Ultrasonic welding of dissimilar sheet materials

Abstract

A ultrasonic welding method of joining dissimilar-material workpieces, such as sheet materials, and the joined components formed thereby. The method includes applying ultrasonic energy to a thermoplastic piece to fill a hole of a dissimilar piece to form a weld point that is made up with polymer from the thermoplastic piece. In general, the geometry of the thermoplastic piece is not altered during the process. The dissimilar piece generally has a higher melting temperate and can be metal, thermoset polymers, or other thermoplastic material. The welded pieces can be arranged in a lap, laminate, or double lap configuration. In some embodiments, the hole of the dissimilar sheet material includes undercut features that improve the mechanical interlock between the dissimilar pieces. In some embodiments, the weld point has a mushroom cap to improve mechanical interlock.

We claim: 
     
         1 . A welded component, formed by ultrasonic welding together dissimilar-material pieces, comprising:
 a thermoplastic piece; and   a higher melting temperate (HMT) piece having at least one hole and being joined to the thermoplastic piece by a weld point comprising material from the thermoplastic piece filing the hole;   wherein the hole has at least one undercut feature filled with the material from the thermoplastic piece to create part of the weld point.   
     
     
         2 . The welded component of  claim 1 , wherein the at least one hole is a through hole or a blind hole, and the at least one undercut feature includes a step, an internal thread, or a combination thereof. 
     
     
         3 . The welded component of  claim 1 , wherein the thermoplastic piece and the HMT piece are joined to form a lap joint or a laminate joint. 
     
     
         4 . The welded component of  claim 1 , wherein said hole is one of a plurality of holes of the HMT, each being filled with the material from the thermoplastic piece to form a plurality of weld points. 
     
     
         5 . The welded component of  claim 4 , wherein:
 the weld point includes a convex lower head of material of the thermoplastic piece connecting the material of the thermoplastic piece filling each of the plurality of holes; and   the convex lower head overlaps a portion of a lower surface of the HMT piece.   
     
     
         6 . The welded component of  claim 1 , wherein:
 the thermoplastic piece is a first thermoplastic piece;   the welded component further comprises a second thermoplastic piece;   the first and second thermoplastic pieces sandwich the HMT piece, forming a double lap joint;   said hole is one of a first set of holes of the HMT piece, the first set of hole being filed with the material of the first thermoplastic piece to form a first set of weld points; and   the HMT piece comprises a second set of holes being filled with material of the second thermoplastic piece and/or the material of the first thermoplastic piece, to form a second set of weld points.   
     
     
         7 . The welded component of  claim 1 , wherein:
 the thermoplastic piece is a first thermoplastic piece;   the welded component further comprises a second thermoplastic piece sandwiching the HMT piece with the first thermoplastic piece to form a double lap joint; and   the at least one hole of the HMT piece is filled with thermoplastic from the first and the second thermoplastic pieces.   
     
     
         8 . The welded component of  claim 1 , wherein:
 the HMT piece is a first HMT piece;   the welded component further comprises a second HMT piece abutting the first HMT piece;   the two HMT pieces are joined together by the thermoplastic piece to form a butt joint;   the at least one hole of the first HMT piece is a first set of holes;   the second HMT piece comprises a second set of holes; and   all holes are filled with thermoplastic from the thermoplastic piece.   
     
     
         9 . The welded component of  claim 1 , wherein:
 the HMT piece is a first HMT piece;   the welded component further comprises a second HMT piece stacked with the first HMT piece;   the two HMT pieces are joined together with the thermoplastic piece;   the at least one hole of the first HMT is a first set of holes;   the second HMT piece comprises a second set of holes aligned with the first set of holes of the first HMT piece in the stack; and   all holes are filled with thermoplastic from the thermoplastic piece.   
     
     
         10 . A method, of forming a welded component of dissimilar-material pieces by ultrasonic welding, comprising,
 placing a thermoplastic piece atop a higher melting temperate (HMT) piece, wherein the HMT piece comprises at least one hole, to cover the hole in the HMT piece; and   applying ultrasonic energy to the thermoplastic piece above the hole of the HMT piece using an ultrasonic horn to melt material of the thermoplastic piece so that material melted fills the hole of the HMT piece to create a weld point joining the thermoplastic piece and the HMT piece to form the welded component.   
     
     
         11 . The method of  claim 10 , wherein the at least one hole has at least one undercut feature and some of the material melted fills the undercut feature. 
     
     
         12 . The method of  claim 11 , wherein the at least one undercut feature comprises a step, internal threads, or a combination thereof. 
     
