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A method and apparatus for welding thermoplastic materials with a stir welding system using a rotating element pin or element with a geometry to induce frictional energy from the rotating element. A floating constraining surface that has a motion independent of the rotation the pin (preferably stati

A method and apparatus for welding thermoplastic materials with a stir welding system using a rotating element pin or element with a geometry to induce frictional energy from the rotating element. A floating constraining surface that has a motion independent of the rotation the pin (preferably stationary) is used to constrain ejection of material from the zone where the weld is being formed. Molten material is retained in the weld region, avoiding weakness and voids at the weld joint. Optionally a system for introducing thermal energy into the weld zone in addition to the frictional energy is used. The system for introducing the thermal energy may be in association with the constraining shoe and/or the rotating tool, or a system independent of these.

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1. A method for welding thermoplastic material comprising;rotating an element and directing the rotating element into a thermoplastic material and advancing the rotating element along a path in thermoplastic material where a weld is to be formed, the element having a geometry, and rotated at a speed

1. A method for welding thermoplastic material comprising;rotating an element and directing the rotating element into a thermoplastic material and advancing the rotating element along a path in thermoplastic material where a weld is to be formed, the element having a geometry, and rotated at a speed and advanced at a rate relative to the thermoplastic material such that the rotation of the element against the thermoplastic material introduces frictional energy into thermoplastic material in a weld forming region sufficient to heat the thermoplastic material in the weld forming region to a temperature to fuse thermoplastic material,constraining the thermoplastic material in the weld forming region with a constraining surface directed along the path that has a motion independent of rotating motion of the rotating element, such that the independent motion and construction of the constraining surface inhibit expulsion of heated thermoplastic material from the weld forming region resulting from the rotation and advancement of the element, inhibit lateral forces induced in the rotating element from the constraining surface, assist in consolidation thermoplastic material that is heated and fused. 2. A method for welding thermoplastic material comprising;rotating an element and directing the rotating element into a thermoplastic material and advancing the rotating element along a path in thermoplastic material where a weld is to be formed, the element having a geometry, and rotated at a speed and advanced at a rate relative to the thermoplastic material where the rotation of the element against the thermoplastic material introduces frictional energy into thermoplastic material in a weld forming region,introducing thermal energy into at least a portion of the weld forming region where the frictional energy and the thermal energy are sufficient to heat the thermoplastic material to a temperature to fuse the thermoplastic material in the weld forming region,constraining the thermoplastic material in the weld forming region with a constraining surface directed along the path that has a motion independent of rotating motion of the rotating element, such that the independent motion and construction of the constraining surface inhibit expulsion of heated thermoplastic material from the weld forming region resulting from the rotation and advancement of the element, inhibit lateral forces induced in the rotating element from the constraining surface, assist in consolidation thermoplastic material that is heated and fused. 3. The method of claim 2 wherein the thermal energy is introduced through structure comprising a portion the constraining surface and a generator of thermal energy. 4. The method of claim 2 wherein the thermal energy is introduced through structure comprising the rotating element and a generator of thermal energy. 5. The method of claim 1 where the constraining surface is in at least in part insulated to reduce the dissipation of the heat from the weld region. 6. The method of claim 2 where the constraining surface is in at least in part insulated to reduce the dissipation of the heat from the weld region. 7. The method of claim 2 wherein the generator of thermal energy comprises an inductive heater, resistance heater, a gas flame, fluid heat exchanger with a heated fluid, a sonic generator, a chemical reaction, or a combination of the above. 8. The method of claim 2 wherein the thermal energy is introduced by directing a heated gas at the weld forming region. 9. The method of claim 2 wherein the thermal energy is introduced by introducing mechanical energy into the weld forming region. 10. The method of claim 2 wherein the thermal energy is introduced by introducing electromagnetic energy into the weld forming region. 11. The method of claim 10 wherein the thermal energy is introduced by energy source comprising ultraviolet light, infrared light, microwave, plasma, electron beam, or combination of the above. 