Method for reducing the regenerative chatter of chip-removal machines

Abstract

A method for reducing regenerative chatter in chip-removal machines wherein a tool head (2) machines walls of a workpiece (1) by means of at least one chip-removal tool and during this machining, the tool head is vibrationally excited and a loose additional mass (m.sub.z) is moved by the vibration. The additional mass randomly touches the tool head (2) in first position or randomly has no connection to the tool head (2) in second position, and thus the total mass of the tool head (2) is randomly changed by the amount of the additional mass (m.sub.z). This change in mass of the tool head in turn changes the frequency of vibration.

Claims

1. Method for reducing regenerative chatter of a chip removal machine in that a workpiece (1) rotates in relation to a tool head (2) having at least one chip-removal tool (3, 3a, 3b, 3c) arranged at one end of the tool head (2), the tool head (2) machines walls of the workpiece (1) by means of the at least one chip-removal tool (3, 3a, 3b, 3c), the tool head (2) is vibrationally excited during the machining, a loose additional mass (m.sub.z) is moved by the vibration, which additional mass randomly touches the tool head (2) in first positions or randomly has no connection to the tool head (2) in second positions, and thus the total mass of the tool head (2) is randomly changed by the amount of the additional mass (m.sub.z) and the vibrational behaviour of the tool head (2) is changed because of the mass change and thus counteracts regenerative chatter, and in that a receptacle (51), by means of which the tool head (2) can be exchangeably placed onto a spindle, is arranged at another end of the tool head (2) opposite the one end, wherein the additional mass (m.sub.z) is of annular construction and has in the second position no contact and no connection to the tool head (2) and the wall is formed as an outer wall (71) with a radius (r1) and the corresponding wall is formed as a corresponding inner wall (72) with the corresponding radius (r2) which is greater than the radius (r1) and the additional mass (m.sub.z), which is of annular construction is held by a cramp (61) at the tool head (2).

2. Chip-removal machine with a tool head (2) with at least one chip-removal tool (3, 3a, 3b, 3c) arranged on one end of the tool head for machining a wall of a workpiece (1), a loose additional mass (m.sub.z) which can have randomly different positions relative to the tool head (2) and which touches the tool head (2) in first positions and which has no connection to the tool head (2) in second positions, wherein the tool head (2) has a first vibrational behaviour in the first positions and a second vibrational behaviour in the second positions and with a receptacle (51), by means of which the tool head (2) can be exchangeably placed onto a spindle, is arranged at another end of the tool head (2) opposite the one end, wherein the additional mass (m.sub.z) is of annular construction and has in the second position no contact and no connection to the tool head (2) and the wall is formed as an outer wall (71) with the radius (r1) and the corresponding wall is formed as a corresponding inner wall (72) with the corresponding radius (r2) which is greater than the radius (r1) and the additional mass (m.sub.z), which is of annular construction, is held by a cramp (61) at the tool head.

3. Chip-removal machine according to claim 2, characterised in that the tool head (2) has a wall which, in operation, rotates about a longitudinal axis and the additional mass (m.sub.z) has a rotating corresponding wall, which, along its entire extent, in the second positions is spaced apart from the rotating wall.

4. Chip-removal machine according to claim 2, characterised in that a wall (53, 71) is cylindrically shaped and a corresponding wall (57, 72) is likewise cylindrically shaped.

Description

(1) The invention is described with reference to two embodiments in seven drawings. In the drawings:

(2) FIG. 1 shows a physical schematic view for explanation of the physical chatter of a chip-removal machine during chip removal on a surface,

(3) FIG. 2 shows a physical schematic view for explanation of the chip-removal machine according to the invention with an additional mass,

(4) FIG. 3 shows an arrangement of a tool head according to the invention relative to the workpiece during the chip-removal operation,

(5) FIG. 4 shows a perspective view of the tool head according to the invention in a first embodiment,

(6) FIG. 5 shows a sectional view in the longitudinal direction in FIG. 4 with an inner mass according to the invention,

(7) FIG. 6 shows a second embodiment of a tool head according to the invention,

(8) FIG. 7 shows a sectional view in the longitudinal direction in FIG. 6 with an outer mass according to the invention.

