Blasting Erosion Arc Machining Research Articles

Study of arc behavior and machining effects of the novel magnetic field assisted blasting erosion arc machining method

Electrical Arc Machining (EAM) is a high-efficiency, cost-effective method for machining electrical conductive materials especially difficult-to-cut ones. Because this thermal process relies on high-density energy to melt and remove material, effective arc control is crucial to maintain stable machining without overheating the workpiece. However, due to the limited discharge gap, it is difficult for the existing arc breaking methods to manage the arc plasma in a timely and uniform manner. This paper proposes a novel method named Magnetic Field Assisted Blasting Erosion Arc Machining (M-BEAM). This method introduces a magnetic field to enhance the control effect on arc plasma by directly influencing charged particles. Initially, the arc control and material removal mechanisms were revealed through an analysis and experiments of single arc discharge. Both simulated particle trajectory and high-speed photographs demonstrated that the arc plasma deflects much earlier in the magnetic field than that of traditional BEAM. Moreover, the expulsion effect of molten metal was significantly improved, resulting in a larger volume crater. Building on this, the magnetic-assisted arc control mechanism was utilized to enhance the performance of BEAM. Experimental results indicate that compared with traditional BEAM, Magnetic Field assisted BEAM increases its Material Removal Rate (MRR) by 10.09% while significantly reducing the Tool Wear Ratio (TWR) by 29.02%. Additionally, surface roughness (Sa) is decreased by 47.73%, and the thickness of the recast layer is decreased by 78.54%. Therefore, M-BEAM can further improve the machining performance and build a good foundation for subsequent machining.

Experimental study of processing γ-TiAl by blasting erosion arc machining

γ-TiAl alloy is an ideal material for aerospace components due to its low density, high specific strength and outstanding oxidation resistance at high temperature. However, γ-TiAl is difficult to cut because of its high temperature strength, poor plastic toughness as well as low thermal conductivity. Blasting Erosion Arc Machining (BEAM) has an excellent performance in processing difficult-to-cut materials such as nickel-based superalloy and titanium alloy. Thermal machining model simulated in COMSOL Multiphysics shows the feasibility of processing γ-TiAl by BEAM. Machining experiments are designed to study the effects of different machining parameters (open circuit voltage, electrode diameter, cutting depth) on the machining performance. The experimental results show that the maximum material removal rate can reach up to 4,484.9 mm3/min, the tool wear ratio being 2.74%, and the surface roughness Sa is 74.14 μm, when the peak current is 400 A. Material removal rate is mainly affected by cutting depth. Tool wear ratio is mainly affected by electrode diameter. Surface quality is sensitive to all three parameters. Suitable processing parameters should be selected when different processing objectives are pursued. Considering the recasting cutting depth (< 50 μm) and residual stress influence depth (about 400 μm) after BEAM, it is recommended to reserve at least 500 μm thickness allowance for subsequent processing.

Improving surface quality in BEAM with optimized electrode

Blasting erosion arc machining (BEAM) introduces a high-efficiency and low-cost machining technique in dealing with difficult-to-cut materials. Despite its high machining efficiency, the machined surface is quite rough. It leads to an excessive allowance for subsequent processing. This paper presents an optimized tool electrode design that enables an enhanced hybrid arc breaking mechanism. Both flow field simulation and machining test verify that the optimized electrode can guarantee a much better gap flow field and debris expelling effect. The corresponding machined surface is significantly improved in aspects of surface roughness, smoothness, uniformity, recast layer as well as heat affected zone.

Study on Residual Stress of Blasting Erosion Arc Machined Ti6Al4V and TiAl Alloys

In this paper, Blasting Erosion Arc Machining (BEAM) was applied to perform high efficiency rough machining of difficult-to-cut materials such as Ti6Al4V and TiAl alloys. In order to investigate the influence of BEAM on workpiece surface quality and material properties, the formation mechanism of residual stress was studied based on simulations and experiments. First of all, a thermo-elastoplastic simulation model was established to predict the residual stress after discharging. Then, a single arc discharge experiment was carried out under different discharge parameters. The results showed that after discharging, a high tensile residual stress existed on the surface, and the peak value increases with the increasing of discharge energy. The highest tensile residual stress of Ti6Al4V could reach up to 679 MPa when the peak current was 500 A and the pulse duration was 8 ms. The residual stress of Ti6Al4V decreases rapidly beneath the machined surface and is close to the material matrix at the depth of 700 μm. But for TiAl, the residual stress increased first and then decreased with increasing depth. A probable reason for the difference is that longer and wider cracks existed on the surface of TiAl and they can release residual stress partially. The simulation predicted the large tensile residual stress and the trend of residual stress distribution, which agrees well with the experiment results.

