铣刀的力学和动力学广义建模

本文介绍工业上使用最多的立铣和镶齿铣刀的广义数学模型.立铣刀的几何形状用环绕刀体参量外形的螺旋槽建模.镶齿铣刀的刀刃几何,用每一刀片的局部坐标系定义,并用刀具总坐标系在刀体上对其定位和定向.对两种情况用数学表达了刀刃的坐标.使用铣削时的纯运动学,包括刀具和工件两者的结构振动,估计每一切削点处的切屑厚度.用沿与工件接触的每一切削刃或刀齿积分处理,可预断出任意立铣刀和镶齿铣刀的切削力、振动、表面粗糙度及颤振稳定性图.对螺旋锥球头、大圆孤立铣刀和镶片铣刀,预断和测量出的切削力、表面粗糙度和稳定性图,为提出的广义立铣分析的有效性作了说明.集成到先进切削加工模拟程序中的算法,可用于铣削加工中的工艺计划,以避免颤振、扭矩和功率极限约束及尺寸形成误差.     

机器人铣削加工让刀误差建模与分析

在机器人切削加工工艺过程中,让刀误差是影响切削加工精度的重要因素之一。以球头铣刀铣削加工为研究对象,视其为准静态运动过程,根据机器人静弹性力学模型和球头铣刀切削力模型,建立了机器人切削过程的让刀误差数学模型。同时,提出了一种基于基因遗传算法的刀具姿态优化方法,以减小切削过程的让刀误差。最后,通过仿真分析了切削参数、刀具姿态和机器人刚度等因素对让刀误差的影响,验证了刀具姿态优化方法的可行性。     

整体叶轮五轴侧铣加工的铣削力预测模型研究

为了对整体叶轮等复杂曲面的半精或精加工过程进行仿真和铣削力预测,提出了采用锥度球头铣刀五轴侧铣加工叶片型面的刀轴运动和铣削力计算模型。将锥度球头铣刀沿刀轴方向分解成一定数量的微元,为每个微元创建独立的进给坐标系,并将各微元的总进给速度朝垂直刀轴和平行刀轴等两个方向进行分解,进而得到水平和垂直方向的进给量,由此精确建立微元的总切屑厚度模型。通过斜角切削的正交实验计算相应的摩擦角、剪切应力和剪切角等参数,得到各微元被作用的铣削力,即可预测刀具和工件接触的总铣削力。仿真计算和实验结果对比表明:所建立的铣削力预测模型仿真计算结果与实测一致性好,基本符合实际加工规律。     

基于ANSYS的高速五轴数控加工中心球头铣刀切削温度仿真研究

以VMC656高速五轴数控加工中心为研究对象,研究了采用球头铣刀进行切削时,切削热所产生的温度对工件加工精度的影响。基于传热学和金属切削理论,建立了数控加工中心高速切削铝材时球头铣刀温度场数学模型,利用有限元软件ANSYS,仿真分析了球头铣刀在典型工况不同切削参数条件下温度场分布及变化规律,以及切削速度、切削厚度、进给量等参数对切削温度的影响。研究结果表明,在金属切削过程中,切削温度对刀具寿命和工件加工精度都有很大影响,因此必须采取措施,降低切削温度,有助于提高刀具寿命和加工质量。     

摆线铣削淬硬钢工件上的槽

在淬硬工件上铣槽一直是切削加工中的难题之一,其原因有三：①加工时,刀具的大部分切入工件中,会产生很大的切削力和较多的切削热;②每个刀齿上切屑的载荷不均匀,切人工件最多的刀齿载荷最大,其它位置的刀齿载荷较小;③随着容屑槽逐渐被切屑填满,排屑空间变小,切屑的重切机率增大。     

通用螺旋立铣刀的力学和动力学模型(一)

