MXPA99000217A - Apot rotary acoustic horn - Google Patents

Abstract

The present invention relates to a rotating acoustic horn for imparting energy at a selected wavelength, frequency and amplitude, characterized in that the horn comprises: a base portion having an axial inlet end and an axial output end; of weld faces operatively connected to the base portion, each with a diameter that is larger than the diameter of the base portion and which can expand and contract with the application of acoustic energy at the inlet end of the base portion, where the weld faces are separated from each other, and where the weld faces are mounted in a series and are parallel to each other.

Description

ROTARY ACOUSTIC HORN STACKED TECHNICAL FIELD The present invention is concerned with acoustic welding horns. More particularly, the present invention is concerned with rotating acoustic welding horns.

BACKGROUND OF THE INVENTION In acoustic welding, such as ultrasonic welding, two parts to be joined (usually thermoplastic parts) are placed directly beneath an ultrasonic horn. In plunger welding, horn pistons (they travel to the parts) and transmit ultrasonic vibrations to the upper part. The vibrations travel through the upper part to the interface of the two parts. Here, the vibrational energy is converted into heat due to the intermolecular friction that melts and fuses the two parts. When the vibrations stop, the two parts solidify under force, to produce a weld on the joint surface. Continuous ultrasonic welding is normally used to seal fabrics, films and other parts. In continuous mode, the ultrasonic horn is usually stationary and the part is moved under it. Sweeping or scanning welding is a type of welding REF. 29141 continuous in which the part of the plastic is scanned or swept under one or more stationary horns. In transverse welding, the table over which the parts pass and the part that is welded remain stationary with respect to each other, as long as they move under the horn or as the horn moves over them. Many uses of ultrasonic energy for the joining or adhesion and cutting of thermoplastic materials involve horns or ultrasonic tools. A horn is an acoustic tool usually having a length of half the wavelength of the horn material and made of, for example, aluminum, titanium or sintered steel that transfers the mechanical vibratory energy to the part. (Normally, these materials have wavelengths of approximately 25 cm (10 inches)). The displacement or amplitude of the horn is the movement from peak to peak of the face of the horn. The ratio of the output amplitude of the horn to the input amplitude of the horn is called gain. The gain is a function of the ratio of the mass of the horn in the input and output sections of the vibration. In general, in the horns, the direction of amplitude on the face of the horn coincides with the direction of the mechanical vibrations applied. Traditionally, ultrasonic cutting and welding uses horns that vibrate axially against a rigid anvil, with the material to be welded or cut between the horn and the anvil. Alternatively, in welding or cutting at continuous high speed, the horn is stationary while the anvil is rotated and the part passes between the horn and the anvil. In these cases, the linear velocity of the part is matched to the tangential velocity of the working surface of the rotary anvil. There are however, some limitations to this system. Because the part to be welded is passed continuously between the narrow space formed by the anvil and the horn, compression variations are created due to the disuniformities of the thickness of the part. There is drag between the part and the horn and may cause residual stress in the welded region. These factors affect the quality and strength of the weld which in turn limit the line speeds. Also, the space between the rotary anvil and the horn limits the compressible volume or thickness of the parts to be joined. One way to minimize these limitations is to form the working surface of the horn to obtain a progressive convergent or divergent space depending on the part. This does not completely solve the problem of moving the material to be joined beyond a stationary horn, since an intimate contact is necessary for efficient acoustic energy transfer.

The best way to obtain high-quality, high-speed ultrasonic welding is to use a rotating horn with a rotating anvil. Normally, a rotating horn is cylindrical and rotates around an axis. The input vibration is in the axial direction and the output vibration is in the radial direction. The horn and the anvil are two cylinders close to each other, which rotate in opposite directions with equal tangential velocities. The part to be joined passes between these cylindrical surfaces at a linear speed that is equal to the tangential velocity of these cylindrical surfaces. The correspondence or coincidence of the tangential speeds of the horn and the anvil with the linear speed of the material is intended to minimize the drag between the horn and the material. The excitation in the axial direction is similar to that in conventional plunger welding. U.S. Patent No. 5,096,532 describes two kinds of rotary horn. The patent compares a commercially available rotary horn, manufactured by Mecasonic-KLN, Inc., of Fullerton, California (Mecasonic horn) and a rotating horn described in the '532 patent. Figure 1 shows a Mecasonic rotary horn and Figure 2 shows a configuration of the rotating horn of the '532 patent. A significant difference between these two types of horns is the width of the radial weld face and the uniformity of the amplitude across the radial face. The Mecasonic Horn is a full-length horn, which has a total length of approximately 25 cm (10 inches) for aluminum and titanium horns. The axial vibration excites the cylindrical bending mode (or curvature) to provide radial motion and the vibration mode depends on the Poisson's ratio. (If the Poisson's ratio of the horn material is zero, the radial vibration modes are not excited). The radial movement of the weld face is in phase with the excitation, and there are two nodes (where the amplitude of vibration is zero), for axial movement and two nodes for radial movement. However, the amplitude of vibration is the highest in the center of the radial weld face and decreases towards the end to result in uneven weld strength. The Mecasonic horn is a partially hollow cylinder. The horn of the? 532 patent is a half-wavelength horn, which has a total length of about 12.7 cm (5 inches) for aluminum and titanium horns. Due to the shape of the horn, axial vibration provides radial movement. In this horn, the vibration mode is independent of the Poisson's ratio. The radial movement of the weld face is out of phase with the excitation and there is only one node, at the geometric center of the weld face. The amplitude of vibration is relatively uniform across the face of the weld. The shape of the horn of the '532 patent differs from that of the Mecasonic horn; the horn of the x532 patent is solid, and the Mecasonic horn is a partially hollow cylinder. There is a need for an acoustic welding configuration that can weld parts over a wide width (such as greater than 12.7 cm).

