立铣刀齿数和螺旋角对铣削变截面涡旋盘影响仿真研究

变截面涡旋盘加工精度要求高,刀具的选择直接影响加工质量。通过分析涡旋压缩机工作原理以及刀具参数对铣削变截面涡旋盘的影响,建立了高速铣削HT250铸铁变截面涡旋盘的仿真模型及简化后的二维铣削模型,利用ABAQUS软件分析了刀具齿数和螺旋角对铣削力和铣削温度的影响规律。试验表明,随着刀具齿数的增加,切向力F_x、径向力F_y和轴向力F_z都增大,铣削温度也逐渐增大;随着螺旋角度的增大,切向力F_x和径向力F_y减小,轴向力F_z增大,铣削温度先减小后增大。分析表明,合理的刀具参数可以减小涡旋齿的变形,本研究可为加工变截面涡旋盘时选择合理的刀具齿数和螺旋角提供依据和参考。     

利用数值模拟估算TBM刀具磨损量的方法

采用有限元方法建立滚刀与岩石相互做作用模型。模拟了单刀破岩过程中盘形滚刀的受力与运动情况。并依据体积磨损量与摩擦能量之间的关系建立方程,对刀具磨损量以及刀具寿命进行了估算。研究结果表明:利用数值模拟得到的垂直力、滑移量估算刀具使用寿命的方法可行;对于同一种地质条件,滚刀存在一个最佳贯入度使得磨损量最小;安装半径与刀盘转速的增大会使刀具磨损量增大;同条件下单轴抗压强度越大的岩石对刀具磨损越严重。     

轧件不对称滞后变形下动态轧制力建模及仿真研究

通过分析轧制过程中轧辊振动对轧件弹塑性变形状态的影响,研究不同轧辊振动方向下轧制力的变形特点及其表达形式,建立一种具有不对称滞后变形作用的动态轧制力模型。基于不对称动态轧制力模型,通过以某厂1780轧机实际参数进行数值仿真,得到轧辊半径、轧辊转速、前张力、后张力及入口厚度等因素变化下动态轧制力与轧辊振动位移之间的滞后关系曲线。从仿真结果中可以得出,随着轧辊半径的不断增大,滞后区域会逐渐增大,导致系统的耗散能量增大;减小轧辊的转速、板带的入口厚度都会使滞后区域减小,从而减少耗散的能量;同时还通过前、后张力对滞后曲线的影响规律验证热连轧机的微张力控制特点。以上结论为进一步研究和抑制轧机振动问题提供了理论基础。     

高速电火花多次线切割电极丝振动模型建立

为了建立高速多次线切割电极丝非线性流固耦合振动模型,首先通过定义一个平均摩擦系数,将多次切割切缝转换成等价的同心环柱流道,然后对电极丝在电介质流体中的受力情况进行分析,建立起多次切割电极丝的空间力学模型,同时推导出各个力的表达式。在此基础上,根据力平衡方程,建立了多次切割电极丝振动模型。最后采用四阶Runge-Kutta法分析了参数对电极丝动态特性的影响,为解决目前多次切割的加工精度稳定性较差问题,提供基础理论依据。     

摆线钢球行星传动十字槽等速输出机构的力学性能

针对锥形或球形槽截面对十字槽等速输出机构啮合点力学性能的影响,提出等曲率半径双圆弧的十字槽结构。利用啮合点法向变形量与轴向微位移的几何关系,根据赫兹接触理论推导出轴向微位移计算公式。建立了十字槽四点接触力学模型;通过轴向力和力矩平衡方程,求得十字槽啮合点的法向力;分析了参数对法向力和接触区应力的影响规律。结果表明:十字槽啮合点的法向力呈周期性变化,钢球数对法向力的影响最大,输入轴偏心距对法向力的影响最小;增大钢球半径可减小接触区正应力以及切应力峰值,减小半径系数可减小接触区正应力以及切应力峰值。     

