Abstract Thread forming screws are being increasingly used, particularly in the automobile industry. They are designed to directly assemble two parts by displacing material to form their own thread. This specificity implies knowledge of the screwing torque needed for the thread to be formed in the lower plate of the assembly and of the tightening torque necessary so as to establish the preload in the assembly. The experimental study presented in this paper is divided into two parts. The first concerns the thread forming process and shows the influence of the geometrical parameters of the thread forming screw and of the work-piece, and the influence of the process parameters on the maximum forming torque. A compromise can be proposed for the choice of the lead hole diameter, which is the most important parameter to be considered in order to keep a reasonable forming torque while obtaining threads deep enough to avoid stripping problems. The second part concerns the tightening process. An original experimental device is used to enable an empirical formula to be proposed, based on the ISO standard screw formula giving the tightening torque according to the preload applied inside the assembly.
[1]
Lakmal Seneviratne,et al.
An experimental investigation of torque signature signals for self-tapping screws
,
2000
.
[2]
Guillaume Fromentin,et al.
Precision and surface integrity of threads obtained by form tapping
,
2005
.
[3]
Pierre Stéphan,et al.
Analytical study of maximal tapping torque during forming screw process
,
2011
.
[4]
Alain Daidié,et al.
3D Finite Element Modeling of an Assembly Process With Thread Forming Screw
,
2009
.
[5]
Richard E. DeVor,et al.
Modeling Forces Including Elastic Recovery for Internal Thread Forming
,
2003
.
[6]
Richard E. DeVor,et al.
Modeling and analysis of internal thread forming
,
2002
.
[7]
Kaspar Althoefer,et al.
Theoretical modelling of the self-tapping screw fastening process
,
2001
.
[8]
Masujiro Hayama.
Estimation of Torque in Cold Forming of Internal Thread
,
1972
.
[9]
Richard E. DeVor,et al.
Experimental Investigation of Thread Formation in Form Tapping
,
2005
.