Effect of Process Parameter Variations on Triangular Microcavity Fabrication Using Micro-EDM

Abstract

This research study examines the effects of process parameters on fabricated triangular micro holes using micro-EDM (Micro Electrical Discharge Machining). The micro-EDM process utilized a 400 μm tungsten carbide electrode shaped as an equilateral triangle. The machining parameter assessment involved measuring errors in the corner radius and the included angle of the microcavity. The corner radius of the triangular microcavity ranged from 5 to 15 μm. Simultaneously, the included angle varied between 61 and 64°. These variations were attributed to adjustments in capacitance, voltage, and feed settings, which spanned from 1 nF, 90 V, and 5 μm to 100 nF, 130 V, and 15 μm, respectively. Statistical analysis using ANOVA revealed that voltage and capacitance significantly impacted the alterations in corner radii and included the angle of the manufactured triangular microcavities. FESEM is used to analyze the recast layer formation on the edges of the microcavity. It will help to decrease the error in fabricating triangular cavities using micro EDM.

1. Introduction

Precision is essential in the field of micromanufacturing. High dimensional accuracy is an essential target requiring extreme attention to every aspect of production. Fabricating micro polygonal profiles is difficult to create using traditional machining processes [1]. Maintaining corner and angular precision in polygonal profile products may be difficult despite its importance. As a result, many manufacturers are looking at new technologies and techniques that will enable them to achieve more precision and accuracy in their micromanufacturing processes. Sophisticated machining processes can meet the demands of modern industry. Electrochemical machining (ECM) [2], a technique that dissolves metal using a conductive fluid, is often used in the aerospace and medical sectors. Laser beam machining (LBM) is utilized in the electronics and automotive sectors to remove material with a strong laser. Ultrasonic machining (USM) frequently removes material using ultrasonic vibrations and produces micro-components. Electron beam machining is predominantly used in aerospace to remove material using an electron beam. For high-precision and high-speed machining in aerospace and medical applications, electrochemical discharge machining (ECDM) is a hybrid technique that combines electrical discharge machining (EDM) and electrochemical discharge machining (ECM). Electrical discharge machining (EDM) [3] is a non-contact technique that erodes material using electrical sparks. It is best suited for machining complicated structures and harder materials like titanium, carbide, and tool steels. Among these, EDM is particularly noteworthy for its ability to machine any conductive material, regardless of hardness, and create complex shapes with high precision. Micro-EDM is the most commonly used variant, especially for micro-structures (holes, slots) and complicated 3D profiles [4].

The Micro EDM process has two major limitations: its material removal rate is comparatively low compared to other processes, and the tool wear rate during EDM is high. Various approaches and methods are used for predicting and optimizing the TWR and MRR of micro EDM. Bellotti et al. [5] used data-driven methods to create regression models that could predict tool wear and material removal rates (MRR and TWR) in micro-EDM blind holes. By using process monitoring data as input for their regression models, the researchers reduced errors in predicting MRR and TWR by approximately 65 and 85%, respectively. Pragadish et al. [6] greatest impact on material removal rate (MRR) and tool wear rate (TWR) while drilling silicon steel and optimizing the micro EDM process parameters to achieve high MRR with reduced tool wear rate in coated tools and found dielectric cardanol oil has major influence and at gap voltage of 50 V, Green dielectric (%) of 05 and coating thickness of 1 μm, got optimum MRR of 9.69 mm3/min and a tool wear rate (TWR) of 1.09 mm3/min. Arunnath et al. [7] fabricated a hole on T6 aluminum alloy using aluminum 7075 nano boron carbide metal matrix composites using EDM, and ANOVA was used to analyze the experimental results to know the percentage of contribution of each parameter on MRR and TWR. Sanghani et al. [8] developed a mathematical model using a regression equation of MRR and TWR in EDM based on a fraction-of-energy approach. Vidya et al. [9, 10] investigated the dimensional accuracy of micro holes and microchannels fabricated EN-24 alloy steel using die sinking EDM process and found that the micro holes have a roundness error of 46.33 μm, and the microchannels have a straightness tolerance of 13.51 μm. Geometric tolerance greatly affects the performance and lifetime of the mechanical parts. Microcavity was created by Abhinav et al. [11] discovered that the diametral length of the microcavity varied between 748 and 800 μm.

