Electrical discharge machining (EDM) is a modern technology that is widely used in the production of difficult to cut conductive materials. The basic problem of EDM is the stochastic nature of electrical discharges. The optimal selection of machining parameters to achieve micron surface roughness and the recast layer with the maximal possible value of the material removal rate (MRR) is quite challenging. In this paper, we performed an analytical and experimental investigation of the influence of the EDM parameters: Surface integrity and MRR. Response surface methodology (RSM) was used to build empirical models on the influence of the discharge current I, pulse time ton, and the time interval toff, on the surface roughness (Sa), the thickness of the white layer (WL), and the MRR, during the machining of tool steel 55NiCrMoV7. The surface and subsurface integrity were evaluated using an optical microscope and a scanning profilometer. Analysis of variance (ANOVA) was used to establish the statistical significance parameters. The calculated contribution indicated that the discharge current had the most influence (over the 50%) on the Sa, WL, and MRR, followed by the discharge time. The multi-response optimization was carried out using the desirability function for the three cases of EDM: Finishing, semi-finishing, and roughing. The confirmation test showed that maximal errors between the predicted and the obtained values did not exceed 6%.

Multi-Response Optimization of Electrical Discharge Machining Using the Desirability Function

Monitoring and controlling of metal cutting processes is an essential task in any modern precision machining setup. The implementation of proper monitoring process leads to promising results in terms of cutting tool life, machining costs, and production rates. Several techniques have been used to detect, monitor, and analyze different parameters associated with the cutting processes such as cutting tool wear, chip breakage and fracture, chatter vibrations, and formation of built-up edge (BUE). In this work, a review study is presented to discuss the research activities using the acoustic emission (AE) signals to monitor and control various machining processes. The discussed work does not only present an investigation of the AE signals, measured variables, and AE sensor setup during machining processes, but also shows several methods used for analyzing and processing the AE signals. The work focuses on studies, which employed AE in monitoring, and analyzing some specific characteristics such as chip formation and morphology, surface quality, and tool wear evolution for different machining operations and materials.

Application of acoustic emissions in machining processes: analysis and critical review

Waterjet machining has attracted great attention in the conditions of hard-to-machine materials, microstructures, or complicated industrial components, and it has become well-established in all major areas of theoretical researches and already been found across the broad spectrum of technical application areas especially in the specific sectors of scientific frontiers, including the mechanical precision component, advanced functional material, intelligent automotive engineering, aerospace equipment, renewable energy science, leading medical instruments, etc. This paper reviews the historical and latest research developments and integrated applications of waterjet machining in the domains of mechanism and performances, which covers a lot of key aspects such as waterjet machining optimization, dynamic simulation and process monitoring of machining process, and the influence mechanism of waterjet machining as well. Its machining mechanism, performance capability, functional advantages, and inherent disadvantages are characterized and assessed in detail, so that the integrated applications of multifield-assisted waterjet machining can be introduced and focused thereafter. Finally, various future development prospects in all the abovementioned aspects of waterjet machining are discussed systematically and explored subsequently, which contribute to the acquirement of a series of comprehensive conclusions. This review can be used as suitable and effective tools to study and summarize the complicated correlations between waterjet machining mechanism and its actual working performances in different environmental conditions; therefore, this proposed investigation facilitates the precision manufacture or characteristic improvements of industrial product with higher efficiency and better quality in return.

Waterjet machining and research developments: a review

The hybrid micro-machining process employs simultaneous or ensuing action of two or more machining processes or takes aid of some energy assistance in material removal to enhance advantages and min...

Current status and applications of hybrid micro-machining processes: A review:

Experimental research on high-pressure abrasive water-jet cutting of a popular titanium alloy, grade 5 (Ti6Al4V), is presented. Three types of abrasive material, garnet, olivine, and a cheaper alternative—crushed glass abrasive, were investigated. The influence of basic cutting parameters such as traverse speed and concentration of abrasive on cutting depth was shown, as was the effect of the ratio of the diameter of the water nozzle to the diameter of the focusing tube on the cutting depth. A slower traverse speed resulted in a deeper depth of cut for all abrasive materials. The variation of cutting depth became irrelevant when the concentration of the jet was increased. On basic regression analysis, the cutting depth control models were formulated. The cutting efficiency and the focusing tube wear for all abrasives were compared in order to determine the degree of effectiveness for each abrasive.

Experimental research into alternative abrasive material for the abrasive water-jet cutting of titanium

The paper presents the results obtained for abrasive electro-discharge grinding (AEDG) of Ti6Al4V titanium alloy with the use of super hard grinding wheels of cubic boron nitride with a metal bond. The experimental investigations were focused on process monitoring for sharp and worn grinding wheels. For the evaluation of the grinding process, the grinding force amplitude and a few descriptors of the high-frequency stress waves were investigated in both time and frequency domains. The results show that during the AEDG, specific elastic waves are generated. Since these waves have characteristic amplitudes, frequencies, and other different descriptors dependent on the current grinding wheel cutting ability and discharge parameters, they can be applied to estimate a statistically significant regression function. For each measurement signal, a few statistical features are calculated and used as input for data selection and classification procedures. Registration and classification of forces and acoustic emission signals can be used to analyse the abrasive electro-discharge grinding process and allow for the determination of the machining results and the lifespan of super hard grinding wheels.

