Abstract:This study describes the use of ultrasonic-assisted end milling to improve the quality of the machined surface of hard Stavax (modified AISI 420) mold steel and to reduce the amount of work involved in the final polishing process. The effects of input voltage, the stretch length and cutter holding force on the amplitude of the ultrasonic vibration used were measured. The effect of ultrasonic frequency (25 and 50 kHz) and amplitude (0, 2.20 and 3.68 µm) as well as the effect of the rake angle (6 • and −6 • ) and the cutter helix angle (25 • , 35 • and 45 • ) on tool wear and quality of the workpiece surface finish were also investigated. It was found that the ultrasonic amplitude increased with cutter stretch length and input voltage, as expected. The amplitude remained constant when the cutter holding force exceeded 15 N. The experimental results showed that the ultrasonic amplitude had an optimum value with respect to surface finish. However, large amplitude ultrasonics did not necessarily improve quality. Furthermore, the cutters used for ultrasonic-assisted milling show less wear than those used for normal milling. It was also found that a positive rake angle and cutters with a large helix angle gave a better surface finish.

This paper presents a novel lubrication method for milling processes that employs cooling system-assisted minimum quantity lubrication (CSMQL) using a thermoelectric cooling system. The CSMQL method improves the cooling effect in the cutting area and enhances processing quality, in addition to reducing energy consumption. Four different coolant strategies including CSMQL, dry, minimum quantity lubrication (MQL), and wet methods were compared in processing mill die steel (SKD11), which is widely used in industry. Different aspects of the milling performance (e.g. surface roughness, morphology, milling temperature, and milling forces) were investigated using these coolant strategies. The experimental results show that not only is the surface roughness of steel milled using CSMQL better than that of steel milled using dry and MQL methods, but CSMQL also produces fewer tool marks on the workpiece surface. In addition, it was found from observations of chip color that using the CSMQL method reduced the cutting temperature by 27% and the cutting force by 22%, compared with dry machining. In summary, the use of CSMQL can not only improve the surface roughness and reduce the cutting force and cutting temperature, but also promote processing quality. This study will help researchers develop more efficient cooling strategies in the future.

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This paper presents a combined diamond disk that is designed and manufactured to markedly improve the leveling of diamond tips, thereby reducing the amount of diamond grit. First, a small brazed diamond disk was manufactured. Second, 12-or 24-disk brazed diamond disks were mounted onto a substrate with a diameter of 108 mm for completing the combined diamond disk. Four types of disks were fabricated, and their performances were compared with that of a conventional diamond disk. The experimental results showed that the combined diamond disk has more complete diamond crystal shapes and distribution with better leveling, which increases the effectiveness of the working diamond grits. Compared to a conventional diamond disk, the combined diamond disk achieved a higher wafer removal rate and better uniformity while consuming less pad material. The number of diamond grits required was significantly lower. Roughly, 7,600 and 12,000 diamond grits were used for the 24-and 12-disk brazed diamond disks, respectively, in the new disk, whereas 20,000 diamond grits were used in a conventional diamond disk. In the case of the conventional diamond disk, the diamond tips are leveled to more than 50 μm. However, in the case of the combined diamond disk, the diamond tips can be leveled to less than 30 μm because the diamond tips are already leveled. These results contribute to the understanding of conditioning techniques and further improvement of the chemical mechanical polishing process.