Optimal Design and Experimental Verification of Ultrasonic Cutting Horn for Ceramic Composite Material

We developed and optimized a block-type ultrasonic horn that can be used for cutting hard materials. The proposed block-type sonotrode consists of an aluminum horn and a tungsten carbide blade to increase the cutting of hard materials. We designed an initial ultrasonic block horn that has double slots and an exponential stepped profile. We developed a finite element model of the initial model and analyzed the characteristics of natural frequency and displacement. We formulated a DOE table and response surface to perform sensitivity analysis and analyze the correlation between the design variables and characteristics of the proposed block horn. The optimal ultrasonic block horn was derived via a multi-objective optimal design problem to maximize the amplitude uniformity of the proposed horn and frequency separation. We fabricated the optimal block horn and verified it experimentally. An ultrasonic cutting experiment was conducted to find the ultrasonic cutting force with hard ceramic composite materials. A cutting test with a conventional cutting machine under the same condition was also conducted to compare the cutting force. The proposed optimal ultrasonic cutter requires 70% less cutting force than the conventional cutter to cut a ceramic composite material and the cutting surface with the application of the proposed optimal ultrasonic cutter is much cleaner with no crack and delamination than that with the application of the conventional cutter

Numerical Determination of the Frictional Coefficients of a Fluid Film Journal Bearing Considering the Elastohydrodynamic Lubrication and the Asperity Contact Force

This paper proposes a numerical method to investigate the frictional characteristics of a fluid film journal bearing considering the elastohydrodynamic lubrication and the asperity contact force. We solved the average Reynolds equation by utilizing the FEM to determine the hydrodynamic force developed by the lubricant of the journal bearing. We also used a modified GT model (Greenwood–Tripp model) developed by Greenwood and Tripp to decompose the asperity contact force into normal and tangential directions. Once we applied those forces to a rotor, we solved the equations of motion of a flexible shaft to determine the friction coefficient. We verified the proposed method by comparing the calculated friction coefficient with the measured one of journal bearings conducted by prior researchers. Then, the proposed method was applied to investigate the frictional characteristics of a journal bearing of a scroll compressor on which dynamic loads are applied. This paper can contribute to developing robust rotor systems supported by journal bearings

Crawling Magnetic Robot to Perform a Biopsy in Tubular Environments by Controlling a Magnetic Field

We developed a crawling magnetic robot (CMR), which can stably navigate and perform biopsies remotely in tubular environments by controlling a magnetic field. The CMR is composed of a crawling part and a biopsy part. The crawling part allows the CMR to crawl forward and backward via an asymmetric friction force generated by an external precessional magnetic field. The biopsy part closes or opens the cover of a needle to use the biopsy needle selectively with the control of the external precessional magnetic field. The cover of the biopsy part prevents damage to the tubular environments because the biopsy needle is inside the cover while the CMR is navigating. We developed the design of the proposed CMR using magnetic torque constraints and a magnetic force constraint, and then we fabricated the CMR with three-dimensional printing technology. Finally, we conducted an experiment to measure the CMR’s puncturing force with a load cell and conducted an experiment in a Y-shaped watery glass tube with pseudo-tissue to verify the crawling motion, the uncovering and covering motion of the biopsy needle, and the CMR’s ability to extract tissue with the biopsy needle

Effects of Laminar, Turbulent, and Slip Conditions in a Fluid Film on a Dry Gas Seal

A dry gas seal is a mechanical seal that prevents leakage of gas from rotating machines utilizing gas as a medium. Fluid film in a dry gas seal can exhibit laminar, turbulent, and slip behavior due to operating conditions and design parameters. A modified Reynolds equation that considers the effects of laminar, turbulent, and slip behavior of a fluid film was proposed and solved using the finite-element and Newton–Raphson methods to calculate the pressure, opening force, and leakage rate. The accuracy of the developed program was verified by comparing the simulated pressure with that of prior research, and the measured leakage with simulated leakage. The characteristics of a T-groove dry gas seal were investigated according to laminar, turbulent, and slip behavior in the fluid film. The results show that the effects of laminar, turbulent, and slip behavior in a fluid film on a dry gas seal should be considered to accurately predict the characteristics of a dry gas seal