Volumetric Relative Wear Research Articles

Interfacial bonding and wear behavior of macroscopic TiC particulates reinforced iron-based composites fabricated by infiltration casting process

In this study, the interfacial bonding, mechanical properties and wear behavior of TiC particulates reinforced iron-based composites fabricated by infiltration casting process were investigated. TiC serves as a carbon source to formed (Fe,Cr)7C3 nearby, which facilitates the formation of metallurgical bonding between TiC and iron matrix. The maximum hardness values of TiCP zone for different specimens are over 3 times higher than iron matrix. The morphological changes of composites in real-time during three-body wear process were presented “shadow effect” and “peak-valley phenomenon”. The volumetric relative wear resistance of TiCP/Fe composites with different content of TiC particles increased by 18.2–66.7 % compared with matrix. This work contributes to the potential of millimeter-level TiC as a reinforcement particle of composites in industrial application.

Influence of different grades of CuW electrodes when die sinking ED-machining of cemented carbide

This work investigates the influences of two different grades of copper–tungsten (CuW) electrodes with 65% and 85% of tungsten when sinking ED-machining cemented carbide (WC-Co) with 10% Co. In EDM, literature research works evaluating the influence of different grades of CuW electrodes when ED-machining the same WC-Co workpiece material were not found. In this work, rough, semi-finish, and finish EDM regimes were applied to evaluate process performance aspects as material removal rate (Vw) and volumetric relative wear (ϑ). Workpiece surface integrity was evaluated in terms of surface roughness, hardness, and chemical composition. From the results, the CuW85 electrode presented lower volumetric relative wear (ϑ) and higher material removal rate (Vw) than that of CuW65 electrode. Micro-cracks, from recast layer in direction to heat affected zone, were observed for both grades of CuW electrodes for rough ED-machining. Nanoindentation showed a hardness reduction of about 10% in heat-affected zone in relation to the base material for finishing regime with both CuW electrode grades. EDS revealed that the presence of Co and WC was not altered in recast layer and heat-affected zone.

Study of alternating current flow in micro-EDM through real-time pulse counting

Following the general guidance on the influence of the machining polarity in micro-EDM, usually a straight polarity is applied (with the tool electrode being connected to the negative pole of the generator output), since the bombarding of the “light” electrons on the workpiece is assumed to be the primary material removal mechanism. Therefore, a flipping of the polarity in the micro-EDM machining process shall result in a high volumetric relative wear, which has been experimentally verified. The initial objective of this research is to reduce the tool wear by inserting a diode in the discharge circuit to block the reverse current flow. However, in the experiments an even higher volumetric relative wear has been observed with the inclusion of a diode. To investigate in depth the influence of the alternating current flow on the tool-material interaction, a pulse counting method based on the detection of the current peak has been proposed to count the number of effective pulses. This counting of the effective sparks enables the subsequent analysis of the mean material removal per discharge and tool wear per discharge. The analysis of the measurements obtained in both sparking cases, with a diode and without a diode, indicates that the reverse current is contributing positively to the material removal on the workpiece and the volumetric relative wear. Therefore, it is not economically proper to block the reverse the current flow in micro-EDM milling. At lower open voltage, the simple empirical linear model without reverse current flow can still serve as a reference for the in-situ tool wear prediction and the subsequent tool wear compensation. However, a correction to the model has to be made at a setting of higher open voltage.

Development and application of new composite materials as EDM electrodes manufactured via selective laser sintering

The cost of a part manufactured by electrical dischargeEDM machining (EDM) is mainly determined by electrode cost. The production of electrodes by conventional machining processes is complex, time consuming, and can account for over 50 % of the total EDM process costs. The emerging additive manufacturing (AM) technologies provide the possibility of direct fabrication of EDM electrodes. Selective laser sintering (SLS) is an alternative AM technique because it has the possibility to directly produce functional components, reducing the tool-room lead time and total EDM costs. The main difficulty of manufacturing an EDM electrode using SLS is the selection of an appropriate material, once both processes require different material properties. The current work focused on the investigation of appropriate materials that fulfill EDM and SLS process demands. Three new metal-matrix materials composed of Mo–CuNi, TiB2–CuNi, and ZrB2–CuNi were developed and characterized. Electrodes under adequate SLS conditions were manufactured through a systematic methodology. EDM experiments using different discharge energies were carried out, and the performance evaluated in terms of material removal rate and volumetric relative wear. The results showed that the powder systems composed of Mo–CuNi, TiB2–CuNi, and ZrB2–CuNi revealed to be successfully processed by SLS, and the EDM experiments demonstrated that the new composite electrodes are promising materials. The work also suggests important topics for future research work on this field.