在工业上使用各种形状的螺旋立铣刀.在航空和宇航、汽车和模具工业上,广泛使用螺旋圆柱、螺旋球头、圆锥螺旋球头、大圆角和专用立铣刀.每种铣刀的形状可能不同,但在每个刀刃切削点切削过程的力学和动力学是共同的.本文介绍工业上使用的大多数螺旋立铣刀的广义数学模型.立铣刀形状用绕参数包络包缠的螺旋槽建模.沿参数螺旋槽的刀刃点的坐标用数学表出.应用包含刀具和工件两者振动结构的纯铣削运动学,估计出每一切削点处的切屑厚度.沿和工件接触的每一切削刃进行积分,对任意立铣可预测出切削力、振动、尺寸表面粗糙度和颤振稳定性图.预测出的切削力、表面粗糙度和稳定性图,对于球头、螺旋锥球头和大圆角立铣,可证实本文提出的广义立铣分析方法的可行性.     

内冷可转位精铣球头铣刀的研制

模具多种复杂立体曲面的仿形加工,多采用硬质合金整体铣刀或高精度可转位精铣球头铣刀。本文通过对已有精铣球头铣刀结构的改造,在刀具内部形成了内冷通道,成功研制出带内冷功能的可转位精铣球头铣刀。切削实验研究表明,运用此带内冷功能的可转位精铣球头铣刀切削模具材料,在刀具正常磨损范围内,工件表面质量可稳定保持在R_a1.0μm以下,较不带内冷刀具,可以大幅提高加工表面质量,满足生产工艺要求。本研究成果具有生产成本低,适用性强的特点,可广泛应用于模具行业的曲面加工。     

Gcr15单/二次高速切削的切削性能比较

为了比较单次和二次切削加工的切削性能,在不预设分离层的前提下,文章采用ABAQUS/Explicit6.14分别建立了GCr15单次和二次高速切削热力耦合有限元模型。对比单次/二次切削过程中的切削力、切削温度、以及已加工表面质量,发现二次切削的第二步切削力、刀具最高温度以及温度域均小于第一步,二次切削工件已加工表面质量略好于单次切削。并将模拟所得切屑形态与文献中实验所得切屑形态进行对比,验证了模拟的准确性。模拟结论对指导实际切削中在给定目标切深下,合理安排走刀次数,以得到最优切削结果具有重要意义。     

球头铣刀微切削Ti6Al4V合金仿真与试验研究

为研究每齿进给量对球头铣刀加工钛合金过程中微铣削力以及温度的变化规律和加工后表面形貌的影响,首先,基于有限元方法,使用Deform-3D有限元软件对钛合金进行微铣削仿真;其次,通过试验对铣削力进行验证;最后在超景深显微镜下观察不同每齿进给量对加工表面形貌的影响。研究表明:铣削力随着每齿进给量的增大呈现缓慢波动后快速增大的过程;工件温度随着每齿进给量的增大而增加,在刀-屑接触区温度达到最高,且升温速率也呈现升高的趋势;不同每齿进给量对加工表面存在不同程度的切屑粘连现象,每齿进给量越大,其切屑粘连现象越严重。     

行星复合铣削及其刀具研究

行星复合铣削方法是复合加工方法的一种实现形式,该加工方法所产生的切削力较普通端铣加工的切削力有大幅度的降低,从而能有效地降低切削热、减少工件变形、提高刀具寿命。行星复合铣削方法切削力大幅度地降低的主要原因是该方法的切削轨迹使其能将厚切削层分解为细小的切削层,而该方法中的立铣刀的螺旋角和半径对实际切削力的影响很小。行星复合铣削方法在刀盘低速旋转时就能实现高速切削,有效地避开了高速旋转刀盘的动平衡问题,结合其切削力小的优势,通过增大刀盘直径并增加立铣刀数量来提高加工效率。行星铣刀采用行星轮系结构,能够达到行星复合铣削方法切削轨迹要求,具有扭矩大、运转可靠等优势。     

Process simulation using finite element method — prediction of cutting forces, tool stresses and temperatures in high-speed flat end milling

