Browsing by Author "Tekkaya,A.E."

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Citation - Scopus: 4
2d Fe Modelling of Machining: a Comparison of Different Approaches With Experiments
(2005) Bil,H.; Tekkaya,A.E.; Kiliç,S.E.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
[No abstract available]
Analysis of Force-Indentation Measurements on Anisotropic Metals
(Edizioni libreria progetto, 2005) Koray,E.; Topcu,N.; Tekkaya,A.E.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
Indentation tests are widely used with simultaneous measurements of indentation depth and force especially for determining material properties. In this study, findings on parameters affecting the force-displacement curves obtained from indentations on anisotropic metals using special not self-similar indenters will be presented. Parameters such as specimen dimensions, friction, surface roughness, specimen clamping and indentation spacing have been investigated by finite element analysis and by experiments. Optimum values of these parameters to achieve higher repeatability and accuracy are determined.
Citation - Scopus: 4
Comparison of Conventional Deep Drawing, Hydromechanical Deep-Drawing and High Pressure Sheet Metal Forming by Numerical Experiments
(American Institute of Physics Inc., 2005) Önder,I.E.; Tekkaya,A.E.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
Increasing use of new technologies in automotive and aircraft applications requires intensive research and developments on sheet metal forming processes. This study focuses on the assessment of sheet hydroforming, hydro-mechanical deep drawing and conventional deep-drawing processes by performing a systematic analysis by numerical simulations. Circular, elliptic, rectangular and square cross-section cups have been selected for the geometry spectrum. Within the range of each cross section, depth, drawing ratio and fillet radii have been altered systematically. St14 stainless steel has been used as the material throughout the study. The deformation behavior has been described by an elasto-plastic material model and all numerical simulations have been carried out by using a dynamic-explicit commercial finite element code. During the analyses each workpiece is produced by the three competing processes. The analyses results such as sheet thickness distribution, necking, forming of radii etc., are used for assessing the success of each forming process alternative. The analyses revealed that depending on the workpiece geometry and dimensional properties certain processes are preferable for obtaining satisfactory products. The process windows for each process have been established based on the analyzed parameters of the three different product geometries. This data is expected to be useful for selecting the appropriate production process for a given workpiece geometry. © 2005 American Institute of Physics.
Citation - Scopus: 2
Comparison of the Deep Drawability of Aluminum and Steel Using Numerical Simulation Experiments
(American Institute of Physics Inc., 2005) Sönmez,C.; Tekkaya,A.E.; Gür,C.H.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
Sheet metal forming processes, especially deep drawing processes give diverse results by various materials. Extreme differences occur between steel sheets and aluminum sheets. The main causes of these differences are variances in micro- and macroscopic material properties, such as anisotropy. In this study, the behavior of two distinct materials, steel and aluminum alloy, during an axisymmetrical cup drawing operation has been studied numerically. For this purpose, finite element (FE) simulations of a simple cup drawing process, which was studied in the benchmarks of the NUMISHEET 2002 have been conducted using a commercial dynamic-explicit FE-analysis package. The materials analyzed have been 6111-T4 aluminum alloy and mild steel graded as deep drawing quality. Basic process parameters, which are the blank holding force and the lubrication condition, have been varied to obtain a "successful" product and the process windows for these two materials have been compared and investigated. Thickness distributions in the blank, force requirements for the process and product quality have been used for the basis of comparison. The results are also compared with an analytical model developed by Ramaekers. © 2005 American Institute of Physics.
Effects of Local Heating on Material Flow in Free Forming Process
(2006) Okman,O.; Huwiler,H.; Özmen,M.; Tekkaya,A.E.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
A novel manufacturing method is investigated, in which a proper temperature gradient is created within workpiece in order to control local material flow during free forming. The main motivation is to produce complicated shapes by reducing the flow stress on the regions, where local deformation is desired to take place. A sufficient control of temperature within the material results in the required product shape even in the absence of complicated dies. Besides the lower tooling costs the process provides, the heat energy applied to the workpiece is less than that in conventional hot forming processes, which is currently a strong alternative for manufacturing of such products. In the study, heating is realized by means of induction heating and laser beam scanning. The process is investigated experimentally on circular cylinder specimens made of different materials, namely Ti6Al4V, X5CrNi18/9 and 16MnCr5. The effect of process parameters on the mode of deformation is analyzed by finite element method (FEM). The thermo-mechanical analysis of induction heating is supported by electromagnetic calculations. The two alternative heating methods are compared. Affects of heating on multiple locations is investigated for induction heating applications. A brief overview of the process is presented and conclusions are drawn on the effectiveness, limitations, failure modes and applicability of the process. Copyright © 2006 by ASME.
