Abstract Threads are essential mechanical elements in industrial applications, valued for their reliability and ease of assembly. Among internal thread manufacturing processes, thread forming has gained increasing importance due to its chipless nature and the associated improvements in mechanical performance. However, the influence of tool geometry—particularly the curved lobe profile of fluteless taps—has not yet been systematically quantified within a unified geometric framework. This study introduces a geometry-based representation of the lobe profile of fluteless taps using a reduced set of global parameters. On the basis of this formulation, physically interpretable descriptors of the tool–workpiece interaction—namely, contact area and contact angle—are derived. A Box-Behnken design of experiments, combined with analysis of variance (ANOVA), is employed to evaluate the influence of geometric parameters on forming torque and thread quality. The results indicate that the contact angle exhibits the highest statistical sensitivity among the investigated geometric descriptors, followed by contact area and the number of forming lobes. Nonlinear effects and interaction terms suggest a coupled influence of tool geometry on the forming process. Although local material flow is not explicitly resolved, the proposed descriptors capture the dominant trends within the investigated parameter space. The agreement between experimental data and regression models indicates that the essential process behavior is well represented within the proposed framework. Overall, this study provides a consistent quantitative relationship between tool geometry and process responses, enabling geometry-driven optimization of fluteless tap design.
Neçetin et al. (Tue,) studied this question.