WO2022035924A1

WO2022035924A1 - Self leveling stack assembly with front-loaded amplitude uniform ultrasonic welding horn

Info

Publication number: WO2022035924A1
Application number: PCT/US2021/045475
Authority: WO
Inventors: David Lee CYPHERT; Byoung Soo OU; Jason E. Smith
Original assignee: Tech-sonic Inc.
Priority date: 2020-08-12
Filing date: 2021-08-11
Publication date: 2022-02-17
Also published as: EP4196310A1; KR20230049665A; JP2023538468A

Abstract

An ultrasonic welder (10) has a booster (50) and stack assembly (34) carrying an ultrasonic horn (14). The stack assembly is self-leveling and rotational. Also, the ultrasonic horn is annular and is mounted against the booster, which has a threaded cavity, by a threaded bolt (52) that passes through the annular ultrasonic horn and into the threaded cavity of the booster. The horn includes a shaft portion (35) attachable to a source of high-frequency ultrasonic vibration, a transition (37) having a height and a width and being smaller in cross- sectional area than the shaft cross-sectional area by tapering its height. The transition is attached to an intermediate holder (31) and has a cross-sectional area that is smaller than the transition cross-sectional area. The intermediate holder has a concave width dimples. The intermediate holder carries a rectangular welding tip (33) having a cross-sectional area larger than the intermediate holder cross-sectional area.

Description

SELF LEVELING STACK ASSEMBLY WITH FRONT-LOADED AMPLITUDE UNIFORM ULTRASONIC WELDING HORN

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of both U.S. provisional applications serial numbers 63/064,423 and 63/183,204 filed, respectively, August 12, 2020, and May 3, 2021.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Not applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM

Not applicable.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR

Not applicable.

BACKGROUND OF THE INVENTION

The present disclosure relates to high-frequency ultrasonic welding and more particularly to a new horn design therefor. The use of high-frequency ultrasonic vibrations to create a weld between materials has been known since the 1960s. Ultrasonic welders create a weld using friction generated by the ultrasonic vibrations applied to the materials, rather than application of heat to the materials. Ultrasonic welding has proven to be effective in joining both plastics and metals, and has been applied in a number of industries, from toy production to the automotive and aerospace industries. Ultrasonic welds are popular due to the ease with which a weld can be created and the low cost per weld. Ultrasonic welds are ideal for joining small parts.

Ultrasonic welding is an alternative method to arc or heat welding, or soldering, eliminating consumables, such as solder or flux, component burn back, cooling water requirements and high-energy use. An additional advantage of ultrasonic welding operations is the minimal heat that is generated during the welding process, minimizing component damage.

Ultrasonic metal welding is adapted for the assembly of similar and dissimilar non-ferrous metals used in electronic components and pipe sealing. Parts to be joined by ultrasonic welds are held together under pressure between the ultrasonic horn and anvil. Ultrasonic vibrations of a frequency of about 20 to 40 kHz are applied, and vibration of the horn causes the parts to scrub together, with resultant shear forces removing surface contaminants and exposing bare metal areas.

This intense friction applied to the weld as the two parts are simultaneously pressed together breaks the oxide skins of the substrate metals. When applied to metals, a weld is achieved not by melting materials, but through the creation of a solid-state weld. The ultrasonic vibrations cause shearing and deformation of surface asperities, which disperses oxides and contaminants existing on the subject materials, which allows for metal-to-metal contact and bonding of the adjacent surfaces. These processes bring the two materials into sufficiently intimate contact for atomic level bonding to occur. The materials’ atomic structures are co-mingled creating a strong, surface molecular, solid-state bond that is clean and has low electrical resistance. The relatively slight rise in temperature created by the friction is well below melting point and plays no essential part in creating the weld.

Ultrasonic welds are achieved in plastics and metals through different processes. When applied to plastics, the friction created by the ultrasonic vibrations is sufficient to melt the joined portions of the materials, creating a weld when cooled. The weld time for an ultrasonic weld is typically very short, with weld times generally ranging between 200 and 400 milliseconds. For additional general disclosure regarding ultrasonic welding, see New Developments in Advanced Welding, Nasir Ahmed, ed. (2005).

