轴向功率超声珩磨力学模型的建立及仿真

功率超声珩磨技术在发动机缸套的精密加工中能够得到较好的表面质量,其中珩磨力的大小与超声振动特点有关,是影响工件材料去除、磨削热及表面质量的重要因素之一。基于超声珩磨材料去除机理,考虑了油石表面磨粒分布规律,建立了包括材料切屑变形和磨粒与工件摩擦两种情况的超声珩磨力学模型。由力学模型仿真结果可知:功率超声珩磨磨削力与加工参数及加工过程中材料物理变化均有关,特别是材料应变率效应更加明显;在相同加工条件下,超声珩磨磨削力比普通珩磨平均降低50%以上,并且法向力与切向力比值增大,有利于材料的去除;超声振动能够减小磨粒与工件的平均动态摩擦系数,从而减小平均切向摩擦力大小,有利于提高工件表面质量;珩磨深度较主轴转速对珩磨力影响更大,当主轴转速高于620 r/min时,珩磨力开始逐渐减小。     

21NiCrMo5H齿轮钢超声磨削力建模研究

磨削力的建模研究是认识超声磨削机理的重要基础。在超声磨削单颗磨粒运动特性分析基础上,基于工件上被切削掉的磨屑体积应等于砂轮磨削去除的体积的原则,推导出超声磨削平均未变形磨屑厚度公式,得到切屑变形力模型;考虑超声振动对摩擦因数的影响,建立磨粒与工件摩擦力模型。综合切屑变形力模型、摩擦力模型,推导出超声辅助磨削下的磨削力模型,进行21NiCrMo5H齿轮钢材料渗碳淬火后超声磨削试验研究,确定磨削力模型中相关材料系数,得到超声磨削力模型。与现有文献的计算模型相比较,给出的超声磨削力模型与磨削试验测量结果具有更好的一致性,并对超声磨削机理提出了新的认识,为后续研究提供更多的参考与基础。     

轴向超声辅助磨削陶瓷的磨削力模型

基于单颗磨粒的最大未变形切屑厚度,建立了轴向超声振动辅助陶瓷磨削的磨削力数学模型,模拟得到了不同磨削深度、砂轮线速度和工件运动速度下的磨削力并进行了试验验证。结果表明:法向磨削力的计算值与试验值的误差为15%左右,切向磨削力的计算值与试验值的误差为20%左右;由于前后磨粒的运动轨迹会存在重合,模型计算的磨削力比试验值大;磨削力随着砂轮边缘速度的增加而减小,随着磨削深度和工件速度的增加而增大。     

轴向超声振动辅助磨削的磨削力建模

以单颗磨粒为对象,分析轴向超声振动下磨粒的运动特性。在此基础上,将磨削力分为切屑变形力和摩擦力两部分,分别分析了轴向超声振动对切屑变形力和摩擦力的影响。在切屑变形力方面,轴向超声振动改变了磨粒运动方向与主切削方向间的夹角;在摩擦力方面,轴向超声振动降低了磨粒与工件间的摩擦因数。基于此建立了轴向超声振动辅助磨削的磨削力模型。通过对21Ni Cr Mo5H进行了轴向超声振动辅助磨削的磨削力试验,确定了模型中的常数,并验证了所建模型的正确性。建立的磨削力模型是轴向超声振动辅助磨削的磨削力预测的一种有效方法,对轴向超声振动辅助磨削机理的认识具有较大意义。     

基于DEFORM-3D单颗磨粒切削仿真与研究

建立了单颗磨粒几何模型,运用DEFORM-3D有限元软件模拟Al2O3磨粒与45钢不同相对位置(旋转角度)时磨削力、等效应力、等效应变与磨削温度的变化规律,仿真结果表明:随着磨粒旋转角度的增大,法向磨削力和切向磨削力都增大,其比值约为(1~1.3),磨削温度先增大后减小,磨粒旋转角度越小,越易形成切屑,等效应力最大位置是磨粒耕犁作用产生的堆积材料挤压周围材料的那部分区域,而等效应变的最大位置是磨粒前刀面与工件接触的区域。单颗磨粒切削仿真为磨削加工之前磨削力与磨削温度的预测提供理论依据,也为砂轮的制备提供了参考。     

