Abstract:
A friction stir weld system for welding and weld repair has a base foundation unit connected to a hydraulically controlled elevation platform and a hydraulically adjustable pin tool. The base foundation unit may be fixably connected to a horizontal surface or may be connected to a mobile support in order to provide mobility to the friction stir welding system. The elevation platform may be utilized to raise and lower the adjustable pin tool about a particular axis. Additional components which may be necessary for the friction stir welding process include back plate tooling, fixturing and/or a roller mechanism.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/111,418 filed Dec. 8, 1998. 
    
    
     ORIGIN OF THE INVENTION 
     This invention was made by an employee and a contractor of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or thereof. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a friction stir welding apparatus comprising multiple sub-components which collectively perform as one integrated welding system allowing the apparatus to be operated and maintained in a variety of environments while permitting reduced size of the unit. The integrated nature of the sub-components gives the operator more flexibility in the type and size of workpiece that can be welded and effectively expands the utility of the friction stir welding process. 
     2. Description of Related Art 
     Friction stir welding is a method of welding based upon the principle of “rubbing” of articles to be joined together so as to generate a sufficient amount of heat. A probe of a harder material than the treated work pieces is typically applied in a welding process. The probe is subjected to cyclic movement relative to the work pieces. Merging the probe and work pieces together has been found to create a plasticized region in the work pieces due to generated frictional heat. When the relative cyclic movement of the probe stops, the plasticized material solidifies to create a weld joint. 
     The Friction Stir Weld (FSW) process, as it exists today, is believed to be limited to few manufacturing floors. Almost all known systems are restricted to laboratory/development environments. Development and laboratory equipment consists of large off-the-shelf machinery such as machining molds, modified to accommodate the FSW process. The large size of the laboratory equipment places size constraints upon manufacturing and tooling requirements, as a result, it is impractical and cost prohibitive to use machining mills for most manufacturing FSW applications. Additionally, the working envelope of the machining mills prohibits large pieces of hardware to be welded. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the prior art devices in that large individual components may be replaced with sub-components attached or housed within a common base foundation unit to allow an operator to move the apparatus to the manufacturing floor where a greater range of devices can be operated on. 
     Accordingly, it is an object of this invention to provide a new and improved friction stir welding apparatus which permits the FSW procedure to be performed on the manufacturing floor, and in other environments that have traditionally been unavailable for use of FSW because of the size and lack of mobility of prior art FSW systems. This system may operate under loads exceeding 20,000 pounds. In addition to welding, the system can also operate as a precision controlled machining center by replacing the pin tool with an end mill/cutting tool. 
     An integrated welding system is taught herein which features multiple sub-components that are combined to create a self contained and mobile FSW apparatus. A base foundation unit (BFU) serves to either attach or house, or connect, other components. The BFU may be connected directly to a floor for a static welding environment or may be adopted to be mobile for dynamic weld environments. The BFU may accommodate significant axial and radial loads, estimated to be up to 20,000 lbs. or less axial and 2,000 lb. radial. An elevation platform (EP) may be movable in three dimensions and is connected to the BFU. An adjustable pin tool (APT) may be attached to the EP allowing the APT to be positioned in three dimensions . The APT may have movement independent of the EP such as rotational capabilities so it can be introduced into the weld joint at a pre-selected angle. A backplate tooling component may be attached to the exterior of the BFU to act as a backing bar during FSW weld operation. A fixturing component may be attached to the exterior of the BFU for holding and securing the workpiece during welding. A roller mechanism may be also attached to the exterior of the BFU and integrated with the APT to remove any bowing in the material before the joint is welded. Additionally, a real-time adaptive computer numerical control (CNC) and process control system (APCS) may be housed within the BFU. The APCS may be a digital computer system that incorporates common robotic position/motion control electronics and software. The APCS may also have electronics and software for monitoring the parameters of the FSW process. The APCS may analyze these parameters, and dynamically adapt the weld parameters to maintain weld performance. 
     In a preferred embodiment the integrated movement of the EP and the APT may be performed by hydraulics. The hydraulic system would preferably include a pump and fluid reservoir housed within the BFU. Hydraulic connections may be integrated with the EP and APT such that the operator can guide the pin tool to a desired position on the workpiece. Once the weld position is fixed, the APCS monitors the parameters of the FSW process, analyzes those parameters, and dynamically adapts the pin tool position to maintain weld performance. 