The basic components of ultrasonic welding systems are a press, an anvil, an ultrasonic stack assembly, an ultrasonic generator or power supply, and an electronic controller. The workpieces to be welded are placed between the press and the anvil, with the press applying pressure to the pieces. The anvil allows the ultrasonic vibrations to be directed to the surfaces of the materials. The nest or anvil, where the workpieces (parts) are placed, allows the high frequency vibration generated by the stack assembly to be directed to the interfaces of the weld substrates.

The ultrasonic stack assembly is commonly composed of a converter, a booster, and a sonotrode or “horn.” The converter converts the electrical energy into a mechanical vibration; the booster modifies the amplitude of the vibration; and the sonotrode applies mechanical vibration to the parts to be welded. These three elements are typically tuned to resonate at the same ultrasonic frequency (typically 20, 35 or 40 kHz). These stack assembly components are connected to an electronic ultrasonic generator that delivers high power AC signal to the stack assembly, while matching the resonance frequency of the stack assembly.

The user issues commands for the system via the controller, which controls the movement of the press, actuates the stack assembly power supply, conveying weld inducing electrical signal to the ultrasonic stack assembly. The converter portion of the stack assembly converts the electrical signal into a mechanical vibration, while a booster can be utilized to modify the vibration amplitude. The horn applies the vibrations to the workpiece. Welding horns generally are formed from a shank attached to a welding tip.

The quality and success of an ultrasonic weld is dependent on a number of factors, including signal amplitude, weld time, weld pressure, weld speed, hold time, and hold pressure. The appropriate amount of each of these factors is affected by the types of subject materials for the weld and can also vary within a single material. For the majority of the history of the industry, the only variables that could be effectively controlled were amplitude, force, and weld time or duration. Amplitude was controlled through a combination of frequency selection, the design of the horn and booster, and modulation of electrical inputs to the converter.

User control of the variables and processes of an ultrasonic weld is key to achieving effective welds consistently. Better process control generally translates to improved quality of welds, as well as improved consistency and repeatability of welds. Common products in the industry produce welds with standard deviations of 2% to 4% when the weld quality between individual products is examined.

Laminate lithium ion batteries (alternating copper and aluminum plies) find wide use in electric vehicles, both cars and trucks. In order to provide a longer range and/or more power to the electric vehicles, laminate batteries are increasing in width and in size by adding more and more laminates. This increase in battery size has created challenges for ultrasonic welding systems. In particular, conventional horns have difficulty in maintaining a uniform weld across the width of the laminate batteries. Due to the ply thinness, corners of the plies can become folded or “dog-eared” usually at the corner during handling and before welding. The dog-eared ply, then, will not be welded across its width and will not be active in the later formed battery. It is to the detection of such folds that the present invention is addressed.

BRIEF SUMMARY OF THE INVENTION

An ultrasonic welder (10) has a booster (50) and stack assembly (34) carrying an ultrasonic horn (14). The stack assembly is self-leveling and rotational. The ultrasonic horn is annular and is mounted against the booster, which has a threaded cavity, by a threaded bolt (52) that passes through the annular ultrasonic horn and into the threaded cavity of the booster.

The horn (14) for high-frequency ultrasonic welding includes a shank formed from a shaft portion (35) attachable to a source of high-frequency ultrasonic vibration, a transition (37) having a height and a width. The transition cross-sectional area is smaller than the shaft cross-sectional area by tapering its height. The transition is attached to an intermediate holder (31) having a height and a width, and a cross-sectional area that is smaller than the transition cross- sectional area. The intermediate holder has a uniform height and side concave width dimples. The intermediate holder carries a rectangular welding tip (33) having a cross-sectional area larger than the intermediate holder cross-sectional area. The opposite disposed concave areas result in a more uniform weld across the entire horn welding edge.

A method for detecting a folded edge of a foil in a stack of foils included welding the stack of foils with an ultrasonic welder (10) having a booster (50) and stack assembly (34) carrying an ultrasonic horn (14), wherein the stack assembly is self- leveling and rotational.

