A simplified method for local tool interference detection and tool position modification during five-axis ball-end milling process

Five-axis ball-end milling is commonly used to machine the complex surfaces. Local tool interference phenomenon which often occurs in five-axis milling should be urgently solved. In this paper, a simplified method to detect the occurrence of local tool interference and modify tool position is proposed. First, the detection matrix is established to detect local tool interference at all the cutter location points on tool path simultaneously in five-axis ball-end milling of complex surfaces. The algorithm of detection matrix based on point arithmetic is simple. Secondly, the new coordinates of the modified interfering-free points are obtained precisely by using the genetic algorithm. The feasibility of the method is validated by simulation in Matlab. This research is benefit to simplify the calculation of local tool interference detection and tool position modification.

The Extraction Method of Cutting Engagement in Ball-end Milling Simulation

Ball-end mill is widely used in workpiece processi ng with free-form surfaces. Such models that can predict processing character istics precisely are very necessary to the aim of cost reducing, quality improvi ng and productivity progressing, the cutting force prediction is the most import ant among these models. To explore the physical essence of metal cutting, model researchers commonly simplify the geometric conditions in cutting process, and a ssume that the geometric parameters that are needed to solve the physical models have already been predefined, so it results in the separation between model res earch and practical application. In this paper, for the representative cutting f orce models of ball end milling, a new extraction method of geometric parameters is suggested, which makes it possible for physical model to actually serve for the practical manufacturing, and take in the inspection of real production.

Analysis and correction of the machining errors of small plastic helical gears by ball-end milling

Many small-size precise plastic helical involutes gears are used in electrical appliances to transmit rotary movements con- tinuously and smoothly. Ball-end milling is an effective method for trial manufacture or small batch production of this type of gear, but the precision of the gear is usually low. In this research, the main sources of the errors of the gear, machining errors of the tooth profile and trace of the gear obtained were analyzed. The correction amounts for these errors are then determined by using a CNC gear tester. They are used to generate a new 3D-CAD model for gear machining with better nrecision.

A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators

Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are difficult to polish it.Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface.Therefore,this method is suitable for polishing HSR.However,the material removal rate of the ordinary small ball-end magnetorheological polishing is low,leading to long polishing time and low output of HSR.To solve this problem,a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research.The influence rule of processing parameters on the material removal rate is studied experimentally.A set of optimal processing parameters is obtained to maximize the material removal rate.Compared with the ordinary method,the material removal rate of the new method can be improved by 143%.Subsequently,an HSR is polished by the new method.The results show that the polishing time can be reduced by 55%,and the polished surface roughness can reach 7.7 nm.The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR.

双圆弧斜齿齿轮泵转子加工刀轨规划及仿真

针对双圆弧斜齿齿轮泵转子加工方法中存在的加工效率和精度比较低等问题,提出了利用球头铣刀在数控铣床上加工双圆弧斜齿齿轮泵转子的方法。研究目标是:根据双圆弧斜齿齿轮泵转子方程,结合空间啮合原理,建立了双圆弧斜齿轮的加工坐标系,根据各坐标系之间的转换矩阵,建立了双圆弧斜齿齿轮泵转子的齿面方程,模拟使用球头铣刀进行加工过程,计算出加工刀具中心在平面和空间轨迹,同时给出判定球头铣刀不发生干涉的最大半径的方法。利用VERICUT软件建立虚拟制造环境并进行铣齿仿真加工,验证了双圆弧斜齿齿轮泵转子齿面数控加工方法的正确性及其可行性。

