Taylan Altan

Bio: Taylan Altan is an academic researcher from Ohio State University. The author has contributed to research in topics: Forging & Finite element method. The author has an hindex of 59, co-authored 270 publications receiving 14494 citations. Previous affiliations of Taylan Altan include University College of Engineering & DuPont.

Cold and Warm Hydroforming of AA754-O Sheet

Abstract: The sheet hydroforming with punch (SHF-P) process offers great potential for low and medium volume production, especially for forming: (1) lightweight sheet materials such as aluminum (Al) and magnesium (Mg) alloys and (2) thin gage high strength steels (HSS). Mg and Al alloys are being increasingly considered for automotive applications, primarily due to their lightweight and high strength-to-weight ratios. However, there is limited experience-based knowledge of process parameter selection and tool design for SHF-P of these materials. Thus, there is a need for a fundamental understanding of the influence of process parameters on part quality. This paper summarizes analyses of the SHF-P process of AA5754-O sheet using finite element (FE) simulations. FE simulations and preliminary experiments of SHF-P were conducted to determine the process parameters (blank holder force versus punch stroke and pot pressure versus stroke) to form a challenging shape (a cylindrical cup with a reverse bulge) successfully at room and elevated temperature (~150℃). The material properties of the sheet material were obtained from tensile tests at room temperature up to 260℃ as presented by [1]. The FE model was established using PAMSTAMP 2G, Version 2009. SHF-P experiments were conducted in order to (ⅰ) evaluate the formability of the part at room and elevated temperatures and (ⅱ) validate FE simulation results. This study shows that the SHF-P at elevated temperature can form a cup with larger cup height and better reverse bulge profile than SHF-P at room temperature. Moreover, the FE predictions of part profiles and thinning distributions matched reasonably well with the experimental results.

Tube and Sheet Hydroforming-Advances in Material Modeling, Tooling and Process Simulation

Abstract: Tube Hydroforming is a well accepted production technology in automotive industry while sheet hydroforming is used in selected cases for prototyping and low volume production Research in advanced methods (warm sheet and tube hydroforming, double blank sheet hydroforming, combination of hydroforming and mechanical sizing, use of multi-point and elastic blank holders) is expanding the capabilities of hydroforming technologies to produce parts from Al and Mg alloys, as well as Ultra High Strength Steels In the development of advanced hydroforming methods, experience based knowledge is not readily available Thus, robust process simulation is required, along with adequate material modeling and identification of friction coefficients as input to process simulation This paper gives an overview of advanced hydroforming methods, including examples of novel machine and tooling designs The use of reliable process simulation is illustrated with examples that demonstrate the significance of material and friction date for making accurate predictions Advanced simulation methods for warm forming and for programming multiple-point blank holder are also discussed This review illustrates that hydroforming continues to make advances and has the potential to make many contributions to production technology in the near future

State of the art electrical discharge machining (EDM)

Abstract: 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.

Metal Forming and the Finite-Element Method

Abstract: 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.

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

Abstract: 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 (