Perhaps, not readily apparent in FIG. 8 and the use of threaded bolt 52, is that horn assembly 14 fits into rotational stack assembly 34 from the front and is held in position by threaded bolt 52 against booster front mount 50. In the field or in a plant, such method of assembly means that horn assembly 14 can be easily removed by the simple removal of threaded bolt 52; thus, making rotation of horn assembly or its removal and replacement easy. More importantly, such method of construction enables changing of the horn without the need for any further disassembly of ultrasonic welding machine 10 or any of its other components. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the present method and process, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is an isometric view of a high-frequency ultrasonic self-leveling welding system disclosed herein;

FIG. 2 is a side view of the welding head showing the horn welding an edge of a stack of battery plies;

FIG. 3 is a front view of the high-frequency ultrasonic self-leveling welding system with its front cover removed;

FIG. 4 is a close up front view of the welding horn;

Fig 4A is a perspective view of the encoder. The encoder bracket 25 has a encoder sensor 27 attached to its back side that reads the position of the encoder strip 29 in a slot of booster mounting ring 40;

FIG. 5 is an isometric view of the welding assembly;

FIG. 6 is an isometric view of the self-aligning stack;

FIG. 7 is a front view of the horn;

FIG. 8 is a sectional view taken along line 8-8 of FIG. 7;

Fig 8A is an enlarged view of the vibration absorbing O rings and mounting of the booster 50;

FIG. 9 is an isometric expanded view of the stack assembly components;

FIG. 10 is an isometric view of a stack of battery plies show one of the plies being dogeared (folded); and

FIG. 11 is a close up front view of the welding assembly in its welding position.

FIG. 12 is a side elevational view of the disclosed novel horn of FIG. 3;

FIG. 13 is a front view of the disclosed novel horn of FIG. 3;

FIG. 13A is a sectional view taken along line 13A-13A of FIG. 12;

FIG. 14 is a top/bottom view of the disclosed novel horn of FIG. 12;

FIG. 15 is an isometric view of the disclosed novel horn with side cut-outs or niches or concaves;

FIG. 16 is an isometric view of a prior art horn without the side cut-outs or niche.

FIG. 17 graphically displays the experimental amplitude results (gauge measurement) of the Example for one embodiment of the novel horn actuated at various power levels of the welding unit over various points across the welding horn;

FIG. 18 graphically displays the experimental amplitude results (gauge measurement) of the Example for the prior art horn actuated at various power levels of the welding unit over various points across the welding horn;

FIG. 19 graphically displays the experimental amplitude results (laser measurement) of the Example for one embodiment of the novel horn actuated at various power levels of the welding unit over various points across the welding horn;

FIG. 20 graphically displays the experimental amplitude results (laser measurement) of the Example for the prior art horn actuated at various power levels of the welding unit over various points across the welding horn;

FIG. 21 is an isometric view of one embodiment of the novel horn showing several numerically labelled points across the horn and several alphabetically labelled points along the longitudinal length or the horn;

FIG. 22 graphically displays the experimental results of the Example for the novel horn of FIG. 12 actuated at 100% of the power of the welding unit;

FIG. 23 is an isometric view of the prior art horn showing several numerically labelled points across the horn and several alphabetically labelled points along the longitudinal length or the horn; and

FIG. 24 graphically displays the experimental results of the Example for the prior art horn of FIG. 14 actuated at 100% of the power of the welding unit

The drawings will be described in greater detail below and in connection with the Example.

DETAILED DESCRIPTION OF THE INVENTION

The popularity of electric vehicles has launched battery development and the need to weld the edges of very thin electrode plies. Detecting the uniformity of the edge welds is one technique to ensure that none of the plies are folded. Such folded plies mean that the folded ply is not welded across the entire edge. The disclosed ultrasonic welding machine addresses this problem in its novel design.

Referring initially to FIG. 1 , an ultrasonic welding machine, 10, has a stack of electrode plies, 12, in position for an edge to be ultrasonically welded by a horn assembly, 14, held in position by a booster mounting ring, 40 (see FIG. 2). Most of the stock components are housed within a case, 18, and which will be disclosed below. A base, 20, supports ultrasonic welding machine 10 and sits on adjustable feet, 22A and 22B, visible in FIG. 1. Located beneath horn assembly 14 is an anvil assembly, 23. Adjacent to horn assembly 14 is a leveling spring assembly, 21 , and a tilt encoder assembly, 25, (see FIG. 4). Horn assembly 14 is housed within a carriage block assembly, 31 (see also FIG. 5), to be described in greater detail below. Above horn assembly 14 is a key assembly, 35. Also seen is a servo motorized vertical pressure screw assembly, 28, (see also FIG. 3) for exerting vertical downward pressure for holding a carriage block, 31 , (see FIG. 5) to be described later herein.