取向型微沟槽高速球铣加工制备方法及其减摩性能研究

探究直接利用高速球铣加工工艺制备取向型表面微沟槽织构的方法,并对该类型表面微织构的减摩性能进行研究.鉴于高速球铣加工工艺走刀路径灵活可变、表面材料残留几何尺寸与分布形态具备可控性的特点,利用Matlab仿真对高速球铣加工表面形貌进行预测,通过高速球铣加工试验验证仿真结果,并基于流体动压润滑理论,结合Fluent流体仿真分析与高速环-块摩擦磨损试验,对该类型表面微织构的减摩性能进行分析.当切削参数选用径向切深明显大于每齿进给量的组合时,高速球铣加工表面残留材料能够形成明显的微沟槽形貌,且微沟槽特征的取向可由球头铣刀的走刀路径进行控制;微沟槽承载能力与其取向密切相关,随着微沟槽取向角由90°减小至20°,负压区与正压区范围呈现扩大趋势,油膜内逆流效应逐渐减弱,动压效应逐渐增强,微沟槽承载能力提高了20.64%,表面摩擦系数由0.02845降低至0.02165;然而,当取向角过小时,负压区与正压区的范围过小,不能形成有效的收敛楔,微沟槽承载能力下降,表面摩擦系数上升.通过高速球铣加工工艺能够实现取向型表面微沟槽织构的可控制备,且该类表面的减摩性能与取向角α密切相关,在本文研究范围内,取向角为20°时表现出最小的摩擦系数与最高的油膜承载力.本文研究结果可为表面织构造型方法提供一种新思路,能够为满足零件表面的减摩需求提供很好的解决方法.

Third-order point contact approach for five-axis sculptured surface machining using non-ball-end tools(II): Tool positioning strategy

Based on the mathematical model describing the third-order approximation of the cutter envelope surface according to one given cutter location(CL),a tool positioning strategy is proposed for efficiently machining free-form surfaces with non-ball-end cutters.The optimal CL is obtained by adjusting the inclination and tilt angles of the cutter until its envelope surface and the design surface have the third-order contact at the cutter contact(CC)point,which results in a wide machining strip.The strategy can handle the constraints of machine joint angle limits,global collision avoidance and tool path smoothness in a nature way,and can be applied to general rotary cutters and complex surfaces.Numerical examples demonstrate that the third-order point contact approach can improve the machining strip width greatly as compared with the recently reported second-order one.

Prediction of cutting forces in ball-end milling of 2.5D C/C composites

Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, burr, poor surface quality and rapid wear of cutters. Accurate and fast pre- diction of cutting forces is important for milling C/C composite materials with high quality. This paper presents an alternative cutting force model involving the influences of the directions of fiber. Based on the calculated and experimental results, the cutting forces＂ coefficients of 2.5D CC com- posites are evaluated using multiple linear regression method. Verification experiment has been car- ried out through a group of orthogonal tests. Results indicate that the proposed nmdel is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.

Interference and grinding characteristics in ultra-precision grinding of thin-walled complex structural component using a ball-end grinding wheel

As for ultra-precision grinding of difficult-to-process thin-walled complex components with ball-end grinding wheels,interference is easy to occur.According to screw theory and grinding kinematics,a mathematical model is established to investigate the interference and grinding characteristics of the ball-end wheel.The relationship between grinding wheel inclination angle,C axis rotation angle,grinding position angle and grinding wheel wear are analyzed.As the grinding wheel inclination angle increases,the C axis rotatable range decreases and the grinding position angle increases.The grinding position angle and wheel radius wear show a negative correlation with the C axis rotation angle.Therefore,a trajectory planning criteria for increasing grinding speed as much as possible under the premise of avoiding interference is proposed to design the grinding trajectory.Then grinding point distribution on the ball-end wheel is calculated,and the grinding characteristics,grinding speed and maximum undeformed chip thickness,are investigated.Finally,a complex structural component can be ground without interference,and surface roughness and profile accuracy are improved to 40.2 nm and 0.399 lm,compared with 556 nm and 3.427 lm before ultra-precision grinding.The mathematical model can provide theoretical guidance for the analysis of interference and grinding characteristics in complex components grinding to improve its grinding quality.

基于接触区齐次变换的球头铣削力预报与分析

精准求解球头铣刀-工件接触区(Cutter-workpiece engagement,CWE)已成为研究其力学行为的关键问题。现有球头CWE的求解方法存在效率低、通用性不佳和工程适用性不强等局限性。为此,本文提出一种基于齐次变换矩阵的CWE求解方法并借此实现球头铣削力预报和分析。首先,以铣削过程的几何特性分析为切入点,构建无倾角CWE解析方程组;然后,从多体系统理论的视角出发,通过齐次变换方法将球头铣姿态参数表征为坐标矩阵,由此推导出其在任意姿态下的解析表达式,进而将铣削过程时域离散化并对CWE内有效铣削刃及其演化过程进行分析。在此基础上,开展球头铣削力测试试验来检验该求解方法与铣削力分析的可靠性和精准性。研究结果表明,所提CWE求解方法可在较大程度上简化求解过程,且对铣削力的预报可靠、精准性高;前倾角或侧倾角的增大会减少切削刃在铣削周期中的铣削时间,并使得铣削周期内的平均铣削力降低;采用较小的前倾角时可获得较大的铣削力。

