Abstract: In a general aspect, a method for additive manufacturing can include depositing a liquid on a first portion of an article, the liquid containing a dopant, the article including a feedstock material. The method can also include heating, at a first temperature, the article to, at least one of, evaporate or decompose the liquid. The heating at the first temperature can leave the dopant on the first portion of the article. The method can further include heating, at a second temperature, the article. The heating at the second temperature can result in the feedstock material melting and the dopant mixing with the feedstock material in a second portion of the article. The second portion of the article can include the first portion of the article.

Abstract: 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.

Abstract: 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.