Satoshi Ema

Damping characteristics of an impact damper and its application

Abstract In this stuffy, in order to improve the damping capability of long, thin cutting tools, such as boring tools or drills, an impact damper with the following features was developed: small and simple in construction; easy to mount on the main vibratory systems; and no need to adjust parameters of an impact damper to the vibratory characteristics of the main vibratory systems. Using this impact damper, the characteristics of the impact damper were investigated in detail when the main vibratory system was vibrated in the direction of gravity and perpendicular to it. Furthermore, application of the impact damper to improve the damping capability of drills was attempted.

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.

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.

New type drill with three major cutting edges

Abstract Drilling performance of a new type twist drill is described. The new type drill has three major cutting edges, three chisel edges and three flutes. This drill is an efficient means of making a hole with high accuracy and no reaming. Recently, some research on drill materials including surface coating, drill point geometry, cutting forces and tool life have been carried out in order to increase the cutting performance of drills. All the drills used in these experiments were ordinary drills with two major cutting edges. The authors calculated the point geometry of the new type drill, and also examined the cutting characteristics of the drill with respect to cutting forces, hole accuracy and tool vibration. The experimental results showed that the whirling vibration which frequently occurs in an ordinary drill with two major cutting edges disappears when the new type drill is used, and thereby rifling marks do not result on the hole surface. Consequently, a hole with high roundness and straightness is obtained.

Cutting performance of drills with three cutting edges (effects of chisel edge shapes on the cutting performance)

Abstract In this paper an investigation of the cutting performance of drills with three cutting edges is reported. Six drills having different chisel edge shapes were used and drilling tests were performed in which the accuracy of machined holes, surface roughness and cutting force were measured. The cutting performance of the drills was assessed using variance analysis. The investigation showed that drills with small inclination angles of thinned chisel edges are generally more effective than conventional drills. The effect of corner radius of thinned chisel edges is insignificant.

An experimental investigation of circular saw vibration via a thin plate model

Abstract This paper deals with important practical problems related to vibration reduction in a circular saw used for wood cut-offs. An investigation is made of the static and dynamic characteristics of thin plate structures as a model of a circular saw, to obtain fundamental knowledge to improve circular saw performance. The circular saw is represented experimentally by a thin rectangular plate clamped by two shims. The bending rigidity and damping capacity of a structure are measured for six different clamping methods. The results are evaluated by a coefficient, which is introduced through Merritts regenerative chatter vibration theory. The most effective thin plate structure is found to improve vibration-proof capacity. This structure is easily applicable to an actual circular saw.

Chucking Performance of a Wedge-Type Power Chuck. Effects of Taper Angle of Top Jaw Gripping Surface.

In order to investigate the effects of the shape of the top-jaw gripping surface on the chucking performance of a wedge-type power chuck, bending tests and gripping tests in the chuck-work system were performed. The investigation showed that the bending stiffness in the unloading process increases ( i ) when the diameter of the top-jaw gripping surface is a few millimeters smaller than the work diameter, ( ii ) when the gripping force is adjusted to the gripping area of the top jaw, or (iii) when the work is gripped at the base of the top jaw. Although the fluctuation of the bending stiffness in the loading process depends on the shape of the top-jaw gripping surface and the bending load direction to the top jaw, the absolute value significantly decreases with the gripping force. There is no effect of the shape of the top-jaw gripping surface on the gripping accuracy.

Gripping Characteristics of a Wedge-Type Power Chuck. Effects of Gripping Conditions on Gripping Characteristics.

In this paper, an investigation of gripping characteristics of a wedge-type power chuck with three top jaws is reported. Bending tests and impulse tests of works with different diameters were performed for several gripping forces and gripping lengths in which the bending stiffness, logarithmic decrement and dynamic compliance of the chuck-work system were measured. The investigation showed that the bending stiffness varies with the direction of the bending load acting a jaw. The bending stiffness tends to decrease with the gripping force because of the increase of the clearance between the top of a jaw and a work. The greater the gripping force or the smaller the work diameter in comparison with the gripping length, the lower the damping efficiency of the system and the greater the dynamic compliance. Therefore, small values of the gripping force should be chosen for the works used in the experiment.

Contact rigidity of turning tools - Relative slip and damping characteristics of turning tools (2nd report)

This paper presents the experimental investigation on the contact rigidity between turning tool shank and the tool post. The obtained results are as follows : (1) The contact rigidity is influenced by the bending stiffness of tool shank, contact area in tool shank and the Vickers hardness number of shank material. (2) The effects of these parameters on the contact rigidity are estimated by brief empirical expressions. (3) The contact rigidity in the normal direction to the contact plane is susceptible to stronger influence from the bending stiffness of tool shank and that in the parallel direction to the contact plane is to the contact area in tool shank.