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?

Survey of the die and mold manufacturing industry - practices in Germany, Japan, and the United States

Prediction and elimination of springback in straight flanging using computer-aided design methods: Part 2: FEM predictions and tool design

Flow Stress of Metals and Its Application in Metal Forming Analyses

Hard roller burnishing is a cost-effective finishing and surface enhancement process where a ceramic ball rolls on the machined surface to flatten the roughness peaks The ball is supported and lubricated by hydrostatic fluid in a special tool holder The process not only improves surface finish but also imposes favorable compressive residual stresses in functional surfaces, which can lead to long fatigue life Most research in the past focused on experimental studies There is still a special need for a reliable finite element method (FEM) model that provides a fundamental understanding of the process mechanics In this study, two-dimensional (2D) and three-dimensional FEM models for hard roller burnishing were established The developed 2D FEM model was used to study the effects of process parameters (ie, burnishing pressure, feed rate) on surface finish and residual stresses The simulation results were evaluated and compared to the experimental data Results show that the established FEM model could predict the residual stresses and provided useful information for the effect of process parameters Both FEM and experiments show that burnishing pressure is the most influence, where high burnishing pressure produces less roughness and more compressive residual stress at the surface

Finite Element Modeling of Hard Roller Burnishing: An Analysis on the Effects of Process Parameters Upon Surface Finish and Residual Stresses

Zinc phosphate coatings plus metal soap lubrication system is required in nearly all steel cold forging operations. However, the chemical byproducts of this lubricant system are difficult to dispose of and have a negative environmental impact. In order to replace zinc phosphate based lubricants partially or completely, candidate lubricants were sought from lubricant manufacturers worldwide. The performance evaluation of these lubricants was conducted using the double cup backward extrusion test developed at the Engineering Research Center for Net Shape Manufacturing (ERC/NSM). With the use of the commercial FEM code DEFORM, friction factor calibration curves, i.e. cup height ratio vs. punch stroke, were established for different friction factor values. By matching the cup height ratio and the punch stroke from experiment to that obtained from FE simulations, the friction factor of the lubricants was determined. Three lubricants; namely, MEC Homat, Daido AquaLub, and MCI Z-Coat, were found to perform comparable to or better than zinc phosphate.

/pdf/evaluation-of-new-cold-forging-lubricants-without-zinc-2sv3mv594x.pdf

Taylan Altan

Papers

Survey of the die and mold manufacturing industry - practices in Germany, Japan, and the United States

Prediction and elimination of springback in straight flanging using computer-aided design methods: Part 2: FEM predictions and tool design

Flow Stress of Metals and Its Application in Metal Forming Analyses

Finite Element Modeling of Hard Roller Burnishing: An Analysis on the Effects of Process Parameters Upon Surface Finish and Residual Stresses

Evaluation of new cold forging lubricants without zinc phosphate precoat