https://link.springer.com/content/pdf/10.1007%2Fs00170-017-1011-9.pdf

The estimation of machining results and efficiency of the abrasive electro-discharge grinding process of Ti6Al4V titanium alloy using the high-frequency acoustic emission and force signals

Purpose: This work is focused on determination of effects of grinding conditions on effectiveness of abrasive electrodischarge grinding (AEDG) process applied for removal of machining allowance and forming of surface geometrical texture (SGT). These results were compared with one obtained for conventional grinding. Design/methodology/approach: The experimental investigations of deep-seated surface grinding of Ti6Al4V titanium alloy using CBN grinding wheel with metal bond were the ground for this elaboration. The effectiveness of AEDG process was assessed based on specific tangential grinding force and energy of spark electric discharge and machining results were estimated on geometrical structure parameters. Findings: The effectiveness of machining allowance removal depended on conditions of AEDG process. Significant differences in SGT formed by AEDG process and conventional grinding were revealed. Practical implications: Abrasive electrodischarge grinding is useful to be particularly suitable for efficient and effective grinding of very hard structural materials such as high-alloy steel, sintered carbides, metal-based composite materials etc. Originality/value: AEDG experiments were carried out using the typical surface finishing grinder and especially adapted generator of spark discharge pulses. The majority of such experiments in the world were performed with the electrodischarge machine tool equipped with extra grinding wheel mounted on the grinding pin and functioning as one of the electrodes put into operation via pneumatic drive.

Experimental investigation of abrasive electrodischarge grinding of Ti6Al4V titanium alloy

In this work the results related to the influence of selected electrical parameters of the abrasive electrodischarge grinding process on the surface layer temperature and morphology of machined samples in comparison to the conventional grinding method are presented. The basis of this work has been investigations of the deep grinding of surfaces of the samples made of titanium 5553 β, Inconel 617, Hastelloy X and magnesium AZ31 using a cubic boron nitride (CBN) grinding wheel with metallic binding agent. For the comparative evaluation of the conventional grinding and abrasive electrodischarge grinding, measurements of the specific grinding energy, temperature on the surface layer (at the contact of the grinding wheel‐workpiece) and geometric structure of the surface layer have been used.

/pdf/investigations-of-surface-layer-temperature-and-morphology-1y6b0ifsif.pdf

Investigations of surface layer temperature and morphology of hard machinable materials used in aircraft industry during abrasive electrodischarge grinding process

Titanium and its alloys are widely recognized as the hardly machinable materials, especially due to their relatively high hardness, low thermal conductivity and possible subcritical superplasticity. Then, a thorough control of the machining process parameters shall be maintained. In this paper, we have concentrated on the grinding of the Ti6Al4V titanium alloy using cBN (boron nitride) grinding wheel combined with the AEDG (abrasive electrodischarge grinding) process. The mathematical model we have dealt with has been based mainly on Jaeger model of the heat taking over between sliding bodies with substantial upgrades related to:


estimation of the frictional heat generating based on friction forces distribution,


spatial, not only planar, shape of the contact area,


generated heat partition between different parties of the grinding process,


heat transfer in the multilayered environment.



The experimental verification of the theoretical predictions has been carried out. Fundamental difficulty in such a research is placing temperature probes sufficiently close to the ground surface with possibly low space devoted for probes due to the temperature field deformation with relation to the real conditions of grinding. The temperature field in the machined workpiece has been investigated using electronic data logging and DSP methods. Obtained results exhibit clearly that distribution of heat generation in the contact zone could be of the relatively complicated shape due to the external cooling and the very specific heat transfer and accumulation in the titanium workpiece surface layer.

/pdf/modeling-and-research-of-temperature-distribution-in-surface-4l04pyfzps.pdf

Modeling and research of temperature distribution in surface layer of titanium alloy workpiece during AEDG and conventional grinding

W artykule przedstawiono wyniki badań temperatury warstwy wierzchniej w procesie elektroerozyjnego szlifowania (AEDG) i porównawczo w procesie szlifowania konwencjonalnego materiałów trudno-obrabialnych (stopu tytanu 6TiAl4V i węglików spiekanych S20S). W porównywanych procesach szlifowania zastosowano ściernice supertwarde ze ścierniwa z regularnego azotku boru (CBN) i diamentu syntetycznego (SD) ze spoiwem metalowym.

Robert Święcik

Papers

The estimation of machining results and efficiency of the abrasive electro-discharge grinding process of Ti6Al4V titanium alloy using the high-frequency acoustic emission and force signals

Experimental investigation of abrasive electrodischarge grinding of Ti6Al4V titanium alloy

Investigations of surface layer temperature and morphology of hard machinable materials used in aircraft industry during abrasive electrodischarge grinding process

Modeling and research of temperature distribution in surface layer of titanium alloy workpiece during AEDG and conventional grinding

Badania porównawcze temperatury warstwy wierzchniej w procesie elektroerozyjnego szlifowania (AEDG) materiałów trudnoobrabialnych