Modelling chip formation of alloy 718

The aim of this article is to investigate the effect of different fracture criteria on the chip formation process, focusing on the formation of segmented chips and what happens around the cutting edge. Furthermore, it is investigated how well the finite element model is able to capture the transition from continuous to segmented chip formation in alloy 718. Machining alloy 718 at lower cutting speeds (below 50 m/min) the chip produced is long and continuous. At higher cutting speeds (above 100 m/min) the chip produced is segmented. The conclusion from this study is that the transition from continuous chip to segmented chip is caused by both thermal softening and material damage. Furthermore it is concluded that a fracture criterion with a hydrostatic dependency shall be used for accurate modelling of chip segmentation.     

Modelling and simulation of process: machine interaction in grinding

This article presents an overview of current simulation methods describing the interaction of grinding process and grinding machine structure, e.g., vibrations, deflections, or thermal deformations. Innovative process models which describe the effects of the grinding wheel–workpiece interaction inside the contact zone are shown in detail. Furthermore, simulation models representing the static and dynamic behaviour of a grinding machine and its components are discussed. Machine tool components with a high influence on the process results are modelled more detailed than those with low influence. The key issue of the paper is the coupling of process and machine tool models for predicting the interactions of process and machine. Several coupling methods are introduced and the improvements of the simulation results are documented. On the basis of the presented simulation approaches, grinding processes and machines can be designed more effectively resulting in higher workpiece quality and process stability.     

Chip formation in grinding: an experimental study

Due to high cutting speeds and low single grain chip thicknesses no reliable approach to interrupt the cut in grinding was realized so far. This paper presents a new method to experimentally obtain and analyze chip roots during up-grinding. By means of high resolution SEM-micrographs several chip roots are analyzed, classified and discussed with regard to the fundamental chip formation and material removal mechanisms. Furthermore, there are conclusions drawn about the distribution and number of the active grains, which are in a good correlation with the Abbott-curve of the grinding wheel layer and the process parameters.     

Modelling of the mist formation in a segmented grinding wheel system

It has been found that using a segmented grinding wheel with a fluid chamber can significantly minimise the quantity of coolant while improving the ground surface integrity. The present investigation aims to explore the fluid flow mechanism in such a wheel system. To this end, the Weber theory for Newtonian jet instability was applied to quantitatively determine the contribution of coolant flow rate to mist and ligament modes. A semi-analytical model was then developed to predict the mist flow rate by taking into account both the grinding parameters and fluid properties. It was shown that the model prediction was in good agreement with experimental measurements. Because of the comprehensive integration of variables in the formulation, the model provides a good fundamental understanding of the mist formation and offers a practical guideline for the selection and use coolant in minimising the mist flow rate.     

Analytical and experimental investigation of coolant velocity in high speed grinding

Use of water-base coolant is a pre-requisite in an high speed grinding process to avoid thermal damage and to achieve better surface integrity as well as higher grinding ratio. However, the presence of hazardous chemical additives in the coolant causes environmental problems. As a result, stringent government legislation is being practiced for the coolant use and disposal, which consumes 7–17% of the total machining cost. This paper reports the coolant flux minimization through controlled jet impingement so as to prolong the coolant replenishment cycle. Control of coolant flux was achieved through development of a “metered quantity coolant” (MQC) nozzle which supplies the required amount of coolant to the grinding zone. Also, this investigation has shown that coolant velocity has a significant influence on the high speed grinding performance. When the coolant velocity is inadequate, coolant could not penetrate into the grinding zone. The increase in coolant velocity was realized with reduction in nozzle opening area and does not use a large quantity of coolant. This is of significance to reduce environmental pollution and machining costs through extended coolant replenishment period.     

超声辅助内圆磨削不锈钢研究

针对航空发动机燃油喷嘴用材料3Cr13不锈钢进行超声辅助内圆磨削试验,并对超声辅助内圆磨削不锈钢的表面形成机理进行了初步的分析。在此基础上,研究了超声作用、主轴转速和磨粒粒度尺寸对孔表面粗糙度的影响规律。结果表明:超声振动有助于降低不锈钢孔的加工表面粗糙度,但超声作用效果随着主轴转速的提高而减弱;不锈钢孔表面粗糙度值随着主轴转速的提高而下降;使用小粒度尺寸磨粒进行超声辅助内圆磨削不锈钢时,能明显降低加工表面粗糙度。     

NC车削加工切屑形成机理的有限元仿真

有限元分析已经被广泛的应用于金属切削加工过程中切屑形成的建模与仿真。根据切屑的几何参数，给出了不同类型切屑的三维实体模型；介绍了三维卷曲切屑的有限元建模的方法和切屑折断的条件；并对其中的一例模型进行了有限元建模和分析，将有限元仿真结果和实验分析结果进行了比较，具有很好的一致性。证实了有限元仿真对切屑形成的预测能力。最后。提出切屑形成机理和有限元发展中存在的问题以及未来的研究方向。     

单颗磨粒磨削钛合金TC4成屑过程仿真研究

采用有限元模拟技术对钛合金TC4材料的单颗磨粒磨屑形成过程进行了仿真研究.研究表明:钛合金TC4在单颗磨粒磨削过程中发生绝热剪切,形成锯齿状磨屑;磨削过程中单颗磨粒磨削力成周期变化;磨粒负前角增大,锯齿化程度加深;磨削速度提高,磨屑剪切带宽度减小;仿真分析得到的磨屑形态与实验结果相一致.     

