1 Introduction

Electrical discharge machining (EDM) is a flexible, non-traditional machining technology that can be used to process any conductive material regardless of its mechanical properties [1]. The mass machining processes like milling, drilling, and turning are the foreknown process where the MRR will be high at the same time the profile of cut having limitation [2, 3]. However, in EDM process, also when mass output is required in industrial activities, the sluggish characteristic of EDM becomes obvious [4]. Additionally, this technique has disadvantages such as poor surface quality, residual stress, and a heat-affected zone. Numerous researchers have proposed numerous approaches to enhance the capabilities of EDM by using novel materials or technology [5-7]. Powder Mixed EDM (PMEDM) is a sophisticated EDM process in which fine abrasive electrically conductive powder is mixed into the dielectric fluid [8]. Metallic particles suspended in dielectric deteriorate its insulating characteristics, hence raising the inter-electrode gap conditions, which increases EDM performance and results in a superior surface quality when compared to conventional EDM [9]. The PMEDM method is based on the principle that when an appropriate voltage is supplied, an electric field is created, inducing positive and negative charges on the powdered particles [10]. As these pushed powder particles move in a zigzag manner, the spark gap between the electrodes is increased. This chain assists in bridging the discharge gap between the electrodes by decreasing the insulating strength of the dielectric fluid and increasing the spark gap. These conditions are extremely beneficial when cutting extremely hard alloys [11].

Kumar et al. [12] have done a quantitative analysis of bubble size and electrodes gap at different dielectric conditions in powder-mixed EDM process. In this, EDM experiments were conducted using ordinary deionized (DI) water, nonconductive Al2O3 powder-mixed DI water, and conductive Al powder-mixed DI water. The experimental results demonstrate that the conductive powder-mixed EDM process is more stable and capable of producing a higher quality surface topography than previous processes. Tran et al. [13] have done the electrical discharge machining with SiC powder-mixed dielectric to machining of hardened 90CrSi steel. It was discovered that SiC powder had a beneficial effect on surface roughness reduction. The roughness was reduced by 30.02% when the optimal powder concentration of 4 g/L was used, compared to when traditional EDM was used. Similarly, erosion characteristics of electrical discharge machining using graphene powder in deionized water as dielectric was the work of Wang et al. [14]. Experimental results indicate that graphene bubbles may have an effect on the erosion properties and machinability of titanium alloys. In comparison to traditional EDM methods, the material removal rate was enhanced by 28%, the surface roughness was reduced by 55%, and the relative electrode wear was reduced by 43%. Kiran et al. [15] have done a surface modification study through sustainable micro-EDM process using powder-mixed bio-dielectrics. In this study, they used both environmentally acceptable and commercially accessible dielectric liquids (EDM oil, EDM oil + MoS2 powders (EDP), sunflower oil (SF), and sunflower oil + MoS2 powders (SFP)) to modify the surface of a Ti6Al4V sheet using the micro-EDM technique. The results suggest that when MOS2 was combined with sun flower oil, the maximum microhardness of 694.02 HV was obtained. Zhu et al. [16] investigated the processing characteristics of micro electrical discharge machining for surface modification of TiNi shape memory alloys using a TiC powder dielectric. According to the results, the TiC powder’s addition had a positive effect on increasing the electro-discharge frequency and MRR, reducing the surface roughness, and the maximum MRR and the minimum surface roughness occurred at a mixed powder concentration of 5 g/L. Moreover, the recast layer had good adhesion and high hardness due to metallurgical bonding. Moreover, the use of treated biosilica filler in the EDM process was also explained through the author’s previous literature [17]. In this, the author confirmed that the silane-treated biosilica had a positive effect in MRR, TWR, and surface roughness than the as-received biosilica. This phenomenon was due to the lesser agglomeration effect of hydroxide state biosilica particle.

