Computational modelling of impact damage in brittle materials

Electrical discharge machining (EDM) is a well-established machining option for manufacturing geometrically complex or hard material parts that are extremely difficult-to-machine by conventional machining processes. The non-contact machining technique has been continuously evolving from a mere tool and die making process to a micro-scale application machining alternative attracting a significant amount of research interests. In recent years, EDM researchers have explored a number of ways to improve the sparking efficiency including some unique experimental concepts that depart from the EDM traditional sparking phenomenon. Despite a range of different approaches, this new research shares the same objectives of achieving more efficient metal removal coupled with a reduction in tool wear and improved surface quality. This paper reviews the research work carried out from the inception to the development of die-sinking EDM within the past decade. It reports on the EDM research relating to improving performance measures, optimising the process variables, monitoring and control the sparking process, simplifying the electrode design and manufacture. A range of EDM applications are highlighted together with the development of hybrid machining processes. The final part of the paper discusses these developments and outlines the trends for future EDM research.

http://zclient.persiangig.com/ScienceDirect/M02.pdf

State of the art electrical discharge machining (EDM)

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.

/pdf/metal-forming-and-the-finite-element-method-5ev6lca5h5.pdf

Metal Forming and the Finite-Element Method

http://digitalknowledge.cput.ac.za/bitstream/11189/4942/3/Makinde_Oluwole_D_Aziz_A_Eng_2011.pdf

Boundary layer flow of a nanofluid past a stretching sheet with a convective boundary condition

An account is given of the development of the idea of a yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time. Originally, it was accepted that the yield stress of a solid was essentially the point at which, when the applied stress was increased, the deforming solid first began to show liquid-like behaviour, i.e. continual deformation. In the same way, the yield stress of a structured liquid was originally seen as the point at which, when decreasing the applied stress, solid-like behaviour was first noticed, i.e. no continual deformation. However as time went on, and experimental capabilities increased, it became clear, first for solids and lately for soft solids and structured liquids, that although there is usually a small range of stress over which the mechanical properties change dramatically (an apparent yield stress), these materials nevertheless show slow but continual steady deformation when stressed for a long time below this level, having shown an initial linear elastic response to the applied stress. At the lowest stresses, this creep behaviour for solids, soft solids and structured liquids can be described by a Newtonian-plateau viscosity. As the stress is increased the flow behaviour usually changes into a power-law dependence of steady-state shear rate on shear stress. For structured liquids and soft solids, this behaviour generally gives way to Newtonian behaviour at the highest stresses. For structured liquids this transition from very high (creep) viscosity (>106 Pa.s) to mobile liquid (

The yield stress—a review or ‘παντα ρει’—everything flows?

Use of Electronic Geometry Transfer and FEM Simulation in the Design of Hot Forming Dies for a Gear Blank

This paper presents an overview on the application of FE simulation as a virtual manufacturing tool in designing manufacturing processes for precision parts. The processes discussed include forging, sheet metal forming and hydroforming. Determination of reliable input parameters to simulate a process is a key element in successful application of process simulation for process design in all the mentioned areas. These issues are discussed in detail. Practical examples of application of FE simulation are presented for improvement of the existing metal forming process and/or designing new metal forming process for manufacturing discrete precision parts in forging, sheet metal forming and hydroforming.

Process modeling for precision forming of discrete parts: State of the technology and critical issues

Tailored solutions are one key to the lightweight construction challenges of the future. Only tailored solutions allow the combination of soft and hard zones for the best possible crash performance and minimum weight. The safety cage of future vehicles may completely be designed with hot formed components. In order to achieve the desired properties of the component, a heat treatment operation is necessary, and it comprises a significant part of the hot forming process. This poses additional challenges to the automotive industry as the heat treatment process is a function of many parameters and depends strongly on the forming process. In addition, only perfectly heat-treated parts will fulfill specifications. Virtual Prototyping makes sure that component manufacturing and assembly processes yield the designed tolerances and crash performance. ESI GROUP aims at providing all necessary tools for virtual prototyping of lightweight constructions designed and assembled with tailored solutions, specifically hot forming. This paper outlines what is needed for realistic virtual prototyping, and the status of the simulation solution. Validated realistic engineering examples are used to illustrate the capabilities in the field of virtual die design, forming, quenching, cooling channel engineering, assembly, and product performance.

Virtual Prototyping of Hot Formed Tailored Light-weight Designs

Progressive and transfer dies are used for forming of sheet metal parts in large quantities. For a given part, the design of progressive die sequence involves the selection of the number of forming stages as well as the determination of the punch and die dimensions at each stage. This design activity is largely experience-based and requires prototyping involving several trial and error operations. In some cases, empirical data and the experience based design procedure can be combined with Finite Element Method (FEM) based analysis to reduce time and cost. Often, when using FEM in progressive die design, friction and its effect upon temperatures is not adequately considered. However, at each forming station the plastic deformation and the tribological conditions influence the material flow as well as the temperatures and pressures at the tool/workpiece interface. The performance of the lubricant and coolant, used in progressive die forming, is affected significantly by interface pressure and temperatures. Therefore, a progressive process and die design methodology should include the consideration of metal flow as well as temperatures and pressures. Heat transfer coefficient, friction, plastic deformation, forming speed at each forming stage, time for part transfer from one stage to the next, and the ability of the used lubricant to cool the dies, have considerable effect upon a successful stamping. This paper describes a method for designing a progressive die sequence for forming axisymmetric sheet metal parts. The methodology for process sequence design combines experience based empirical data obtained through previous designs, design rules and numerical simulations including plastic deformation and friction. The initial experience-based design was refined using FEM and the thinning of the material in each successive drawing stage was calculated. The thermo-mechanical model was obtained using a constant friction coefficient along the tool/workpiece contact zone. Finally, the tool/workpiece interface temperature and the normal pressures were estimated in order that the lubricant can be selected based on these process conditions. The design predictions, made by using empirical data and FEM, were compared with experimental data.

Design of Progressive Die Sequence by Considering the Effect of Friction, Temperature and Contact Pressure

In this study, the effectiveness of recent 3D FEM simulations of orbital forming was investigated by (a) measuring the computation time and (b) by comparing the results of simulations with experiments Commercial FEA software DEFORM™ 3D v40 that has an efficient computation numerical algorithm for simulating incremental forming process was used for the simulations and the amount of savings in computation time was shown Two measurable quantities from experiments are (1) deformed tab geometry of the spindle and (2) maximum forming load Therefore, the accuracy of 3D FEM simulation was evaluated by comparing the differences between the predicted and measured deformed tab geometry and maximum forming load In order to provide reliable flow stress for the simulation, a finite element based inverse analysis technique was used to identify the parameters of the flow stress equation from upset test by minimizing a least‐square functional of differences between predicted and measured forming loads Thank to a new development in the DEFORM 3D, the computation time required for simulating the incremental orbital forming process has been dramatically reduced The predicted load and the diameter of the formed tab were within 15% and 2% of measured values, respectively Thus, this study showed that 3D FEM is a reasonably reliable tool for process design in orbital forming

Taylan Altan

Papers

Use of Electronic Geometry Transfer and FEM Simulation in the Design of Hot Forming Dies for a Gear Blank

Process modeling for precision forming of discrete parts: State of the technology and critical issues

Virtual Prototyping of Hot Formed Tailored Light-weight Designs

Design of Progressive Die Sequence by Considering the Effect of Friction, Temperature and Contact Pressure

3D Finite Element Analysis of Orbital Forming and Inverse Analysis for Determination of Flow Stress of the Workpiece