BRIEF DESCRIPTION OF THE INVENTION A rotating acoustic horn imparts energy at a selected wavelength, frequency and amplitude. The horn includes a base portion having an axial inlet end and an axial outlet end and a plurality of welding faces operably linked to the base portion. Each weld face has a diameter that is larger than the diameter of the base portion and which expands and contracts with the application of acoustic energy to the inlet end of the base portion. The welding faces are spaced apart and are mounted either in series or in parallel with each other. The distance between the midpoints of the adjacent welding faces is at least a multiple of one half wavelength of the horn material. The amplitude of vibration of each welding face may differ from the amplitude of vibration of the adjacent welding faces. The expansion and contraction of at least one welding face may be substantially in phase with the movement of the axial input end of the horn. Each welding face can move substantially in phase with the expansion and contraction of the alternative welding faces. The horn may be an ultrasonic horn and may include a way to change the gain in the radial weld face by changing the mass at the axial inlet end of the horn. The axial length of the welding face can be up to half a wavelength of the horn material. In a modality, the axial length of the horn can be substantially equal to a wavelength of the material of the horn. In this embodiment, the expansion and contraction of the welding face may be substantially in phase with the movement of the input end of the horn. The horn can exhibit two nodal points for axial movement. In another embodiment, the axial length of the horn may be less than or equal to half the wavelength of the horn material. In this embodiment, the expansion and contraction of the welding face can be substantially out of phase with the movement of the input end of the horn. This horn can exhibit a nodal point or axial movement.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a Mecasonic horn. Figure 2 is a schematic view of a horn of the type of the patent 5 532. Figure 3 is a schematic view of a horn according to the invention having multiple welding faces in series. Figure 4 is a schematic view of a horn according to another embodiment of the invention having multiple weld faces in series. Figure 5 is a schematic view of a horn similar to that of Figure 3 having multiple welding faces in parallel. Figure 6 is a schematic view of a horn similar to that of Figure 4 having multiple welding faces in parallel. Figure 7 is a schematic view of two horns mounted on both sides or staggered, of Figure 5.

DETAILED DESCRIPTION The rotary horn of this invention can be a full-wavelength acoustic rotary horn, as shown in Figures 1, 4 and 6, or a half-wavelength horn, as shown in Figures 2, 3 and 5. As shown, the horn is an ultrasonic horn and imparts energy at a selected wavelength, frequency and amplitude. The horn can ultrasonically weld parts in a relatively long width with a desired amplitude. For the full-wavelength horn, the radial movement is in phase with the excitation and the horn has two nodal points for axial movement and two nodal points for radial movement. For the half-wavelength horn, the radial motion is out of phase with the excitation and the horn has a nodal point for axial movement and a nodal point for radial movement. With reference to Figure 3, the rotary horn 10 has an axial inlet end and an axial outlet end 13. A plurality of weld faces 16 are located in the horn 10. In figures 1, 4 and 6, the horn 10 may have a hollow portion 15 which may extend for more than half the axial length of the horn 10 and may be longer than the weld face 16. The diameter of the weld face may be larger than the diameter of the rest of the horn 10. Each welding face 16 has a diameter that expands and contracts with the application of ultrasonic energy. The gain (ratio of output amplitude of the horn to the input amplitude of the horn based on the axial input) can be changed on the welding face 16 by changing the mass 18 at the input end 11 of the horn. To weld on an anvil with a width greater than the width of the welding face 16 without using multiple rotating horns (either in rotating or flat anvils), the horns having multiple welding faces 16 or single-sided horns can be used. welding can be stacked along its length in a single unit. The configuration would be similar to a "shish-kebab" structure. The distance between the midpoints of the adjacent weld faces 16 may be one or more multiples of one half the wavelength of the horn material. Also, the amplitude of vibration of each welding face may differ from the amplitude of vibration of the adjacent welding faces. This horn assembly configuration can be driven and rotated with a single feed, boost, converter and drive system. To fully cover the wider width of the anvil, two or more of these configurations, mounted on both sides for a distance of up to the width of the weld face, can be used, as shown in Figure 7. Welding faces in each horn they may have different widths than that of the welding faces on the other horn. The welding faces can be mounted in series with each other, as shown by the horns 10 and 10 'in Figures 3 and 4, or in parallel to each other, as shown by the horns 10' 'and 10' '' in Figures 5 and 6. Figures 3 and 4 are examples of horns stacked in series. The configuration is classified as stacking the rotary horn in series because the output of one horn in the axial direction becomes the input for the next horn. The first horn drives the second rotating horn and so on. In figure 3, the axial length of the horn is a multiple of one half wavelength of the horn material. The distance between the center of the successive welding faces is one half wavelength of the horn material. The radial movement of the alternative welding faces may be out of phase with the excitation and the horn exhibits an axial nodal point for each welding face. In Figure 4, the axial length of the horn is a multiple of a wavelength of the horn material. The distance between the center of successive welding faces is one wavelength of the horn material. The radial movement of each welding face is in phase with the excitation and the horn exhibits two axial nodal points for each welding face. The configuration shown in Figures 3 and 4 can be realized by stacking individual horns or by machining a single one-piece structure integrally formed.

