Method for holding high speed friction spot joining tools

Abstract

The invention utilizes vibration control, precision manufacturing tolerances for certain components of the system, and techniques for limiting thermal expansion of components, including passive insulation and active cooling techniques, in order to enable high speed tool rotation for Friction Stir Spot Joining of Advanced High Strength Steels.

1 . A high speed friction stir spot joining (FSSJ) system for joining metal work pieces, said FSSJ system comprised of:
 a FSSJ tip comprised of a shank, a shoulder and a pin, an extended shank for holding the FSSJ tip against work pieces, and a shank holder for holding the extended shank; and   a means for turning the FSSJ system at a rotational rate that is at least 4000 revolutions per minute.   
     
     
         2 . The high speed FSSJ system as defined in  claim 1  wherein the FSSJ system is further comprised of:
 a FSSJ tip cavity in a working end of the extended shank; and 
 a thermal insulating material disposed in the FSSJ tip cavity for regulating thermal conditions of the FSSJ tip. 
 
     
     
         3 . The high speed FSSJ system as defined in  claim 1  wherein the extended shank is further comprised of at least one internal cooling channel for regulating the temperature of the FSSJ tip by passing a cooling liquid or gas through the at least one cooling channel to thereby regulate temperature and prevent axial expansion of the extended shank and to thereby increase accuracy of the FSSJ system. 
     
     
         4 . The high speed FSSJ system as defined in  claim 1  wherein the extended shank is further comprised of a length that is greater than other FSSJ systems to thereby enable the FSSJ system to be used on work pieces that cannot be disposed immediately adjacent to the FSSJ system. 
     
     
         5 . The high speed FSSJ system as defined in  claim 1  wherein the FSSJ system is further comprised of:
 a shank holder cavity in a working end of the shank holder; and 
 at least one set screw through a wall of the shank holder for holding the extended shank in the shank holder cavity. 
 
     
     
         6 . The high speed FSSJ system as defined in  claim 1  wherein the extended shank is further comprised of a plurality of external grooves around the surface of the extended shank to thereby regulate temperature and prevent axial expansion of the extended shank and to thereby increase accuracy of the FSSJ system. 
     
     
         7 . The high speed FSSJ system as defined in  claim 1  wherein the extended shank is further comprised of a plurality of external fins around the surface of the extended shank to thereby regulate temperature and prevent axial expansion of the extended shank and to thereby increase accuracy of the FSSJ system. 
     
     
         8 . The high speed FSSJ system as defined in  claim 1  wherein the FSSJ system is further comprised of a collet holding system disposed around a portion of the extended shank and coupled to the shank holder to thereby prevent rotation of the extended shank relative to the shank holder. 
     
     
         9 . The high speed FSSJ system as defined in  claim 8  wherein the collet holding system is further comprised of ball bearings in the shank holder to thereby enable accuracy of extended shank positioning when the extended shank is coupled to the shank holder. 
     
     
         10 . The high speed FSSJ system as defined in  claim 1  wherein the FSSJ system is further comprised of a vibration measurement device that can determine when an undesirable vibration is being generated on the FSSJ tip so that rotation of the FSSJ tip can be stopped. 
     
     
         11 . The high speed FSSJ system as defined in  claim 1  wherein the FSSJ system is further comprised of an automatic tool changing system to thereby enable the FSSJ system to be used in machining applications other than spot joining. 
     
     
         12 . A method for performing high speed friction stir spot joining (FSSJ) of metal work pieces, said method comprising the steps of:
 1) providing a FSSJ tip comprised of a shank, a shoulder and a pin, providing an extended shank for holding the FSSJ tip against work pieces, and providing a shank holder for holding the extended shank;   2) rotating the FSSJ tip at a rate of speed that is greater than 4000 revolutions per minute (RPM); and   3) plunging the FSSJ tip into and then removing the FSSJ tip from at least two metal workpieces to thereby perform high speed FSSJ of the at least two metal work pieces in a FSSJ process.   
     
     
         13 . The method as defined in  claim 12  wherein the method further comprises the step of rotating the FSSJ tip at a speed greater than 4000 revolutions per minute to thereby preserve the benefits of using Advanced High Strength Steels (AHSS) that have been hardened as the work pieces. 
     
     
         14 . The method as defined in  claim 13  wherein the method further comprises the step of reducing the weight of vehicles by using AHSS in their construction and joining the AHSS members by using FSSJ. 
     
     
         15 . The method as defined in  claim 12  wherein the method further comprises the step of increasing heat input to the FSSJ process by providing a thermal insulating material to increase the temperature of the FSSJ tip. 
     
     
         16 . The method as defined in  claim 12  wherein the method further comprises the step of cooling the extended shaft to thereby regulate temperature and prevent axial expansion of the extended shank and to thereby increase accuracy of the FSSJ system. 
     
     
         17 . The method as defined in  claim 16  wherein the step of cooling the extended shaft is selected from the group of cooling methods comprised of using an internal cooling channel in the extended shaft and a plurality of grooves or fins disposed on the external surface of the extended shaft. 
     
     
         18 . The method as defined in  claim 12  wherein the method further comprises the step of providing the extended shaft in order to increase a reach of the FSSJ tip so that the FSSJ process can reach objects that cannot be brought immediately adjacent to the FSSJ tip. 
     
     
         19 . The method as defined in  claim 12  wherein the method further comprises the step of providing a collet holding system disposed around a portion of the extended shank and coupled to the shank holder to thereby prevent rotation of: the extended shank relative to the shank holder. 
     
     
         20 . The method as defined in  claim 19  wherein the method further comprises the step of providing ball bearings in the shank holder to thereby enable improved accuracy of extended shank positioning when the extended shank is coupled to the shank holder. 
     
     
         21 . The method as defined in  claim 12  wherein the method further comprises the step of providing a vibration measurement device that can determine when an undesirable vibration is being generated on the FSSJ tip so that rotation of the FSSJ tip can be stopped. 
     
     
         22 . The method as defined in  claim 12  wherein the method further comprises the step of providing an automatic tool changing system to thereby enable the FSSJ system to be used in machining applications other than spot joining. 
     
     
         23 . The method as defined in  claim 12  wherein the method further comprises the step of modifying a CNC machining center to perform the FSSJ process such that the machine is capable of performing both CNC and FSSJ functions.