Estimation of die service life for a die cooling method in a hot forging process

Dies may have to be replaced for a number of reasons, such as changes in dimensions due to wear or plastic deformation, deterioration of the surface finish, breakdown of lubrication, and cracking or breakage. In this paper, die cooling methods are suggested to improve die service life with regards to wear and plastic deformation in a hot forging process. The yield strength of die decreases at higher temperatures and is dependent on hardness. Also, to evaluate die life due to wear, a modified Archard’s wear model has been proposed by considering the thermal softening of die expressed in terms of the main tempering curve. This paper describes the effects of die cooling methods such as cooling hole and direct spray cooling on the life of finisher die during the hot forging of an automobile part. It is shown that the cooling hole method during hot forging is necessary for an effective die service life to be obtained.     

Wear analysis of hot forging dies

In hot forging, die wear is the main cause of failure. In this paper, the wear analysis of a closed hot forging die used at the final stage of a component has been realized. The simulation of forging process was carried out by commercially available software based on finite volume method and the depth of wear was evaluated with a constant wear coefficient. By comparing the numerical results with the measurement taken from the worn die, the wear coefficient has been evaluated for different points of the die surface and finally a value of wear coefficient is suggested.     

Experimental Study of Wear Behaviour of Hot Forging Tool Steels Under Dry Conditions: 40CrMoV13 Against C35E

The dimensions and quality of forged-steel components are significantly affected by the action of friction and wear. The thermal and mechanical operating conditions of hot forging tools provoke serious degradation, such as oxidative wear, thermal fatigue, plastic damage and mechanical cracking. This slowly causes the tools to lose their original geometry and thus they must be either reformed or discarded [1]. The knowledge and control of this damage is essential and must be taken into consideration, both in die design and in the choice of tool material and the type of surface conditioning. The degradation has direct effects on the lifespan of the tools, and consequently on the cost of the components. This paper deals with the sliding wear behaviour of 40CrMoV13 Steel against C35E in the 700 to 850 °C temperature range under ambient conditions. This steel is used frequently as hot forging die material. This study focuses on the effect of the test temperature and the role of the oxide scales. The purpose of these experiments was to obtain tribological data (friction coefficient, wear rate, etc.), in order to include it in numerical simulations of damage to hot forging tools for the purpose of optimizing the tools' lifespan.     

The prediction of maximum forging load and effective stress for different material of bevel gear forging

The manufacture of gears by applying hot or cold bulk forming processes is a quite widespread production method due to its well-known basic advantages such as material and time cost reduction and the increased strength of the teeth. However, the associated process planning and tool design are more complicated. In the precision forging of gears, the workpiece volume, the die design, the power requirement and careful processing are more critical than traditional forging technology. For complete filling up, predicting the power requirement is an important feature of the near net-shape forging process. In this paper, a finite element analysis is utilized to investigate the material properties such as yielding stress, strength coefficient and strain hardening exponent effects on forming load and maximum effective stress. The adductive network was then applied to synthesize the data set obtained from the numerical simulation. The predicted results of the maximum forging load and maximum equivalent stress of bevel gear forging from the prediction model are consistent with the results obtained from FEM simulation quite well. After employing the prediction model one can provide valuable references in prediction of the maximum forging load and maximum equivalent stress of bevel gear forging under a suitable range of material parameters.     

2D FEM estimate of tool wear in turning operation

Finite element method (FEM) is a powerful tool to predict cutting process variables, which are difficult to obtain with experimental methods. In this paper, modelling techniques on continuous chip formation by using the commercial FEM code ABAQUS are discussed. A combination of three chip formation analysis steps including initial chip formation, chip growth and steady-state chip formation, is used to simulate the continuous chip formation process. Steady chip shape, cutting force, and heat flux at tool/chip and tool/work interface are obtained. Further, after introducing a heat transfer analysis, temperature distribution in the cutting insert at steady state is obtained. In this way, cutting process variables e.g. contact pressure (normal stress) at tool/chip and tool/work interface, relative sliding velocity and cutting temperature distribution at steady state are predicted. Many researches show that tool wear rate is dependent on these cutting process variables and their relationship is described by some wear rate models. Through implementing a Python-based tool wear estimate program, which launches chip formation analysis, reads predicted cutting process variables, calculates tool wear based on wear rate model and then updates tool geometry, tool wear progress in turning operation is estimated. In addition, the predicted crater wear and flank wear are verified with experimental results.     

