Applied Mechanics and Materials Vol. 889

Abstract: Bulk moulding compounds (BMCs) are composite materials of thermosetting polymer matrix reinforced by short glass fibers. BMCs have known as the alternative of the traditional materials thanks to their optimal properties such as lightweight, durability, corrosion under certain environment, formable, high electrical resistance... The previous study mentioned the process of manufacturing composite materials BMCs from unsaturated polyester resin reinforced with short glass fiber and CaCO₃ filler by Z axis mixer and applying in the circuit breaker bottom, [1, 2]. To improve the thermal resistance of BMCs under high temperature condition in the industry, in this research, alumina filler was added to investigate the influence of alumina with the different content of 15wt.% and 20wt.% on the mechanical, thermal and electrical properties of BMCs. Specimens manufactured with and without alumina filler content were compared. The results show clearly that adding alumina could improve the thermal properties whereas this might decrease the tensile strength of BMCs. The experimental results also indicated the influence of mass fraction of alumina filler content on properties of BMCs.

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: This article presents preliminary investigations on the cutting ability of the singer layer metal-bonded cBN grinding wheel manufactured by electroplating method at Vietnamese laboratory. The cutting ability of the grinding wheel is evaluated by two factors: grinding ratio G and surface roughness of workpiece. These results are compared to those of the Japanese grinding wheels. The experimental results showed that the fabricated cBN grinding wheel has good cutting ability with high grinding ratio G. The value of the grinding ratio was 600 to 1800 in the grinding process of SKD11 steel (hardness of 62-63HRC) at the grinding speed V of 12.56m/s, feed rate S of 300mm/min, depth of cut t of 0.01mm. The maximum grinding ratio (1800) is equivalent to the average grinding ratio of the Japanese grinding wheel. The grinding ratio is also maintained up to 26 cutting hours. The good grinding surface was achieved with the average Ra of 2.5μm. In addition, the bonding of cBN abrasive to the wheel body was observed with scanning electron microscope (SEM) of the surface of grinding wheel after the cutting process. The SEM image shown that the cBN abrasive particles were not removed from the wheel surface.

Abstract: Metal cutting is one of the most important machining processes in manufacturing industry. Thorough understanding of metal cutting process facilitates the optimization in selection of cutting tools and machining parameters. There are several methods used for studying phenomena in metal cutting process. Using a quick-top device is an efficient technique for investigation cutting process in which cutting action is stopped so suddenly that the “froze” specimen called the chip root honestly depicts what happened during cutting action. Design strategies of a quick-stop are accelerating cutting tool away from the workpiece or decelerating the workpiece remaining in engagement with the tool. Operation of a quick-stop device can be either mechanically or by explosive. Quick-stop devices can be utilized for various types of machining processes such as: turning, milling, drilling. This paper described the analysis, fabrication, and testing of a quick-stop device which is used for researching on chip formation in hard turning. This device has simple and safe operation which utilizes spring forces to retract the tool from workpiece during cutting. The results of performance at cutting speed of 283 m/min show that the separation distance is quite small, less than 0.2mm so that the deformations on the root chip are close to that while actual machining process. This indicates that the device has satisfied the requirements of an equipment for studying on chip formation.

Abstract: In this research, an effective method to fabricate various metallic nanoand micro structure patterns is developed by combination of chemical stamping and selective peeling off technique. The feasibility of the process is experimentally studied and demonstrated. In this paper, the authors present the effects of the chemical treatment on the substrate surface on the formation of the nanodots array and its absorbance property. The results show that the chemical treatment by dropping Acetone solution on the quartz glass substrate strongly affects the morphology and absorbance property of the nanodots array. With the Acetone treatment on the substrate, the nanodots become smaller and more uniform in size through thermal dewetting process. Simultaneously, it results in blue shifted of the absorbance peak and enhancement of the absorbance peak intensity. The improvement of the optical property of the nanodots array is useful for plasmonic solarcell and bio sensing applications.

Abstract: EDM die sinking (called shortly EDM) is a non-traditional machining. This method is applied in concave area which cannot machining by traditional method such as deep concave, thin wall which is smaller than normal cutting tool, and especial the steel after heat treatment .

Abstract: The use of freeform (sculptured) surfaces in the product design process is accelerating at an exponential rate driven by functional as well as esthetics demands. CAD/CAM software is a must in their design are relatively well-covered, issues still remain when it comes to the actual manufacture of freeform surfaces. The major issues are related to the chosen feed rate, toolpaths and step over that would assure the required surface quality, the minimization of the total machining time, etc. This research presents an experimental study to define the effects of machining’s parameters (including: feed rate; toolpath and step over) for CNC 3-axis ball end milling process. The result shows a model for cutting is formulated and incorporated into the parameters of machining that is compatible with all CAD/CAM systems. This result can be used to choose parameters of optimum including federate, toolpath and step over when machining of other freeform surfaces. Keywords: Freeform surface; tool path; ball end milling

Abstract: Electrical discharge machining (EDM) process is widely used to process hard materials in the industry. The process of electrical discharge is changed and called PMEDM when alloy powder is added in the oil dielectric. In the current study, the effect of tungsten carbide alloy powder added in the dielectric on the surface roughness (R_a) and the micro hardness of surface (HV) status of the workpiece SKD61 after machining is investigated. Studies show that the surface roughness and the micro hardness of surface obtained by PMEDM is generally better than that by normal EDM. The method can be applied for improving surface quality such as improving strengthening of molds and machine parts.

Abstract: Nowadays, increasing the productivity and the quality of machining become major challenges of the metal cutting process. Due to the complexity of the chip formation process, in particular, at high cutting speeds, finite element model (FEM) has been frequently used as an alternative solution. Chip shrinkage coefficient and cutting force are the two basic parameters of the cutting process, which determines the productivity and quality of the workpiece. This study uses a Grey correlation relationship to analyze and select the common set of parameters for cutting force and chip shrinkage coefficient of the chip. Simulation of the A6061 aluminum alloy high-speed milling is done by Bao-Wierzbicki's (B-W) model. The optimal parameters are determined cutting depth 1 mm, clearance angle 6^o and rake angle 10^o. This parameter set adjusts the cut parameters so that the cutting process achieves the highest machining efficiency.

Abstract: Body shell of anti-tank rocket which is a pipe part working under extreme conditions of high pressure and temperature, is manufactured from low-alloyed high quality steel 30X3MФ. The steel 30X3MΦ made in Vietnam appropriates of standard to produce body shell anti-tank rocket. The shell ensure technical requirements of composition, with very low rate of P, S and has good mechanical properties. After casting, steel billets were backward extrusion, includes 3 steps of thinned stamp, heat treatment and drawing processes, body shell fabrication is satisfied requirment of technique for anti-tank rocket shell. Results of fire testing of the body shells are in agreement with that of Russian ammunition. The body shells of anti-tank rocket which were manufactured in Vietnam conditions, satisfied desired technical requirement.