Experimental and numerical investigations of single abrasive-grain cutting

The present work will provide an in-depth analysis of the abrasive-grain cutting process using a combination of experimental observations and finite element simulations. The workpiece material was AISI 4340. The cutting tool was spherical in shape with a 0.508 mm radius and was fabricated from diamond. The experiments were conducted at cutting speeds of 5−30 m/s in 5 m/s increments and depths of cut from 0.3 to 7.5 μm. The analysis provided a comprehensive understanding of the abrasive-grain cutting process related to the friction between the cutting tool and the workpiece, the material mechanics of the workpiece, and the cutting mechanics of the operation. It was found that the normal forces increased as cutting speed increased due to strain-rate hardening of the workpiece and that the tangential forces decreased as cutting speed was increased due to a reduction in tool-workpiece friction and due to a change in cutting mechanics. The scratch profiles showed that the cutting mechanics changed as cutting speed was increased due to a reduction in material pile-up height. The approximate uncut chip thicknesses for the transitions from elastic, elastoplastic, and fully plastic cutting were identified and were found to increase as cutting speed was increased.     

Chip geometries during high-speed machining for orthogonal cutting conditions

The originality of this work consists in taking photographs of chips during the cutting process for a large range of speeds. Contrary to methods usually used such as the quick stop in which root chips are analyzed after an abrupt interruption of the cutting, the proposed process photographs the chip geometry during its elaboration. An original device reproducing perfectly orthogonal cutting conditions is used because it allows a good accessibility to the zone of machining and reduces considerably the vibrations found in conventional machining tests. A large range of cutting velocities is investigated (from 17 to 60 m/s) for a middle hard steel (French Standards XC18). The experimental measures of the root chip geometry, more specifically the tool-chip contact length and the shear angle, are obtained from an analysis of the pictures obtained with a numerical high-speed camera. These geometrical characteristics of chips are studied for various cutting speeds, at the three rake angles −5, 0, +5° and for different depths of cut reaching 0.65 mm.     

管锥相贯焊接坡口数控切割

利用空间解析几何的原理建立了管锥相贯数学模型，用参量方程描述了管端相贯线焊接坡口的几何形状，该数学模型可应用于三轴联动火焰数控切管机。针对三轴联动火焰数控切管机，分析了管锥相贯焊接坡口数控切割运动，将切割运动分解为割炬绕被切管的回转、沿管轴线的平移及在轴剖面内的倾斜三轴联动，给出了数控切割所需相贯线、两面角、实际切割角等参数的参量表达式。并研究了应用过渡切割方法解决小角度存在的问题，给出了过渡切割时各参数的数学表达式。切割试验结果表明，所切焊接坡口完全符合美国石油协会标准(API)规范。     

A unified instantaneous cutting force model for flat end mills with variable geometries

A new and unified instantaneous cutting force model is developed to predict cutting forces for flat end mills with variable geometries. This model can routinely and efficiently determine the cutting properties such as shear stress, shear and normal friction angles (SSSNFAs) involved in the cutting force coefficients by means of only a few milling tests rather than existing abundant orthogonal turning tests. Novel algorithms are developed to characterize these properties using following steps: transformation of cutting forces measured in Cartesian coordinate system into a local system on the normal plane, establishment of explicit equations to bridge SSSNFAs and the transformed cutting forces, determination of SSSNFAs by solving the equations and fitting SSSNFAs as functions of process geometries. Results definitely show that shear stress can be treated as a constant whereas shear and normal friction angles should be characterized by Weibull functions of instantaneous uncut chip thickness. Experiments verify that the proposed unified model is effective to predict the cutting forces in flat end milling in spite of cutter geometries and cutting conditions.     

Marble cutting with single point cutting tool and diamond segments

An investigation has been undertaken into the frame sawing with diamond blades. The kinematic behaviour of the frame sawing process is discussed. Under different cutting conditions, cutting and indenting-cutting tests are carried out by single point cutting tools and single diamond segments. The results indicate that the depth of cut per diamond grit increases as the blades move forward. Only a few grits per segment can remove the material in the cutting process. When the direction of the stroke changes, the cutting forces do not decrease to zero because of the residual plastic deformation beneath the diamond grits. The plastic deformation and fracture chipping of material are the dominant removal processes, which can be explained by the fracture theory of brittle material indentation.     

Effect of direction of parameterization on cutting forces and surface error in machining curved geometries

The present paper investigates the effect of two variables, namely direction of parameterization and cutter diameter on process geometry, cutting forces, and surface error in peripheral milling of curved geometries. In machining of curved geometries where the curvature varies continuously along tool path, the process geometry variables, namely feed per tooth, engagement angle, and maximum undeformed chip thickness too vary along tool path. These variations will be different when a given geometry is machined from different parametric directions and with different cutter diameters. This difference in process geometry variations result in changed cutting forces and surface error along machined path. This aspect has been studied for variable curvature geometries by machining from both parametric directions and using cutters of different diameter. The computer simulation studies carried out show considerable amount of shift in the location of peak cutting forces with the change in cutting direction and cutter diameter, particularly in concave regions of workpiece geometry. A new parameter γ that relates the instantaneous curvature of workpiece with cutter radius is defined. The larger value of γ is an indicator of greater shift in the location of peak forces from the point of maximum curvature on the workpiece. The simulation results are validated by carrying out machining experiments with curved workpiece geometry and are found to be in good agreement.     