有限元网格的圆角过渡特征提取及网格修改

根据过渡曲面的曲率特性，提出了一种有限元网格的圆角过渡特征提取及网格局部修改算法。通过曲率估算、过渡区域圆弧识别和圆弧分组等步骤，计算出一系列截面轮廓线来描述圆角过渡特征，同时将过渡区域网格从模型中提取出来。直接调整圆弧半径，快捷、准确地修改网格模型中等半径及变半径过渡区域网格。应用该算法，能够在有限元网格模型中直接修改零件或模具的过渡圆角形状，提高设计与CAE分析的效率。     

An Automated Process Planning and Die Design System for Quasi-Axisymmetric Cold Forging Products

This paper deals with an automated computer-aided process planning and die design system with which a designer can determine operation sequences even after only a little experience in process planning and die design of quasi-axisymmetric cold forging products by multistage former working. The approach is based on knowledge-based rules, and a process knowledge base consisting of design rules is built. Knowledge for the system is formulated from plasticity theories, empirical results and empirical knowledge of field experts. Programs for the system have been written in AutoLISP for AutoCAD with a personal computer. An attempt is made to link programs incorporating a number of expert design rules with the process variables obtained by commercial FEM software, DEFORM and ANSYS, to form a useful package. The system is composed of three main modules and five submodules. The process planning and die design module considers several factors, such as the complexities of preform geometry, punch and die profiles, specifications of available multiformers, and the availability of standard parts. The system uses 2D geometry recognition and is integrated with the technology of process planning, die design, and CAE analysis. The standardisation of die parts for wheel bolts requiring a cold forging process is described. The system developed makes it possible to design and manufacture quasi-axisymmetric cold forging products more efficiently.     

A study on life estimation of hot forging die

In this study, the forging die life was investigated using fatigue life and wear quantity, which are generally considered for estimation of die life. The main aim is development of the equations to adapt finite element analysis to life estimation for a hot forging die. The Archard’s model was used to estimate the wear life of the die and Goodman’s and Gerber’s equations, using the stress-life method, were applied to estimation of the fatigue life. These techniques were applied to die life estimation for the hot forging die of a ball joint socket used in an autovehicle system. Rigid-plastic finite element analysis was first carried out for the forging process of the ball joint socket and then the elastic stress analysis was performed for the die in order to obtain fundamental data for the prediction of fatigue life. The die stress analysis requires the deforming loads of the workpiece to be translated into the contact loading of the die. In this case, the size of finite elements of the die and the workpiece is important for good interpolation of the loading. Therefore, the influence of element sizes on the interpolation results of the contact loading was also investigated. The wear volume of the die was measured using a 3-dimensional scanner of probe type. It was found that the measurement had a good agreement with the results of the finite element analysis for the die life estimation.     

Wear at the die radius in sheet metal stamping

In sheet metal stamping, it is known that wear is unevenly distributed over the die radius and that multiple wear mechanisms may occur simultaneously. However, there has been little or no work that details the types of wear mechanisms, and quantifies the locations at which they occur. Furthermore, the link between recently identified time-dependent contact conditions and the wear response is currently unknown. An experimental study is presented in this paper to examine the location, type and severity of wear that occurs over the die radius during a typical sheet metal stamping process. It is found that the wear over the die radius consists of a combination of ploughing and galling mechanisms. The relative severity of the ploughing mechanism is divided into two distinct zones on the die radius, which correlate well with the contact pressure and sliding distance behavior predicted in our recently published numerical study. The galling mechanism results in failure of the stamping process and is, therefore, critical to the overall tool wear response. Our analysis indicates that the severe contact pressure/small sliding distance conditions, which occur during the initial stage of the process, cause the galling behavior observed over the radius. Therefore, it is concluded that the overall tool wear response and tool life is primarily dependent on the initial transient stage of the stamping process.     

Knife-edge interferometry for cutting tool wear monitoring

This paper presents a novel technique for more easily measuring cutting tool wear using knife-edge interferometry (KEI). Unlike an amplitude splitting interferometry, such as Michelson interferometry, the proposed KEI utilizes interference of a transmitted wave and a diffracted wave at the cutting tool edge. In this study, a laser beam was incident on the cutting tool edge, and the photodetector was used to determine the interference fringes by scanning a cutting tool edge along the cutting direction. The relationship between the cutting tool wear and interferometric fringes generated by edge diffraction phenomena was established by using the cross-correlation of KEI fringes of two different cutting tool-edge conditions. The cutting tool wear produced the phase shift (attrition wear) and the decay of oscillation (abrasive wear) in the interferometric fringe. The wear characteristics of the cutting tool with a radius of curvature of 6 mm were investigated by measuring the interferometric fringes of the tool while cutting an aluminum work piece in a lathe. As a result, the attrition and abrasive wear of cutting tool showed a linear relationship of 5.62 lag/wear (μm) and 1.14E-3/wear (μm), respectively. This measurement technique can be used for directly inspecting the cutting tool wear in on-machine process at low-cost.     

