微切削加工7050-T7451铝合金的尺度效应研究

通过一系列单因素直角切削试验,对用硬质合金刀具微切削7050-T7451铝合金的尺度效应进行了研究。在试验过程中,对切削力进行了实时测量,并通过计算获得了不同切削深度下的单位切削力。基于试验结果和微加工理论,分析了不同刀具刃口半径微切削尺度效应的特点,总结了刃口半径、切削速度、切削深度等切削参数对微切削过程中尺度效应的影响规律。     

基于钝圆尺寸效应的微细切削机理试验研究

通过微细车削试验,研究了微细切削加工参数对切削力、表面质量、切屑形成的影响,发现切削厚度与刃口半径的比值是影响微细切削的关键因素,当该比值过小时,刃口尺寸效应作用极其显著,导致切削比能迅速增大,表面质量恶化,切屑形成困难。根据这一结论可确定微细切削加工参数选择的下限范围,从而为微细切削加工参数选择提供理论依据。     

超精密切削时刀具切削刃的作用机理分析

分析了金刚石刀具切削刃的切削作用、脆性材料超精密切削时切屑形成机理；对金刚石刀具切削刃钝圆半径、切削厚度、切削角三者之间的关系进行了描述。结果表明：脆性材料可以实现塑性域超精密切削加工；控制切削参数可以加工出满足要求的表面粗糙度和表面波纹度，为生产实际提供可靠的工艺条件及技术参数。     

Cutting force model considering tool edge geometry for micro end milling process

The analysis of the cutting force in micro end milling plays an important role in characterizing the cutting process, as the tool wear and surface texture depend on the cutting forces. Because the depth of cut is larger than the tool edge radius in conventional cutting, the effect of the tool edge radius can be ignored. However, in micro cutting, this radius has an influence on the cutting mechanism. In this study, an analytical cutting force model for micro end milling is proposed for predicting the cutting forces. The cutting force model, which considers the edge radius of the micro end mill, is simulated. The validity is investigated through the newly developed tool dynamometer for the micro end milling process. The predicted cutting forces were consistent with the experimental results.     

Finite element optimization of diamond tool geometry and cutting-process parameters based on surface residual stresses

In this paper, a coupled thermo-mechanical plane-strain large-deformation orthogonal cutting FE model is proposed on the basis of updated Lagrangian formulation to simulate diamond turning. In order to consider the effects of a diamond cutting tool’s edge radius, rezoning technology is integrated into this FE based model. The flow stress of the workpiece is modeled as a function of strain, strain rate, and temperature, so as to reflect its dynamic changes in physical properties. In this way, the influences of cutting-edge radius, rake angle, clearance angle, depth of cut, and cutting velocity on the residual stresses of machined surface are analyzed by FE simulation. The simulated results indicate that a rake angle of about 10° and a clearance angle of 6° are the optimal geometry for a diamond tool to machine ductile materials. Also, the smaller the cutting edge radius is, the less the residual stresses become. However, a great value can be selected for cutting velocity. For depth of cut, the ‘size effect’ will be dependent upon it. Residual stresses will be reduced with the decrement of depth of cut, but when the depth of cut is smaller than the critical depth of cut (i.e., about 0.5 μm according to this work) residual stresses will decrease accordingly.     

Investigation of cutting forces,surface integrity,and tool wear when high-speed milling of high-volume fraction SiC<Subscript>p</Subscript>/Al6063 composites in PCD tooling

This paper focused on high-speed milling of Al6063 matrix composites reinforced with high-volume fraction of small-sized SiC particulates and provided systematic experimental study about cutting forces, thin-walled part deformation, surface integrity, and tool wear during high-speed end milling of 65% volume fraction SiC_p/Al6063 (Al6063/SiC_p/65p) composites in polycrystalline diamond (PCD) tooling. The machined surface morphologies reveal that the cutting mechanism of SiC particulates plays an important role in defect formation mechanisms on the machined surface. In high-speed end milling of Al6063/SiC_p/65p composites, the cutting forces are influenced most considerably by axial depth of cut, and thus the axial depth of cut plays a dominant role in the thin-walled parts deformation. Increased milling speed within a certain range contributes to reducing surface roughness. The surface and sub-surface machined using high-speed milling suffered from less damage compared to low-speed milling. The milling speed influence on surface residual stress is associated with milling-induced heat and deformation. Micro-chipping, abrasive wear, graphitization, grain breaking off, and built-up edge are the dominated wear mechanism of PCD tools. Finally, a series of comparative experiments were performed to study the influence of tool nose radius, average diamond grain size, and machining parameters on PCD tool life.     

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.     