2RX 安全壳钢衬里截锥体纵缝的焊接

秦山二期核电站的2号反应堆安全壳钢衬里是由底板、截锥体、筒身及穹顶组成的封闭结构.其主要作用是防止放射性物质释放的密封屏障.安全等级二级、抗震类别Ⅰ类、质保等级一级.     

Multiscale simulation of nanometric cutting of single crystal copper —— effect of different cutting speeds

A multiscale simulation has been performed to determine the effect of the cutting speed on the deformation mechanism and cutting forces in nanometric cutting of single crystal copper. The multiscale simulation model, which links the finite element method and the molecular dynamics method, captures the atomistic mechanisms during nanometric cutting from the free surface without the computational cost of full atomistic simulations. Simulation results show the material deformation mechanism of single crystal copper greatly changes when the cutting speed exceeds the material static propagation speed of plastic wave. At such a high cutting speed, the average magnitudes of tangential and normal forces increase rapidly. In addition, the variation of strain energy of work material atoms in different cutting speeds is investigated.     

PCBN刀具干湿切削加工淬硬钢时的磨损对比

本文研究了在一定切削参数下干、湿式切削加工淬硬钢时四种PCBN刀具的刀具寿命、磨损形式和磨损机理。通过扫描电子显微镜观察不同切削行程下刀尖形貌和刀具后刀面磨损量,并对刀具前后刀面进行能谱分析。结果表明湿式切削时的后刀面磨损量小于干式切削,说明刀具湿切比干切时具有较好的性能;PCBN刀具的磨损形式有前刀面磨损、后刀面磨损,其中前刀面磨损的表现形式为月牙洼磨损,磨损机理为机械磨损、氧化磨损和黏结剂磨损,而后刀面磨损机理有机械磨损、氧化磨损、黏结剂磨损和扩散磨损等;同时还发现CBN含量下降,刀具的后刀面磨损量也有下降趋势,即刀具的切削寿命有延长趋势。     

Development of micro milling tool made of single crystalline diamond for ceramic cutting

In order to machine micro aspheric ceramic molds precisely and efficiently, micro milling tools made of single crystalline diamond (SCD) are developed. Many cutting edges are fabricated 3-dimensionally on the edge of a cylindrical SCD by a laser beam. Flat binderless tungsten carbide mold was cut with the developed tool to evaluate the tool wear rate and its life. Some micro aspheric molds of tungsten carbide were cut with the tool at a rotational speed of 50,000 min⁻¹. The molds were cut in the ductile mode. The form accuracy obtained was about 100 nm P–V and the surface roughness 12 nm R_z.     

Optimization of cutting conditions for single pass turning operations using a deterministic approach

An optimization analysis, strategy and CAM software for the selection of economic cutting conditions in single pass turning operations are presented using a deterministic approach. The optimization is based on criteria typified by the maximum production rate and includes a host of practical constraints. It is shown that the deterministic optimization approach involving mathematical analyses of constrained economic trends and graphical representation on the feed-speed domain provides a clearly defined strategy that not only provides a unique global optimum solution, but also the software that is suitable for on-line CAM applications. A numerical study has verified the developed optimization strategies and software and has shown the economic benefits of using optimization.     

单晶锗纳米切削过程分子动力学仿真与实验研究

为深入理解单晶锗纳米切削特性,提高纳米锗器件光学表面质量,采用三维分子动力学(MD)模拟方法研究了单点金刚石压头与单晶锗表面的接触和滑动过程。研究了压头在滑动切削过程中的材料变形、切削力、切屑堆积、表面形貌尺寸。仿真结果表明,随着垂直载荷的增加,切削力、表面形貌尺寸、切屑堆积在接触过程中逐渐增加,且与切削速度无明显关联。切削过程中切削力波动的根本原因是由于单晶锗晶格破坏引起位错的产生和能量波动。为了验证仿真结果的正确性,使用纳米划痕仪对单晶锗进行了纳米切削实验。实验结果与仿真结果一致,验证了MD模型的正确性和有效性。     

Identification of the specific cutting force for geometrically defined cutting edges and varying cutting conditions

Cutting force modeling is a major discipline in the research of cutting processes. The exact prediction of cutting forces is crucial for process characterization and optimization. Semi-empirical and mechanistic force models have been established, but the identification of the specific cutting force for a pair of tool and workpiece material is still challenging. Existing approaches are depending on geometrical idealizations and on an extensive calibration process, which make practical and industrial application difficult. For nonstandard tools and five axis kinematics there does not exist a reasonable solution for the identification problem.In this paper a co-operative force model for the identification of the specific cutting forces and prediction of integral forces is presented. The model is coupled bidirectionally with a multi-dexel based material removal model that provides geometrical contact zone information. The nonlinear specific forces are modeled as polynomials of uncut chip thickness. The presented force model is not subjected to principal restrictions on tool shape or kinematics, the specific force and phase shift are identified with help of least square minimization. The benefit of this technique is that no special calibration experiments are needed anymore, which qualifies the method to determine the specific forces simultaneously during the machining process. In this paper, experiments with different cutting conditions are analyzed and systematically rated. Finally, the method is validated by experiments using different cutting conditions.     

