Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/12—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding
  • B23K20/122—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding using a non-consumable tool, e.g. friction stir welding
  • B23K20/1245—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding using a non-consumable tool, e.g. friction stir welding characterised by the apparatus
  • B23K20/1255—Tools therefor, e.g. characterised by the shape of the probe
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/04—Steel or steel alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/04—Steel or steel alloys
  • B23K2103/05—Stainless steel

Definitions

• This invention relates generally to friction stir welding. More specifically, the present invention relates to spot welding of high melting temperature alloys.
• RSW resistance spot welding
• AHSS Advanced High Strength Steels
• AHSS pose far more process control issues than existing steels made in today's vehicles.
• one process control issue is load. It is necessary to pinch the materials that are to be resistance spot welded.
• Another issue is that of the gap between the parts to be welded. The parts need to be flush, or the strength of the weld may be compromised.
• Another issue is the amount of electricity needed to perform RSW on AHSS .
• FSSW friction stir spot welding
• Figure 1 is a perspective view of a tool being used for friction stir welding that is characterized by a generally cylindrical tool 10 having a shoulder 12 and a pin 14 extending outward from the shoulder.
• the pin 14 is rotated against a workpiece 16 until sufficient heat is generated, at which point the pin of the tool is plunged into the plasticized workpiece material.
• the workpiece 16 is often two sheets or plates of material that are butted together at a joint line 18.
• the pin 14 is plunged into the workpiece 16 at the joint line 18.
• the frictional heat caused by rotational motion of the pin 14 against the workpiece material 16 causes the workpiece material to soften without reaching a melting point.
• the tool 10 is moved transversely along the joint line 18, thereby creating a weld as the plasticized material flows around the pin from a leading edge to a trailing edge.
• the result is a solid phase bond 20 at the joint line 18 that may be generally indistinguishable from the workpiece material 16 itself, in comparison to other welds.
• the area to be welded and the tool are moved relative to each other such that the tool traverses a desired length of the weld joint.
• the rotating FSW tool provides a continual hot working action, plasticizing metal within a narrow zone as it moves transversely along the base metal, while transporting metal from the leading face of the pin to its trailing edge.
• As the weld zone cools there is typically no solidification as no liquid is created as the tool passes. It is often the case, but not always, that the resulting weld is a defect-free, . re- crystallized, fine grain microstructure formed in the area of the weld.
• Travel speeds are typically 10 to 500 mm/min with rotation rates of 200 to 2000 rpm. Temperatures reached are usually close to, but below, solidus temperatures. Friction stir welding parameters are a function of a material's thermal properties, high temperature flow stress and penetration depth.
• superalloys are nickel, iron-nickel, and cobalt-based alloys generally used at temperatures above 1000 degrees F. Additional elements commonly found in superalloys include, but are not limited to, chromium, molybdenum, tungsten, aluminum, titanium, niobium, tantalum, and rhenium.
• Titanium is also a desirable material to friction stir weld. Titanium is a non- ferrous material, but has a higher melting point than other nonferrous materials .
• a tool is needed that is formed using a material that has a higher melting temperature than the material being friction stir welded.
• a superabrasive was used in the tool .
• the embodiments of the present invention are generally concerned with these functionally unweldable materials, as well as the superalloys, and are hereinafter referred to as "high melting temperature” materials throughout this document .
• friction stir processing is also aspects of the invention that must be considered. It is noted that friction stir processing and welding may be exclusive events of each other, or they may take place simultaneously. It is also noted that the phrase "friction stir processing" may also be referred to interchangeably with solid state processing. Solid state processing is defined herein as a temporary transformation into a plasticized state that typically does not include a liquid phase. However, it is noted that some embodiments allow one or more elements to pass through a liquid phase, and still obtain the benefits of the present invention.
• a tool pin In friction stir processing, a tool pin is rotated and plunged into the material to be processed. The tool is moved transversely across a processing area of the material. It is the act of causing the material to undergo plasticization in a solid state process that can result in the material being modified to have properties that are different from the original material .
• Friction stir mixing can also be an event that is exclusive of welding, or it can take place simultaneously. In friction stir mixing, at least one other material is being added to the material being processed or welded.
• FSW friction stir welding
• This tool When this tool is used with the proper friction stir welding machine and proper steady state cooling, it is effective at friction stir welding of various materials.
• This tool design is also effective for using a variety of tool tip materials besides PCBN. Some of these materials include refractories such as tungsten, rhenium, iridium, titanium, etc. Since these tip materials are often expensive to produce this design is an economical way of producing and providing tools to the market place.
