考虑刀杆柔性的周铣加工表面创成模型—实验验证

以圆柱螺旋铣刀周铣加工过程为研究对象,在考虑主轴偏心以及刀杆的静,动态变形等影响因素的前提下,建立一种考虑刀杆柔性的周铣加工表面创成模型。基于该模型,用相应的高效数值仿真算法,对给定稳态和非稳态两种切削条件下的铣 加工表面形貌进行仿真,并与实测加工表面进行对比,用以验证该模型的有效性。     

曲轴在内铣加工中粘刀和变形问题

曲铀是柴油机的重要零件,曲轴内铣加工是曲轴加工过程中切除余量最多的一道工序。我厂斯太尔柴油机曲轴在进行内铣加工时,出现过两种现象: 1)有严重粘刀现象,造成刀片散热受阻而烧坏。 2)内铣加工后的曲轴变形大,变形量达1mm以上,与工艺要求(见图1)严重超差,因而不能进行其后道工序的加工。     

Y轴丝杠热膨胀对包络铣齿加工精度的影响

基于包络铣齿和齐次坐标变换原理,建立包络铣齿热误差对齿廓误差影响分析模型。分析了机床结构与加工特点确定机床丝杠热特性。将丝杠热变形量代入机床误差传递矩阵中,获得刀具螺旋面偏差,研究了丝杠热膨胀与齿廓误差的关系。结果表明:丝杠轴向热膨胀会引起刀具螺旋面产生偏移,造成相应的齿廓误差。     

侧铣加工刀具回转轮廓误差预测技术研究

在侧铣加工中,刀具磨损和变形引起的刀具回转轮廓误差在实际加工前难以准确预测。提出一种工件形状刀具轮廓映射的辨识试验方法来获取加工过程刀具回转轮廓误差,并通过多因素正交试验获取了不同工况下刀具回转轮廓误差数据库。基于误差数据,采用最小二乘支持向量机（LS-SVM）技术建立了刀具回转轮廓误差预测模型。运用遗传算法优化对所提模型有重要影响的核函数参数和错误惩罚因子, 建立了基于遗传算法优化的最小二乘支持向量机(GA-LS-SVM)模型,并与未经遗传算法优化的LS-SVM模型进行了对比,试验结果表明,GA-LS-SVM预测模型能更好地适用于刀具回转轮廓误差预测。     

端铣加工中刀具的热破损

本文运用激光束冲击实验,测量了动态铣削刀具的温度场,并用有限元方法进行了计算和理论分析。发现当前人们普遍接受的刀具热破损理论有误,端铣加工中刀具的热裂纹和热破损不是在切出瞬间生成的。     

基于机床几何误差模型的数控加工形位误差预测

影响加工形位误差的因素众多,机床几何误差是其中最关键的因素。其影响零件的功能要求、配合性质和自由装配性,是评估机床加工精度的重要指标。本文通过构建机床几何误差和零件形位误差之间的映射关系对加工形位误差预测方法进行研究,建立了基于机床几何误差模型的三轴机床刀具位姿误差模型,并以刀具位姿误差为中间量建立了平面度误差和圆柱度误差预测模型。使用TH6920型镗铣床进行试验验证,与零件形位误差检测值对比,圆柱度预测误差为9.3%,平面度预测误差为4.8%,预测效果较好,验证了预测方法的有效性。     

顺逆混合铣-铣复合加工方法的切削力分析

难加工材料已广泛应用,但加工过程中出现了的切削力大、刀具寿命短等诸多问题,提出了在不降低材料去除率的前提下有效地降低切削力的大小的新方法铣-铣复合加工方法,顺逆混合铣-铣复合加工方法是铣-铣复合加工方法的一种形式,顺逆混合铣-铣复合加工方法中的刀盘在低转速下就能实现高速切削。顺逆混合铣-铣复合加工方法中将总磨损量平均到了不同立铣刀的不同的切削刃上从而提高了整个刀具的寿命,从方法上解决了难加工材料加工中刀具寿命短的难题。实验结果表明顺逆混合铣-铣复合加工方法发挥了铣-铣复合加工方法组合优势,部分切削力能够相互抵消,从而减小加工工件的受力。     

基于铣削力精确建模的工件表面让刀误差预测分析

航空航天制造业结构件的高速铣削加工中,在切削力作用下由整体铣削刀具挠度变形所引起的工件表面让刀误差,严重制约零件的加工精度和效率。针对这一问题,通过建立铣削力精确预测模型,结合刀具刚度特点,对工件让刀误差进行预测分析。将切削速度和刀具前角对切削力的影响规律引入二维直角单位切削力预测模型,并通过试验进行相关系数标定。借助等效前角将直角切削力预测系数应用到斜角切削力的预测,通过矢量叠加构建整体刀具三维切削力模型。分析刀具挠度变形对铣削层厚度及铣削接触中心角范围影响规律。基于离散化的刀具模型和切削力模型,建立铣削载荷条件下刀具等效直径悬臂梁模型弯曲变形计算方法。构建以刀具变形对铣削过程影响作用规律为反馈的刚性工件表面让刀误差及切削力柔性预测模型,通过整体铣刀铣削试验验证所建立理论模型的预测精度。     

圆周铣削参数多目标模糊优化建模

金属切削加工参数优化问题本质上是一个模糊问题。分析了圆周铣削传统优化模型的缺点 ,建立了圆周铣削参数多目标模糊优化模型 ,并根据模糊集合原理 ,将其转化为一个传统的单目标约束优化问题 ,从而可用任一非线性规划求解器进行求解。算例表明 ,模糊优化解具有优越性。     

