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Article

Machinability of Drilling on Metallic Glass for Micro-Hole with Renewable Dielectric in an Electric Discharge Machining Process

1
Henan Key Lab of Intelligent Manufacturing of Mechanical Equipment, Zhengzhou University of Light Industry, Zhengzhou 450002, China
2
Guangdong Provincial Key Laboratory of Digital Manufacturing Equipment, Guangdong HUST Industrial Technology Research Institute, Dongguan 523808, China
*
Author to whom correspondence should be addressed.
Metals 2025, 15(4), 415; https://doi.org/10.3390/met15040415
Submission received: 28 February 2025 / Revised: 29 March 2025 / Accepted: 3 April 2025 / Published: 7 April 2025

Abstract

:
Electric discharge machining (EDM) stands out for its ability to perform no-contact machining of materials with desired forms by multi-pulse discharges. In this investigation, the machinability of drilling on Ti56Zr18Cu12, metallic glass, for micro-hole is investigated with renewable dielectrics in the EDM process. Machinability is investigated by examining performance indicators including material removal rate (MRR), overcut, edge deviation, and energy efficiency per volume (EEV) in relation to the process parameters, such as electrical and non-electrical parameters. The edges of the drilled holes are examined to investigate the micro-structural changes that occur in metallic glass as a result of micro-machining. The experimental results show that the maximal value of MRR of 0.0103 mm3/min is achieved when the pulse-on time of 30 μs and sunflower oil renewable dielectric is selected, and the minimum overcut and edge deviation of micro-hole drilling in Ti56Zr18Cu12 is 39.99 and 9.41 μm, respectively. Minimum overcut and edge deviation are obtained for colza oil, optimized by 38% and 70%, respectively, over the worst-case conditions. Multi-objective optimization on the basis of ratio analysis (MOORA) results in a 70% reduction in energy consumption of EEV compared to the conventional paraffin media process. In addition, a range of pulse-on time, pulse duty cycle, and renewable dielectric are identified using the MOORA technique while EDM drilling in metallic glass Ti56Zr18Cu12.

1. Introduction

Metallic glass is characterized by a metastable structure with long-range disorder and short-range order in the atomic arrangement and is a metallic alloy with an amorphous structure [1]. Due to its unique amorphous atomic structure, metallic glass overcomes the crystal defects of traditional crystalline alloys and exhibits excellent hardness, strength, corrosion, and wear resistance. Its homogeneous and dense microstructure effectively resists chemical attack and mechanical abrasion, demonstrating good performance in extreme environments and precision devices [2,3,4]. With the development of preparation technology, the critical size of bulk metallic glass (BMG) has gradually reached the centimeters scale and has been used in consumer electronics frames and housings [5], precision medicine [6], small functional components [7], microelectromechanical systems (MEMS) [8] and permanent magnet generators [9,10]. Morrison et al. [6] found that titanium-based amorphous alloys are closer to the modulus of elasticity of human bone, which is expected to solve the problem of mismatch between the modulus of elasticity of implants and that of human bone. Chu et al. [11] found that thin-film metallic glass coating (TFMG) surfaces have hydrophobic properties and can improve blade sharpness by about 27%.
Thermoplastic forming (TPF), also known as superplastic forming or thermoforming, is the main method for designing and manufacturing BMG parts, where it exists as a high-viscosity liquid during the forming process. Schroers et al. [12] introduced the TPF process as a manufacturing method for microelectromechanical systems and microstructures for BMG. The results showed the ability of this method to replicate features below 100 nm in a manner similar to plastics and to obtain high-strength parts with uniform, no internal stress, and porosity. In addition, Schroers [13] reviewed the processing of BMG, and found that TPF was unique in metal processing methods. However, as reported by [14], the parts made by the TPF process due to high temperature exposure lead to performance changes. Moreover, the manufacturing of composite micro geometry of mold required by the TPF process is also an arduous work [15], which limits the application in micro manufacturing of BMG.
To obtain complex geometric shapes of BMG, some researchers have studied turning, drilling, and milling processes. Bakkal et al. [16] surveyed the turning process on Zr-based BMG material and found that the machining performance of BMG was similar to that of Al6061 and SS304, and it could also obtain good machining quality. Bakkal et al. [17] discovered that when the cutting speed was higher than the critical cutting speed, the oxidation of zirconium would produce a higher flash temperature and cause crystallization, which will destroy the amorphous characteristics of the BMG material. Zhu et al. [18] conducted conventional drilling in Zr-based BMG with a thickness of 1.2 mm to produce micro-holes without crystallization. However, Bakkal et al. [17] investigated tool wear in drilling BMG and found that tool life was adversely affected by high heat generation. In addition, the high heat generated during these processes can easily lead to thermal softening of the hole, thereby deteriorating the edge and geometry of the hole. Therefore, it may not be possible to acquire the geometric shapes that meet the desired tolerances through the traditional machining methods for manufacturing BMG micro-components. Therefore, this requires further secondary finishing to achieve the required dimensional accuracy.
For precision micro-sized parts with high hardness materials and complex shapes, such as the MEMS, optical and photonic applications, fortunately, non-traditional machining methods have great applicability and development potential [19]. Ma et al. [20] investigated the Zr-based BMG materials machining performance by femtosecond pulsed lasers. At lower laser fluences, some random structures were produced on the laser spot, with almost no melting marks. However, under high laser fluences, part of the re-solidification liquid flow produced a bulge in the irradiation center, which could be caused by the intense thermal ablation process. Since BMG is very sensitive to temperature changes, the thermal process in the laser process may cause BMG to crystallize and oxidize, thereby destroying its amorphous structure [21]. Kuriakose et al. [22] adopted the ultrasonic machining method to realize the micro-hole for Zr-based metallic glass. Experiments demonstrated that the ultrasonic machining had no effect on the amorphous structure of these materials. However, compared with other machining methods, the efficiency of ultrasonic machining method is low and the machining time required is long. Other non-traditional machining processes, such as plasma machining [23,24], electron beam machining [25,26], and hybrid machining [27] have their own set of benefits and drawbacks, according to various studies. Fortunately, among the various micromachining methods, electric discharge machining (EDM) stands out for its ability to perform no-contact machining of materials with desired forms by creating a pulse discharge channel with a temperature of more than 10k degrees, which melts and vaporizes the materials.
Thereafter, Yeo et al. [28] performed a series of studies to show that micro-EDM may be adopted to fabricate microslots/microgrooveson a Zr-based BMG surface. Experimental results revealed that with a low discharge energy (0.9 µJ), the surface roughness, and the burr width were reduced by 43–51% and 63%, respectively. Huang et al. [29] performed an experimental study on the micro-EDM performance of Zr-based BMG using different electrical parameters through orthogonal experiments. They found that the size and distribution of the discharge craters produced after micro-EDM strongly depended on the electrical parameters and their positions, which in turn affected the surface roughness. In addition, they found that micro-EDM under low discharge energy could maintain an amorphous structure while cutting the Zr-based BMG materials. Zhang and Huang [30] reviewed micro-machining BMG by the EDM process, and the literature revealed that because of its high MRR and ability to almost preserve the amorphous structure, micro-EDM had a lot of potential for BMG micro-machining.
Conventional EDM generally uses creosote as the dielectric medium, which generates 53 different gases, of which 13 and 40 types (including hazardous substances such as benzene and toluene) are below and above C6, respectively [31,32]. Fortunately, several researchers have discovered that utilizing vegetable oil as an EDM dielectric might reduce hazardous gas emissions while simultaneously increasing machining efficiency [33,34,35]. Therefore, for the EDM of BMG materials, the existing research rarely involves important hole features such as hole overcutting and edge deviation, especially since the processing of Ti-based BMG materials is even rarer. In addition, studying the feasibility of the BGM materials considering MRR and TWR in a renewable dielectric environment is particularly important for sustainable green manufacturing. In response to the technological challenges and green manufacturing needs of BMG machining, high efficiency and precision machining of metallic glass microvias has been achieved through the innovative use of renewable dielectrics and system parameter optimization. The theoretical mechanism is revealed, providing an environmentally friendly and low-consumption EDM solution for industry. New solutions are being proposed at the intersection of materials processing and green manufacturing, providing new ideas and technical support for future applications of EDM technology in high-end manufacturing.
In this investigation, the machinability study of micro-hole drilling in Ti56Zr18Cu12 BMG using renewable dielectric in the EDM process is performed. For optimal machining performance, shaped micro tools were fabricated in accordance with sustainable manufacturing requirements. The input process parameters (pulse-on time, pulse duty cycle, and dielectric) were chosen, as well as their ranges. Experimentation was performed by altering the process parameters in relation to the whole factorial design. The output machining performances of the hole’s features (overcut and edge deviation), MRR, TWR, and removed debris distribution (RDD) were selected to evaluate the machinability while drilling the micro-hole in Ti56Zr18Cu12 materials using renewable dielectric in EDM process. Also, the effect of the input process parameters on the machining performance was investigated in detail. By examining the output performances of micro-machining, the multi-objective optimization on the basis of ratio analysis (MOORA) approach was utilized to efficiently discover the best input process parameters. Finally, we discussed three several topics such as the feasibility of machining BMG with renewable dielectric, multiobjective optimization under green manufacturing, and the impact of sustainable EDM.