Figures 5 and 6 show the rotary horns stacked in parallel. In these figures, two or more rotating horns are stacked along their length using a resonant rod 20. This configuration is a parallel system because the main drive or input source is the cylindrical rod that joins these rotating horns. In this rotary horn configuration, each welding face can be driven independently of the adjacent weld face. The characteristics of the horn of the figures. 1-6 can be combined in any way, to mix and match features and components to form many different configurations. The length of a horn with multiple weld faces is a multiple of the wavelength of the horn material that is used. The location of the successive weld faces is at a distance (center-to-center distance between the adjacent weld faces) of a half wavelength of the horn material for the horns of Figures 3 and 5. The distance of Center to center for the horns of Figures 4 and 6 is of a wavelength of the horn material. If desired, the intermediate weld faces can be removed in such a manner that the weld faces are positioned at full wavelength of the horn material for the horns of Figures 3 and 5.

The configuration of Figures 5 and 6 can be made by stacking individual horns or by using an integrally formed one-piece structure. To cover a wider weld width, several rotating multi-face welding horns of any configuration can be stacked or mounted on both sides as shown in Figure 7. This minimizes the number of stacked horns that must be used and their it reduces the number of accessories, such as converters, reinforcers, power supplies and drive systems, necessary to accommodate the increased anvil widths. This also reduces the maintenance and assembly of the entire configuration. The horn and the welding face can be concentric cylindrical of constant diameter. However, they may have variable or non-concentric radii and the weld portion does not need to be cylindrical to work with various weld configurations. For example, the weld portion could be a non-cylindrical conical section. It could be elliptical in the radial direction or it could be spherical. It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers.

Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. Claims 1. A rotating acoustic horn for imparting energy at a selected wavelength, frequency and amplitude, characterized in that it comprises: a base portion having an axial input end and an axial output end; a plurality of welding faces operably linked to the base portion, each having a diameter that is larger than the diameter of the base portion and which expands and contracts with the application of acoustic energy to the input end of the portion of base, wherein the weld faces are spaced apart from each other and where the weld faces are mounted in parallel to each other.
2. 2. A rotating acoustic horn for imparting energy at a selected wavelength, frequency and amplitude, characterized in that it comprises: a base portion having an axial input end and an axial output end; a plurality of welding faces operably linked to the base portion, each having a diameter that is larger than the diameter of the base portion and which expands and contracts with the application of acoustic energy to the input end of the portion of base wherein the welding faces are spaced apart from one another, wherein the welding faces are mounted in series with each other and wherein the output of one horn in the axial direction becomes the input for the next horn.
3. The horn according to claim 1 or 2, characterized in that the distance between the midpoints of the adjacent welding faces is at least a multiple of one half wavelength of the horn material.
4. The horn according to claim 1 or 2, characterized in that the amplitude of vibration of each welding face differs from the amplitude of vibration of the adjacent welding faces.
5. The horn according to claim 1 or 2, characterized in that the axial length of the horn is substantially equal to one or more multiples of a half wavelength of the material of the horn and wherein the base portion is hollow by less part of its axial length.
6. The horn according to claim 1 or 2, characterized in that the base portion is cylindrical, the welding face is cylindrical, and the welding face is coaxial with the base portion.
7. The horn according to claim 1 or 2, characterized in that at least one expansion and contraction of the welding face move substantially in phase with the movement of the axial entry end of the horn and wherein each expansion and contraction of the the welding face moves substantially in phase with the expansion and contraction of the welding face of the alternative welding faces.
8. 8. The horn according to claim 1 or 2, characterized in that it is an ultrasonic horn.
9. The horn according to claim 1 or 2, characterized in that it further comprises means for changing the gain in the radial welding face when changing the mass at the axial entry end of the horn.
10. 10. A rotary acoustic horn installation for imparting energy at a selected wavelength, frequency and amplitude, characterized in that the installation comprises first and second horns in accordance with claim 1 or 2, wherein the welding faces on the first horn they are at selected spaced longitudinal sites and the weld faces on the second horn are at other spaced longitudinal sites selected such that the weld faces on both horns combine to exhibit a total weld face that is continuous.