Abdulkadir Erden

RESIDUAL STRESS STATE AND HARDNESS DEPTH IN ELECTRIC DISCHARGE MACHINING: DE-IONIZED WATER AS DIELECTRIC LIQUID

ABSTRACT Procedures and results of experimental work to measure residual stresses and hardness depth in electric discharge machined surfaces are presented. Layer removal method is used to express the residual stress profile as a function of depth caused by a die sinking type EDM. Thin stressed layers are removed from machined samples by electrochemical machining. Corresponding deformations due to stress relaxation are recorded for each removal to determine the stress profile from elasticity theory. The relational dependence of the machining parameters with residual stresses is obtained and a semi-empirical model is proposed for plastic mold steel for de-ionized water as dielectric liquid. These stresses are found to be increasing rapidly with respect to depth, attaining to its maximum value, around the yield strength, and then fall rapidly to compressive residual stresses in the core of the material since the stresses within plastically deformed layers are equilibrated with elastic stresses.

Geometry and surface damage in micro electrical discharge machining of micro-holes

Geometry and subsurface damage of blind micro-holes produced by micro electrical discharge machining (micro-EDM) is investigated experimentally to explore the relational dependence with respect to pulse energy. For this purpose, micro-holes are machined with various pulse energies on plastic mold steel samples using a tungsten carbide tool electrode and a hydrocarbon-based dielectric liquid. Variations in the micro-hole geometry, micro-hole depth and over-cut in micro-hole diameter are measured. Then, unconventional etching agents are applied on the cross sections to examine micro structural alterations within the substrate. It is observed that the heat-damaged segment is composed of three distinctive layers, which have relatively high thicknesses and vary noticeably with respect to the drilling depth. Crack formation is identified on some sections of the micro-holes even by utilizing low pulse energies during machining. It is concluded that the cracking mechanism is different from cracks encountered on the surfaces when machining is performed by using the conventional EDM process. Moreover, an electrically conductive bridge between work material and debris particles is possible at the end tip during machining which leads to electric discharges between the piled segments of debris particles and the tool electrode during discharging.

An Experimental Study on the Geometry of Microholes in Microelectric Discharge Machining

Shape and dimensional geometry of blind microholes produced by microelectric discharge machining (micro-EDM) is investigated experimentally to explore the relational dependency with respect to machining time. For this purpose, microholes are machined with machining times ranging from 1–80 min on plastic mold steel samples using tungsten carbide tool electrode and hydro carbide dielectric liquid composed of mineral and synthetic oils. All other operational machining parameters such as pulse time, gap voltage, average current, and so forth, are kept constant during machining. Depth, diametric expansions, end-tip shape, wall side parallelisms of holes were analyzed both on surface and cross-sections of the samples. Consequently, nine different end-tip shape formations were observed, and these shapes discussed on basis of dielectric liquid circulation and sparking conditions during machining. Enlargement in hole diameter was predicted by defining a band-width of 20 µm hole expansion. Moreover, parallel wall-side length was expressed as the microhole depth where 5% reduction in entrance diameter was measured at the tapered section.

Bioinspired conceptual design (BICD) approach for hybrid Bioinspired robot design process

The term “Bioinspired” represents translation of any idea, structure, process, and/or material from biological domain into engineering domain to increase human comfort. Creative and innovative engineering processes and products are the expected outputs of this approach. A systematic Bioinspired Design (BID) methodology is required to guide the translation process. This paper introduces a preliminary study on a new Bioinspired Conceptual Design (BICD) approach. The BICD aims at developing concept variants for hybrid bioinspired robots based on inspirations from multiple biological systems.

The multidisciplinary international virtual design studio (MIVDS)

The International Virtual Design Studio (MIVDS) that was originated between the Departments of Mechanical Engineering of Union College (UC) and the Middle East Technical University (METU) is now extended to include the Mechanical Engineering Department at Queens University in Canada, the Computer Systems Engineering/Electrical Engineering Department at UC, and the Electrical/Electronics Engineering Department of METU. The design teams that participate in this project are composed of various combinations of mechanical, electrical, and computer systems engineering students. Design project topics are selected to cover mechatronic concepts that force students toward mechatronic design solutions. After years of experience, it is now possible to draw some conclusions and report on the concept and implementation of the multidisciplinary IVDS (MIVDS) project. One important conclusion is that a strong combination of institutional support and multidisciplinary faculty commitment is required for project initiation. Success in MIVDS is highly dependent on well-defined project specifications, a single source of project information, incentives for students to participate, travel to participating countries, a balanced team structure, common design and productivity tools, 24-hour access to MIVDS facilities, and participation by all students in the manufacturing phase of the project.

Characteristics of Surface Damage in Micro Electric Discharge Machining of Micro Holes

Micro Electric Discharge Machining is mostly used micromachining technique for manufacturing of micro holes and mini cavities. It is a thermal material removal process achieved by application of recursive electrical sparks between two conductive materials immersed in dielectric liquid. There are many electrical and technological parameters, which are effective in the machining characteristics and machined material surface integrity. In this study, effects of pulse energy on characteristics of surface damage in micro electric discharge machining of micro holes are investigated. To observe the influences of investigated pulse forms, a series of micro-holes were machined and cut from cross sections for metallurgical examinations. Unconventional etching agents were applied to examine the metallurgical transformations using optical and scanning electron microscopy. It was observed that heat-damaged segment is composed of three distinctive layers, have relatively high thicknesses (0.2 to 10 μm) when compared with the size of the micro holes and varies noticeably with respect to drilling dept. Different morphological structures and deformations in the subsurface of micro-hole walls at several sections were illustrated. Finally, analyzed machining parameters and variation of hat damaged layer thicknesses were discussed in terms of drilling depth.