Electrical Discharge Machining Milling Research Articles

Experimental Study on the Comparison between Network Microstructure Titanium Matrix Composites and Ti6Al4V on EDM Milling.

Network microstructure titanium matrix composites (NMTMCs), featuring Ti6Al4V as the matrix and network-distributed TiB whiskers (TiBw) as reinforcement, exhibit remarkable potential for diverse applications due to their superior physical properties. Due to the difficulty in machining titanium matrix composites, electrical discharge machining (EDM) stands as one of the preferred machining techniques for NMTMCs. Nevertheless, the compromised surface quality and the recast layer significantly impact the performance of the workpiece machined by EDM. Therefore, for the purpose of enhancing the surface quality and restraining the defects of NMTMCs, this study conducted comparative EDM milling experiments between NMTMCs and Ti6Al4V to analyze the effects of discharge capacitance, charging current, and pulse interval on the surface roughness, recast layer thickness, recast layer uniformity, and surface microcrack density of both materials. The results indicated that machining energy significantly influences workpiece surface quality. Furthermore, comparative experiments exploring the influence of network reinforcement on EDM milling revealed that NMTMCs have a higher melting point, leading to an accumulation phenomenon in low-energy machining where the reinforcement could not be completely removed. The residual reinforcement in the recasting layer had an adsorption effect on molten metal affecting the thermal conductivity and uniformity within the recasting layer. Finally, specific guidelines are put forward for optimizing the material's surface roughness, recast layer thickness, and uniformity, along with minimizing microcrack density, which attain a processing effect that features a roughness of Ra 0.9 μm, an average recast layer thickness of 6 μm with a range of 8 μm, and a surface microcrack density of 0.08 μm-1.

Hybrid Additive and Subtractive Manufacturing Method Using Pulsed Arc Plasma.

In this study, a novel hybrid additive and subtractive manufacturing method using pulsed arc plasma (PAP-HASM) was developed to better integrate additive and subtractive processes. The PAP-HASM process is based on the flexible application of pulsed arc plasma. In this PAP-HASM method, wire arc additive manufacturing using pulsed arc plasma (PAP-WAAM) and dry electrical discharge machining (EDM) milling were used as additive and subtractive techniques, respectively; both are thermal machining processes based on pulsed arc plasma, and both are dry machining techniques requiring no working fluids. The PAP-HASM can be easily realized by only changing the pulsed power supply and tool electrodes. A key technological challenge is that the recast layer on the part surface after dry EDM milling may have a detrimental effect on the component fabricated by PAP-HASM. Here, the hybrid manufacturing method developed in this study was validated with commonly used 316L stainless steel. Preliminary experimental results showed that the PAP-HASM specimens exhibited excellent tensile properties, with an ultimate tensile strength of 539 ± 8 MPa and elongation of 46 ± 4%, which were comparable to the PAP-WAAM specimens. The recast layer on the surface after dry EDM milling has no significant detrimental effect on the mechanical properties of the parts fabricated by PAP-HASM. In addition, compared with components fabricated by PAP-WAAM, those fabricated by PAP-HASM showed significantly better surface roughness.

Experimental study of EDM milling of 3D-shaped diffuser for film cooling holes on turbine blades

Cylindrical and diffuser-shaped film cooling holes on aero-engine turbine blades are usually machined by electrical discharge machining (EDM) by means of drilling and die-sinking approaches in a sequence. However, this sequential machining on different types of EDM machines is prone to deteriorate the machining accuracy since the inevitable secondary clamping error. Besides, since the nature of electrode wear, the shape of the tip of tool electrode is constantly changing during machining. To ensure the geometry accuracy of the diffuser, the worn tool electrode has to be replaced or dressed online frequently, resulting in a low machining efficiency. To address these problems, this paper proposes a machining method for diffuser shaped film cooling holes by a compound approach in combination of high speed EDM drilling and milling implemented on an EDM drilling machine with tubular electrodes and high-pressure inner flush. To obtain the optimal machining parameters, experimental investigation is carried out based on the experimental design method. Machining performance in terms of longitudinal tool electrode wear ratio, machining time, and machining stability under different machining parameters, such as pulse duration, pulse interval, peak current, capacitance, spindle speed, and flushing pressure, were taken into account. And the range analysis method is then adopted to obtain an optimal set of machining parameters. By applying the obtained optimal machining parameters, the proper compensation parameter and tool path overlapping ratio of the EDM milling process can be obtained. In the milling of an inversed pyramid, the material removal rate can reach as high as 14.02 mm3/min, the relative geometrical error can be controlled within 3.58%, and the maximum recast layer thickness was 6.8μm. Machining experiments of diffuser shaped film cooling holes verify the capability and effectiveness of the proposed method.

