齿厚与螺旋角对人字齿行星轮动态特性的影响

利用多尺度法分析人字齿行星轮轮齿厚度和螺旋角对人字齿行星轮系统动态特性影响。建立人字齿行星轮的动力学模型,该模型考虑时变啮合刚度、脱齿等非线性因素。利用该模型,分析齿厚与螺旋角对人字齿行星轮动态响应影响,多尺度法与数值模拟的计算结果一致。结果表明,齿厚与螺旋角对时变啮合刚度各阶波动幅值有着周期性影响,选取适当的齿厚与螺旋角可明显降低系统各自由度振动幅值和动态传递误差。     

波动负载对齿轮系统振动特性及边频调制影响研究

齿轮传动系统在工作时常承受复杂多变的外部波动载荷,导致轮齿啮合特性和系统振动响应频率特征复杂。基于时变啮合刚度的能量法合成模型,建立考虑系统扭振和横振响应影响的时变啮合刚度动态修正模型。建立单级齿轮传动系统的弯扭耦合模型,用Newmark法求解系统的振动响应。利用啮合刚度动态修正模型和齿轮系统弯扭耦合模型,通过数值算例分析波动负载对啮合刚度和系统振动响应的影响。结果表明,在波动负载作用下,啮合刚度和系统振动响应均存在明显的以波动负载频率为调制频率的边频调制现象,且被调制的中心谐波频率越高,调制现象越明显;外部波动负载的幅值越大,啮合刚度和系统振动响应的调制现象越明显,且当波动负载幅值较小时,表现为窄带调频和调幅的叠加,啮合频率两侧仅各有一条明显的边频谱线。     

基于小波变换的时变及典型非线性振动系统识别

用Morlet小波变换方法对时变振动系统和典型非线性振动系统进行参数识别。首先,通过Morlet小波变换提取振动响应的小波脊线,从而获得瞬时频率和瞬时幅值,然后,通过最小二乘曲线拟合即可估计系统的非线性阻尼和刚度系数。分别以时变阻尼自由振动系统、达芬有阻尼非线性简谐振动系统和范德波尔非线性自由振动系统为例子来说明小波变换方法对识别时变振动系统和非线性振动系统的有效性。     

考虑易损件的斜支承包装系统振动特性的研究

以考虑易损件的斜支承包装系统为研究对象,建立了系统无量纲非线性动力学方程,利用龙格-库塔法对易损件振动响应特性进行了数值分析。讨论了系统支承角、系统频率比以及系统质量比等对易损件加速度及位移响应的影响规律。研究结果表明:系统支撑角、系统频率比等对易损件加速度及位移响应影响显著;随系统支承角的减小,易损件加速度及位移响应幅值减小;增加系统频率比可使易损件加速度及位移响应幅值明显降低;低频率比条件下,增大质量比可抑制易损件加速度及位移响应幅值。研究结论可为斜支撑减振系统的设计提供理论依据。     

一类变质量振动系统的近似求解

当振动系统的参振质量随时间变化时,该系统即为变质量振动系统.采用改进的多尺度方法对变质量振动系统进行近似解析求解,并与四阶Runge-Kutta数值法进行比较,两种方法解得的振动响应一致.由计算结果可知,变质量振动系统的响应具有周期性;参振质量的时变方程中幅值变化系数ε的不同只影响系统振幅的大小,而不改变系统振动响应的周期.ε越大,系统响应的突变性越强;ε越小,振动响应越趋于平稳.     