     
         13 . The method of  claim 10 , wherein:
 said hole is one of a plurality of holes of the HMT piece; and   the placing and the applying are performed to fill each hole with the material of the thermoplastic piece melted.   
     
     
         14 . The method of  claim 10 , further comprising, prior to applying ultrasonic energy, placing the HMT piece on an anvil having a generally flat top surface, wherein a bottom of the weld point being formed is kept flat by the generally flat top surface of the anvil as the melted thermoplastic material fills the hole. 
     
     
         15 . The method of  claim 10 , further comprising:
 placing the HMT piece on an anvil prior to applying ultrasonic energy;   wherein:
 the anvil has a top surface and a concavity in the top surface; 
 the concavity is wider than the hole of the HMT piece, forming an under-piece feature when the HMT piece is placed on the anvil; and 
 when the material of the thermoplastic piece is melted by the ultrasonic energy, the melted material fills the hole and the concavity of the anvil, including beneath the under-piece feature, forming a convex bottom portion of the weld point overlapping a bottom surface of the HMT piece. 
   
     
     
         16 . The method of  claim 10 , wherein:
 the thermoplastic piece is a first thermoplastic piece;   the at least one hole of the HMT piece is a first set of holes, each having an opening at a top surface of the HMT piece;   the first thermoplastic piece is placed adjacent the top surface of the HMT piece;   the HMT piece further comprises a second set of holes, each having an opening at a bottom surface of the HMT piece; and   the method further comprises:
 placing a second thermoplastic piece adjacent the bottom surface of the HMT piece, covering the second set of holes in the HMT piece, sandwiching the HMT piece with the first thermoplastic piece; and 
 applying ultrasonic energy to the second thermoplastic piece above the second set of holes of the HMT piece, so that material of the second thermoplastic piece melts and flows into the second set of holes. 
   
     
     
         17 . The method of  claim 10 , wherein the method is performed to form a double lap joint to join the thermoplastic and HMT pieces of the welded component, wherein:
 the ultrasonic horn is a first ultrasonic horn; and   applying the ultrasonic energy to the second thermoplastic piece is performed using a second ultrasonic horn having a larger diameter than the first ultrasonic horn.   
     
     
         18 . The method of  claim 10 , wherein:
 the HMT piece is a first HMT piece;   the at least one hole of the first HMT piece is a first set of holes; and   the method further comprising butting the first HMT piece with a second HMT piece having a second set of holes before placing the thermoplastic piece on top of the holes of the first and second HMT pieces and applying the ultrasonic energy to fill all of the holes of the first and second sets with the material from the thermoplastic piece to form the butt joint joining the first and second HMT pieces to the thermoplastic piece.   
     
     
         19 . The method of  claim 10 , wherein:
 the HMT piece is a first HMT piece; and   the at least one hole of the first HMT piece is the first set of holes and the method further comprises stacking a second HMT piece comprising a second set of holes with the first HMT piece and aligning the first set of holes with the second set of holes before applying ultrasonic energy to the thermoplastic piece above the holes of the first and second HMT pieces to fill all of the holes with material melted from the thermoplastic piece to join the first and second HMT pieces to the thermoplastic piece.   
     
     
         20 . A method, for joining dissimilar-material workpieces, comprising:
 positioning a higher melting temperature (HMT) piece adjacent an anvil-cutting apparatus;   moving a cutter of the apparatus into a hole of the HMT piece;   extending a cutting insert of the cutter and rotating the cutting insert to form a void in a side wall of the hole;   retracting the cutting insert;   retracting the cutter from the hole;   positioning a thermoplastic piece atop the HMT piece; and   applying ultrasonic energy to the thermoplastic piece causing material of the thermoplastic piece to melt and move into the hole until the material melted contacts a top of the cutter of the anvil-cutter arrangement, thereby filling the hole and the void formed.   
     
     
         21 . The method of  claim 20 , wherein:
 the anvil-cutter arrangement has a slot in which the cutter is slidably positioned;   the slot is wider than the hole of the HMT piece;   retracting the cutter includes retracting the cutter into a body of the cutter-anvil arrangement so that a top surface of the cutter is lower than an adjacent top surface of the body, so that a lower surface of the HMT piece exposed can act as an under-piece feature for receiving material melted from the thermoplastic piece; and   by application of the ultrasonic energy, the melted material fills a space between sides of the slot, atop the top surface of the cutter, and beneath the under-piece feature formed by the exposed surface of the HMT piece.