热等静压工艺制备的Ti-6Al-4V薄壁筒的切削加工

为了能够提高钛合金薄壁筒的加工效率,利用热等静压工艺制备了两个具有不同结构的Ti-6Al-4V薄壁筒,研究了夹具、填充泥浆和筒结构对Ti-6Al-4V薄壁筒的外圆表面粗糙度和精度的影响。结果显示,Ti-6Al-4V热等静压薄壁筒经过切削加工能够达到精度要求,填充泥浆降低了弹性回弹,提高了薄壁筒外圆精度;筒结构的内圆环和粗大端能够提高刚度,有效降低了外圆表面粗糙度值;夹具尺寸误差对圆度和同轴度影响较大,较大的尺寸误差显著降低了筒的外圆精度。     

一种薄壁悬臂叶片数控加工非均匀余量刚度补偿方法

 在数控加工过程中,因受到切削力的影响,薄壁悬臂叶片容易出现弯曲、扭转变形等问题而导致被加工曲面误差较大。针对该问题,提出了一种非均匀余量刚度补偿方法,将非均匀余量偏置面作为粗加工/半精加工零件面以提高叶片精加工时的抗弯刚度。首先,分析了集中力载荷下截面厚度对薄壁工件变形的影响;然后,对叶片径向和截面线方向分别采用线性变化和正弦函数变化两种方法进行叶片曲面非均匀余量刚度补偿设计;最后,基于叶片原始截面线,采用放样法构造出叶片曲面的非均匀余量偏置面。试验结果表明,采用非均匀余量刚度补偿方法可以提高被加工叶片精加工时的刚度,加工出的叶片满足了设计误差要求。     

薄壁件加工变形主动补偿方法

研究薄壁件加工过程中受力变形产生的回弹误差控制,提出了分层完全补偿和优化补偿两种加工路径补偿方法,建立了加工路径补偿优化模型,考虑了多次走刀间加工变形和切削力的耦合作用,并应用迭代算法求解路径补偿优化模型。以航空薄壁件单刃端铣加工为例,对完全补偿、分层完全补偿和优化补偿进行了仿真分析和试验分析。结果表明,分层完全补偿和优化补偿能更好地减少加工误差,为薄壁件受力变形控制提供了参考依据。     

Elliptical vibration cutting of large-size thin-walled curved surface parts of pure iron by using diamond tool with active cutting edge shift

Large-size thin-walled curved surface parts of pure iron are crucial in aerospace, national defense, energy and precision physical experiments. However, the high machining accuracy and surface quality are difficult to achieve due to the serious tool wear and deformation when machining the parts with conventional cutting tools. In this paper, an elliptical vibration cutting (EVC) with active cutting edge shift (ACES) based on a long arbor vibration device is proposed for ultra-precision machining the pure iron parts by using diamond tool. Compared with cutting at a fixed cutting edge, the influence of ACES on the EVC was analyzed. Experiments in EVC of pure iron with ACES were conducted. The evolutions of the surface roughness, surface topography, and chip morphology with tool wear in EVC with ACES are revealed. The reasonable parameters of ultra-precision machining the pure iron parts by EVC with ACES were determined. It shows that the ACES has a slight influence on the machined surface roughness and surface topography. The diamond tool life can be significantly prolonged in EVC of pure iron with ACES than that with a fixed cutting edge, so that high profile accuracy and surface quality could be obtained even at higher nominal cutting speed. A typical thin-walled curved surface pure iron part with diameter ∅240 mm, height 122 mm, and wall thickness 2 mm was fabricated by the presented method, and its profile error and surface roughness achieved PV 2.2 μm and Ra less than 50 nm, respectively.     

Vibration suppression of thin-walled workpiece machining considering external damping properties based on magnetorheological fluids flexible fixture

Milling of the thin-walled workpiece in the aerospace industry is a critical process due to the high flexibility of the workpiece. In this paper, a flexible fixture based on the magnetorheological(MR) fluids is designed to investigate the regenerative chatter suppression during the machining.Based on the analysis of typical structural components in the aerospace industry, a general complex thin-walled workpiece with fixture and damping constraint can be equivalent as a rectangular cantilever beam. On the basis of the equivalent models, natural frequency and mode shape function of the thin-walled workpiece is obtained according to the Euler–Bernoulli beam assumptions. Then,the displacement response function of the bending vibration of the beam is represented by the product of all the mode shape function and the generalized coordinate. Furthermore, a dynamic equation of the workpiece-fixture system considering the external damping factor is proposed using the Lagrangian method in terms of all the mode shape function and the generalized coordinate, and the response of system under the dynamic cutting force is calculated to evaluate the stability of the milling process under damping control. Finally, the feasibility and effectiveness of the proposed approach are validated by the impact hammer experiments and several machining tests.     