基于VSSPMP的非线性立铣加工过程振动控制研究

综合考虑了再生振动效应与刀具偏心模型对动态铣削厚度的影响,建立了非线性立铣加工过程消耗能量表达式,以此作为目标函数提出了铣削振动状态预估与控制措施;利用铣削过程虚拟仿真系统对该方法的有效性和实用性进行了验证。     

A Cutter Orientation Modification Method for the Reduction of Non-linearity Errors in Five-Axis CNC Machining

In the machining of sculptured surfaces, five-axis CNC machine tools provide more flexibility to realize the cutter position as its axis orientation spatially changes. Conventional five-axis machining uses straight line segments to connect consecutive machining data points, and uses linear interpolation to generate command signals for positions between end points. Due to five-axis simultaneous and coupled rotary and linear movements, the actual machining motion trajectory is a non-linear path. The non-linear curve segments deviate from the linearly interpolated straight line segments, resulting in a non-linearity machining error in each machining step. These non-linearity errors, in addition to the linearity error, commonly create obstacles to the assurance of high machining precision. In this paper, a novel methodology for solving the non-linearity errors problem in five-axis CNC machining is presented. The proposed method is based on the machine type-specific kinematics and the machining motion trajectory. Non-linearity errors are reduced by modifying the cutter orientations without inserting additional machining data points. An off-line processing of a set of tool path data for machining a sculptured surface illustrates that the proposed method increases machining precision.     

Redesigned Surface Based Machining Strategy and Method in Peripheral Milling of Thin-walled Parts

Currently, simultaneously ensuring the machining accuracy and efficiency of thin-walled structures especially high performance parts still remains a challenge. Existing compensating methods are mainly focusing on 3-aixs machining, which sometimes only take one given point as the compensative point at each given cutter location. This paper presents a redesigned surface based machining strategy for peripheral milling of thin-walled parts. Based on an improved cutting force/heat model and finite element method(FEM) simulation environment, a deflection error prediction model, which takes sequence of cutter contact lines as compensation targets, is established. And an iterative algorithm is presented to determine feasible cutter axis positions. The final redesigned surface is subsequently generated by skinning all discrete cutter axis vectors after compensating by using the proposed algorithm. The proposed machining strategy incorporates the thermo-mechanical coupled effect in deflection prediction, and is also validated with flank milling experiment by using five-axis machine tool. At the same time, the deformation error is detected by using three-coordinate measuring machine. Error prediction values and experimental results indicate that they have a good consistency and the proposed approach is able to significantly reduce the dimension error under the same machining conditions compared with conventional methods. The proposed machining strategy has potential in high-efficiency precision machining of thin-walled parts.     

加工复合材料铣刀的研制

复合材料的切削加工性很差,复合材料加工刀具已严重影响了复合材料的加工质量和效率。为解决复合材料的加工存在质量差和效率低的问题,笔者针对复合材料的加工性能、刀具材料及其结构,进行了系统的研究。掌握了加工复合材料铣刀的设计和制造技术,并通过对刀具结构参数的优化,提高了复合材料切削加工质量和效率。     

Improved Dynamic Cutting Force Model in Peripheral Milling. Part I: Theoretical Model and Simulation

The accurate prediction of cutting forces is important in controlling the tool deflection and the machining accuracy. In this paper, the authors present an improved theoretical dynamic cutting-force model for peripheral milling with helical end-mills. The theoretical model is based on the oblique cutting principle and includes the size effect of undeformed chip thickness and the influence of the effective rake angle. A set of closed-form analytical expressions is presented. Using the cutting forces measured by Yucesan [1] in tests on a titanium alloy, the cutting-force coefficients are estimated and the cutting- force model verified by simulation. The simulation results indicate that the improved dynamic cutting-force model does predict the cutting forces in peripheral milling accurately. Simulation results for a number of particular examples are presented. ID="A1" Correspondence and offprint requests to: Prof K. Cheng, School of Engineering, Leeds Metropolitan University, City Campus, Calverley Street, Leeds LS1 3HE, UK. E-mail: k.cheng@lmu.ac.uk     

外圆旋风铣削加工直线度误差分析

外圆旋风铣床是一种用于批量铣削细长轴类零件外圆表面的机床。通过分析外圆旋风铣床的运动原理及其组成结构,结合轴线弯曲的表达方式,从几何结构角度建立直线度误差模型进行求解,得出铣削前后细长轴类零件直线度误差的校正范围。     

Predicting Machining Errors in Turning Using Hybrid Learning

A recent model-based approach for predicting the compensation required on the next part to be turned on a CNC machine solely on the basis of three independent measurements conducted at selected locations on a limited set of previously machined parts under a similar cutting set-up is reviewed. A new method of achieving the same objective through the use of the learning capability of an adaptive neuro-fuzzy network is developed and tested against experimental data for cylindrical turning. This method requires only one on-machine measurement per sample. It is conducted by a novel contact sensor that probes with the tool and facilitates automation by providing proximity information as the tool approaches the workpiece.     

弧面凸轮两旋转坐标联动数控加工中心距误差对廓面误差的影响

以具体实例分析和计算了采用专用数控机床加工弧面凸轮时 ,中心距误差 Δ a对凸轮廓面法向误差的影响规律 ,对凸轮廓面修形以及机构预紧提供理论依据