时变载荷激励的空调滑片式压缩机用球轴承振动特性分析

基于滚动轴承动力学理论，建立了时变载荷激励的空调滑片式压缩机用球轴承非线性动力学方程组，采用Gear Stiff(GSTIFF)变步长积分算法对其进行求解，就球轴承的结构参数和工况参数对球轴承振动特性的影响进行了分析。结果表明：时变载荷激励下球轴承的振动响应频率以时变载荷频率为主，表现出强迫振动，且振动速度幅值远高于恒定载荷下轴承振动速度幅值；结构参数中，原始径向游隙对球轴承振动特性影响显著，采取零游隙或负游隙能够有效地抑制时变载荷对轴承的冲击；保持架兜孔间隙对轴承振动影响较小，存在最优的保持架兜孔间隙使得保持架振动最小；考虑时变载荷的影响，对空调滑片式压缩机用球轴承施加0.3%～0.6%额定动载荷的轴向预紧力可实现降低轴承振动目的。     

考虑滑动轴承时变动力学参数的齿轮系统建模及分析

为了对齿轮系统进行更加深入的研究,综合考虑时变轴承动力学参数以及动态齿侧间隙的影响,建立了齿轮系统动力学模型并进行了振动响应分析。以圆柱直齿轮为研究对象,将动压润滑轴承模型与齿轮啮合模型相结合,并计入动态齿侧间隙的影响,建立了系统的动力学微分方程。提出了一种齿轮-滑动轴承耦合系统的求解方法,分别研究了轴承间隙、齿侧间隙以及转速对系统振动响应的影响。结果表明:滑动轴承动力学参数的时变特性有助于改善系统的振动响应;在一定范围内增加轴承间隙以及齿侧间隙可以减小齿轮动态啮合力以及径向振动;随着齿轮转频的增加,系统的振动响应幅值减小,运动趋于平稳。     

浮基两刚体模型强迫振动动力响应分析

为分析浮基在外力作用下产生的强迫振动对浮基多体系统动力响应影响,将浮基多体系统简化为光滑铰接的两刚体模型,用多体动力学离散时间传递矩阵理论,并编写程序对浮基多体系统动力响应求解。分别计算浮基在周期横摇角强迫振动与波浪作用下浮基两刚体动力响应,获得浮基两刚体系统运动响应曲线。数值模拟结果表明,当横摇角强迫振动幅值、频率增加时,起吊重物的摆动更剧烈,绳索长度变化对重物摆动影响不大。在横向规则波作用下,浮基与重物的摆动幅值随绳索长度、吊臂仰角的增加而增大,随起吊重物质量变化先增大后减小。     

转子系统瞬态不平衡响应的有限元分析

推导了简单Jeffcott转子几何中心运动的解析表达式及转子系统瞬态振动的幅值，详细讨论了转子系统通过临界转速时初始条件引起的瞬态振动、同频振动和伴随自由振动的特性以及阻尼和启动加速度对系统瞬态响应的影响。此外建立了弹性转子系统的有限元模型，通过直接积分法求得系统的瞬态响应．得到系统通过临界转速时的共振幅值，并与试验取得一致的结果。本文的分析对工程中合理地进行转子系统参数设计，考虑共振区的迟滞现象。尽可能错开转子系统固有频率和工作转速频率提供一定的理论参考。     

完整约束下齿轮啮合转子系统的弯扭耦合振动稳态响应

在不脱齿等基本假设下，根据齿轮啮合原理和轮齿的齿面方程，推导了齿轮形心的横向位移和齿轮扭转角之间的约束关系式，从Lagrange方程出发，同时考虑齿轮啮合和不平衡效应，建立了直齿齿轮啮合转子-轴承系统的弯扭耦合动力学模型。分别在质量偏心和扭转激励作用下，分析了系统的弯扭耦合振动稳态响应。结果表明：两者均会引起弯曲振动和扭转振动，并且响应的幅值与系统的参数有关。     

ANALYSIS OF INTERFACE STRESSES IN CUTTING TOOL

In this paper the Filon's transformed equations have been applied successfully to evaluate the chip-tool interface stresses of a cutting tool from the photo-elastic data. This method is shown to be advantageous over the shear difference method, particularly for negative rake tools. The analysis was carried out to study the effect of rake angle and depth of cut on the stress distribution and total forces on the rake face, involved in the orthogonal machining process.     