考虑刀具尺寸效应和刀具跳动的球头铣刀五轴微细铣削力预测

五轴微细铣削技术广泛应用于微小型零件的精密加工过程。铣削力作为加工过程中最重要的参数之一,直接影响零件的加工精度、刀具磨损和加工过程中的振动等。在球头铣刀五轴微细铣削过程中,刀—工接触几何CWE(Cutter Workpiece Engagement)及未变形切屑厚度瞬态变化,使其求解过程变得复杂和困难。综合考虑不同前倾、侧倾角度下的刀—工接触几何,推导出考虑最小切屑厚度、刀具跳动和工件材料弹性恢复的未变形切屑厚度数学表达式,建立了五轴微细铣削力的预测模型,获得铣削力的仿真结果。进行五轴微细铣削实验获得实测铣削力,并与预测铣削力进行比较,结果表明,铣削力预测值与实测值误差均在20%以内,验证了铣削力预测模型的有效性。

五轴数控工具磨床制程能力与过程能力的定量评价研究

为考察五轴数控工具磨床的制程能力,选用两种不同品牌的五轴数控工具磨床加工硬质合金球头立铣刀,测量了立铣刀球头的曲率、刀具球头与圆柱部分衔接处的刃口崩边大小和砂轮磨痕间距来定量评价磨床加工复杂刀具的能力(即制程能力);通过过程能力指数C_(p),从刀具跳动、刀刃直径、球头半径R和球头曲率等四个参数评价磨床的过程能力。

某车型电动尾门撑杆球头脱落的故障解析及优化方案

汽车电动尾门撑杆属于机电一体化的传动结构,由于受不同车型的布置位置及安装结构的影响,存在一定概率发生汽车电动尾门撑杆球头脱落故障。通过市场故障数据分布、故障件及样件抽验以及结构原理进行了故障机理解析,通过技术方案的优化并进行实际验证,确保了技术方案的可行性。针对市场故障形式进行了故障机理解析并在原有的技术方案上进行优化,从而较好地避免了汽车电动尾门撑杆球头脱落的故障,同时也为后续产品设计优化提供新的思路。

三维振动铣削加工振幅对铣削力的影响研究

三维振动辅助铣削是一种新型获得复杂表面结构形貌的特殊加工方式,三个方向振幅对能够反映表面加工质量的工艺参数—铣削力有着重要影响。文章旨在探究振动幅值对铣削力的影响规律,首先根据振动辅助加工原理,建立了球头铣刀三维振动轨迹模型;其次,通过ABAQUS软件,基于铝合金7050-T6的J-C本构模型,建立了球头铣刀三维振动辅助铣削过程三维有限元模型;最后,检测了施加三维振动辅助后,仿真过程中球头铣刀的空间位移瞬态响应,对不同振动幅值下各个方向的输出铣削力进行分析。结果表明,三维振动辅助能够在一定程度上减小铣削力;增大振幅,使三个方向的最大铣削力增大,但纵向进给方向和横向进给方向的平均铣削力呈下降趋势,而垂直进给方向的平均铣削力增加到最大值后,振幅的增加对其平均铣削力影响变小。

Experimental Study on Titanium Alloy Cutting Property and Wear Mechanism with Circular-arc Milling Cutters

Titanium alloy has been applied in the field of aerospace manufacturing for its high specific strength and hardness.Nonetheless,these properties also cause general problems in the machining,such as processing inefficiency,serious wear,poor workpiece face quality,etc.Aiming at the above problems,this paper carried out a comparative experimental study on titanium alloy milling based on the CAMCand BEMC.The variation law of cutting force and wear morphology of the two tools were obtained,and the wear mechanism and the effect of wear on machining quality were analyzed.The conclusion is that in contrast with BEMC,under the action of cutting thickness thinning mechanism,the force of CAMC was less,and its fluctuation was more stable.The flank wear was uniform and near the cutting edge,and the wear rate was slower.In the early period,the wear mechanism of CAMC was mainly adhesion.Gradually,oxidative wear also occurred with milling.Furthermore,the surface residual height of CAMC was lower.There is no obvious peak and trough accompanied by fewer surface defects.

