A MEANS FOR DAMPING VIBRATIONS, FOR EXAMPLE SELF-GENERATED OSCILLATIONS IN BORING BARS AND SIMILAR

Abstract: A damping means is constituted by a substantially cylindrical damper body (1) with an axial through bore (6), where the bore (6) accomadates a central pipe (3) which e.g. can lead a cooling liquid. The central pipe (3) is connected ridigly to or into the machine element to be damped, preferably in a cylindrical and axial cavity in a boring bar (9). Ring-shaped, elastic spring elements (2) placed in the ends of the damper body (1) and between the central pipe (3) and the damper body (1), as well as damping oil (4) in the clearance between the central pipe (3) and the damper body (1) transform motion energy into heat and provide the damping action. The stiffness of the spring elements (2) can optionally be adjusted.

Description: A MEANS FOR DAMPING VIBRATIONS, FOR EXAMPLE SELF-GENERATED OSCILLATIONS IN BORING BARS AND SIMILAR The present invention concerns a damping means which is particularly, however not exclusively, adapted for damping boring bars and similar tool supporting rods which are used in tool machinery. Typical examples are boring rods used in chip cut machining (lathing, milling etc.) / and in machining weak constructions, shafts and similar. The self-generated vibrations or oscillations typically arise as a consequence of the dynamic stiffness of the construction being too weak. Similar types of damping means are previously known, and a related device is disclosed in Norwegian Patent no. 128.725. Said Norwegian patent relates to a damper body which necessarily must be placed in a bore in a boring bar, because the bore itself constitutes an essential part of the damping means, i.e. the damping effect is a result of an interaction between the damper body and the bore itself, via resilient elements located therebetween. However, there is a tendency toward, higher speeds, and consequently high temperatures at the cutting edge, and in modern machinery there is a growing demand for the option of leading a cooling medium all the way up to the cutting edge, However, the possibilities of leading a cooling medium through or past the previously known type of damping means, are small, and this is almost impossible when it comes to boring rods with smaller dimensions. As previously mentioned, high rotation speeds are used quite often, and it is therefore also important that a damping system is able to tolerate high speed rotation. This has also turned out to be difficult when using the prior art damping systems. Furthermore, usually the space for accomodating damping oil is in the previously known damping systems located between the damper body and a bore for the damper body inside the bulk of the boring bar. The volume of this space around the damper body then becomes so large that it can only be filled partially with oil. If this space is completely filled with oil, the damping will be too strong, so that the damper body will not provide the desired effect. However, also a partially filled such space will create problems, namely in connection with the rotation and regarding from what direction the vibrations impinge onto the damper body (vertically or horizontally) . Further, it will not be possible to change the damper body weight without also changing the volume of the oil space. The present invention solves the above mentioned problems by providing a new damping means. The damping means in accordance with the invention is adapted to damp vibrations in objects like boring bars, tool supporting rods, machine elements and also flat objects which can be exposed to undesired vibrations, and the damping means comprises a substantially sylindrically shaped damper body to be placed inside or on the object to be damped, and said damper body has an axial through bore and a central pipe which extends axially through said bore and which is rigidly connectable to the object to be damped. The novel damping means is characterized particularly by the fact that the damper body is connected to the central pipe via resilient spring elements located in cutouts in each end of the damper body, said resilient spring elements being retained in place by means by exterior washers, and in that the outer diameter of the central pipe is adapted to the bore diameter with a small clearance for accomodating damping oil. In a preferred embodiment of the damping means in accordance with the invention, at least one of the washers is equipped with means for adjustable limitation of the expansion of the corresponding spring element, and thereby for adjusting the natural frequency of the damper body. In such a case a preferred solution is that said at least one washer is two-part, an outer part being rigidly connectable to the central pipe and including a countersunk adjusting screw adapted to offset an inner part of the washer axially along the central pipe when turning the set screw, to obtain a more or less strong engange ent against the corre¬ sponding spring element. In one embodiment of the invention the spring elements may comprise