球头铣刀多轴铣削加工的切削刃微元点轨迹模型

切削刃微元点轨迹是描述瞬时未变形切削厚度的基础,瞬时未变形切削厚度是铣削力预测的关键.为此,针对球头铣刀多轴铣削加工过程,建立利用位置矢量来准确描述切削刃微元点的轨迹模型.首先,通过建立工件和刀具瞬时坐标系的空间变换模型来描述刀具的位置和位姿;然后,在此基础上结合球头铣刀切削刃的几何特点建立切削刃微元点的空间位置矢量,并进一步推导描述切削刃微元点轨迹的矢量形式;最后,利用C++编程语言和OpenGL图形接口实现切削刃微元点轨迹仿真,并通过对比分析仿真结果与跟踪球头铣刀1∶1三维模型上标记点的位置数据,验证了切削刃微元点轨迹模型的正确性.     

一个考虑刀具切削刃钝圆影响的正交切削模型

对正交切削过程的力学边界提出了合理假设,用试探法建立了考虑切削刃钝圆影响的滑移线场模型及相应的速度场模型。分析表明,该模型基本满足静可容和动可容的要求。并采用这一模型对切屑卷曲现象进行预测和分析。     

麻花钻三维建模及切削刃几何参数研究

麻花钻切削刃由主切削刃、副切削刃及横刃组成,形状复杂,几何参数不易测得。基于部分结构参数建立麻花钻三维模型,在此模型上进行切削刃参数测量,并分析了参数的变化规律及对切削性能的影响。     

单刃—圆锥面刀具的几何建模与加工

单刃—圆锥面刀具是一种新型刀具,只有一条圆弧切削刃,副切削刃被异化为圆锥面。切削时,该刀具能将工件表层金属与基体分离但并不去除,被分离的表层金属在圆锥面的挤压作用下形成翅片。通过研究单刃—圆锥面刀具的切削过程,建立了刀具几何模型,并根据刀具参数建立了圆弧切削刃、主后刀面和副后刀面的数学模型。利用该数学模型,在数控工具磨床上加工出了单刃—圆锥面刀具。     

微径球头铣刀铣削力建模与仿真

以微径球头铣刀铣削力为研究对象,分析了刀具刃线模型.将刀具沿刀轴方向离散为若干切削单元,分别依照单齿切削及两齿切削求得各切削单元的实际瞬时切削厚度.基于实体造型的方法提取了参与切削的切削刃段,并通过实验识别了瞬时切削力系数及主轴径向跳动参数,建立了综合考虑主轴径向跳动、微细铣削所特有的尺度效应的影响及可能出现的单齿切削现象的微径球头铣刀铣削力模型.实验结果验证了所提模型的有效性和可行性.     

涡旋弧切削刃刀片

目前,现有的食品切断或切片机器都采用切削刃为直线刃或圆弧刃刀片。直线刃刀片切削时,因切削刃的切线垂直于(或接近垂直于)合成速度方向,因此切削性能差,表现为切削抗力大,有冲击,被切物体易变形。圆弧切刃刀片切削时,因刀片旋转,切削刃的切线不垂直合成速度方向。所以切削性能好,但切削效率低。两种刃片在切削时都需要被切削物体与刀片之间有轴向与径向进给运动。这使得以这两种刀片为刀具的机器结构复杂,切削效率低,耗能较多。涡旋弧切削刃刀片排除了直线刃刀片切削性差的缺点,保持了圆弧刃刀片切削性能好的优点,同时在切削时,可以减少径…     

介绍两种镗铰刀

用单刃和多刃镗铰刀进行内孔的精密加工,是目前较广泛受到重视的一项加工工艺。为解决我厂生产的实际问题,我们使用以下两种结构的单刃和多刃镗铰刀,来加工鼓风机叶轮轴孔和联轴器销孔,效果很好.一、单刃镗铰刀图1为单刃镗铰刀的结构图,其特点是:(1)在切削刃后方90°和180°位置上有两条导向支承块,切削刃和支承块的外径座落在同一圆周上.切削刃刀片和支承块的材料均为 YG6.(2)刀片切削刃被分割成内、外、斜刃三部分,刀     

读者信箱

问:磨削工件光洁度差,怎么办? 答:磨削后,特别是精磨后工件光洁度达不到要求,是生产中的常见问题。为了较为有效地解决这个问题,首先必须了解影响磨削工件光洁度的因素。一般说来,影响被磨工件光洁度的因素主要有以下三方面: 1.砂轮切削刃相对于被加工表面运动的几何因素:包括砂轮工作表面切削刃的数量、切削刃的分布以及切削刃相对于工件的运动。这些主要取决于砂轮特性、砂轮修整用量和磨削用量。     

镗削加工切削力模型系数的识别

由于镗刀刀尖圆弧半径、刀具几何形状和刃倾角的变化,同时受断屑槽和刀一屑接触长度的限制,镗削时刀片前刀面的面积变化情况复杂。以下介绍的模型识别切削系数可以建立符合实际应用的力学模型。     