双臂自适应夹具加工变形控制方法

在叶片加工过程中,由于叶片的薄壁和曲率多变特点,易受装夹、切削力和残余应力的影响而产生弯曲、扭转变形。针对该问题,本文提出了一种双臂自适应夹具加工变形控制方法,将加工过程中产生的变形逐层消除。首先,对叶片的变形成因进行分析;然后,通过对无应力装夹和加工应力释放原理进行研究,设计了一种可提供6个自由度的自适应装夹机构,并对该机构进行了工程设计和机构分析;最后,基于这种6自由度双臂自适应装夹机构,形成了本文提出的加工变形控制工艺,不需多次修复基准和更换机床,就可以逐层消除新产生的变形。实验结果表明,采用双臂夹具自适应加工变形控制方法,可以有效控制叶片加工过程中产生的变形,使叶片的轮廓误差降为原来的50%,提高了其加工精度。     

薄壁件周铣切削力建模与表面误差预测方法研究

薄壁件加工变形是影响加工精度与质量的关键因素,而切削力建模则是预测表面加工误差的基础。针对两种典型的切削力模型,系统地研究了薄壁件周铣加工过程中切削力变化及表面变形误差分布的有限元计算方法,提出了基于三维非规则网格的刀具/工件变形的耦合迭代格式以及恒定网格下材料去除效应的变刚度处理方法等关键技术,仿真过程充分考虑了切屑厚度变化及不同切削参数对预测结果的影响。以典型钛合金航空材料构件为例,数值计算结果与实验参考数据比较表明,两种切削力模型对同一切削过程的预测均具有很好的一致性。     

Influence mechanism of machining angles on force induced error and their selection in five axis bullnose end milling

In the machining of complicated surfaces, the cutters with large length/diameter ratios are used widely and the deformation of the machining system is one of the principal error sources. During the process planning stage, the cutting direction angle, the cutter lead and tilt angles are usually optimized to minimize the force induced error. It may lead to a low machining efficiency for bullnose end mills, as the material removal rates are different largely for different machining angles. In this paper, the influence mechanism of the machining angles on the force induced error is studied based on the models of the instantaneous cutting force when the cutter flute traveling through the cutting contact point and the stiffness of the machining system. In order to evaluate the machining angles, the force induced error/efficiency indicator (FEI) is defined as the division of the force induced error and the equal volume sphere of the removed material. FEI is dimensionless, with the lower FEI, the lower force induced error and the higher machining efficiency. For optimal selection of the machining angles, the critical FEI is calculated with the constraint of force induced error and the desired material removal rate, and the critical FEI separate the set of the machining angles into two subsets. After the feed rate scheduling process, the machining angles in the optimal subset would have higher machining accuracy and efficiency, while the machining angles in the other subset have lower machining accuracy and efficiency. Through the machining experiment of five axis machining and freeform surface machining, the effectiveness and superiority of the proposed FEI method is verified with a bullnose end mill, which can improve the machining efficiency with the constraint of force induced error.     

基于动力学仿真技术的TC4整体叶轮铣削参数优化

针对某航空发动机TC4整体叶轮在数控加工过程中存在颤振、加工效率低及因加工变形而导致局部超差等问题,提出了相应的铣削参数优化解决方案。在进行切削力系数辨识试验获取TC4材料的切削力系数及锤击试验获取加工系统动力学特性参数的基础上,通过综合使用自行开发的铣削加工动力学仿真软件SimuCut和国外的CutPro软件进行动力学仿真与优化,获得了优化的切削参数。使用优化的切削参数进行加工,有效地消除了颤振和因加工变形引起的局部超差,提高了加工效率。     

随形固定自适应夹具加工变形控制方法

叶片的加工精度及其稳定性对航空发动机的性能有直接的影响,由于叶片的薄壁和曲率多变特点,易受装夹、切削力和残余应力的影响而产生弯曲、扭转变形。针对该问题,本文提出了一种随形固定自适应夹具加工变形控制方法,可以将叶片无应力装夹,并将加工过程中产生的变形逐层消除。实验结果表明,采用随性固定自适应夹具加工变形控制方法,可以有效控制叶片加工过程中产生的变形,提高加工精度。     

