Papers by Keyword: Ultrasonic Vibration

Abstract: Nowadays, microstructures have an important role in optical products as well as in optical systems. Beside machining methods, hot glass embossing is recently a novel technology to manufacture microstructures in optical components with high quality and low cost. Especially, this technology has been assisted efficiently by ultrasonic vibration. Previous studies showed that high energy of ultrasonic vibration would lead to the temperature rise inside the glass so that the material was easily embossed into the microcavities on the mold. Thus, micro-formability of glass material has been especially improved efficiently. However, there were no studies focusing on effect of ultrasonic vibration on embossing speed in this process. Therefore, this work is aimed to utilize ultrasonic vibration to improve the embossing speed of hot glass embossing process. K-PSK100 optical glass was used as the material for all experiments. Pyramid array with size of 30 × 30 × 20 μm and period of 150 μm was created on the mold. Microstructure hot embossing experiments were conducted for both conventional process (without ultrasonic vibration) and ultrasonic vibration-assisted process (frequency of 35 kHz and amplitude of 3 μm). By fixing the embossing temperature of 430 °C, the embossing speeds of 0.05 mm/min, 0.10 mm/min and 0.15 mm/min were applied, respectively. Experimental results showed that in case of conventional process, the faster embossing speed, the smaller final height of pyramid structures. Nevertheless, this obstacle was resolved by ultrasonic vibration. Under heating effect of ultrasonic vibration, the glass still filled well into the pyramid cavities on the mold even when the high embossing speed was applied. Measurements indicated that in the same experimental conditions (temperature and speed), ultrasonic vibration could improve the filling ability of the glass to 18 %. This finding could be used to optimize the experimental conditions to increase the productivity of the microstructure hot glass embossing process.

Abstract: Generally nano-SiC particles are difficult to be added into molten aluminum metals because of poor wettability. Nano-SiC particles reinforced A356 aluminum alloy composites were prepared by a new process, i.e., a molten-metal process combined with mechanical stirring at semi-solid state and ultrasonic vibration method. The nano particles were β-SiC_p with an average diameter of 40 nm, and pre-oxidized at about 850°C to form an oxide layer with thickness of approximately 3.6 nm. The SEM analysis results show that nano-SiC particles are dispersed well in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the 2wt.% nano-SiC_p/A356 composite in as-cast state are 259 MPa and 5.3%, and they are improved by 20% and 15% respectively compared with those of the A356 alloy.

Abstract: In this work, ultrasonic rheocasting was used to refine the microstructures of Mg alloys reinforced with long period stacking ordered (LPSO) phase. The semisolid slurries of Mg-Zn-Y and Mg-Ni-Y alloys were prepared by ultrasonic vibration (UV) and then formed by rheo-squeeze casting under high squeeze pressure (~ 400 MPa). The effects of UV and squeeze pressure on microstructure and mechanical properties of the Mg alloys were studied. The results reveal that UV and rheo-squeeze casting can significantly refine the LPSO structure and alpha-Mg matrix in Mg alloys, but they cannot change the phase compositions of the alloys or the type of LPSO phase. When the squeeze pressure is 400 MPa, the average thickness of LPSO phase is decreased, and the block LPSO structure is completed eliminated and uniformly distributed at the grain boundaries. Compared with the gravity cast alloys without UV, mechanical properties of the rheocast Mg alloys were enhanced and reached the maximums when the squeeze pressure was 400 MPa.

Abstract: According to the removal mechanism of ductile regime machining of nanoZrO2 ceramics and the dynamic characteristics of ultrasonic vibration assisted diamond flying cutting (UVADFC), the model of the material removal rate (MRR) of nanoZrO₂ ceramics under UVADFC and diamond flying cutting (DFC) have been proposed by infinitesimal method,. In this paper, the experiment of three factors and four levels was carried out to study the relationships between MRR and the machining parameters (cutting depth , spindle speed n and feed rate c). The results of the experiment shows that UVADFC is a cost-effective method which is applied to the machining of nanoZrO₂ ceramics, and the MRR of nanoZrO₂ ceramics under UVADFC is 1.3-2 times greater than that of DFC, and the degree of the factors significantly influence on the MRR of nanoZrO2 ceramics are feed rate, cutting depth, spindle speed in a sequence whether it is DFC or UVADFC. The results will shed more light on the material removal mechanism of UVADFC.

Abstract: Ultrasonic-assisted metal forming have been studied numerously in conventional macro scale. However, ultrasonic dynamic impact effect, occurring in micro scale, has never been studied thoroughly, which makes the characteristics of material deformation more unpredictable in ultrasonic-assisted micro forming. The purpose of this study is to confirm the critical condition for occurrence of ultrasonic dynamic impact effect and to investigate the dimensional height dependency of ultrasonic dynamic impact effect on material deformation. In this paper, commercially pure aluminum 1100 with varying height (φ2×2mm, φ2×1.5mm, φ2×1mm) were selected for conventional static (without ultrasonic vibration) and ultrasonic-assisted compression tests. Ultrasonic-induced stress reduction was evaluated and the contour shape of deformed specimens was compared to investigate the ultrasonic dynamic impact effect on material deformation. The results showed that, as dimensional height of specimen decreased, ultrasonic vibration can reduce forming stress more effectively. In addition, a surprising anti-barreling shape and a significant contact surface area expansion were observed near contact surfaces in every specimen compressed with ultrasonic-assistance, indicating that additional plastic deformation can be produced by ultrasonic dynamic impact effect. An ultrasonic dynamic impact factor (y) is proposed and estimated by an exponential type trend line as y = 2.42e^-1.48x for different dimensional specimen height (x) to quantify the ultrasonic dynamic impact effect. The promising prospect of ultrasonic vibration in micro-forming was demonstrated by the findings above, which helped to provide a basis to understand the underlying mechanism of ultrasonic-assisted micro forming and design the process in the future.

