Sung-Ki Lyu

Characteristic of quenching refrigerant for heat treatment deformation control of SM45C steel

This study deals with the characteristic of quenching refrigerant for heat treatment deformation control of SM45C steel. Heat-treatment deformation must be controlled for the progress of production parts for landing gear. Most of deformation is occurred on inconsistent cooling. The inconsistent cooling is caused by a property of quenching refrigerant. When a heated metal is deposited in the quenching refrigerant, the cooling speed is so slow in early period of cooling because of a steam-curtain. After additional cooling, the steam-curtain is destroyed. In this progress, the cooling speed is very fast. The object of this study is to control the deformation of heat-treatment for landing gear by improving the conditions of quenching. The cooling curves and cooling rates of water, oil and polymer solution are obtained and illustrated. From the characteristics of the quenching refrigerant, the effects of heat-treatments on thermal deformation and fatigue strength are also investigated.

Elongation of contact length on the line of action in roll forming of gears

The elongation of contact length on the line of action is considered with particular reference for roll forming of gears, and for dynamic behavior of the tooth in meshing. However there is no paper that discuss the elongation of contact length in the load meshing of gears. Based on our investigation, the contact length on the line of action elongates more than the kinematically calculated value. In rolling, as the tool approaches the workpiece, the center distance of the gears decreases by a small amount. But, the elongation of contact length is sensitive. Therefore, the contact point on the line of action is difficult to be determined, which complicates the tooth analysis. In this study, the exact relation between the elongation of contact length and the tooth space over the recess or before the approach are revealed by experiments and kinematic theory. This analytical result applies not only for rolling, but also for the single flank meshing which is done under constant center distance.

Mathematical model and analysis on cycloid planetary gear

Cycloid planetary gear plays an important role in precision transmission. Accuracy control of transmission is an extra crucial requirement for design and manufacture. Firstly presented a mathematical approach for precision analysis on cycloid gear, it enable predict mesh stiffness, backlash and angular transmission error with consideration of manufacture tolerance, elastic deformation in cycloid gear. Secondly, the solution was developed for angular transmission error analysis in K-H-V reducer, in which includes effect from bearing (stiffness and initial mounting conditions), crank shaft (offset error and flexibility). Finally, experimental study was conducted for validation which showed good agreement with simulation.

Effect of MoS2-based composite coatings on tribological behavior and efficiency of gear

MoS2 -based Ti composite coatings were deposited on the AISI 4118 alloy and gears using an RF magnetron sputtering (RFMS) system. While MoS2 coating had been coated on the silicon substrate. The coatings structures were compared to each other to find the effect of Ti. The composite coatings have been performed by a ball-on-disk tribometer to investigate tribological behavior at various conditions. The structure of the coatings has been extensively studied by a variety of techniques, including X-ray diffraction (XRD) and scanning electron microscopy (SEM), etc, respectively. The composite coatings were also applied the gears of a reduction gearbox. The efficiencies of uncoated and coated gear with MoS2 based Ti coatings were measured and compared at various input rotating speed under absorption oil film condition. It was found that the efficiency of gear had significantly improved after MoS2 -based Ti composite coatings deposition.Copyright

Development of a Wearable Haptic Feedback System for Limb Movement Symmetry Training

Arm swing asymmetry brought on by hemiparesis or hemi-neglect due to stroke causes increased ground reaction moments during walking. Thus, increasing loading asymmetry of the lower limbs and the metabolic load of walking. The system presented here consists of wearable bracelets, designed to help decrease arm swing asymmetry in people with stroke. Design of the bracelets and outcomes of pilot tests with a healthy subject with artificially induced arm swing asymmetry are presented. The healthy subject was able to utilize the vibration feedback to reduce arm swing asymmetry with involuntary increase in arm swing magnitude. Thus, exploration of the effects of using this system with stroke patients is warranted.