(9) FIG. 1 shows schematically a workpiece which is substantially circular in cross-section, for example a pipe section 1 which is substantially circular in external cross-section. However, the workpiece can also be a solid profile or a profile which is solid and hollow in some sections. The workpiece is preferably made of metal, particularly preferably made of steel; however, other materials can also be envisaged. The pipe section 1 is machined by a tool head 2 which has precisely one individual cutting plate 3 in the schematic view. Naturally, the tool head 2 can also have two, three or any higher number of cutting plates 3. The tool head 2 and the pipe section 1 rotate relative to one another. In this case the tool head 2 can be held fixedly in space and relative to the chip-removal machine (not shown), and the pipe section 1 can be rotated about a longitudinal axis oriented in the longitudinal direction L, or the pipe section 1 can be fixed in space and relative to the chip-removal machine, and the tool head 2 can be rotated about the longitudinal axis about the pipe section 1, and in this case the cutting plate 3 rotates externally about the pipe section 1. During the rotation operation the cutting tool removes chips from an outer wall 4 of the pipe section 1. During the chip-removal operation load changes of the chip-removal forces occur, for example because the outer wall 4 is not exactly circular, which is actually always the case, so that in reality the removed chips have slightly different thicknesses. Even with ideally circular pipe sections 1, load changes can occur which lead to the tool head 2 first of all being set in slight vibrational movements which, however, can be periodically strengthened by continuous relative rotation of the tool head 2 and the pipe section 1 and lead to the so-called regenerative chatter.

(10) The corrugation of the outer surface 4 of the pipe section 1 periodically repeatedly excites the tool head 2 to the same vibrations. Usually tool heads 2 rotate at for example 5,000 r.p.m.; however, other rotational speeds are also conceivable. In particular the tool head 2 can be operated with a lower, but also with a higher rotational speed. The tool head 2 is mounted on a rotating spindle (not shown) oriented in the longitudinal direction L and can vibrate out of the longitudinal direction L. The vibrational behaviour of the tool head 2 is determined substantially by a rigidity c of the tool head 2 mounted on the spindle, a damping d and a mass m of the tool head 2 with the spindle. In particular a natural frequency f.sub.eigen of the tool head 2 is a function of these three parameters. In this case natural frequency f.sub.eigen means the natural frequency with which the tool head 2 mounted on the spindle vibrates out of the longitudinal direction L.

(11) The invention makes use of the idea, as shown in FIG. 2, of changing a total mass of the tool head 2 randomly and temporarily by an additional mass m.sub.z and as a result randomly and temporarily changing the vibrational behaviour.

(12) The tool head 2 is rotated about the pipe section firmly gripped and fixed in a receptacle, and a total mass of the tool head 2 changes, depending upon whether the additional mass m.sub.z is connected to the tool head 2 or does not touch it and is not connected to it. If the additional mass m.sub.z is connected to the tool head 2, for example in that the additional mass m.sub.z touches the tool head 2, the natural frequency of the tool head 2 decreases; if the additional mass m.sub.z has no connection to the tool head 2 the natural frequency of the tool head 2 increases.

(13) Due to the change of the vibrational behaviour of the tool head 2 a malfunction is more or less introduced into the chip-removal operation and counteracts a periodically strengthening vibration. A periodic excitation of the tool head 2 due to corrugations in the wall of the pipe sections 1 during the rotational movement does not lead to any resonance catastrophe in the form of a regenerative chatter, because the resonant frequency of the tool head 2 changes due to the change of mass.

(14) FIG. 3 shows one end of a pipe section 1. This is a metal pipe. With the aid of the tool head 2 according to the invention with the aid of three cutting plates 3a, 3b, 3c an internal chamfer, an outer chamfer and a flat face are introduced into the metal tube, specifically in this correlation. The tool head 2 rotates with respect to the pipe section 1 which is gripped relative to the chip-removal machine. The pipe section 1 and the tool head 2 have the common longitudinal direction L. The tool head 2 rotates about a longitudinal axis oriented in the longitudinal direction L, and the longitudinal axis corresponds to the longitudinal axis of the pipe section 1.

(15) FIG. 4 shows the tool head 2 according to the invention in a front view. In this case three cutting plates 3a, 3b, 3c are provided facing the pipe section 1 (not shown) and are mounted replaceably in corresponding holders on the tool head 2. The tool head is rotatable about the longitudinal direction L in both directions.

(16) The tool head 2 illustrated in FIG. 4 is shown in FIG. 5 in a sectional view in the longitudinal direction L. The tool head 2 has an outer housing 50 with the tool head mass m. The three cutting plates 3a, 3b, 3c are arranged at one end of the tool head 2. A receptacle 51, by which the tool head 2 can be fitted on the chip-removal machine, is provided at another end. The one end and the other end are preferably opposite one another.

(17) The additional mass m.sub.z according to the invention is constructed here as a loose, cylindrically shaped body arranged in a tool head 2. The tool head 2 has an interior space 52 with a cylindrical inner wall 53 and two end faces 54, 56. The two end faces 54, 56 are parallel to one another and are in each case arranged perpendicularly on the cylindrical inner wall 53.

(18) In cross-section according to FIG. 5 the interior space 52 is rectangular. The dimensions of the rectangle can deviate from the illustrated form; a square interior cross-section can also be provided. The additional mass m.sub.z is constructed as a cylinder, wherein a corresponding radius r2 of the cylinder is somewhat smaller than a radius r1 of the cylindrical interior space 52, so that the cylindrical additional mass m.sub.z has a clearance 60 circumferentially along an entire corresponding wall 57 and also on its end faces 58, 59, that is to say is spaced apart with respect to the cylindrical inner wall 53 and with respect to the end faces 54, 56 of the interior space.

