SPINDLES FOR FRICTION STIR ADDITIVE MANUFACTURING SYSTEMS, DEVICES, AND METHODS

1 . A friction stir additive welding screw comprising:

a first portion configured to be coupled to a friction stir additive welding device; and

a second portion configured to penetrate a work-piece, the second portion comprising:

a plurality of large threads, each large thread extending in a generally longitudinal direction;

a plurality of fine threads positioned along an edge of each large thread; and

a plurality of teeth at a tip of the second portion.

2 . The friction stir additive welding screw of claim 1 , wherein the plurality of fine threads extend generally perpendicular to a longitudinal axis of the friction stir additive welding screw.

3 . The friction stir additive welding screw of claim 1 , wherein each thread of the plurality of large threads curves from a first height at a first position along a longitudinal axis of the friction stir additive welding screw to a second height at a second position along the longitudinal axis of the friction stir additive welding screw, the second position different than the first position.

4 . The friction stir additive welding screw of claim 1 , wherein each thread of the plurality of fine threads has a generally triangular shape.

5 . The friction stir additive welding screw of claim 1 , further comprising a smooth surface positioned between adjacent edges of the plurality of large threads.

6 . The friction stir additive welding screw of claim 1 , wherein the tip of the second portion is not flat.

7 . The friction stir additive welding screw of claim 1 , wherein the plurality of fine threads are configured to cut and break material into smaller pieces of material.

8 . The friction stir additive welding screw of claim 7 , wherein the plurality of large threads are configured to compress the smaller pieces of material and move the compressed smaller pieces toward the tip.

9 . The friction stir additive welding screw of claim 1 , wherein the plurality of teeth are configured to plasticize and compress material along a weld line.

10 . The friction stir additive welding screw of claim 9 , wherein the plurality of teeth are configured to move plasticized material toward a weld line.

11 . The friction stir additive welding screw of claim 1 , wherein each large thread of the plurality of large threads comprises a first portion extending in a first direction away from a central axis of the screw and a second portion extending in a second direction toward the central axis of the screw.

12 . The friction stir additive welding screw of claim 1 , wherein each thread of the plurality of fine threads comprises a sharp edge.

13 . The friction stir additive welding screw of claim 1 , wherein the plurality of fine threads are recessed into surfaces of the plurality of large threads.

14 . A method of joining a first work-piece and a second work-piece with a stiffener comprising:

advancing a friction stir additive welding device along a weld line between the first work-piece and the second work-piece, a first portion of the stiffener extending above first surfaces of the first work-piece and the second work-piece and a second portion of the stiffener extending below second surfaces of the first work-piece and the second work-piece opposite the first surfaces, the friction stir additive welding device comprising a rotating screw;

contacting the stiffener with the rotating screw;

cutting and breaking the stiffener into smaller pieces using a plurality of fine threads of the rotating screw;

compressing and moving the smaller pieces toward the weld line using a plurality of large threads of the rotating screw; and

plasticizing and compressing material along the weld line using a plurality of teeth of the rotating screw.

15 . The method of claim 14 , further comprising penetrating a thickness of the first work-piece and the second work-piece with a tip of the rotating screw.

16 . The method of claim 15 , wherein an entire thickness of the first work-piece and an entire thickness of the second work-piece are penetrated by the rotating screw.

17 . The method of claim 14 , further comprising receiving the stiffener through a slot in a nosecone of the friction stir additive welding device.

18 . The method of claim 14 , wherein a longitudinal axis of the rotating screw is angled relative to surfaces of the first work-piece and the second work-piece as the friction stir additive welding device is advanced along the weld line.

19 . The method of claim 14 , wherein the smaller pieces are moved down smooth surfaces between adjacent edges of the plurality of large threads.

20 . The method of claim 14 , further comprising feeding material through a shoulder into a central channel of the friction stir additive welding device, and plasticizing the material using the rotating screw.