Taylan Altan

Metal forming and the finite-element method

Introduction Metal forming process Analysis and technology in metal forming Plasticity and viscoplasticity Methods of analysis The finite element method (1) The finite element method (2) Plane-strain problems Axisymmetric isothermal forging Steady state processes of extrusion and drawing Sheet metal forming Thermo-viscoplastic analysis Compaction and forging of porous metals Three dimensional problems Preform design in metal forming Solid formulation, comparison of two formulations, and concluding remarks Index.

A finite element analysis of orthogonal machining using different tool edge geometries

Abstract This paper summarizes the effects of edge preparation of the cutting tool (round/hone edge and T-land/chamfer edge) upon chip formation, cutting forces, and process variables (temperature, stress, and strain) in orthogonal cutting as determined with finite element method (FEM) simulations. The results obtained from this study provide a fundamental understanding of the process mechanics for cutting with realistic cutting tool edges and may assist in the optimization of tool edge design. The Lagrangian thermo-viscoplastic cutting simulation of 0.2% carbon steel was conducted until the steady chip flow and cutting forces were obtained. The predicted cutting forces and chip geometries for the hone tools with different edge radii were compared with the experimental results given in the literature. Tool temperatures and tool stresses on the tool rake face were predicted while the material flow at the vicinity of the edge radius was characterized by the location of the stagnation point. A similar process model and the relevant analyses were extended to the application of chamfer tools with different chamfer widths and chamfer angles.

Tube Hydroforming - State-of-the-Art and Future Trends

Abstract With the availability of advanced machine designs and controls, tube hydroforming has become an economic alternative to various stamping processes. The technology is relatively new so that there is no large “knowledge base” to assist the product and process designers. This paper reviews the fundamentals of tube hydroforming technology and discusses how various parameters, such as tube material properties, pre-form geometry, lubrication and process control affect product design and quality. In addition, relations between process variables and achievable part geometry are discussed. Finally, using examples, the status of the current technology and critical issues for future development are reviewed.

An overall review of the tube hydroforming (THF) technology

Abstract Increasing use of hydroforming in automotive applications requires intensive research and development on all aspects of this relatively new technology to satisfy an ever-increasing demand by the industry. This paper summarizes a technological review of hydroforming process from its early years to very recent dates on various topics such as material, tribology, equipment, tooling, etc., so that other researcher at different parts of the world can use it for further investigations in this area.

Application of 2D FEM to chip formation in orthogonal cutting

Abstract This paper summarizes the results of an investigation where the FE code DEFORM 2D was applied to simulate a plane strain cutting process. To perform the simulation with reasonable accuracy and to study continuous and segmented chip formation it was necessary to modify the existing version of the code. Damage criteria have been used for predicting when the material starts to separate at the initiation of cutting for simulating segmented chip formation. For this purpose, special subroutines have been implemented and tested. The influence of several parameters such as cutting speed, rake angle, and depth of cut has been studied. Results of extensive FEM simulations and the comparison with experimental data are reported.

Estimation of tool wear in orthogonal cutting using the finite element analysis

Abstract 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 temperatures and stresses on the tool face predicted by the finite element analysis (FEA) simulation, tool wear may be estimated with acceptable accuracy using 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 proposed has 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 tool wear calculation and tool geometry updating. The last part includes the experimental validation of the developed methodology. The focus of this paper is on the modifications made to the commercial FEM code in order to make reasonable tool wear estimates.

Material fracture and burr formation in blanking results of FEM simulations and comparison with experiments

Abstract This paper summarizes the results of simulating the blanking process by means of a modified DEFORM-2D FEM (Finite Element Method) code. Several modifications were made to this code in order to simulate the material fracture. Unlike most other approaches, it was possible to obtain each of the zones of a blanked part edge such as roll over, shear zone, rupture zone and burr. Several blanking simulations were performed and the results were compared with our experimental studies. It was shown that the influence of process variables such as punch-die clearance, material properties and punch and die wear could be simulated with a good correlation to experimental results. Furthermore, the simulated and experimentally obtained load stroke curves show the same changes of shape and absolute value due to variations in process conditions.

Manufacturing of Dies and Molds

Abstract The design and manufacturing of dies and molds represent a significant link in the entire production chain because nearly all mass produced discrete parts are formed using production processes that employ dies and molds. Thus, the quality, cost and lead times of dies and molds affect the economics of producing a very large number of components, subassemblies and assemblies, especially in the automotive industry. Therefore, die and mold makers are forced to develop and implement the latest technology in: part and process design including process modeling, rapid prototyping, rapid tooling, optimized tool path generation for high speed cutting and hard machining, machinery and cutting tools, surface coating and repair as well as in EDM and ECM. This paper, prepared with input from many CIRP colleagues, attempts to review the significant advances and practical applications in this field.

Determination of workpiece flow stress and friction at the chip-tool contact for high-speed cutting

Abstract This paper presents a methodology to determine simultaneously (a) the flow stress at high deformation rates and temperatures that are encountered in the cutting zone, and (b) the friction at the chip–tool interface. This information is necessary to simulate high-speed machining using FEM based programs. A flow stress model based on process dependent parameters such as strain, strain-rate and temperature was used together with a friction model based on shear flow stress of the workpiece at the chip–tool interface. High-speed cutting experiments and process simulations were utilized to determine the unknown parameters in flow stress and friction models. This technique was applied to obtain flow stress for P20 mold steel at hardness of 30 HRC and friction data when using uncoated carbide tooling at high-speed cutting conditions. The average strain, strain-rates and temperatures were computed both in primary (shear plane) and secondary (chip–tool contact) deformation zones. The friction conditions in sticking and sliding regions at the chip–tool interface are estimated using Zorevs stress distribution model. The shear flow stress ( k chip ) was also determined using computed average strain, strain-rate, and temperatures in secondary deformation zone, while the friction coefficient ( μ ) was estimated by minimizing the difference between predicted and measured thrust forces. By matching the measured values of the cutting forces with the predicted results from FEM simulations, an expression for workpiece flow stress and the unknown friction parameters at the chip–tool contact were determined.

Process simulation using finite element method — prediction of cutting forces, tool stresses and temperatures in high-speed flat end milling

Abstract End milling of die/mold steels is a highly demanding operation because of the temperatures and stresses generated on the cutting tool due to high workpiece hardness. Modeling and simulation of cutting processes have the potential for improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. The main objective of this study was to develop a methodology for simulating the cutting process in flat end milling operation and predicting chip flow, cutting forces, tool stresses and temperatures using finite element analysis (FEA). As an application, machining of P-20 mold steel at 30 HRC hardness using uncoated carbide tooling was investigated. Using the commercially available software DEFORM-2D™, previously developed flow stress data of the workpiece material and friction at the chip–tool contact at high deformation rates and temperatures were used. A modular representation of undeformed chip geometry was used by utilizing plane strain and axisymmetric workpiece deformation models in order to predict chip formation at the primary and secondary cutting edges of the flat end milling insert. Dry machining experiments for slot milling were conducted using single insert flat end mills with a straight cutting edge (i.e. null helix angle). Comparisons of predicted cutting forces with the measured forces showed reasonable agreement and indicate that the tool stresses and temperatures are also predicted with acceptable accuracy. The highest tool temperatures were predicted at the primary cutting edge of the flat end mill insert regardless of cutting conditions. These temperatures increase wear development at the primary cutting edge. However, the highest tool stresses were predicted at the secondary (around corner radius) cutting edge.