation (DIC) system with the help of a high-speed camera was used to measure the displacements fields. It calculates strain fields during burr initiation and development in orthogonal cutting of T7 heat-treated cast aluminum alloy ENAC-AlSi7Mg0.3 as well. Those results are then qualitatively compared with a numerical model of the burr with chamfer formation developed and simulated using a finite element method, to ensure a good correspondence between experiments and simulation. This model is used to complete the DIC study of burr with chamfer formation mechanisms during crack propagation leading to chamfer formation. The analysis of numerically obtained stress triaxiality fields and of DIC observations from experiments are compared to the assumptions made from analytical models. Finally, necessary improvements of an existing burr formation analytical model are proposed.     

Analytical modelling of slot milling exit burr size

A computational model was recently proposed by authors to approximate the tangential cutting force and consequently predict the thickness of the exit up milling side burr. To calculate the cutting force, the specific cutting force coefficient with respect to material properties was used. The model was sensitive to material yield strength and few cutting and tool geometrical parameters. However, the effects of cutting speed, tool coating, and tool rake angle on burr size were neglected. Other phenomena that could affect the burr size such as friction and abrasion were not taken into account either. Therefore, in the current work, a mechanistic force model is incorporated to propose a burr size prediction algorithm. The tangential and radial forces are calculated based on using specific cutting force coefficients in each direction. Furthermore, using the new approach, the burr size is predicated and the effects of a broad range of cutting parameters on burr size and friction angle are evaluated. Experimental values of burr size correlated well with prediction. It was found that the cutting speed has negligible effects on force and burr size. Lower friction angle was recorded when using larger feed per tooth. Consequently, thinner exit up milling side burr was obtained under high friction angle.     

地铁盾构刀盘改造的有限元分析

对改造后的地铁盾构刀盘进行有限元分析,利用Solidwork软件对改造刀盘进行模拟仿真,得出刀盘施工状态下的应力云图,为改造后的刀盘能够正常施工提供理论及实验依据.     

Influence of cutting edge radius on surface integrity and burr formation in milling titanium

The influence of the cutting edge micro geometry on cutting process and on tool performance is subject to several research projects. Recently, published papers mainly focus on the cutting edge rounding and its influence on tool life and cutting forces. For applications even more important, however, is the influence of the cutting edge radius on the integrity of the machined part. Especially for titanium, which is used in environments requiring high mechanical integrity, the information about the dependency of surface integrity on cutting edge geometry is important. This paper therefore studies the influence of the cutting edge radius on surface integrity in terms of residual stress, micro hardness, surface roughness and optical characterisation of the surface and near surface area in up and down milling of the titanium alloy Ti–6Al–4V. Moreover, the influence of the cutting edge radius on burr formation is analysed. The experiments show that residual stresses increase with the cutting edge radius especially in up milling, whereas the influence in down milling is less pronounced. The influence of the cutting edge radius on surface roughness is non-uniform. The formation of burr increases with increasing cutting edge radius, and is thus in agreement with the residual stress tests.