Rotating short arc EDM milling method under composite energy field

• A new EDM milling method with rotating short arcs under composite energy field was proposed. • A mathematical model to describe the trajectory of particles in the composite field was established. • Rotating short arc was generated by the Lorentz force, the electrical force and the high-speed rotation of electrode. • The MRR of rotating short arc machining is increased by 46 % compared with traditional EDM. • An increase in the strength of the magnetic field increases the MRR and decreases the TEWR. Electrical discharge machining (EDM) is a rapidly developing technique amongst nontraditional techniques. However, low processing efficiency significantly hinders its application in industry. This study proposes a new high-speed EDM milling method using rotating short arcs under a composite energy field. By the combined effect of the Lorentz force, electric field force, and high-speed rotation of the tool electrode, rotating short arcs are generated between the tool electrode and the workpiece, which in turn provide constant erosion of materials. The proposed method can increase the discharge energy density by converging the electric arcs through the composite energy field, and increase the energy obtained by the workpiece. By this means, it improves the material removal rate. During processing, a portion of debris is attracted by the magnetic field and adheres to the end surface of the electrode, which can protect the electrode and reduce the electrode wear rate. Compared with traditional EDM, the material removal rate of the rotating short arc milling was increased by 46 %, while the tool electrode wear rate decreased by 62 %. Furthermore, an increase in the strength of the magnetic field increases the material removal rate of the rotating short arc milling and decreases the tool electrode wear rate and surface roughness. Therefore, high-efficiency and high-quality EDM milling can be achieved by using the proposed method.

Sustainable and high-efficiency green electrical discharge machining milling method

Conventional electrical discharge machining (EDM) milling methods have some disadvantages when used to machine difficult-to-cut materials, including low machining efficiency, high energy consumption, severe electrode wear, and poor processing environments. In this paper, a sustainable and high-efficiency EDM milling method is proposed for solving the above problems. A high-efficiency green pulse power supply with high energy is designed and different environmentally friendly working fluids are used for machining experiments. The energy utilization rate, environmental performance, and machining performance under different conditions of this new method are studied. The results show that the proposed method presents high machining efficiency, low energy consumption, mild electrode wear, and environmentally friendly features. The material removal rate can reach 900.66 mm3/min and the relative electrode wear rate is 1.20% when machining the 17-4 PH stainless steel workpiece. It is found that the new pulse power supply increases the energy utilization rate by more than 200%. Compared with the conventional EDM milling methods, the proposed method can meet the requirements of energy-saving and sustainable production.

Method of Machining Diffusors in Inconel 718 Turbine Blades for Film Cooling using EDM Drilling and Shaping

Electrical Discharge Machining (EDM) is a well-known process, which is mainly used to machine difficult-to-cut, conductive materials. Die-sinking EDM, wire EDM and EDM drilling are widely used in turbine blade machining. Optimization of EDM machining strategies is permanently aimed to achieve the highest precision in minimal machining time, and therefore, to reach better quality and higher efficiency. Reduction of the process chain, which is proposed in this work by performing more operations using a single machine tool, allows the reduction workpiece reclaiming and leads to positioning error minimization. The new strategy in EDM milling and shaping described in this work allows to machine complex geometries by using a standard cylindrical shape rotary electrode, which with some limitations can be used instead of the complex die-sinking electrode. This new strategy is used for complex-shaped diffusors machining in Inconel 718 turbine blades. The comparison between state-of-art layer-by-layer milling strategy and the new method is shown. Correlation of the electrode wear pattern after EDM drilling and EDM milling with the geometry of the machined cavities is applied. The presented new method is more than 15% faster in comparison with the layer-by-layer machining strategy, whereas has higher geometrical accuracy at the same time.