铣齿断续切削机理的研究

大模数齿轮铣削具有多刃断续切削和变切屑厚度等特点,属于典型的非自由强力切削.主要从切削力、切屑形态、表面质量等方面对铣齿断续切削的机理进行研究.采用指数经验模型,应用微段切削刃受力积分获得单个刀片瞬时合成转矩,随后考虑刀盘上刀片的分布情况,获得刀盘周期性的载荷,提出铣齿断续切削转矩的计算模型.应用间接测量的试验方法,采集三相异步电动机的主轴输入电流,重构得到切削力,另外通过试验测量出切削变形比,应用理论公式获得切削力.将试验数据和理论计算结果与计算模型进行比较,验证了铣齿加工切削转矩模型的正确性.对切削过程中的残余高度进行几何分析,获得其计算方法.初步完成对铣齿断续切削机理的分析,对铣齿加工精度提供指导作用.     

MODELING APPROACHES AND SOFTWARE FOR PREDICTING THE PERFORMANCE OF MILLING OPERATIONS AT MAL-UBC

The author has been conducting research in the area of metal cutting mechanics, metal cutting dynamics, machine tool vibrations, precision machining and machine tool control in his Manufacturing Automation Laboratory, at The University of British Columbia, Canada since 1986. This article summarizes the research conducted in mechanics and dynamics of metal cutting in our laboratory. Modeling of mechanics of metal cutting is summarized first. The models include orthogonal to oblique cutting transformation, mechanistic modeling of cutting coefficients, slip line field and Finite Element modeling. The author mostly focused on milling. The kinematics of milling with and without structural vibrations is modeled. The geometric model of end mills and inserted cutters with arbitrary geometry are modeled. The prediction of forces, torque, power and dimensional surface finish is explained for milling operations. The chatter stability for milling operations is presented. The metal cutting knowledge is transferred to manufacturing industry by combining all the models in shop friendly software.     

Chatter and dynamic cutting force prediction in high-speed ball end milling

Machine tool chatter is a serious problem which deteriorates surface quality of machined parts and increases tool wear, noise, and even causes tool failure. In the present paper, machine tool chatter has been studied and a stability lobe diagram (SLD) has been developed for a two degrees of freedom system to identify stable and unstable zones using zeroth order approximation method. A dynamic cutting force model has been modeled in tangential and radial directions using regenerative uncut chip thickness. Uncut chip thickness has been modeled using trochoidal path traced by the cutting edge of the tool. Dynamic cutting force coefficients have been determined based on the average force method. Several experiments have been performed at different feed rates and axial depths of cut to determine the dynamic cutting force coefficients and have been used for predicting SLD. Several other experiments have been performed to validate the feasibility and effectiveness of the developed SLD. It is found that the proposed method is quite efficient in predicting the SLD. The cutting forces in stable and unstable cutting zone are in well agreement with the experimental cutting forces.     

Multi-objective optimization of oblique turning operations using finite element model and genetic algorithm

Multi-objective optimization of oblique turning operations while machining AISI H13 tool steel has been carried out using developed finite element (FE) model and multi-objective genetic algorithm (MOGA-II). The turning operation is optimized in terms of cutting force and temperature with constraints on required material removal rate and cutting power. The developed FE model is capable to simulate cutting forces, temperature and stress distributions, and chip morphology. The tool is modeled as a rigid body, whereas the workpiece is considered as elastic–thermoplastic with strain rate sensitivity and thermal softening effect. The effects of cutting speed, feed rate, rake angle, and inclination angle are modeled and compared with experimental findings. FE model is run with different parameters with central composite design used to develop a response surface model (RSM). The developed RSM is used as a solver for the MOGA-II. The optimal processing parameters are validated using FE model and experiments.     

Effect of dynamics on the process of formation of holes during honing

A model of the process of honing holes with a specified initial error of the surface shape is developed. The process of improvement of the error of the shape of holes during the treatment is numerically analyzed. The tool shaft is schematized as a rotating rod transmitting rotation to a hone holder with cutting bars and guide bars elastically mounted on it. Cutting forces are modeled as friction forces that depend on a normal pressure on a contact surface, and removal of allowance during passage of the surface by cutting bars is modeled according to Preston’s hypothesis. The effect of technological parameters on integral criteria of treatment quality is analyzed.     