2. Experimental Design and Procedure

2.1. Materials and Dielectric

In this investigation, the micro-hole drilling experiments were performed using EDM (EDM-350) of Zhonghang Co., Ltd., Suzhou, China. The metallic glass utilized for this investigation was Ti56Zr18Cu12 of thickness 2.5 mm, synthesized by arc melting. XRD analysis was performed in X-ray diffractometer (D8 Advance, Karlsruhe, Germany) using a copper target (in Figure 1) and confirms the complete amorphous structure of metallic glass Ti56Zr18Cu12.
The schematic diagram of drilling micro-hole on a BMG workpiece using the renewable dielectric is depicted in Figure 2. The cone tool electrode is made of copper with a diameter (small end face) of 410 μm and a taper deference of 1°. The reason why copper was selected as the tool’s material was because it has a low tool wear ratio and good machining surface quality. Therefore, for 1500 μm deep drilling, it was necessary to check the tool wear after each machining, through trimming or replacement methods, to keep the processed shape in line with the requirements. The machined workpiece was held on the table with magnets, as shown in Figure 2b,c.
The dielectric acts as an insulator under normal conditions and remains non-conductive until the required voltage breakdown is achieved in the EDM process. In addition, it can also be used as a good cooling medium to take away the removal of material particles produced during processing. In general, the dielectric must have a high flash point characteristic and good wetting ability to guarantee proper processing of the pulse discharge [36,37]. Compared with traditional mineral oil, renewable vegetable oil has the characteristics of high viscosity, high flash point, and biodegradability, which not only enhances the sustainability of manufacturing but also reduces the emission of toxic gases during processing [38]. Past studies have found that 53 gases are produced when Kerosene is used as a dielectric. These include 13 gases below C6 and 40 gases above C6, containing benzene, toluene, and other toxic and harmful gases. These gases are not only harmful to the human body but also pollute the ecosystem [39]. Vegetable oil could be a better alternative to Kerosene. On the one hand, the choice of sunflower oil and colza oil is based on their advantages in terms of environmental friendliness, degradability, and low toxicity; on the other hand, the two oils are representative of their physical properties. Therefore, sunflower oil and colza oil were chosen for this study as renewable dielectrics to investigate the feasibility of drilling metallic glass Ti56Zr18Cu12. The characteristics of kerosene and renewable dielectrics are listed in Table 1 [40,41].

2.2. Machining Indicators

To investigate the machining performance, the full factorial design of experiments was used in Ti56Zr18Cu12 samples by changing one input process parameter at a time. There was a total of 20 experiments conducted for micro-hole drilling on Ti56Zr18Cu12 (in Table 2). To realize micro-hole machining, the minimum value of the machining current of 1A was selected, and other input process parameters were kept constant, such as the server voltage and polarity.
This study adopted an ultra-depth field microscope (Leica DVM6) to quantify the machining performance following EDM drilling. The measurement was used to obtain optical microscopic images of the machined holes, from which the machining time, overcut, and edge deviation of the micro-holes were computed. Figure 3 illustrates the schematic diagram used to measure the overcut and edge deviation, the two evaluation indexes.
The overcut is the difference between the radius of the drilled hole and the radius of the tool (in Figure 3a), as given in Equation (1).
Overcut = D w D t 2
where Dt is the outer diameter of the tool, and Dw is the average diameter of the hole, which is calculated as the average of the inscribed circle diameter of the irregularity of the drilled hole. In these investigations, eight measurements were taken at an interval of 22.5° to evaluate the inscribed circle. Hence, the maximum and minimum of the measured values were the inscribed circle diameter of the maximum irregularity (Dmax) and minimum irregularity (Dmin), respectively.
The edge deviation of the micro-hole is related to the surface finish of itself. By analyzing the difference between the maximum and minimum diameter of the irregular edge of the micro-hole, it is an important index to evaluate the machining quality of the hole. The edge deviation of the hole is completed by evaluating the edge of the micro-hole, which is determined by Equation (2).
Edge   deviation = D max D min 2
MRR is defined as by Equation (3).
MRR = π D w 2 h 4 t
where h is the cutting depth of hole and t is the machining time.
The energy efficiency per volume (EEV) is defined as the required input energy for removing 1 mm3 of workpiece (J/mm3). As a result, Equation (4) provides the EEV definition.
EEV = U I η × 60 / 1000 MRR
where I is the discharge current, U is the discharge voltage, and η is the pulse duty cycle.