Abstract: The method of imparting ultrasonic vibration to the cutting tool is known to improve the shape accuracy and finished surface roughness. However, a uniform evaluation of this function in drilling has not been achieved, and the cutting process cannot be checked from the outside. The aim of this study is to investigate the cutting characteristics in deep hole drilling when an ultrasonic vibrator on the table of a machining center provides vibration with a frequency of 20 kHz to the work piece. The ultrasonic vibrations in this system reach the maximum amplitude in the center of the work material. We evaluated the change in finished surface roughness between the section where drilling starts to the point of maximum amplitude with ultrasonic vibration. The main cutting conditions are as follows: cutting speed (V) 12.6 (mm/min); feed rate (s) 30, 60 (mm/rev); depth of cut (t) = 32 (mm); work material, tool steel; cutting tool material, HSS; point angle (σ) 118 (°); and drill diameter (φ) 4 (mm). Lubricant powder was also added to clarify the cutting effect, and compared the condition in which there was no ultrasonic vibration. The results showed that surface roughness at the point of maximum amplitude was better than that with no vibration.

Abstract: Ultrasonic-Assisted Milling (UAM) combines the material removal mechanism of grinding and the milling kinematics with ultrasonic assistance. The process is suitable for hard-to-cut materials used in many industrial applications. UAM is a novel process, still under investigation to clarify the product accuracy and the process performance. This paper presents a literature review covering the development of the experimental work related to UAM. A summary of key research problems is concluded and a systematic study using the design of experiments is suggested in order to investigate the effects of the main process parameters on its performance.

Abstract: In this study, the modification effects and mechanism of manganese (Mn) and ultrasonic vibration (USV) on the needle-like Fe-containing intermetallic compounds of Al-20Si-xFe-2.0Cu-0.4Mg-1.0Ni (x=1, 2 wt.%) alloy have been studied respectively. The effect of Fe-containing phases on volume fraction of hard phases is also investigated. The results show that the mechanism and effect of Fe-containing intermetallic compounds improved by Mn are in close relationship with Fe content. Mn can promote to form less harmful α-Al₁₅(Fe,Mn)₃Si₂ phase, or replace some Fe atoms of β-Al₅FeSi and δ-Al₄FeSi₂ according to different Fe content. When USV was applied to this alloy containing 2%Fe near liquidus temperature, most of the acicular β phases formed in traditional process are substituted by fine plate δ phases. With the combined effects of 0.5%Mn and USV, the acicular β phases are almost repressed and the Fe-containing phases exist in form of fine Al₄(Fe,Mn)Si₂ and Al₅(Fe,Mn)Si particles about 20~30μm. Consequently, the total volume fraction of hard phases which are composed of primary silicon particles and Fe-containing phases increases significantly.

Abstract: Metal matrix nanocomposites (MMNCs) have excited great interest in recent years, due to their very good properties. In this work, an efficient process by combining high-energy ball milling (HBM) with ultrasonic vibration (UV) was employed to prepare MMNCs. The composite granules containing nanoSiC_P were produced by milling the nanoSiC and Al powders, and then were remelted in the matrix melt and treated by UV to prepare MMNCs. The MMNCs were finally formed by squeeze casting. The results indicate that globular nanoSiC_P/Al compound granules with diameters between 1.5-2mm are obtained by dry HBM, and the nanoSiC particles are uniformly distributed in the granules. After remelting, nanoSiC particles in compound granules release in the matrix melt and are uniformly dispersed by UV within 2min. In MMNCs, nanoSiC particles concentrate mainly around eutectic phases, but no agglomeration is observed. The tensile strength of the MMNCs with 1wt.% nanoSiC_P is increased by 19%, compared to the matrix A356 alloy.

Abstract: Mg-Zn-Y alloys containing a thermally stable icosahedral quasicrystal phase (I-phase) will have wide application future on condition that primary α-Mg dendrite and the I-phase can be refined during the casting process. In this research, the microstructure and mechanical properties of the rheo-squeeze casting (RSC) Mg-6Zn-1.4Y alloys have been investigated. The Mg alloy melt was exposed to ultrasonic vibration (USV) with different acoustic power densities from 0 W/mL to 9 W/mL, and then the slurry was formed by squeeze casting. The results show that good semi-solid slurry with fine and spherical α-Mg particles could be obtained with the acoustic power density of 6 W/mL, and the average grain size and shape factor of primary α-Mg were 32 μm and 0.76, respectively. Meanwhile the coarse eutectic I-phase (Mg₃Zn₆Y) was refined obviously and dispersed uniformly. Compared with the samples without USV, the tensile strength and elongation of the RSC casting samples with 6 W/mL acoustic power density were elevated by 10.6% and 55.5%, respectively.