Thread milling as a manufacturing process for API threaded connection: Geometrical and cutting force analysis

Thread connection is one of the main unions for oil tubing and casing and its failure leads to deterioration of seal performance and connection strength. The machining process that produces threads by milling allows a higher speed velocity with a lower feed per tooth and, as a consequence, it promotes the lower forces compared to other manufacturing processes. Thread milling forces has been studied in metrical threads but there are not similar studies on API thread manufacturing. This article presents a study on thread milling cutting forces for API connection. Geometrical chip load analysis and mechanistic model are presented and experimental tests are developed using different feed per tooth. The experimental force data was used to calculate cutting pressure for force model. Surface quality is analyzed using the roughness data from machined surfaces. Flank and face surfaces did not present different roughness level. Also feed per tooth and vertical position did not presented influence on thread surface roughness. As a conclusion, the thread milling process is considered a good option for the manufacturing of API threads with force prediction that can be used to define machining parameters.