3. Results and Analysis

To study the machinability of metallic glass Ti56Zr18Cu12 with renewable dielectric, different process parameters were selected as shown in Table 3. The machined experimental samples are depicted in Figure 4. Each EDM input process parameter was adopted to investigate the effects of those on MRR, overcut, edge deviation, EEV, TWR, and RDD.

3.1. Analysis of Machinability Responses

3.1.1. MRR

As shown in Figure 5, the MRR initially increases as the PDC increases, and begins to decrease after reaching the maximum, whether pulse-on time is 30 or 50 μs. In addition, when sunflower oil or colza oil is used as a renewable dielectric, the optimal value of MRR is obtained under a middle PDC of 0.2. The POT of 30 μs demonstrates a more favorable machining speed with an average MRR of 0.0078 mm3/min than that of 0.0052 mm3/min with a pulse-on time of 50 μs. Moreover, the maximal value of MRR of 0.0103 mm3/min is achieved when the pulse-on time of 30 μs and sunflower oil renewable dielectric is selected. The difference in MRR between sunflower and rapeseed oils stems from the combination of their viscosity, dielectric constant, and thermal conductivity: sunflower oil at low viscosity is significantly superior at low energies but lacks debris management at high PDC. Canola oil at high dielectric constant and thermal conductivity performed better at medium to high PDC, but viscosity limited efficiency at low energy. This finding is consistent with the green manufacturing goal [38] that efficiency and energy consumption can be balanced by optimizing dielectric selection.
Generally speaking, greater discharge energy means deeper and wider discharge craters in the EDM process, which can significantly improve the MRR [35,42]. However, for EDM micro drilling, the debris removal conditions after discharge are poor with the increase in machining depth. Therefore, excessive discharge energy easily leads to large-size debris removal while micro drilling in metallic glass Ti56Zr18Cu12 affects the machining stability and reduces MRR. Figure 6 shows the statistics of discharge waveform in the machining of metallic glass, in which the discharge waveform of 300 milliseconds is sampled five times. As depicted in Figure 6a, the total proportion of the open and arc status under the pulse-on time of 30 μs is less than that under 50 μs while sunflower oil renewable dielectric and 0.2 PDC are adopted. The proportion of spark discharge in 30 μs pulse-on time is larger than that in 50 μs in this situation. This is because the longer pulse-on time means greater discharge energy, which will produce more debris in micro-hole drilling (further analysis in Section 3.1.6), reducing the machining stability. This indicates that the 30 μs pulse-on time is beneficial to micro-hole drilling in metallic glass Ti56Zr18Cu12. A similar phenomena can be observed in the machining process while colza oil renewable dielectric was utilized (in Figure 6b).
In addition, when the discharge energy is low, the MRR with sunflower oil is greater than that with colza oil. However, when the discharge energy is high (pulse-on time = 50 μs), its MRR with sunflower oil is smaller compared with colza oil. This may be because the fluidity of sunflower oil with low viscosity is better than that of colza oil with high viscosity at low discharge energy, which is more conducive to bringing debris out of the drilling area. When the discharge energy increases, which is conducive to the flow of colza oil with high viscosity, so as to enhance the carrying capacity of debris.

3.1.2. Overcut

According to Table 3, the average values of 43.59 and 56.94 μm are obtained for the overcut under the pulse-on time of 30 and 50 μs, respectively. Also, the average values of 49.30 and 51.22 μm are gained for the overcut under the sunflower oil renewable dielectric and colza oil renewable dielectric, respectively. A least overcut of 39.99 μm of the micro-hole drilling is achieved by EDM using the pulse-on time of 30 μs and colza oil renewable dielectric. Figure 7 demonstrates that the overcut increases as PDC increases. In EDM, the discharge energy has a main effect on the overcut. The discharge gap between the electrode and workpiece also increases when the discharge energy increases. In addition, the discharge energy increment will also generate a larger discharge crater size. Hence, with the pulse-on time and PDC increasing, the overcut increases. Furthermore, the binding force on the discharge channel under renewable colza oil dielectric is high due to its high viscosity. Thus, the discharge energy concentrates and discharge gap increases while renewable dielectric is changed from sunflower oil to colza oil.
As reported by Kuriakose et al. [22], average values of 40.92 μm and 31.58 μm were obtained for the overcut at entry for grits 400 and 600, respectively. Overcut at the exit value also followed the same trend with 39.58 μm and 28.48 μm corresponding to 400 grit and 600 grit. In their study, the hydrocarbon oil dielectric and tungsten electrode with 513 μm were selected. However, compared with their research the depth–diameter ratio of the machined micro-holes in this paper (3.42) is much larger (0.04). This means that the performance of the overcut can be acceptable for the micro-hole drilling in metallic glass Ti56Zr18Cu12 using renewable dielectric in the EDM process. Figure 8 presents the sketch of the measurement of the micro-holes in the best and worst categories while these two renewable dielectrics are applied. From Figure 8a,b, the minimal and maximal values of the overcut with sunflower oil renewable dielectric are 40.76 and 59.27 μm, respectively. Similarly, the minimal and maximal values of the overcut (in Figure 8c,d), with colza oil renewable dielectric, are 39.99 and 65.10 μm, respectively. This means that selecting appropriate input process parameters is necessary to reduce the overcut. Whether using sunflower oil or rapeseed oil, the overcut increases as the discharge energy increases. In addition, excessive discharge energy also leads to a larger measurement range of overcut of micro-holes (in Figure 8b,d).