     Thus the friction stir weld (FSW) process as disclosed can be expanded to include a great variety of materials by integrating the individual components of large milling machines into a single integrated welding system. The process offers significant opportunities relative to costs, manufacturing, quality assurance, and health and safety standpoints for the welding of aluminum and other materials. Advantages of the process have been found to include: (1) a simple machine tool may be extremely energy efficient: a single pass 12.5 millimeter deep weld can be made in 6xxx series alloy using a gross power of less than 3 kW; (2) equipment maintenance has been found to be minimal; (3) the welding operation does not require consumable materials such as filler wire or shielding gas; (4) special pre-weld joint edge profiling may be eliminated; (5) the careful removal of oxide from the joint area immediately prior to the welding may not be required; (6) the equipment is suited for automation and integration with other machine tool operations; (7) good mechanical and metallurgical quality welds may be confidently made in aluminum alloys such as 2xxx, 5xxx and 7xx series which previously had problems such as solidification cracking and/or liquation cracking; (8) high joint strengths may be created in heat treatable alloys; (9) welds may be consistently made which are free of voids and porosity; (10) metallurgical properties in the weld material may be retained such that mechanical and fatigue properties are similar to those of the parent metal; (11) butt and lap seam welds may be created between wrought, cast and extruded materials; (12) weld repeatability is very good when weld energy input and mechanical mechanisms direct and control the working and forging of the weld metal; (13) the welding machine may be simplified to three controls: tool heel plunge depths, tool rotation speed, and welding speed; (14) health hazards such as welding fumes or radiation are severely reduced if not eliminated resulting in a clean process; and (15) alloys other than aluminum may be utilized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects, objects and advantages of this invention will become apparent to those skilled in the art from the following description taken in conjunction with the following drawing, in which: 
     The FIGURE is a side elevational view of the friction weld stir weld system with interior portions shown in phantom. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the FIGURE, a friction stir weld (FSW) system  10  according to the preferred embodiment of the invention is shown. The FSW system  10  comprises a base foundation unit (BFU)  12 , an elevation platform (EP)  14 , an adjustable pin tool (APT)  16  and a process control system  18 . Additionally, the FSW system  10  may utilize backplate tooling illustrated as anvil  20 , fixturing, illustrated as clamps  22 , and a roller mechanism  24 . The FSW system  10  may be utilized for welding and weld repairs such as initial welding and weld repairs to friction weld and fusion welds (TIG, MIG, VPPA, etc.). The FSW system may also be used as a machining center by replacing the APT with an end mill. 
     The base foundation unit  10  may be bolted directly into a floor to create a stationery welding environment. Alternatively, the BFU  10  may be connected to at least one mobile support  28 . Mobile support  28  may comprise ways equipped with floor anchors  48  or any other suitable structure known in the art. Utilizing at least one mobile support  28 , the FSW system  10  may be utilized to create dynamic weld environments. Accordingly, the BFU  10  may be mobile. The BFU  10  may at least partially house some of the hydraulics such as the pump and fluid reservoir  30 . Additionally, the BFU  10  may house the process control system  18  which preferably comprises a real-time adaptive computer numerical control (CNC)  32  and process control system (APCS)  34 . Hydraulic connections  36  may be utilized to connect the pump and fluid reservoir  30  to the elevation platform  14  and the adjustable pin  16 . 
     The elevation platform  14  is preferably moveable at least along the N axis  38  which may be utilized at least partially in locating the adjustable pin tool  16  to a predetermined location. A portion of the elevation platform  14  may be housed within the base foundation unit  12 . The movement of the EP  14  may allow the pin tool  16  to be centered into a weld joint  40  for welding. In addition to movement along the N axis  38 , the elevation platform  14  may also exhibit three dimensional movement while capable of functioning under operating pressures. The movement of the elevation platform  14  may be necessary to attain proper pin tool  16  location with respect to the center of a weld joint  40 . Three axis movement may be achieved through a variety of different mechanisms known in the art. 
     The elevation platform  14  may also pivot relative to at least a portion of the BFU  12 . Pivot adjustments  56  and  58  may be utilized to assist in the positioning of the pin tool  16 . Additionally, the position adjustment  60  may be utilized to control movement of the elevation platform  14  along the N axis  38 . Furthermore, the process control system  18  may be utilized in conjunction with or completely replace any or all of the pivot adjustments  56 ,  58  and position adjustment  60 , such as for some automated welding operations. Elevation platform  14  preferably exhibits three axes of movement capable of functioning under operating pressures. This movement has been found effective in attaining the proper pin tool  16  location respective to the center of the weld joint  40 . 
     The adjustable pin tool (APT)  16  is preferably directly integrated into the EP  14 . The APT  16  includes a probe which performs the friction stir welding process. The APT  16  preferably has rotational capabilities illustrated as pivoting housing  42  to allow the APT  16  to be introduced into the weld joint  40  at a preselected angle. The backing tool shown as anvil  20  may act as a backing bar during FSW weld operation. Additionally, fixturing such as clamps  22  may be utilized to hold a first and a second member  44 ,  46  to be utilized to hold and secure one or more work pieces during the welding process. Additionally, a roller mechanism  24  may be utilized in conjunction with the adjustable pin tool  16  to remove any bowing in the material before the joint  40  is welded. The roller mechanism  24  may preferably have two rollers  26  which may be positioned on either side of the weld joint  40 . 
     The process control system  18  utilized within the FSW system  10  is preferably a digital computer system that incorporates common robotics positioning/motion control electronics and software. The APCS  34  may also have electronics and software for monitoring the parameters of the FSW process. Furthermore, the APCS  34  may also have electronics and software for analyzing the parameters of the FSW process and dynamically adapting the APCS  34  to maintain weld performance. 
     The FSW system  10  illustrated in the drawing shows the pin tool  16  acting along the N axis  38 . In this embodiment, the N axis  38  is illustrated as being approximately 45 degrees to a horizontal surface. The N axis  38  is shown substantially perpendicular to a first surface  50  of the BFU  10 . Alternatively, the N axis  38  could be located at other angles relative to the horizontal. Other embodiments could include the N axis  38  being substantially perpendicular to the second surface  52  or the third surface  54  of the BFU  12 . 
     In a preferred embodiment, the BFU  12  accommodates the internal mechanical entities of various subsystems as described above. Additionally, the BFU  12  is preferably designed to operate under the radial and axial loads associated with the FSW process. The radial and axial loads are estimated to be 10,000 pounds or less axial and 2,000 pounds radial. 
     The positioning and control of the pin tool  16  is believed to be a unique feature of the FSW system  10 . This FSW system  10  may be utilized for welding and weld repair on the manufacturing floor and/or a laboratory environment for a wide variety of welding and weld repair applications. 
     Numerous alternations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.