Experimental studies on the cryogenic machining of biodegradable ZK60 Mg alloy using micro-textured tools

Reducing the contact area between the cutting tool rake surface and chip promotes the machining performance of the work material and increases the tool life. Magnesium alloys are ductile-lightweight materials that form continuous chips during machining. The present investigation discusses the orthogonal turning of ZK60 magnesium alloy with linearly textured cutting inserts under both dry and liquid nitrogen (LN₂) cooling conditions. Linear grooves that are parallel and perpendicular to chip flow direction were created using Nd-YAG laser on the tungsten carbide cutting inserts. The effect of texturing combined with the application of LN₂ cooling is studied by evaluating the machining temperature and forces, microhardness, surface roughness and tool wear. Textured tools considerably minimize the liaison area of the chip with the rake plane compared to non-textured tools, which resulted in favorable effects in machinability. In case of cryogenic machining, textured tools substantially minimize the friction by the coupled effect of micro-pool lubrication and the formation of thin-film lubrication between the tool–chip/tool–work interfaces. Parallel-textured tools aided with cryogenic cooling exhibit superior performance during machining among the different types of tools employed in the present investigation.     

Strain rate analyses during elliptical vibration cutting of Inconel 718 using finite element analysis,Taguchi method,and ANOVA

The high strain rate in metal cutting significantly affects the mechanical properties of the work piece by altering its properties. This study outlines the material strain rates during elliptical vibration cutting. The finite element analysis, Taguchi method, and analysis of variance (ANOVA) were employed to analyze the effects and contributions of cutting and vibration process parameters (feed rate, rake angle, tangential amplitude, and frequency of vibration) on the variation of strain rates during machining of Inconel 718. Taguchi signal-to-noise analysis on an L₁₈ (2¹×3³) orthogonal array was used to determine the optimum parametric combination for the maximum strain rate, and ANOVA was applied to evaluate the significance of control parameter factors on the strain rate. The results of the finite element analysis under different conditions illustrated that the feed rate and rake angle were negatively related to the strain rate, whereas the tangential amplitude and frequency had a positive response. Furthermore, ANOVA results indicated that the effect of the feed rate, tool rake angle, vibration frequency, and tangential amplitude on the strain rate were all statistically significant, with a reliability level of 95%. Of these, the dominant parameter affecting the strain rate was the feed rate, with a percentage contribution of 40.36%. The estimation of the optimum strain rate and confirmation tests proved that the Taguchi method could successfully optimize the working conditions to obtain the desired maximum strain rate.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00315-0     

On chip flow direction in oblique free cutting of ductile metals

The paper addresses the available methods of determination of the chip flow angle h on the tool face in oblique free cutting of ductile metals. A method for assessing this angle by the chip contraction is put forward; it is based on determination of the effecting (working) rake γ_eff of the tool in the plane normal to cutting plane and passing through the chip flow direction. Comparative calculation results are given; it is noted that the proposed method offers advantages of simplicity and accuracy of determination of the angle η.     

Minimum energy criterion applied to the orthogonal machining of polymers

The paper deals with the orthogonal machining characteristics of anisotropic and normal stress sensitive polymers. Tensile and compression tests were carried out to define the mechanical properties of the chosen polymers, nylon and polycarbonate. The deformation during cutting is assumed to occur under plain strain conditions and a suitable yield equation is chosen to describe the material yielding behaviour. For the cutting process, a single shear plane model is assumed and the minimum energy criterion applied to the appropriate yield criterion to develop a representative shear angle relationship, which depends on the mechanical state of the chosen polymer. Orthogonal cutting tests were carried out varying three main parameters; cutting speed, tool rake angle and depth of cut. Measured forces and shear angles are compared with the values predicted from the theoretical analysis and an excellent correlation is obtained. It is concluded that, for the assumed mode of deformation, the minimum energy criterion applied to a representative yield equation is justified in explaining polymer behaviour under orthogonal cutting conditions.     