基于刚粘塑性有限元模拟的汽轮机叶轮模锻的预成形优化

针对汽轮机叶轮模锻的预成形设计,本文建立了以打击能耗最低和模具作用载荷最小为目标函数,以完全填充为约束条件,以坯料初始高径比为优化变量的预成形坯料优化方案。利用刚粘塑性有限元方法模拟汽轮机叶轮等温模锻成形过程,具体分析了不同坯料初始高径比对成形载荷、塑性应变能以及分流面的影响。数值模拟结果表明获得的预成形H/D最佳尺寸可明显减少模锻锤击次数和模具磨损。所提出的有限元模拟预成形优化方法十分有效,克服了以往凭经验设计的弊端。     

Effect of tool stiffness upon tool wear in high spindle speed milling using small ball end mill

Longer tool life can be tentatively achieved at a higher feed rate using a small ball end mill in high spindle speed milling (over several tens of thousands of revolutions per minute), although the mechanism by which tool life is improved has not yet been clarified. In the present paper, the mechanism of tool wear is investigated with respect to the deviation in cutting force and the deflection of a ball end mill with two cutting edges. The vector loci of the cutting forces are shown to correlate strongly with wear on both cutting edges of ball end mills having various tool stiffnesses related to the tool length. The results clarified that tool life can be prolonged by reducing tool stiffness, because the cutting forces are balanced, resulting in even tool wear on both cutting edges as tool stiffness is lowered to almost the breakage limit of the end mill. A ball end mill with an optimal tool length showed significant improvement in tool life in the milling of forging die models.     

Factors affecting die wear

Simple upsetting tests were used to assess the wear of hot forging dies. The influence of forging variables such as die-billet contact time and lubrication is described. A “white” layer is formed at the surface of lubricated dies when die-billet contact times exceed 5 ms. This layer was identified as martensite of increased wear resistance. Lubrication affects the frictional condition at the die-billet interface thus facilitating the relative movement of the billet material over the die surface resulting in the increased wear of flat dies.     

Microstructure and properties of surfacing layers of dies manufactured by bimetal-gradient-layer surfacing technology before and after service

The purpose of this article is to investigate the microstructure and mechanical properties of surfacing layers (wear layer and transition layer) of a hot forging die manufactured by the bimetal-gradient-layer surfacing method, which is based on ZG29MnMoNi cast steel before and after forged 5761 parts on a 63MN hot die forging press. The finite element model of a die was established. Subsequently, a simulation was conducted to analyze the temperature field of the die and its cycle features under working conditions. Microstructure and mechanical property were measured. Results indicated that the microstructure of the wear layer mainly consists of temper sorbite, ferrite and carbides. The transition layer before and after service is mainly composed of both temper sobrite, lower bainite, and a small amount of temper martensite. The mechanical properties of wear and transition layers declined significantly after service. The tensile strength, yield strength, reduction of area, and elongation of wear layer declined by 41.6, 32.5, 28.3, and 24.5 %, respectively. With those indexes the transition layer decreased by 36.6, 34, 24.4, and 19.8 %, respectively. Microhardness and impact energy of wear and transition layers have showed a decrease of 17, 6 % and 51.2, 32.6 %, respectively. The impact fracture mode of both wear and transition layers is typically intergranular fracture after service. As a conclusion, it was determined that the service process sufficiently influenced the mechanical properties of the surfacing layers.     

A FINITE ELEMENT ANALYSIS OF BURR FORMATION IN FACE MILLING OF A CAST ALUMINUM ALLOY

The research discussed in this article focuses on the effects of tool geometry (i.e., rake angle and cutting edge radius) and flank wear upon burr formation in face milling of a cast aluminum alloy. As to tool edge preparation, the use of a tool with variable cutting edge radius was investigated using FEM, and compared for its cutting performance (i.e., burr reduction and tool life) with a conventional tool with uniform cutting edge radius. In order to evaluate 3D face milling through 2D orthogonal cutting simulations, the cross-sections that consist in the cutting speed direction and chip flow direction were selected at different locations along the tool rounded corner. At these cross-sections, the local value of cutting edge radius and their associated tool rake angles as well as the effective uncut chip thickness were determined for 2D cutting simulations. In addition, 3D face milling simulations were conducted to investigate more realistic chip flow and burr generation. Comparisons were made for burrs produced from 3D simulations with a sharp tool, 3D simulations with a worn tool and face milling experiments. Finally, recommendations for cutting tool design are made to reduce burr formation in face milling.     