刀杆外径对热缩刀杆与刀具配合的力学特性影响分析

为探究刀杆外径对热缩刀杆与刀具配合的力学特性的影响,对热缩刀杆与刀具配合模型进行理论研究,利用有限元软件ANSYS对静态、径向力作用下及感应加热情况下的不同刀杆外径的热缩刀杆与刀具配合等效应力、接触压力、热变形及热应力等力学特性进行对比分析。结果表明,随着刀杆外径的增大,热缩刀杆与刀具配合的总的接触压力、最大等效应力及热应力增大,配合面的最小热位移差值减小。在径向力的作用下,热缩刀杆上的接触应力不再均匀,最大接触应力明显增大,刀具也因径向力的作用而产生变形。在此基础上进一步给出了热缩刀杆外径的控制方法与流程,对热缩刀杆的合理设计和选用具有一定的现实指导意义。     

蜂窝复合材料超声切割力建模及工艺参数选择研究

针对Nomex蜂窝复合材料超声切割加工因缺乏系统化的理论指导以及工艺参数选择的盲目性而导致导致工件加工质量差的问题,对蜂窝复合材料直刃刀超声切割力以及工艺参数的选择进行了研究,基于刀具运动学特性分析建立了超声切割力与工艺参数的关系理论模型。基于该模型,研究了施加超声波振动能量后引起切割力变化情况,基于该模型,通过运用Matlab软件仿真分析,研究了工艺参数对超声切割力的影响规律。研究结果表明,与普通加工相比,采用超声复合切割蜂窝复合材料可以有效地降低切割力。刀尖角、刀刃面夹角对切割力的影响较为显著,其次是前倾角,刀具摆角对切割力的影响最小,该结果为工艺合理选择及进一步优化奠定了较好的理论基础。     

斜尖针穿刺软组织建模及针尖轨迹预测

在经皮穿刺过程中,当带斜尖的针穿刺软组织时,针与其周围组织相互作用,导致针体产生弯曲变形,针尖偏离预定方向,进而直接影响穿刺手术的定位精度。将针穿刺软组织的过程视为准静态过程,并进行离散化,建立针-组织相互作用模型。在该模型中,考虑到软组织的非线性与各向异性,将针视为由一系列非线性弹簧支撑的悬臂梁,且各点的弹簧刚度彼此不同。建立针-组织相互作用中的摩擦力及切割力模型,借助于穿刺实验,将穿刺力分解为摩擦力和切割力,进而获得力模型中的各个参数。基于虚拟非线性弹簧模型和穿刺力模型,根据最小势能原理,采用瑞利-里兹法预测针的偏转,进而获得进针过程中针尖的轨迹。仿真及实验结果表明,该模型能够精确地预测针尖位置,为穿刺路径规划提供理论依据。     

考虑工件变形的五轴侧铣薄壁件铣削力建模

针对铣削加工过程中工件和刀具接触关系的时变性所导致铣削力预测不精准的问题,提出一种综合考虑工件变形作用下的五轴侧铣铣削力建模方法。首先,基于机械Ⅱ型力学模型,综合考虑剪切力和犁切力作用,建立五轴铣削加工微元铣削力模型;其次,利用欧拉-伯努利梁理论计算工件在任意切削深度下的变形量;进而,更新工件变形量引起的切削深度变化,构建考虑工件变形的五轴侧铣薄壁件铣削力模型;最后,通过试验与模型预测结果对比,得出在考虑变形的情况下,X、Y方向上铣削力的平均峰值误差分别减小了4.42%和0.62%,验证了模型的有效性。     

碳纤维增强复合材料水导激光切割试验研究

采用正交试验方法对影响水导激光切割碳纤维增强复合材料（CFRP）的关键工艺参数进行了深入研究,得出了进给速度、水射流速度、脉冲频率和激光功率对切割CFRP的影响规律,并用直接对比法和极差分析法所得最优参数进行单次划槽切割对比。研究结果表明：在极差分析法所得最优参数下切割CFRP时,切缝深度增大3.2%、切缝宽度减小9.2%、切缝锥度减小11.8%、线粗糙度减小40.2%。通过与干式激光加工方法对比发现,水导激光加工技术在切割CFRP方面优势明显,由于水射流的冲刷和冷却作用,材料切割表面几乎无热影响区和纤维拔出。另外,采用正交试验所得最优工艺参数实现了4 mm厚度CFRP的无锥度切割。     

