Papers by Author: Dong Sam Park

Abstract: For joining and cutting non-woven fabrics, an ultrasonic wide-blade horn is expected to be used effectively. During the joining and cutting process, this horn can work as the punch in the punching and blanking systems. The performance of a wide-blade horn is normally relevant to the resonance at the operating frequency, the vibration amplitude, and the uniformity of the amplitude on the output surface. In this study, an ultrasonic wide-blade horn is optimally designed and fabricated for joining and cutting non-woven fabrics, and it is tuned to operate at 20 kHz, the resonant frequency of the converter. Analytic and experimental results show that based on the modal and harmonic response analysis and repeated tuning, the wide-blade horn could be optimally designed and fabricated. The resonant frequency of the developed horn was 19,979 Hz, and the amplitude uniformity of the output surface was 76%.

Abstract: In this research, a new ultrasonic horn is designed and fabricated for welding thin Ni plates by vibration analysis. Two types of the horn tip are fabricated to evaluate the effect of horn’s tip on the weldability. Modal analysis, harmonic response analysis and FFT analysis are carried out for verifying the adequacy of the developed horn. To evaluate weldability of two types of horn tip, welding strength and the microstructure of the weld surface are experimentally investigated with various welding parameters such as pressure, time and vibration amplitude. Finally, the new horn with resonant frequency of 40 kHz is developed, and it is shown that welding strength and the microstructure of the weld surface are largely affected by horn’s tip shape.

Abstract: This paper gives a description of an experimental study on the ultrasonic welding of metals. In ultrasonic metal welding, high frequency vibrations are combined with pressure to join two materials together quickly and securely, without generating large amount of heat. Horn, a key part of ultrasonic welding machine, should be designed very accurately to get the natural frequencies and vibration mode required. In this study, a horn is designed and developed for ultrasonic welding of Cu sheets. The tensile strength of welded parts is investigated for evaluation of weldability. Experimental parameters of welding test is set as follows; welding time 0.4s ~ 3.4sec. and vibration amplitude 40%, 60%, 80% and welding pressure 1.5bar, 2.0bar, 2.5bar. Samples are Cu sheets of 0.1mm thickness. Experimental results showed that the tensile strength increase as welding parameters increase, but when welding pressure is excessive, the tensile strength decrease due to fracture of the Cu sheets caused by over-welding. These results could be successfully applied for ultrasonic metal welding in various fields of manufacturing industry.

Abstract: Ultrasonic energy is spotlighted as a skill which connects detailed parts accurately and safely. So we designed the horn needed for attaching Tubular type of metal parts such as slip ring used for providing electricity for a body of rotation. We considered mainly booster’s size, slip-ring’s size, and nature frequency of horn. This design fixed the frequency given from ultrasonic metal welder as 40,000Hz, so it decided the approximate length of horn which makes maximum vibration amplitude through formula. And we designed the horn as a step shape with fillet for increasing the amplitude and decreasing stress concentration. Horn’s tip is designed 10mm length in view of the shape of slip-rings. And we calculated and analyzed the natural frequency by the modal analysis and harmonic analysis using Ansys that is analysis program. Through this study, we could examine the manufacturing possibility of the horn for ultrasonic metal welding of tubular type.

Abstract: In this study, the machining characteristics of developed AlN-hBN composites were investigated in the end-milling and precision lapping processes. To achieve the objectives, material properties of the developed AlN-hBN composites were evaluated according to the variation of hBN contents. And, required experimental works were performed to investigate the machining characteristics of the composites. First, the machiniability of the composite was evaluated in the end-milling process under various cutting conditions, such as spindle speed, feederate, and depth of cut variations. Also, generated micro cracks caused by the cutting process were investigated via SEM photographs. Next, precision lapping experiments were performed under various conditions, and the results were estimated.

Abstract: In this study, micro patterns were formed on the developed AlN-hBN composites using powder blasting techniques, which have been considered as one of the most appropriate micro machining methods for hard and brittle materials such as ceramics. To achieve the objective, first, material properties of the developed AlN-hBN composites were evaluated according to the variation of h-BN contents. And, a series of required experiments were performed, and the results were analyzed. As the results, it was investigated that the machiniability of the developed AlN-hBN composites increased with the increase of the h-BN contents in the composites. From the experimental results, it was possible to determine optimum blasting conditions for micro pattern making on the developed AlN-hBN composites.

Abstract: Powder blasting is similar to sand blasting and effectively removes hard and brittle materials. With an increase in the need for machining of ceramics, semiconductors, electronic devices and LCDs, micro abrasive jet machining has become a useful technique for micro-machining. In this study, we first investigated the effects of the blasted glass surface’s characteristics and shape under different blasting parameters; second, we examined the predictive models for material removal and surface roughness that have been developed in terms of blasting pressure, scanning speed and abrasive flow, using response surface methodology by experimental data. The established equation shows that the blasting pressure was the main factor influencing the material removal and surface roughness. In addition, analysis of variance for the firstorder model of material removal and surface roughness shows that the coefficient of determination (R2) is 99% and 98%, respectively. The associated p-value for the two models was lower than 0.01, indicating that the models are statistically significant.

Abstract: In this study, powder blasting techniques are applied for micro groove forming on the developed AlN/hBN composites. First, material properties of the composites are evaluated according to the variation of h-BN contents. And, a series of required experimental works are performed to determine optimum powder blasting conditions for micro groove forming. The experiments are performed for the prepared samples with masked patterns. As the results, it can be observed that the machiniability of the developed AlN/hBN composites increases as h-BN contents in the composites. Also, from the experimental results, it is possible to determine the optimum blasting conditions for micro groove forming on the developed AlN/hBN composites.

Abstract: The effects of h-BN content on the microstructure, mechanical properties, and machinability of Si3N4 ceramics were investigated. The relative density of the sintered compact decreased with increasing BN content. The flexural strength also decreased with h-BN content, mainly due to lower Young’s modulus of h-BN compared to Si3N4. With increasing h-BN content, Si3N4/h-BN based ceramic composites revealed enhanced crack resistance (R-curve) behavior. The Vickers indentation crack paths in specimens are sinusoidal due to bridging and pull out of grains during crack propagation. The grain size of ß-Si3N4 slightly decreased with h-BN content. During milling and micro-drilling process, monolithic Si3N4 ceramic could not be machined, due to brittle fracture. However, thrust forces measured for Si3N4/h-BN composites decreased with increasing h-BN content, showing the excellent macro and micro machinabilty.