HIPSN陶瓷磨削力试验研究与仿真

为探索金刚石砂轮磨削HIPSN(热等静压氮化硅)陶瓷时,磨削工艺参数对法向、切向磨削力的影响情况。设计正交试验重点研究磨削深度、砂轮线速度、工件进给速度等磨削工艺参数对法向、切向磨削力的影响规律,同时基于ABAQUS建立单颗金刚石磨粒切削HIPSN陶瓷有限元仿真模型,将试验结果与仿真结果进行对比。结果表明,提高砂轮线速度、减小磨削深度、降低工件进给速度,法向、切向磨削力均减小。磨削力比在(8～15)之间。试验结果与仿真输出结果基本一致,验证了该仿真模型的正确性。     

不锈钢配件加工中几个关键问题的探讨

在日常生产和维修中,常遇到加工不锈钢材料的配件,由于不锈钢含有较多的铬镍钛元素,材料的导热性差、韧性大、强度高,给加工带来了很大困难,尤其在切削、磨削、拉削深孔当中,难度更大。 一、切削的难点是切断 在车床上用切断刀切断不锈钢工件时的特点: 1.切屑变形较大 切断时由于切屑排出受到切槽两侧摩擦、挤压作用,随着切断处的直径逐渐减小,相对的切削速度也逐渐减小,挤压现象更为严重,以致切屑变形较大。 2.切削力较大 由于切断过程中切屑与刀具、工件与刀具的摩擦力和切屑变形较大,所以在切削用量相同的条件下,车削力比一般外圆切削力大20％～25％。     

钛基复合材料高速磨削加工磨削力仿真分析

为了探究颗粒增强钛基复合材料磨削过程中的磨削力,建立了PTMCs磨削仿真模型对PTMCs磨削力进行仿真分析,通过磨削试验验证了模型的准确性。结果表明,在磨削过程中,PTMCs的基体以锯齿状切屑方式塑性去除,去除过程中磨削力呈现规律性的波动; PTMCs的颗粒增强相以块状切屑方式脆性去除,去除过程中磨削力呈现很大幅度的波动。此外研究表明,法向磨削力和切向磨削力随着单颗切厚和切削速度的增大均增大。     

20CrMnTi钢齿面磨削力模型构建与分析

为了深入研究20CrMnTi钢的磨削力生成机制与规律,基于Lawn压痕模型接触变形区和三角形截面切屑的基础上,构建立了单颗磨粒的磨削力、最大未变形切屑厚度、齿面磨削力的理论数学模型。磨削力主要源于切屑变形和摩擦,且存在磨削尺寸效应。磨削力随着磨削深度、进给速度、材料硬度和磨粒顶锥角等因素的增大而增大,然而却随着磨削速度与砂轮直径等因素的增大而减小。在砂轮磨损过程中,砂轮特性参数改变对磨削力产生较大影响。结合理论模型分析,开展了齿面局部磨削试验研究,详细分析了不同α常数情况下磨削力随磨削用量变化拟合曲线的残差和拟合优度F值。     

TC4钛合金平面磨削力分析与验证

磨削力对磨削温度、砂轮磨损等有重要影响,是评判TC4钛合金磨削性能的关键指标。由于砂轮磨粒大小、形状差异以及分布的随机性,磨削过程难以定量表述,已有磨削力模型的推导大部分基于一定的假设,与实际存在偏差。通过磨屑变形力与磨粒横截面积的关系以及法向压力与压入深度的关系建立了单颗磨粒磨削力模型;基于磨屑的横截面积与工件体积去除率,建立单颗磨粒磨削力与单位宽度磨削力的联系,进一步推导出TC4钛合金的平面磨削单位宽度磨削力模型。结合实验数据,得到试验条件下的磨削力解析式。分析表明：法向磨削力的平均相对误差为4.9%,切向磨削力的平均相对误差为5.1%。     