The manufactured micro holes using micro EDM show extremely less circularity variation. Near the edges of the machined holes, some recast layer development that varies between 6.5 and 7.5 μm was observed. According to Huan et al. [12], it is necessary to compensate for micro-electrode wear to maintain the dimensional consistency and accuracy of micro-hole arrays in micro-EDM drilling. Mouralova et al. [8] studied the fabrication of a precise slot of size 5000 × 170 μm in a copper foil with a thickness of 125 μm and used the same copper foil as a tool in micro EDM. Unune et al. [13] studied the dimensional accuracy and surface quality of micro-channels with low-frequency vibration assistance in micro-electro-discharge milling. They found that the discharge energy significantly affected the amount and size of the globules formed during μ-ED milling. Rafaqat et al. [14] produced non-circular holes of three shapes (square, triangle, and hexagon) in AISI D2 steel. They evaluated the performance of three response characteristics: material removal rate, tool wear rate, and land wear.

These limitations impact the dimensional accuracy of the machined feature. Researchers continuously improve the material removal rate and reduce the tool wear rate. In this investigation, the performance of micro EDM was evaluated in fabricating a polygonal structure, specifically a triangular profile. Non-circular shaped holes, commonly used in the mold industry, were selected as the machining profiles. The performance was evaluated against two triangle features, included angle between sides and corner radius, by varying the input parameters such as voltage, capacitance, and feed.

2. Experimental details

This study experimented on a MIKROTOOLS DT110 (hybrid micro-EDM), as shown in Figure 1, which includes micro-drilling, micro-milling, micro-grinding, micro-turning, and micro-EDM. The experiment used the Taguchi design, a robust design modeling method. Taguchi’s philosophy of robust design focuses on making products and processes less sensitive to sources of variation, such as environmental conditions or manufacturing fluctuations. An L8 orthogonal array was constructed for this experiment. Orthogonal arrays are pre-arranged tables that allow researchers to explore multiple factors and their interactions with relatively few experimental runs, thereby saving time and resources. The equilateral triangle tool of tungsten carbide having a side of 400 μm and a corner radius of 8 μm, as shown in Figure 2(a), is used. The designed experiment was further optimized using ANOVA, a statistical method used to analyze the variance in data by partitioning the total variability into different sources, such as the variability between groups and within groups. In optimization, ANOVA helps identify significant factors and interactions that influence the response variable, enabling practitioners to make informed decisions to improve processes and achieve optimal outcomes [15, 16]. The corner radius and included side angle of the triangular hole are calculated using image analysis with the help of the Zeiss AXIO Scope A1 optical microscope equipped with the inbuilt AXIO Vision software (Table 1).

Figure 1.

Hybrid micromachining Centre-MIKROTOOLS DT110.

Figure 2.

(a) Tool of an equilateral triangle of side 400 μm, included angle 60°, and initial corner radius of 8 μm (b) triangular hole generated through micro-EDM.

Sl. No	Voltage (V)	Capacitance (nF)	Feed (μm/sec.)	Corner radius (μm)	Included angle (°)
1	90	10	5	35.08	61.12
2	90	100	5	37.45	62.31
3	90	10	20	35.24	61.27
4	90	100	20	38.20	62.78
5	120	10	20	39.71	61.78
6	120	100	20	40.05	63.69
7	120	10	5	40.95	61.41
8	120	100	5	41.08	63.59

Table 1.

L8 Taguchi design of experiment with responses corner radius and included angle.

3. Results and discussions

3.1 Corner radius

In the field of micro-EDM, the corner radius of a triangle microcavity is of utmost importance. For numerous reasons, it is crucial to precisely manage this dimension, defined as the curvature or rounding at the microcavity’s corners. A lower radius produces sharper corners, which has an impact on the geometric correctness of the workpiece. It has an impact on machining accuracy, first and foremost. Table 2 defines that in the case of corner radius, voltage contributed 4.9%, capacitance 94%, and feed 0.03%.

Source	DF	Adj SS	Adj MS	F-Value	P-Value	Contribution %
Voltage (V)	1	3.1001	3.1001	25.68	0.007	4.937
Capacitance (nF)	1	59.187	59.187	490.32	0	94.259
Feed (μm/sec.)	1	0.0221	0.0221	0.18	0.691	0.035
Error	4	0.4829	0.1207			0.769
Total	7	62.792

Table 2.

Analysis of variance for corner radius of triangular microcavity.

Figure 3 presents a main effect plot that graphically illustrates the impact of varying key process parameters, namely input voltage (V), capacitance (μF), and feed rate (μm/sec), on the corner radius of triangular microcavities manufactured using Micro-EDM. The plot provides a clear depiction of how changes in these parameters influence the corner radius of the microcavities. The plot represents two different input voltage levels, specifically 90 and 120 V. Each voltage level is associated with a data point on the graph. It is evident that as the input voltage increases from 90 to 120 V, there is a noticeable upward trend in the corner radius of the microcavities. It suggests that higher input voltage settings result in larger corner radii. As capacitance increases from 10 to 100 μF, the corner radius of the microcavities also increases. An upward slope on the graph represents this relationship. It indicates that higher capacitance settings lead to larger corner radii.

Figure 3.

