CN116490342A - Self-leveling stack assembly with front loading amplitude uniform ultrasonic welding horn - Google Patents

Abstract

An ultrasonic welder (10) has a booster (50) carrying an ultrasonic horn (14) and a stack assembly (34). The stacking assembly is self-leveling and rotatable. Furthermore, the ultrasonic horn is annular and is mounted against the booster having a threaded cavity by a bolt (52) passing 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, the cross-sectional area of which is smaller than the cross-sectional area of the shaft by tapering the height. The transition is attached to the intermediate holder (31) and has a cross-sectional area that is smaller than the cross-sectional area of the transition. The intermediate retainer has a concave width recess. The intermediate holder carries a rectangular welding tip (33) having a cross-sectional area greater than the cross-sectional area of the intermediate holder.

Description

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

Cross Reference to Related Applications

The present application is a continuation-in-part application of U.S. provisional application Ser. Nos. 63/064423 and 63/183204, filed 8/12 and 5/3 2021, respectively.

Statement regarding federally sponsored research and development

Is not applicable.

Names of parties to a joint research agreement

Is not applicable.

Mention of "sequence Listing", tables or computer programs

Is not applicable.

Statement regarding inventors or co-inventors prior disclosure

Is not applicable.

Technical Field

The present invention relates to high frequency ultrasonic welding and, more particularly, to a new horn design. The use of high frequency ultrasonic vibrations to create welds between materials has been known since the 60 s of the 20 th century. Ultrasonic welders utilize friction generated by ultrasonic vibrations applied to the material to create welding, rather than applying heat to the material. Ultrasonic welding has proven to be effective in joining plastics and metals and has been used in many industries, ranging from toy production to the automotive and aerospace industries. Ultrasonic welding is popular because it is easy to form a weld and the cost per weld is low. Ultrasonic welding is an ideal way of joining small parts.

Background

Ultrasonic welding is an alternative to arc welding or thermal welding or soldering, eliminating consumables such as solder or flux, component burns, cooling water requirements, and high energy use. Another advantage of the ultrasonic welding operation is that the amount of heat generated during the welding process is minimized, thereby minimizing component damage.

Ultrasonic metal welding is suitable for the assembly of similar and dissimilar nonferrous metals used in electronic components and duct seals. Parts joined by ultrasonic welding are held together under pressure between an ultrasonic horn and an anvil. Ultrasonic vibrations are applied at a frequency of about 20 to 40kHz and the vibrations of the horn rub the parts together, the resulting shear forces removing surface contaminants and exposing bare metal areas.

This strong friction applied to the weld breaks the scale of the base metal when the two parts are pressed together at the same time. When applied to metals, welding is not achieved by melting the material, but rather by creating a solid state weld. Ultrasonic vibration causes shearing and deformation of surface asperities, which disperses oxides and contaminants present on the host material, allowing metal-to-metal contact and bonding of adjacent surfaces. These processes bring the two materials into sufficiently close contact for atomic scale bonding to occur. The atomic structures of the materials mix together to form strong surface molecular solid state bonds that are clean and low in electrical resistance. The relatively slight temperature rise caused by friction is well below the melting point and does not play an important role in producing the weld.

Ultrasonic welding is achieved in plastics and metals by different processes. When applied to plastics, the friction generated by ultrasonic vibration is sufficient to melt the joined portions of the materials, creating a weld when cooled. The welding time for ultrasonic welding is typically very short, typically between 200 and 400 milliseconds. For additional general disclosure of ultrasonic welding, please see New Developments in Advanced Welding, nasir Ahmed, ed. (2005).

The basic components of an ultrasonic welding system are a press, an anvil, an ultrasonic stack assembly, an ultrasonic generator or power supply, and an electronic controller. The workpiece to be welded is placed between a press and an anvil, the press applying pressure to the workpiece. The anvil allows ultrasonic vibrations to be directed at the surface of the material. Nesting or anvil of the placed workpieces (parts) allows high frequency vibrations generated by the stacked assembly to be directed to the interface of the weld base.