Influence of wire-EDM textured conventional tungsten carbide inserts in machining of aerospace materials (Ti–6Al–4V alloy)

Importance of this present investigation is to identify the influence of modified tool (tool with texturing) on the process of orthogonal turning of Ti–6Al–4V work material. To achieve the enhanced turning conditions, four different types of textures (plain conventional, cross, perpendicularly textured and parallel textured tool to the chip flow direction) were fabricated on the rake face of the tool insert and the lubricant used during the machining process is molybdenum disulfide (MoS₂). Machining forces (the force of cutting and feed), angle of shear, chip morphology, temperature distribution between tool and chip were measured. Shear strain and strain rate were also computed and compared with all type of cutting tools. Experimental results revealed that the cross-textured cutting tool exhibit an effective reduction in cutting force, friction, shear strain and strain rate. The favorable metal removal condition of curling chip with low diameter was achieved through cross-textured tool.     

Ranges of application of free-cutting steels and recommended tool materials

Abstract

Four low carbonfree-cutting steels (0·11% carbon resulphurised, 0·11% carbon leaded–resulphurised, 0·08% carbon resulphurised, and 0·15% carbon leaded) were turned, dry, with a series of six types of cutting tool in which rake angle, tool material, and coating were varied (5° rake, high speed steel, TiN coated and uncoated; 15° rake, high speed steel, TiN coated and uncoated; 5° rake, cemented carbide, TiN coated and uncoated) in order to determine the optimum tool–workpiece combination for three cutting speed ranges: a low speed range in which the built-up edge (BUE) was forming or about to form; a speed range covering the BUE regime; and a higher speed range in which the BUE became a built-up layer (BUL). Tool–workpiece interaction was assessed by measurement of cutting forces, chip form, surface finish, tool temperature, and wear. It is suggested by the results that the best combination in the low speed range is that of leaded–resulphurised steel and uncoated high speed steel. In the BUE range, the combination of leaded steels and uncoated tools should be avoided; at higher speeds, coated tools are preferred, with non-resulphurised leaded steel giving the lowest tool temperatures and highest cutting speeds before ultimate failure. These recommendations should be treated with caution and used only as guidelines.

MST/867     

Design and construction of a dynamometer to evaluate the influence of cutting tool rake angle on cutting forces

In this study, the influence of cutting tool rake angle on the cutting forces developed during turning operation was evaluated. For this purpose, a dynamometer was designed and constructed to measure cutting forces. In this dynamometer design, measurement of the cutting tool deflection under the cutting forces was aimed using two beam type load cells located suitably according to the cutting tool. In order to examine the influence of rake angle, turning tests were carried out on AISI 1040 steel workpiece using eight different rake angles. The turning tests at each rake angle were conducted at five different cutting speeds while depth of cut and feed rate were kept constant. The results showed that cutting forces decreased with increasing the rake angle.     

Special features of the cutting process in the first and last workpiece revolutions during the cutting tool engagement and disengagement with the workpiece

A method of calculation of stresses in a cutting tool during its engagement and disengagement with a workpiece is described. It has been found out that during the workpiece first and last revolutions the tool rake significantly differs from the values typical of the stationary stage of turning. The rake variations have an influence on the magnitude and sign of stresses on the tool face and flank surface; taking it into account permits calculating the stresses and then assessing the tool failure probability.     

Investigating the Machinability of AISI 420 Stainless Steel Using Factorial Design

This work aims at studying the machining characteristics of high-strength materials using carbide cutting tool inserts at different cutting conditions. This is an essential step in building up an accurate machining information system. The tested material is high-strength stainless steel of the AISI 420 type. Machining tests were carried out using orthogonal cutting conducted to investigate the machining characteristics for high-strength stainless steel AISI 420 at different cutting conditions and tool rake angles. This assessment is achieved by investigating the effect of cutting parameters (cutting speed, feed, depth of cut, and tool geometry) on cutting forces, specific cutting energy, shear angle, coefficient of friction, shear stress, shear strain, and shear strain rate. Empirical equations and a correlation for the behavior of each of the output responses were investigated as a function of the independent variables. Main effect and interaction plot were presented for the most influential factors affecting the main cutting force and the power consumed.