Microlens array fabrication on WC mold using EDM milling with in situ electrode trimming

Precision glass molding (PGM) has been developed and improved to produce various functional lenses in the optical industry. Tungsten carbide (WC) molds have received increasing attention due to the low thermal expansion coefficient and long service time but the molds are difficult to machine using micro-cutting or micro-grinding methods. Electrical discharge machining (EDM) milling is a promising method for the fabrication of WC molds used for microlens arrays but the significant electrode wear results in low machining accuracy. In this paper, a new method is proposed to address the electrode wear by utilizing in situ electrode trimming during EDM milling; the objective is to improve the accuracy of the WC mold used for microlens array fabrication. The feasibility of the proposed in situ electrode trimming method is verified by comparing the surface roughness of the pits on the mold surface fabricated by EDM milling with and without electrode trimming. In addition, the structure of the copper–tungsten electrode is redesigned to improve the electrode stiffness during in situ trimming. Furthermore, an in situ trimming setup is developed and the trimming process of the electrode is optimized.

Fabrication of micro punching mold for micro complex shape part by micro EDM

Micro punching process is suitable for mass production of micro parts. It is a challenge to fabricate micro punching mold with complex cross-sectional shape on-machine. The micro punching system’s structure design has to meet the requirement of large punching force. In this study, a micro punching system has been developed with a micro electrical discharge machining (EDM) module. A series of machining operations, from the fabrication of micro molds to punching, have been completed with no secondary clamping error. The micro die and reversed electrode are prepared using micro EDM milling. The micro punch is fabricated using reversed electrode. The punching clearance is around 11 μm. Complex shape punched holes and blanked parts have been successfully fabricated on copper, brass, 304 stainless steel, and 3J21 alloy. After punching, there was no damage on the edges of micro die and micro punch. The key dimensional error of blanked part varies by different materials, which is less than 2.5 μm.

Machining characteristics and removal mechanisms of moving electric arcs in high-speed EDM milling

Low machining efficiency is the major challenges of conventional electrical discharge machining (EDM). To resolve this problem, a novel machining method of high-speed EDM milling with moving electric arcs was developed, which can remove material continuously without discharge intervals of pulse power supply and achieve extremely low tool-electrode wear for the direct-current power supply employed. An EDM milling equipment was devised to explore machining characteristics and removal mechanisms of moving electric arcs in high-speed EDM milling process. Firstly of all, the motion characteristics of moving electric arcs were investigated. The theoretical analysis shows that the arcs maintain an independent movement relative to the tool-electrode and workpiece. Then, the plasma channels were captured by high-speed video camera, which contributed to develop the model of removal mechanisms of moving electric arcs. Finally, the machining experiments were carried out based on titanium alloy, which verified that a much higher material removal rate could be easily achieved by moving electric arc. Moreover, the tool-electrode wear in high-speed EDM milling is much lower than conventional EDM due to the protective layer formation.

Technology of ablation milling by fast-moving electrode

To improve the efficiency of conventional electrical discharge machining (EDM) milling, this study proposes a highly efficient machining method that employs continuous oxygen feeding and fast-moving electrode. High-efficiency machining is achieved by the method of feeding with small thickness, allowing the electrode suspended above the workpiece to reduce short circuit and using a high discharge probability to ignite the workpiece in order to realizing high efficiency machining with great chemical energy released from metal combustion. Comparative tests for conventional EDM milling, EDM ablation milling, and ablation milling by fast-moving electrode were performed in the milling process. In this study, we analyzed the mechanism, machining efficiency, electrode relative wear ratio, and machining quality. The machining efficiency of EDM ablation milling was 6.8 times higher than that of conventional EDM milling, and the relative tool wear ratio was 20% of conventional EDM milling; the machining efficiency of ablation milling by fast-moving electrode can reach 11.2 times higher than that of conventional EDM milling, and the electrode relative wear ratio decreased by 86%.

Improvement in machining speed with working gap control in EDM milling

High-speed electrical discharge machining (EDM) milling is investigated with working gap control. EDM milling has a merit that does not need complex electrode fabrication; however, it is necessary to improve the removal rate in EDM milling. Rotation of the electrode improves the removal rate, but this rotation causes a periodic change in the working voltage. As a consequence, the periodic change causes a disturbance that decreases the control performance. EDM milling realizes a high machining precision by the scanning method. A small working area allows for fast scanning. If the working gap is appropriate, it becomes longer because the machined surface of the workpiece is removed. Therefore, the conventional controller remains at the steady offset and lowers the machining efficiency. The proposed controller introduces a notch filter, which eliminates the frequency component due to rotation of the electrode. It also has a feed-forward compensator to eliminate the steady offset. The controller for each machining condition is derived from a coordinate transformation and the least-squares approximation. It is confirmed that the proposed controller achieves machining speeds that are 2–6 times faster in a straight line and greater than 30% higher in the profile machining than in the conventional one.