Investigation and prediction of chip geometry in diamond turning

Management of the chips generated in diamond turning is often critical, because contact between chips and the workpiece can result in superficial damage to the finished surface. Controlling chip motion is not a trivial process as the proper positioning of an oil or air stream requires an understanding of the dynamics of a diamond turned chip and the machining parameters that affect it. Work has been performed to investigate the effects of cutting speed, depth of cut, tool geometry, tool wear, and workpiece material properties on chip motion and geometry. Utilizing radius of curvature data from cutting experiments, a parameter has been proposed that can be used to predict chip radius of curvature for a wide range of machining conditions. This chip curvature parameter, χ, exhibits a power law relationship with chip radius of curvature as a function of tool geometry, depth of cut, cutting speed, and both elastic and plastic properties of the workpiece material.     

Mechanisms in oxide-carbide ceramic BOK 60 grinding

The paper presents an experimental study of micro-cutting intended to aid the optimization of the grinding process of the oxide–carbide ceramic BOK 60. The necessity for investigating the mechanisms occurring between the abrasive material and the ceramic is imposed by the fact that grinding is the dominant technology used to achieve the required quality of the workpiece surface finish. The investigations were carried out to determine the normal and tangential cutting forces, the critical penetration depth, and the crack generation angle on the workpiece surface as a function of the grain penetration speed and depth. The micro-cutting process was performed with a single diamond cone-shaped grain at varying depths of cut. It was found that the critical grain penetration depth separating ductile flow from brittle fracturing ranges from 3 to 5?μm, while radial cracks on the ceramic’s surface are distributed at an angle from 35° to 75°, measured relative to the direction of the diamond grain’s motion.     

Finite element analysis of the influence of tool edge radius on size effect in orthogonal micro-cutting process

The size effect in metal cutting is evident in the nonlinear scaling phenomenon observed in the specific cutting energy with decrease in uncut chip thickness. It has been argued by many researchers that this scaling phenomenon is caused mainly by the cutting tool edge radius, which purportedly affects the micro-cutting process by altering the effective rake angle, enhancing the plowing effect or introducing an indenting force component. However, the phenomenological reasons why the tool edge radius causes size effect and the relationship between the tool edge radius and the characteristic length scale associated with the size effect in micro-cutting has not been sufficiently clarified. In this paper, a strain gradient plasticity-based finite element model of orthogonal micro-cutting of Al5083-H116 alloy developed recently is used to examine fundamentally the influence of tool edge radius on size effect. The applicability of two length scales—tool edge radius and the material length scale l in strain gradient plasticity—are also examined via analysis of data available in the literature.     

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.     

Experimental study on size effect of tool edge and subsurface damage of single crystal silicon in nano-cutting

A method for fabricating a diamond tool with controllable edge radius was proposed. Using diamond tools with different edge radii at a low speed, nano-cutting tests were performed on single crystal silicon using a special instrument with SEM online observation. The chip morphology and deformation coefficient were analyzed to study the size effect of tool edge in the ductile-cut region. Electron back-scattered diffraction and laser micro-Raman spectroscopy were employed to detect subsurface damage in the machined silicon. The results indicated that the cutting-induced amorphous layer thickness is strongly dependent on the depth of cut and tool edge radius. In the beginning, the amorphous damage layer thickness decreases rapidly with the depth of cut, and then it increases gradually with the further increase in the depth of cut. The minimum amorphous damage can be obtained when the depth of cut is comparable to the tool edge radius.     

单晶金刚石微型刀具刃磨试验研究

采用金刚石砂轮对单晶金刚石微型刀具进行了刃口机械刃磨试验,利用莱卡光学显微镜观察了单晶金刚石刀具刃口和表面形貌,以研究不同参数对磨削过程的影响,通过优化相关参数来获得更好的单晶金刚石微型刀具并提高刃磨效率。试验选择砂轮粒度、磨削速度以及进给速率作为刃磨参数。通过正交试验设计,比较磨削力、刃口半径和表面形貌,从而筛选出最优参数。试验得出小粒度砂轮、较高磨削速度和中等进给速度可以得到较好的刃磨结果。     

TOOL FORCE MODEL FOR DIAMOND TURNING

A new tool force model to be presented is based upon process geometry and the characteristics of the force system, in which the forces acting on the tool rake face, the cutting edge rounding and the clearance face have been considered, and the size effect is accountable for the new model. It is desired that the model can be well applicable to conventional diamond turning and the model may be employed as a tool in the design of diamond tools. This approach is quite different from traditional investigations primarily based on empirical studies. As the depth of cut becomes the same order as the rounded cutting edge radius, sliding along the clearance face due to elastic recovery of workpiece material and plowing due to the rounded cutting edge may become important in micro-machining, the forces acting on the cutting edge rounding and the clearance face can not be neglected. For this reason, it is very important to understand the influence of some parameters on tool forces and develop a model of the relatio     

