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.     

镍基高温合金高速超高速磨削成屑过程的三维仿真研究

建立单颗磨粒磨削GH4169镍基高温合金的三维有限元仿真模型,研究高速、超高速磨削条件下的磨屑形貌演化过程及磨削力变化规律,观察磨削区域内的应力应变、温度等物理参量的分布和变化,分析磨削速度和单颗磨粒切厚对磨屑形貌、成屑频率及沟槽隆起特征的影响。结果表明:高速、超高速磨削镍基高温合金时,易出现锯齿形磨屑;磨削力呈周期性变化,其周期与磨屑形成过程对应;磨削过程中的温度、应变以及应变率主要集中在剪切带区域,而应力则集中在剪切带的两侧。随磨削速度增大,磨屑锯齿间间距变小,锯齿化程度增强,成屑频率呈线性增大趋势,沟痕隆起比升高。此外,单颗磨粒磨削GH4169的临界成屑切厚约为0.3 μm,当切厚为0.8 μm时有锯齿形磨屑出现,且随单颗磨粒切厚增大,锯齿化程度增强,但成屑频率降低。      

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。     

Single point diamond dressing of aluminium oxide grinding wheels and its influence in cylindrical traverse grinding

An investigation conducted at Loughborough University of Technology into the dressing of grinding wheels using single point diamond tools [1], has shown the importance of the correct selection of dressing variables when preparing the grinding wheel for both rough and finish cylindrical traverse grinding operations, since they influenced both the useful working life of the wheel when rough grinding, and the resulting workpiece surface finish when fine grinding.This particular paper deals with those aspects of wheel dressing which influence rough grinding conditions, and highlights the usefulness of grinding force as a means of assessing the severity of dressing on wheel performance at the start of grinding; and force ratio and grinding ratio through their ability to pinpoint the various stages of wheel wear.The dressing variables found to have the greatest influence on both rough and finish cylindrical traverse grinding conditions were the cross-feed rate and diamond geometry, with the depth of cut being of secondary importance.     

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.     

Exploratory investigation of chip formation and surface integrity in ultra-high-speed gear hobbing

Gear hobbing is widely employed to manufacture automotive gears, where the productivity depends on the cutting speed. Currently, gear hobbing is performed at ～300 m/min using high-speed steel hob cutters. In this study, ultra-high-speed gear hobbing was attempted using a large-diameter cemented carbide hob cutter on a gear grinder. This enabled a cutting speed up to 2450 m/min. Many interesting phenomena were acquired in this speed range. Chips were severely oxidized, whereas the gear surface was not affected. Compressive residual stress was generated at the gear surfaces with low surface roughness and high hardness, while the wear of hob cutter was insignificant.     

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.     

Modelling and experimental investigation on nanometric cutting of monocrystalline silicon

A new model to understand the behaviour of how materials are removed from workpiece in nano cutting is proposed. This model postulates that the mechanism of nanometric scale material removal is based on extrusion, which is different from the shearing mechanism in conventional cutting. It also explains why brittle materials are removed in ductile mode. Analytical results from molecular dynamics and nano indentation show good agreement with the proposed modelling. Experiments are conducted to verify the new model for nanometric cutting of monocrystalline silicon. The theoretical modelling and experimental verification present a good understanding of nano-scale material removal and provide an approach to fundamentally control the machining performance.     

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。     

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.     

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.     

An experimental investigation of system matching in ultrasonic vibration assisted grinding for titanium

This paper presents a fundamental investigation of the system matching mechanisms involved in ultrasonic vibration assisted grinding (UAG) of titanium processing. The effects of system matching on grinding force and surface roughness are studied experimentally. The design of experiments and experimental equipment are described in detail. In this investigation, a five-variable four-level fractional factorial design is used to conduct experiments. The experiments are employed to reveal the main effects as well as the interaction effects of the ultrasonic parameters on the process outputs such as material removal rate (MRR), grinding force, surface topography and surface roughness. Experimental results showing that the application of system matching in UAG can improve the work piece grinding quality.