End milling of die/mold steels is a highly demanding operation because of the temperatures and stresses generated on the cutting tool due to high workpiece hardness. Modeling and simulation of cutting processes have the potential for improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. The main objective of this study was to develop a methodology for simulating the cutting process in flat end milling operation and predicting chip flow, cutting forces, tool stresses and temperatures using finite element analysis (FEA). As an application, machining of P-20 mold steel at 30 HRC hardness using uncoated carbide tooling was investigated. Using the commercially available software DEFORM-2D™, previously developed flow stress data of the workpiece material and friction at the chip–tool contact at high deformation rates and temperatures were used. A modular representation of undeformed chip geometry was used by utilizing plane strain and axisymmetric workpiece deformation models in order to predict chip formation at the primary and secondary cutting edges of the flat end milling insert. Dry machining experiments for slot milling were conducted using single insert flat end mills with a straight cutting edge (i.e. null helix angle). Comparisons of predicted cutting forces with the measured forces showed reasonable agreement and indicate that the tool stresses and temperatures are also predicted with acceptable accuracy. The highest tool temperatures were predicted at the primary cutting edge of the flat end mill insert regardless of cutting conditions. These temperatures increase wear development at the primary cutting edge. However, the highest tool stresses were predicted at the secondary (around corner radius) cutting edge.     

Mechanics and dynamics of general milling cutters.: Part I: helical end mills

A variety of helical end mill geometry is used in the industry. Helical cylindrical, helical ball, taper helical ball, bull nosed and special purpose end mills are widely used in aerospace, automotive and die machining industry. While the geometry of each cutter may be different, the mechanics and dynamics of the milling process at each cutting edge point are common. This paper presents a generalized mathematical model of most helical end mills used in the industry. The end mill geometry is modeled by helical flutes wrapped around a parametric envelope. The coordinates of a cutting edge point along the parametric helical flute are mathematically expressed. The chip thickness at each cutting point is evaluated by using the true kinematics of milling including the structural vibrations of both cutter and workpiece. By integrating the process along each cutting edge, which is in contact with the workpiece, the cutting forces, vibrations, dimensional surface finish and chatter stability lobes for an arbitrary end mill can be predicted. The predicted and measured cutting forces, surface roughness and stability lobes for ball, helical tapered ball, and bull nosed end mills are provided to illustrate the viability of the proposed generalized end mill analysis.     

Cutting force prediction in ball end milling of sculptured surface with Z-level contouring tool path

This paper presents an approach to predict cutting force in 3-axis ball end milling of sculptured surface with Z-level contouring tool path. The variable feed turning angle is proposed to denote the angular position of feed direction within tool axis perpendicular plane. In order to precisely describe the variation of feed turning angle and cutter engagement, the whole process of sculptured surface milling is discretized at intervals of feed per tooth along tool path. Each segmented process is considered as a small steady-state cutting. For each segmented cutting, the feed turning angle is determined according to the position of its start/end points, and the cutter engagement is obtained using a new efficient Z-map method. Both the chip thickness model and cutting force model for steady-state machining are improved for involving the effect of varying feed turning angle and cutter engagement in sculptured surface machining. In validation experiment, a practical 3-axis ball end milling of sculptured surface with Z-level contouring tool path is operated. Comparisons of the predicted cutting forces and the measurements show the reliability of the proposed approach.     

Simulation of flank milling processes

The paper presents prediction of cutting forces when flank milling ruled surfaces with tapered, helical, ball end mills. The geometric model of the workpiece is imported from standard CAD systems, and the tapered helical ball end mill is modeled as the combination of sphere and cone primitives in ACIS^© solid modeling environment. The intersection of cutter and part with a ruled surface is evaluated, and the cutter entry into and exit angles from the work material are modeled, and stored as a function of tool center coordinates along the path. The cutter entry and exit angles, the immersion angles, are used as boundary conditions in predicting the cutting forces along the path. The methodology allows prediction of cutting load distribution on the tool and part, as well optimization of machining cycle times by scheduling the feedrate in such a way that torque, power and static deflections can be maintained at safe levels.     