An edge reversal method for precision measurement of cutting edge radius of single point diamond tools

A method, which is referred to as the edge reversal method, is proposed for precision measurement of the cutting edge radius of single point diamond tools. An indentation mark of the cutting edge which replicates the cutting edge geometry is firstly made on a soft metal substrate surface. The cutting edge of the diamond tool and its indentation mark, which is regarded as the reversal cutting edge, are then measured by utilizing an atomic force microscopy (AFM), respectively. The cutting edge radius can be accurately evaluated through removing the influence of the AFM probe tip radius, which is comparable to the cutting edge radius, based on the two measured data without characterization of the AFM probe tip radius. The results of measurement experiments and uncertainty analysis are presented to demonstrate the feasibility of the proposed method.     

Distribution of unit forces on the tool edge rounding in the case of finishing turning

An experimental investigation was conducted to determine the effects of tool cutting edge geometry on the cutting forces in finish turning, where the applied feed and depth of cut are small and often comparable with the tool edge radius. If a tool with large tool edge radius is used in finish turning, the ploughing effect begins to determine the machined surface. This paper presents the results of analytical considerations concerning the unit forces on a cutting edge. The aim of this paper is to indicate possibilities of modelling the unit forces and stress distribution based on cutting resistance. The forces calculated in the feed and cutting speed directions were projected onto the tangential and normal directions of the rounded cutting edge surface. An important assumption in all the considerations was that the thermo-mechanical properties of the materials used remained constant. The minimum thickness of cut was defined, and some characteristic points were identified dividing the cutting zone into three subregions: where a chip is formed, where the machined surface is formed and an unstable region.     

微切削加工技术

在探讨切削技术发展动力的基础上给出了机械加工的尺度划分方法。通过综述微制造技术,介绍了微切削加工装备和微切削刀具,提出了利用应变梯度塑性理论进行微切削机理研究的设想,从分子动力学模拟仿真、最小切削厚度、切屑形态、微切削力、切削温度、工件材料的微量加工性、刀具变形、表面粗糙度与切削稳定性、毛刺、积屑瘤、刀具磨损等不同方面分析了微切削机理的研究现状和存在问题。最后介绍了微铣削CAD/CAM技术,并指出了微切削加工技术的发展趋势。     

A study of the effect of tool cutting edge radius on ductile cutting of silicon wafers

Ductile mode cutting of silicon wafers can be achieved under certain cutting conditions and tool geometry. An experimental investigation of the critical undeformed chip thickness in relation to the tool cutting edge radius for the brittle-ductile transition of chip formation in cutting of silicon wafers is presented in this paper. Experimental tests for cutting of silicon wafers using diamond tools of different cutting edge radii for a range of undeformed chip thickness are conducted on an ultra-precision lathe. Both ductile and brittle mode of chip formation processes are observed in the cutting tests. The results indicate that ductile cutting of silicon can be achieved at certain values of the undeformed chip thickness, which depends on the tool cutting edge radius. It is found that in cutting of silicon wafers with a certain tool cutting edge radius there is a critical value of undeformed chip thickness beyond which the chip formation changes from ductile mode to brittle mode. The ductile-brittle transition of chip formation varies with the tool cutting edge radius. Within the range of cutting conditions in the present study, it has also been found that the larger the cutting edge radius, the larger the critical undeformed chip thickness for the ductile-brittle transition in the chip formation.     

Investigation of the direction of chip motion in diamond turning

Management of the chips generated in diamond turning is often critical since contact between chips and the workpiece can result in superficial damage to the finished surface. Controlling chip motion is not a trivial process as the proper positioning of an oil or an air stream requires an understanding of the dynamics of a diamond turned chip and the machining parameters that affect it. Previous work [1] introduced the chip curvature parameter, χ, which is useful in predicting chip radius of curvature over a wide range of cutting speeds, depths of cut, tool geometries and workpiece material properties. To control chip motion, however, an understanding of the direction chips leave the tool/workpiece interface must also be obtained. Cutting experiments were performed investigating the influence of cutting speed, depth of cut, feed rate, tool path angle, tool geometry and tool orientation on the directional characteristics of the motion of diamond turned chips. Flow angle measurements obtained during cutting were found to remain within ± 10° of predictions from a simple geometrical model originally proposed for conventional machining.     

高精度金刚石刀具研磨关键技术研究

金刚石刀具刃口锋利度对所加工零件的表面质量有着重要影响。通过确定合理的研磨设备结构和合理的研磨工艺参数,获得的刀具刃口锋利度从300 nm提高到了50nm,刀面表面粗糙度从15nm提高到了0.5nm,刀具刃口质量得到了明显改善。