System and method of joining overlapping workpieces

An improved fusion welding system having a perforating device and a heating combination is adapted for welding in tandem a set of adjacent overlapping workpieces. The system preferably includes a first laser that perforates the workpieces to produce an opening spaced from the edges; and the combination preferably includes a second laser and electrode for cooperatively melting fusible material into the opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fusion welding systems, and more particularly to a fusion welding system having a perforating or cutting device configured to produce an opening within a plurality of workpieces and a heating combination configured to produce a lap weld within the opening.

2. Discussion of Prior Art

The process of material joining and treatment is a necessary condition for the industrial progress. As such, fusion-welding systems have been developed for joining multi-component workpieces. One such system, metal-arc robotic welding, utilizes an arc discharge to provide a more affordable and less expensive heat energy source during joining, and is commonly used, for example, in the automotive industry. These conventional systems are typically used to produce fillet welds along seams formed by adjacent workpieces, as shown inFIG. 1; and provide good gap bridgeability, weld penetration, and low cost. The electrodes that produce the arc may also be fusible by the process, so that metallic drippings are produced to contribute to the weld. Other welding systems, such as conventional hybrid laser-arc systems, which feature the simultaneous application of heat generated from laser radiation and an electric arc, have also been developed.

Due to workpiece dimension variations, improper fixture designs, and distortions from welding, however, weld bead misalignment (also shown inFIG. 1) presents a major issue during the use of these and other systems. Although various seam tracking devices have been used, they have not been successful due in part to long cycle time, arc lighting interference with camera and other technical difficulties. As a result, part inspection and repair provisions have been added to the production process, which thereby increase production time and total man-hours.

The increase in costs associated therewith, results in a need in the art for a more efficient welding process that reduces the likelihood of weld misalignment.

BRIEF SUMMARY OF THE INVENTION

Responsive to these and other concerns caused by conventional fusion welding systems, the present invention provides an improved system for increasing the consistency and alignment of weld bead placement, and thereby reducing the costs associated with inspection and repair of weld misalignment. This invention provides a method of welding overlapping workpieces using multiple sources for in tandem perforation and welding.

More particularly, a first aspect of the present invention concerns a system for welding a plurality of overlapping adjacent workpieces to form a lap weld, wherein each work-piece presents an outer edge. The system includes a perforating device configured to engage at least a portion of the plurality of workpieces, so as to produce an opening in the portion. The system also includes a heating combination configured to heat a zone adjacent the opening to a minimum zone temperature, so as to cause a weld to form at least predominately within the opening. Finally, the opening is adjacent to and spaced from the outer edges of each of the plurality of workpieces.

A second aspect of the present invention concerns a method of welding a plurality of workpieces to form a lap weld, and includes the following steps. First, a portion of the workpieces is perforated to produce an opening adjacent to and spaced from the edges of each of the workpieces. Next, an arc is created adjacent an outermost surface of the workpieces, and a first laser beam is directed into or next to the arc, so as to form a hybrid laser-arc column and release heat energy sufficient to heat a zone adjacent the opening to a minimum Zone temperature. Then, a fusible material having a melting range less than or close to the minimum zone temperature is positioned within the zone, so that the material flows into the opening and contacts each of said workpieces as it melts. Finally, the molten material is cooled to a temperature less than the melting range and allowed to re-solidify.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns an improved fusion welding system10for welding a plurality (i.e., two or more) of overlapping adjacent workpieces, such as automotive sheet metal and engine cradle parts, to produce a lap weld12. In the illustrated embodiments shown inFIGS. 3a,band4, a plurality of two workpieces14,16of equal thickness are shown; however, the system10may be utilized to weld a greater plurality or structural components having variable thickness. The workpieces may be formed of a wide range of materials including iron alloys, aluminum alloys, magnesium alloys, titanium and molybdenum. As best shown inFIG. 2, the positioned workpieces14,16present at least one outermost surface18that defines in part an outer edge and is exposed to the system10. Although described herein with respect to workpieces, it is well within the ambit of the present invention for the system10to be used in other ways, wherein repair or welding is desired, such as patching an existing structure.

Turning to the configuration of the system10, a perforating device20is provided for perforating a portion of the workpieces14,16so as to create an opening22therein. A heating combination24follows the device20and is operable to melt fusible material, preferably metal, adjacent or near the opening22, so that the opening is filled by the molten material. The device20and combination24may be manually controlled, or controlled by electro-mechanical means (not shown). More preferably, the system10is robotically controlled along multi-axes and is programmably adjustable.

As shown inFIGS. 2 through 4, the device20is linearly translatable with respect to the workpieces14,16and is operable to cut a continuous slot opening through the portion. The perforated portion consists of at least each succeeded workpiece so that the preferred opening22is adjacent each of the workpieces. The preferred device20is further configured to space the opening22from the outer edges of the workpieces a distance, D, greater than the axial tolerance of either workpiece14,16, and more preferably greater than the maximum tolerance plus 1 cm. Thus, the overlap between the workpieces preferably: presents a minimum width not less than 2D plus the lateral width of the opening.

As further shown inFIGS. 3a,b, the preferred device20includes a first laser26. The laser26engages the outer surface18with a laser beam26ahaving appropriate power to perforate the portion. More preferably, the laser26ais configured to produce a variable power output not to exceed 10 kW. The beam26aperforates the portion by a combination of spawling and compression, which results in extruded material14abeing presented along the perimeter of the opening22. While other perforating devices can be utilized, such as drills and punching mechanisms, it is appreciated by those ordinarily skilled in the art that the laser beam26aprovides precise and consistent conventional means for perforating the workpieces as desired.

