超声振动改善深孔镗削加工质量

深孔加工在航空发动机制造过程中广泛存在,由于其刚性弱,静态让刀量大,导致加工颤振和刀具磨损严重,使得其加工质量难以得到保证。超声振动切削作为一种特种切削加工手段,具有降低切削力,提高系统刚性和抑制加工颤振等优势。将超声振动应用于深孔镗削,进行了断屑条件验证,孔径误差测量,已加工表面粗糙度测量以及表面形貌观测等试验。试验结果表明,超声振动镗削能够有效缓解深孔镗削过程中的堵屑问题,减小孔径误差和表面粗糙度,抑制切削颤振,从而改善深孔镗削加工质量。     

Influence of magnetorheological elastomer on tool vibration and cutting performance during boring of hardened AISI4340 steel

During boring process, tool vibration is a major concern due to its overhanging length, which results in high cutting force, poor surface finish, and increase in tool wear. To suppress tool vibration and improve cutting performance, a novel technique in rheological fluid was designed and developed. In this work, a magnetorheological elastomer (MRE) was developed, and parameters, such as piston location, current intensity, and coil winding direction, were considered. Cutting experiments were conducted to obtain a set of parameters that can efficiently control vibration during boring of hardened AISI 4340 steel. Taguchi method was used to optimize the cutting condition, and findings show that the cutting tool embedded with the MRE reduced tool vibration and effectively increased cutting performance.

     

Specific cutting force coefficients modeling of end milling by neural network

In a high precision vertical machining center, the estimation of cutting forces is important for many reasons such as prediction of chatter vibration, surface roughness and so on. The cutting forces are difficult to predict because they are very complex and time variant. In order to predict the cutting forces of end-milling processes for various cutting conditions, their mathematical model is important and the model is based on chip load, cutting geometry, and the relationship between cutting forces and chip loads. Specific cutting force coefficients of the model have been obtained as interpolation function types by averaging forces of cutting tests. In this paper the coefficients are obtained by neural network and the results of the conventional method and those of the proposed method are compared. The results show that the neural network method gives more correct values than the function type and that in the learning stage as the omitted number of experimental data increase the average errors increase as well.     

多刃均布式镗杆系统振动耦合问题研究

深孔镗削过程中,由于镗杆的悬伸量较大,刚度差,强度低,在镗削过程中易产生振动。自激振动是金属切削过程中产生的振动类型之一,同时其振动机理的揭示以及对它的控制相对于受迫振动的研究而言较为困难。本文针对多刃均布式镗杆系统,在建立其力学模型的基础上,计算镗刀所受的动态切削力,并对镗杆振动系统耦合微分方程进行推导计算,对该耦合系统的稳定性进行分析,最后得出引起该系统产生自激振动的条件。     

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。     

An improved cutting force model for micro milling considering machining dynamics

Micro milling, as a versatile micro machining process, is kinematically similar to conventional milling; however, it is significantly different from conventional milling with respect to chip formation mechanisms and uncut chip thickness modelling, due to the comparable size of the edge radius to the chip thickness, and the small per-tooth feeding. Considering tool runout and dynamic displacement between the tool and the workpiece, the contour of the workpiece left by previous tool paths is typically in a wavy form, and the wavy surface provides a feedback mechanism to cutting force generation because the instantaneous uncut chip thickness changes with both the vibration during the current tool path and the surface left by the previous tool paths. In this study, a more accurate uncut chip thickness model was established including the precise trochoidal trajectory of the cutting edge, tool runout and dynamic modulation caused by the machine tool system vibration. The dynamic regenerative effect is taken into account by considering the influence of all the previous cutting trajectories using numerical iteration; thus, the multiple time delays (MTD) are considered in this model. It is found that transient separation of the tool-workpiece occurring at a low feed per tooth, caused by MTD and the existing cutting force models, is no longer applicable when transient tool-workpiece separation occurs. Based on the proposed uncut chip thickness model, an improved cutting force model of micro milling is developed by full consideration of the ploughing effect and elastic recovery of the workpiece material. The proposed cutting force model is verified by micro end milling experiments, and the results show that the proposed model is capable of producing more accurate cutting force prediction than other existing models, particularly at small feed per tooth.     

飞机交点孔超声椭圆振动精密加工技术

针对常规方法加工30mm以上的飞机翼身交点孔存在动力不足、孔径精度差和表面质量不高等问题,采用超声椭圆振动镗削的方法,研制了超声椭圆振动镗削装置,并对30mm以上不同材料的翼身交点孔进行了镗削加工,取得了很好的工艺效果,充分体现了超声椭圆振动镗削技术在飞机交点孔加工中的优势。     

Adiabatic Shear Mechanisms for the Hard Cutting Process

The most important consequence of adiabatic shear phenomenon is formation of sawtooth chip. Lots of scholars focused on the formation mechanism of sawtooth, and the research often depended on experimen...     