Ultrasonic stack assemblies are typically composed of transducers, enhancers (boost), and sonotrodes or "horns". The converter converts the electrical energy into mechanical vibration; the booster changes the amplitude of the vibration; and the sonotrode applies mechanical vibrations 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 components are connected to an electronic ultrasonic generator that delivers a high power AC signal to the stack while matching the resonant frequency of the stack.

The user issues commands to the system through the controller, which controls the movement of the press, actuates the stack assembly power supply, and transmits a welding-induced electrical signal to the ultrasonic stack assembly. The transducer portion of the stacked assembly converts the electrical signal into mechanical vibrations while the vibration amplitude can be varied using the booster. The horn imparts vibrations to the workpiece. The welding horn is typically formed from a shank attached to a welding tip.

The quality and success of ultrasonic welding depends on many factors, including signal amplitude, welding time, welding pressure, welding speed, hold time, and hold pressure. The appropriate amount of each of these factors is affected by the type of host material used for the weld and may also vary within a single material. In most of the industry's history, the only variables that can be effectively controlled are amplitude, force, and weld time or duration. The amplitude is controlled by a combination of frequency selection, horn and booster design, and modulation of the electrical input to the transducer.

User control of the variables and processes of ultrasonic welding is critical to continuously achieving effective welding. Better process control generally means improved weld quality, as well as improved weld consistency and repeatability. When checking the quality of welds between individual products, common products in the industry produce welds with standard deviations of 2% to 4%.

Stacked lithium ion batteries (alternating layers of copper and aluminum) are widely used in electric vehicles, including cars and trucks. In order to provide longer mileage and/or more power to an electric vehicle, laminate batteries are increasing in width and size by adding more and more laminate layers. This increase in battery size presents challenges for ultrasonic welding systems. In particular, conventional welding heads have difficulty maintaining uniform welding across the width of the laminate cell. Because the plies are thinner, the corners of the plies may fold or "dog-ear" typically during handling and prior to welding. In this way, the folded plies will not be welded across their width and will not function in a later formed battery. The present invention is directed to the detection of such folding.

Disclosure of Invention

An ultrasonic welder (10) has a booster (50) and a stack assembly (34) carrying an ultrasonic horn (14). The stacking assembly is self-leveling and rotatable. The ultrasonic horn is annular and is mounted against the booster having a threaded cavity by bolts (52) passing through the annular ultrasonic horn and into the threaded cavity of the booster.

A horn (14) for high frequency ultrasonic welding includes a shank formed of a shaft portion (35) attachable to a source of high frequency ultrasonic vibration, a transition (37) having a height and a width. By gradually reducing its height, the transition cross-sectional area is smaller than the shaft cross-sectional area. The transition is attached to an intermediate holder (31) having a height and a width and a cross-sectional area smaller than the transition cross-sectional area. The intermediate retainer has a uniform height and undercut width recess. The intermediate holder carries a rectangular welding tip (33) having a cross-sectional area greater than the cross-sectional area of the intermediate holder. The oppositely disposed recessed regions result in a more uniform weld across the weld edge of the horn.

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

Perhaps not readily apparent in the use of fig. 8 and bolts 52, the welding head assembly 14 is assembled into the rotary stack assembly 34 from the front and held in place against the booster front mount 50 by the bolts 52. In the field or in a factory, this method of assembly means that the horn assembly 14 can be easily removed by simply removing the bolts 52; thus, rotation of the horn assembly or removal and replacement thereof is facilitated. More importantly, this construction method enables the horn to be replaced without further disassembly of the ultrasonic welder 10 or any other component thereof.

Drawings

For a fuller understanding of the nature and advantages of the present method and process, reference should be made to the following detailed description taken in conjunction 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 a welding head showing a welding head welding edges of stacked battery plate layers;

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

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

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

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

FIG. 6 is an isometric view of a self-aligned stack;

FIG. 7 is a front view of a bonding tool;

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

FIG. 8A is an enlarged view of the installation of the shock absorbing O-ring and enhancer 50;

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

FIG. 10 is an isometric view of stacked battery plies, showing one of the plies being folded (folded);

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

FIG. 12 is a side view of the novel bonding tool disclosed in FIG. 3;

FIG. 13 is a front view of the novel bonding tool disclosed in FIG. 3;