The front cover of case 18 has been removed in FIG. 3 to reveal the components located therewithin. Servo motorized vertical pressure screw assembly 28 is seen to include a ball-screw assembly, 32, that exerts pressure against carriage block assembly 30 within which houses a rotational stack assembly, 34, (see FIG. 9) that includes horn assembly 14, a booster assembly, 50, (see FIG. 9) and a converter, 38, (see FIG. 5), each of which will be described further below. Rotational stack assembly 34, and its components, operate in convention fashion for imparting vibrational energy to horn assembly 14, which vibrates against anvil assembly 23.

Referring additionally to FIGS. 8 and 9, the components of self-leveling stack rotational assembly 34 are shown in broken away alignment. It will be observed that horn assembly 14 extends from its welding tip into a booster mounting ring, 40, (see also FIG. 6), which in turn extends inside carriage block 30. Booster mounting ring 40 in turn has a threaded end that screws into internally threaded end of a booster mounting sleeve, 42, with a locking nut, 44, holding them firmly threaded together. A large deep groove ball bearing (single row), 46, fits over an end of booster mounting ring 40 and against locking nut 44. Booster front mount 42 is screwed into a self-leveling shell, 48. A booster front mount, 50, extends through self-leveling shell 48, booster mounting sleeve 42 and against horn assembly 14. Horn assembly 14 is held tight against booster front mount 50 by a threaded bold, 52. At the other end, a booster locking ring, 54, screws into self-leveling shell 48 with an O-ring gland, 56, and an O-ring, 58, in position. Trapped against self-leveling shell 48 are a locking nut, 64, large deep groove ball bearing (single row), 62, and an O-ring, 60. Rotational stack assembly 34, then, has a pair of ball bearing rings at either end for it to rotate in both directions. The stack assembly’s ability to rotate can be measured by an encoder assembly (consisting of encoder bracket 25, encoder sensor 27, and encoder strip 29) and is returns to its neutral horizontal position by leveling spring assembly 21.

Perhaps, not readily apparent in FIG. 8 and the use of threaded bolt 52, is that horn assembly 14 fits into rotational stack assembly 34 from the front and is held in position by threaded bolt 52 against booster front mount 50. In the field or in a plant, such method of assembly means that horn assembly 14 can be easily removed by the simple removal of threaded bolt 52; thus, making rotation of horn assembly or its removal and replacement easy. More importantly, such method of construction enables changing of the horn without the need for any further disassembly of ultrasonic welding machine 10 or any of its other components.

FIG. 10 shows a stack of electrode plies, 66, with a bent corner, 68. When stack 66 is inserted for end welding into disclosed ultrasonic welding machine 10 with the stack’s ability to rotate, the encoder assembly (consisting of encoder bracket 25, encoder sensor 27, and encoder strip 29), and leveling spring assembly 21 , bent corner 68 makes that side of the weld edge thicker than the opposite corner that can be sensed by the encoder assembly and no welding procedure initiated. This ability to sense folded plies results in less rejection of edge welded electrode plies and the recovery of such stack by removal of the bend electrode ply for proper edge welding.

High-frequency ultrasonic welding unit 10 can be a pneumatically actuated ultrasonic welding system, as are common in the industry. These systems utilize pneumatic cylinders to control the force and down speed of the stack. In a pneumatic system, the entry and exhaust rate at which the air contained moves through the pneumatic actuators of the system is limited. Consequently, the pneumatic systems are unable to achieve abrupt changes in direction and velocity, as well as limiting the system’s distance control. A system that is able to adjust its velocity instantaneously to adapt to variations in the materials would ideally produce perfectly consistent welds. Reduced deviations in weld quality will occur when the system’s control over velocity and distance is improved.

Pneumatic systems also use static pressure to compress parts engaged by the system. As variations in the subject materials may affect the ideal pressure to be employed, a static pressure is more likely to result in a weaker weld than a system that can apply dynamic pressure to adapt to the conditions presented by the materials. The character of pneumatic systems further provides limited control over the movement and positioning of the horn face. The weaknesses in pneumatic ultrasonic welding systems lead to greater than ideal standard deviations between welds, as well as reduced adaptability to outside contaminants and weld material variations.