Cutting deflection control of the blade based on real-time feedrate scheduling in open modular architecture CNC system

Machining accuracy of thin-walled parts which have low-rigidity is greatly influenced by cutting deflection in flank milling. In this paper, cutting deflection of aero-engine blade during processing is controlled within a required dimensional accuracy based on the strategy of real-time feedrate scheduling which is integrated into an open modular architecture CNC system (OMACS) of five-axis milling machine. The maximum deflection position of blade is determined through combining analytical cutting force model in flank milling and finite element analysis (FEA)-based transient dynamic analysis. Then, the numerical model of blade deflection is established to obtain the numerical relationship among feedrate, cutting force, and blade deflection, which is usually used to get optimized cutting force and feedrate by setting allowable value of blade deflection. To implement blade deflection control during machining, a real-time control strategy of feedrate scheduling based on nonlinear root-finding algorithm of Brent-Dekker and principle of feedrate smooth transition is developed and integrated into OMACS which has functions of real-time cutting force signal processing and real-time feedrate adjustment. Experimental results show that blade deflection is effectively controlled by proposed strategies, machining accuracy, and efficiency are improved.     

微机控制的服装裁剪机结构设计

通过对数控裁服装剪机裁剪过程以及相关辅助和支持功能的研究,结合计算机控制的特点,对数控裁服装剪机的自动裁剪、裁剪刀智能纠偏、自动抬刀和落刀、裁剪刀高速往复振动和裁剪过程自动磨刀等机构进行了设计,所设计的数控裁剪机具有低成本、高性价比的特点。样机试制和试验结果表明设计达到了预期目标。     

Toolpath dependent chatter suppression in multi-axis milling of hollow fan blades with ball-end cutter

Aiming at the issue of toolpath dependent machining vibration in multi-axis milling of hollow fan blades, this paper presents an optimal selection method of cutting parameters based on single-line toolpath to suppress cutting chatter. Firstly, the impact of hollow structure on the blade structural modal was analyzed by using the modal analysis method. And the unstable regions of hollow blade surface have been predicted, which were prone to induce machining deformation and vibration. Secondly, the relationship between the hollow structure and the dynamic characteristics was revealed by analyzing the dynamic responses to the different cutting positions of blade surface. Thirdly, the optimization of cutting parameters based on single-line toolpath was proposed by establishing the 3D stability lobe diagram. Finally, the feasibility and effectiveness about the analysis of dynamic characteristics and the suppression method of cutting chatter were verified by a milling experiment of hollow blade.     

Micromechanisms of deformation and fracture in shearing aluminum alloy sheet

A systematic experimental investigation is presented on trimming of aluminum alloy autobody sheets. The variations of cut surface quality and burr height are related to the cutting parameters of clearance, blade sharpness and cutting angle. It was discovered that, contrary to conventional wisdom requiring the blade to travel perpendicularly to the sheet (0°-“cutting angle”), at appropriate cutting angles the surface quality becomes insensitive to the blade sharpness, and almost zero burrs are produced for large clearances and extremely dull blades. The findings suggest that the robustness of current shearing practices for aluminum sheets can potentially be greatly improved, requiring much less frequent tool-sharpening and less restrictions on clearance control. A counter-intuitive phenomenon was revealed. At certain cutting angles and intermediate clearances, instead of burr heights and cut surface roughnesses monotonically increasing with decreases in the blade sharpness as expected, they first increased and then surprisingly decreased. Instability conditions exist at which cut surface quality and burr height are extremely sensitive to the cutting parameters.     