Citation - Scopus: 3
Experimental Investigation of Residual Stresses After Heat Treatment and Grinding Processes in the Production of Ball Bearing Rings
(Trans Tech Publications Ltd, 2008) Güley,V.; Tekkaya,A.E.; Savaş,T.; Özhan,F.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
Experimental investigation of residual stresses after heat treatment and grinding processes in the production of ball bearing rings has been carried out. The residual stresses were measured by X-ray diffraction method utilizing chromium radiation, which has an average penetration depth of 5 μm incident on 100Cr6 (AISI-E52100) ball bearing steel. The process parameters of heat treatment and grinding processes were varied so as to represent the extreme values that can be applied in the respective processes. Hardness and percent retained austenite limit the heat treatment process parameters; while roundness, surface roughness and form the grinding process. Tensile surface residual stresses on the raceway of ball bearing rings changes to compression after grinding in both circumferential and axial directions. In grinding relatively higher compressive stresses were measured in axial direction compared to the circumferential direction. This experimental investigation also showed that the influence of heat treatment process parameters on the magnitude and distribution of residual stresses survived even after grinding process; i.e. heat treatment and grinding processes cannot be evaluated independently in process design for favourable residual stresses.
Experimental Investigation of Residual Stresses After Heat Treatment and Grinding Processes in the Production of Ball Bearing Rings
(Trans Tech Publications Ltd, 2008) Güley,V.; Tekkaya,A.E.; Savaş,T.; Özhan,F.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
Experimental investigation of residual stresses after heat treatment and grinding processes in the production of ball bearing rings has been carried out. The residual stresses were measured by X-ray diffraction method utilizing chromium radiation, which has an average penetration depth of 5 μm incident on 100Cr6 (AISI-E52100) ball bearing steel. The process parameters of heat treatment and grinding processes were varied so as to represent the extreme values that can be applied in the respective processes. Hardness and percent retained austenite limit the heat treatment process parameters; while roundness, surface roughness and form the grinding process. Tensile surface residual stresses on the raceway of ball bearing rings changes to compression after grinding in both circumferential and axial directions. In grinding relatively higher compressive stresses were measured in axial direction compared to the circumferential direction. This experimental investigation also showed that the influence of heat treatment process parameters on the magnitude and distribution of residual stresses survived even after grinding process; i.e. heat treatment and grinding processes cannot be evaluated independently in process design for favourable residual stresses.
Citation - Scopus: 163
The Increased Forming Limits of Incremental Sheet Forming Processes
(Trans Tech Publications Ltd, 2007) Allwood,J.M.; Shouler,D.R.; Tekkaya,A.E.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
Incremental sheet forming is known to give higher forming limits than conventional sheet forming processes, but investigation of this effect has been impeded by the computational cost of process models which include detailed predictions of through thickness behaviour. Here, a simplified process is used to gain insight into the mechanics of a broad class of incremental forming processes. The simplified process is described and shown to give increases in forming limits compared to a conventional process with the same geometry. A model of the process is set up with a commercial finite element package, validated, and used to trace the history of a 'pin' inserted perpendicularly into the workpiece. The history of the deformation of the 'pin' demonstrates significant through thickness shear occurring in the direction parallel to tool motion. This insight is used to modify an existing analysis used to predict forming limit curves. The analysis shows that for a sheet with uniform proportional loading, the forming limit is increased when through thickness shear is present, and this is proposed as an explanation for the increased forming limits of incremental sheet forming processes.
Citation - Scopus: 2
Influence of Heat Treatment and Grinding Conditions on Surface Residual Stresses in the Production of Rollers
(Trans Tech Publications Ltd, 2006) Güley,V.; Tekkaya,A.E.; Savaş,T.; Özhan,F.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
The aim of this study is to investigate surface residual stresses after heat treatment and grinding processes in the production of rollers. The residual stresses were measured using the X-ray diffraction method utilizing chromium radiation, which has an average penetration depth of 5 μm incident on AISI-E52100 (100Cr6) ball bearing steel. Taguchi design of experiments (DOE) is applied to define the set of experiments for grinding, which facilitates evaluation of the individual influences of process parameters on residual stresses and also eliminates unnecessary experiments. Response of residual stresses to each parameter is evaluated with the help of the results of residual stress measurements by X-ray diffraction. In grinding with aluminum oxide wheels, it was concluded that the lower the cutting speed and the higher the workpiece speed the higher the magnitude of surface compressive residual stresses. Higher compressive stresses were measured in axial direction compared to the circumferential direction after the grinding process.
Influence of Heat Treatment and Grinding Conditions on Surface Residual Stresses in the Production of Rollers
(Trans Tech Publications Ltd, 2006) Güley,V.; Tekkaya,A.E.; Savaş,T.; Özhan,F.; Manufacturing Engineering; 06. School Of Engineering; 01. Atılım University
The aim of this study is to investigate surface residual stresses after heat treatment and grinding processes in the production of rollers. The residual stresses were measured using the X-ray diffraction method utilizing chromium radiation, which has an average penetration depth of 5 μm incident on AISI-E52100 (100Cr6) ball bearing steel. Taguchi design of experiments (DOE) is applied to define the set of experiments for grinding, which facilitates evaluation of the individual influences of process parameters on residual stresses and also eliminates unnecessary experiments. Response of residual stresses to each parameter is evaluated with the help of the results of residual stress measurements by X-ray diffraction. In grinding with aluminum oxide wheels, it was concluded that the lower the cutting speed and the higher the workpiece speed the higher the magnitude of surface compressive residual stresses. Higher compressive stresses were measured in axial direction compared to the circumferential direction after the grinding process.