Systems and methods for friction bit joining

1. A tool for friction bit joining a workpiece material, the tool comprising:

a bit rotatable around a rotational axis, the bit having:

a pin having a frustoconical face and a face angle of greater than forty-five degrees between the frustoconical face and the rotational axis, the pin configured to friction stir the workpiece material and displace the workpiece material radially outward as the pin friction stirs the workpiece material;

a non-cutting tip protruding axially downward from the frustoconical face of the pin, the non-cutting tip having a maximum width perpendicular to the rotational axis;

a first curved transition between the non-cutting tip and the frustoconical face, wherein the first curved transition is curved along the rotational axis;

a top surface opposite the pin with at least one feature recessed in the top surface, the at least one feature configured to transmit torque to the bit to rotate the bit around the rotational axis;

a flat shoulder between the pin and the top surface, the flat shoulder configured to contain workpiece material displaced by the pin;

a cylindrical side surface of the pin extending upward from the frustoconical face;

a second curved transition between the cylindrical side surface of the pin and the flat shoulder, the second curved transition configured to direct workpiece material displaced by the pin toward the flat shoulder wherein the second curved transition is curved along the rotational axis;

the frustoconical face tapering from a maximum outer diameter thereof at the cylindrical side surface to a minimum outer diameter thereof at the first curved transition; and

the maximum width of the non-cutting tip is less than half of a difference between the maximum outer diameter and the minimum outer diameter of the frustoconical face of the pin.

2. The tool of claim 1 , wherein the top surface of the bit includes an outer periphery; and

wherein the at least one feature is radially inward of the outer periphery of the top surface.

3. The tool of claim 1 , the non-cutting tip including a flat lower surface and an axial side surface; and

wherein the face angle is less than ninety degrees.

4. The tool of claim 1 , the face angle being less than ninety degrees.

5. The tool of claim 1 , the face of the pin having one or more surface features configured to engage and flow workpiece material.

6. The tool of claim 1 , the bit having a bit height that is between 10% and 50% of a total diameter of the bit.

7. The tool of claim 6 , the bit having a pin height that is less than 50% of a total diameter of the bit.

8. The tool of claim 1 , wherein the at least one feature comprises a plurality of recesses spaced radially outward from the rotational axis and angularly spaced from one another about the top surface.

9. A tool for friction bit joining, the tool comprising:

a bit and a driver for driving the bit into a workpiece;

the driver comprising:

a driver body rotatable around a rotational axis;

a lower seating surface of the driver body;

a cutter radially outward of the lower seating surface to remove excess material from the workpiece, the cutter having a cutting edge and a cutter surface extending upwardly from the cutting edge;

a tapered surface of the driver body adjacent the cutter surface and tapering radially outwardly as the tapered surface extends upwardly from the lower seating surface of the driver body, the tapered surface configured to direct material removed by the cutter away from the bit; and

at least one mechanical interlocking feature protruding from the lower seating surface of the driver body; and

the bit comprising a pin having a face and a face angle between the face and the rotational axis, the bit further including a non-cutting tip protruding axially from the face of the pin and a top surface opposite the pin, the top surface of the bit configured to seat against the lower seating surface of the driver body, the top surface including at least one recess in the top surface configured to transmit torque to the bit from the at least one mechanical interlocking feature to rotate the bit around the rotational axis;

wherein the pin is configured to friction stir a workpiece material;

wherein the bit includes a flat shoulder between the pin and the top surface; and

wherein the bit includes a curved transition between the pin and the flat shoulder, wherein the curved transition is curved along the rotational axis.

10. The tool of claim 9 , wherein the cutter comprises a plurality of cutters radially outward of the lower seating surface.

11. The tool of claim 9 , the cutting edge of the cutter being positioned axially even with the top surface of the bit.

12. The tool of claim 9 , the driver further comprising a magnet in the driver body and configured to apply a magnetic force to the bit in an axial direction.

13. The tool of claim 12 , the magnet being an electromagnet.

14. The tool of claim 9 , the bit including a ferromagnetic material.

15. A tool for friction bit joining a workpiece material, the tool comprising:

a bit rotatable around a central rotational axis and including a ferrous material, the bit comprising:

a pin having a face and a face angle between the face and the rotational axis;

an axial side surface portion of the pin;

a non-cutting tip protruding axially from the face of the pin, the non-cutting tip including a lowermost end of the bit;

an uppermost, flat top surface of the bit opposite the pin;

a central portion of the uppermost, flat top surface of the bit intersected by the central rotational axis of the bit, the central portion of the uppermost, flat top surface including ferrous material configured to magnetically interact with a magnet of a driver;

a plurality of recesses in the uppermost, flat top surface of the bit to receive a plurality of drive protrusions of the driver, each of the recesses spaced radially outward from the central rotational axis of the bit so that the recesses are disposed about the central portion of the uppermost, flat top surface of the bit;

a flat shoulder between the pin and the top surface;

a lower, flat annular surface portion of the flat shoulder;

a curved transition connecting the axial side surface portion of the pin and the lower, flat annular surface portion of the flat shoulder, wherein the curved transition is curved along the rotational axis.

16. The tool of claim 15 wherein the non-cutting tip includes a flat lower surface and an axial side surface;

wherein the face angle is less than ninety degrees; and

wherein the bit includes a lower curved transition between the face of the pin and the axial side surface of the non-cutting tip, wherein the lower curved transition is curved along the rotational axis.

17. The tool of claim 15 wherein the top surface of the bit includes an outer periphery; and

wherein the plurality of recesses are radially inward of the outer periphery of the upper surface.

18. The tool of claim 15 wherein the face is frustoconical and the face angle is less than ninety degrees.

19. The tool of claim 15 wherein the plurality of recesses each include a flat extending downward from the uppermost, flat surface of the bit to be engaged by one of the drive protrusions of the driver.

20. The tool of claim 15 wherein the recesses are evenly angularly spaced about the central portion of the uppermost, flat top surface of the bit.

21. The tool of claim 15 wherein the recesses are non-circular.