Modeling of flow and debris ejection in blasting erosion arc machining in end milling mode

Blasting erosion arc machining (BEAM) is a typical arc discharge machining technology that was developed around 2012 to improve the machinability of difficult-to-cut materials. End milling BEAM has been successfully developed and preliminarily applied in industry. However, owing to the high complexity of the flow field and the difficulty of observing debris in the discharge gap, studies of the flow and debris in end milling BEAM are limited. In this study, fluid dynamics simulations and particle tracking are used to investigate the flow characteristics and debris ejection processes in end milling BEAM. Firstly, the end milling BEAM mode is introduced. Then the numerical modeling parameters, geometric models, and simulation methods are presented in detail. Next, the flow distribution and debris ejection are described, analyzed, and discussed. The velocity and pressure distributions of the axial feed and radial feed are observed; the rotation speed and milling depth are found to have almost no effect on the flow velocity magnitude. Further, debris is ejected more rapidly in the radial feed than in the axial feed. The particle kinetic energy tends to increase with increasing milling depth, and smaller particles are more easily expelled from the flushing gap. This study attempts to reveal the flow field properties and debris ejection mechanism of end milling BEAM, which will be helpful in gaining a better understanding of BEAM.

A novel tool design procedure for arc sweep machining technology

ABSTRACTElectric arc sweep machining is a thermal process derived from blasting erosion arc machining specialized for high efficient open channel machining. In this technology, high pressure inner flushing undertakes a critical role in plasma arc control and evacuating debris from craters. Hence, to find the best tool design procedure, contour of effective fluid velocity distribution in the gap distance is simulated for different flushing hole patterns and then, experiment conducted to measure machining performance. Empirical findings demonstrated higher material removal rate relative to bigger effective flushing region. Based on this, principle of tool design optimization is introduced when d = 3 mm is the best flushing hole diameter arranged along the centerline and holes with d = 2 mm are located symmetrically adjacent to the centerline.

High performance hybrid machining of γ-TiAl with blasting erosion arc machining and grinding

The excellent high temperature performance of gamma titanium aluminium (γ-TiAl) intermetallic not only makes itself a promising aero-engine material to replace Ni-based supperalloys but also poses machining challenges. A novel hybrid machining process namely blasting erosion arc grinding (BEAG) is proposed to process γ-TiAl. In this process, a creatively designed tool is implemented to perform high efficiency blasting erosion arc machining (BEAM) with an electrode and further polish the arc machined surface with the grinding part simultaneously. The experimental results illustrate that compared to BEAM and grinding, BEAG obtains a considerable material removal rate with a good surface quality.

Electric arc sweep milling of open channels

Electric arc sweep milling is an arc machining process derived from blasting erosion arc machining (BEAM). Purpose of this technology is to increase machining performance of open channels which are extensively used in blisks. In this process, a tool electrode slides above the workpiece surface layer by layer and erodes material by thermal effect to form a complete groove. In this paper, capability of this process is studied initially and effects of input energy on material removal rate (MRR), tool wear ratio (TWR), surface roughness as well as cross section morphology are investigated and the MRR can reach up to 8000 mm3/min with TWR of 2.9%. Based on principle of electric arc sweep milling, in order to machine a groove, there are different possibilities for tool pathway. Therefore, influence of two different tool pathways for machining a simple groove is proposed. Comparison of reciprocating and rectangle pathway shows that in the latter, machining performance improves. The reason is wider clearance between tool electrode and groove wall in rectangle tool pathway that enhances fluid flow and debris particle evacuation in the gap. Therefore, to achieve a good machining result, tool pathway should also be considered for a better fluid distribution.