基于多级排样方式的单一矩形件卷材下料算法

讨论了单一矩形件卷材下料问题,即采用剪切工艺将卷材切割出一定数量的同种矩形件,目标为使得所耗费的卷材长度最小.提出一种基于隐式枚举法和动态规划算法的优化下料算法.切割过程由2个阶段组成,第1阶段将卷材切割成宽度相同、长度不大于剪刃长度的段,第2阶段将段切割成矩形件.首先,采用隐式枚举法确定所有需要考察的段的长度,并采用...     

切削温度与切削力综合测量的虚拟仪器

介绍了综合测量切削平均温度和三向切削力并对其进行分析处理的虚拟仪器.利用PCI-1 200卡采集热电偶测温仪和电阻应变式测力仪传输的数据.利用LabVIEW平台开发.具有显示 力和温度波形曲线、热电偶标定和测力仪刻度标定、确定切削温度和切削力指数公式的能力 .提出了基于切削力和切削温度信息的切削状态判定方法.     

切削温度与切削力综合测量的虚拟仪器

介绍了综合测量切削平均温度和三向切削力并对其进行分析处理的虚拟仪器。利用PCI－1200卡采集热电偶测温仪和电阻应变式测力仪传输的数据。利用Lab VIEW平台开发。具有显示力和温度波形曲线、热电偶标定和测力仪刻度标定、确定切削温度和切削力指数公式的能力。提出了基于切削力和切削温度信息的切削状态判定方法。     

不同形状结构锯片锯切性能对比分析

试验采用九种不同形状结构的φ105冷压小尺寸金刚石锯片切割花岗石,其锋利性、寿命和锯切质量表现出有很大的不同,文中从理论上分析了这些差异产生的原因,提出了通过改变锯片的形状结构实现锯片锯切性能的改善,如适当增加节块前端的耐磨性。这对于指导小锯片的设计和制造具有很好的参考价值。     

PCD和CVD金刚石刀具切削性能对比及失效机理初探

通过切削实验,观察切削前后刀具的表面和刃口形貌、金刚石刀片组成成分、以及被加工工件表面粗糙度,比较两种刀具的切削性能,探讨其失效机理。结果表明:在同等条件下,CVD金刚石刀具的切削性能要明显优于PCD刀具。在车削过程中,PCD刀具的失效机理主要是结合剂与被加工材料中化学成分发生化学反应使结合剂流失,导致刀具结构疏松,从而导致磨粒团脱落。CVD刀具的失效机理为产生变质层磨损。切削过程中随着加工时间的进一步延长,切削区温度不断升高,当达到热化学反应温度时,就会在刀具表面形成变质层,从而带来切削过程中刀具的磨损;同时高温状态下CVD金刚石的晶界疲劳破坏,也可能会造成CVD金刚石刀具的磨损失效。     

CVD金刚石厚膜工具制作工艺和切削实验研究探讨

采用特殊的活性焊料对CVD膜与硬质合金基体进行真空焊接，获得了大于500MPa的剪切强度，此强度已经接近金刚石膜的剪切强度。针对不同工艺的CVD刀具与PCD刀具对切削力和被加工材料表面粗糙度进行了切削试验对比，在铜材和硅铝合金的切割实验中CVD刀具达到的表面粗糙度达到表面粗糙度1．3μm和0.9μm，远高于使用PCD刀具获得的表面粗糙度2．9μm和1．4μm；结果表明CVD刀具较PCD刀具有明显的优势。     

Mechanistic force modeling of single point cutting tool in terms of grinding angles

The cutting tool angles have conventionally been presented using projective geometry in terms of the projections of cutting edges on respective planes, which makes the visualization of geometry difficult, particularly for complex tools. Modeling a cutting tool using the actual grinding angles can simplify the geometric definition of the tools and provide a comprehensive and simple definition of tools for downstream applications. The paper presents the 3D definition of the faces of a single point cutting tool (SPCT) in terms of 3D rotational grinding angles and maps the new tool nomenclature with the ASA, ORS and NRS nomenclatures. A mechanistic model is subsequently proposed to predict the forces in terms of the grinding angles, chip thickness and velocity using second degree polynomial function, unlike the conventionally used logarithmic ones. The model has been calibrated for HSS tool and Mild Steel workpiece combination for end turning of a tubular workpiece based on the regression analysis of a central composite design of the experiments. The results have been discussed and the model has been validated for a new set of experimental data. The model shows a good correlation to the observed results.