Thus, based on the previous studies, it is clear that the powder-mixed dielectric fluid has significant effect on machining characteristics on harder alloys and metals due to the improved arc length, standoff distance, and spark density. There are many studies explicating the deployment of nano- or microparticle in water dielectric as property booster. However, the biosilica-based water dielectric and its machining characteristics are not yet reported by any researcher. Since the biosilica is a bio product and not produce any harmful effect, its deployability makes more advantages in machining sciences. Moreover, its cooling effect is also better than the other ceramics in the peer group. Thus, the present study aimed to investigate the machining characteristics such as MRR, TWR, and surface roughness of Ti-6Al-4 V titanium alloy. This enhanced machining process of hard alloys and metallic materials could be utilized in deep drilling, cavity making, and other engineering application processes.

2 Experimental procedure

2.1 Silane-treated WHB preparation

Making wheat husk biosilica from biomass involves two distinct procedures. To produce wheat husk ash, the wheat husk was first completely burned at 700 °C in a thermal reactor on a sand bed with a separate air supply unit. In the second stage, the generated wheat husk ash was mixed with varied concentrations of NaOH solution at 80 °C and continuously agitated for 1 h to form sodium silicate solution. The sodium silicate was titrated with 1 N HCL to a pH of 7 at room temperature. At the conclusion of the stirring procedure, silica gels were created and left to mature for 24 h. At the conclusion of the operation, the aged silica gels and distilled water were combined to make silica slurry. To create xerogel silica, the slurries were rinsed numerous times with distilled water and then soaked for approximately 20 h at 70 °C in a beaker. Following that, the xerogel silica was grounded in a mortar for several hours to achieve a fine size. The particle size of the synthesized biosilica particle was determined using a particle size analyzer and was reported to be between 40 and 50 nm [18, 19]. Second, the thermochemically generated wheat husk biosilica was subjected to an acid hydrolysis silane treatment in accordance with published procedures [20, 21]. Figure 1 depicts the graphical illustration of silane-treated wheat husk biosilica developed in this investigation.

Fig. 1
figure 1

Graphical illustration of silane-treated biosilica preparation

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2.2 WHB-water dielectric synthesis

Silane surface–treated wheat husk biosilica particles and deionized water were used to make the dielectric fluid for this study. Biosilica particles are gently combined with deionized water and ultrasonically agitated for 10 min in this procedure. To start the silane reaction with deionized water, the resultant solution was slightly heated to 60 °C and agitated for additional 10 min. The biosilica particles are then finely dispersed and cooled to room temperature before being machined. DF0, DF0.25, DF0.5, and DF1 are the dielectric samples that were created. The subscripts 0, 0.25, 0.5, and 1.0 correspond to the weight of biosilica in this research.

2.3 Microdrilling process

In this present study, using the help of an Ocean OCT-3525NA electrical discharge machine and the drilling parameters listed in Table 1, micro-EDM drilling was completed. The equipment can create tiny holes ranging in size from 0.3 to 0.5 mm with a 50-A pulse generator. For the drilling sample, deionized water was used as the dielectric fluid, and silane-treated biosilica was used in conjunction with deionized water. A brass electrode with a diameter of 0.47 mm was used to make deep holes. Drilling was done on a Ti-6Al-4 V alloy that was 10 mm thick. Figure 2 depicts the micro-EDM machining setup utilized in this experiment, and Fig. 3 displays a SEM image of a drilled hole on a work piece specimen.

Table 1 Description of process variables
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Fig. 2
figure 2

Micro EDM setup used in this present investigation

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Fig. 3
figure 3

Machined micro holes on work piece

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3 Characterization

3.1 Material removal rate (mm3/min)

The material removal rate (MRR) is the rate at which material is removed from a workpiece per unit of time. In micro-EDM, the MRR is determined using the volume of material removed or the weight difference between the workpiece before and after the machining operation, as specified in Eq. 1:

$$\mathrm{MRR}\left(\mathrm{mm}^3/\min\right)=\frac{\mathrm{Difference}\;\mathrm{in}\;\mathrm{weight}\;\mathrm{of}\;\mathrm{the}\;\mathrm{work}\;\mathrm{piece}\;\mathrm{before}\;\mathrm{and}\;\mathrm{after}\;\mathrm{maching}}{\mathrm{machining}\;\mathrm{time}}$$
(1)

