Experimental study on control parameters for automated application and in- situ performance assessment of joints with self-tapping timber screws

The paper in hand presents findings from experimental insertion tests with the purpose of establishing and quantifying necessary parameters for an automated application of the investigated self-tapping timber screws. The effects of input parameters such as contact force and revolutions per minute are examined and control parameters such as insertion moment and insertion length are recorded continuously. The biting-behaviour of screws is highly influenced by the contact force and the material parameters such as screw-diameter, screw-tip as well as the density and growth characteristics of the timber. With continuous control of insertion length and insertion moment a tight fit of the screw can be ensured, without damaging the screw or the surrounding timber. Given automatically applied screws with continuous recording of insertion moment and insertion length, the insertion energy can be calculated easily. As an in-situ performance assessment of automatically applied screws the hypothesis of estimating withdrawal characteristics on the basis of insertion energy is made. To validate this hypothesis, given experimental data of combined insertion and withdrawal tests is re-evaluated. A remarkable potential of predicting withdrawal properties with the insertion energy is found. This allows to thoroughly re-consider the design-to-execution process and the implementation of a research informed design process.