Analytical model of cutting force in axial ultrasonic vibration-assisted milling in-situ TiB2/7050Al PRMMCs

Ultrasonic vibration-assisted milling has been widely applied in machining the difficult-to-cut materials owing to the remarkable improvements in reducing the cutting force. However, analytical models to reveal the mechanism and predict the cutting force of ultrasonic vibration-assisted milling metal matrix composites are still needed to be developed. In this paper, an analytical model of cutting force was established for ultrasonic vibration-assisted milling in-situ TiB₂/7050Al metal matrix composites. During modeling, change of motion of the cutting tool, contact of tool-chip-workpiece and acceleration of the chip caused by ultrasonic vibration was considered based on equivalent oblique cutting model. Meanwhile, material properties, tool geometry, cutting parameters and vibration parameters were taken into consideration. Furthermore, the developed analytical force model was validated with and without ultrasonic vibration milling experiments on in-situ TiB₂/7050Al metal matrix composites. The predicted cutting forces show to be consistent well with the measured cutting forces. Besides, the relative error of instantaneous maximum forces between the predicted and measured data is from 0.4% to 15.1%. The analytical model is significant for cutting force prediction not only in ultrasonic-vibration assisted milling but also in conventional milling in-situ TiB₂/7050Al metal matrix composites, which was proved with general applicability.     

超声振动方向对TC4钛合金铣削特性的影响

为充分发挥超声铣削钛合金的优势，改善钛合金的加工效果，增强表面服役性能，分别对刀具和工件施加超声振动，以寻求合适的振动方向和加工参数。理论推导了侧刃断续切削时的临界速度，试验研究了不同振幅和切削速度对表面形貌、切屑形态、切削力和刀具磨损的影响，同时探究了表面微织构对摩擦特性的影响。试验表明在两种振动方向下，增大振幅均使切屑的锯齿化程度降低，并且增加轴向振幅可使锯齿形切屑转变为带状切屑。轴向振动更有利于表面形成微织构、减小切削力、减缓刀具磨损、减小工件摩擦时的磨合时间，但需合理控制切削速度和超声振幅。同时，对切削力进行频谱分析，为工作状态下超声振动频率的测量提供了一种参考方法。     

In-process adaptive milling for large-scale assembly interfaces of a vertical tail driven by real-time vibration data

Assembly interfaces, the joint surfaces between the vertical tail and rear fuselage of a large aircraft, are thin-wall components. Their machining quality are seriously restricted by the machining vibration. To address this problem, an in-process adaptive milling method is proposed for the large-scale assembly interface driven by real-time machining vibration data. Within this context, the milling operation is first divided into several process steps, and the machining vibration data in each pro...     

石英纤维增强聚酰亚胺复合材料超低温铣削实验

石英纤维增强聚酰亚胺复合材料是一种非均匀的各向异性材料,采用传统铣削方法对其进行加工时存在刀具磨损严重、切削力较大、加工效率低等问题。为此本文采用超低温冷却铣削方法对石英纤维增强聚酰亚胺复合材料进行铣削实验,并与传统干铣削方式进行了对比,分析了包括加工表面形貌、粗糙度、切削力和刀具磨损等切削性能。结果表明:两种工况下,表面粗糙度随主轴转速的提高而降低,随切深的增加呈先降低后增大趋势;相对于干铣削,不同切削速度下超低温冷却铣削有效抑制了低速干铣削纤维起毛、高速干铣削黏结剂烧蚀缺陷,表面质量都得到改善,刀具耐用度得到提高。超低温冷却引起的复合材料切削力增大,纤维断屑方式的改变以及切削热的有效降低是提高加工质量的主要原因。     

Milling surface roughness for 7050 aluminum alloy cavity influenced by nozzle position of nanofluid minimum quantity lubrication