单颗磨粒高速磨削45钢和20Cr钢的研究

进行单颗磨粒高速磨削45钢和20Cr钢的试验。研究塑性隆起、面积去除比率和切屑形态,以及速度、磨削截面积对单颗磨粒磨削力的影响。基于摩擦系数的数学模型和试验结果,获得单颗磨粒磨削的摩擦系数。讨论了速度、材料和磨粒对摩擦系数的影响。     

Modeling and simulation of cutting forces generated during vertical micro-grinding

Micro-grinding using micro-tools has become very prevalent due to the miniaturization of products with increased process requirements. Moreover, this process provides an edge over other competitive processes, especially as a final process step. The quality of the part produced by the micro-scale grinding process can be influenced by various factors, particularly by the induced mechanical forces. Therefore, predictive model of cutting force can provide guidance for further development and optimization of the process. Although there has been a lot of a research conducted on conventional grinding, little knowledge has been accumulated on micro-scale grinding due to the fact that it is an emerging field of research. The early grinding models developed are mostly based on parameters such as wheel and workpiece velocity, depth of cut and grit size of the grinding wheel. Those early models narrated that the grits penetrate and cut the material from the workpiece surface with the generated grinding forces proportional to the removed material. However, those models may not be appropriate for micro-scale grinding due to the mode of material removal and the method of contact between surfaces which is different from the macro-scale method. In addition to that, due to the small feed rate used in brittle material machining, ploughing force needs to be considered intensively in addition to the chip formation force. Therefore, a new analytical model has been proposed to evaluate cutting forces of micro-grinding process based on the process configuration, workpiece material properties and micro-grinding tool topography. The size effect of micro-machining has been carefully considered in this proposed model. Therefore, this approach allows the derivation of cutting force comprising of both the chip formation force and ploughing force. Experimental investigation in a micro-grinding configuration has been pursued to validate the proposed predictive model. The estimated cutting force showed a good correlation with the experimental values except for higher depth of cut and lower feed rate. Additionally, paired T test has been performed to quantify the difference between the predicted and experimental results.     

An exploration of friction models for the chip–tool interface using an Arbitrary Lagrangian–Eulerian finite element model

A better understanding of friction modeling is required in order to produce more realistic finite element models of machining processes to support the goals of longer tool life and better surface quality. In this work an attempt has been made to explore and evaluate various friction models used in numerical metal cutting simulations. A finite element model, based on the ALE approach, was developed for orthogonal machining and used to study the conditions prevailing at the chip–tool interface for hardened steel. The ALE approach does not require any chip separation criteria and enables an approximate initial chip shape to smoothly evolve into a reasonable chip shape, while maintaining excellent mesh properties. The results, for a wide range of feed values, were obtained using different friction models and are compared to previously published experimental findings. A reasonable agreement was obtained between the measured and predicted forces with some discrepancy between the cutting and feed force depending on the friction model: if agreement with the cutting forces was good, then the feed force was underestimated; if the feed force agreed well, then the cutting force was overestimated. In all cases the chip thickness was well estimated but the chip–tool contact length was underestimated.     

硬质合金刀具螺旋槽缓进给磨削力研究

用离散化方法将砂轮看作是由一组不同直径的单位厚度薄片组成的,分析了硬质合金刀具螺旋槽缓进给成形磨削的磨削力;基于工件轴向磨削力和力矩建立了一个表征砂轮锐利程度的磨削力比数学模型。通过建立的测力系统测量了螺旋槽缓进给磨削过程中轴向磨削力和力矩,并对其信号进行了分析。在理论和实验的基础上获得了两种磨削参数下的磨削力比。研究结果表明,磨削力比可作为硬质合金刀具螺旋槽缓进给磨削过程的评价参数。     

