Etsuo Marui

A fundamental study on impact dampers

Abstract A fundamental study on impact dampers is reported in which the performance of impact dampers was investigated from free damped vibration generated when a step function input was supplied to a leaf spring with a free mass. The investigation showed that the damping capability of impact dampers results from collision between the free mass and the main mass. The frequency of the system with an impact damper varies with the natural frequency of the main vibratory system and the mass ratio. The optimum damping effect is achieved in combinations of the mass ratio and a clearance, i.e. motion extent of the free mass. The use of a free mass of only 25% of the main mass and a clearance of 0.6 mm, for example, can improve the damping capability of the main vibratory system at least 10 times or more, even though the clearance and the free mass are not adjusted to an amplitude of the main vibratory system. The critical amplitude where the impact damper does not function is determined by the natural frequency and the acceleration of gravity.

Forced vibration of a base-excited single-degree-of-freedom system with Coulomb friction

Using the “stopping region of motion” concept, a brief analytical technique is worked out for the behavior of the linear forced vibratory system under the influence of a Coulomb friction force. The following points are clarified by the above technique: 1. The behavior of the system is completely determined by the three non-dimensional parameters of nondimensional friction force, frequency ratio and damping ratio. 2. The vibratory system undergoes a periodic vibration with stopping periods when the mass cannot move. These stopping periods increase at lower exciting frequencies, owing to Coulomb friction. 3. The relation between the kind of motion occurring in the system and the above three parameters can be obtained theoretically and verified experimentally.

Research on the wear characteristics of hypereutectoid steel

Abstract In this research, the wear behavior of hyper-eutectoid steel was examined at ambient temperature ranging from room temperature to a high temperature of 400 °C. A common asymmetric test rig was used, where a pin specimen of hyper-eutectoid steel is pressed against a disk of carbon steel for machine structure use. Two types of pin specimen were prepared: an as-received specimen and a quenched specimen.. As a result, the following was clarified. The protective surface film of iron oxide is not a main factor in determining the wear behavior of the hyper-eutectoid steel of as-received pin specimens. The wear behavior is closely related to the separation of the oxide film from bulk material when the sliding conditions are severe. The wear behavior of a quenched pin specimen is strongly influenced by a microstructural transition and a reduction in hardness of the pin specimen at elevated temperature.

Effects of slots on the lateral vibration of a circular saw blade

In the majority of cases, wood is cut at a high feed rate and high rotational speed by circular saw blades with tungsten carbide tips brazed on the periphery of metal circular plates. Slots are made at several places from the periphery towards the center of a saw blade to prevent lateral vibration, both in idling and cutting, and to prevent a drop in critical rotational speed caused by heat expansion on the blade periphery during the cutting operation. In this paper, variations of lateral vibration mode, natural frequency and critical rotational speed of a slotted circular saw blade are investigated experimentally and by numerical calculations. The lateral deflection of a circular saw blade at the critical rotational speed and at the rotational speed near it is examined by a timber-cutting experiment.

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.

Experimental research on cutting force variation during regenerative chatter vibration in a plain milling operation

Abstract A plain milling operation is characterized by a transient and intermittent cutting process, in which undeformed chip thickness varies continuously. The reverse is the case in variations of undeformed chip thickness in the processes of up- and down-milling. In the present study, the property of regenerative chatter vibration in a plain milling operation is investigated from the viewpoint of cutting force variation. With primary chatter vibration, the vibration energy supply is closely related to the collision of the cutting tool flank against the workpiece surface during vibration, which is induced by the bending vibration or the torsional vibration of the arbor. In addition to this factor, the regenerative effect is considered to be one of the main causes of the chatter excitation in regenerative chatter vibration. The simulation result of the cutting force variation during regenerative chatter vibration agrees well with the experimental result, when considering these factors. It is shown that the regenerative chatter vibration in the-down-milling process occurs more easily than in the up-milling process.

Effect of reciprocating and unidirectional sliding motion on the friction and wear of copper on steel

From the practical necessity to obtain the friction and wear characteristics of materials used in machinery, various types of wear-testing machines have been developed and used. To obtain useful data for practical application, it is desirable that the investigation is carried out by a full-scale wear-testing apparatus having approximately similar contact conditions. Generally speaking, the obtained wear characteristics are different for every wear-testing apparatus used. When the type of wear-testing machine is not suitable, one cannot obtain the required wear characteristics. There are various parameters in wear-testing machines, such as configuration of contact surface and form of the relative motion between the test specimens. Thus, in this report, the effect of relative motion between contacting pair and friction process on obtained test results is investigated, for the combination of a copper pin specimen and a flat steel specimen. The microscopic structure of the pin specimen may be varied due to the friction and wear process. An optical microscope is used for the observations. The pin specimen is made from pure copper, which can be deformed easily.

Plate insertion as a means to improve the damping capacity of a cutting tool system

Effective chatter prevention during cutting operations is achieved by increasing the damping capacity of a cutting tool system. It is well known that damping capacity is generated through (i) micro-slip at the interface between the tool shank and tool post, (ii) slip at the grain boundary within a vibrating body (that is, internal friction), and (iii) friction between the surface of the vibrating body and the surrounding air. Among these three causes of damping capacity, micro-slip at the interface between the tool shank and tool post is the greatest factor affecting the damping capacity of the cutting tool system. In the research investigation, it is shown that the damping capacity of a cutting tool system is improved by friction acting between the inner wall of a rectangular hole made at the overhanging shank of the cutting tool system and the surface of a plate inserted into this rectangular hole. The damping capacity improvement proposed in this paper is realized by a mechanism similar to the inner friction mechanism.

Prototype fretting-wear testing machine and some experimental results

Abstract A new prototype fretting-wear testing machine is developed, and its performance is evaluated. In this testing machine, a spherical specimen is oscillated by a lead-zirconate-titanate semiconductor (PZT) actuator, driven by means of computer control. Thus, an arbitratry input waveform, such as sinusoidal wave, triangular wave and so on, can be easily operated to a spherical specimen. This is the special feature of our testing machine. As an example, a fretting experiment is carried out, using a steel flat specimen and a bearing steel sphere specimen. A sinusoidal input wave is added by a PZT actuator. It is clarified that there is a boundary fretting amplitude, beyond which fretting wear mass or volume increases abruptly.

Experimental research on cutting force variation during primary chatter vibration occuring in plain milling operation

Abstract Plain milling operation is characterized by a transient and intermittent cutting process, in which undeformed chip thickness varies continuously. The undeformed chip thickness variation is opposite in the up milling and down milling processes. First, the property of primary chatter vibration in plain milling operation is investigated. In the up milling process, the transient vibration generated in the initial stage of the cutting operation develops into primary chatter vibration, along with the chip thickness increase. On the other hand, a large amount of vibration energy is supplied during the initial collision of the cutting edge with the workpiece at a large undeformed chip thickness in the down milling process; and immediately after this collision, the primary chatter vibration of almost stable amplitude continues. Secondly, the vibration energy supply during the primary chatter vibration of plain milling operations is investigated on the basis of the experimental results. The exciting mechanism can be explained by considering the interference between the tool flank and the workpiece surface accompanying the arbor vibration. An unusual phenomenon is also discussed, in which the normal cutting force component has two maxima during one period of vibration in up milling. From the above results, the cutting edge shapes (effective relief angle and cutting edge radius), and the torsional rigidity of the milling arbor must be carefully determined, to prevent the primary chatter vibration in plain milling operation.