Abstract
Purpose. Research of the influence of the process parameters on the quality of threaded connections, notably, thread formation axial force on the opposite sides of the roots. Determination the thread formation axial force for screws with a wide groove. Design/methodology/approach. In a paper it is shown, that action of uncompensated thread formation axial force increases the defects and imperfectness of the strengthened layer. Proposed the theory about changes in the traditional self-stretching thread-formation method on the implementation process with a constant axial force. The external axial load must be equal to the largest axial component force of the thread-formation. The method uses the slip-line method with a model taking into account the interaction between two consecutive formed threads and enables the mean pressure on the thread flank to be obtained as a function of the formed thread height. From these results and a knowledge of the forming screw end geometry, an analytical method is proposed for the maximum axial force, the physical phenomena of the displacement of material in the tapping process is illustrated and the significantly influential parameters highlighted. Findings. This study proposes an analytical model based on a previous study concerning radial penetration of a rigid acute wedge into a perfectly plastic material. An experimental study seeks to determine the optimal lead hole on the work piece for an M8 screw. The experimental results are compared favorably with the results of the analytical study in order to validate the forming screw model. Originality/value. It is shown the influence of the geometrical parameters of the thread forming screw and of the work-piece on the axial force, and the influence of the process parameters on the quality of threaded connections. This sets limits on the forming axial force and conserves a sufficiently well formed thread shape for good stripping resistance. The experimental results are compared favorably with the results of the analytical study in order to validate the forming screw model.
Highlights
Screw connections are the most labor-intensive and the most difficult to automate
Tapping screws are used in steel, aluminum, die-castings, cast iron, forgings, plastics, reinforced plastics, and resin-impregnated plywood
The action of uncompensated force increases the defects and imperfectness of the strengthened layer and imposes compressive stress on the stretching stress in the grooved area, resulting into their relaxation. It neutralizes the positive effect of plastic deformation and reduces the quality of the formed screw-thread
Summary
Self-cutting screws drill their own tapping hole to close tolerances and from their mating themselves. It neutralizes the positive effect of plastic deformation and reduces the quality of the formed screw-thread. Application of an axial force in the thread-formation by the Self-Drilling Thread-Forming Screws leads to approaching methods of drilling and rolling.
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