薄壁零件的高速铣削稳定性研究

薄壁结构零件在加工过程中极易发生变形和切削振动,这对提高加工质量和加工效率十分不利.在考虑刀具和工件两个方向自由度的基础上,分析了薄壁零件的动态铣削模型.针对2A12铝合金薄壁结构零件,利用MIKRON UCPDUR0800 高速加工中心和相关仪器、软件,通过铣削力辨识实验和模态实验,进行了高速铣削薄壁零件的稳定域分析和实验验证.     

三维有限元分析在高速铣削温度研究中应用

高速切削过程中切削温度对刀具磨损、工件加工表面完整性及加工精度有极大的影响。应用有限元法对高速铣削铝合金薄壁件过程中工件与刀具接触面温度、工件内部的温度分布进行了仿真研究,仿真过程中考虑了切削速度、进给量对切削温度的影响。通过红外热像仪对不同主轴转速下工件表面温度的测量,验证了仿真结果与试验结果比较接近。得出在高速切削铝合金过程中,随着切削速度的增加,刀具与工件接触区的温度变化存在二次效应。该结论对铝合金薄壁件加工具有重要的实用价值。     

基于Z-MAP方法的球头铣刀铣削力的建模

瞬时刚性切削力的建模是铣削加工物理仿真的基础,然而,球头铣刀的刀齿形状复杂,加工过程中姿态多变,瞬时刚性铣削力的建模难度较大。在考虑刀具姿态调整的情况下,通过齐次坐标变换建立了刀齿的运动轨迹,提出了一种识别刀具和工件瞬时接触区的改进Z-MAP算法,通过计算当前刀齿的参考线与工件的边界面或刀齿扫掠面的交点求出瞬时未变形切屑厚度,并采用非线性回归的方法辨识了切削力系数,在此基础上使用微元积分法建立了瞬时切削力的计算模型。为了验证仿真模型的可靠性,分别进行了垂直加工和倾斜加工试验,试验和仿真结果具有较高的一致性,表明该建模仿真方法是有效的,可以为实际加工中参数的选择和优化提供理论依据。     

轨道车辆薄壁铝型材的典型加工工艺

从铝合金材料的性能及工艺特点入手,介绍了轨道车辆所用铝合金材料,并列举了几种典型薄壁铝型材的截面结构。阐述了薄壁铝型材件的加工设备选型、铣削刀具选用和夹具布设的工艺设计过程,从加工余量、铣削力和铣削热等方面对薄壁铝型材的加工工艺进行了探讨,提出了影响薄壁铝型材加工质量的主要因素——变形,而影响变形的主要因素是装夹方式。总结出了装夹方式、选用刀具和铣削参数等合理的加工工艺方案,解决了轨道车辆薄壁铝型材的加工变形和薄壁撕裂等问题,提高了成品合格率．     

Mechanical behavior and semiempirical force model of aerospace aluminum alloy milling using nano biological lubricant

Aerospace aluminum alloy is the most used structural material for rockets, aircraft, spacecraft, and space stations. The deterioration of surface integrity of dry machining and the insufficient heat transfer capacity of minimal quantity lubrication have become the bottleneck of lubrication and heat dissipation of aerospace aluminum alloy. However, the excellent thermal conductivity and tribological properties of nanofluids are expected to fill this gap. The traditional milling force models are mainly based on empirical models and finite element simulations, which are insufficient to guide industrial manufacturing. In this study, the milling force of the integral end milling cutter is deduced by force analysis of the milling cutter element and numerical simulation. The instantaneous milling force model of the integral end milling cutter is established under the condition of dry and nanofluid minimal quantity lubrication (NMQL) based on the dual mechanism of the shear effect on the rake face of the milling cutter and the plow cutting effect on the flank surface. A single factor experiment is designed to introduce NMQL and the milling feed factor into the instantaneous milling force coefficient. The average absolute errors in the prediction of milling forces for the NMQL are 13.3%, 2.3%, and 7.6% in the x-, y-, and z-direction, respectively. Compared with the milling forces obtained by dry milling, those by NMQL decrease by 21.4%, 17.7%, and 18.5% in the x-, y-, and z-direction, respectively.     

超声振动铣削加工参数对切削力的影响

为了改善传统铣削钛合金的加工条件,研究了进给方向超声振动辅助铣削对切削力的影响。定值计算了不同振动频率、振幅、铣削速度时的净切削时间比,建立了对工件施加超声振动的铣削加工三维有限元模型,根据仿真结果讨论了加工参数对进给方向切削力瞬时值的影响,并结合净切削时间比分析了加工参数对三个方向切削力平均值的影响。研究表明:施加超声振动后切削力明显减小;振动频率小于40kHz和振幅小于30μm时切削力平均值同净切削时间比变化趋势一致,当频率或振幅超过上述值时,刀具、工件间的摩擦力对切削力平均值的影响显著。     

