Showing papers by "Taylan Altan published in 2011"

Selection of die materials and surface treatments for increasing die life in hot and warm forging

Abstract: In warm and hot forging, the dies are subjected to high contact pressures and temperatures. The selection of the die material, hardness and coating is critical for increasing die life in precision forging. In addition to traditionally used hot work die steels, latest studies have also shown improvements in die life by use of ceramics and surface treatments including vapor depositions techniques. This paper reviews the latest state of technology on die materials and surface treatments used in hot and warm forging of steel. Finite Element Analysis (FEA) based methods have also been used to estimate abrasive wear and plastic deformation on forging dies. These estimations can help to evaluate the life of die materials and coatings as well as in estimating die costs for a given production run.

Cold and Warm Hydroforming of AA754‐O Sheet: FE Simulations and Experiments

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...

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.

Evaluation of Stamping Lubricants in Forming Galvannealed Steels for Industrial Application

Abstract: There are various tribotests that are used to evaluate the performance of stamping lubricants.As these tests are performed under laboratory conditions, it is important that they emulate the conditions found in stamping plants. The tribotests widely used to evaluate lubricants include strip draw test (SDT), draw bead test, sliding test, and limited dome height test. Strip reduction test was introduced by Andreasen et al. [1] and was used to evaluate lubricants for galling of the tool while ironing stainless strips. Twist compression test was used by many investigators [2] in order to estimate the coefficient of friction (COF) of stamping lubricants. Many of the above tests fail to emulate real-world production conditions in terms of contact pressure, plastic deformation of the sheet material, temperature, and forming velocities. These factors influence the performance of the stamping lubricant and hence need to be considered while choosing a test to evaluate lubricants. The deep draw test (DDT) used in this study to evaluate the stamping lubricants represents very closely the conditions that exist in the production of sheet metal parts. Therefore, it was selected for this study. However, SDT was also used for prelimi

Investigation of Galling In Forming Galvanized Steel Sheet

Abstract: The major purpose of the present study is to evaluate the performance of various galvanized (GI) or galvannealed (GA) mild steels and AHSS in stamping applications. Finite Element Analysis (FEA) of selected stamping operations was conducted to estimate the critical pressure boundary conditions that exist in practice. Using this information, laboratory tribotests, e.g. Twist Compression (TCT), Deep Drawing (DDT) and Strip Drawing (SDT) Tests, were developed to evaluate the performance of selected lubricants and die materials/coatings in forming galvanized steels of interest. The sheet materials investigated included mild steels and AHSS (e.g. DP600 GI/GA, DP780 GI/GA, TRIP780 GA and DP980 GI/GA). Experimental results showed that galvanized material resulted in more galling, while galvannealed material showed more powdering and flaking. The surface roughness and chemical composition of galvanized sheet materials affected the severity of galling under the same testing conditions, i.e. lubricants and die materials/coatings. The results of this study helped to determine the critical interface pressure that initiates lubricant failure and galling in stamping selected galvanized sheet materials. Thus, to prevent or postpone the critical interface conditions, the results of this study can be used to select the optimum combination of galvanized sheet, die material, die coating and lubricant for forming structural automotive components.