Yongbo Wu

Inconel 718 has been widely used in industries because of its excellent mechanical properties. However, the machining process, particularly the turning/grinding, of Inconel 718 is still costly due to high cutting force and heavy tool damage. Fortunately, a promising material removal technique, that is, ultrasonic-assisted turning/grinding (called UAT/UAG for simplicity), could potentially play a great role in the high efficiency precision machining of Inconel 718 due to its excellent features such as smaller turning/grinding force, better surface quality, longer tool working life and lower heat generation. However, few attempts have been done on UAT/UAG of Inconel 718. Therefore, in this work, in order to confirm the feasibility of machining Inconel 718 by UAT/UAG, experimental apparatus/equipment has at first been constructed by installing an ultrasonic cutting-unit/spindle on a NC lathe/surface grinder for UAT/UAG operations, and then experimental investigations have been performed to elucidate the fundamental machining characteristics involving Inconel 718 workpiece including the effects of the ultrasonic vibration and the cutting/grinding speed on the work-surface finish, the machining force and temperature, the chip formation, the tool/wheel wears and so on. The obtained results show that grinding forces and surface roughness were decreased in UAT/UAG.

The working surface condition of abrasive tool is one of the important issues in grinding process. This article discusses the effects of the ultrasonic vibration on the working surface condition involving chips adhesion and abrasive grains wear during ultrasonic-assisted grinding (UAG) of Inconel 718 with an electroplated cBN grinding quill as the abrasive tool. In this study, scanning electron microscopic (SEM) observations were performed on the quill working surface before and after grinding at different vibration amplitudes, and the SEM images were filtered, extracted, and binarized by using image-pro plus to evaluate the quill working surface condition. The obtained results demonstrated that (1) the wear of grinding quill is dominantly attributed to chips adhesion, grains releasing, and grains fracture; (2) both the percentage of chips adhesion area and the size of chips adhered tend to decrease as the vibration amplitude increases; in contrast, the effect of ultrasonic vibration on the number of chips adhesion is not noticeable; (3) the percentage of the number of grains released/fractured decreases as the vibration amplitude rises, e.g., the percentage in UAG at vibration amplitude of A_p–p = 9.4 μm was decreased by 40% compared to that in conventional grinding (CG); and (4) higher distribution density of effective cutting edges can be achieved under larger vibration amplitude, and the mean area of effective cutting edges in UAG is smaller than that in CG, demonstrating that the ultrasonication enhances the grinding quill sharpness.

A novel magnetic field-assisted polishing technique was proposed for finishing 3D structured surface using a magnetic compound (MC) slurry. The MC slurry was prepared by blending carbonyl-iron-particles, abrasive grains and α-cellulose into a magnetic fluid which contains nano-scale magnetite particles. An experimental setup was constructed firstly by installing an oscillation worktable and a unit onto a polishing machine. Then, experimental investigations were conducted on oxygen-free copper workpiece with parallel distributed linear V-grooves to clarify the influence of the polishing time and abrasive impact angle on the grooves surface qualities. It was found that (1) the groove form accuracy, i.e. the form retention rate η varied with the polishing locations. Although the form retention rate η deteriorated during the polishing process, the final η was greater than 99.4%; (2) the effective impact angle θ_m affected the material removal and form accuracy seriously. An increase of the absolute value θ_m resulted with an increase of material removal rate and a decrease of the form accuracy; (3) the work-surface roughness decreased more than 6 times compared with the original surface after MC slurry polishing. These results confirmed the performance of the proposed new magnetic field-assisted polishing method in the finishing of 3D-structured surface.

In nano-precision surface finishing of engineering materials using MCF (magnetic compound fluid) slurry, the water-based MCF slurry is preferable from the viewpoint of the environmental issue and the running cost of cleaning workpiece and equipment. However, the uncoated-CIPs (carbonyl-iron-powders) within the conventional MCF slurry have low ability against aqueous corrosion, leading to the performance deterioration and working life shortening of the conventional MCF slurry. This study proposed a new MCF slurry containing ZrO₂-coated CIPs instead of the uncoated CIPs. Its performance in the polishing of oxygen-free copper was compared experimentally with that of the conventional one. The results showed that the work-surface finish polished with the new slurry was in the same level as that with the conventional one when the slurry was used soon after prepared, i.e., the settling time was 0 min; however, as the settling time increased the uncoated-CIPs got rusty, leading to a deterioration in the slurry performance. By contrast, no rust was observed on ZrO₂-coated CIPs even the settling time reached several days, indicating the employment of ZrO₂-coated CIPs prolonged the working-life of the MCF slurry greatly.

Inconel 718, a nickel-based superalloy, exhibits desirable properties over a wide temperature range, and it is widely used in industry. However, Inconel 718 is typically difficult to cut because of its strong work hardening, high temperature tensile strength, and shear strength. To improve the machinability of Inconel 718, this study proposes ultrasonic turning by applying elliptical vibration to the base plane. The principle and features of the ultrasonic elliptical vibration are discussed in detail. Experiments were conducted on a commercial ultrasonic cutting unit installed onto a commercial numerical control (NC) lathe; the cutting forces were found to be lower in the new method than in conventional turning (CT). Microchip particles were observed on both chip and work surface in CT but were almost absent on the surfaces prepared by ultrasonic elliptical vibration assisted turning (UEVT). Furthermore, the cutting tool used in CT developed built-up edge (BUE), and its flank wear became heavier; in contrast, negligible BUE and less flank wear were found on the cutting tool used in UEVT. The theoretical surface roughness of UEVT was calculated and it agreed much well with the measured surface roughness.

Electroless nickel–phosphorus (Ni–P)-plated mold for hot press of optical lens must be manufactured to nanolevel surface roughness. The single-crystal diamond turning (SCDT) process is generally used to machine the Ni–P plating layer to attain the required form and ultrafine surface finish. However, this process frequently causes concentrically arranged tool marks to appear on the work surface. In this study, the Ni–P plating layer was polished with magnetic compound fluid (MCF) slurry to remove the tool marks. Two MCF slurries were used, one containing high-quality carbonyl iron particles (CIPs) and alumina (Al₂O₃) abrasive particles (1 µm), and the other containing CIPs coated with zirconia (ZrO₂) abrasive particles (50–100 nm). First, spot polishing without relative motion between the center of the MCF carrier and the workpiece was carried out using both slurries. Then, scanning polishing with the MCF carrier moving along a motion path was carried out using only the MCF slurry containing ZrO₂-coated CIPs. Although both slurries removed the SCDT-induced tool marks on the work surface, the MCF slurry containing relatively large Al₂O₃ abrasive particles left scratches and frequently caused CIPs to be embedded in the Ni–P plating surface, which inversely worsened the work surface roughness. In contrast, the MCF slurry containing relatively small ZrO₂ abrasive particles resulted in an improved work surface roughness, without scratches or the embedding of particles. The cross-sectional profile of the polishing spot manifests a characteristic symmetrical W-shape. The dot-shaped scratches were induced at the spot center, and the lengths of these scratches increase with the increase in the distance from the spot center. In scanning polishing, the W-shaped polishing spot moves along the designed scanning path and instantaneous overlapping occurs, which significantly improves the flatness of the Ni–P plating layer from 0.2 to 0.1 µm. In addition, almost all the particles can move relative to the work surface, and the surface finish of the Ni–P plating layer was improved, without scratches or the embedding of particles. The preliminary results show that the MCF polishing is applicable to the nanolevel finishing of soft magnetic materials.