A Study on Optimum Design of Worm Gear Reducer Output Pinion

Reducer is a device to transmit and change torque and speed from drive shaft to driven shaft with excellent transmission efficiency, and it is widely used in many areas today. Reduction gear consists of two axes, gear, bearing supporting axes, and housing. The simplest method to transmit rotation or power to multiple axes is to attach circular plates to two axes and contact each other. However, in this case, if increasing number of rotations or if contact pressure is small, because of slipping, it cannot transmit power. For problems for the current reducer case, it is heavy and its assembling and repair is difficult. In addition, there are few studies about manufacturing and performance testing of worm gear reducer, causing lack of the foundation to improve the product competition and the performance.

Improvement of Positioning Error on a Ball Screw Drive System by Liquid-Cooling

The demand for higher productivity and tight part tolerances requires machine tools to have faster and more accurate feed drive system. As tried and tested technology, ball screw drive systems are still used in majority of machine tools due to their low cost and high stiffness. A high speed ball screw drive system natually generates more heat and results in greater positioning error, adversely affecting the accuracy of machined parts. In order to estimate the positioning error of the ball screw system and effectiveness of the liquid-cooling system, all possible heat gain-loss sources were analyzed and calculated as calculation factors. The following paper also presents degree of positioning error improvement which employed circulation liquid-cooling system and forced liquid-cooling system. Comparing the experimental results and the forcasts, it shows that sensational cooling performance and high consistency of reality and prediction are displayed.Copyright

A Study on Tooth Modification for Spur Gear for Articulated Hauler

Construction equipment is heavily loaded during normal operation. In recent years, there is a trend that lower gear noise levels are demanded for driver to avoid annoyance and fatigue of operation. For articulated haulers, meshing transmission error (T.E.) is the excitation that leads the tonal noise known as gear whine, and radiated gear whine is also the dominant source of noise in gearbox. This paper presents a method for the analysis of the tooth modification, and the prediction of transmission error under the loaded torque for the spur gear pair of the articulated hauler’s final drive. And the transmission error, contact stress, root stress and load distribution are also calculated and compared before and after tooth modification under one torque. The simulation result shows that the transmission error and stress under the load can be minimized by the appropriate tooth modification. It is a good approach where the simulated result is used to improve the design before the prototype is available for the test.Copyright

Tribological behavior of C-N coated spur gear by plasma source ion implantation

The C-N coating can provide outstanding performance on the surface of spur gear. SCM415 specimens and test gears with steel surface were treated with carbon nitrogen by the plasma source ion implantation (PSII) method. The composition and structure of the surface layer were analyzed and compared with that of PVD coated TiN layer. It was found that both of friction coefficients of C-N coating decreased with the increase of load, however, C-N coating showed relatively lower friction coefficient than that of TiN coating. The effect of C-N coating was investigated on hardness, friction and wear. The TiN coated gear showed a more serious friction phenomenon than that of C-N coated gear. It was considered that coating of TiN, which was conducted at a vacuum chamber at about 500°C, resulted in a tempering of base material that caused microstructure change, which in turn resulted in decreasing of hardness, the C-N coated gear and pinion had higher wear resistance than that of TiN coated gear and pinion. C-N coating significantly improved the friction and wear resistance of gears.

A Study on Reducing the Gear Tooth Profile Error by Finish Roll Forming

This paper deals with the tooth profile error of spur gears that have been finished by roll forming. First, we present experimental data that confirms that the tooth profile error is a synthesis of a concave error and a pressure angle error. Since various types of tooth profile errors appear in the experiments, evaluation parameters are introduced for rolling gears so that profile quality may be objectively evaluated. Using these evaluation parameters, the relationship among the tooth profile error, the addendum modification factor (A. M. factor), and the tool loading force are verified. The character of concave error, pressure angle error and tool loading force of finish roll forming by using a forced displacement method are verified. This study makes clear that the tool loading force of finish roll forming is a very important factor that affects involute tooth profile error. The results of the experiment and analysis show that the proposed method reduces both concave and pressure angle errors.Copyright