Main effect plot for corner radius.

The effect of feed rate on the corner radius appears to be relatively minimal compared to the other parameters. There is only a slight change in the corner radius as the feed rate varies between 5 and 15 μm/sec. It is represented by a nearly horizontal line on the graph, suggesting that changes in feed rate have less pronounced effects on the corner radius when compared to input voltage and capacitance variations. Figure 4 provides a comprehensive view of the residuals from the model used to predict the corner radius of triangular microcavities. It includes visualizations and analyses to assess whether the residuals meet key assumptions, such as normality and independence, which are crucial for the reliability of the model’s predictions. These diagnostic tools are essential for validating the model and ensuring its suitability for practical applications in micro-EDM microcavity fabrication. Figure 5 shows an interaction plot for corner radius, which clearly shows the interrelation of voltage, feed, and capacitance with the combination of one to another in a single figure.

Figure 4.

Residual plot for corner radius.

Figure 5.

Interaction plot for corner radius.

3.2 Included angle

The included angle of a triangular microcavity is a critical parameter of interest. This angle, formed by the two sidewalls of the triangular cavity, holds immense importance in micro EDM for several reasons. Firstly, it directly affects the shape and dimensions of the machined feature, which is pivotal in achieving precise geometries in micro components. Secondly, the included angle impacts the EDM process stability and efficiency, influencing factors such as discharge energy distribution and material removal rates. Also, studying the included angle is essential for optimizing electrode design and machining parameters, ensuring that the microcavities meet various industries’ specific requirements, including microelectronics, medical device manufacturing, and microfluidics. Table 3 defines that in the case of the included angle of the triangular microcavity, voltage contributed 24.3%, capacitance 61%, and feed 0.5%.

Source	DF	Adj SS	Adj MS	F-Value	P-Value	Contribution %
Voltage (V)	1	5.445	5.445	7.25	0.055		24.365
Capacitance (nF)	1	13.7812	13.7812	18.34	0.013		61.668
Feed (μm/sec.)	1	0.1152	0.1152	0.15	0.715		0.515
Error	4	3.0061	0.7515				13.452
Total	7	22.3475

Table 3.

Analysis of variance for the included angle of triangular microcavity.

Figure 6 illustrates the impact of varying input voltage (V), capacitance (μF), and feed rate (μm/sec) on the included angle of triangular microcavities fabricated using micro-EDM. Higher input voltage and capacitance levels result in larger corner radii, as evidenced by the upward trends in the graph. In contrast, changes in feed rate between 5 and 20 μm/sec have a comparatively minimal effect on the included angle, as indicated by the nearly horizontal line on the plot. Figure 7 describes the residual plot for the included angle of microcavity. Figure 8 shows an interaction plot for the included angle of microcavity, which clearly shows the interrelation of voltage, feed, and capacitance with the combination of one to another in a single figure.

Figure 6.

Main effect plot for included angle.

Figure 7.

Residual plot for included angle.

Figure 8.

Interaction plot for included angle.

3.3 Optimization using ANOVA

Optimization using Analysis of Variance (ANOVA) in Minitab involves using statistical techniques to determine the optimal settings or conditions for a process or system by analyzing different factors or variables that affect the response variable—the model to perform optimization using ANOVA, as shown in Figure 9. The optimum solution for both corner radius and included angle of triangular microcavity achieved through ANOVA is 90 V, 10 nF, and 5 μm/sec, as in Figure 10.

Figure 9.

Process optimization using ANOVA.

Figure 10.

Optimal solution.

4. Conclusions

This investigation has systematically probed the influence of input parameters on the corner radius and included angle of triangular micro cavities produced via micro-electrical discharge machining (micro EDM). The empirical observations offer the following conclusions.

• A discernible relationship between the corner radius of the microcavity and the included angle was discerned as the corner radius expanded from 5 to 15 μm, resulting in an associated variation in the included angle from 62 to 67°. The dynamic response elucidates the pronounced sensitivity of the micro EDM process to modifications in input parameters, thus accentuating the paramount importance of precise parameter manipulation to attain the desired geometrical outcomes.

• Applying statistical and analysis of variance (ANOVA) techniques underscored that capacitance substantially influenced both the corner radius and included angle.

• The investigation unveiled that the most favorable operational conditions for minimizing variation in microcavity geometry comprised a voltage of 90 V, a capacitance of 10 nF, and a feed rate of 5 μm/sec. is preferable to include a Conclusion(s) section which will summarize the content of the book chapter.

Acknowledgments

All authors fulfill the criteria for authorship.

Conflict of interest

The authors declare no conflict of interest.

Funding

There is no funding received.

Notes/thanks/other declarations

Special thanks to Department of Production and Industrial Engineering, Birla Institute of technology Mesra for providing the research facilities.