Masatoshi Hashimoto

Some considerations of slideway friction characteristics by observing stick-slip vibration

It is important to clarify the frictional characteristics of a slideway and to prevent unstable vibration, such as stick-slip vibration, for the improvement of kinematic performance and for precise positioning. In this research, the relations among the dynamic friction characteristics, the pitching motion or the floating up of the slider, the surface roughness of a slideway, and the lubricant property are investigated experimentally. As a result, some points necessary for the kinematic performance improvement of the slider are clarified.

Dissipation of kinematic energy by slip at the interface of mating surfaces

Abstract Damping is necessary to limit the peak stresses of machine elements subjected to near-resonant cyclic forces or to suddenly applied forces. Damping capacity of the machine structure is mainly originated from two mechanisms. One is material damping originated by inelastic and elastic dislocation movements within grains and also by slip at grain boundaries in materials. The other is structural damping, which offers excellent capacity for large energy dissipation, initiating from the interface shear at separable structural joints. In this paper, the slip at the interface and the energy dissipation by structural damping are measured for several kinds of mating surfaces composed of various materials and having different surface roughness.

Estimation of contact stiffness at interfaces in machine structures by a beam model on an elastic foundation

Abstract The dynamic properties of machine structures are significantly influenced by an interaction at the mating surfaces of machine elements. This interaction is called contact stiffness, and the development of a simple method for contact stiffness estimation is an important tribological objective. In this paper the contact stiffness is estimated by a beam model vibrating on an elastic foundation. The effects of clamping condition and mating surface topography on the contact stiffness obtained are quantitatively and accurately represented by experimental equations.

Damping Characteristics of Structures Packed with Balls (1st Report). Damping Capacity Improvement by Glass Ball Packing.

This paper deals with an experimental investigation on damping characteristics of structures packed with balls. Test structures are square pipes packed with glass balls. The effects of impulse magnitude, square pipe dimensions and ball size on damping characteristics are investigated. The experiments show that the damping characteristics are markedly affected by the ball size and the damping capacity is improved by ball packing. It is also shown that the damping capacity is affected by packing arrangements, packing ratio and repulsion coefficient. The effective damping capacity improvement is achieved by remaining small space between packed balls and an inner surface of square pipe. This fact is confirmed by the experiment.

Considerations on Damping Characteristics of Turning Tools. (3rd Report). Initiation Mechanism of Damping Capacity.

This paper examines the initiation mechanism of the damping capacity of turning tool. Turning tool is treated as the beam on elastic foundation. Parameters of the model elastic foundation are estimated from the experimental result of the frequency of free damped vibration. In the next place, the magnitude of damping energy is calculated from the friction resistance and the relative slip between tool shank and elastic foundation during both tangential and vertical vibrations. The calculated result of damping energy agrees well with the experimental result of the damping capacity qualitatively, in the changes of clamping load and surface topography. This result indicated that the damping capacity of turning tool system is mainly caused by the relative slip at tool shank.

Some considerations on the response of the hydraulic servomechanism controlled by the throttle valve. Effect of system dimensions.

In this report, the response characteristics of a hydraulic servomechanism controlled by a throttle valve to the step function response are investigated for the improvement of the electrohydraulic servomechanism for position control. The investigated characteristics are the settling time, which represents the damping and the quick response characteristics of the mechanism, and the initiation boundary of the unstable vibration. The response characteristics are influenced by many system dimensions. Above all, the equivalent damping abilities of the throttle valve and the positioning piston have the most serious effect. It is clarified that the damping abilities are first adjusted to the optimum values corresponding to the input signal and applied load in the design of the servomechanism. Other parameters are subsequently determined to obtain the superior response characteristics.

On the occurring mechanism of chatter vibration in a spindle-workpiece system.

Chatter vibration occurring in the spindle-workpiece system of a lathe is treated theoretically, considering the phase lags of cutting force and chatter marks, the dynamic variation effects of cutting velocity, and rake angle under vibration on cutting force. As a result, it is clarified that chatter vibration is mainly induced by the phase lag of the cutting force (primary chatter) and by the phase lag of chatter marks in successive cutting (regenerative chatter) . The dynamic variations of cutting velocity and rake angle make the spindle-workpiece system more unstable under vibration. The effect of cutting velocity variation is more remarkable than that of rake angle in both types of chatter. Chatter vibration can effectively be suppressed by enlarging the damping capacity of the system.

Characteristics of Cutting Force in Plain Milling Operation Using a Helical Cutter

A unique optical method is developed in order to measure the cutting force. The variation of the horizontal component of cutting force in the direction of feed, the vertical component which acts vertically to the arbor and the axial component are precisely measured corresponding to a variation of the undeformed chip thickness. Characteristics of the cutting force and influences of the helix angle are compared and discussed both for up and down milling, and also on the basis of the force variation ratio proposed. The cutting force component and the thrust force component are derived, and the normal and frictional force on tool rake face, the apparent friction angle and the chip flow direction are also obtained. The mechanics of the milling process is discussed basing upon the experimental results. The role of the helix angle is experimentally clarified and the concept of the effective rake angle is criticized.