Laser predrilling for high-precision positioning and installation of fully threaded screws in glued-laminated timber (glulam)

Wood Material Science and Engineering, vol. 18, pp. 491–506

Abstract

In many applications of joining and reinforcing timber elements with self-tapping fully threaded screws, the exact positioning of the screws becomes difficult as the screws tend to “stray” from their designated axis during insertion in wood and wooden semi-products. Experimental investigations show that besides natural local discontinuities like knots or resin inclusions, the screw-to-grain angle and the screws stiffness have an influence on the insertion process and thus can be identified as factors to a deviation of fully threaded screws. Mechanical predrilling cannot solve this problem, as the drills also stray during the predrilling process. As an alternative, a pyrolytic method of predrilling based on laser radiation proved suitable for obtaining guide holes with adequate straightness. This paper includes a description of the developed drilling processes using different lasers beam sources. The resulted borehole geometries of a QCW fiber laser, as well as an ultrashort pulsed laser, show satisfying results. Furthermore, the short- and long-term bond behavior of fully-threaded screws in a glued-laminated timber matrix, installed in laser predrilled guide holes, was tested and evaluated. The results show that with the new innovative wood processing method an exact positioning of fully-threaded screws is possible, almost without loss of withdrawal resistance of the screws.

Authors 8

1. Martin Trautz corresponding Aachen Chair of Structures and Structural Design (Trako)

   RWTH Aachen University

   Affiliation as printed

   Chair of Structures and Structural Design (trako), RWTH Aachen University, Aachen, Germany

2. Denis Grizmann Aachen Chair of Structures and Structural Design (Trako)

   RWTH Aachen University

   Affiliation as printed

   Chair of Structures and Structural Design (trako), RWTH Aachen University, Aachen, Germany

3. Andrija Pranjic Aachen Chair of Structures and Structural Design (Trako)

   RWTH Aachen University

   Affiliation as printed

   Chair of Structures and Structural Design (trako), RWTH Aachen University, Aachen, Germany

4. Michael Raupach Aachen Institute of Building Materials Research

   RWTH Aachen University

   Affiliation as printed

   Institute of Building Materials Research (ibac), RWTH Aachen University, Aachen, Germany

5. Clarissa Glawe Aachen Institute of Building Materials Research

   RWTH Aachen University

   Affiliation as printed

   Institute of Building Materials Research (ibac), RWTH Aachen University, Aachen, Germany

6. Arnold Gillner Aachen Chair for Laser Technology

   RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology (LLT), RWTH Aachen University, Aachen, Germany

7. Benedikt Bornschlegel Aachen Chair for Laser Technology

   RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology (LLT), RWTH Aachen University, Aachen, Germany

8. Dennis Haasler Aachen Chair for Laser Technology

   RWTH Aachen University

   Affiliation as printed

   Chair for Laser Technology (LLT), RWTH Aachen University, Aachen, Germany