基于大数据模糊 PID 控制的切削机械加工稳定性分析

针对切削机械加工稳定性分析未考虑切削力信号和切削机械磨损之间的关系,导致切削机械加工稳定性较差的问题,提出一种基于大数据模糊 PID 控制的切削机械加工稳定性分析方法,对加工过程建模,同时通过历史切削机械加工数据组建切削力信号和磨损之间的映射关系。分析切削机械的加工性能,在构建数学模型的基础上,设计一种大数据模糊 PID 控制方法对切削机械加工稳定性实时控制,通过模糊控制规格对控制器参数实时调整,最终有效控制切削机械加工稳定性。仿真实验结果表明,在切削机械加工过程中,该方法可以有效控制切削机械加工稳定性。     

The effect of the cutting parameters on performance of WEDM

In this study, variations of cutting performance with pulse time, open circuit voltage, wire speed and dielectric fluid pressure were experimentally investigated in Wire Electrical Discharge Machining (WEDM) process. Brass wire with 0.25 mm diameter and AISI 4140 steel with 10 mm thickness were used as tool and work materials in the experiments. The cutting performance outputs considered in this study were surface roughness and cutting speed. It is found experimentally that increasing pulse time, open circuit voltage, wire speed and dielectric fluid pressure increase the surface roughness and cutting speed. The variation of cutting speed and surface roughness with cutting parameters is modeled by using a regression analysis method. Then, for WEDM with multi-cutting performance outputs, an optimization work is performed using this mathematical models. In addition, the importance of the cutting parameters on the cutting performance outputs is determined by using the variance analysis (ANOVA).     

Finite element simulation of high-pressure water-jet assisted metal cutting

Experimental studies have shown that improved metal cutting efficiency can be obtained when a high-pressure water/coolant jet is injected at the tool–chip interface. The pressure exerted on the chip face by the jet is expected to reduce, for example, friction along the tool–chip interface, temperature rise in the chip and the workpiece, the cutting force, and residual stress in the finished workpiece, leading to a longer tool life and a better surface integrity for the finished workpiece. This paper presents the results of finite element simulations of high-pressure water-jet assisted orthogonal metal cutting, in which the water jet is injected directly into the tool–chip interface through a small hole on the rake face of the tool. The mechanical effect of the high-pressure water jet is approximated as a pressure loading at the tool–chip interface. The frictional interaction along the tool–chip interface is modeled by using a modified Coulomb friction law. Chip separation is modeled by a nodal release technique and is based on a critical stress criterion. The effect of temperature, strain rate and large strain is considered. Cooling effect of the high-pressure jet on the temperature distribution is modeled with a convective heat-transfer coefficient. The effect of water jet hole position and pressure is studied. Contour plots showing the distributions of steady-state temperature and stress and the residual stress are presented. The simulation results show a reduction in temperature, the cutting force and residual stresses for water-jet assisted cutting conditions. The mechanical effect of the water jet is found to reduce the contact pressure and shear stress along the tool–chip interface and also the contact zone length for certain water jet hole locations.     

Workpiece response in turning due to spatially moving random metal cutting forcesResponse d'une piece lors du tournage due aux forces stochastiques en mouvement spatial resultant de la coupe

The nonstationary random response of a workpiece subjected to a constantly varying cutting tool contact in a metal turning operation is investigated. The ensemble of the applied forces is modeled as a white noise process. The workpiece is considered to be a uniform beam with fixed-hinged boundaries and with viscous damping. The results indicate that the workpiece response at the cutting tool contact is not significantly influenced by the tool feed rate for normal metal turning operations.     

单颗金刚石磨粒切削氮化硅陶瓷仿真与试验研究

为探索氮化硅陶瓷单颗磨粒切削加工的机理,进行单颗金刚石磨粒切削氮化硅陶瓷的仿真与试验。选用截角八面体模拟金刚石磨粒,基于Johnson-Holmquist ceramic硬脆材料本构模型,采用有限元网格法进行单颗磨粒直线切削仿真,分析工件材料的切屑去除、划痕形貌、应力动态变化与分布、切削力变化等现象,以及工艺参数对切削力的影响。制备单颗金刚石磨粒工具,在平面磨床上进行单颗磨粒切削氮化硅陶瓷的试验,进一步分析划痕形貌、切削力的变化,并验证有限元仿真的正确性。研究表明,划痕光直平整,塑性隆起很少,边缘存在较大尺寸的破碎,划痕内有局部小尺寸的破碎;划痕的深度和宽度比磨粒的切削深度和宽度尺寸略大。应力与切削力存在动态波动。随着砂轮速度的增加,切向力和法向力减小;随着切削深度的增加,切向力和法向力增大。切削力比在4～6之间变化。     

金属切削过程的三维显式动力分析

利用非线性有限元程序LS-DYNA,对低碳钢直角自由切削过程进行三维显式动力分析.模型采用单点积分Lagrange算法的三维显式实体单元solid164,以各向同性应变率相关分段线性塑性材料本构模拟切削层材料,以面-面固连断开接触算法模拟切屑与工件母体的分离过程,以同时考虑滑动摩擦与粘结摩擦的模型模拟切屑与前刀面的接触关系.显式分析结果预测低碳钢切削过程中切削力的大小,切削力分析值与已有实验值相比误差为0.6%;模拟出切屑变形过程中金属晶粒的剪切滑移和流动现象;获得切屑的变形形态及切屑中压力及应力应变的分布情况.