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

fig. 14 is a top/bottom view of the novel bonding tool disclosed in fig. 12;

FIG. 15 is an isometric view of the disclosed novel bonding tool with side cuts or pockets or depressions;

FIG. 16 is an isometric view of a prior art bonding tool without side cuts or pockets;

FIG. 17 graphically illustrates experimental amplitude results (gauge measurements) of an example of one embodiment of a novel horn actuated at different points on a welding horn at different power levels of a welding unit;

FIG. 18 graphically illustrates experimental amplitude results (meter measurements) of an example of a prior art horn actuated at different points on a welding horn at different power levels of a welding unit;

FIG. 19 graphically illustrates experimental amplitude results (laser measurements) of an example of one embodiment of a novel horn actuated at different points on a welding horn at different power levels of a welding unit;

FIG. 20 graphically illustrates experimental amplitude results (laser measurements) of an example of a prior art horn actuated at different points on a welding horn at different power levels of a welding unit;

FIG. 21 is an isometric view of one embodiment of a novel bonding tool illustrating a plurality of digitally marked points across the bonding tool and a plurality of alphabetically marked points along the longitudinal length of the bonding tool;

FIG. 22 graphically illustrates experimental results for an example of the novel welding head of FIG. 12 actuated at 100% power of the welding unit;

FIG. 23 is an isometric view of a prior art weld head showing a plurality of digitally marked points across the weld head and a plurality of alphabetically marked points along the longitudinal length of the weld head; and

fig. 24 graphically illustrates experimental results for an example of the prior art welding head of fig. 14 actuated at 100% power of the welding unit.

The drawings will be described in more detail below in connection with examples.

Detailed Description

The popularity of electric vehicles has driven battery development and has required welding the edges of very thin electrode plates. Detecting uniformity of the edge weld is a technique that ensures that no plies fold. Such a folded ply means that the folded ply is not welded over the entire edge. The disclosed ultrasonic welder solves this problem with its novel design.

Referring first to fig. 1, an ultrasonic welder 10 has a stacked electrode sheet layer 12 in a position where the edges are ultrasonically welded by a horn assembly 14, the horn assembly 14 being held in place by a booster mounting ring 40 (see fig. 2). Most of the stacked components are housed within a housing 18, as will be disclosed below. The base 20 supports the ultrasonic welder 10 and is positioned on adjustable feet 22A and 22B as shown in fig. 1. Anvil assembly 23 is positioned below horn assembly 14. Adjacent to the horn assembly 14 is a leveling spring assembly 21 and a tilt encoder assembly 25 (see fig. 4). The horn assembly 14 is housed within a carrier block assembly 31 (see also fig. 5), which will be described in more detail below. Above the horn assembly 14 is a key assembly 35. Also seen is a servo motor driven vertical pressure screw assembly 28 (see also fig. 3) for applying a vertically downward pressure to hold a carrier block 31 (see fig. 5), as will be described below.

In fig. 3, the front cover of the housing 18 has been removed to reveal the components located therein. It can be seen that the servo motor driven vertical pressure screw assembly 28 includes a ball screw assembly 32 that applies pressure to a carrier block assembly 30, the carrier block assembly 30 housing a rotary stack assembly 34 (see fig. 9), the rotary stack assembly 34 including a horn assembly 14, a booster assembly 50 (see fig. 9), and a transducer 38 (see fig. 5), each of which is described further below. The rotary stack assembly 34 and its components operate in a conventional manner to transfer vibrational energy to the horn assembly 14 vibrating against the anvil assembly 23.