Surface integrity of Inconel 718 in high-speed electrical discharge machining milling using air dielectric

This paper proposes a novel, efficient, and environmental friendly machining method named high-speed dry electrical discharge machining (EDM) milling. The material removal rate of this method is much higher than that of conventional EDM and is also higher than that of traditional mechanical machining method for materials that are “difficult to machine.” Nickel-based superalloy Inconel 718 is widely used in the aerospace field as its surface integrity exerts significant effects. In this study, the microscopic characteristics, such as surface roughness, re-solidified layer, micro-hardness, micro-crack, and micro-void, of the machined Inconel 718 in high-speed EDM milling using air dielectric were studied compared with those using liquid dielectric. The formation mechanism of the microscopic characteristics was revealed. Experimental results showed that the machined Inconel 718 in high-speed EDM milling using air dielectric exhibited smaller surface roughness, thinner thickness of re-solidified layer, and smaller and less micro-cracks compared with those using liquid dielectric. Theoretical and technical foundations were laid for the industrial application of this novel machining method.

Fabrication of rectangle diagnostic hole in Au hohlraum using EDM-milling

The rectangle diagnostic hole on the side of Au hohlraum was machined using electrical discharge machining milling (EDM-milling) by layer technology. The zone of the EDM was controled under the electrode and the side of the electrode was not machined. The size of diagnostic hole was characterized by OLYMPUS STM6 measuring microscope. The results indicate that the dimension precision of diagnostic hole is less than 5 m.

Real time power consumption monitoring for energy efficiency analysis in micro EDM milling

Sustainability has become a major concern in many countries and is leading to strict regulations regarding the impact of products and services during their manufacturing, use, and disposal. Power consumption monitoring in manufacturing companies can lead to a reduction of machine tools energy wastes and consequently to lower expenses. To this end, a complete transparency of energy usage among the entire manufacturing facilities is required. Despite the small volume of material processed, micro manufacturing processes are energy intensive and the optimization of energy usage becomes critical for manufacturing sustainability. Electrical discharge machining (EDM) is considered an attractive solution for the manufacturing of microcomponents. In this paper, a low cost and modular data acquisition system, based on open-hardware and open-source software, for online energy consumption monitoring, is presented. The system described is applied for energy efficiency analysis of the micro EDM milling process by using a state of the art commercial machine tool. A number of sensors is connected to the data acquisition system to measure the energy consumption of the main sub-systems of the machine tool, data is recorded through a microcontroller, and sent to the main computer via Wi-Fi for data storage and analysis. Results show that the process efficiency depends on machine parameters but it is always far below 0.01 %. Solutions are suggested to improve the energy efficiency of the machine tool considered in this work.

Compound machining of titanium alloy by super high speed EDM milling and arc machining

A novel compound machining of titanium alloy (Ti6Al4V) by super high speed electrical discharge machining (EDM) milling and arc machining was proposed in this paper. The power supply consisted of a pulse generator and a DC power source which were isolated from each other. A rotating pipe graphite electrode was connected to the negative pole of the power supply. The plasma channel was able to deionize, and maximum material removal rate (MRR) reached 21,494mm3/min with a relative electrode wear ratio (REWR) of 1.7% because of high current and efficient flushing. Compared with traditional EDM, the compound machining achieved a significantly higher MRR but a similar REWR. To investigate the characteristics of the compound machining, the effects of electrode polarity, peak voltage, peak current, and flushing pressure on the performance of the process, including its MRR, REWR, and radius of overcut (ROC), were determined. In addition, scanning electron microscopy, X-ray diffraction, and microhardness analysis were conducted. Result shows that the proposed method can machine difficult-to-machine materials efficiently.