基于有限元数值模型和进给速度优化的薄壁件侧铣变形在线控制

为实现在加工过程中对薄壁件侧铣产生的较大切削变形进行在线控制,提出基于有限元数值模型和进给速度优化的在线控制策略。根据薄壁件切削过程的有限元仿真结果,建立数控机床进给速度、切削力、工件切削变形间的数值模型,进而确定用于控制变形的最优目标切削力。在具有开放式模块化的数控系统平台上开发了切削力信号实时采集、滤波功能和基于Brent-Dekker算法的进给速度在线优化策略,并根据滤波后的切削力及相应算法在加工过程中实时调整机床进给速度,保证切削力逐渐接近最优控制目标而实现切削变形的在线控制。试验结果表明,经过进给速度在线优化后的切削过程可将薄壁件侧铣变形控制在规定范围内,同时提高了切削效率。     

基于刀具跳动的环形铣刀切削厚度模型的切削力计算

数控铣削过程中,切削变形引起的瞬时切削厚度是影响铣削加工切削力建模的重要参数之一,针对环形铣刀的切削特点,在考虑刀具跳动的情况下,对真实刀刃轨迹运动进行分析。将微细铣削的加工过程用宏观铣削来表示,从而建立了基于宏观铣削过程中刀具跳动下精密加工的瞬时切削厚度。通过仿真模拟和切削力试验来预测切削力,预测结果和试验结果具有一致性,表明该模型可以更好的预测加工过程中的切削力。     

Predictive framework for cutting force induced cylindricity error estimation in end milling of thin-walled components

The static deflections of cutting tool and workpiece are the primary source for the deviation of machined components from the design specifications during end milling of thin-walled geometries. The deviations are expressed as per the Geometric Dimensioning and Tolerancing (GD&T) principles using size, form, and orientation of the features. This paper proposes a computational framework to estimate cutting force induced cylindricity error during end milling of thin-walled circular components. The framework combines computational elements such as Mechanistic force model, Finite Element Analysis (FEA) based workpiece deflection model, Cantilever beam formulation based tool deflection model, and Particle Swarm Optimization (PSO) based cylindricity estimation algorithm. It has been observed that the static deflections of a cutting tool and thin-walled component influence the cylindricity error considerably. The inevitable aspects associated with the end milling of thin-walled circular components such as concave-convex side machining and workpiece rigidity are investigated subsequently. It was observed that the cylindricity error during concave side machining is considerably smaller due to geometric configuration imparting adequate stiffness to thin-walled components. The study also demonstrated that an appropriate combination of productive cutting conditions and the component thickness could reduce cylindricity error considerably. The outcomes of the present study are substantiated by conducting a set of computational simulations and end milling experiments over a wide range of cutting conditions. The computational framework proposed in the present study can assist process planners in selecting appropriate cutting conditions to manufacture thin-walled circular components within tolerance limits specified by the designer.     

薄壁铸铝合金高速铣削加工试验研究

以铸铝合金薄壁件为加工对象,分别研究不同的切削速度、每齿进给量、径向切深对表面质量和切削力的影响规律,并优化切削参数的选择,力求为合理选择高速切削加工参数提供可靠依据。     

硬质合金立铣刀高速铣削铝合金切削力实验研究

采用试验分析和经验建模相结合的方法对硬质合金立铣刀高速切削铝合金时的切削力及其变化规律进行了研究,重点分析了切削用量对切削力的影响规律。同时通过建立切削力在不同主轴转速下的时频信号间的联系,进一步揭示切削力对切削机理、表面质量和切削效率等的作用规律。建立了基于现场的7075铝合金切削力经验模型,试验结果表明,利用该经验模型对切削力进行预测,结果精确可靠。     

薄壁工件铣削加工变形的预测

以铣削力模型和ABAQUS有限元分析软件为基础,采用考虑了刀具/工件变形耦合效应、材料去除效应以及工件变形引起铣削力加载点变化等因素的仿真预测方法,建立了薄壁工件加工变形预测的有限元分析模型,并对航空钛合金框体工件进行了铣削加工变形预测及试验验证,仿真结果与试验数据吻合较好。     

Stability improvement and vibration suppression of the thin-walled workpiece in milling process via magnetorheological fluid flexible fixture

In aerospace industry, thin-walled workpiece milling is a critical task. Also, the machining vibration is a major issue for the accuracy of the final part. In this study, a new dynamic analytical model is proposed to determine the effect of damping factor on the dynamic response of thin-walled workpiece in machining. A complex structure workpiece is equivalent to a thin plate. The fixture constrains and the damping factor are crucial elements of this thin plate. Therefore, the magnetorheological fluid flexible fixture is designed to suppress the machining vibration in machining process. Then, the general dynamic cutting force model and the damping force model are proposed for the key dynamic equation for the prediction of dynamic response to evaluate the stability of the milling process with and without the damping control. Finally, the feasibility and effectiveness of the proposed model is validated by machining tests. The predicted values match on the experiment results.     

