Apparatus and method of laser welding inside bellows joints...

Electric heating – Metal heating – By arc

Reexamination Certificate

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C219S121640

Reexamination Certificate

active

06262387

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to manufacturing of metal bellows, and, more particularly, to an apparatus, method and spacer for welding metal bellows.
BACKGROUND OF THE INVENTION
Precision metal bellows are widely used in a number of applications where movement is required, but where sealing is also desired. For example, where it is desirable to have a vacuum on the exterior or interior of the bellows, the bellows provides environmental sealing. In other words, a bellows may be used as a boot for protective sealing. A bellows may also be used as a mechanical actuator by controlling pressure within the bellows, for example.
A bellows may be formed by joining together a series of bellows diaphragms in a predetermined pattern. A typical diaphragm is a generally circular disk with concentric folds formed therein. The diaphragms are joined together so that adjacent inside edges are connected together and adjacent outside edges are connected, etc.
The conventional approach to joining the diaphragms has been to tungsten inert gas (TIG) weld both the inside and outside joints. Unfortunately, TIG welding is relatively slow and may produce inconsistent quality welds.
In general, when TIG welding a pair of diaphragms are positioned in side-by-side relation and the interior weld is first formed using an inside diameter welding machine. Once a sufficient number of welded pairs or convolutions are made, these are assembled and positioned on a spindle or arbor. Copper “chill rings” or spacers are positioned between opposing outer portions. The chill rings help control the heating and heat dissipation of the diaphragms. The assembled convolutions and chill rings are rotated on the arbor, and each outer seam is TIG welded. The arc welding torch is indexed to each of the seams for welding. An operator watches the welding arc through a stereo microscope for alignment before and during welding. This off, ration may be very tedious for the operator. Moreover, the outcome of the bellows depends largely on the skills, experience, acuity, attentiveness, and the physical condition of the operator.
Once the outer welds are completed the structure is removed from the arbor, and the copper chill rings are then removed and discarded. Unfortunately, the copper chill rings must be made to relatively exacting tolerances and are therefore relatively expensive. Moreover, once used the copper rings may be discarded, and new rings may be supplied and used for making the next bellows. Accordingly, the cost of manufacturing is increased because of the cost of the copper chill rings.
Precision metal bellows manufacturing has been relying on gas tungsten arc (GTAW) or TIG welding for metal bellows for the past 20 years. Many improvements nave been made to the process including power control, pulsing techniques and torch configuration. Unfortunately, the conventional arc welding process has inherent limitations in terms of productivity and quality. The welding speed is relatively slow (10-20 inches per minute) and the weld quality degrades as the welding tip wears out. Constant adjustments and finesse are needed to maintain the weld quality. In addition, the weld quality depends largely on the skill and the acuity of the operator. The process is labor intensive and is not well suited for automation. The costs of disposable and consumable items are also high.
U.S. Pat. No. 3,918,622 to Larsen discloses tungsten inert gas (TIG) welding of the outer joint of a plurality of stacked diaphragms and with optical tracking of a weld immediately following the formation thereof to maintain precise torch alignment with the weld joint. The diaphragms to be welded are stacked on a rotatable arbor. A radiation source such as a lamp, is focused by a lens and directed by a mirror to the seam. Reflected light from the seam is sensed by two side-by-side phototransducers so that a difference in the two output signals indicates the lateral displacement of the seam. Unfortunately, the split photosensor system described may not accurately indicate the position of the relatively small seams of many commercially desirable bellows.
Also relating to joining diaphragms to form a metal bellows, U.S. Pat. No. 3,626,582 to Melill discloses diffusion bonding for the stacked diaphragms. The fabrication requires pressuring fixture tooling including an external steel cylindrical retainer ring and an internal steel cylindrical retainer plug, together with a force transmitting annular ram and multiple thin steel pressure support rings using to transmit the bonding forces of the high pressure ram. The process, unfortunately, is relatively complicated and expensive at it requires elevated temperatures of 1600-1700 degrees F. at 500 PSI pressure for 5 hours for typical thin sheet metal titanium diaphragms.
Laser and electron beam apparatus have also been disclosed for disclosed the joints of metal bellows. For example, U.S. Pat. No. 4,760,236 to Stoll discloses a laser welding apparatus wherein the outer diameter welds are made one at a time to form pairs of diaphragms. The pair of diaphragms are pressed between opposing tooling fixture portions to ensure alignment. To form the inner welds, a series of pairs are positioned within an evacuated chamber and the laser beam is directed through the center opening to the inner weld positions. For both the inner and outer welds, the laser beam is directed at an oblique angle. Unfortunately, an oblique angle may cause a nonsymmetrical and low quality weld. Moreover, precise positioning of the laser beam for the inside welds may be difficult and result in poor quality welds.
U.S. Pat. Nos. 5,478,983 and 5,410,123 both to Rancourt disclose an apparatus for forming a bellows bladder using a laser beam to form the inner and outer welds. An oblong shaped laser spot is used for welding. In addition, a comb structure is used to separate and position interior joints and exterior joints for laser welding. Precise relative positioning requires high accuracy of the comb and little or no variations in the convolutions. In short, precise positioning of the laser beam relative to the weld areas may be difficult to achieve.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the present invention to provide an apparatus and related methods for forming a precision weld at the interior joints of a metal bellows. It is another object of the present invention to provide a spacer and related methods for reducing the manufacturing cost for making a metal bellows.
These and other objects, advantages and features of the present invention are provided by an apparatus for laser welding an inner joint between first and second bellows diaphragms. The apparatus preferably includes a first clamp having an opening therein and having portions adjacent the opening defining a first clamping surface. The apparatus also preferably includes a second clamp having portions defining a second clamping surface, and wherein the first and second clamps are relatively movable to clamp the first and second metal bellows diaphragms together between the first and second clamping surfaces so that the openings in the bellows diaphragms are generally aligned with the opening in the first clamp.
The apparatus also preferably includes a laser for generating a laser beam, and laser beam directing means having at least a portion positioned in the opening of the first clamp and the openings of the first and second bellows diaphragms for directing the laser beam to weld the inner joint between the first and-second bellows diaphragms. The second clamp may also have a recess in a medial portion thereof receiving the laser beam directing means therein. The opening of the first clamp and the recess of the second clamp are preferably sized to expose a predetermined radially inwardly extending portion of the first and second bellows diaphragms to facilitate welding with the laser beam. In addition, the apparatus also preferably includes rotating drive means for relatively rotating the first and second clamps, and

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