Study of Dry EDM Milling Integrated with Electrode Wear Compensation and Finishing

An experimental investigation of electrical discharge machining milling in gas combined with electrode wear compensation and finish machining is reported in this work. Comparative experiments using compressed air and kerosene demonstrated that dry electrical discharge machining (EDM) milling (EDMM) exhibits a higher processing precision than conventional EDMM as a consequence of low electrode wear. Nevertheless, appropriate electrode wear compensation is necessary under certain conditions. Considering the requirements of finishing and the presence of the electrode wear in dry EDMM (DEDMM), a decomposition segmental machining approach addressing both electrode wear compensation and finishing is proposed. Finish machining is achieved by running each numerical control (NC) program segment developed in this study twice to avoid an uneven gas distribution. The electrode wear is compensated by redefining the reference point coordinates relative to the start point coordinates using NC codes in each segment. DEDMM experiments verified the feasibility of the approach. The advantages of the method include small accumulative error, no wear calculation, and easy operation. This approach can potentially be applied to other types of EDMM because of its flexibility.

Tool wear compensation in 3D micro EDM based on the scanned area

Abstract Complex 3D micro-structures can be fabricated layer by layer in alloys by micro electrical discharge machining (EDM) using simple shaped electrodes. However, electrode wear is a serious problem which significantly affects machining accuracy. The electrode wear compensation method is a key issue in micro EDM milling and effectively solves this problem. This paper proposes a new compensation method based on the scanned area (BSA) in each layer machining. The new method is integrated with a CAD/CAM system to generate 3D micro cavities. Experimental results have been compared with those using the uniform wear method (UWM) and those using a combination of linear compensation with UWM. It was found that using the proposed method machining efficiency was improved and tool wear ratio was reduced.

Development of Strip EDM

Electrical discharge machining (EDM) is a widespread machining method for the die and mold industry. This method can machine all conductive materials, including hard-to-cut metals, because the machining process uses electro-thermal energy without a cutting force. During EDM, discharge sparks remove not only the material of a workpiece but also the material of an electrode. This machining mechanism thereby causes electrode wear, which creates serious problems, including make-shape errors and low productivity. In order to overcome such problems, a new EDM method using a strip electrode (strip EDM) was developed in this study. Strip EDM uses a continuously applied strip electrode similar to the wire electrode in wire EDM. In the suggested strip-electrode method, a conductive strip moves on the electrode guide. The worn strip is removed, and a new one is supplied continuously. Therefore, the tool electrode acquires no wear during the machining process. This method uses a conductive strip that is made of brass. In the practical machining process, the strip EDM method was applied to EDM milling and EDM turning and their machining characteristics were compared with general EDM methods.

Tool Path Planning for Near-Dry EDM Milling With Lead Angle on Curved Surfaces

This research investigates the strategy to achieve high material removal rate in tool path planning for the near-dry electrical discharge machining (EDM) milling process using tubular electrode with a lead angle. The proposed strategy to prevent leakage of dielectric mist from the tubular electrode is different from the conventional end milling process due to the difference in material removal mechanism. Tool positions and orientations to engage the electrode into workpiece, machining of workpiece edge, minimum lead angle to machine a curved surface, and minimum and maximum path interval to prevent the mist leakage are derived. Experiments are conducted to validate the model prediction of path planning. Experimental results show plunge method has the highest material removal rate for engaging method, and electrode hole must be located within the workpiece surface when edge of workpiece is machined. For curvature machining, the proposed path planning strategy yields higher material removal rate compared with that from the conventional strategy, which only avoids gouging. This study also reveals that, due to the tool wear and crowning of electrode tip, it is difficult to accurately determine the minimum path interval which will cause the mist leakage.

Fabrication of Fuel Cells with High Power Density Using Micro Electrical Discharge Machining Milling

Light and thin bipolar plates are essential in increasing the power density of a fuel cell. To construct high-aspect-ratio micro flow channels in such plates is, however, a big challenge. This study reports on machining micro flow channels in metallic bipolar plates using micro electrical discharge machining milling (micro EDMM) with a tungsten carbide electrode. We successfully machined metallic bipolar plates with 500μm channel and rib widths, height of 600μm in a reaction area of 20mm × 20mm, on 1mm thick of SUS316L stainless steel. The optimal operating parameters were explored and discussed. The performance of resulting fuel cell (Metallic-FC) was compared with a commercial available fuel cell composed of graphite bipolar plates (Graphite-FC). The high temperature of Metallic-FC increases its electrochemical reaction rate and consequently yields higher power density (723 mWcm-2) then that of Graphite-FC (687.3 mWcm-2)