Ultrasonically Vibrated Die Rings

Abstract

An ultrasonically vibrated die comprises a generally cylindrical die ring supported by a coaxial resonant mounting tube. The die ring is vibrated in a radial bending mode of vibration, in which an end surface of the die ring oscillates between a concave and a convex state. The mounting tube joins the end surface of the die ring at a radius R where the amplitude of the oscillation of the end surface is at a minimum, in order to reduce transmission of the vibration into the mounting tube.

Claims

1. A die, comprising: a generally cylindrical die ring comprising an end surface and having a radial bending mode of vibration in which the end surface oscillates between a concave and a convex state; and a mounting tube coaxial with the die ring and extending from the end surface of the die ring; characterized in that the mounting tube joins the end surface of the die ring at a radius where the amplitude of the oscillation of the end surface is at a minimum.

2. The die according to claim 1, wherein the end surface is annular.

3. The die according to claim 1, wherein, at the frequency of the radial bending mode of the die ring, the mounting tube vibrates in a mode in which the amplitude of vibration is a local minimum at the junction of the mounting tube and the die ring.

4. A method of operating a die that comprises a generally cylindrical die ring having an end surface, and a mounting tube coaxial with the die ring and extending from the end surface, the method comprising vibrating the die ring in a radial bending mode, in which the end surface of the die ring oscillates between a concave and a convex state, characterized in that the minimum amplitude of the oscillation of the end surface occurs at a radius where the mounting tube joins the end surface.

5. The die according to claim 2, wherein, at the frequency of the radial bending mode of the die ring, the mounting tube vibrates in a mode in which the amplitude of vibration is a local minimum at the junction of the mounting tube and the die ring.

Description

THE DRAWINGS

[0013] FIGS. 1A to 1C are perspective views of a computer model of an annular component undergoing vibration in radial bending mode RB0.

[0014] FIG. 1D is a schematic sectional view of the end wall of the component of FIG. 1A, shown at the two extremes of its vibration.

[0015] FIGS. 2A and 2B are perspective views in different orientations of a die in accordance with the invention.

[0016] FIG. 3 is a longitudinal section of the die of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] FIG. 1D schematically shows the end wall of the component of FIG. 1A at the two extremes of its vibration in the radial bending mode RB0. Dotted lines 30 show the component in its hourglass configuration, corresponding to FIG. 1B. Solid lines 32 show the component in its barrel configuration, corresponding to FIG. 1C. It can be seen that the movement of any point on the surface of the end wall between the two extremes is principally in a direction parallel to the axis 34. A point P on the radially outer part of the end surface moves between a greater axial elongation in the barrel configuration and a smaller axial elongation in the hourglass configuration, while a point Q on the radially inner part of the end surface does the opposite, oscillating 180 out of phase with the outer part. At a point in between, at an intermediate radius R, the amplitude of the oscillation of the end surface must be at a minimum. In fact, the movement of the points on the end surface is not in general purely axialthere is also a radial componentbut it is still true that at an intermediate radius there exists a circle of points on the end surface where the amplitude of the oscillation of the points is at a minimum.

[0018] The amplitude may be defined in various ways. Preferably, it is the straight-line distance between the corresponding points at the two extremes of the oscillation. Alternatively, the amplitude may be measured along the path that a point on the surface follows between those two extremes. Another possibility is to measure only the component of the movement parallel to the axis. If preferred, the amplitude may be defined as one half of any of the aforementioned values, to conform to the conventional definition for a waveform; this makes no difference to identifying the radius at which the minimum value occurs.

[0019] FIGS. 2A, 2B and 3 illustrate a die 1 according to an embodiment of the present invention. The die 1 incorporates a die ring 2 that defines a central axis 3. The die ring 2 is formed integrally with a resonant mounting tube 4. The mounting tube 4 is coaxial with the die ring 2 and extends axially from an end surface 5 of the die ring 2. Part way along the tube 4 is a radially projecting flange 6, which is used for mounting the die 1 on a forming machine (not shown) to support the die ring in use. As can be seen in FIG. 3, the section of the tube 4 between the die ring 2 and the flange 6 is thin-walled so as to be relatively flexible and to minimize the coupling of the vibration of the die ring 2 into the tube 4.

[0020] The die ring 2 has a central aperture 8 that opens to the axial end remote from the mounting tube 4. The interior wall of the aperture 8 defines a working surface 10 that is profiled to form a tubular workpiece (not shown) as it is driven into the aperture against the working surface 10. The die ring 2 is vibrated ultrasonically to assist the forming process.

[0021] The outer surface 12 of the die ring 2 is generally cylindrical. At one point on its circumference there is formed a planar surface, parallel to the axis, that acts as an interface 14 for an ultrasonic transducer (not shown). The interface surface 14 has a threaded bore 16 in its centre for receiving a stud (not shown) that is used to secure the transducer.

[0022] The shape and material of the die ring 2 are chosen such that, when an ultrasonic transducer is coupled to the interface 14 and introduces energy at a predetermined frequency, the die ring 2 vibrates in the previously described radial bending mode RB0. During this vibration, the end surface 5 oscillates between a convex and a concave configuration as illustrated in FIG. 1D. The radius R of the mounting tube 4 where it joins the end surface 5 is equal to the radius where the amplitude of this oscillation of the end surface 5 is at a minimum. More precisely, the circle of points on the end surface where the oscillation is a minimum lies within the thickness of the wall of the mounting tube.

[0023] Because the mounting tube 4 is thin-walled and flexible, to a first approximation the vibration modes of the die ring 2 can be considered independently from those of the mounting tube 4. The mounting tube 4 joins the end surface 5 of the die ring 2 where the amplitude of vibration is at a minimum, so it is desirable to design the mounting tube 4 such that at the operating frequency the vibration of the mounting tube 4 is also at a minimum at that junction. The mounting tube 4 typically vibrates in an axisymmetric mode with nodes and antinodes of vibration distributed along its length. At the frequency of the radial bending mode (RB0) of the die ring 2, a node of the mounting tube preferably coincides with the junction of the mounting tube and the die ring so that the amplitude of vibration is at a local minimum there.