3.1.3. Edge Deviation

The average edge deviation values of 20.65 and 17.52 μm are obtained under the POT of 30 and 50 μs, respectively. Also, average edge deviation values of 17.89 and 20.28 μm are gained under the sunflower oil and colza oil renewable dielectrics, respectively. This illustrates that the POT and the type of renewable dielectric have little effect on the edge deviation. However, the PDC has an important effect on the edge deviation. Figure 9 gives the edge deviation vs. PDC for renewable dielectrics of different POTs. As depicted in Figure 9a, on the whole, the edge deviation initially increases when the PDC increases, and then decreases after reaching the peak while the POT is 30 μs. The minimal values of edge deviation using the sunflower oil and colza oil renewable dielectrics are 11.53 and 9.54 μm, respectively. But the edge deviation initially decreases with the increase in PDC and then increases after reaching the bottom while the POT is 50 μs (in Figure 9b). In this situation, the minimal values of edge deviation using the sunflower oil and colza oil renewable dielectrics are 15.11 and 9.41 μm, respectively. Thereafter, a medium PDC of 0.2 to 0.3 and a POT of 30 μs are found to be acceptable for minimizing edge deviation.
The above investigation in this study has shown that higher PDC increases MRR. With the high MRR, the discharge pulse can make the drilled hole edge become more even. This means that there is a contradiction between reducing the deviation and decreasing the overcut. Higher PDC will give rise to poor machining conditions after discharge. The removal of debris after machining is not conducive to flow out of the micro-machining gap between the workpiece and tool and affects the edge deviation. Even if the lower PDC reduces the discharge energy per unit time for machining, the MRR slightly increases because the discharge interval becomes longer and the flow capacity of removing debris from the micro-machining gap increases. So, a lower PDC of 0.2 or medium PDC of 0.3 favors lesser edge deviation and higher MRR while using renewable dielectrics.

3.1.4. EEV

As listed in Table 3, average values of 59.73 and 88.65 kJ/mm3 are obtained for the EEV under the POT of 30 and 50 μs, respectively. Also, average values of 76.22 and 72.16 kJ/mm3 are gained for the EEV under the sunflower oil renewable dielectric and colza oil renewable dielectric, respectively. The least EEV of 23.01 kJ/mm3 of the micro-hole drilling was achieved with a POT of 30 μs and sunflower oil renewable dielectric. Figure 10a,b demonstrates that the value of EEV rises as the PDC rises. The EEV is not only affected by the MRR but also affected by the discharge energy. As the PDC rises, the energy consumed per unit of time increases exponentially. However, the growth rate of MRR did not catch up with the growth rate of discharge energy. In addition, when PDC is greater than 0.4, it gradually decreases after reaching the peak using colza oil renewable dielectric. Therefore, the value of EEV increases as PDC increases, according to Equation (4).
In our previous study, we suggested a system for optimizing cutting parameters during the EDM of Al 6061 and SKD 11 to reduce energy consumption and emissions in green manufacturing [43]. The EEV reduced as the discharge current and PDC rose, but increased as the POT grew, according to the experimental data. The effect of POT on EEV is similar, whether EDM with kerosene dielectric is used to machining metal materials or EDM with renewable dielectric is adopted to drill amorphous alloys. However, the effect of PDC on EEV is obviously different, which can be attributed to the machining conditions of EDM drilling micro-hole in amorphous alloy materials being more complex than EDM metal materials for traditional shapes. In Zhang et al. study [44], the debris particles in the hole showed uneven distribution, resulting in the non-uniformity of discharge breakdown probability, which affected the machining stability. Therefore, it needs to consider the comprehensive effect of process parameters for improving the EEV in drilling amorphous alloy, which involves the optimization of process parameters.

3.1.5. TWR

After each micro-hole was processed, we compared the tool weight before and after machining and found that the weight of the tool had almost no change (accurate to 0.1 mg). In addition, it was supported by relevant SEM photos, which are depicted in Figure 11. This means that there is no obvious consumption of the tools while machining micro-hole drilling of metallic glass Ti56Zr18Cu12.

3.1.6. RDD

Since debris particles are constantly generated during the EDM process, the accumulation of debris will affect the stability of the process and even cause short circuits if they cannot be flushed in time. Therefore, it is also very important to analyze the size of the removed debris particles after drilling the micro-hole. We took 1 mL as the sample from two kinds of renewable dielectrics with a POT of 30 and 50 μs and PDC of 0.2, respectively. Different size distribution ratios of debris in the renewable dielectrics were analyzed using ultra-depth of field optical microscopy (LEICA DVM6). Figure 12a,b compares the diameters of the debris in colza oil and sunflower oil, where it is found that there is generally more large-diameter debris (≥50 μm) in colza oil and more small-diameter debris (0–15 μm) in sunflower oil with POT = 30 μs and PDC = 0.2. Also, a similar phenomenon can be found, as depicted in Figure 12c,d, in colza oil and sunflower oil when POT is 50 μs and pulse duty cycle is 0.2. The reason is that colza oil has a high viscosity and a strong binding force on the discharge channel during EDM, thus obtaining a higher energy density and energy utilization ratio. Higher energy is generated in the process of machining, and the impact on the workpiece is stronger, resulting in large pieces of debris falling off from the melting zone. On the contrary, sunflower oil has low viscosity, little restriction on discharge channels, and a low density of discharge energy, so the generated fragments are small. A similar phenomenon was found in the research of Jilani et al. [45], and they confirmed that different viscosities of dielectrics would affect the restriction of the discharge channel, and the lower viscosity dielectrics would have fewer restrictions on the discharge channel.
Figure 13 depicts the relationship between POT and RDD. From Figure 13a, when the PDC is 0.2 and the POT is 30 μs, the proportion of large-diameter debris in colza oil is 9.24% and that of small-diameter debris in colza oil is 58.16%. However, when the pulse time is 50 μs, the proportion of large-diameter debris in colza oil is 4.31%, and the proportion of small-diameter debris is 76.18%. There is a trend that the proportion of large-diameter debris decreases while the POT rises. Similarly, when a renewable dielectric such as sunflower oil is used, a similar phenomenon can be observed in the processing of waste oil, as depicted in Figure 13b. This is because as the pulse width increases, the discharge time becomes longer, and more energy makes the gasification in the molten area of the workpiece more intense. In addition, this also increases the amount of vaporization of the dielectric. These two factors make the metallic glass in the molten area expel more violently from the matrix. Therefore, with the increase in POT, large-sized debris will be dispersed into several small-sized debris, resulting in a large proportion of small-sized debris. In micro-hole drilling, due to poor debris removal conditions, the increase in debris will affect the discharge status, which can be confirmed from the statistical data of the discharge waveform in Section 3.1.1. Therefore, excessive POT has a negative effect on the machining stability of micro-hole drilling of metallic glass.