高速硬切削参数对切削力影响的数值模拟

建立了淬硬钢高速切削的有限元模型,通过Johnson-Cook（JC）工件材料模型及JC失效准则来模拟切屑的形成过程;并研究了背吃刀量、刀具前角和刀尖圆弧半径等参数对切削力的影响规律.     

凸曲面拼接模具球头铣刀的瞬时铣削力预测

在曲面模具拼接区域球头铣刀铣削过程中,刀具载荷变化大,瞬态铣削力有突变现象,影响模具拼接区域的加工精度和表面质量。为了预测拼接区域球头铣刀的瞬态铣削力,首先,建立考虑冲击振动的球头铣刀三维次摆线轨迹方程,得到瞬时未变形切屑厚度模型;然后,基于铣削微元的思想,建立凸曲面双硬度拼接模具球头铣刀的瞬态铣削力模型,该模型能够综合考虑拼接区冲击振动、硬度变化、刀具工件切触角度变化对瞬态铣削力的影响;最后,进行凸曲面拼接区域球头铣刀铣削加工实验。实验结果表明,预报的瞬态铣削力和实验测量结果在幅值上和变化趋势上具有一致性,在平稳切削时最大铣削力预测误差值基本在15%以内,验证了该模型能有效地预报凸曲面模具拼接区域球头铣刀的瞬态铣削力。     

SiC单晶片加工过程中切割力的分析与建模

SiC单晶具有优良的物理和机械性能,在微电子和光电领域得到了广泛应用,然而由于其高硬度和脆性,晶片的制造非常困难、效率低下。为提高SiC单晶片的加工质量和加工效率,分析了SiC单晶片线锯切割过程中的受力情况;从切屑变形和摩擦两个方面,建立单颗磨粒的法向和切向受力模型,进而得到线锯切割力与工艺参数及线锯物理属性的关系模型;设计了切割力的试验装置,通过不同加工参数下的试验研究,确定了关系模型中的应力系数;通过理论值与试验值的对比校验,法向力和切向力预测值的误差小于9.18%,并对误差产生原因作了分析。结果表明,该切割力理论模型可以对SiC单晶片在同等线锯切割环境下的切割力进行有效预测,为切削力的优化控制提供了理论依据。     

Modelling of segmentation-driven vibration in machining

Excessive vibration, such as chatter, is a common problem in machining processes. Meanwhile, numerous hard, brittle metals have been shown to form segmented chips, also known as sawtooth chips, during machining. In the literature, a cyclic cutting force has been demonstrated where segmented chips are formed, with the force cycle corresponding to the formation of segments. Segmented chip formation has been shown to be linked to high vibration levels in turning and milling processes. Additionally, it has been proposed that the amplitude of chatter vibrations can be limited by interference between the tool flank and wavy workpiece surface, a phenomenon known as tool-flank process damping. In this contribution, a model is proposed to predict the amplitude of forced vibration arising due to the formation of segmented chips during turning. The amplitude of vibration was calculated as a function of cutting parameters. It was demonstrated that the model can be extended to account for the effect of tool-flank process damping. For validation, titanium Ti6Al4V alloy was turned using a flexible toolholder, with surface speed ranging from 10 to 160 m/min, feed rate from 0.1 to 0.7 mm/rev and width of cut from 0.35 to 4 mm. In the experimental validation, 25 of 68 test cuts exhibited high-amplitude vibration. In 16 of these cases, the main cause was concluded to be chip segmentation, which can be predicted by the model. The model is thus considered of practical value to machinists.     

Improved dynamic cutting force model in peripheral milling. Part II: experimental verification and prediction

Cutting trials reveal that a measure of cutter run-out is always unavoidable in peripheral milling. This paper improves and extends the dynamic cutting force model of peripheral milling based on the theoretical analytical model presented in Part I [1], by taking into account the influence of the cutter run-out on the undeformed chip thickness. A set of slot milling tests with a single-fluted helical end-mill was carried out at different feed rates, while the 3D cutting force coefficients were calibrated using the averaged cutting forces. The measured and predicted cutting forces were compared using the experimentally identified force coefficients. The results indicate that the model provides a good prediction when the feed rate is limited to a specified interval, and the recorded cutting force curves give a different trend compared to other published results [8]. Subsequently, a series of peripheral milling tests with different helical end-mill were performed at different cutting parameters to validate the proposed dynamic cutting force model, and the cutting conditions were simulated and compared with the experimental results. The result demonstrates that only when the vibration between the cutter and workpiece is faint, the predicted and measured cutting forces are in good agreement.     

