The Impact of Magnetic Abrasive Finishing (MAF) Process Parameters on the Microhardness of Stainless Steel SUS420 Bubble Cups

improve microhardness (MH) most are, in order, gap distance, voltage, time, p article size, and spindle speed. The percentage change in microhardness (%∆MH) increases with higher voltage and time values and decreases with higher particle size and spindle speed values. This study observes an exception to this trend for the gap distance value of 1.2 mm. The use of smaller particle sizes in the range of (20-63) µm showed the most significant enhancement in microhardness (MH) at 21.20%, whereas larger particle sizes (125-250 µm) exhibited lower enhancement in microhardness (MH) at 4.12%.


Introduction
Bubble cups, which are frequently created via the deep drawing process, are widely used in distillation towers, where they are subjected to high pressure and temperature levels.Nonetheless, the presence of faults and the high production costs need to improve the surface quality of bubble cups [1][2][3].Increasing metal surface microhardness has many benefits.Improved fatigue, wear, and abrasion resistance enhance component lifespan.Strong scratch and corrosion resistance improves lifespan in severe situations.Stronger surfaces increase load-bearing capacity and mechanical strength.Increased heat resistance helps hightemperature applications.Elevated microhardness improves material dependability, minimizes maintenance, and extends metalbased product lifespan across sectors, improving customer satisfaction and cost-effectiveness [4][5][6][7][8].Due to some metals having specific properties, conventional finishing techniques like grinding, honing, and lapping are insufficient for achieving a satisfactory finish on these materials.Magnetic abrasive finishing (MAF) and other modern finishing techniques may provide a workable solution by enhancing surface quality and microhardness [9].In contrast to conventional finishing techniques, magnetic abrasive finishing controls machining forces using a magnetic field.Cost-effective finishing may be achieved by inserting magnetic polishing components into existing machine tools, eliminating the need for expensive, stiff, and error-free equipment.For the MAF method, a spindle chuck firmly holds a cylinder of work material.Whether the workpiece is made of steel or ceramic, it is affected by the magnetic field lines passing through it.Magnetic abrasive particles (MAP) are distributed between the workpiece and the magnet's poles in the working region.The abrasive grains of magneto abrasive brushes are flexible so that they may match the contours of the work surface [10].Magnetic abrasive particles can be made by combining magnetic particles (ferrous particles) with abrasive materials like aluminum oxide (Al2O3), silicon carbide (SiC), or diamond.Bounded, semi-bounded, and unbounded MAP models exist.Finishing with magnetic abrasives may be broken down into cylindrical (interior and exterior) and flat [11,12].As shown in Figure 1   Several previous studies machined stainless steel metals of different classifications with various numbers of input parameters.Firstly, the effect of five parameters (current, machining gap, speed, abrasives concentration, and time) on microhardness in the MAF process was studied by Ahmad et al. [6].Singh et al. [12]improved the microhardness surfaces of specimens by four input parameters (mesh size, speed, time, and abrasive weight).Microhardness was studied by Ahmed et al. [13].After Single Point Incremental Forming (SPIF), the MAF process was utilized as a finishing process with four input parameters (speed, feed rate, gap, and current).Nahy and Kadhum [14] proposed studying six input parameters (oil viscosity, powder quantity, gap distance, pole diameter, rotational speed, and Current).Zhang et al. [15] proposed using the MAF process as a flexible finishing technique to polish the samples generated by the selective laser melted (SLM) process with different slope angles and studied the MAF process effect on the microhardness of the sample surfaces.Teng et al. [16] studied the microhardness as a response factor of the MAF process after machining the workpieces by selective laser melted (SLM) process with varying one parameter (abrasive type).Mousa [17] studied the improvement of the hardness of stainless steel plate 321 by the MAF process with five input parameters (groove number, voltage, speed, time, and powder volume).Amineh et al. [18] studied the effects of four input parameters of the MAF process (gap, time, abrasive mesh size, and speed).They studied their effect on the microhardness of specimens to remove recast layers.
The machining processes involved in modern industries need to produce high-level quality products of bubble cups during the magnetic abrasive finishing process.This study aimed to investigate the effect of five parameters on the microhardness of bubble cups by using magnetic abrasive finishing techniques to produce high-level quality products.The parameters of interest include (supply voltage, finishing time, gap distance, rotational speed, and magnetic abrasive particle size).Using the Taguchi design methodology and ANOVA allows for efficient experimentation and analysis, enabling us to identify the optimal parameter settings that minimize surface roughness variation and enhance the surface quality of bubble cups.

