METHOD OF JOINING PARTS WITH SEMI-TUBULAR RIVETS

Abstract: A rivet for joining fiber reinforced plastic laminates has an alloy of titanium columbium. The rivet is semi-tubu­ lar in shape. The tubular open end portion (16) is shaped with an outwardly tapered inner wall to provide for expan­ sion of the tubular open end portion (16) without expand­ ing the balance of the shank (14).

Description: SEMI-TUBULAR RIVETS Assembly of fiber reinforced plastic laminates is accomplished by adhesive bonding or by joining with fasteners. in installations- where fasteners are required and weight savings are a consideration it would be desirable to join the laminates with rivets instead of threaded fasteners; however, rivets create a problem as expansion of the rivet during the forming operation causes the laminate to be weakened as is evidenced by crazing in the area of the matrix around the formed rivet. In U.S. patent 4,022,310 a rivet tubular throughout the length of the shank is shown in combination with an adhesive for joining clutch friction discs. In U.S. patent 1,591,478 a rivet tubular throughout part of the length of the shank is used to join and compress a dust guard of fiberboard or leatherboard covering a compressible absorbent body portion. It was found that a special shaped semi-tubular rivet can be used to fasten together fiber reinforced plastic laminates without creating a weakness in the laminates. A rivet of titanium columbium alloy is tubular for a distance in from the end away from the head, and the inside walls of the tubular section is tapered outwardly at an angle of about 15 degrees. One of the purposes of this invention is the joining of plastic laminates so that the main shank of the rivet does not expand against the bore of the laminate. FIGURE 1 shows an exploded side elevational partially sectional view of the rivet of this invention in combination with a fragmented sectional part to be joined. FIGURE 2 shows the rivet and part of FIGURE 1 with the rivet inserted and ready to be formed. FIGURE 3 shows the rivet being formed with forming dies. FIGURE 4 shows the rivet joined part. In rivet 10 the head 12 of the rivet is of the flush type and is at an angle of 1000 to fit into a 1000 countersink. The shank 14 is of a constant diameter and is open ended opposite the head to form a tubular end 16. The inside walls 18 of the tubular section are tapered outward at an angle of about 150 and terminate on a radius at 20. The rivets are used to join fiber reinforced laminates or fiber reinforced laminates to metals. It is imperative the rivet firmly hold the laminates without having the main part of the shank of the rivet expand during the forming process as the expanding shank sets up cracks in the laminate which causes structural failure. These rivets are made of an alloy of titanium and columbium to be compatible with laminates using graphite fibers as the reinforcement, but are not restricted to such use as the rivets are also used to join laminates of other materials. The alloy is preferably about 55% titanium and about 45% columbium. Straight walled tubular rivets and tubular rivets with inside walls tapered at 30 were completely unsatisfactory. Aluminum rivets may not be used to join laminates containing graphite as aluminum reacts chemicallywith the graphite. In the figures an airplane elevator 22 is shown which is made up of a pair of laminates 24 and 26 joined with titanium columbium rivets 14. The laminates are of graphite fibers in an epoxy resin, are drilled through with bore 28 and are countersunk to 1000 at each side at 30 and 32. When joining the laminates the rivet is selected of a diameter to provide a net to a clearance fit into the bore, the rivet inserted and forming dies 34 and 36 located in a riveting machine not shown, are advanced to form a button 38 on tubular end 16 with the button pressing against the countersink 30. In forming the button the forming die uses contacting surface 40 that is at an angle of about 1300 instead of a conventional angle for a die, which would be at about the same angle as the countersink. Preferably the depth of the tubular section of the shank is greater than the depth of the countersink against which the button is formed. These figures show a flush head rivet; however, it is not intended to limit the rivet to a flush head as other types of manufactured heads may be used as long as the opposite end of the rivet is tubular as shown.

Claims: CLAIMS 1. A rivet comprising: a titanium columbium alloy; a head; a shank sized to give a net to a clearance fit in a plastic part to be joined and having a concentric opening extending part way inward to form a tubular end to the shank; characterized in that the inside wall of the tubular end tapers outward at an angle of about 15 degrees to permit a button to be formed on the tubular end without expanding the shank of the rivet. 2. A rivet as- in claim 1 characterized in that the rivet comprises about 55% titanium and about 45% columbium. 3. A rivet, that when formed joins laminates containing reinforced plastic with a double flush head and without the rivet expanding against the bore of the reinforced plastic, the rivet comprises: an alloy of about 55% titanium and about 45% columbium; a manufactured flush head; a constant diameter shank having an open end with tubular walls along part of its length;characterized in that the inside wall tapers outward at an angle of about 15 degrees to permit the end of the shank to be deforme outward to fill a countersink area without exerting outward pressure throughout the balance of the shank. 4. A method of joining parts at least one of which is a fiber reinforced plastic laminate characterized by the steps of: drilling a hole through parts to be joined; countersinking the parts on at least one side; selecting a semi-tubular rivet of titanium columbium alloy having a head and having an inside wall on the tubular open end portion that tapers outwardly at about 15 degrees; inserting the rivet with a net to a clearance fit in the hole in the parts; insuring that the open end of the tubular rivet is on the countersink side; placing a die on the open end with said die tapered at an angle greater than the angle of the countersink; and, squeezing the rivet at a pressure sufficient to set the rivet by forming the open end of the rivet against the countersink. 5. A method joining parts as in claim 4 characterized by cutting the countersink at an angle of 1000; and, using an angle of about 1300 on the rivet forming die.

Inventors: HUFNAGL, GERHART, ZEHNDER, CLARK ROY
Applicants: THE BOEING COMPANY
Application year: 1980
Main classification: F16B19
IPC codes: F16B19