磁悬浮铣削电主轴转子-刀具变质量不平衡系统动态特性研究

针对磁悬浮铣削电主轴在切削过程中因切屑进入刀具容屑槽中而导致“刀具-主轴”系统质量变化,进而引起系统回转精度不稳定的问题,以变质量质点理论为依据建立“切屑-刀具-主轴”系统的变质量动力学模型。分析系统的不平衡质量变化时所引起的系统振动,进而导致磁悬浮轴承定/转子间气隙磁场不均所产生不平衡磁拉力,并利用等效磁路法建立不平衡磁拉力模型。利用Riccati传递矩阵法求解磁悬浮铣削电主轴转子-刀具系统的稳态动力学模型,得到系统的模态参数和初始偏心质量影响下的不平衡响应。考虑铣削力、变质量力、切屑质量不平衡离心力和不平衡磁拉力等因素,采用Newmark-β算法求解磁悬浮铣削电主轴转子-刀具变质量系统的瞬态动力学模型。对系统从起动到切削过程的动态响应进行仿真分析,结果表明,质量不平衡是影响磁悬浮铣削电主轴转子-刀具系统稳态响应的主要因素;在切削过程中,变质量力是影响系统瞬态响应的主要因素;不平衡磁拉力对系统响应的影响与系统的稳定性成负相关与系统的振幅成正相关。     

Modelling the cutting forces in micro-end-milling using a hybrid approach

This paper presents the development of a cutting force model for the micro-end-milling processes under various cutting conditions using a hybrid approach. Firstly, a finite element (FE) model of orthogonal micro-cutting with a round cutting edge is developed for medium-carbon steel. A number of finite element analyses (FEA) are performed at different uncut chip thicknesses and velocities. Based on the FEA results, the cutting force coefficients are extracted through a nonlinear algorithm to establish a relationship with the uncut chip thickness and cutting speed. Then, the cutting force coefficients are integrated into a mechanistic cutting force model, which can predict cutting forces under different cutting conditions. In order to account for the cutting edge effect, an effective rake angle is employed for the determination of the cutting force. A comparison of the prediction and experimental measured cutting forces has shown that the developed method provides accurate results.     

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。     

车削中三维复杂断屑槽刀具断屑仿真研究

为有效缩短现有断屑槽刀具的设计周期、降低设计成本,采用有限元方法模拟了切削过程中切屑折断过程。利用Solid Works软件建立了三种刀具的三维模型,并在Deform 3D软件中对车削45钢工件过程进行了三维切削仿真。其中,工件材料采用了Johnson-Cook模型和Cockroft-Latham韧性断裂准则,仿真模型采用了有效参数设置以保证数值计算精度与效率。通过仿真研究了不同切削参数下的切屑形态、断屑过程及主切削力等。研究结果表明,仿真结果与试验结果吻合良好,该仿真模型及方法能有效应用于断屑槽刀具断屑性能研究,是三维复杂断屑槽刀具设计和切削参数优化的一种新方法。     

Study on the cutting force of cylindrical turning with novel restricted contact tools

Analysis of cutting force is important in research and development of metal cutting process and in designing cutting tools. This paper reports the theoretical computational formulae for cutting force for cylindrical turning using novel restricted contact tools that have inconstant tool/chip restricted contact length. These formulae are based on the minimum energy principle. The results of extensive cutting tests show that the derived theoretical computational formulae can predict the cutting force, especially the main cutting force, with reasonable accuracy. The novel RC tools-type II and type III can reduce cutting force as well as the conventional RC tools-type I. In addition, they can also effectively control the direction of chip curling, and type III RC tools may have a longer tool life due to the high strength of its cutting edge and the possibility of liquid coolant approaching the cutting zone. Finite element models have been developed to study the cutting force, and the results indicate that the main cutting force can be accurately predicted, while there are some inaccuracies for the feed force and thrust force because of the simplifications adopted during modeling.     

高速铣削淬硬钢时切削载荷平稳化研究

和传统的铣削加工相比,高速铣削淬硬钢更需要稳定的切削载荷,以尽可能减少刀具碎裂和过度磨损。本研究借助三向压电石英测力仪,使用TiAlN涂层球形端铣刀,在13500 r/min的转速下,对淬火45#钢(47HRC~48HRC)进行了高速铣削试验,建立了高速铣削下的多项式切削力试验模型,模拟了以恒定切削力为目标、优化进给率的加工实例。结果显示,稳定的切削载荷能有效地提高加工效率,避免刀具剧烈磨损。     

高温合金振动钻削断屑实验研究及机理分析

对振动钻削理论进行了分析,建立了振动钻削时断屑的数学模型,利用自制的振动钻削实验装置,采用不同的振动钻削参数进行高温合金振动钻削试验,对轴向振动钻削的断屑效果以及轴向钻削力和扭矩进行了研究,分析了各加工参数对加工过程的影响,发现振动钻削力随钻削参数的变化比较平稳,在大进给量或高转速状态下,振动钻削的钻削力比普通钻削力小得多。通过比较振动钻削与普通钻削所得切屑可知:振动钻削有利于断屑,切屑体积小,排屑顺畅。