ESTIMATION OF TOOL WEAR OF CARBIDE TOOL IN ORTHOGONAL CUTTING USING FEM SIMULATION

In metal cutting, tool wear on the tool-chip and tool-workpiece interfaces (i.e. flank wear and crater wear) is strongly influenced by the cutting temperature, contact stresses, and relative sliding velocity at the interface. These process variables depend on tool and workpiece materials, tool geometry and coatings, cutting conditions, and use of coolant for the given application. Based on the predicted temperatures and stresses on the tool face from the finite element analysis (FEA) simulation, tool wear may be estimated with acceptable accuracy by incorporating an empirical wear model.

The overall objective of this study is to develop a methodology to predict the tool wear evolution and tool life in orthogonal cutting using FEM simulations. To approach this goal, the methodology is proposed with three different parts. In the first part, a tool wear model for the specified tool-workpiece pair is developed via a calibration set of tool wear cutting tests in conjunction with cutting simulations. In the second part, modifications are made to the commercial FEM code used to allow for tool wear calculation and tool geometry updating. The last part includes the validation of the developed methodology. This paper is mainly focused on the modifications made to the commercial FEM code in order to make reasonable tool wear estimates (the second part).     

ESTIMATION OF TOOL WEAR OF CARBIDE TOOL IN ORTHOGONAL CUTTING USING FEM SIMULATION

In metal cutting, tool wear on the tool-chip and tool-workpiece interfaces (i.e. flank wear and crater wear) is strongly influenced by the cutting temperature, contact stresses, and relative sliding velocity at the interface. These process variables depend on tool and workpiece materials, tool geometry and coatings, cutting conditions, and use of coolant for the given application. Based on the predicted temperatures and stresses on the tool face from the finite element analysis (FEA) simulation, tool wear may be estimated with acceptable accuracy by incorporating an empirical wear model.

The overall objective of this study is to develop a methodology to predict the tool wear evolution and tool life in orthogonal cutting using FEM simulations. To approach this goal, the methodology is proposed with three different parts. In the first part, a tool wear model for the specified tool-workpiece pair is developed via a calibration set of tool wear cutting tests in conjunction with cutting simulations. In the second part, modifications are made to the commercial FEM code used to allow for tool wear calculation and tool geometry updating. The last part includes the validation of the developed methodology. This paper is mainly focused on the modifications made to the commercial FEM code in order to make reasonable tool wear estimates (the second part).     

汽车前轴精密辊锻成形过程的数值模拟

汽车前轴的精辊-模锻工艺是一种用小成形力锻造设备成形较大型前轴锻件的塑性加工技术,其工艺关键在于精密辊锻。前轴的精密辊锻分4个道次,是典型的局部成形工艺。辊锻工艺由于旋转的模具与辊锻件之间的接触区域在不断变化,一直以来成为数值模拟的难点。对4个道次的模具建立了模型,采用三维刚塑性有限元程序DEFORM-3D模拟了前轴精密辊锻工艺,分析了辊锻过程中金属变形的规律,研究了模具参数对成形质量的影响以及辊锻力矩的变化规律。模拟结果对于改进辊锻工艺设计、提高模具设计水平具有指导作用。     

Estimation of springback in double-curvature forming of plates: Experimental evaluation and process modeling

This paper presents the results obtained from a series of experiments on double-curvature forming of 300 mm square and 15 mm thick plates of type 316L(N) stainless steel to evaluate the inherent springback and also to validate finite element method (FEM) based process model developed for forming of multiple-curvature sectors of large size vessels. The experimental results show that twisting of the plate occurs during pressing, which is unavoidable in an actual forming setup on the shop floor. Twisting increases with increase in slope of the die cavity. Springback in the plate changes in an ascending order towards the centerline of the plate from the edges. The final radius of curvature (ROC) on the pressed plate after springback does not remain constant along a particular axis although the die and the punch had constant ROC along that axis because of varying constraint to opening up of the plate from centerlines to the edges. Springback also increases with reduction in the stiffness of the die and punch. The simulated plate profiles obtained from the FEM process model for multiple-curvature plate forming compared well with the experiments, the maximum error being within 6%. The process model used a sequential dynamic explicit formulation for the plate pressing phase and a static implicit formulation for the unloading (springback) phase in the Lagrangian framework. Reduced integration shell elements were used for the plate and the die and the punch were considered rigid. Dynamic explicit FEM for pressing and static implicit FEM for the unloading phase are adequate and economic for modeling of plate forming process by using FEM. The necessary material and frictional property data needed for the FEM process model were generated in-house. This model can be applied to design of dies and punches for forming the petals of large pressure vessels. The FEM process model predicts the final shape of the product and the residual cold work level for a given die, punch and plate configuration and this information can be used to correct the die and punch shapes for springback to manufacture the petals to the desired accuracy.     

有限元法及CAE技术在钻柱研究中的应用

在回顾了CAE技术和有限元法发展历史的基础上,介绍了有限元法的基本思想,分析了其发展趋势,研究了有限元法在钻柱研究中的应用。