Observation and analyzation of plasma channel evolution behavior in air flushing electrical arc machining

Blasting erosion arc machining (BEAM) is a novel and promising electrical machining process for difficult-to-cut material processing. In this research, air is applied as an alternative dielectric to investigate the feasibility of dry BEAM. An arc plasma observation experiment is designed and conducted based on a four-channel intensified charge-coupled device (ICCD) high-speed camera in order to observe and investigate the arc plasma expansion and deflection behavior. Furthermore, the influence of the aerodynamic force on plasma column deflection is also studied through comparing the images under different airflow velocities. Voltage and current waveforms were captured to verify the positive effect of air flushing on plasma channels’ deflection behavior. Additionally, crater geometries on the workpiece and electrodes were also observed and discussed as a means to analyze the effect of airflow on machining characteristics. The experimental results reflected that aerodynamic arc disturbing mechanism can be realized in air flushing BEAM, which is a promising process of working fluid for BEAM.

Influence of reinforcement particles on the mechanism of the blasting erosion arc machining of SiC/Al composites

Electrical arc machining has shown its remarkable efficiency in processing difficult-to-cut materials, especially high-temperature alloys and metal-based composites. Despite several studies about the material removal mechanisms of the electrical arc machining of metal alloys, few of these reports relate to the mechanism of machining composites with electrical arcing. Considering that reinforcements such as SiC particles have different thermal and electrical properties with metal alloys, research on the influence of SiC reinforcement on the electrical arc machining process is important and necessary. Based on comparison experiments using 20 and 50 vol.% SiC/Al composites, this research focused on the influence of SiC particles on the machining performance and material removal mechanism of blasting erosion arc machining (BEAM), and further analyzed the influence of reinforcements on composite material removal mechanisms. Analysis revealed that the molten material expelling mechanism is also influenced by the SiC fraction difference. For the BEAM of lower SiC fraction composites, both the SiC particles and the molten aluminum are mainly pumped and ejected by the flushing dielectric. In greater SiC fraction composites, most SiC particles are directly sublimed by heat. In addition, the mechanism of BEAM in the material removal and tool wear of SiC/Al composites was discussed based on heat transfer simulation and observation. Furthermore, the results disclosed that many chemical reactions take place during machining that have an obvious influence on the tool wear rate.

Combined machining of SiC/Al composites based on blasting erosion arc machining and CNC milling

In this study, a combined method is proposed for the machining of SiC/Al matrix composites to achieve high efficiency and better surface quality based on blasting erosion arc machining (BEAM) and computer numerical control (CNC) milling. The combined method consists of two stages. BEAM is adopted in the first stage to achieve a high machining efficiency. During this stage, the negative BEAM is used for improving material removal rate (MRR) while positive BEAM is adopted to reduce roughness of machined surface. In the second stage, CNC milling is utilized to achieve a fine surface. Firstly, in order to perform the combined processing, a special machine tool system is designed. Secondly, machining efficiency of the combined processing is discussed. It is disclosed that in the negative BEAM step, when peak current is 600 A, MRR of 20 vol.% SiC/Al and 50 vol.% SiC/Al composites can be as high as 10,200 and 7500 mm3/min separately. Thirdly, comparison experiments are designed and surface integrity (e.g., surface topography, surface roughness, heat affect zone, surface hardness, compositions) of each machining stage is analyzed. It is demonstrated that in the CNC milling stage, side effects of BEAM on the workpiece (e.g., rough surface, thick heat affect zone) can be eliminated effectively. The roughness of the machined surface can be lower than Ra 0.5 μm; heat affect zone (HAZ) and debris almost cannot be observed. Finally, a SiC/Al workpiece is machined to demonstrate the advantages of the combined machining of SiC/Al matrix composites.

Influence of Gap Air Flushing on Plasma Channel and Crater Geometry in Single Blasting Erosion Arc Discharge

Blasting erosion arc machining (BEAM) is a promising method for machining difficult-to-cut materials. In BEAM, high pressure inner flushing is implemented to increase machining efficiency in terms of material removal. However, effects of flushing on plasma arc evolution and material removal mechanism in BEAM are still unknown. In this research, air was blown to a single arc discharge as an alternative to water based dielectric in BEAM process. Using an ultra-fast four channel ICCD camera, influence of cross directional air jet on plasma channel development and crater formation was studied. Observation showed that plasma arc channel is obviously disturbed in presence of high speed air flushing. In other word, arc plasma column moves along the air flushing direction. Consequently, crater geometry and electrode wear will highly be influenced by air flushing in the gap. High speed air flushing increases molten metal flushed away from molten pool compare to the stationary air medium condition. This indicates that there is a decrease in recast layer on machined surface and as a result, volume of removed material will increase. Moreover, using high speed air flushing in single arc discharge decreases tool electrode wear volume significantly. Finally, based on the experimental results and theoretical analysis, high speed air flushing proves aerodynamic arc disturbing phenomenon during single arc discharge which is a potential evident to hydrodynamic arc breaking mechanism in BEAM.