In nanofluid minimum quantity lubrication (NMQL) milling of aviation aluminum alloy, it is the bottleneck problem to adjust the position parameters (target distance, incidence angle, and elevation angle) of the nozzle to improve the surface roughness of milling, which has large and uncontrollable errors. In this paper, the influence law of milling cutter speed, helical angle, and cavity shape on the flow field around the milling cutter was studied, and the optimal nozzle profile parameters were obtained. Using 7050 aluminum alloy as the workpiece material, the milling experiment of the NMQL cavity was conducted by utilizing cottonseed oil-based Al₂O₃ nanofluid. Results show that the high velocity of the surrounding air flow field and the strong gas barrier could be attributed to high rotating velocities of the milling cutter. The incidence angle of the nozzle was consistent with the helical angle of the milling cutter, the target distance was appropriate at 25–30 mm, and the elevation angle was suitable at 60°–65°. The range and variance analyses of the signal-to-noise ratio of milling force and roughness were performed, and the chip morphology was observed and analyzed. The results show that the optimal combination of nozzle position parameters was the target distance of 30 mm, the incidence angle of 35°, and the elevation angle of 60°. Among these parameters, target distance had the largest impact on cutting performance with a contribution rate of more than 55%, followed by incidence angle and elevation contribution rate. Analysis by orthogonal experiment revealed that the nozzle position parameters were appropriate, and R_a (0.087 μm) was reduced by 30.4% from the maximum value (0.125 μm). Moreover, R_sm (0.05 mm) was minimum, which was 36% lower than that of the seventh group (R_sm = 0.078 mm).     

单激励超声椭圆振动车削薄壁筒实验研究

通过对普通夹心式超声椭圆振动换能器结构的研究,设计了一种能够在单一纵向激励的情况下产生椭圆振动的换能器结构,利用有限元分析工具对换能器的结构进行分析,并且利用光纤测振仪对单一纵向激励换能器进行了测量,验证了可以通过单向激励产生椭圆振动。利用这种结构研制了一套单激励超声椭圆振动车削系统,采用PCD刀具对LY12实心件和薄壁筒工件进行了精密切削实验,实验结果表明椭圆振动切削可以大幅度降低切削力,明显改善薄壁工件的形状精度,同时工件还具有较好的表面粗糙度。     

基于最小加工表面裂纹的TiAl合金铣削参数优化

TiAl合金以其优异的性能被广泛应用于航空、航天制造领域,但由于TiAl合金自身的物理、化学特性,导致其切削性能较差,加工过程中容易出现工件表面烧伤、表面微裂纹等问题。为了研究TiAl合金铣削加工过程中切削工艺参数对加工表面裂纹的影响规律,设计了TiAl合金切削参数与加工表面裂纹之间的正交试验。结果表明:切削速度对TiAl合金铣削表面裂纹的影响最大,其次是切削深度和切削宽度,每齿进给量对表面裂纹的影响最小。基于遗传算法,以表面裂纹长度为目标函数,优化得到的最优参数组合为:ae=0. 2 mm、ap=0. 2003 mm/z、fz=0. 02001 mm/z、vc=20. 0004 m/min。采用优化后的参数铣削TiAl合金,发现工件表面的实际加工裂纹长度和经过算法优化的裂纹长度相差较小,该优化方法可行性较高,误差较小。     

基于响应曲面法的高速内冷铣削AISI304不锈钢铣削力

针对硬质合金刀具高速内冷铣削AISI304不锈钢时,切削力大、切削温度高及加工表面质量低的问题。基于响应曲面中心复合设计方法进行高速内冷铣削实验,建立了铣削力分量二阶回归预测模型,并进行了实验验证。对比了干式与内冷铣削后的加工表面质量,分析了铣削参数对铣削力分量的影响规律,以铣削力分量最小为目标优化了铣削参数。结果表明:进给力和径向力的预测值与实验值的误差分别为4. 77%和6. 16%;内冷铣削的Ra为0. 193～0. 327μm;对铣削力分量的影响是铣削深度转速进给量,随着铣削深度和转速的增加,进给力先升高后降低,径向力逐步增加,铣削深度与转速的交互作用对进给力和径向力的影响显著;转速11 643. 63 r/min、铣削深度1 mm、进给量0. 08 mm/r为最优铣削参数组合。     

Five-axis flank milling tool path generation with curvature continuity and smooth cutting force for pockets

In order to ensure machining stability, curvature continuity and smooth cutting force are very important so as to meet the constraints of both cutting force and kinematics of machine tools. For five-axis flank milling, it is difficult to meet both of the constraints because tool path points and tool axis vectors interact with each other. In this paper, multiple relationships between tool path points and tool axis vectors with cutting force and kinematics of machine tools are established, and the strategies of corner-looping milling and clothoidal spirals are combined so as to find feasible solutions under both of the constraints. Tool path parameters are iterated by considering the maximum cutting force and the feasible range of the tool axis vector, and eventually a curvature continuity five-axis flank milling tool path with smooth cutting force is generated. Machining experimental results show that the conditions of cutting force are satisfied, vibration during the process of machining is reduced, and the machining quality of the surface is improved.     