Experimental Setup
Figure 2 shows this study's experimental setup.A drilling machine, magnetic pole, sample fixation, workpiece, power supply, and abrasive powder are included.The magnetic pole used was with 6000 turns of 0.75 mm copper wire.This coil was mounted on a 15-mm-diameter, 100-mm-long carbon steel shaft.The tool head was 20 mm in diameter and 30 mm long, with 2 mm grooves along the wall and base to increase magnetic force at the center, particle retention, rotational speed, and a homogeneous machining surface.Bubble cups were chopped into tiny pieces for this study's trials.Table 1 shows the chemical composition of the stainless steel 410 cup.The studies used 2:2:1 iron powder, resin, and AL 2 O 3 abrasive powder.After 24 hours in a 250°C furnace, the mixture solidified.The solidified slurry was milled at 350 rpm for 90 minutes to separate particles.
Following are the materials specifics and the experimental setup :

Experimental Procedure
Table 3 displays the selected triad of values for each of the five parameters: voltage, duration, gap distance, spindle speed, and particle size.The experimental design utilized the Taguchi L27 orthogonal array methodology in conjunction with Minitab-17.The constraints for each parameter were determined based on the most prevailing and commonly observed limitations in recent studies [19][20][21][22][23][24][25][26][27].The amount of abrasive powder used in each experiment equals 2 grams.

The Microhardness Measurement
The method used for computing the percentage of improvement in microhardness is measured by taking an average for three device readings before and after finishing the process in Nanotechnology and Advanced Materials Research Center/University of Technology.The indentation was done with a weight equal to 250 grams for 15 seconds with device information: Digital Micro Vickers Hardness Tester, Model: TH715, SN: 0006, TIME ( Bei Jing TIME High Technology Ltd).The values of ∆% were computed as explained in Equation 1 [28] (1)

Taguchi Design
To optimize product and process performance, reducing variability and enhancing quality is essential.Taguchi's designs employ fractional factorials to facilitate comprehensive research with minimal effort.This strategy conserves time and resources while yielding valuable insights.Robustness is achieved by mitigating the impact of external factors, particularly those beyond control [29].Taguchi designs are helpful in many different areas, including manufacturing, engineering, and product creation.These methods are helpful to businesses because they help cut costs, improve performance, and increase customer happiness [30,31].The experimental plans of the tests designed by Taguchi's L27 orthogonal array are recorded in Table 4 below.

