Precision and surface integrity of threads obtained by form tapping

Largely applied to internal threading of extruded tubes, cold form tapping is now becoming a promising process for internal threading of holes in non ferrous and ferrous solid components, more particularly for mass production in the automotive industry. The aim of this study is to present the surface properties of the threads resulting from form tapping. Geometrical characterization, surface texture, mechanical and metallurgical observations are investigated. The results obtained are discussed according to the input parameters of the process, and are compared to those obtained from cut tapping. The strength of the work material and the influence of the lubricant are the two main parameters affecting the process, and a correlation with the tapping torque is proposed. Finally, the characteristics of the thread surface depend on the parameters of the tapping operation, thus it has to be taken into account in the design approach when this tapping process is chosen.