Force modeling of microscale grinding process incorporating thermal effects

Grinding at the microscale is an essential process in view of its competitive edge over other processes in the fabrication of micro-sized features and parts. The quality of the parts produced by the microscale grinding process can be influenced by various factors related to the mechanical forces induced. Therefore, the predictive modeling of microscale grinding in the context of forces is useful to provide guidance for further development and optimization of this process. In this study, a new model to address mechanical and thermal interactions between the workpiece and an individual single grit on a microscale grinding wheel was developed. This developed model integrates the ploughing and associated friction effects and a moving heat source on the micro-grinding zone under given machining conditions to estimate the thermal effect in microscale grinding process. The ratio of heat partition into the workpiece in the thermal model was also experimentally calibrated using embedded thermocouple measurement followed by analytical calculations. This model quantitatively predicts microscale grinding forces incorporating material properties as functions of strain, strain rate, and temperature. In order to verify this developed model, the experiments based on a surface microscale grinding setup were performed for changing depths of cut. In addition to this, the sensitivity analysis of this model behavior was conducted to identify main effective factors. A comparison between the experiment data and predictions shows that the force model captures the main trend of the microscale grinding physics within the computed range of parameters.     

Molecular dynamics modeling of a single diamond abrasive grain in grinding

In this paper the nano-metric simulation of grinding of copper with diamond abrasive grains, using the molecular dynamics (MD) method, is considered. An MD model of nano-scale grinding, where a single diamond abrasive grain performs cutting of a copper workpiece, is presented. The Morse potential function is used to simulate the interactions between the atoms involved in the procedure. In the proposed model, the abrasive grain follows a curved path with decreasing depth of cut within the workpiece to simulate the actual material removal process. Three different initial depths of cut, namely 4 ?, 8 ? and 12 ?, are tested, and the influence of the depth of cut on chip formation, cutting forces and workpiece temperatures are thoroughly investigated. The simulation results indicate that with the increase of the initial depth of cut, average cutting forces also increase and therefore the temperatures on the machined surface and within the workpiece increase as well. Furthermore, the effects of the different values of the simulation variables on the chip formation mechanism are studied and discussed. With the appropriate modifications, the proposed model can be used for the simulation of various nano-machining processes and operations, in which continuum mechanics cannot be applied or experimental techniques are subjected to limitations.     

An experimental study on the grinding of alumina with a monolayer brazed diamond wheel

A monolayer diamond grinding wheel was fabricated by brazing in vacuum. The wheel was then used to grind alumina at three different grinding speeds. The horizontal and vertical grinding forces, and the grinding temperatures were measured during grinding. SEM observations were made for the ground workpiece surfaces. The influences of the peripheral wheel speed on the grinding forces, specific grinding energy and grinding temperatures were analyzed under different combinations of depth of cut and workpiece velocity. The dependence of the average grinding force per grain and specific grinding energy on the maximum undeformed chip thickness was discussed respectively. It was found that an increase in the peripheral wheel speed reduced grinding force, but increased force ratio, specific grinding energy, and grinding temperature.     

面齿轮磨削力建模与工艺影响分析

建立了碟形砂轮磨削面齿轮的理论模型.应用切斜面磨削理论,将不规则的曲面齿面等效转化为平面,结合Gleason点接触椭圆等特征,方便对磨削力进行分析求解.将砂轮上的工作磨粒数均匀划分成单颗磨粒成屑力与滑擦力个体,精确阐述砂轮在磨削面齿轮时的磨削力.经过实验结果与仿真数值的比照分析得到磨削力对磨削用量的影响参数,实验结果表明,砂轮转速与面齿轮磨削力成反比例关系,工件进给速度与磨削速度与面齿轮磨削力成正比例关系.通过磨削力的实验结果与仿真数值对比分析,可得出最大相对误差为１７.９％,此数据证明了建立的模型与实验结果较为契合,能够很好地反映磨削力与磨削用量之间的关系变化,在提高面齿轮磨削精度与工艺上提供了基础的理论依据.