Variably-Weighted Ultrasonic Welding Horn

1. Field of Invention:

This invention relates to an ultrasonic welding horn provided with variable weights which can be removed and added to the horn in order to achieve a uniform distribution of the amplitude of ultrasonic vibration across the face of the worksurface of the horn.

2. Description of the Prior Art:

Ultrasonic welding may be used for several purposes, including the joining of metals or plastics. Ultrasonic welding is often used in applications where high temperatures would be impractical, such as in connecting fine wires to microchips, sealing plastic bags and hermetically closing toothpaste or similar tubes. The application of a high frequency of vibration is used in place of the application of heat causing the intermolecular bonding of overlapping worksurfaces.

In applications where a broad area must be welded, as in the aforementioned examples of sealing a plastic bag or the rolled end of a toothpaste-like tube, care must be taken to provide a uniform weld lest any portion of the welded area not adhere to itself, thus frustrating an aesthetic and hermetic seal.

In order to obtain uniform amplitude of vibration in the ultrasonic welding horn, it was recognized that the welding horn should be balanced so that its wave energy is distributed uniformly in its attachment to a sound wave booster or amplifier which in turn is connected to the source of ultrasonic energy. This has been accomplished in the prior art by carefully machining the horn to achieve the balance. More precisely, it was normal practice to cut grooves in the input side of the horn in order to remove whatever material necessary to achieve such a balance. Such a process is expensive and does not allow for later adjustment.

In accordance with the present invention, an ultrasonic welding horn is provided which has provision for the attachment of variable weights in order to assure a uniform distribution of amplitude of vibration and a resultant uniform bond in an ultrasonic welding application.

The welding horn has a worksurface which is large, thereby being well suited for sealing plastic bags or tubes such as toothpaste and other similar products which are packaged. Ultrasonic energy is transmitted to the horn from an ultrasonic generator and energy converter which is attached directly or indirectly through a booster to the input surface of the welding horn. This input surface is opposite from the worksurface and variable sized weights can be secured to either or both sides of the horn where it is attached to the ultrasonic energy converter and/or booster. Adjustment of the magnitude and position of these weights allows the operator to fine-tune the distribution of the amplitude of vibration across the worksurface of the welding horn thereby assuring a uniform weld across the workpiece.

Further objects and advantages of the invention will become apparent from the following description and claims and from the accompanying drawings, wherein:

FIG. 1 is a perspective view of the welding horn of the invention, in position against a workpiece and an anvil, and

FIG. 2 is a cross-sectional view of the welding horn taken substantially along the plane indicated by line 2--2 of FIG. 1.

Referring now to the drawing in detail wherein like numerals indicate like elements throughout the several views, the welding horn 10 of the present invention has a long and narrow worksurface 12.

Opposite from and parallel to this worksurface 12 is an input surface 14. In the center of the input surface 14 is a threaded bore 16 into which a driving shaft 18 is threadedly inserted perpendicularly to the input surface 14. Ultrasonic vibration is transmitted from an external energy source (not shown) to the welding tip 10 through the driving shaft 18.

On either side of the threaded bore 16 and longitudinal axis of the welding tip 10, is a threaded hole 20 whose longitudinal axis is parallel to the longitudinal axis of the threaded bore 16. Balancing weights 22 can be adjustably screwed into one or both of the threaded bores 20. The magnitude of the balancing weights 22 may be chosen or adjusted so as to assure that the ultrasonic vibrations have a uniform distribution of amplitude across the face of the worksurface 12.

A workpiece 24 to be welded or sealed is held between the welding horn 10 and a backing anvil 26. Welding is effected by ultrasonic vibrations being transmitted through the driving shaft 18 to the welding horn 10.