Researcher List

Department of Mechanical Engineering

Improvement of the machining accuracy on the five-axis machining centers

Pyramid shape machining using a 5-axis machining center
Pyramid shape machining using a 5-axis machining center

In the field of machining, machining centers are widely used because drilling, face milling, and end milling, can all be done on one machine. In particular, five-axis machining centers are increasingly popular because of the improvements they offer in production efficiency, and their ability to machine complex shapes, since the tool can be adroitly inclined as it travels along the workpiece. However, the machining accuracy of a five-axis machining center is typically lower than that obtainable using a common three-axis control machine. The more complex machine's structure is a potential source of assembly errors that accumulate, so one solution begins by finding the origin of the errors that degrade the accuracy. The sophisticated nature of five-axis machining centers demands well-trained users, or else various errors in the results may appear due to an operator's limited understanding of their characteristics.
In practice, tool shape error and the thermal deformation of the machine may appear as a machining error.
Our laboratory also does research on the accuracy of machine evaluation methods, and the application of International Standards to the evaluation of these errors.

Research and Development of Electric Rocket Engines for Space Propulsion

Exhaust plasma plume of Hall-type ion rocket engine.
Exhaust plasma plume of Hall-type ion rocket engine.
Nano-satellite with pulsed plasma rocket engine
Nano-satellite with pulsed plasma rocket engine

At the Advanced Rocket Laboratory, several kinds of electric rocket engine, such as arcjet engines, pulsed plasma engines, and Hall-type ion engines, are investigated for application in space propulsion. Our laboratory has a number of large vacuum chambers with high-speed pumping systems. Thrust characteristics are measured to improve performances, and numerical simulation is also carried out to understand the details of flowfields inside the rocket engines. We also are developing nano-satellites that rely on low-power electric rocket engines, which will be launched into space.

Operational transfer path analysis method for improving vehicle noise and vibration

Operational transfer path analysis method for improving vehicle noise and vibration
Operational transfer path analysis method for improving vehicle noise and vibration

To improve the comfort of automotive interiors, interior noise must be decreased, and seat and steering column vibrations must be minimized. The search for sophisticated solutions must consider fuel efficiency and dynamic performance, so only minimal weight increase is tolerable. To obtain an optimal solution, the parts that contribute most toward interior noise and vibration must be identified and improved. Transfer path analysis (TPA) is one method to obtain the contributions to interior noise and vibration that come from sound and vibration sources such as the engine, and many kinds of TPA methods have been proposed. Our laboratory focuses on an operational TPA method using principal component regression, to efficiently obtain information about the contributing sources. We consider the TPA accuracy evaluation index and accuracy improvement method, and how to best make use of this method for real-world applications.

Multiscale simulation of functional materials for MEMS

A multiscale simulation in the size range from crystal structures to micro and macro structures is conducted to design and develop high-performance functional materials for MEMS actuators and sensors. Electron, atom and molecular-level simulations based on first principle calculations are applied to crystal structures to investigate structural stability, material characteristics and crystal growth on substrates. A primary focus of our systematic research is to develop functional materials for medical devices, novel materials composed of biocompatible elements. We construct a homogenization-theory-based multiscale simulation between micro and macro structures to estimate the macrostructural homogenized properties as a volume average of the inhomogeneous micro structures, and to evaluate the microstructural behavior in response to an external load applied to the macro structure. For instance, the EBSD-measured crystal morphologies were incorporated into the micro structure and the relation with the macro homogenized properties is quantitatively analyzed. Additionally, the multiscale simulation was applied to an optimal problem of the macro homogenized properties as a function of the micro structure. Our approach has led to the discovery of some remarkable polycrystalline micro structures beyond those of a single crystal.

Research and development of a roll caster for aluminum alloy

Schematic illustration of a vertical-type high-speed twin roll caster, and deep drawing of roll cast A356 strip.
Schematic illustration of a vertical-type high-speed twin roll caster, and deep drawing of roll cast A356 strip.
Fig. 52 Schematic illustration of a roll caster for casting clad strip, and cross-section of as-cast clad strip.
Fig. 52 Schematic illustration of a roll caster for casting clad strip, and cross-section of as-cast clad strip.

A roll caster offers several advantages, such as process and energy savings, and rapid solidification. Our research seeks to find ways to increase casting speed and the cooling rate of the cast strip. A vertical type of high speed twin roll caster (VHSTRC ref. Fig.1) was developed, which can cast aluminum alloy strip at speeds up to 120m/min. The cooling rate of the cast strip reaches 3000oC/s, which enables the VHSTRC to reduce impurities when using recycled alloy, due to its superior cooling ability. We also pioneered the development of a roll caster for casting clad strip directly from molten metal (ref. Fig.2), a design that also provides outstanding process savings. Clad strips ranging from two to five layers can be cast directly from molten metals without interface between element strips. Furthermore, the element strips were accurately united, with neither strip remelting nor diffusion of alloy elements occurring at the interfaces.

Combustion Control by Control of Low-Temperature Oxidation in Internal Combustion Engines

Propagation of Reaction Zones in Optical Engine
Propagation of Reaction Zones in Optical Engine
Propagation of Reaction Zones in Optical Engine
Major Reaction paths in Ignition Process of Methyl Butanoate

Extended image

In the automotive industry, combustion control in a gasoline premixed leanburn engine is obtained by controlling turbulence, and combustion control in a gasoline direct injection engine is obtained by control of air fuel mixing. The next target for combustion control is to control the low-temperature oxidation chemistry in diesel engines or premixed charge compression ignition engines. Experimental and chemical kinetic computational approaches to solve this problem have been investigated in the Internal Combustion Engine Laboratory. Using an optical engine, we discovered that a spark discharge synchronized with low-temperature oxidation can activete the combustion induced by compression ignition. This is a new engine category, spark-assisted compression ignition engine. Using reaction path analysis of detailed chemical kinetic models, we found that fatty-acid methyl esters, biodiesel fuel surrogates, can provide shorter ignition delays than conventional alkane fuels do, because a carbonyl group in the molecule plays a key role in activating initial OH formation and heat release.