钛合金铣削刀具/工件接触区域温度预测

钛合金（Ti-6Al-4V）因其优良的综合性能广泛应用于航空航天领域中,然而由于其导热系数低、弹性模量低等特性,铣削加工过程中刀具/工件接触区域温度过高,从而导致刀具磨损严重,影响已加工表面质量。因此研究切削过程中刀具/工件接触区域温度具有重要意义。从切削机理出发,将切削区域的3个热源等效为螺旋线热源,其中热流密度计算类比铣削力预测模型中铣削力计算方法,提出包含铣削热系数的热流密度计算模型,并通过实验标定铣削热系数,结果表明热流密度随切削厚度增加接近于线性增加。建立刀具/工件接触区域温度预测模型,通过半人工热电偶测温实验对模型的可行性与准确性进行了验证,实验值与预测值的相对误差在10%之内。提高了刀具/工件接触区域温度的计算精度,并为切削参数的合理选择提供理论基础。     

损伤演化对Ti6Al4V高速切削仿真结果的影响

利用ABAQUS有限元分析软件建立了Ti6Al4V二维切削仿真模型,在模型其他参数（本构参数、初始损伤参数等）固定不变时,得到了不同损伤演化特征参数（断裂能）取值下的切削力、切削温度和切屑形貌,以此来研究损伤演化过程对仿真结果的影响。研究发现随着断裂能取值的减小,仿真的切削力、切削温度会降低,切屑的锯齿化程度会变得严重。在切削速度为180 m/min,进给量为0.1 mm/r的条件下进行了Ti6Al4V正交切削实验,测量了切削力,将仿真得到的主切削力和切屑锯齿化程度与实验结果进行对比,确定了适合本研究建立的仿真模型的合理断裂能值。结果表明,在使用此断裂能取值时,仿真得到的切削力和切屑形态与实验值有很好的一致性。在消除了能量密度对仿真模型的影响后,进行了4组验证实验,仿真结果与验证实验的结果相吻合,证明了断裂能取值的准确性。     

Feedrate scheduling method for constant peak cutting force in five-axis flank milling process

It is extremely important to select appropriate feedrates for the stable machining of parts with ruled surface in modern aviation industrial applications. However, the current studies take too much time to achieve this goal. Therefore, this paper presents an efficient feedrate optimization method for constant peak cutting force in five-axis flank milling process. The solution method of the instantaneous undeformed chip thickness (IUCT) is proposed using least squares theory with the cutter entry angle and feedrate as variables. Based on this method, an explicit analytical expression of the peak cutting force for each cutting point is established. Furthermore, a feedrate scheduling method is developed to quickly solve the appropriate feedrate under constant peak cutting force. To verify the proposed IUCT model, the fitting IUCT is compared with the accuracy data at different feedrates. Additionally, some experiments of five-axis flank milling are conducted to demonstrate the effectiveness of the peak force model and the feedrate scheduling method. And the surface roughness before and after feedrate scheduling is detected. The results show that the proposed feedrate scheduling method can quickly adjust the feedrate and ensure constant peak force during machining. At the same time, the surface quality is kept at a high level.     

Wire electrochemical machining with axial electrolyte flushing for titanium alloy

Titanium and its alloys have found very wide application in aerospace due to their excellent characteristics although their processing is still a challenge. Electrochemical machining is an important issue in the fabrication of titanium and titanium alloys. Wire electrochemical machining (WECM) is mainly used for workpiece cutting under the condition of different thickness plates. It has a great advantage over wire electro-discharge machining, which is the absence of heat-affected zone around the cutting area. Moreover, the wire electrode in WECM could be used repetitively because it is not worn out. Thus, much attention has been paid to WECM. The effective way of removing electrolysis products is of importance to WECM. In this paper, the axial electrolyte flushing is presented to WECM for removing electrolysis products and renewing electrolyte. The Taguchi experiment is conducted to optimize the machining parameters, such as wire feedrate, machining voltage, electrolyte concentration, etc. Experimental results show that WECM with axial electrolyte flushing is a promising issue in the fabrication of titanium alloy (TC1). The feasibility of multi-wire electrochemical machining is also demonstrated to improve the machining productivity of WECM.     