3.2 Tool wear rate (mm 3 /min)

The tool wear rate was calculated using mass loss of tool before and after drilling with respect to the time. The weight of both work piece and tool was weighed using a three decimal accurate digital balance machine. The machining time, which is used for calculating the tool wear rate, was calculated using a digital stop watch. Equation 2 shows the formula for calculating TWR:

$$\mathrm{TWR}\left(\mathrm{mm}^3/\min\right)=\frac{\mathrm{Difference}\;\mathrm{in}\;\mathrm{weight}\;\mathrm{of}\;\mathrm{the}\;\mathrm{tool}\;\mathrm{before}\;\mathrm{and}\;\mathrm{after}\;\mathrm{maching}}{\mathrm{machining}\;\mathrm{time}}$$
(2)

3.3 Surface roughness (Ra)

The surface roughness of the drilled holes was determined using a Mitutoyo version 2.0 surface roughness tester from Japan. Roughness measurements were taken on the samples’ inner drilled portion by sectioning them as two pieces. Ra, Rq, and Rz values were determined for all samples using a cut-off value of 0.88 mm. The test was carried out in compliance with ISO 1997 specifications.

3.4 Microstructure analysis

The microstructure of the welded portion was examined using an optical microscope (Moticam 1000, China) with a 25 × lens zooming capability. The specimens were grounded using a series of abrasive sheets with grit sizes ranging from 60 to 5/0 (US system). Followed by colloidal alumina paste and etching chemicals like potassium dichromate and Keller solution, the polishing was done. Finally, the specimen’s surface was cleaned with distilled water, and all micrograph images were taken using polarized light.

4 Results and discussion

4.1 Material removal rate

In the machining of Ti-6Al-4 V alloy, Fig. 4 demonstrates the material removal rate of various kinds of deionized biosilica-activated dielectric fluid. It should be noted that using pure water as a dielectric resulted in a material removal rate of 31.33 mm3/mm, which is much lower. The high hardness of the base metal and the less focused spark from the tool toward the workpiece were caused by the reduced material removal rate [22]. As a result, a lower erosive force on the workpiece was unable to remove material uniformly. However, the MRR was improved by adding wheat husk biosilica in silane-treated form. Machining with silane-treated biosilica activated dielectric at precise machining conditions yielded a maximum MRR of 40.82 mm3/mm. When compared to regular deionized water, this is a 30.29% improvement. For DF0.25 and DF0.5, the dielectric fluid improves MRR to 35.26 and 38.26 mm3/min, respectively. This equates to improvements of 12.54% and 22.11%.

Fig. 4
figure 4

Material removal rate of EDM drilling

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In powder-dispersed dielectric fluid, this significant improvement is the reason for increased effective spark length and standoff distance. When biosilica particles are present between the tool tip and the workpiece, effective polarization occurs, resulting in the production of longer sparks [23]. As a result, there is a greater amount of material removed from the substance. It is observed that there is a considerable MRR detected even with a high volume of particle loaded up to 1 wt. %. Because of silane-treated particle, the uniformity in the orientation helps to produce healthy sparks, which eventually improve the MRR [24].

4.2 Tool wear rate

The tool wear rate of several dielectric fluid micro EDM processes is shown in Fig. 5. The tool wear rate of the deionized water–equipped EDM technique produces a significantly higher TWR of 0.336 mm3/min. This is due to deionized water’s average heat absorption capacity. The tool tip is vulnerable to thermal fatigue when sparks are repeatedly created. If the tool is encased in a high-convective heat-carrying dielectric fluid, thermal fatigue may be reduced, resulting in less tool wear. In this, the erosion wear mechanisms account for the majority of tool material loss and result in poor machining results. The presence of a considerable volume of WHB particle in the dielectric, on the other hand, reduced the tool wear rate. The addition of 0.5 weight % WHB to the dielectric results in a lowered TWR of 0.21 mm3/min. The addition of 0.25 and 1.0 weight percent biosilica, on the other hand, raised the wear rate even further. The speak length variation and the intensity were the responsible for this difference [25].