Referring additionally to fig. 8 and 9, the components of the self-leveling stack rotation assembly 34 are shown in a broken alignment. It will be observed that the horn assembly 14 extends from its welding end into the booster mounting ring 40 (see also fig. 6), the booster mounting ring 40 in turn extending into the interior of the carrier block 30. The enhancer mount ring 40 in turn has a threaded end that is screwed into the internally threaded end of the enhancer mount sleeve 42 with a lock nut 44 to securely screw them together. A large deep groove ball bearing (single row) 46 is mounted at one end of the booster mounting ring 40 and rests on the lock nut 44. The enhancer front mount 42 is threaded into the self-leveling housing 48. The booster front mount 50 extends through the self-leveling housing 48, the booster mounting sleeve 42, and against the horn assembly 14. The horn assembly 14 is secured to the booster front mount 50 by bolts 52. At the other end, the enhancer locking ring 54 is threaded into the self-leveling housing 48 with the O-ring 56 and O-ring 58 in place. The lock nut 64, large deep groove ball bearings (single row) 62 and O-ring 60 are constrained to the self-leveling housing 48. The rotating stack assembly 34 then has a pair of ball bearing rings at either end for rotation in both directions. The rotational capacity of the stack assembly can be measured by the encoder assembly (which is made up of encoder bracket 25, encoder sensor 27 and encoder strip 29) and returned to its neutral horizontal position by leveling spring assembly 21.

Perhaps not readily apparent in the use of fig. 8 and bolts 52, the welding head assembly 14 is assembled into the rotary stack assembly 34 from the front and held in place against the booster front mount 50 by the bolts 52. In the field or in a factory, this method of assembly means that the horn assembly 14 can be easily removed by simply removing the bolts 52; thus, rotation of the horn assembly or removal and replacement thereof is facilitated. More importantly, this construction method enables the horn to be replaced without further disassembly of the ultrasonic welder 10 or any other component thereof.

Fig. 10 shows an electrode plate layer stack 66 with curved corners 68. When the stack 66 is inserted into the disclosed ultrasonic welder 10 for end welding, the stack is able to rotate the encoder assembly (which is made up of the encoder bracket 25, encoder sensor 27, and encoder bar 29) and leveling spring assembly 21, the curved corner 68 makes that side of the welding edge thicker than the opposite corner that the encoder assembly can sense, and does not initiate the welding process. This ability to sense folded electrode sheets results in less scrap of edge welded electrode sheets and restores the stack by removing the bent electrode sheets for proper edge welding.

The high frequency ultrasonic welding unit 10 may be a pneumatically actuated ultrasonic welding system as is common in the industry. These systems utilize pneumatic cylinders to control the force and rate of descent of the stack. In pneumatic systems, the rate of ingress and egress of contained air through the pneumatic actuators of the system is limited. Thus, pneumatic systems cannot achieve abrupt changes in direction and speed, and also limit the distance control of the system. A system that can adjust its speed on the fly to accommodate material changes will ideally produce a perfectly consistent weld. As the system control over speed and distance is improved, the variation in weld quality will be reduced.

Pneumatic systems also use static pressure to compress the parts engaged by the system. Since variations in the host material may affect the desired pressure to be employed, static pressure is more likely to result in weaker welds than systems that can apply dynamic pressure to accommodate the conditions exhibited by the material. The features of the pneumatic system further provide limited control over the movement and positioning of the head surface. The weaknesses of pneumatic ultrasonic welding systems result in greater than ideal standard deviation between welds and reduced adaptability to external contamination and weld material variations.

A preferred ultrasonic apparatus 10 uses a motor to bring the sonotrode into contact with the welding material in order to generate the compressive force for ultrasonic welding. A sensor such as a load cell measures the pressure generated. The sensor can directly measure the load on the solder head, independent of system losses. The software algorithm may compensate for the deflection of the load cell sensor and lost motion in the motor actuation motion. Such a servomotor ultrasonic welding device is described in commonly owned USSN15/927114 filed on 3/21 of 2018.

12-14, the intermediate retainer 31 has a concave cutout in its side face. Such a cutout or "recess" results in retainer 31 having a smaller cross-sectional area near its midpoint and a larger cross-sectional area toward welding tip 33. Fig. 13A shows a smaller cross-sectional area near the midpoint of the retainer 31.

While the area with the recess or depression does have a smaller cross-section, this does not in itself allow the ultrasonic waves to propagate more uniformly to the welding tip 33 of the horn 14. The location, radius and depth of the concave features are critical. Only by repeated analysis using simulation or Finite Element Analysis (FEA) can the shape ultimately produce a uniform amplitude across the weld end 33 of the horn 14.