3.2. Optimization

3.2.1. MOORA Method

As a multi-objective optimization method, MOORA can help decision makers select the most suitable object according to certain optimization principles [46,47], which adopts an independent mathematical calculation process for income criterion and cost criterion, and is scientific and objective, and meets the evaluation requirements of green sustainable manufacturing for the selection of manufacturing process. At the same time, according to the different degrees of attention to each objective in the calculation process, the adjustment of dynamic weight can be used in this method. Compared with other common multi-objective optimization methods, non-dominated sorting genetic algorithm II is computationally more expensive and requires more iterations and population sizes, the variable-fidelity surrogate model has a high computational cost and complex model structure. Moreover, it relies on high-precision data calibration and has weak interpretability, making it difficult to quickly adapt to multi-objective decision-making scenarios. Grey relational analysis is susceptible to the subjectivity of the selection of reference sequences [48,49,50]. Therefore, the MOORA method adopted in this study has a simple and intuitive calculation process, low data dependence, and strong robustness, and its weight allocation mechanism is more flexible, thus showing significant advantages in solving the multi-objective antagonism problem in EDM processing.
According to Refs. [22,47], the MOORA technique is a simple to use multi-objective decision-making tool that provides precise ranks. Equations (5)–(7) are used in the analysis. The output values are arranged in a decision matrix as illustrated in Equation (5).
X = x 11 x 1 n x m 1 x m n
where xij represents the ith alternative’s performance on the jth criterion, and m and n are the number of experiments and output parameters, respectively.
Then, the matrix is normalized by following Equation (6).
y i j = x i j i = 1 m x i j
To compute the assessment value, it is need to add the parameters to be maximized and subtract the parameters to be minimized using Equation (7).
R i = j = 1 g ω j y i j j = g + 1 n ω j y i j
j = 1 n ω j = 1
where g indicates the number of parameters to be maximized, (n-g) is the number of parameters to be minimized, ωj indicates the weight of jth objectives, and Ri indicates ith experiment’s overall assessment value. When placed in decreasing order, the best experiment is the one with greatest assessment value.
The quality evaluation criteria are minimizing overcutting, edge deviation, EEV and TWR, and maximizing MRR. The structural changes are analyzed by SEM analysis to find the optimal input parameter level combination, based on the MOORA method, for drilling the highest quality holes in metallic glass Ti56Zr18Cu12 using the renewable dielectric in the EDM process.

3.2.2. MOORA for Optimum Conditions

Selecting input process parameter levels for a mix of the desired output performance is difficult for multi-objective decision-making. Using Equation (5), a decision matrix of 20 × 4 is created for MOORA. There is a total of 20 trials (drilled micro-holes) with four output performances. The assessment values are derived by adding the criterion to be maximized and subtracting the criteria to be minimized, as given in Equations (6) and (7), after normalizing the choice matrix. The normalized decision matrix of output performance using MOORA is shown in Table 4. In this scenario, the criteria to be minimized are overcut, edge deviation, and EEV, whereas the criterion to be maximized is MRR. The best drilling condition in metallic glass Ti56Zr18Cu12 is determined by checking the trial run with the highest assessment value.
According to the analysis data in Table 4, the assessment values of the top five are experiments No. 2, 1, 12, 17, and 3. The best input process parameters are obtained near the middle PDC of 0.2–0.3. PDC is the most important parameter affecting the micro-hole quality of the metallic glass Ti56Zr18Cu12. The appropriate PDC shortens the machining time and greatly reduces the overcut. The results also show that most of the input process parameters in the top five of the assessment values are 30 μs of pulse on time obtained. POT of 30 μs is acceptable for the desired edge deviation. Because overcutting is significantly reduced, the reduction in it decreased by 23.45% while POT from 50 to 30 μs. In addition, a low PDC is desired to obtain good machining quality for micro-hole drilling. Therefore, considering the whole machining performance, the hole machining quality with POT of 30 μs is better than that with POT of 50 μs while EDM drilling of metallic glass. According to the assessment values, the holes with the worst, good, and best quality are classified. A representative micro-hole is selected from each category, and the shear band, stress-affected zone, heat-affected zone or material property changes at the micropore edge are analyzed. Micro-hole morphology in the best and worst categories is presented in Figure 14 and Figure 15, respectively. The results show that the burr height under 30 μs of pulse on time and 0.1 of PDC is less than that under a pulse on time of 50 μs and a PDC of 0.4, because the smaller discharge energy reduces the heat-affected area size, thereby improving the accuracy.
The burr on the micro-hole edge and the place somewhat outside the edges were subjected to EDS examination. Figure 16 and Figure 17 demonstrate the EDS results for hole edge burr in the best and worst categories, respectively. The material’s chemical composition is mostly unchanged in micro-hole drilling in metallic glass Ti56Zr18Cu12, according to EDS data. The proportion of carbon or Cu content in the edge burrs of the worst-category micropores is somewhat higher than that of the best-category micropores, according to the comparison between Figure 16 and Figure 17. The reason for this is the long pulse discharge and high PDC used in EDM, which results in excessive renewable dielectric pyrolyzed deposition in the burr or on the workpiece surface following carbonization, and in many depositions from Cu elements of the electrode under high discharge energy.
Metallic glass has mechanical properties that are distinct from crystalline alloys. Metallic glass has a similar elastic modulus to crystalline alloys with the same composition, but the strength of metallic glass is substantially higher, according to Atroshenko et al. [51]. In a study of shear band deformation in metallic glass, Zhao et al. [52] discovered that metallic glass does not strain harden, and there was unequal strain in the shear bands, culminating in catastrophic failure. After the input process parameters are optimized by EDM with renewable dielectric, there is no evidence of the shear band and stress-affected zone in the drilling area, according to SEM and EDS analysis in this investigation. Therefore, this study is applicable to microchannels, square holes, special-shaped holes, or other complex micro shapes in EDM processing metal glass, and is used in the fields of implant material replacement, small functional metal parts, and MEMS.

4. Discussion

As stated above, the micro-hole drilling on Ti56Zr18Cu12 with renewable dielectric in the EDM process is feasible. In this section, we discuss this investigation from the following three aspects: the feasibility of machining BMG with renewable dielectric, the multi-objective optimization under green manufacturing, and the impact of sustainable EDM.