gas-filled rings of rubber or a plastic material In a preferred embodiment thereof, at least one of the spring elements is equipped with a nipple for adjusting the gas pressure, and thereby for adjusting the natural frequency of the damper body. Thus, firstly the present invention provides good oppor¬ tunities, when it is used in a boring bar, regarding supplyin a cooling fluid all the way up to the cutting edge of the boring bar, by the construction allowing the cooling fluid to be passed directly through the axial part of the damping means. This construction also allows that the same cavity in the boring bar now can accomodate a larger damper body, i.e. larger damping mass than previously. This is because the gap between the damper body and the cavity wall can be reduced substantially, so that the diameter of the damper body is larger. Furthermore, in the present invention the spring elements are located "inside" the damper body, and therefore remove less mass from the damper be-'y than in previously known constructions. And even more important: The accomodation space for damping oil is in the present invention merely a narrow, sylindrical gap between the damper body and the central pipe, and this feature together with the "inside" or central location of the spring elements, provide greater stability and larger freedom for dimensioning the parameters weigth, gap width and spring constant independently from each other. The damping means in accordance with the invention shall now be described closer by means of embodiment examples, and with reference to he appended drawings, where fig. 1 shows the damping means in its simplest and most basic form, fig. 2 shows an embodiment of the damping means where its natural frequency is adjustable, fig. 3 shows an embodiment where the spring elements are air-filled rubber rings, fig. 4 shows a damper in accordance with fig. 2, built into a boring bar, fig. 5 shows a mounting mode for the damping means when it is to be placed on a flat object which should be damped, and fig. 6 shows a detail study regarding adjusting the natural frequency. Fig. 1 discloses an example of a simple embodiment of the damping means in accordance with the invention. The substantially cylindrical damper body 1 is provided with a through axial bore 6. Inside said bore there is a central pipe 3 which quite generally ia adapted to be secured rigidly with its outer ends inside a boring bar or to the object to be damped. The central pipe 3 is preferably adapted to lead a cooling fluid through itself in communication with a duct leading further into the boring bar. In each outer end of the damper body 1 there is provided ring-shaped recesses containing ring-shaped spring elements 2, e.g. of rubber. The spring elements 2 constitute support elements between the central pipe 3 and the damper body 1. The spring elements 2 are held in place by adjustable washers 5, which are screwed on to the pipe 3 in order to provide a suitable spring constant in the spring elements 2 (refer in this connection to the discussion below regarding fig. 6) . Thus, when this damping means of the simplest type is mounted inside a boring bar, it is not possible to adjust the stiffnesses of the spring elements, and the natural frequency of the system is therefore constant. Therefore, this type of damping means is intended for use in e.g. short tools with a fixed overhang. Fig. 2 discloses a damping means of somewhat more advanced type, i.e. this damping means is constructed in such a manner that the natural frequency can be adjusted from outside. Thus, this type of damping means is intended for use in e.g. tools with adjustable overhangs, and therby connected varying natural frequency. In order to control the natural frequency of the damping means itself, at least one of the adjusting washers 5 is therefore constructed in two parts, see reference numerals 5a, 5b. The outer part 5b, which lies fixedly on pipe 3, is equipped with an adjusting screw 7 which when turned, displaces the inner part 5a of the adjusting washer axially inwards to and outwards from the spring element 2. This influences the stiffness of the spring element, and consequently also the natural frequency of the damping means. In a third embodiment which is disclosed in fig. 3, the spring elements 2 are embodied as gas-filled rings, preferably made of rubber. Normally air will be used in the rings, which of course also can be manufactured from a plastic material with suitable characteristics as to resiliency and strength. For the rest the damping means has a construction corre¬ sponding to that which is shown in fig. 1, except that the stiffness of the spring elements, and consequently the natural frequency of the damping means, is controlled by varying the gas pressure by means of nipples 8. In fig. 4 is shown a damping means of the adjustable type shown in fig. 2, built into a boring bar 9. As shown in the drawing, the boring rod 9 has a cooling duct 11 in direct communication with the central pipe 3, and these are aligned along the boring bar axis 12. Through an opening 10 in