(19) FIG. 5 shows the tool head 2 in one of the second positions in which the additional mass m.sub.z does not touch the tool head 2. If the tool head 2 is not in operation, the tool head 2 is located in one of the first positions, in which the cylindrical additional mass m.sub.z rests its corresponding outer wall 57 on a section of the inner wall 53 of the tool head 2. During the operation the tool head 2 rotates with a substantial number of revolutions, for example 5,000 r.p.m. During a starting operation the inner cylinder initially rubs with its corresponding outer wall 57 on the inner wall 53 of the tool head 2 until due to friction the inner cylinder has taken on the rotational speed of the tool head 2. During the chip-removal operation, at the moment in which a regenerative chatter begins to form, the tool head 2 is set in slight vibration. In FIG. 5 these vibrations extend perpendicularly to the longitudinal axis oriented in the longitudinal direction L. The size of the clearance 60 is such that it has at most the amplitude of the still permissible chatter. If the tool head 2 begins to vibrate, during the vibration operation there are moments in which the cylindrical additional mass m.sub.z actually has no contact with the tool head 2, that is to say the corresponding outer wall 57 everywhere is circumferentially spaced apart from the inner wall 53 of the tool head 2, so that the total mass m+m.sub.z of the tool head 2 decreases by the additional mass m.sub.z to the tool head mass m. In this way the natural frequency f.sub.eigen of the tool head 2 changes, albeit only temporarily, but it changes so that the vibrational behaviour of the tool head 2 changes, so that it can no longer be excited increasingly by periodic excitation, and regenerative chatter is prevented.

(20) The tool head 2 with the touching additional mass m.sub.z has a mass m+m.sub.z and thus a first natural frequency f.sub.eigen (c, d, m+m.sub.z), and the tool head 2 without touching the additional mass m.sub.z has a mass m and a second natural frequency f.sub.eigen (c, d, m), which is different from the first natural frequency f.sub.eigen (c, d, m+m.sub.z).

(21) Experiments have shown that a regenerative chatter can be prevented exceptionally effectively by the simple measure of providing a loose additional mass m.sub.z in the tool head 2.

(22) FIG. 6 shows a second embodiment of the invention, in which the loose additional mass m.sub.z is placed externally as an outer ring about the tool head 2. The additional mass m.sub.z is annular in shape and is provided with a corresponding inner wall 72, which in first positions rests on an outer wall 71 of a cylindrical tool head which is likewise in the section. A cramp 61 is shown which holds the ring-shaped additional mass on the tool head.

(23) FIG. 7 shows the tool head 2 in FIG. 6 in a sectional view. The tool head 2 has the cylindrical outer wall 71 which has the radius r1, and the additional mass m.sub.z is of annular construction with the annular corresponding inner wall 72, which has the corresponding radius r2 which is somewhat greater than the radius r1. In second positions, of which one is illustrated in FIG. 7, the annular additional mass m.sub.z actually has no contact and no connection to the tool head 2. It is spaced therefrom by the clearance 60.

(24) The operating principle is the same as in the first embodiment. Usually the outer ring rests with its corresponding inner wall 72 somewhere to the outer wall 71 of the tool head 2, and thus the tool head 2 has a mass m+m.sub.z which comprises the mass of the outer ring. During the chip-removal operation the tool head 2 is again excited to small vibrations at the start of the regenerative chatter, and the outer ring does not participate in these vibrations because of its inertia, so that during short periods of time it can occur that the outer wall 71 of the tool head 2 actually has no contact with the corresponding inner wall 72 of the outer ring and thus the mass m of the tool head 2 is reduced by the additional mass m.sub.z of the outer ring and thus in turn the natural frequency f.sub.eigen of the tool head, which is definitively determined by the mass m of the tool head 2 or m+m.sub.z, is changed, so that regenerative chatter is prevented in a very simple manner.

LIST OF REFERENCE SIGNS

(25) 1 pipe section 2 tool head 3 cutting plate 3a cutting plate 3b cutting plate 3c cutting plate 4 outer wall 50 outer housing 51 receptacle 52 interior 53 cylindrical inner wall 54 end face 56 end face 57 corresponding wall 58 end face 59 end face 60 clearance 71 cylindrical outer wall 72 annular corresponding inner wall c rigidity d damping m mass m.sub.z additional mass 27 radius r2 corresponding radius f.sub.eigen natural frequency f.sub.eigen (c,d,m) second natural frequency f.sub.eigen (c,d,m+m.sub.z) first natural frequency L longitudinal direction