Dimitrios Sagris

Influence Analysis of Micro-Milling Vibrational Phenomena on Workpiece Topomorphy

In metal machining processes, it is necessary to study the vibration phenomena which take place in cutting area between the cutting tool and the workpiece in order to ascertain the factors that affect them. Subject of this paper is the analysis of the influence of vibration phenomena during micro-milling on chip formation mechanisms and thereby on the workpiece topomorphy. In particular, the cutting parameters, such as the cutting speed, the feed rate and the axial cutting depth, which affect the workpiece topomorphy are experimentally studied. Based on cutting force measurements correlated with the workpiece topomorphy under various cutting process parameters useful results are extracted. In this way, the impact of vibration phenomena, taking place in micro-milling due to the cutting process, on the workpiece topomorphy can be evaluated.

Off-line Robot Optimization with Hybrid Algorithm

Having developed a hybrid optimization methodology for mechatronics system movements in space, the task is to efficiently control of robotic system with 6 degrees of freedom. In this work, hybrid methodology is compared with a simple genetic algorithm. It is applied in a simulation environment of a 6-degrees of freedom robotic arm and the results are compared with the mathematical model developed to support this methodology. The results of the research show that the optimization with the hybrid method compared to the simple GA, which is calculated by the mathematical model, is confirmed by more than 90% of the robotic arm simulation model examples.

The delamination effect of drilling and electro-discharge machining on the tensile strength of woven composites as studied by X-ray computed tomography

The presence of stress concentration especially from any induced delamination around a hole causes substantial perturbation of the stress and strain field in the structure under service loads. Therefore, it is of great practical interest to accurately analyse and quantify any delamination and its effect to the load bearing capacity of the structure. Two types of open-hole machining - drilling and electro-discharge machining (EDM) - were applied in order to examine their effect on the tensile strength of carbon/epoxy laminates. Pulse durations of 100 µs 200 µs and 300 µs with a current of 3 A and voltage 100 V were used for the EDM. An X-ray computed tomography (CT) was employed to examine the delaminations; while three delamination factor models provided the measuring quantities for assessment. An infrared thermography was used for monitoring the fracture behaviour of the carbon/epoxy open-hole specimens during tensile testing. A finite element model (FEM) computed the stress concentrations around the holes; while the Whitney-Nuismer point stress criterion employed successfully in order to predict the failure strengths of the laminates. The results indicate that the CT process is a very effective tool for capturing the delaminations from open-hole machining and showed that the 100 µs pulse duration induce lower delaminations; slightly comparable with the ones of the drilling procedure.

Experimental and Numerical Investigation on the Torsional Behaviour of Filament Winding-Manufactured Composite Tubes

The present work is focused in the examination of the torsional behaviour of composite tubes by a combined experimental and numerical approach. Glass and carbon composite tubes were manufactured by the filament winding technique. All the tubes were fabricated with glass and carbon Fiber orientation at ±45°. The effect of the torsional loading on the mechanical strength of the glass and carbon composite tubes was initially studied experimentally. Angular velocity of 5° per min was used as torsion test speed while torque-twisting angle changes were recorded. The torsional behaviour of composite tubes was also simulated using Finite Element Analysis (FEA). An elastic orthotropic composite model was used for the simulations. The normal and shear stress contours were obtained from the FE models, while the theoretical relation of the torque versus the twisting angle was calculated. Comparison of the numerical and experimentally obtained results has shown a relatively similar torsional behaviour.

Experimental Analysis of Ti6Al4V Orthogonal Cutting

The chip formation mechanism in orthogonal cutting is a phenomenon that attracts the attention of many researchers. This paper investigates experimentally the orthogonal cutting of Ti6Al4V at different cutting conditions aiming at the understanding of the chip formation mechanism. Serrated chip formation is obtained during orthogonal cutting of Ti6Al4V in a wide range of cutting speeds. The results are analyzed in order to extract useful indices relevant to chip geometry, as the adiabatic zone angle and other dimensions that describe the serrated chip. The cutting forces and the acoustic emission are measured. Finally, by the aid of 3D Computed Tomography (CT) the chip morphology is analyzed to better understand the segmentation process.

Orthogonal Cutting of Ti6Al4V Alloy Using Experimental and Theoretical Analysis

The current paper deals with the orthogonal cutting of Ti6Al4V alloy. Initially, the cutting process is simulated using the Finite Element Method (FEM). Various cutting conditions including cutting speed and feed rate are considered. Based on this computational analysis the chip creation mechanism is studied. The simulation results describe adequately the chip generation and flow, delivering quantitative data concerning temperature and stress distribution, as well as chip geometry. In addition, orthogonal cutting experiments are conducted on a CNC lathe machine with the same cutting conditions. The experimental results are compared with the analytical ones and useful conclusions regarding the chip formation can be drawn.