The ultrasonic waves are affected by the concave features in such a way that as the cross-sectional area begins to increase toward the welding tip 33, the ultrasonic waves bend outwardly and reach the extreme end of the welding tip 33, similar in intensity to those of continuous straight-ahead ultrasonic waves. This is based on the test measurements reported in provisional 63/064423 cited above.

While the apparatus, system, and method have been described with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope and spirit of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to 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. In addition, all citations cited herein are expressly incorporated herein by reference.

Example I

Concave welding head

Referring to fig. 15 and 16, bonding tools 114 and 120 use a bonding tool made of Dassault Systemes SolidWorks Corporation,175Wyman Street,Waltham,MA02451The simulation performs an amplitude analysis. Both bonding tools 114 and 210 are manufactured by Tech-Sonic, inc.,2710Sawbury Blvd, columbus, OH 43235 USA.

To confirm the FEA results, a laser was used to collect actual horn amplitude data on both horns. The amplitude was measured at the left end, left middle, right middle and right edge of each horn.

To ensure that the bonding tools are as similar as possible to each other, the knurl pattern and the dimensions of the bonding tools are identical. The two welding heads are also attached to the same booster, converter and housing (fig. 1), the only difference being the concavity of the sides of the welding heads (fig. 23) compared to a welding head without a concave side. The two welding heads will measure their amplitude at 5 points on the face of the welding head (as shown in fig. 15 and 16), all points being positioned as close as possible to the knurl to simulate the amplitude experienced by the welding surface during welding.

Both welding heads are measured with an amplitude meter and a laser amplitude measurer to ensure that the results are as accurate as possible. The provision of an amplitude meter includes the meter being fixed to the machine to ensure that the meter does not move easily due to vibration of the horn or any other external forces. The laser settings are also fixed to the machine. Laser readings were taken 3 times and the average was recorded.

The results are graphically shown in fig. 17-20. It is apparent that at all tested powers, the new horn exhibited a more uniform amplitude across the width of the weld tip. The following table shows that this uniformity can be more easily seen when comparing the edge amplitude with the intermediate amplitude as a percentage of the amplitude difference.

Table 1: laser and instrument reading concave-free side welding head of two welding heads, laser average

Non-concave side welding head, meter reading

% amplitude of vibration	Left end (1)	Left middle (2)	Middle (3)	Right middle (4)	Right end (5)
						45％	19	21	21	20	19
50％	22	24	24	22	22
						60％	27	29	30	28	26
70％	32	33	36	32	31
						80％	37	38	42	37	36
90％	40	43	47	42	40
						100％	45	49	52	48	45

Laser averaging with concave side welding head

% amplitude of vibration	Left end (1)	Left middle (2)	Middle (3)	Right middle (4)	Right end (5)
						45	26.83	27.00	27.33	26.83	27.17
50	29.00	29.17	29.17	29.00	29.00
						60	32.50	32.83	32.17	32.33	32.33
70	36.00	37.17	37.17	36.67	36.33
						80	39.33	41.00	40.00	40.33	39.67
90	43.00	44.17	43.83	44.83	44.50
						100	47.00	48.17	47.67	47.83	47.67

With concave side heads, meter readings

Table 2: the percent amplitude differences for different points on the horn compared to the midpoint.

Straight side welding head laser

Straight side welding head instrument

Concave side welding head laser

Concave side welding head instrument

The disclosed undercut welding heads exhibit a more uniform amplitude over their welding surfaces, while the welding heads without the undercut sides have a significantly higher amplitude in the center than the sides shown in fig. 17-20. The difference in amplitude is particularly pronounced at the lower amplitude% and at the higher end. The amplitude differences of the horn without the concave side were very pronounced compared to the concave side (table 2). For a laser reading recorded at 45%, the horn without the concave side had an amplitude difference of-38.52% from the left end (point 1) and-39.45% from the right end (point 5) compared to the middle (point 3). The difference between the left end (point 1) with respect to the middle (point 3) and the right end (point 5) with respect to the midpoint was-1.86% and-0.61%, respectively, compared to a new horn with concave sides. This difference is also evident at higher amplitudes where the horn without the concave side has an amplitude difference of-18.08% left end (point 1) to middle (point 3) and a right end (point 5) to middle amplitude difference of-18.53%, with the concave side horn having a left end to middle amplitude difference of-1.42% and a right end to middle amplitude difference of 0%.