After the laser beam26apasses, the heating combination24is directed along the opening22at an energy level sufficient to heat a zone adjacent, and more preferably encompassing, the opening22to a minimum zone temperature. The preferred combination24includes an electrode28, a second laser30, and fusible material32having a melting range less than or close to the minimum zone temperature, such as an aluminum, aluminum alloy, magnesium alloy, copper, or copper alloy filler rod32b(see,FIG. 3b). As shown inFIGS. 3a,b, the electrode28is configured to form an electric arc28abetween the workpieces14,16and electrode28. The heat generated by the arc28aextends to its full depth into the workpieces14,16, so as to heat the full depth simultaneously. A suitable process for use in this configuration is more commonly known as Tungsten Inert Gas (TIG) welding, which utilizes a non-consumable tungsten electrode to form the arc, and feeds gas (i.e., Argon, Argon/Helium, or Argon/Hydrogen combination) to shield the arc and weld pool from outside reactants.

The second laser30is configured to direct a second laser beam30atowards the outer surface18and into the zone of influence of the arc28a. More preferably, the beam30ais directed into or close to the arc28a,as is typical in hybrid laser-arc welding processes, wherein it is appreciated that the hybrid combination produces greater welding efficiency than the sum of its parts. The electric arc heating of the material32increases the thermal absorptiveness of the material32, and therefore the effectiveness of the laser beam30a. The arc28aand beam30acombination also improves the stability and productivity of the arc28a. Finally, the combination also causes a change in the entire energy balance of the arc28aand spatial distribution of the beam30a,which cooperatively provide extra energy.

More preferably, as shown inFIG. 3a, the electrode28and at least a portion of the material32are integrally formed to present a fusible distal portion32aof the electrode, that melts during the welding process. In this configuration, the electrode28is positioned so that the drippings fall into the opening22to fill the slot. A suitable process for use in this configuration is commonly known as Gas Metal Arc welding (GMAW). Most preferably, a covered electrode having a protective outer coating34comprising material (e.g., cellulose, Calcium fluoride, etc.) configured to form a protective shield36over the arc upon disintegration is utilized.

The preferred workpieces14,16are fusible by the heated zone in lieu of or addition to the provision of outside fusible material32a,b,so that the heating combination24is operable to melt a separate portion of the workpieces14,16adjacent the opening22(see,FIG. 3c). As alternatively shown inFIGS. 3a,b,drippings from the fusible portion32aof the electrode28, or the fusible filler rod32b,can be further intermixed with the molten workpiece material to fill the opening22. However, it is certainly within the ambit of this invention to utilize drippings from both a fusible electrode and a filler rod during the process.

As further shown inFIG. 3c,the second beam30apreferably presents a broader diameter than does the perforating beam26a,and more preferably a diameter approximately equal to twice the diameter of the perforating beam26a,so that the beam30adirectly engages the workpiece14, including the extruded material14a. Finally, after the heating combination24passes, the weld pool is cooled by the surrounding unheated material and atmosphere to solidify and form a lap weld12having an aggregate tensile strength.

Alternatively, the combination24may include other conventional welding processes, such as the plasma-arc welding process shown inFIG. 4. In this configuration, the electrode28is coaxially aligned with and spaced from a first end of a conductive sleeve38, and configured to cooperatively form an arc therebetween. The sleeve38is fluidly coupled to a gas source (not shown), so that the source, electrode28, and sleeve38are cooperatively configured to direct a gaseous stream through the arc, and produce a plasma column between the electrode28and outer surface18. Also shown inFIG. 4, a fusible rod can be placed at least near the plasma column to provide filler material as previously described. A second laser beam (also not shown) can be configured to interact with the zone of influence of the plasma column to result in increased efficiency similar to the aforementioned TIG and GMAW combinations.

Suitable first and second lasers26,30to be used in the present invention may include YAG lasers pumped using laser diodes. It is appreciated that these lasers are more energy efficient and require less maintenance than conventional flash-lamp pumped lasers. It is further appreciated that higher power (i.e. 4 to 10 kW) continuous wave (CW) Nd: YAG lasers are capable of welding materials 0.8 mm (car body steel) to 15 mm (ship steel) in thickness. Each of the lasers26,30may also be a CO2or fiber laser, preferably with a 2 to 8 kW power output, and an individual or simultaneous processing capacity.

The laser beams26a,30amay be produced by a single laser and delivered via fiber optic conduit and in conjunction with articulated arm robots, in order to work on components of complex shape. The laser beams26a,30amay also be split from a single initial laser beam created by the single laser, and configured such that the second laser immediately follows the first. Finally, a plurality of devices20and combinations24may be interconnected and simultaneously operable, so as to concurrently weld an equal plurality of sets of workpieces.

Thus, a preferred method of welding a plurality of workpieces to produce a lap weld is presented, and includes the following steps. First, a portion of the workpieces is perforated by a laser beam to produce an opening adjacent to and spaced from the edge of each work-piece. Next, an electric arc is created adjacent an outermost surface of the workpieces, and a second laser beam is directed into or close to the arc, so that a hybrid laser-arc column is formed and heat energy sufficient to heat a zone adjacent the opening to a minimum zone temperature is released. A fusible material having a melting range less than the minimum zone temperature is then positioned within the zone, and more preferably spaced directly above the opening, so that the material flows into the opening and contacts each of said workpieces as it melts.: Finally, the molten material is cooled to a temperature less than the melting range and allowed to re-solidify. The laser beams may be emitted from separate first and second lasers, or may be split from an initial laser beam emitted from a single source.

Obvious modifications to the exemplary embodiments and methods of operation, as set forth herein, could be readily made by those skilled in the art without departing from the spirit of the present invention. As used herein, the term “plurality” shall mean two or more. The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any system not materially departing from but outside the literal scope of the invention as set forth in the following claims.