Performance and Surface Integrity of Ti6Al4V After Sinking EDM with Special Graphite Electrodes

Titanium and its alloys have high chemical reactivity with most of the cutting tools. This makes it difficult to work with these alloys using conventional machining processes. Electrical discharge machining (EDM) emerges as an alternative technique to machining these materials. In this work, it is investigated the performance of three special grades of graphite as electrodes when ED-Machining Ti6Al4V samples under three different regimes. The main influences of electrical parameters are discussed for the samples material removal rate, volumetric relative wear and surface roughness. The samples surfaces were evaluated using SEM images, microhardness measurements, and x-ray diffraction. It was found that the best results for samples material removal rate, surface roughness, and volumetric relative wear were obtained for the graphite electrode with 10-μm particle size and negative polarity. For all samples machined by EDM and characterized by x-ray (XRD), it was identified the presence of titanium carbides. For the finish EDM regimes, the recast layer presents an increased amount of titanium carbides compared to semi-finish and rough regimes.

Aspects of Finite Element Analysis of Microdrilling by Ultrasonically Aided EDM and Related Knowledge Management

Ultrasonic vibrations of electrode-tool and workpiece were applied successfully in specific cases to increase some parameters at micro-EDM, this working mode being characterized through machining instability due to vary narrow working gap. Our researches proved that all main technological parameters of micro-EDM can be improved by ultrasonic aiding (μEDM+US) in terms of machining rate, volumetric relative wear and surface roughness if some optimization conditions of working parameters are fulfilled. A multiphysics Finite Element Analysis (FEA) of material removal mechanism was achieved using two time dependent modules of Comsol 4.2 in order to attain the working parameters optimization. The FEA results compared to experimental data aiming at model validation led to some useful measures to optimize the working parameters. The knowledge management process was approached in order to suggest how human resource from an organization that uses μEDM+US can apply and improve the research results. Our EDM+US strategy is based on relative long pulse time with very low current overlapped on collective bubbles implosion occurring at the final of a liquid ultrasonic stretching semiperiod, and relative low consumed power on ultrasonic chain, contributing to increase the main output technological parameters mentioned above.

Performance of sinking EDM electrodes made by selective laser sintering technique

Electrical discharge machining (EDM) is a nonconventional machining process widely applied for the manufacture of intricate shapes in hard materials which are not easily machined by conventional machining processes. The production of geometrically complex EDM electrodes is difficult, time consuming, and it can account for about 50 % of the total process costs. Selective laser sintering (SLS) can be an alternative technique to produce EDM electrodes in a faster way. This work conducted an experimental study on the performance of EDM electrodes made by SLS using pure copper, bronze–nickel alloy, copper/bronze–nickel alloy, and steel alloy powders. Important EDM performance measures such as material removal rate and volumetric relative wear were investigated and discussed for finishing, semifinish, and roughing regimes. This work contributes with an insight into the production of EDM electrodes via selective laser sintering, as an alternative technique to conventional machining processes, as well as to evaluate the performance of the electrodes, and also provide directions for future research on this field.

Solutions for technological performances increasing at ultrasonic aided electrodischarge machining

The paper deals with researches concerning phenomenology and solutions for technological parameters improvement at finishing through electrodischarge machining (EDM) aided by ultrasonic (US) longitudinal vibrations of electrode-tool (EDM + US). The stability of EDM + US finishing process was obtained increasing the working gap through ignition voltage growing and amplitude decrease of US oscillations. Pulse energy minimization aimed to reduce the craters volumes produced by discharge. We used consumed power values to supply the acoustic chain (PcUS) so the created acoustic pressure was over the cavitation threshold, but simultaneously, the PcUS value was minimized in order to not damage the surface quality and even to reduce the surface roughness. The number of discharges within an oscillation period was maximized and thus, material amount removed by ultrasonically induced cavitation was increased. Machining high content carbon and alloy elements materials by frontal flat surface electrodes improves volumetric relative wear. The flexibility concerning acoustic chain construction can be increased by Computer Integrated Machining, CNC processing acoustic horns and electrodes, previously elaborated through CAD and CAE.