FEA modeling and simulation of shear localized chip formation in metal cutting

The finite element analysis (FEA) has been applied to model and simulate the chip formation and the shear localization phenomena in the metal cutting process. The updated Lagrangian formulation of plane strain condition is used in this study. A strain-hardening thermal-softening material model is used to simulate shear localized chip formation. Chip formation, shear banding, cutting forces, effects of tool rake angle on both shear angle and cutting forces, maximum shear stress and plastic strain fields, and distribution of effective stress on tool rake face are predicted by the finite element model. The initiation and extension of shear banding due to material's shear instability are also simulated. FEA was also used to predict and compare materials behaviors and chip formations of different workpiece materials in metal cutting. The predictions of the finite element analysis agreed well with the experimental measurements.     

An experimental investigation into soft-pad grinding of wire-sawn silicon wafers

Silicon is the primary semiconductor material used to fabricate microchips. A series of processes are required to manufacture high-quality silicon wafers. Surface grinding is one of the processes used to flatten wire-sawn wafers. A major issue in grinding of wire-sawn wafers is reduction and elimination of wire-sawing induced waviness. Results of finite element analysis have shown that soft-pad grinding is very effective in reducing the waviness. This paper presents an experimental investigation into soft-pad grinding of wire-sawn silicon wafers. Wire-sawn wafers from a same silicon ingot were used for the study to ensure that these wafers have similar waviness. These wafers were ground using two different soft pads. As a comparison, some wafers were also ground on a rigid chuck. Effectiveness of soft-pad grinding in removing waviness has been clearly demonstrated.     

Analytical and experimental study of shear localization in chip formation in orthogonal machining

A simplified theory of instability of plastic flow is applied to analyze the formation of shear localized chips in orthogonal machining. A flow localization parameter is expressed in terms of associated cutting conditions and properties of the workpiece material. The analysis, which indicates the important parameters in the cutting process, is used to investigate the effect of cutting conditions on the onset of shear localization and the formation of adiabatic shear banding in metal cutting. Comparisons are made between the analysis and experiments in which the flow localization parameter is obtained for several workpiece materials. The results of this investigation seem to support the analysis and its potential benefits in analyzing and/or remedying problems associated with chip formation and temperature generated in metal cutting. Presently at Advanced Technology Center, Valenite, Inc., Madison Heights,MI 48071, USA     

6061铝合金超薄壁管的充液压弯数值模拟与试验

针对6061铝合金超薄壁弯管在成形过程中极易出现破裂和截面畸变等问题,采用单向拉伸试验获得6061铝合金超薄壁管在O态、W态、T6态下的基本力学性能参数,并通过DYNAFORM有限元模拟软件进行数值模拟,对6061铝合金超薄壁管的充液压弯工艺进行优化,获得最优工艺参数。结果表明,合理控制超薄壁管的充液压力和压弯加载路径,可以有效提高超薄壁管的成形性能;适当的压弯间距,能够提高弯管壁厚分布的均匀性和成形极限,显著改善成形件质量。     

Modelling of grinding gap macro geometry and workpiece kinematics in throughfeed centreless grinding

The paper discusses the simulation of a throughfeed centreless grinding process in a virtual environment (VE). The developed simulations are based on an analytical grinding gap model describing the grinding gap macro geometry and workpiece kinematics. First of all, the model is embedded in a desktop application (Cegris), which facilitates regulating wheel truing and the determination of set-up variables, both of which yield an optimal grinding gap macro geometry in a reduced set-up time. Finally, the Cegris is ported to a CAVE (CAVE Automatic Virtual Environment) for an interactive visualisation of the process, an application used to train machine tool operators.     

Modeling and experimental study of grinding forces in surface grinding

Grinding forces are composed of chip formation force and sliding force. A new mathematical model of grinding forces in surface grinding is developed in this paper. Effectiveness of this model is proved by comparison of the experimental results and the model calculation results. Chip formation energy can be divided into static chip formation energy and dynamic chip formation energy which is mainly influenced by shear strain, shear strain rate and heat in the metal removal process. A formula for calculating the chip formation force is proposed by analyzing the relationship between specific chip formation energy and chip formation force. Combined with the achievements of other researchers, a new formula for calculating sliding force considering the influence of processing parameters on friction coefficient is obtained.     

