Workpiece temperature and extrusion rate effects on stress-strain condition and defect formation in a drill pipe with a protector

The paper addresses the importance of using aluminum for the production of drill pipes. It also discusses one of the problems associated with the production of drill pipes having a protective thickening (central upset), such as the formation of a “streak delamination” type defect in the protector formation zone. Pipes with internal end and central upsets made of alloy D16T were selected as study objects. The extrusion process was performed under the following two experimental conditions: workpiece metal temperature—440 °C, punch travel speed—1.4 mm/s (option 1) and workpiece metal temperature—4 00 °C, punch travel speed—0.9 mm/s (option 2). It has been experimentally established that lowering the workpiece metal temperature by 40 °C and punch travel speed by 0.5 m/s during the extrusion process promotes the formation of a homogeneous macrostructure. By simulating the described experimental options of the processes, it was found that a 40 °C decrease in the workpiece metal temperature and a 0.5 m/s decrease in the punch travel speed during the extrusion process lead to a 50% reduction in the maximum deformation rate in the deformation zone, and to a 14% reduction in the degree of deformation. By calculating the stress condition parameter in the deformation zone, it became possible to show that performing the process according to option 2 results in a more favorable stress condition of the metal compared to option 1, which could also contribute to the reduction in the number of “streak delamination” type defects in the protector zone.