涂层刀具低温铣削SiCp/Al复合材料表面质量研究

在加工过程中,相反的两相特性增加了SiC_p/Al复合材料加工难度,难以获得良好的表面质量。层和TiAlSiN涂层两种铣刀的切削性能。结果表明,在低温条件下,两种刀具的切削力增加,铣削后表面铝基体的开裂及剥落等缺陷均显著改善,加工表面损伤减小且粗糙度降低,低温铣削能获得更好的表面质量。此外,在常温与低温条件下TiAlSiN涂层比TiAlN涂层铣刀的切削力小,低温条件下TiAlSiN涂层铣刀表面完整性和切屑形貌优于TiAlN涂层铣刀。     

基于粘弹性材料的五轴铣削加工被动抑振技术

针对薄壁件在铣削过程中极易出现颤振,且动力学特性快速变化导致切削稳定性多变的特点,研究基于粘弹性材料的被动阻尼技术,以增加薄壁零件阻尼、提升切削稳定性。提出阻尼层、约束层以及质量层的设计方案,模态试验表明该技术能大幅提升薄壁件阻尼,且对多阶振动模态有抑制作用。最后,将其应用于薄壁S样件的五轴铣削加工试验,多组切削参数下的试验结果表明,工件切削振动幅值最大可下降约97%。     

高低频复合振动钻削CFRP/钛合金叠层结构试验

针对碳纤维增强复合材料（CFRP）和钛合金叠层结构在传统钻削过程中切削温度高、加工质量差等问题,基于低频振动钻削和高频（超声）振动钻削的优势,提出了高低频复合振动钻削的加工方法。采用自主研制的高低频复合振动钻削装置,对CFRP/钛合金叠层结构进行了制孔试验,对比研究了普通钻削、超声钻削、低频振动钻削和高低频复合振动钻削4种方式下的切削力、钛合金切屑形貌、切削温度和CFRP孔加工质量。结果表明：4种加工方式中,高低频复合振动钻削的轴向力波动相对较大,切削温度显著降低,产生的钛合金切屑呈不连续扇形且整体尺寸最小,CFRP孔出入口及孔壁的损伤程度最低,显著提高了加工质量,为复合材料叠层结构一体化制孔加工提供了指导意义。     

旋转超声钻削碳纤维复合材料钻削力和扭矩的研究

针对碳纤维增强树脂基复合材料(CFRP)加工过程中的问题,对金刚石套料钻旋转超声钻削CFRP-T700型复合材料展开了研究。研究发现,钻削力随主轴转速的增加具有减小的趋势,而扭矩则随着主轴转速的增加,呈现增大的趋势;与传统加工相比,旋转超声振动钻削可降低切削力及扭矩达56.6%和39.1%,有效抑制加工缺陷的产生。初步建立了切削力和扭矩之间的数学模型,并通过试验对切削力和扭矩之间的比例常数k加以验证。研究结果表明,旋转超声钻削CFRP在降低切削力和扭矩方面有较大优势。     

SiC_p/Al复合材料高速铣削切削力模型建立

使用聚晶金刚石(PCD)刀具并采用正交试验设计法,对含不同体分比的碳化硅颗粒增强铝基复合材料(SiCp/2009Al)进行高速铣削试验。在测量切削力和切屑厚度的基础上,建立了剪切角、剪切应力和摩擦角的预测模型,并结合金属切削基本理论公式建立了切削力的预测模型。该模型包含铣削速度、每齿进给量、径向切宽、增强颗粒体分比等重要参数,模型对进给方向最大铣削力预测值的平均误差为5.9%,对铣刀径向切深方向最大铣削力预测值的平均误差为9.2%,皆高于普通经验公式的预测精度,从而可对SiCp/2009Al复合材料高速铣削时的铣削力进行有效预测。     

单向CFRP螺旋铣削力建模

螺旋铣削加工工艺具有降低轴向力,改善排屑、散热条件等优点,螺旋铣削力是其重要过程指标之一。对单向CFRP螺旋铣削力建模方法展开研究,预测给定加工参数下的螺旋铣削力。首先,通过对螺旋铣削过程进行运动学分析和切屑几何分析,建立了螺旋铣削过程中侧刃、底刃动态切屑层模型,纤维切削方向角度模型和动态切削力计算模型。然后,分别通过侧刃直线槽铣实验和底刃半齿插铣实验,对各个切削方向角度下侧刃、底刃切削力系数进行了标定,并利用人工神经网络对切削力系数进行拟合。最后,将标定所得的切削力系数代入动态切削力计算模型中,建立了单向CFRP螺旋铣削过程动态切削力预测模型,并通过实验验证了模型的准确性。与现有模型相比,该模型不仅能够预测刀具螺旋运动周期内的切削力变化情况,还可以对每个刀具自转周期内的细节进行预测,通过考虑纤维切削方向角度对切削力系数的影响,反映了单向CFRP材料的各向异性,较为准确地预测了螺旋铣削力。