Results and Discussion
The microhardness values were measured before and after the MAF process for all experiments and are in Table 5.It can be seen that all experiments have an improvement in microhardness.The range of the percentage increase (4.12-21.20)%was notable.From the experimental results shown in Table 5, The most substantial enhancement in microhardness was observed (27), with a remarkable increase of 21.20%.This improvement was achieved through the use of the smallest particle size (offering more cutting edges), a high voltage (resulting in greater magnetic force), a moderate gap size (providing optimal magnetic force), and a lower rotational speed (creating higher cutting force).
The improvement of microhardness in the present work is reasonable compared to other works, as shown in Table 6.However, other works used a different number of parameters with different ranges.It is important to remember that the limits are still governed by the successful performance of the tool adapted and the optimal experiment.Therefore, the close improvement of the present work with others' improvements indicates the good ranges chosen for the parameters and the procedure despite using five input parameters.From Taguchi analysis results, the gap distance parameter had the main or maximum parameter effect on microhardness that has rank (1) as shown in Table 7, followed by voltage, time, particle size, and spindle speed.As can be seen in this table, the levels of the parameters are equivalent to the levels of the experiment (27) already achieved, as shown in Table 5.In Figure 3, the first part shows a consistent increase in the percentage change in microhardness (%∆MH) as the voltage was raised, as noticed in previous studies [17] [13].The increase in %∆MH leads to a large rigidity of abrasive chains that exert a stronger impact on the specimen's surface when the applied magnetic flux increases.So, a large magnetic force with a proper gap distance raised MH surfaces.Longer finishing time enhanced %∆MH with a certain proper gap distance (magnetic force), where as Mousa [17] found the opposite with a big gap distance (low magnetic force).Gap distances (1.2, 0.8, 1.6) mm clearly influence %∆MH.Among these, the 1.2 mm gap distance yielded the most favorable result because this gap distance facilitated optimal brush flexibility and effective abrasive force and abrasive movement.Although the 0.8 mm narrow gap produced high magnetic force, it constrained abrasive movement, while the 1.6 mm wide gap resulted a reduction in %∆MH due to the increased distance between the pole and workpiece, weakening the rigidity of the chain of abrasives.As the spindle speed increased, the  [13,33,17], because the centrifugal force increased, pushing the abrasives further away from the tool center.Small abrasive particle size in this work showed the highest (%∆MH) and reduced continuously as the particle size grew.Therefore, the smaller abrasive particle size has more cutting edges than those with larger particles and the smaller particle size improved the brush flexibility [12].In previous studies, a larger range of particles size was adapted and obtained opposite behaviour with microhardness.Therefore in this study, the maximum effect on microhardness can be observed with particle sizes of ((20-63), (63-125), and (125-250)) µm.Within the chosen ranges of the parameters and from Taguchi analysis as appeared in Table 7, the optimum parameters obtained are the level 3 in the voltage range (30V), level 3 of time (20 min), gap distance (level 2 (1.2 mm), spindle speed (level 1, 220 rpm) and particle size with level 3 (20-63 µm).The Equation 2shows the (%∆MH) regression equation.From ANOVA analysis-General Linear Model (%∆MH) versus voltage (V), time (min), Gap distance (mm), Spindle Speed (rpm) and particle size (mm) are given in Table 8. that shows the results of Analysis of Variance.
The Regression Equation model    The ANOVA analysis is illustrated in Figure .4, elucidating the interactions among input factors for %∆MH.The top row initially elaborates on the behavior of %∆MH concerning three voltage levels in correlation with other parameters.Voltage interacts with time, gap distance, and speed but does not interact with particle size.The second row shows the behavior of %∆MH regarding three-time levels in conjunction with other parameters, where time interacts with gap distance and speed.The third row illustrates the interaction of gap distances with the speed parameter.In the last row, it's noted that spindle speed levels do not interact with the particle size.

Conclusion and Future Work
This study examined the microhardness of stainless steel SUS420 bubble cups at the MAF process for bubble cups.Brush flexibility, which changes depending on the tools' electromagnetic design, affects the MAF process's performance.By analyzing the experimental data using Taguchi Analysis in Minitab 17, the study determined the relative effects of each parameter on the microhardness as: 1.
The best parameters of %∆MH in the current experimental setting are in experiment 27, which can differ from one design to another.2.
The small abrasive particle size gives good results in %∆MH with a 1.2 mm gap distance.

3.
The analysis showed that the parameters' order affected the (%∆MH) from the largest to the smallest in order (gap distance, voltage, time, particle size, and spindle speed).4.

5.
The very small gap needs higher speed, lower voltage, and/or smaller particle sizes of abrasives to increase the brush's flexibility and vice versa.6.
The (%∆MH) was raised with higher values of (voltage and time) and lowered with higher values of (particle size and spindle speed), with another proper parameter excepting the value of 1.2 mm of gap distance at this work.7.
The optimum percentage increase of microhardness obtained was 21.2%.8.
The study of many input parameters is significant to optimize the MAF process.Still, it is important to expand the levels of the parameters to obtain clearer behavior and determine the limit of each, which is useful for future works that concern designing and manufacturing MAF machines in industrial productions.

Table 1 :
Chemical Composite of Stainless Steel 410

Table 3 :
MAF Process Parameters

Table 6 :
Compares the percentage decrease in %∆MH with other worksHint: * means that the percentages were calculated from data and/or graphs in the reference.
became less, as found in Ayad et al.,Alkarkhi and Mousa

Table 7 :
Most parameter contribution in microhardness from the means

Table 8 :
Analysis of Variance for %∆MH