1. Introduction
Drilling is one of the oldest and most important methods of processing wood and wood-based materials. One of the most widespread wood-based materials is particleboards (PB), widely used nowadays in the production of storage furniture (e.g., kitchen furniture). For the manufacture of this type of furniture, PB (usually pre-laminated) is joined with dowels inserted into holes, which are made by drilling, in addition to other holes made for other purposes (holes for locks, for various accessories, for shelf supports, etc.). This can lead to a dozen holes (made by drilling), and sometimes over one hundred. For example, the IKEA BILLY bookcase (which is not a complex piece of furniture) requires 192 holes.
Given the importance of this processing method, research work has been carried out over time to study it. Hetzel’s research focused on the PB (and plywood) drill [
1]. The investigations aimed to determine the influences of the adhesive on the durability of the cutting edges, the influences of the type of drill, its diameter, and the geometry of the edge on the torque and feed speed (the feed force being kept constant), as well as how the chips are formed in relation to the torque and the feed rate. Radu conducted an extensive study on the geometry of helical drills used in woodworking, the kinematics, and the dynamics of the cutting process [
2]. The experiments aimed to establish the optimal parameters of drills for wood and PB, taking into account the torques, axial forces, and chip evacuation depending on: the type of drill, wood species (oak, beech, spruce, PB), feed rate, and drill depth. The results showed that the torque and the specific cutting resistance decrease, and the axial force increases, with increasing tip angle, for all four processed materials, regardless of the feed direction.
Valarmathi et al., assuming that the thrust force developed during drilling has a major role in gaining a good surface quality and minimizing the delamination tendency, analyzed the cutting conditions, which influence the thrust force in the drilling of PB [
3]. The parameters considered were spindle speed, feed rate, and point angle. The drilling experiments were performed based on Taguchi’s design of experiments and a response surface methodology (RSM). A mathematical model was developed to predict the influence of cutting parameters on thrust force. The results showed that high spindle speed with a low feed rate combination minimizes the thrust force in the drilling of pre-laminated PB. Lilly Mercy et al. proposed a multi-response optimization of drilling parameters for PB processing using Gray Relational Analysis [
4]. The aim was to minimize the roughness of the hole’s internal surface and the thrust force. The parameters considered were the drill rotation speed, the feed rate, and the drill diameter. The authors noted that a smaller feed speed, smaller drill diameter, and higher drill rotation speed are essential for reducing the thrust force and surface roughness in the drilling of PB.
Ispas et al. studied the influence of the tip angle of drills and feed rate on coated PB delamination, but also on the dynamic parameters (thrust force and torque) for two types of drills: flat and helical [
5,
6,
7]. The results showed that the thrust force, the torque, and the surface delamination increased with an increase in the feed rate. An increase in the drill tip angle caused a decrease in the torque trend, which correlated well with a decrease in surface quality (delamination). As far as the thrust force was concerned, a decrease in the drill tip angle caused a decrease in the thrust force, well correlated with the surface quality around the hole.
Podziewski et al. studied the drilling machinability of several wood-based materials, including PB [
8]. The machinability was expressed by the quality of the hole’s edges and the magnitude of the cutting forces and torque. Madhan Kumar and Jayakumar studied PB drilling with helical and spade drills [
9]. Experiments have shown that the roughness of the hole’s internal surface has decreased as the rotational speed of the drills has increased and the feed speed has decreased.
An extensive review of scientific developments in the drilling of wood-based panels is presented in the work elaborated by Górski [
10].
Stimulated by the successful application of artificial neural networks (ANNs) and response surface methodology (RSM) in the wood science area and, also, due to the fact that there is limited information regarding the application of ANN and RSM in the drilling of wood particleboards, in this paper, we aimed to apply the ANN together with RSM to reveal the optimum value of input factors (drill tip angle, tooth bite, and drill type) based on the desired responses during the drilling of PB, such as the delamination factor at the inlet and outlet, thrust force, and drilling torque.
ANN and RSM have been applied in wood science for various topics such as predicting the wood moisture content, prediction of noise emission in the machining of wood materials by means of an artificial neural network, optimum CNC cutting condition, reliability of phytosanitary treatment of wood [
11,
12,
13,
14,
15]. More information about the modeling process with artificial neural networks could be found in the literature [
12,
16]. Moreover, the RSM has been applied to optimize the heat-treated wood dowel joints, processing parameters of medium-density of fiberboards, wood drying conditions, and energy consumption during the mechanical processing of wood [
17,
18,
19,
20]. Moreover, more details about the RSM could be found in the literature [
21,
22].
4. Conclusions
In this work, the artificial neural network modeling technique and response surface methodology were employed to reveal the optimum values of selected factors, namely, drill tip angle, tooth bite, and drill type, on the delamination factor at the outlet and inlet, thrust force, and drilling torque. Both applied modeling techniques (ANN and RSM) could be used to predict the delamination factor at the outlet, the thrust force, and the drilling torque with a higher performance indicator (R2) than in the case of the delamination factor at the inlet. The helical drill leads to a lower delamination factor, a lower thrust force, and a lower drilling torque than the case of a flat drill. The delamination factor at the outlet is more affected by drill type than the drill tip angle and tooth bite, which have almost the same influence. On the other hand, the delamination factor at the inlet is more affected by the tooth bite, followed by drill tip angle and drill type. The most important analyzed factor that affects the thrust force is the drill type followed by the tooth bite and drill tip angle. The drilling torque is most affected by the tooth bite, followed by the drill tip angle and drill type. Other factors that affect the drilling process of wood and wood-based boards must be considered in further studies. These kinds of studies are underway by our group.