Drilling Ability of Self-Drilling Screws in Case of Laser-Cut Pilot Holes

Abstract

Steel truss structures are widely used as high-strength frameworks, but conventional welded joints present limitations such as high costs, lack of reusability, and technical challenges, especially for high-strength and stainless steels. High-strength steel and stainless steel offer excellent mechanical properties, but their application is restricted due to welding-related issues. This thesis research was conducted as part of the industrial-based research project MechJoint, which aims to address these challenges by replacing welded joints with reusable self-drilling screw connections. The study investigates a mechanical joining approach, which uses self-drilling screws with laser-cut pilot holes, enabling efficient assembly without welding while maintaining structural performance. This study examines drilling performance with pre-selected materials and screws: high-strength steel S700, stainless steel EN 1.4162, zinc-plated and bi-metal ZEBRA Pias self-drilling screws. The drilling ability was studied experimentally, in terms of screw insertion time and screw failure statistics. Hardness properties of the screws and materials were measured, and connection between hardness and drilling ability was drawn. Effect of pilot holes pre-cut by laser was evaluated on drilling efficiency. The results of this thesis demonstrate that the approach with self-drilling screws allows to penetrate the material and tap a thread in the steel of high grade, especially in case of laser-cut pilot hole. The achieved results open the ability to successfully utilize self-drilling screws in connections of metal constructions.