Problem definition and objectives: Wooden sandwich composite panels have garnered significant attention in various engineering and construction applications due to their lightweight and high strength. In the use of sandwich panels, particularly in construction and engineering industries, establishing reliable connections between these panels and other structural components is of paramount importance. Drilling, as a critical stage in the manufacturing of such connections, plays a vital role in ensuring the stability, strength, and durability of structures. Since these panels are often subjected to cyclic loads and environmental stresses, the quality and precision of drilling directly influence the final performance of the structure. During drilling, sandwich panels are prone to layer separation, where the interaction between the drill bit and the sandwich panel layers at entry and exit points is the primary cause of process-induced defects such as delamination. Delamination is recognized as a common and unexpected defect in the machining of composite panels, significantly affecting surface quality and structural integrity. However, the optimal selection of machining parameters, proper tool geometry, effective tool types, and suitable operating conditions can minimize or even prevent such defects. These measures not only improve the process quality but also ensure the longevity and functionality of the final product. The main objective of this research is to investigate the effect of key drilling parameters on delamination and to optimize machining conditions to achieve minimal delamination and the best cutting surface quality in wooden-faced sandwich composite panels. This study focuses on machining parameters, including feed rate and drill bit diameter, as well as workpiece characteristics such as the material of the face and core layers, to identify, measure, and analyze their influence on delamination during drilling. The findings of this research provide a robust scientific foundation for optimizing drilling processes in the production of wooden composite panels and related products.
Methodology: For this purpose, panels were fabricated with three types of face materials: medium-density fiberboard (MDF) with a melamine coating, plywood, and balsa wood, combined with a constant extruded polystyrene foam core of 36 mm thickness. Drilling was performed using a CNC machine equipped with an uncoated twist drill bit at three different diameters (4, 8, and 12 mm), two feed rate levels (5 and 13 mm/s), and a fixed cutting speed of 8000 rpm. The evaluation of damaged and affected layers was conducted using digital imaging, and high-precision image processing was carried out using the Digimizer software. Subsequently, the delamination factor was calculated based on relevant scientific relations.  Experimental data were analyzed within a randomized factorial design framework using analysis of variance (ANOVA) and statistical tables generated in SPSS software. The effects of individual factors as well as their interactions were thoroughly examined.
Results: The results indicated that the face material, feed rate, and drill bit diameter had the highest impact on delamination, in descending order of significance. The lowest delamination factor of 1.119 was observed in panels with MDF layers and a melamine coating, drilled with a 4 mm bit and a feed rate of 5 mm/s. Conversely, the highest delamination factor of 3.060 occurred in panels with balsa wood layers, drilled with a 12 mm bit and a feed rate of 13 mm/s.
Conclusion: These findings highlight that reducing feed rate and increasing cutting speed in CNC machining are critical for minimizing delamination in wooden sandwich composite panels, thereby enhancing the final product quality.