Modeling study of the hydrodynamic arc breaking mechanism in BEAM

Blasting erosion arc machining (BEAM) utilizes thermal effect of the arc rather than spark to remove workpiece material. This paper investigates the expansion and distortion rules of the discharge channel based on the analysis of high speed photography and the micrographs of craters to study mechanism of BEAM. Based on these investigations, a thermal finite element model is developed. Then the temperature distributions in workpieces, both with and without flushing, are obtained. The comparisons of the obtained temperature distributions explain the formation of the trailing crater and the effect of hydrodynamic arc breaking mechanism on the efficiency of BEAM.

High efficiency blasting erosion arc machining of 50 vol.% SiC/Al matrix composites

Blasting erosion arc machining (BEAM) is adopted to improve the machining efficiency of high fraction (50 vol.%) SiC/Al matrix composites. Results of the fractional factorial experiments and full factorial experiments indicate that the electrical parameters (peak current, pulse duration and pulse interval) are the main impact factors of the machining efficiency, and when the peak current is 500 A, the pulse duration is 8 ms and the pulse interval is 2 ms, the material removal rate reaches to 6000 [Formula: see text]/min. Furthermore, the material removal rate was optimized and could be as high as 7500 [Formula: see text]/min with the tool wear ratio about 10%. Simulation of the single discharge heat transfer illustrates that the SiC particles have negative influence on the machining performance due to their temperature dependent characteristics. The polarity effect was also studied and it is disclosed that different machining polarities have different influences on the machining performance, surface integrity and even the formation of SiC particles. Finally, a 50 vol.% SiC/Al workpiece was machined with blasting erosion arc machining.

Blasting erosion arc machining of 20 vol.% SiC/Al metal matrix composites

Machining of metal matrix composite is a big challenge in industry for the high cutting tool cost and limited machining efficiency. In this study, blasting erosion arc machining (BEAM) was applied to improve the machining efficiency of SiC/Al composite. The performance of BEAM under negative and positive electrode machining conditions was investigated, and two sets of 3-factor, 2-level full factorial experiments were conducted to disclose the effects between the machining parameters. When the peak current was 500 A and the tool polarity was negative, the obtained MRR (material removal rate) was greater than 8270 mm3/min, and the TWR (tool wear ratio) was about 2 %. The competitive efficiency and economy of BEAM indicate the potential of electrical arcing in handling difficult-to-cut composite materials. The optimization of machining conditions can result in a high MRR which arrived to 10, 200 mm3/min, and the specific MRR was nearly three times of that of EDM. Furthermore, it was disclosed that the MRR in both negative and positive machining was sensitive to the peak current, pulse duration, and pulse interval while the TWR was appeared to be stable as the machining conditions varies within a certain range. The surface topography of the machined workpiece indicates that compared to the negative BEAM, positive BEAM creates a smoother surface under the same machining conditions. Furthermore, in order to study the influence of SiC particles on the machining performance, a complementary experiment was conducted to compare the craters formed on 20 vol.% SiC/Al and pure aluminum. Based on the comparison results, it can be deduced that the discharging condition is possibly influenced by the SiC particles and result in smaller craters. Finally, a workpiece was machined to demonstrate the advantages of BEAM for the machining of SiC/Al composites.

Research on the Surface Quality of the Blasting Erosion Arc Machined Stainless Steel

The Blasting Erosion Arc Machining (BEAM) process is a novel process to efficiently remove the difficult-to-cut materials. Preliminary experiments show that the quality of the machined surface is influenced by the processing parameters including the discharge energy, flushing pressure and discharge polarity. In this paper, a 3-factor, 2-level full factorial experiment was conducted to investigate the influence of the processing parameters on surface roughness with BEAM of stainless steel. The experimental results show that the surface roughness increases with the raising peak current and pulse duration, and declines with the raising flushing pressure. Furthermore, a set of comparative experiment was designed to evaluate the integrity of the stainless steel surface machined with positive and negative polarity BEAM. The experimental results indicated that the negative BEAM results in a rough surface and the Ra was up to 55μm, the heat-affected zone was about 13μm and the recast layer was detected. On the contrast, positive BEAM could achieve a better surface and the Ra was less than 9.5μm, the heat-affected zone was less than 5μm and the recast layer was scarcely seen. In addition, comparing with negative BEAM, the positive BEAMed surface was smoother and brighter.

