STUDY REGARDING THE VARIATION OF THE THRUST FORCE, DRILLING TORQUE AND SURFACE DELAMINATION WITH THE FEED PER TOOTH AND DRILL TIP ANGLE AT DRILLING PRE-LAMINATED PARTICLEBOARD

Drilling of pre-laminated particleboards is a subject insufficiently covered by dedicated research. Therefore, the objective of this study was to examine the relationship of some key drilling parameters and analyze the variation of the thrust force, torque and surface delamination with the feed per tooth and drill tip angle at drilling pre-laminated particleboard. The surface quality was evaluated by the size of delaminations, at the exit side of the drill bit. To assess the defect, two non-dimensional parameters were used: the common delamination factor Fd based on the measurement of diameters of the circle circumscribing the defect and of the processed hole, and a new delamination factor, FdS, proposed by the authors and based on the effective measurements of the defect area with an image processing software. The experiments were performed on a range of feed per tooth rates from 0.1 to 0.7mm and four flat drill tip angles: 30°, 60°, 90°, 120°. The results showed that, a low feed rate generally minimizes both the drilling torque and the thrust force and also the delamination, while a small tip angle increases the drilling torque and generally minimizes the thrust force and delamination. The drill with T30 tip angle made exception from this trend, due to its geometry that caused the highest thrust force. The flat drill with 60° tip angle gave the best quality for small feed rates, while inducing the smallest thrust force, which makes it the preferable recommendation, amongst the tools tested, for drilling pre-laminated particleboards