4.1. Feasibility of Machining BMG with Renewable Dielectrics

In the traditional EDM process, mineral oil such as kerosene is generally adopted as the dielectric. However, with the development of industry, population growth, and the huge demand for energy by human beings, the large-scale exploitation and utilization of fossil oil energy has caused serious environmental pollution and irreversible environmental damage, threatening the sustainable development of the economy and society. In addition, during the processing, the smoke generated by using kerosene as a dielectric is toxic and has a significant impact on the health of operators. Therefore, this study investigates the machinability of micro-hole drilling on Ti56Zr18Cu12 with renewable dielectric. The experimental results demonstrated that the minimal overcut and edge deviation of micro-hole were 39.99 and 9.41 μm, respectively. This means that renewable dielectrics, such as sunflower oil and colza oil, have the potential to replace traditional kerosene dielectrics.
Kuriakose et al. [22] found that input process factors including feed, abrasive slurry concentration, and abrasive grit size had an impact on the effectiveness of micro-USM in drilling micro-holes in Zr-based metallic glass. The maximum overcut and edge deviation, according to the data, were 34 and 62 μm, respectively. The maximum overcut and edge deviation were found to account for 38.04 and 20.86% of the variation when compared to the electrode radius. In this investigation, our maximum relative overcut and edge deviation were 27.78 and 13.6%, respectively, with regard to the electrode radius. On the other hand, our study’s depth-to-diameter ratio (3.42) was 57 times greater than their study’s (0.06). Therefore, it is feasible to use renewable dielectric to drill micro-holes in BMG materials in the EDM process. In their investigation into how process factors affect the precision of micro-hole drilling in Zr-based metallic glass, Kuriakose et al. [53] found that the input process parameters significantly influenced the machined features and their surface characteristics throughout the EDM process. Their findings showed that the maximum deviations of the edge and overcut were 26 and 63 μm, respectively. The maximum overcut and edge deviation in this experiment are 65.10 and 31.92 μm, respectively. However, our study’s hole’s depth-to-diameter ratio (3.42) is greater than theirs (0.04). Naturally, processing becomes more challenging the larger the hole’s depth to diameter ratio. Compared to micro-EDM, thereafter, it is acceptable to adopt renewable dielectric to cut micro-holes in Ti56Zr18Cu12 with good machining performance.
The demand for ecological production techniques is increasing at the moment, especially in the mechanical manufacturing field. Various countries’ laws and regulations have also introduced additional standards for green manufacturing. For example, environmentally friendly processing techniques are already being used in Chinese companies, and environmental management systems (ISO 14000 standards) are consistently applied [54]. Kerosene, which is used for insulation and cooling in the EDM process, does not have renewable properties. In addition, with the progress of agricultural technology, the output of renewable vegetable oil is increasing, and its generation cost is also decreasing. Therefore, through the use of renewable dielectrics such as sunflower oil and colza oil, the new method of electro-discharge machining BMG materials using renewable dielectric is expected to be a sustainable manufacturing process.

4.2. Multi-Objective Optimization Under Green Manufacturing

Green manufacturing is a modern manufacturing model that integrates environmental impact and resource efficiency with product quality and manufacturing costs. Chen et al. [8] fabricated a metal glass microstructure with a high aspect ratio for MEMS. However, the electrochemical machining method used has a great negative impact on the environment. Liu et al. [55] studied the crater sizes of micro-EDM of BMG materials by simulations and experiments. They found that the discharge crater sizes were positively correlated with the discharge energy. But, the energy efficiency of micro-EDM is not further analyzed while machining the BMG materials. To achieve micro-hole, Kuriakose et al. [22] studied the performance (MRR, overcut, deviation, and TWR) of micro-USM while drilling in Zr-based metallic glass. However, the efficiency of ultrasonic machining is low, compared with other machining methods. Therefore, the energy efficiency of this method needs further research to improve the quality of green manufacturing. To enhance green manufacturing in the EDM process, we not only investigated the machinability of micro-hole drilling in Ti56Zr18Cu12 with renewable dielectric but also considered the energy efficiency.
In the process of EDM, there is a contradiction between machining quality and MRR [56]. When the discharge current, pulse on-time, etc., increases, the size of the individual discharge crater becomes larger and therefore the MRR increases significantly. However, when the discharge crater size becomes larger, the surface quality after machining becomes worse. Thereafter, a number of optimization algorithms have been proposed by many researchers to solve this multi-objective optimization problem [43,57,58]. Therefore, the multiple objects, such as overcut, edge deviation, MRR, and EEV, need to be comprehensively considered in this study. Hence, we adopted the MOORA approach to efficiently solve this multi-objective optimization. In this investigation, the weights (ωj in Equation (8)) of overcut, edge deviation, MRR, and EEV were 0.25, 0.25, 0.25, and 0.25, respectively. This means that each of these four goals has the same weight. However, the method may determine the appropriate input process parameters for these restrictions by varying the weights assigned to these various objectives. For instance, the optimized input process parameters could concentrate more on energy efficiency and green manufacturing after raising the weight (ω3) of the EEV. Naturally, increasing the weight (ω3) of the aforementioned green manufacturing target from 0.25 to 0.5 would result in a smaller range of available input process parameters, necessitating future process method improvements.

4.3. Impact of Sustainable EDM

In the sustainable EDM, it is necessary to analyze the impact of renewable dielectric on drilling micro-holes in metallic glass Ti56Zr18Cu12 from the aspects of machining performance, society, and the environment. In this study, the machining performance is evaluated through key indicators such as MRR, overcut, and edge deviation, which are critical for assessing the efficiency and precision of the process, while the social and environmental dimensions are addressed by considering factors like biodegradability, gas evolution, objectionable odor, and the influence on operator health. Although the current investigation primarily provides a preliminary assessment of the feasibility of using renewable dielectrics and examines the economic aspects of processing, it lays the groundwork for more comprehensive future studies. Given that kerosene remains a widely accepted dielectric in industrial settings, future research must focus on identifying additional renewable dielectric options and rigorously comparing them with kerosene, evaluating not only cost-effectiveness and productivity but also availability, environmental impact, and social implications. Ultimately, a careful analysis of these evaluation indicators is imperative for selecting the most practical dielectric for sustainable EDM applications, ensuring that advancements in machining performance are balanced with significant improvements in environmental and societal outcomes.