Investigation of hydrodynamic arc breaking mechanism in blasting erosion arc machining

Blasting erosion arc machining (BEAM) greatly improves the material removal rate (MRR) by utilizing the electrical arcs instead of sparks as in EDM. However, the mechanism in BEAM is still not fully understood. By observing and diagnosing the electrical arc generated in a single pulse, the arc temperature is determined and hydrodynamic arc breaking mechanism that can effectively prevent the arcing damage is observed. Furthermore, this paper compares the craters obtained in negative polarity BEAM with that in positive polarity BEAM and explains why the former results in a higher MRR and the latter leads to a better machined surface.

Blasting Erosion Arc Machining of Turbine Blisk Flow Channel with Laminated Electrode

This paper presents a new process for machining the flow channels of wide gap shrouded blisk. It utilizes the blasting erosion arc machining (BEAM) process with laminated electrode which contains a number of curved flushing holes. The laminated electrode is an integration of several layers (slices) of electrode plates. As a strong inner flushing in the gap is the prerequisite for the hydrodynamic arc breaking mechanism for BEAM, curved flow slots are machined on each electrode plate surface to enable the working fluid to flow through and perform a strong inner flushing. Machining experiment with laminated electrode was carried out to demonstrate the feasibility of this novel machining technology. By optimizing the contour profile of the laminated electrode, the geometry of the inner slots as well as the feeding path, a stable and continuous electro-arcing process of BEAM was achieved and a blisk channel was machined efficiently.

Observation and modeling research of high-velocity flushing effect on the performance of BEAM

Blasting erosion arc machining (BEAM) is a novel high efficiency electrical erosion process, which is characterized by a powerful multi-hole inner flushing. In order to study the influence of the high-velocity flushing on the performance of BEAM, a single discharge experiment is carried out on a specially designed observation apparatus, and the phenomena that occurred during the discharge is observed using a high-speed video camera. During the discharge process, a spray cloud of the removed debris near the downstream side of the discharging point is captured by the camera. Tail shaped crater and erosion-corrosion features are also found on the workpiece and electrode surfaces, respectively. These observed phenomena imply that the high-velocity flushing can greatly improve the melting metal removal from the molten pool thereby improving the material removal rate (MRR). For purpose of exploring the mechanism behind, the flow field and pressure distribution of the high-velocity flushing are analyzed by using computational fluid dynamic (CFD) method. The analyzed results indicate that a low-pressure suction effect exists on the downstream side of the electrodes. With the help of the low-pressure suction effect, the high-velocity flushing can continuously take the molten metal out of the molten pool during the discharge, resulting in the reduction of the overheating of the molten metal and improve the efficiency of the discharging energy. Thereby, the work in this paper helps to explain why the high-velocity flushing can markedly promote the material removal rate.

Influence of flushing holes on the machining performance of blasting erosion arc machining

Blasting erosion arc machining is a novel electrical erosion process depending on the hydrodynamic arc-breaking mechanism to achieve a reliable high-efficiency machining. In blasting erosion arc machining, the high-velocity fluid field in the discharging gap is the precondition of the mechanism to control arc plasma to efficiently remove workpiece material. Therefore, this study mainly investigates the influence of flushing holes on the fluid field distribution directly and on the machining performance indirectly. Three multi-hole solid electrodes with different types of flushing holes are designed out according to the distributing principle. The influence of their flushing holes on the fluid field is conducted by a comparison fluid simulation which demonstrates that the electrode with flushing-hole diameters decreasing gradually from the inner to the outer in the radial direction attains the best flushing velocity distribution on the workpiece surface. Furthermore, the influence of their flushing holes on the blasting erosion arc machining performance is investigated by a comparison machining experiment in order to verify the comparison results of fluid field simulation. The experimental results illustrate that these electrodes have very different machining performance when machining nickel-based high-temperature alloy GH4169 (similar to Inconel 718) under the conditions of same discharge peak current and flushing inlet pressure. The electrode with the best flushing velocity distribution rather than with the highest velocity at a particular point achieves the best machining performance of the highest material removal rate, the least relative tool wear ratio and the least surface roughness (Ra), indicating an optimized design of flushing holes in the multi-hole solid electrode.