纤维方向角对超低温冷却石英纤维复合材料铣削性能的影响

石英增强聚酰亚胺树脂基复合材料是一种非均匀的各向异性材料,其加工性能高度依赖于纤维铺层方向与加工进给方向所成角度,即纤维方向角。本文通过一系列不同纤维方向角的干切削和超低温冷却铣削实验,研究了纤维方向角对表面形貌、表面粗糙度、铣削力及刀具磨损的影响。结果表明:不同纤维方向角,剪应力形式不同,切削断屑形式也不同。纤维方向角为锐角时铣削表面质量均良好,但当纤维方向角增大到90°时,切削表面质量下降,切削力变化幅度增大。相同铣削时间内,在干切削工况下,刀具磨损严重,涂层脱落面积约为测量面积的70%;而在低温切削工况下,涂层未遭到严重破坏,刀具仍处于稳定磨损阶段,刀具耐用度优于干切削工况。     

纤维夹角和铣削参数对CFRP铣削力的影响

为探索CFRP铣削加工中出现的分层、崩边等表面缺陷形成机理,对CFRP进行铣削加工实验。基于单因素实验法获得了纤维夹角对CFRP铣削力的影响规律,基于中心复合曲面设计,获得了硬质合金刀具铣削CFRP过程中铣削速度、每齿进给量和铣削深度对铣削力的影响规律,并构建了铣削力的预报模型。实验结果表明:纤维夹角在0°～90°,铣削力随纤维夹角的增大而降低,而在90°～180°,铣削力随纤维夹角的增大而增大。f_z和a_e对三个方向铣削力影响都较为显著。v_c对y向和z向铣削力影响较为显著,而对x向铣削力影响不显著。铣削力随三个铣削参数的升高而增大,其中每齿进给量对铣削力影响最大。     

CFRP-TC4叠层板的钻削实验

采用硬质合金麻花钻对CFRP-TC4叠层板进行钻削试验,分析了钛合金层加工参数对钻削力、钻削温度和加工孔质量的影响。结果表明:随着转速的增加,钛合金层的轴向力逐渐减小;随着钛合金层进给量的增加,钛合金层与CFRP层的轴向力之比逐渐增加。运用指数公式模型对钛合金层轴向力实验结果进行回归分析,得到轴向力与转速以及进给量之间的关系式:F_z=2 088n~(-0.1222)·f_r~(0.2016),并对该方程进行了检验验证,误差均小于10%;在钛合金层进给量不变时,随着钛合金层转速的增加,CFRP的最大烧伤环直径和层间最高温度逐渐增加。     

次摆线走刀在高速铣削窄槽结构中的应用

在阐述次摆线参数方程的基础上,基于CAM/HSM技术,将次摆线走刀方式应用于窄槽结构的高速铣削试验中,研究了次摆线走刀的铣削力变化规律、窄槽结构的表面粗糙度及其局部形貌,并建立了次摆线走刀高速铣削窄槽结构的铣削力模型。研究表明:次摆线走刀高速铣削窄槽结构有效可行,加工出了高质量的窄槽型腔表面(Ra=0.142μm);次摆线走刀的铣削力呈周期变化,在走刀平面内,次摆线切削宽度方向上的铣削力是进刀宽度方向上的4倍;采用次摆线走刀加环切走刀策略加工窄槽结构,既改善了窄槽的铣削加工条件,又满足了高速铣削粗精加工的要求和原则。     

Influences of milling and grinding on machined surface roughness and fatigue behavior of GH4169 superalloy workpieces

Surface topography of superalloy GH4169 workpieces machined by milling and grinding is different significantly. Meanwhile, surface roughness, as one of the main indicators of machined surface integrity, has a great influence on the fatigue behavior of workpieces. Based on analyzing the formation mechanism and characteristics of surface roughness utilizing different machining processes and parameters, the machined surface roughness curve can be decoupled into two parts utilizing frequency spectrum analysis, which are kinematic surface roughness curve and stochastic surface roughness curve. The kinematic surface roughness curve is influenced by machining process,parameters, geometry of the cutting tool or wheel, the maximum height of which is expressed as R'_z.By subtracting the kinematic part from the measurement curve, the stochastic surface roughness curve and its maximum height R'_zcan be obtained, which is influenced by the defects of cutting tool edge or abrasive grains, built-up edges(BUE), cracks, high frequency vibration and so on. On the other hand, the results of decoupling analysis of surface roughness curves indicate that Raand Rz values of milling GH4169 are 2–5 times and 1–3 times as high as those of grinding, while R'_zvalue of milling is 13.85%–37.7% as high as that of grinding. According to the results of fatigue life tests of specimens machined by milling and grinding, it can be concluded that fatigue behavior of GH4169 decreases with the increase of R'_zmonotonically, even utilizing different machining processes.     