微径球头铣刀微铣削有限元仿真及微铣削力预测

变螺旋角螺旋线的切削刃使得微径球头铣刀微铣削过程复杂且实验研究难度较大,对此,提出有限元建模仿真与多元线性回归分析相结合的微铣削过程量化分析和微铣削力预测方法。结合球面螺旋线模型和实测建立微径球头铣刀的三维模型,以此为基础实现全槽微铣削的有限元仿真,并通过实验验证仿真的正确性。针对主轴转速、进给速度与铣削深度三因素,利用正交实验设计方法确定三因素三水平的微铣削仿真方案,得到不同工艺参数组合下的微铣削力数据,通过多元线性回归分析建立预测微铣削力峰值的经验模型,其拟合优度分析表明预测模型具有较好的准确度和可靠性,可用于工艺参数对微铣削力峰值的影响规律分析,优化控制微铣削过程。

铣削γ-TiAl球头立铣刀几何角度优化设计

钛铝合金具有良好的物理和力学性能,在航空航天及汽车领域具有广泛的应用前景。由于其高温强度高、导热率低及室温脆性等特性,加工时存在切削力较大、切削温度高等问题,是一种典型的难加工材料,因此开发一款针对该种材料加工的球头立铣刀具有十分重要的意义。本文通过三维有限元仿真技术,以降低铣削力和铣削温度为优化目标,求得球头铣刀前角、螺旋角和后角三个几何参数的最优组合;分析这三个几何参数对切削力和切削温度的影响,实现刀具几何参数的优化设计。

考虑机床几何误差的球头刀三坐标NC铣削刀位控制

机床的各种误差是影响机床加工精度的重要因素,其中机床几何误差是主要的误差来源之一。为消除机床几何误差对加工精度的影响,以球头刀三坐标数控(numerical control,NC)铣削加工为研究背景,基于齐次坐标变换理论与刚体运动学方法,结合机床运动链拓扑结构分析,将机床几何误差映射到球头刀刀心的位置误差上。根据球头刀铣削工件表面成形原理,考虑机床几何误差与球头刀刀心位置间的映射关系,构建出刀心曲面与工件表面/设计曲面之间的正逆向计算模型。通过该模型求解出消除机床几何误差的编程刀心曲面,将该曲面导入CAM软件,即可获得消除机床几何误差的NC加工程序。通过曲面实例进行计算和仿真,佐证了该方法的可行性。

基于关键刀轴矢量插值的球头铣刀五轴加工光顺刀轴矢量生成方法

提出基于贪心策略的复杂曲面加工刀具路径关键刀轴矢量序列整体优化方法,以及基于关键刀轴矢量插值的球头铣刀五轴加工复杂曲面光顺刀具姿态生成方法。计算各关键刀位刀触点处的刀轴矢量可行域,基于贪心策略从刀轴矢量可行域中选择关键刀轴矢量序列并且插值关键刀轴矢量序列,检查加工路径刀轴矢量序列是否存在碰撞干涉,进而获得可行的关键刀轴矢量序列集合。根据光顺评价指标从可行的关键刀轴矢量序列集合中选择最优的关键刀轴矢量序列,然后获得整个加工路径光顺的刀轴矢量序列。试验结果表明,该方法生成的复杂曲面加工刀具姿态能够使机床旋转轴运动平稳。

平行砂轮磨削球头立铣刀后刀面的轨迹算法研究

针对磨削球头立铣刀周刃偏心型后刀面的工艺参数化定义不完善,由砂轮姿态突变导致的后刀面磨削宽度不均匀等问题,提出了一种球头立铣刀后刀面采用平行砂轮加工的磨削轨迹算法。该算法首先建立了一种具有齿偏中心量的球头立铣刀刀刃曲线模型,根据模型结构对相关坐标系及其转换关系进行了定义。随后,在描述砂轮姿态的坐标系下构建了砂轮初始磨削姿态模型以及对其工艺参数进行了定义,并根据转换关系对砂轮磨削姿态进行了统一表达。最终,算法的验证通过仿真及实际加工环境进行,并通过测量仪器对后刀面相关参数进行了测量,算法的可行性及准确性得到了进一步验证。