5. Conclusions and Outlooks

In this investigation, the machinability of metallic glass Ti56Zr18Cu12 for drilling micro-holes was studied by EDM using renewable dielectric liquid. Furthermore, the applicability of EDM in metal glass processing and the influence of the change in input process parameters on drilling quality, energy efficiency, and removed debris distribution were studied. Therefore, the following conclusions can be derived from this study:
  • EDM can be utilized to drill micro-holes on Ti56Zr18Cu12 with renewable dielectrics. Moreover, utilizing renewable dielectric, the minimum overcut and edge deviation of micro-hole drilling in Ti56Zr18Cu12 are 39.99 and 9.41 μm, respectively. This indicates that renewable dielectrics like sunflower and colza oil have the potential to take the place of traditional kerosene dielectrics.
  • The maximum value of MRR of 0.0103 mm3/min is achieved when the pulse-on time of 30 μs and sunflower oil renewable dielectric are selected. When sunflower oil or colza oil is used as a renewable dielectric, the optimal value of MRR is obtained under a middle pulse duty cycle of 0.2. In addition, the type of renewable dielectrics and the density of discharge energy have obvious effects on MRR.
  • While drilling micro-holes in metallic glass, it is found that the TWR is very low (near close to zero). In MOORA, the criteria to be minimized are overcut, edge deviation, and EEV, whereas the criterion to be maximized is MRR. According to the analysis, the pulse duty cycle is the most important parameter affecting the micro-hole quality, and near the middle pulse duty cycle of 0.2–0.3 is optimal.
  • The demand for environmentally friendly manufacturing techniques is on the rise right now, particularly in the mechanical manufacturing industry. Through the use of renewable dielectrics such as sunflower oil and colza oil, the new method of EDM BMG materials using renewable dielectrics is expected to be a sustainable manufacturing process.
The shortcomings of this study are as follows: the study mainly focuses on specific metal glass systems and the universality of other material systems has not yet been fully verified; the performance degradation of media recycling needs to be further optimized through material modification; and the bottleneck of chip removal efficiency in high depth-to-diameter ratio machining requires a breakthrough in process innovation. In this regard, this study proposes a sustainable research framework—through the establishment of a standardized multi-parameter evaluation system of ‘material-medium-process’, the integration of industry–university–research collaborative validation network, and the systematic exploration of process adaptability and replicability. In the future, the assessment value of MOORA should include more aspects, such as the cost and source reliability of renewable dielectrics, so as to determine the dielectrics most suitable for applications. In addition, some improvements, such as using effective additives for renewable dielectrics or magnetic field assistance [59,60], could be adopted to enhance machining performance and reduce processing costs.