Prediction of cutting forces in helical milling process

The prediction of cutting forces is important for the planning and optimization of machining process in order to reduce machining damage. Helical milling is a kind of hole-machining technique with a milling tool feeding on a helical path into the workpiece, and thus, both the periphery cutting edges and the bottom cutting edges all participated in the machining process. In order to investigate the characteristics of discontinuous milling resulting in the time varying undeformed chip thickness and cutting forces direction, this paper establishes a novel analytic cutting force model of the helical milling based on the helical milling principle. Dynamic cutting forces are measured and analyzed under different cutting parameters for the titanium alloy (Ti–6Al–4V). Cutting force coefficients are identified and discussed based on the experimental test. Analytical model prediction is compared with experiment testing. It is noted that the analytical results are in good agreement with the experimental data; thus, the established cutting force model can be utilized as an effective tool to predict the change of cutting forces in helical milling process under different cutting conditions.     

内置被动阻尼器减振铣刀的实验测试

提出一种长径比接近8的内置被动阻尼器减振铣刀结构。开展阻尼器模态测试,确定最优结构设计方案。对内置被动阻尼器减振铣刀进行周向模态测试,研究减振铣刀在不同方位的动力学特性。选取铝合金和钛合金工件材料,开展多组切削参数组合下的切削实验测试。在铝合金切削时,减振铣刀的加工噪声、切削力和表面粗糙度比无阻尼铣刀平均下降了52.1%,49.5%和73.4%;在钛合金全槽铣削时,能够在无阻尼铣刀出现明显颤振的切削条件下实现平稳切削。     

薄壁筒件内孔车削振动建模与分析

分析了车削薄壁筒件内孔表面时影响振动的主要因素,以切削加工中工件过渡表面的法线方向为建模方向,重点考虑车削加工中动态切削力的影响,依据振动基本理论建立了薄壁筒件动态车削过程的振动模型方程,通过对方程的数值分析探讨加工过程中的振动问题。分析结果表明:切削用量三要素对动态切削力的影响起主导作用,进而对切削振动产生较大影响。刀具主偏角对动态切削力也有一定影响,车削产生的振动与主偏角之间是非线性的关系。这些结论为薄壁筒件加工中的振动研究提供有益的参考。     

Process modeling and toolpath optimization for five-axis ball-end milling based on tool motion analysis

In free-form surface machining, the prediction of five-axis ball-end milling forces is quite a challenge due to difficulties of determining the underformed chip thickness and engaged cutting edge. Part and tool deflections under high cutting forces may result in poor part quality. To solve these concerns, this paper presents process modeling and optimization method for five-axis milling based on tool motion analysis. The method selected for geometric stock modeling is the dexel approach, and the extracted cutter workpiece engagements are used as input to a force prediction. The cutter entry?Cexit angles and depth of cuts are found and used to calculate the instantaneous cutting forces. The process is optimized by varying the feed as the tool?Cworkpiece engagements vary along the toolpath, and the unified model provides a powerful tool for analyzing five-axis milling. The new feedrate profiles are shown to considerably reduce the machining time while avoiding process faults.     

Development of an automatic arc welding system using SMAW process

In end milling of pockets, variable radial depth of cut is generally encountered as the end mill enters and exits the corner, which has a significant influence on the cutting forces and further affects the contour accuracy of the milled pockets. This paper proposes an approach for predicting the cutting forces in end milling of pockets. A mathematical model is presented to describe the geometric relationship between an end mill and the corner profile. The milling process of corners 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. For the cutting force prediction, an analytical model of cutting forces for the steady-state machining conditions is introduced for each segmented process with given radial depth of cut. The predicted cutting forces can be calculated in terms of tool/workpiece geometry, cutting parameters and workpiece material properties, as well as the relative position of the tool to workpiece. Experiments of pocket milling are conducted for the verification of the proposed method.     

铝合金高速铣削中切削温度动态变化规律的试验研究

切削温度与刀具磨损、工件加工表面完整性及加工精度密切相关。高速切削过程中切削温度随工件材料、所选刀具及切削用量的不同而呈现出与普通切削过程不同的变化规律。本文应用红外热像仪测温系统对高速铣削过程中切削温度的动态变化规律进行试验研究 ,首次给出了铝合金高速铣削过程中存在的临界切削速度关键数据及切削温度随切削速度的变化规律 ,其结论有助于指导铝合金高速铣削加工、优化高速切削工艺及建立高速切削数据库。     

虚拟加工过程薄壁工件铣削变形模型研究

在薄壁工件的切削加工中,工件的受力变形是影响加工过程的一个主要因素,文中针对薄壁工件侧面的立铣加工,建立了不同复杂度的切削过程模型,以仿真工件薄壁在加工中受到切削力发生的变形,虚拟实现受到工件变形影响下的切削过程。通过仿真创成的工件表面形貌与实际切成的工件表面的比较,对文中各模型进行了验证。