Abstract:As a successful solution applied to hard machining, the minimum quantity lubricant (MQL) has already been established as an alternative to flood coolant processing. The optimization of MQL parameters and cutting parameters under MQL condition are essential and pressing. The study was divided into two parts. In the first part of this study, the Taguchi method was applied to find the optimal values of MQL condition in the hard milling of AISI H13 with consideration of reduced surface roughness. The L9 orthogonal array, the signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to analyze the effect of the performance characteristics of MQL parameters (i.e., cutting fluid type, pressure, and fluid flow) on good surface finish. In the results section, lubricant and pressure of MQL condition are determined to be the most influential factors which give a statistically significant effect on machined surfaces. A verifiable experiment was conducted to demonstrate the reliability of the results. In the second section, the optimized MQL parameters were applied in a series of experiments to find out cutting parameters of hard milling. The Taguchi method was also used to optimize the cutting parameters in order to obtain the best surface roughness. The design of the experiment (DOE) was implemented by using the L27 orthogonal array. Based on an analysis of the signal-to-noise response and ANOVA, the optimal values of cutting parameters (i.e., cutting speed, feed rate, depth-of-cut and hardness of workpiece) were introduced. The results of the present work indicate feed rate is the factor having the most effect on surface roughness.

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As a successful solution applied to electrical discharge machining (EDM), powder-mixed electrical discharge machining (PMEDM) has been proposed as an upgrade of the EDM process. The optimization of the process parameters of PMEDM is essential and pressing. In this study, Taguchi methods and analysis of variance (ANOVA) were used to find the main parameters affecting surface roughness in the EDM process with SiC powder-mixed-dielectric of hardened 90CrSi steel. The PMEDM parameters selected were the powder concentration, the pulse-on-time, the pulse-off-time, the pulse current, and the server voltage. It was found that SiC powder exhibits positive effects on reducing surface roughness. The roughness obtained with the optimum powder concentration of 4 g/L was reduced by 30.02% compared to that when processed by conventional EDM. Furthermore, the pulse-off-time was found to be the most influential factor that gave an important effect on surface roughness followed by the powder concentration. The EDM condition including a powder concentration of 4 g/L, a pulse-on-time of 6 µs, a pulse-off-time of 21 µs, a pulse current of 8 A, and a server voltage of 4 V resulted in the best surface roughness.

This paper presents an experimental study of the positive effects of vibration-assisted deep drilling of aluminum alloy Al-6061. The four most important evaluation criteria in drilling-machinability, workpiece temperature, torque, and material removal rate-were chosen to be investigated. Holes with a depth-to-diameter ratio of 13 were drilled by high speed steel (HSS) twist drill bits of 3 mm diameter, using both methods of conventional drilling (CD) and ultrasonic-assisted drilling (UAD). Three levels of axial force of 6 kgf, 9 kgf, and 12 kgf were kept constant for each pair of comparison experiments. It was found that workpiece temperature and torque not only changed from one drill to the other, but were also dependent on the hole depth being drilled. Comparisons were made in-pair between CD and UAD under the same axial force and at the same order of hole numbers. The result shows that the material removal rate with UAD was up to 3.5 times higher than that with CD and the average workpiece temperature and torque in UAD were reduced by 3.5 and 6 times, respectively. Moreover, tool life in UAD was observed to increase from 2.5 to 5 times, in terms of number of holes drilled, compared to that in CD. thrust force, morphology chip, built-up edge, exit burr, and hole oversize from UAD were reported as significantly improved compared with those from CD. In research by Chang and Bone [2], the authors predicted and compared thrust force induced in UAD and CD of Al-6061-T6. The conclusion shows that there is a vibration frequency that minimizes thrust force in different drills and cutting conditions. Burr height reduction of up to 85%, tool life increase (in terms of number of holes drilled), and an up to 20% reduction in the thrust force of UAD compared with those of CD have also been revealed in another study by these authors [3]. In other investigation, Li et al. [4] found that the thrust force of UAD is much smaller than that of CD, with a larger vibration amplitude resulting in the smaller thrust force of the cutting edge. A study by Babitsky et al. [5] verified several improvements in machining characteristics due to UAD in drilling, including faster penetration rates, reduction of tool wear, surface finish, roundness and straightness of holes, and the reduction or complete elimination of burrs when drilling ductile plates. Nevertheless, the effectiveness of UAD in deep hole drilling of aluminum alloys, where the depth-to-diameter ratios are larger than 5, have rarely been found in the literature.Investigations considering the reduction of torque and temperature as a primary factor which leads to major improvements in UAD compared with CD of other materials have also been limited in the literature. An experimental study from Azarhoushang and Akbari [6] drilling Inconel 738-LC considered on improvement in average surface roughness and circularity, hole oversize, and drill skidding, causing discontinuous and finer chips in UAD in contrast to in CD. Advantages of UAD such as reducing the thrust force and the cuttin...

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