A better ultrasonic apparatus 10 uses an electric motor to bring the Sonotrode into contact with the weld material in order to develop a compressive force for ultrasonic welding. A sensor, such as a load cell, measures the compressive force developed. The sensor directly can measure the load on the Horn independent of system losses. A software algorithm can compensate for deflection of the load cell sensor and lost motion in the electric motor actuating movement. Such a servo motor ultrasonic welding apparatus is described in commonly-owned USSN 15/927,114 filed March 21 , 2018.

Referring additionally to FIGS. 12-14, intermediate holder 31 has concave cutouts at its sides. Such cutouts or “dimples” result in holder 31 having a smaller cross-sectional area about its midpoint with a larger cross-sectional area towards welding tip 33. FIG. 13A shows the smaller cross-sectional area about the midpoint of holder 31 .

While the area with the concave cutouts or dimples does indeed have a smaller cross section, that in and of itself does not cause the ultrasonic waves to travel more uniformly to welding tip 33 of the horn 14. The position, radius, and depth of the concave feature are critical. Only through repeated analysis using simulation or finite element analysis (FEA) does the shape eventually result in a uniform amplitude across the entire welding tip 33 of horn 14.

The ultrasonic waves are influenced by the concave features in such a way that, as the cross-sectional area begins to increase towards welding tip 33, the waves bend outwardly and reach the extreme ends of welding tip 33 with a similar strength as those that continue straight ahead. This is based on test measurements, as reported in provisional 63/064,423, cited above.

While the apparatus, system, and method have been described with reference to various embodiments, those skilled in the art will understand that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope and essence of the disclosure. In addition, many modifications may be made to adapt a particular situation or material in accordance with the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that the disclosure will include all embodiments falling within the scope of the appended claims. Also, all citations referred herein are expressly incorporated herein by reference.

EXAMPLE I Dimpled Horn

Referring to FIGS. 15 and 16, horns 114 and 120 were subjected to amplitude analysis using SOLIDWORKS® Simulation by Dassault Systemes SolidWorks Corporation, 175 Wyman Street, Waltham, MA 02451. Both horns 114 and 210 were manufactured by Tech-Sonic, Inc., 2710 Sawbury Blvd., Columbus, OH 43235 USA.

To confirm the FEA results, actual horn amplitude data was collected on both horns using a laser. Amplitude was measured at the left end, left middle, middle, right middle, and right edge of each horn.

To ensure that the horns are as alike to each other as possible, the knurling pattern, as well as the dimensions of the horns, are the same. Both horns are also attached to the same booster, converter, and shell (FIG. 1), the only difference is the concave faces on the side of the horn compared to the horn without the concave side (FIG. 23). Both horns will have their amplitudes measured at 5 points on the horn’s face (as shown on FIGS. 15 and 16), all points are positioned, as close as they can possibly be, to the knurling to simulate the amplitude that a weld surface experiences during a welding process.

The horns are both measured using an amplitude gauge, as well as a laser amplitude measurer, to ensure the results are as accurate as possible. The setup for the amplitude gauge included a gauge is fixed on the machine to make sure that the gauge could not be moved around easily by the horn’s vibration or any other external forces. The laser setup also was fixed onto a machine. The laser readings are done 3 times and the average is recorded.

The results are displayed graphically in FIGS. 17-20. It will be apparent that the novel horn displayed a more uniform amplitude across the width of the welding tip at all powers tested. Such uniformity can be more readily seen when comparing the edge amplitudes to the middle amplitudes in percentage of amplitude difference, as displayed in the following table.

Table 1: Laser and Gauge Reading for Both Horns

With Concave Sides Horn, Laser Average

With Concave Sides Horn, Gauge Reading

Table 2: Amplitude difference in percentage of the different points on the horn compared to the middle point.

Straight Side Horn Laser

Straight Side Horn Gauge

Concave Side Horn Laser

Concave Side Horn Gauge

The disclosed side concave horn shows a more uniform amplitude across its weld surface, while the horn without the concave sides has a significantly higher amplitude in the center compared to the sides as shown on FIGS. 17-20. The differences in amplitude are especially obvious on the lower amplitude % as well as the higher end. The difference in amplitude for the horn without concaved sides compared to the concave sides is quite significant (Table 2). For the laser readings recorded at 45%, the horn without the concave sides has an amplitude difference of -38.52% from the left end (point 1) compared to the middle (point 3), while the right end (point 5) has a amplitude difference of -39.45%. Compared to the novel horn with concave sides where the difference is -1 .86% and -0.61 % left end (point 1) compared to middle (point 3) and right end (point 5) compared to middle respectively. The difference also is apparent at higher amplitudes where the horn without the concave sides has a left end (point 1) to middle (point 3) amplitude difference of -18.08%, while the right end (point 5) to middle is - 18.53%, the concave side horn has a left end to middle amplitude difference of - 1.42% and a right end to middle amplitude difference of 0%.