新型双刃可转位球头立铣刀设计及其加工仿真研究

球头立铣刀是数控机床上加工复杂曲面的高性能结构化刀具,为了提高球头立铣刀的性能,设计了一款新型双刃可转位球头立铣刀,并在CAD/CAM软件Pro/E中建立其三维实体模型;导入金属切削工艺有限元软件AdvantEdge中进行铣削加工模拟仿真,得到加工过程中切削性能参数随时间的变化关系,并与某标准整体式球头立铣刀的铣削加工进行对比分析。结果表明:该铣刀的性能均较优,验证了文中设计的可行性,分析结果为球头立铣刀的设计优化与加工应用提供了参考。     

Prediction of cutting forces in milling of circular corner profiles

This paper proposes an approach to predict the cutting forces in peripheral milling of circular corner profiles in which varying radial depth of cut is encountered. The geometric relationship between an end mill and the corner profile is investigated and a mathematical model is presented to describe the different phases of the cutter/workpiece contact. The milling process for circular corner is discretized into a series of steady-state cutting processes, each with different radial depth of cut determined by the instantaneous position of the end mill relative to the workpiece. A time domain analytical model of cutting forces for the steady-state machining conditions is introduced to each segmented process for the cutting force prediction. The predicted cutting forces can be calculated in terms of tool/workpiece geometry, cutting parameters and workpirece material property, as well as the relative position of the tool to workpiece. Experiments are conducted and the measured forces are compared to the predictions for the verification of the proposed method.     

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.     

An investigation of workpiece temperature variation in end milling considering flank rubbing effect

Better prediction about the magnitude and distribution of workpiece temperatures has a great significance for improving performance of metal cutting process, especially in the aviation industry. A thermal model is presented to describe the cyclic temperature variation in the workpiece for end milling. Owing to rapid tool wear in the machining of aeronautical components, flank rubbing effect is considered. In the proposed heat source method for milling, both the cutting edge and time history of process are discretized into elements to tackle geometrical and kinematical complexities. Based on this concept, a technique to calculate the workpiece temperature in stable state, which supposes the tool makes reverse movement, is developed. And a practicable solution is provided by constructing a periodic temperature rise function series. This investigation indicates theoretically and experimentally the impact of different machining conditions, flank wear widths and cutter locations on the variation of workpiece temperature. The model results have been compared with the experimental data obtained by machining 300M steel under different flank wear widths and cutting conditions. The comparison indicates a good agreement both in trends and values. With the alternative method, an accurate simulation of workpiece temperature variation can be achieved and computational time of the algorithm is obviously shorter than that of finite element method. This work can be further employed to optimize cutting conditions for controlling the machined surface integrity.     

Tool deflection compensation in peripheral milling of curved geometries

This paper presents compensation of surface error due to cutting force-induced tool deflections in a peripheral milling process. Previous research attempts on this topic deal with error compensation in machining of straight geometries only. This paper is concerned with peripheral milling of variable curvature geometries where the workpiece curvature changes continuously along the path of cut. In the case of curved geometries, both process geometry and the cutting forces have shown to have strong dependence on workpiece curvature and hence variation of surface error along the path of cut. This calls for a different error compensation strategy than the one which is normally used for machining straight geometries. The present work is an attempt to improve accuracy in machining of curved geometries by use of CNC tool path compensation. Mechanistic model for cutting force estimation and cantilever beam model for cutter deflection estimation are used. The results based on machining experiments performed on a variety of geometries show that the dimensional accuracy can be improved significantly in peripheral milling of curved geometries.     

Analysis on high-speed face-milling of 7075-T6 aluminum using carbide and diamond cutters

This research is concerned with the analytical and experimental study on the high-speed face milling of 7075-T6 aluminum alloys with a single insert fly-cutter. The results are analyzed in terms of cutting forces, chip morphology, and surface integrity of the workpiece machined with carbide and diamond inserts. It is shown that a high cutting speed leads to a high chip flow angle, very low thrust forces and a high shear angle, while producing a thinner chip. Chip morphology studies indicate that shear localization can occur at higher feeds even for 7075-T6, which is known to produce continuous chips. The resultant compressive residual stresses are shown for the variation of cutting parameters and cutting tool material. The analysis of the high-speed cutting process mechanics is presented, based on the calculation results using extended oblique machining theory and finite element simulation.