Fig. 5
figure 5

Tool wear rate of EDM drilling

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The presence of biosilica induces effective polarization with biosilica particles between the tool’s tip and the workpiece, which thereby decreased the backfired sparks and erosion of tool material [8, 26]. Moreover, the biosilica fine particles absorb a lot of heat and keep the tool from getting too hot. During the machining process, undesirable secondary sparks and uncontrolled spark production were inhibited, resulting in a highly stable tool’s surface. Thus, in the silane surface–treated WHB added water dielectric; the tool did not erode significantly after a long run and maintained its structural integrity. Figure 6 shows the SEM images of (a) as-received EDM tool, (b) plain dielectric machined tool, and (c) the silane-treated biosilica-deionized water machined tool. It is noted that the plain dielectric machined tool shows highly rough and unfinished surface. The erosion of material is highly evidenced in this. However, in the biosilica-activated dielectric, the tool’s surface is not damaged much. Still, it maintains structural integrity after sufficient machining trials done.

Fig. 6
figure 6

SEM images of electro discharge machined tools

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4.3 Surface roughness (µm)

The surface roughness values of several dielectric fluids used in the EDM deep drilling process are shown in Fig. 7. It is noted that the plain deionized water has a higher surface roughness of 4.72 µm. The incorrect evacuation of slurries generated during machining was caused by the greater surface roughness. Due to inert-metallic attraction, these slurries returned to the material and damaged the machined surface once again. Furthermore, because deionized water has a lower cooling impact, it was unable to maintain a reduced cress cross pattern on the workpiece, resulting in excessive surface roughness.

Fig. 7
figure 7

surface roughness values in EDM process

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However, the presence of considerable amounts of wheat husk biosilica particles in the deionized water reduced the surface roughness. EDM machining of titanium alloy utilizing DF0.25, DF0.5 and D1 resulted in surface finish reductions of 33.47%, 43.22%, and 37.71%, respectively. The cause for the effective tool offset from the workpiece is the improvement in silane-treated biosilica dispersion in the dielectric during the deep drilling operation. As a result, the gap between the tool and the work piece is large enough to eject all of the removed material while reducing the risks of colliding [27]. This effect finally reduced the machined surface’s surface roughness and provided a smooth surface. Figure 8 shows the SEM-machined profile image of electrical discharge machined surfaces using various dielectrics. Figure 8 a shows the machined zone of plain dielectric used machining process. The surface is rough and possesses with more pit marks whereas in Fig. 8b, the surface is significantly smooth and less in waviness.

Fig. 8
figure 8

Machined surfaces of Ti-6Al-4 V titanium alloy

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5 Conclusions

The following are the precise outcomes of biosilica-added deionized water dielectric in machining of Ti-6Al-4 V titanium alloy.

  • The MRR was improved by adding biosilica particles to deionized water. The greatest MRR of 40.82 mm3/min was achieved with the addition of 1.0wt.% silane surface–treated biosilica particle.

  • In the EDM process, the silane-treated biosilica-activated dielectric results in a lower tool wear rate of 0.215 mm3/min for 0.5wt.% silane-treated WHB in water. The SEM image of plain dielectric machined EDM tool retains with uneven erosive wear whereas the biosilica-activated dielectric produced high structural integrity.

  • For silane-treated biosilica-activated dielectric in EDM, the machined surfaces exhibited lower surface roughness of 2.68 µm for DF0.5 dielectric fluid designation.

  • The SEM images shows highly rough and pit marked surface for plain dielectric employed machining. However, smooth surfaces were developed for the biosilica-activated dielectric machined Ti-6Al-4 V alloy.

  • In conclusion, the biogenic method, which produced silica nanoparticles from massive biomass wheat husk, worked as an activator at the deionized water dielectric in the EDM process and improving the machining properties.

  • As a result, when cutting hard Ti-6Al-4 V alloys with unconventional machining techniques such as EDM, surface-treated powder-dispersed water dielectric could be used to improve the machining properties.