12. The method of claim 1 additionally comprising removing thermal energy from a portion of the weld forming region to control the temperature of the heated thermoplastic material or assist in consolidation of the heated and fused thermoplastic material. 13. The method of claim 12 wherein thermal energy is removed by cooling the rotating element. 14. The method of claim 12 wherein thermal energy is removed by cooling at least a portion of the constraining surface. 15. The method of claim 1 wherein additional to rotating the element, moving the element in a non-rotating movement that produces frictional energy in addition to that produced from the rotating of the element and the advancing of the element along the path. 16. The method of claim 15 wherein the non-rotating movement is vibration, oscillation, eccentric rotation, expansion, contraction, or a combination of the above. 17. The method of claim 1 wherein the constraining surface is non-rotating with respect to the thermoplastic material. 18. The method of claim 1 wherein the constraining surface rotates in the same direction as the rotating element on the same or different axis of rotation. 19. The method of claim 1 wherein the constraining surface rotates in the opposite direction from the rotating element on the same or different axis of rotation. 20. The method of claim 1 wherein the constraining surface rotates on an axis not parallel to the axis of rotation of the element. 21. The method of claim 1 wherein the constraining surface rotates on an axis not parallel to the axis of rotation of the element and is structured to roll a surface over a portion of the weld forming region. 22. The method of claim 1 wherein the constraining surface is shaped to control the finish of the weld. 23. The method of claim 1 wherein the constraining surface comprises a surface that is flat. 24. The method of claim 1 wherein the constraining surface comprises a surface that is not flat. 25. The method of claim 1 wherein the constraining surface comprises a surface that is cylindrically or spherically concave or convex. 26. The method of claim 1 wherein the geometry of the element comprises structure to control the flow of the heated thermoplastic material to inhibit expulsion of the thermoplastic material from the weld forming region. 27. The method of claim 1 wherein the geometry of the element comprises structure to control the flow of the heated thermoplastic material to assist in consolidation thermoplastic material. 28. The method of claim 1 wherein the geometry of the element comprises threads. 29. The method of claim 1 wherein the geometry of the element comprises a circular cross-section of the element. 30. The method of claim 1 wherein the geometry of the element comprises a non-circular cross-section of the element. 31. The method of claim 30 wherein the non-circular cross-section is any non-circular closed shape that functions to induce friction from the rotating of the element, as opposed to cutting the thermoplastic material. 32. The method of claim 30 wherein the non-circular cross-section is polygonal, star-shaped, lobed, dumb-bell-shaped, ovoid, bladed, s-shaped, crossed, or a combination thereof. 33. The method of claim 1 wherein the geometry of the element comprises variation of cross-sectional shape of the element along an axis of rotation. 34. An apparatus of welding thermoplastic material which comprises;a rotating element with apparatus for advancing the rotating element into a thermoplastic material and directing the rotating element along an path in thermoplastic material where a welded joint is to be formed to introduce frictional energy into a weld forming region in the thermoplastic material by rotation of the element against the thermoplastic material sufficient to heat the thermoplastic material in the weld forming region to a temperature to fuse the thermoplastic material, the rotating element having a geometry that contributes to the frictional energy introduced into th e weld,constraining surface constructed to be directed along the path that has construction for a motion independent of rotating motion of the rotating element, such that the independent motion and the construction of the constraining surface inhibit expulsion of heated thermoplastic material from the weld forming region resulting from the rotation and advancement of the element, inhibit lateral forces induced in the rotating element from the constraining surface, assist in consolidation thermoplastic material that is heated and fused. 35. The apparatus of claim 34 additionally comprising an energy source for introducing thermal energy into at least a portion of the weld forming region in addition to the frictional energy. 36. An apparatus of welding thermoplastic material which comprises;a rotating element with apparatus for advancing the rotating element into a thermoplastic material and directing the rotating element along an path in thermoplastic material where a welded joint is to be formed to introduce frictional energy into a weld forming region in the thermoplastic material by rotation of the element against the thermoplastic material, the rotating element having a geometry that contributes to the frictional energy introduced into the weld,an energy source for introducing thermal energy into at least a portion of the weld forming region in addition to the frictional energy, the frictional energy and the thermal energy sufficient to heat the thermoplastic material in the weld forming region to a temperature to fuse the thermoplastic material,constraining surface constructed to be directed along the path that has construction for a motion independent of rotating motion of the rotating element, such that the independent motion and the construction of the constraining surface inhibit expulsion of heated thermoplastic material from the weld forming region resulting from the rotation and advancement of the element, inhibit lateral forces induced in the rotating element from the constraining surface, assist in consolidation thermoplastic material that is heated and fused. 