On precision improvement by ultrasonics-aided electrodischarge machining

The paper deals with increasing the precision by electrodischarge machining, aided by ultrasonic longitudinal vibration of the electrode tool. Increasing the dimensional precision of machined surfaces is strongly related to the decrease of volumetric relative wear. This essential parameter of electrodischarge machining depends on several input parameters, which are described in detail. Several optimization conditions, concer ning the technological input parameters, are elaborated, aiming at the maximization of the dimensional precision through volumetric relative wear. These conditions address overall parameters as acoustic pressure, discharge energy level and power supply of the ultrasonic chain. Several technological solutions are elaborated like the synchronization of pulses with tool oscillation semiperiods, decreasing the supply power of the acoustic chain and working with frontal flat surfaces of electrodes by generating complex surfaces through 3D technological movements provided by CNC machines. All these can lead to up to 50% decrease of volumetric relative wear.

The behavior of graphite and copper electrodes on the finish die-sinking electrical discharge machining (EDM) of AISI P20 tool steel

The machining parameter settings installed at CNC EDM machines are developed under optimum process conditions. Standard workpiece and electrode materials are used traditionally by machine manufacturers to establish the EDM parameter settings. However, this is not the usual situation of the tooling industry, where many different grades of workpiece and tool electrode materials are used. Consequently, the customers are required to develop their own process parameters, which normally demand many experimental tests. According to the aforementioned argument an experimental investigation on the EDM of AISI P20 tool steel under finish machining has been carried out. The tests were performed with graphite and copper as tool electrodes. Important EDM electrical parameters that influence the process performance were investigated. The measured technological outputs were the material removal rate Vw, volumetric relative wear <FONT FACE=Symbol>J</FONT> and workpiece surface finish Ra . The main conclusions can be summarized as follows: the best results for material removal rate Vw were reached when EDM with negative graphite electrodes. Graphite and copper tools presented similar results of Vw for positive polarity. For graphite and copper tools the lowest values of volumetric relative wear were achieved for positive polarity. The best surface roughness Ra was obtained for copper electrodes under negative polarity.

The influence of generator actuation mode and process parameters on the performance of finish EDM of a tool steel

The AISI P20 steel is applied by the tooling industry as material for injection molding. It is known that the EDM process parameters technology installed at the majority of CNC EDM machines do not cover some of the necessities of the tooling industry concerning process parameters for a wide range of workpiece materials. Considering this situation, the customers are required to develop their own process parameters. With respect to the above discussion an experimental investigation on the EDM of the AISI P20 tool steel under finish machining has been carried out. The material removal rate V w, volumetric relative wear ϑ and workpiece surface texture R a, which are representative of EDM performance aspects, were analyzed against the variation of some of the most important EDM electrical variables using copper tool electrodes. The results are discussed and then some appropriate process parameters for EDM of AISI P20 are suggested.

520 Geometric Simulation of Electrode Wear Based on Volumetric Relative Wear in Generating EDM

This paper presents a new geometric simulator of electrode wear in generating Electrical Discharge Machining with a rotary ball-nosed cylindrical electrode. The simulatation method is based on an assumption that the volumetric relative wear was the same everywhere in every impulse discharge and thus electrode wear can be simulated only by using geometrical processing. In this method, voxel model is adopted for geometric model of tool electrode and work piece, as result, wearing process can be represented by removing voxels which are overlapped by each other. However, removal of electrode voxel had to be suspended till a limit times which is defined by the actual volumetric relative wear. The comparison between the simulated result of the electrode wear and the measured result supports the validity and the utility of the proposed method to simulate electrode wear.

Influence of duty factor on the die-sinking Electrical Discharge Machining of high-strength aluminum alloy under rough machining

The use of high-strength aluminium alloys as material for injection molding tools to produce small and medium batches of plastic products as well as prototyping molds is becoming of increasing demand by the tooling industry. These alloys are replacing the traditional use of steel in the cases above because they offer many advantages such as very high thermal conductivity associated with good corrosion and wear resistance presenting good machinability in milling and electrical discharge machining operations. Unfortunately there is little technological knowledge on the Electrical Discharge Machining (EDM) of high-strength aluminium alloys, especially about the AMP 8000 alloy. The duty factor, which means the ratio between pulse duration and pulse cycle time exerts an important role on the performance of EDM. This work has carried out an experimental study on the variation of the duty factor in order to analyze its influence on material removal rate and volumetric relative wear under roughing conditions of EDM process. The results showed that high values of duty factor are possible to be applied without bringing instability into the EDM process and with improvement of material removal rate and volumetric relative wear.