Author Contributions

Conceptualization, W.M; Validation, Y.Z.; Formal analysis, Y.Z.; Writing—original draft, L.L., C.C. and J.D.; Writing—review & editing, L.L., C.C., Y.Z., S.S. and J.D.; Visualization, S.S.; Funding acquisition, W.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Guangdong Basic and Applied Basic Research Foundation grant number No. A1515140066, Regular Universities Engineering Technology Research Center in Guangdong Province grant number 2021GCZX002, Guangdong HUST Industrial Technology Research Institute, Guangdong Provincial Key Laboratory of Manufacturing Equipment Digitization grant number No.2023B1212060012. And The APC was funded by Zhengzhou University of Light Industry.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. XRD pattern of metallic glass Ti56Zr18Cu12.
Figure 1. XRD pattern of metallic glass Ti56Zr18Cu12.
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Figure 2. The schematic of drilling micro-hole on metallic glass Ti56Zr18Cu12 with renewable dielectric in the EDM process; (a) electrical discharge machine; (b) workpiece attachment for machining; (c) metallic glass after drilled by EDM process.
Figure 2. The schematic of drilling micro-hole on metallic glass Ti56Zr18Cu12 with renewable dielectric in the EDM process; (a) electrical discharge machine; (b) workpiece attachment for machining; (c) metallic glass after drilled by EDM process.
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Figure 3. The schematic diagram of the measurement of the micro-hole performance, (a) measurement of the overcut, and (b) measurement of the edge deviation.
Figure 3. The schematic diagram of the measurement of the micro-hole performance, (a) measurement of the overcut, and (b) measurement of the edge deviation.
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Figure 4. Array of micro drilled holes (a) using sunflower oil dielectric and (b) using colza oil dielectric.
Figure 4. Array of micro drilled holes (a) using sunflower oil dielectric and (b) using colza oil dielectric.
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Figure 5. MRR vs. PDC for renewable dielectrics of (a) pulse-on time = 30 μs, and (b) pulse-on time = 50 μs.
Figure 5. MRR vs. PDC for renewable dielectrics of (a) pulse-on time = 30 μs, and (b) pulse-on time = 50 μs.
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Figure 6. Statistics of discharge waveform in machining metallic glass (a) using sunflower oil renewable dielectric (PDC = 0.2) in EDM process, and (b) using colza oil renewable dielectric (PDC = 0.2) in EDM process.
Figure 6. Statistics of discharge waveform in machining metallic glass (a) using sunflower oil renewable dielectric (PDC = 0.2) in EDM process, and (b) using colza oil renewable dielectric (PDC = 0.2) in EDM process.
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Figure 7. Overcut vs. PDC for renewable dielectrics: (a) pulse-on time = 30 μs; (b) pulse-on time = 50 μs.
Figure 7. Overcut vs. PDC for renewable dielectrics: (a) pulse-on time = 30 μs; (b) pulse-on time = 50 μs.
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Figure 8. Sketches of measurements of the micro-holes in the best and worst categories; (a) under POT = 30 μs and PDC = 0.1 using sunflower oil renewable dielectric; (b) under POT = 50 μs and PDC = 0.4 using sunflower oil renewable dielectric; (c) under POT = 30 μs and PDC = 0.3 using colza oil renewable dielectric; (d) under POT = 50 μs and PDC = 0.4 using colza oil renewable dielectric.
Figure 8. Sketches of measurements of the micro-holes in the best and worst categories; (a) under POT = 30 μs and PDC = 0.1 using sunflower oil renewable dielectric; (b) under POT = 50 μs and PDC = 0.4 using sunflower oil renewable dielectric; (c) under POT = 30 μs and PDC = 0.3 using colza oil renewable dielectric; (d) under POT = 50 μs and PDC = 0.4 using colza oil renewable dielectric.
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Figure 9. Edge deviation vs. PDC for renewable dielectrics of (a) POT = 30 μs and (b) POT = 50 μs.
Figure 9. Edge deviation vs. PDC for renewable dielectrics of (a) POT = 30 μs and (b) POT = 50 μs.
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Figure 10. EEV vs. PDC for renewable dielectrics of (a) POT = 30 μs, (b) POT = 50 μs.
Figure 10. EEV vs. PDC for renewable dielectrics of (a) POT = 30 μs, (b) POT = 50 μs.
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Figure 11. Tool surface morphology after micro-hole drilling.
Figure 11. Tool surface morphology after micro-hole drilling.
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Figure 12. Distribution of debris measured by the ultra-depth of field microscope; (a) under POT = 30 μs and PDC = 0.2 using sunflower oil renewable dielectric; (b) under POT = 30 μs and PDC = 0.2 using colza oil renewable dielectric; (c) under POT = 50 μs and PDC = 0.2 using sunflower oil renewable dielectric; (d) under POT = 50 μs and PDC = 0.2 using colza oil renewable dielectric.
Figure 12. Distribution of debris measured by the ultra-depth of field microscope; (a) under POT = 30 μs and PDC = 0.2 using sunflower oil renewable dielectric; (b) under POT = 30 μs and PDC = 0.2 using colza oil renewable dielectric; (c) under POT = 50 μs and PDC = 0.2 using sunflower oil renewable dielectric; (d) under POT = 50 μs and PDC = 0.2 using colza oil renewable dielectric.
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Figure 13. RDD vs. POT (a) in the sunflower renewable dielectric and (b) in the colza renewable dielectric.
Figure 13. RDD vs. POT (a) in the sunflower renewable dielectric and (b) in the colza renewable dielectric.
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Figure 14. Micro-hole morphology in the best category (No. 1); (a) micro-hole; (b) hole edge.
Figure 14. Micro-hole morphology in the best category (No. 1); (a) micro-hole; (b) hole edge.
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Figure 15. Micro-hole morphology in the worst category (No. 19); (a) micro-hole; (b) hole edge.
Figure 15. Micro-hole morphology in the worst category (No. 19); (a) micro-hole; (b) hole edge.
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Figure 16. In the best category, the EDS analysis of burr on the micro-hole edge.
Figure 16. In the best category, the EDS analysis of burr on the micro-hole edge.
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Figure 17. In the worst category, the EDS analysis of burr on the micro-hole edge.
Figure 17. In the worst category, the EDS analysis of burr on the micro-hole edge.
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Table 1. Characteristics of kerosene, sunflower oil, and colza oil.
Table 1. Characteristics of kerosene, sunflower oil, and colza oil.
PropertiesKeroseneSunflower OilColza Oil
Flash point (°C)52439453
Viscosity (27 °C) (cSt)1.224.95.83
Dielectric constant (27 °C)2.1133.2
Thermal conductivity (W/mK)0.1280.1590.176
Table 2. Input process parameters with their levels.
Table 2. Input process parameters with their levels.
ParametersLevelsValues
Pulse-on time (POT)230 μs, 50 μs
Pulse duty cycle (PDC)50.1 ratio, 0.2 ratio, 0.3 ratio, 0.4 ratio, 0.5 ratio
Dielectric2Sunflower oil, colza oil
Table 3. Machining performance with different input process parameters.
Table 3. Machining performance with different input process parameters.
Exp. No.Input Process ParametersMachining Performance
Pulse-On Time (μs)Pulse Duty Cycle (Ratio)DielectricMRR (mm3/min)Overcut (μm)Edge Deviation (μm)EEV (kJ/mm3)
1300.1Sunflower oil0.006540.7618.223.01
2300.2Sunflower oil0.010344.8811.5328.96
3300.3Sunflower oil0.009143.7923.3349.21
4300.4Sunflower oil0.007149.4121.7884.38
5300.5Sunflower oil0.006841.2511.78108.95
6500.1Sunflower oil0.003452.7019.7742.97
7500.2Sunflower oil0.005757.1315.1152.15
8500.3Sunflower oil0.005849.4418.1476.54
9500.4Sunflower oil0.003759.2721.64158.12
10500.5Sunflower oil0.005454.4117.58137.91
11300.1Colza oil0.00640.7429.2624.70
12300.2Colza oil0.009340.3125.1532.07
13300.3Colza oil0.008939.9923.650.51
14300.4Colza oil0.00647.9731.9299.67
15300.5Colza oil0.007846.759.9495.82
16500.1Colza oil0.003354.9719.2244.76
17500.2Colza oil0.007656.3713.5139.36
18500.3Colza oil0.006758.149.4167.15
19500.4Colza oil0.004465.1022.47133.71
20500.5Colza oil0.005661.9018.31133.85
Table 4. Experiment results of the machined metallic glass.
Table 4. Experiment results of the machined metallic glass.
Exp. NoMRR OvercutEdge DeviationEEV Assessment Value
10.0500.0410.0480.016−0.054
20.0800.0450.0300.020−0.015
30.0700.0440.0610.033−0.068
40.0550.0490.0570.057−0.108
50.0530.0410.0310.073−0.093
60.0260.0520.0520.029−0.107
70.0440.0570.0400.035−0.088
80.0450.0490.0480.052−0.103
90.0290.0590.0570.107−0.194
100.0420.0540.0460.093−0.151
110.0460.0410.0770.017−0.087
120.0720.0400.0660.022−0.056
130.0690.0400.0620.034−0.067
140.0460.0480.0840.067−0.152
150.0600.0470.0260.065−0.077
160.0260.0550.0500.030−0.110
170.0590.0560.0350.027−0.059
180.0520.0580.0250.045−0.076
190.0340.0650.0590.090−0.180
200.0430.0620.0480.090−0.156
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Li, L.; Cao, C.; Zhao, Y.; Sun, S.; Du, J.; Ming, W. Machinability of Drilling on Metallic Glass for Micro-Hole with Renewable Dielectric in an Electric Discharge Machining Process. Metals 2025, 15, 415. https://doi.org/10.3390/met15040415

AMA Style

Li L, Cao C, Zhao Y, Sun S, Du J, Ming W. Machinability of Drilling on Metallic Glass for Micro-Hole with Renewable Dielectric in an Electric Discharge Machining Process. Metals. 2025; 15(4):415. https://doi.org/10.3390/met15040415

Chicago/Turabian Style

Li, Liwei, Chen Cao, Yangjing Zhao, Shuo Sun, Jinguang Du, and Wuyi Ming. 2025. "Machinability of Drilling on Metallic Glass for Micro-Hole with Renewable Dielectric in an Electric Discharge Machining Process" Metals 15, no. 4: 415. https://doi.org/10.3390/met15040415

APA Style

Li, L., Cao, C., Zhao, Y., Sun, S., Du, J., & Ming, W. (2025). Machinability of Drilling on Metallic Glass for Micro-Hole with Renewable Dielectric in an Electric Discharge Machining Process. Metals, 15(4), 415. https://doi.org/10.3390/met15040415

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