Mustafa İlhan Gökler

Experimental investigation of effects of cutting parameters on surface roughness in the WEDM process

Abstract The experimental study presented in this paper aims to select the most suitable cutting and offset parameter combination for the wire electrical discharge machining process in order to get the desired surface roughness value for the machined workpieces. A series of experiments have been performed on 1040 steel material of thicknesses 30, 60 and 80 mm, and on 2379 and 2738 steel materials of thicknesses 30 and 60 mm. The test specimens have been cut by using different cutting and offset parameter combinations of the “Sodick Mark XI A500 EDW” wire electrical discharge machine in the Middle East Technical University CAD/CAM/Robotics Center. The surface roughness of the testpieces has been measured by using a surface roughness measuring device. The related tables and charts have been prepared for 1040, 2379, 2738 steel materials. The tables and charts can be practically used for WEDM parameter selection for the desired workpiece surface roughness.

Finite element analysis of springback in bending of aluminium sheets

Abstract Bending is one of the processes frequently applied during manufacture of aluminium components. The bending operation involves springback, which is defined as elastic recovery of the part during unloading. In manufacturing industry, it is still a practical problem to predict the final geometry of the part after springback and to design appropriate tooling in order to compensate for springback. In this paper, commercially available finite-element analysis (FEA) software is used to analyse bending and springback of different aluminium materials of different thickness. The amount of springback, the total equivalent plastic strains and the equivalent von Mises stresses are presented. The FEA results are compared with empirical data.

Analysis of tapered preforms in cold upsetting

Abstract Upset forging is usually carried out with a sequence of stages and the tapered preforms are commonly used. The preforms should be free from flash formation and buckling injuries. In this paper, the results that depend on elastic–plastic finite element analysis of taper upset forging are given. The buckling analysis was realized by using the Modified Riks method. For a given upset ratio which is the ratio of unsupported length to diameter of the initial billet, reduction in the height of the billet and the diameter ratio are the important design parameters in taper upsetting. For several values of the design parameters, the analysis has been carried out and the results have been compared with the results of the well-known Meyers experiment and Goklers suggestions. In the analysis, the perfectly square end (ideal billet case) and the end with face inclination angle were considered as two different end conditions of the billet. The results for the ideal billet case are in good-agreement with Meyers results. The end-face inclination angle, which is a significant imperfection on the billet, reduces the limits of allowable upset ratio. It has been observed that although the tapered header dies designed at the limits suggested by Meyer produce flashless preforms, in some of the cases, injuries due to buckling are not eliminated. However, Goklers suggested limits provide elimination of both flash formation and injuries due to buckling.

Design of an automatic tool changer with disc magazine for a CNC horizontal machining center

Automatic tool changers (ATCs) are devices used in CNC machine tools to exchange the tool in the spindle with the tool in the magazine. In this paper, the design of the ATC of a CNC horizontal machining center which was realized for a CNC machine tool manufacturer is introduced. After examination of several alternatives, it was decided to implement the disc-type ATC. A magazine was designed with 24 tools with a maximum tool diameter of 150 mm and a maximum tool weight of 8 kgf. The designed ATC can change the closest tool within 4 s and the tool farthest away within 6 s.

Structural Finite Element Analysis of Stiffened and Honeycomb Panels of the RASAT Satellite

This paper describes the structural analysis carried out on the main stiffened and honeycomb panels of the RASAT satellite. The analysis here supports the design process and aims to ensure that the panels survive structural qualification testing. This analysis therefore forms part of the overall qualification process. The stiffened and honeycomb panels being considered in this document form the outer box structure of the satellite. These panels consist of the space-facing facet (SFF), solar panels including solar cells and earth facing facet (EFF). All these panels are key parts of the satellites structure and are critical to mission safety. The separation panel is particularly highly loaded, since it supports the battery pack, reaction wheels, gyro module, magnetorquer rods and sun sensors. The separation panel also supports the solar panel assembly. The solar panels are also of critical importance, their integrity maintaining the required power supply to operate the satellites electronic systems. As being different from the SFF and EFF, the solar panels are made of aluminum honeycomb panels. The solar panels are particularly sensitive, as they carry arrays of delicate ceramic solar cells together with their wiring. Throughout all loading conditions experienced during the mission, the solar panels must continue to support the solar cells without cell failures or wiring disconnections. The EFF is perhaps the least critical of the stiffened panels but still must support the top of the solar panel assembly and must carry various antennae. The main objective of this study is to assess the strength and vibration response properties of the stiffened and honeycomb panels by conducting static stress and modal analyses. For the case of static loading, the reliability can be estimated with great efficiency, whereas for dynamic loading the performance depends on the considered frequency range. The obtained results are very significant in that, they illustrate the feasibility of a full scale analysis for structural reliability in a design context for large-scale structures. The analyses are conducted by means of the finite element method. For the static case, the SFF and EFF are meshed with hex elements and the honeycomb panels are meshed with solid brick and shell elements. For the calculated gRMS value the static analysis had been conducted in each axis of the panel assembly. For the dynamic case, the same finite element mesh and material properties had been used. In this case, the boundary conditions are applied in such a way to determine the mode shapes and the resonance frequencies. Furthermore, the stress values had been determined with respect to the applied static and dynamic loading cases. They had been compared with the allowable stress values of the materials. In this paper the complete finite element analyses procedures are described and the results of the analyses are presented. According to the computed results, some conclusions are drawn in order to guide experimental qualification tests.

Analysis of roller hemming process for a vehicle tailgate closure

Hemming is a sheet metal joining process which is widely used for vehicle closures. As the latest hemming process type, the roller hemming process uses industrial robots therefore; main advantage of the process is achieved as flexibility with improved product quality. Trial and error method is the general approach to design the process in the industry due to limited know-how in the roller hemming. However, due to advantages of the process, the recent studies have also been focused on numerical simulations. In this study, the roller hemming process of the tailgate of a vehicle has been investigated by using the finite element method. The points of interest are selected as cycle time reduction and reducing the undesired wrinkling formation in the process. In the current roller hemming process of the tailgate, three stages including two pre-hemming and one final hemming stages are being applied. For the cycle time reduction, simulations have been performed to complete the hemming process in two stages. Effec...

Effects of forming history on crash simulation of a vehicle

The effects of forming on the crash simulation of a vehicle have been investigated by considering the load paths produced by sheet metal forming process. The frontal crash analysis has been performed by the finite element method, firstly without considering the forming history, to find out the load paths that absorb the highest energy. The sheet metal forming simulations have been realized for each structural component of the load paths and the frontal crash analysis has been repeated by including forming history. The results of the simulations with and without forming effects have been compared with the physical crash test results available in literature.

Analysis of hot forming of a sheet metal component made of advanced high strength steel

To provide reduction in weight while maintaining crashworthiness and to decrease the fuel consumption of vehicles, thinner components made of Advanced High Strength Steels (AHSS) are being increasingly used in automotive industry. However, AHSS cannot be formed easily at the room temperature (i.e. cold forming). The alternative process involves heating, hot forming and subsequent quenching. A-pillar upper reinforcement of a vehicle is currently being produced by cold forming of DP600 steel sheet with a thickness of 1.8 mm. In this study, the possible decrease in the thickness of this particular part by using 22MnB5 as appropriate AHSS material and applying this alternative process has been studied. The proposed process involves deep drawing, trimming, heating, sizing, cooling and piercing operations. Both the current production process and the proposed process are analyzed by the finite element method. The die geometry, blank holding forces and the design of the cooling channels for the cooling process ar...