• the design shown in figure 2 is in part driven by the limited sizes that can be produced by sintering, hipping, and other high pressure equipment capabilities.
• the present invention is a tool for friction stir spot welding of high melting temperature materials, wherein the tool geometry includes a short pin and broad shoulder to enhance mixing of high temperature materials, and wherein the tool includes a superabrasive coating to thereby enable FSSW of high melting temperature materials .
• FIG. 1 is a prior art perspective view of an existing friction stir welding tool capable of performing FSW on high melting temperature materials
• Figure 2 is another prior art perspective view of an existing friction stir welding tool capable of performing FSW on high melting temperature materials .
• Figure 3A is an illustration of one embodiment of a tool that can perform the desired friction stir spot welding of the present invention.
• Figure 3A is a profile view of a tool holder and a PCBN tip disposed therein.
• Figure 3B is a first profile view of the PCBN tip.
• Figure 3C is a second profile view of the PCBN tip.
• Figure 4A is an illustration of another embodiment of a tool that can perform the desired friction stir spot welding of the present invention.
• Figure 4A is a profile view of a tool holder and a PCBN pin disposed therein.
• Figure 4B is a first profile view of the PCBN pin with view F circled.
• Figure 4C is a close-up profile view of the threaded PCBN pin of view F.
• Figure 4D is an end-view of the PCBN pin and toolholder.
• Figure 5 is an illustration of two FSSW spot welds wherein parameters have been modified to obtain different spot welds.
• Figure 6 is an illustration of three friction stir spot welds.
• FSSW is generally going to be performed on relatively thinner workpieces.
• the pin may generally be shorter than on a tool used for FSW. This shorter pin can be used even if the tool is going to penetrate both materials that are being FSSW together.
• pin length to shoulder width ratio is important to FSSW because of friction stir mixing and welding. It is desirable to have a broad area of the workpieces being mixed together. FSSW of a broader area is more easily accomplished having a shoulder that is relatively broad.
• a FSSW joint is achieved using a generally solid state process with minimal or no melting of the materials being joined. Therefore, it is important that the tool geometry enables the material of the workpieces to be processed in such a way that the materials mechanically bond.
• Figure 3A is provided as a profile view of a FSSW toolholder 40 and a FSSW tip comprised of a shoulder 42 and a pin 44.
• Figure 3B is a profile view of the PCBN tip wherein the shoulder 42 and pin 44 are coupled to a short shank 46.
• Figure 3C is a close-up profile view of the PCBN tip where detail of the shoulder 42 and the pin is more plainly visible.
• Figure 4A is provided as a profile view of a FSSW toolholder 50 and a FSSW tip comprised of a pin 54 without any shoulder.
• Figure 4B is a profile view of the PCBN tip wherein the pin 54 is coupled to a short shank 56.
• Figure 4C is a close-up profile view of the PCBN tip showing the stepped spiral threads 58 of the pin 54.
• the stepped spiral threads 58 are created using two threaded starts in this particular embodiment.
• FIG. 4D is an end-view showing the pin 54 and the toolholder 50.
• the area be maximized that is being processed to create the FSSW joint.
• One way to accomplish this objective is to use a large shoulder on the FSSW tool.
• a tool having a shank with a cylindrical working end that might or might not have a pin would maximize the shoulder of the FSSW tool .
• One method for overcoming these difficulties is to increase the size of the joining area. This is accomplished by translating the FSSW tool away from the plunge axis during the FSSW process.
• the FSSW process may also include a dwell period in which the FSSW tool is not moved, or it may have no dwell period and the FSSW tool is kept moving. It is another aspect of the invention that tool geometries that manage the flow of the material being bonded are preferred, and should include design criteria for the flow of the particular material type being FSSW.
• Figure 5 is an illustration of an FSSW tool wherein FSSW parameters have been modified to obtain different spot welds.
• the first spot weld 60 was made using a cycle time of 2.1 second.
• the second spot weld 62 was made using a cycle time of 1.6 second.
• Figure 6 is provided as photomicrographs of spot welds using a FSSW tool that has been performed on DP600, and which shows three different cross sections that were created as a result of changing parameters of the FSSW process.
• Weld 1 (70) had a FSSW cycle time of 2.5 seconds, had a 50mm/min plunge, and a
• Weld 2 (72) had a FSSW cycle time of 1 second, had a 213mm/min plunge, and a 213mm/min extract.
• Weld 3 (74) had a FSSW cycle time of 1.5 seconds, had a 213mm/min plunge, included a dwell time of 0.5 seconds, and had a 213mm/min extract.
• Weld 2 (72) shows that the two materials being joined were not flush, and thus have a gap between them after the spot weld is performed.
• Other aspects of the invention include the use of disposing asymmetric features on the pin and shoulder, using a retractable pin, having a pin with varying degrees of taper radii, parabolic, non-linear geometries, having threads on the pin, having threads on the shoulder, having flats and/or threads on the pin, and moving the FSSW tool so that the FSSW tool is moved in any direction away from the plunge axis to increase the area under the tool .

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• 2006
  • 2006-02-15 CA CA002597727A patent/CA2597727A1/en not_active Abandoned
  • 2006-02-15 EP EP06849719A patent/EP1848567A4/en not_active Withdrawn
  • 2006-02-15 WO PCT/US2006/005507 patent/WO2007086885A2/en active Application Filing
  • 2006-02-15 JP JP2007556294A patent/JP2008529805A/ja active Pending

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