The gauge test also resulted in similar trends. Where the far ends (points 1 and 5) show significantly different amplitudes compared to the middle point (point 3) on the horn without the concave sides. The gauge test has a lot of variance to it so its use in this case is to see whether the trends recorded using the laser test are mirrored on the gauge test, and not necessarily to obtain an accurate reading.

The significantly higher amplitude in the center of the horn becomes an issue during welds since the center may be welded properly; however, the sides may end up being underwelded. Inversely, the center might be overwelded while the sides are welded properly. The underwelded welds are weak and do not provide sufficient bonding to allow proper electrical conduction, while an overwelded welds also are potentially weaker due to the weld being brittle.

EXAMPLE II Rotational Stack

The test outline included 10 good welds, 15 folded welds, and 10 alternating welds to evaluate the welder’s self levelling capability. The welder and rotational horn of FIGS. 1 -11 was used in this example.

The normal or good welds test results are displayed below in Table 1 .

TABLE 3

The folded weld test results are displayed below in Table 4.

TABLE 4

Alternating good/folded welds were conducted in order to determine whether the novel welder was capable of maintaining its thickness difference detection with a mixture of non-folded foils and folded foils. The results are displayed in Table 5. TABLE 5

Again, the ability of the welder to detect fold foils among non-folded foils was excellent.

The disclosed welder design was a success with its capability in detecting fold foils. All of the reported tests were conducted without any retries. The starting height is critical in detecting good foils from those that were folded.

Claims

CLAIMS:

1. In an ultrasonic welder (10) having a booster (50) and a self-leveling and rotational stack assembly (34) carrying an ultrasonic horn (14), the improvement comprising: an intermediate holder (31) for carrying the ultrasonic horn and having a height and a width, the intermediate holder having a uniform height and side concave width dimples.

2. The ultrasonic welder of Claim 1 , wherein the ultrasonic horn comprises:

(a) a shaft portion (35) attachable to a source of high-frequency ultrasonic vibration;

(b) a transition (37) having a height and a width, and a transition cross-sectional area smaller than the shaft cross-sectional area by tapering its height; and

(c) an intermediate holder (31) having a height and a width, a cross- sectional area that is smaller than the transition cross-sectional area, the intermediate holder having a uniform height and side concave width dimples; and

(d) a rectangular welding tip (33) having a cross-sectional area larger than the intermediate holder cross-sectional area and attached to the shank.

3. The ultrasonic welder of Claim 1 , wherein a rectangular welding tip (33) having a cross-sectional area larger than the intermediate hold cross- sectional are and is attached to the intermediate holder.

4. The ultrasonic welder of Claim 1 , wherein the ultrasonic horn is annular and is mounted against the booster, the booster having a threaded cavity, by a threaded bolt (52) that passes through the annular ultrasonic horn and into the threaded cavity of the booster.

5. A method for detecting a folded edge of a foil in a stack of foils, welding the stack of foils with an ultrasonic welder (10) having a booster (50) and stack assembly (34) carrying an ultrasonic horn (14), wherein the stack assembly is self-leveling and rotational.

6. A horn (14) for a high-frequency ultrasonic welding horn, which comprises:

7. In an ultrasonic welder (10) having a booster (50) and stack assembly (34) carrying an ultrasonic horn (14), the improvement comprising: the stack assembly being self-leveling and rotational.

8. In an ultrasonic welder (10) having a booster (50) and stack assembly (34) carrying an ultrasonic horn (14), the improvement comprising: the ultrasonic horn being annular and being mounted against the booster having a threaded cavity by a threaded bolt (52) that passes through the annular ultrasonic horn and into the threaded cavity of the booster.

9. A method for detecting a folded edge of a foil in a stack of foils, welding the stack of foils with an ultrasonic welder (10) having a booster (50) and stack assembly (34) carrying an ultrasonic horn (14), wherein the stack assembly is self-leveling and rotational.