Control of the traverse grinding process using dynamically active workpiece steadies

Three control methods for the workpiece steady based traverse grinding process are examined and a new approach, termed the dynamic workpiece steady control method, is proposed for improved grinding efficiency and accuracy. This method requires that the motion profiles of the steadies vary dependent upon the wheel position. Mathematical models for a steady based traverse grinding system are presented together with an iterative algorithm for the determination of the position profiles of the workpiece steadies. A case study of the grinding process is considered to demonstrate the proposed control method and it is shown that a reduction in grinding error and a higher grinding efficiency involves an increase in the force applied by the steadies, which can affect workpiece surface quality. Accordingly a compromise between these parameters has to be made.     

An experimental investigation of the effects of workpiece and grinding parameters on minimum quantity lubrication—MQL grinding

Coolant is a term generally used to describe grinding fluids used for cooling and lubricating in grinding process. The main purposes of a grinding fluid can be categorized into lubrication, cooling, transportation of chips, cleaning of the grinding wheel and minimizing the corrosion. On the other hand, grinding fluids have negative influences on the working environment in terms of the health of the machine operator, pollution and the possibility of explosion (for oil). Furthermore, the cost of the grinding fluid, filtering and waste disposal of the metal working fluids is even higher than the tool cost and constitutes a great part of the total cost. Additionally, grinding fluids can not effectively penetrate into the contact zone, are health hazard and their consumption must be restricted. Generally, compared to other machining processes, grinding involves high specific energy. Major fraction of this energy is changed into heat, which makes harmful effect on the surface quality as well as the tool wear. Since there is no coolant lubricant to transfer the heat from the contact zone in dry grinding, surface damages are not preventable. Alternatives to current practices are getting more serious consideration in response to environmental and operational cost pressures. One attractive alternative is the minimum quantity lubrication (MQL) grinding or the near dry grinding (NDG). In near dry grinding an air–oil mixture called an aerosol is fed into the wheel-work contact zone. Compared to dry grinding, MQL grinding substantially enhances cutting performance in terms of increasing wheel life and improving the quality of the ground parts. In this research, the influences of workpiece hardness and grinding parameters including wheel speed, feed rate and depth of cut have been studied on the basis of the grinding forces and surface quality properties to develop optimum grinding performances such as cooling, lubrication, high ecological and environmental safety.     

Experimental investigation of surface/subsurface damage formation and material removal mechanisms in SiC grinding

The difficulty and cost involved in the abrasive machining of hard and brittle ceramics are among the major impediments to the widespread use of advanced ceramics in industries these days. It is often desired to increase the machining rate while maintaining the desired surface integrity. The success of this approach, however, relies in the understanding of mechanism of material removal on the microstructural scale and the relationship between the grinding characteristics and formation of surface/subsurface machining-induced damage. In this paper, grinding characteristics, surface integrity and material removal mechanisms of SiC ground with diamond wheel on surface grinding machine have been investigated. The surface and subsurface damages have been studied with scanning electron microscope (SEM). The effects of grinding conditions on surface/subsurface damage have been discussed. This research links the surface roughness, surface and subsurface damages to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grinding-induced damage on grinding conditions.     

异形气雾罐的数值模拟与试验研究

异形金属气雾罐成形中,会产生壁厚减薄严重及皱折破裂等成形缺陷。采用数值模拟的方法,对气压胀形的工艺参数进行优化处理,可以降低胀形区应力,减小壁厚减薄率和改善壁厚分布状况,数值模拟结果与试验验证结果吻合较好,研究结果对工艺优化和过程控制具有实用价值。     

Temperature fields in a chip during high-speed orthogonal cutting—An experimental investigation

During the cutting process, the temperature field in the chip is measured by using the principle of pyrometry in the visible spectral range. The mechanical device developed to reproduce orthogonal cutting conditions and to reach very high cutting speed (up to 120 m/s) is used for a range of velocities from 10 to 70 m/s. The presented experimental results concern two materials chosen following the form of chip generated: a low carbon steel (C15) and a low alloyed medium carbon steel (42CrMo4). The performances of the measurement set-up are completed by the possibility of recording real time photographs of the chip formation. These records make the analysis of temperature maps easier and allow specific parameters as the contact length at the tool-chip interface or the shear angle to be determined. The non-uniform heating in the chip is emphasized by the presence of a maximal temperature area. The temperature fields measured for a cutting speed around 20 m/s present maximums of 870 °C for 42CrMo4 and 630 °C for C15 located near the tool–chip interface. The effects of cutting velocity on the maximum temperature value in the chip and the location of this heat zone are presented. This maximum increases with the cutting velocity contrary to its location which presents few variations. The experimental results are compared with an analytical approach.     

磨料有序化排布砂轮磨削TC4温度实验研究

为了获得磨料有序化排布砂轮磨削TC4的温度变化规律,使用电镀CBN砂轮对TC4合金进行磨削实验。砂轮分别采用叶序、错位和无序3种不同的磨料排布方式。研究了工件表面平均温度与进给速度和磨削深度的关系,并对3种磨料排布方式的电镀CBN砂轮磨削工件时温度的变化形态进行对比。结果表明:在相同磨削条件下,磨料有序化排布能有效降低TC4的磨削温度,使用叶序排布磨料砂轮能获得更低的工件表面温度。