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 C/C 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 model is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.     

超声振动切削对耦合颤振的影响

以耦合颤振为研究对象,通过理论分析和实验测量,研究了超声振动切削(UVC)方法对其影响及机理。超声振动切削可以通过控制系统能量摄入抑制耦合颤振。一方面,确定系统发生耦合颤振具有临界能量阀值,系统摄入能量为瞬时切削功率在净切削时间内的积分;建立的临界切削深度模型,表明超声振动切削可以增大临界切深,这表示系统具有更大的切削功率阀值,其原因是超声振动切削方法净切削时间减少,从而在一定切削时间内维持系统能量摄入总量不变,保证切削系统的稳定。另一方面,在相同条件下,超声振动切削可以有效降低平均切削力,减少系统摄入的能量,从而减弱耦合颤振的振动幅度,对其进行抑制。使用自行研制的弱刚度镗杆进行了对比实验,实验结果表明:超声振动切削可以增大临界切削深度且临界切深与占空比成反比;在相同条件下减小了系统振动幅度,获得了更好的加工质量。     

SiC_(f)/SiC复合材料铣削加工表面质量北大核心CSCD

使用PCD立式铣刀对聚合物浸渍裂解法(PIP)制备的SiC_(f)/SiC复合材料开展单因素铣削试验,通过对加工中产生的切削力和加工后的表面粗糙度进行测量,分析了铣削工艺参数对其的影响;对加工表面、纤维断口进行SEM分析,讨论了SiC_(f)/SiC复合材料加工表面的形成。研究结果表明,表面粗糙度与切削力的变化趋势相同,高主轴转速和小切削宽度有利于得到表面粗糙度较小的加工表面;近孔洞区域与远离孔洞区域的材料去除方式不同;材料中纤维发生面内偏移和层间屈曲,纤维存在多种去除方式。     

Vibration coupling effects and machining behavior of ultrasonic vibration plate device for creep-feed grinding of Inconel 718 nickel-based superalloy

Ultrasonic vibration-assisted grinding(UVAG) is an effective and promising method for machining of hard-to-cut materials. This article proposed an ultrasonic vibration plate device enabling the longitudinal full-wave and transverse half-wave(L2T1) vibration mode for UVAG.The characteristics of two-dimensional coupled vibration in different directions were analyzed on the basis of apparent elastic method and finite element method. Furthermore, a correction factor was applied to correct the freque...     

Experimental and modeling study of surface topography generation considering tool-workpiece vibration in high-precision turning

High-precision turning(HPT) is a main processing method for manufacturing rotary high-precision components, especially for metallic parts. However, the generated vibration between tool tip and workpiece during turning may seriously deteriorate the surface integrity. Therefore,exploring the effect of vibration on turning surface morphology and quality of copper parts using3D surface topography regeneration model is crucial for predicting HPT performance. This developed model can update the machin...     

切深对椭圆超声振动切削机理的影响

以椭圆超声振动切削为研究对象,通过理论分析,有限元仿真和切削实验,研究了切深变量对其切削过程中机理的影响。指出在微小的切深条件下,刀尖钝圆影响不可忽略,其切削过程表现出微细切削特性。一方面,基于微细切削理论,建立了正交椭圆超声振动切削运动学和力学模型,将切削区分为后刀面回弹区、刀尖犁切区、刀尖剪切区和前刀面摩擦区四个区域,并依次对四个区域内不同切深条件下各个切削分力进行计算分析。另一方面,对切削过程进行有限元仿真和切削实验。其结果表明:当切深小于最小切削厚度时,切削过程主要为刀具后刀面的回弹挤压与摩擦和刀尖钝圆的犁切作用,不产生切屑,切深抗力大于主切削力;当切深大于最小切削厚度并逐渐增大时,刀尖剪切和切屑与前刀面的挤压与摩擦作用逐渐凸显并成为主要切削方式,此时主切削力逐渐超过切深抗力并迅速增大。