the boring rod there is access to the adjusting screw 7 for adjusting the natural frequency of the damping means. It is also possible to use the damping means in accordance with the invention for outside damping of e.g. a flat object, and in fig. 5 is shown a mounting means intended for such use. The central pipe 3 is then used as a support in two brackets 13 which in their turn are mounted rigidly to the body to be damped. For the rest, the damping means has the same construction as in fig. 2. Fig. 6 illustrates in closer detail how to achieve the adjustmer* * of the stiffness of the spring element in the embodiment shown in fig. 2. It appears clearly that when screwing the adjusting screw 7 inwards, the inner part 5a of the adjusting washer is displaced in towards the spring element 2, and thereby limits the possibility of an expansion of the spring element in a direction along the central pipe 3. When the damper body 1 moves as shown with an arow, the spring element 2 can then not be deformed out along the pipe 3 to the same extent as previsously. In effect the spring constant of the spring element is changed thereby, and such a change of spring constant has a direct influence on the natural frequency of the oscillating system (the.mass of the damper body on spring element 2) . When using gas-filled spring elements, as shown in fig. 3, the spring constant can also be adjusted by increasing or decreasing the air pressure in the rings, but access to the ring nipples must then be provided. In general the damping means operates in the following manner: When the construction to be damped, e.g. the boring bar, is set in motion due to influence connected with the cutting force, some part of this motion will be transferred via the spring elements to the mass of the damper body. Motion (energy) which is not transferred from the bar through the central pipe and via the spring elements to the damper body, is transformed into heat energy in the spring elements and in the damping oil. Heat is generated by internal friction in the damping oil and in the spring elements, as well as in the various boundary surfaces. In continuous operation a typical oscillating motion appears, and the boring and the damper body will substantially move with the same frequency, however the progress of phase and acceleration will be a little different. The phase difference will cause the necessary deformation/ friction in spring elements and damping oil, thereby providing loss of energy in the form of heat development. Thereby also the acceleration of bar and damper body will be different, and the damping force will be directly related to this difference.

Claims: P A T E N T C L A I M S 1. A damping means for objects like boring bars, tool supporting rods, machine elements and flat objects which can be exposed to undesired vibrations, comprising a substantially cylindrically shaped damper body (1) to be placed in or on the object (9) to be damped, said damper body (1) having an axial through bore (6) and a central pipe (3) which extends axially through said bore (6) and which is rigidly connectable to said object (9) to be damped, c h a r a c t e r i z e d i n that said damper body (1) is connected to the central pipe (3) via resilient spring elements (2) placed in cutouts in each end of said damper body (1) , said resilient spring elements (2) being retained in place by means of outside washers (5, 5a) , and that the outer diameter of said central pipe (3) is adapted to the bore (6) diameter with a small clearance for accomodating damping oil (4). 2. Damping means in accordance with claim 1, c h a r a c t e r i z e d i n that said resilient spring elements (2) are ring-shaped and lie in ring shaped cutouts immediately adjacent to said bore (6) . 3. Damping means in accordance with claim 1 or 2, c h a r a c t e r i z e d i n that at least one of said washers (5a, 5b) is equipped with means (5a, 7) for adjustable limiting of the expansion of the corresponding spring element (2) , and thereby adjustment of the natural frequency of said damper body (1) . 4. Damping means in accordance with claim 3, c h a r a c t e r i z e d i n that said at least one washer (5a, 5b) is two-part, an outer part (5b) thereof being rigidly connectable onto said central pipe (3) and comprising a countersunk adjusting screw (7) adapted, when turned, to displace an inner part (5a) of said washer axially along said central pipe (3) into more or less strong engagement with the corresponding spring element (2) . 5. Damping means in accordance with claim 1 or 2, c h a r a c t e r i z e d i n that said spring elements (2) are gas-filled rings of rubber or a plastic material. 6. Damping means in accordance with claim 5, c h a r a c t e r i z e d i n that at least one of said spring elements (2) is equipped with a nipple (8) for adjusting gas pressure, and thereby adjusting of the natural frequency of said damper body (1) .

Inventors: ANDREASSEN LAURITZ, ANDREASSEN, LAURITZ
Applicants: TEENESS AS
Application year: 1992
Main classification: B23B29
IPC codes: B23B29, F16F7, F16F9, F16F15