涂层硬质合金齿圆锯片的设计与试验

以锯片的实际锯切工况为背景,为适应不同成分钢材工件的锯切要求,选取无涂层硬质合金齿圆锯片以及分别涂覆有TiAlN和A1CrN的涂层硬质合金齿圆锯片作为研究对象,对三种锯片锯切试验的结果进行分析。分析结果表明：涂层硬质合金锯片可使锯片的锯切能力显著提升,使用寿命进一步提高;而且A1CrN涂层比TiAlN涂层更适合锯切难加工金属材料,从而为刀具涂层技术在锯切领域的应用奠定了基础。     

辊切刀三维造型设计方法

辊切刀的曲线刃分布在空间表面上,造成加工困难。经过研究,运用不同的思维方法精确建立了辊切刀的曲线刃数学模型,为刃型加工提供了理论依据。在三种不同的思想方法的指导下,在不同的三维造型设计软件支持下,将刀具轨迹平面展开图曲线向等直径圆柱面上转换生成相应的三维特征,从而得到精确的三维实体模型,为生成G代码进行辊切刀刀刃的数控加工奠定了基础。     

削匀机刀辊切削过程中的“跳刀”和“让刀”的研究

本文针对在皮革削匀切削过程中“跳刀”和“让刀”缺陷的产生机理进行了研究,认为发生“跳刀”和“让刀”是由于螺旋刀片的切割作用不强、推挤压作用过大而造成的,进而提出了增加刀片前角,减小刀片螺旋导角、以减小刀片的结构锋角和工作锋角来增强刀片的切割作用,解决了“跳刀”和“让刀”问题。通过理论探讨,给出了前角和刀片螺旋导角的最佳取值范围。     

高速锯切单晶硅的锯切力和锯缝崩边研究

探讨在单晶硅的高速精密锯切中,锯切用量与锯切崩边幅度大小之间的关系。通过使用金刚石薄锯片对单晶硅进行高速锯切,测量和分析不同参数下的锯切力,并结合锯切力比来分析金刚石锯片对单晶硅的锯切中力与崩边相互联系的特征。结果表明:在高速锯切单晶硅过程中,锯切深度、进给速度增大都能引起锯切力与力比的增大,也造成了单晶硅崩边情况更加严重。但是转速的提高则可以使锯切力大幅降低,并有效抑制加工过程中沟槽侧面的崩边问题。锯切深度与进给速度的增加引起锯切力增大时使单晶硅材料更加倾向于脆性断裂而被去除,但是提高转速降低锯切力后可使单晶硅渐转化为塑性去除,有效提高了加工产品质量。     

Slicing of soft flexible solids with industrial applications

Thin slices of soft flexible solids have negligible bending resistance and hence store negligible elastic strain energy; furthermore such offcuts are rarely permanently deformed after slicing. Cutting forces thus depend only on work of separation (toughness work) and friction. These simplifying assumptions are not as restrictive as it might seem, and the mechanics are found to apply to a wide variety of foodstuffs and biological materials. The fracture toughness of such materials may be determined from cutting experiments: the use of scissors instrumented for load and displacement is a popular method where toughness is obtained from the work areas beneath load–displacement plots. Surprisingly, there is no analysis for the variation of forces with scissor blade opening and this paper provides the theory. Comparison is made with experimental results in cutting with scissors. The analysis is generalised to cutting with blades of variable curvature and applied to a commercial food cutting device having a rotating spiral plan form blade. The strong influence of the ‘slice/push ratio’ (blade tangential speed to blade edge normal speed) on the cutting forces is revealed. Small cutting forces are important in food cutting machinery as damage to slices is minimised. How high slice/push ratios may be achieved by choice of blade profile is discussed.     

减摩槽刀片切削过程的Deform仿真

在刀片上设计减摩槽,理论上可以减小刀屑接触面积,进而减小切削力。目前,对减摩槽刀片的研究仍停留在切削实验阶段。本文用Deform 3D软件对有无减摩槽的两种刀片进行了模拟仿真,分析了减摩槽对切削力大小、切削温度、切屑的有效应力及刀具塑性变形的影响。仿真结果对刀具减摩槽的设计及选用具有参考价值。