Meter testing has also led to a similar trend. Wherein the distal ends (points 1 and 5) exhibit significantly different amplitudes than the midpoint (point 3) on the bond head without the concave side. There are many variations in meter testing, so in this case its purpose is to see if the trend recorded using the laser test is reflected in the meter test, not necessarily in order to obtain an accurate reading.

During welding, a significantly higher amplitude at the center of the horn becomes a problem because the center may be properly welded; however, the sides may be insufficiently welded. Conversely, when the sides are properly welded, the center may be overselded. The insufficiently welded seam is weak and does not provide sufficient bonding to allow proper electrical conduction, while the overly welded seam may be weak due to the brittle seam.

Example II

Rotary stacking

The test summary included 10 good welds, 15 fold welds, and 10 alternate welds to evaluate the self-leveling capability of the welder. The welder and rotary welding head of fig. 1-11 are used in this example.

The normal or good weld test results are shown in table 1 below.

TABLE 3 Table 3

Initial height	Welding head position
		0.278	-0.032
0.28	-0.034
		0.276	-0.034
0.277	-0.032
		0.276	-0.037
0.277	-0.037
		0.279	-0.032
0.278	-0.034
		0.277	-0.031
0.278	-0.03
		0.2776 average	-0.0333 average
0.001633 standard deviation	0.000943 standard deviation

The fold welding test results are shown in table 4 below.

TABLE 4 Table 4

Initial height	Welding head position
		0.274	-0.008
0.275	-0.005
		0.275	-0.067
0.275	-0.063
		0.276	-0.068
0.273	-0.064
		0.277	-0.062
0.273	-0.006
		0.274	-0.005
0.276	-0.003
		0.275	-0.066
0.277	-0.062
		0.274	-0.004
0.276	-0.005
		0.279	-0.008
0.275257 average
		0.001569 standard deviation

Alternating good/fold welds were performed to determine if the new welder could maintain its gauge difference detection with a mixture of non-folded and folded foils. The results are shown in table 5.

TABLE 5

Also, the ability of the welder to detect folded foil in unfolded foil is very excellent.

The disclosed welder design was successful, with the ability to detect folded foil. All reported tests were performed without any retries. The initial height is critical for detecting good foil from folded foil.

Claims (9)

1. In an ultrasonic welder (10) having an enhancer (50) and a self-leveling rotating laminate assembly (34) carrying an ultrasonic horn (14), the improvement comprising:

an intermediate holder (31) for carrying an ultrasonic horn and having a height and a width, the intermediate holder having a uniform height and undercut width recess.

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 having a transition cross-sectional area smaller than the shaft cross-sectional area by tapering the height;

(c) An intermediate retainer (31) having a height and a width, a cross-sectional area less than the transition cross-sectional area, the intermediate retainer having uniform height and undercut width depressions; and

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

3. The ultrasonic welder according to claim 1, wherein the rectangular welding tip (33) has a cross-sectional area greater than the cross-sectional area of the intermediate holder 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 by a bolt (52) passing through the annular ultrasonic horn and into the booster threaded cavity, the booster having a threaded cavity.

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

6. A horn (14) for a high frequency ultrasonic welding horn, comprising:

(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 having a transition cross-sectional area smaller than the shaft cross-sectional area by tapering the height;

(c) An intermediate retainer (31) having a height and a width, a cross-sectional area less than the transition cross-sectional area, the intermediate retainer having uniform height and undercut width depressions; and

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

7. In an ultrasonic welder (10) having an enhancer (50) and a stack assembly (34) carrying an ultrasonic horn (14), the improvement comprising:

the stacking assembly is self-leveling and rotatable.

8. In an ultrasonic welder (10) having an enhancer (50) and a stack assembly (34) carrying an ultrasonic horn (14), the improvement comprising:

the ultrasonic horn is annular and is mounted against the booster having a threaded cavity by a bolt (52) passing 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 foil stack, the foil stack being welded with an ultrasonic welder (10) having a booster (50) and a stack assembly (34) carrying an ultrasonic horn (14), wherein the stack assembly is self-leveling and rotatable.