37. The apparatus of claim 36 wherein the thermal energy source comprises a portion the constraining surface and a generator of thermal energy where the thermal energy is generated by the generator and introduced through the constraining surface. 38. The apparatus of claim 36 wherein the thermal energy source comprises the rotating element and a generator of thermal energy where thermal energy is generated by the generator and introduced through the rotating element. 39. The apparatus of claim 36 wherein the generator of thermal energy comprises an inductive heater, resistance heater, a gas flame, fluid heat exchanger with a heated fluid, a sonic generator, a chemical reaction, or a combination of the above. 40. The apparatus of claim 36 wherein the source of thermal energy comprises a heated gas stream directed at the weld forming region. 41. The apparatus of claim 36 wherein the thermal energy source is a system for introducing mechanical energy into the weld forming region. 42. The apparatus of claim 36 wherein the thermal energy source is a system for introducing electromagnetic energy into the weld forming region. 43. The apparatus of claim 36 wherein the thermal energy source is a system that comprises ultraviolet light, infrared light, microwave, plasma, electron beam, or combination of the above. 44. The apparatus of claim 34 additionally comprising structure for removing thermal energy from a portion of the weld forming region to control the temperature of the heated thermoplastic material or assist in consolidation of the heated and fused thermoplastic material. 45. The apparatus of claim 44 wherein structure for removing thermal energy comprises structure for cooling the rotating element. 46. The apparatus of claim 44 wherein thermal energy for removing thermal energy comprises structure for cooling at least a portion of the constraining surface. 47. The apparatus of claim 34 additional comprising structure for moving the element in a non-rotating movement that produces frictional energy in addition to that produced from the rotating of the element and the advancing of the element along the path. 48. The apparatus of claim 47 wherein the non-rotating movement is vibration, oscillation, eccentric rotation, expansion, contraction, or a combination of the above. 49. The apparatus of claim 34 wherein the constraining surface is non-rotating with respect to the thermoplastic material. 50. The apparatus of claim 34 wherein the constraining surface rotates in the same direction as the rotating element on the same or different axis of rotation. 51. The apparatus of claim 34 wherein the constraining surface rotates in the opposite direction from the rotating element on the same or different axis of rotation. 52. The apparatus of claim 34 wherein the constraining surface rotates on an axis not parallel to the axis of rotation of the element. 53. The apparatus of claim 34 wherein the constraining surface rotates on an axis not parallel to the axis of rotation of the element and comprises a roller to roll a surface over a portion of the weld forming region. 54. The apparatus of claim 34 wherein the constraining surface is shaped to control the finish of the weld. 55. The apparatus of claim 34 wherein the constraining surface comprises a surface that is flat. 56. The apparatus of claim 34 wherein the constraining surface comprises a surface that is not flat. 57. The apparatus of claim 34 wherein the constraining surface comprises a surface that is cylindrically or spherically concave or convex. 58. The apparatus of claim 34 wherein the geometry of the element comprises structure to control the flow of the heated thermoplastic material to inhibit expulsion of the thermoplastic material from the weld forming region. 59. The apparatus of claim 34 wherein the geometry of the element comprises structure to control the flow of the heated thermoplastic material to assist in consolidation thermoplastic material. 60. The apparatus of claim 34 wherein the geometry of the element comprises threads. 61. The apparatus of claim 34 wherein the geometry of the element comprises a circular cross-section of the element. 62. The apparatus of claim 34 wherein the geometry of the element comprises a non-circular cross-section of at least a portion of the element. 63. The apparatus of claim 62 wherein the non-circular cross-section is any non-circular closed shape that functions to induce friction from the rotating of the element, as opposed to cutting the thermoplastic material. 64. The apparatus of claim 62 wherein the non-circular cross-section is polygonal, star-shaped, lobed, dumb-bell-shaped, ovoid, bladed, s-shaped, crossed, or a combination thereof. 65. The apparatus of claim 34 wherein the geometry of the element comprises variation of cross-sectional shape of the element along an axis of rotation.