Milling of Heat-Treated Beech Wood (Fagus sylvatica L.) and Analysis of Surface Quality

Mihai Ispas, Lidia Gurau, Mihaela Campean, Murat Hacibektasoglu, Sergiu Racasan
2016 BioResources  
Several previous studies have investigated the effects of heat treatment on the chemical composition, along with the physical and mechanical properties, of wood from various species. However, the effects of these property changes upon the machining properties and surface quality of machined wood have been studied much less. The main goal of this work was to investigate the comparative cutting power consumption during milling and the resulting surface roughness of heat-treated and untreated
more » ... wood (Fagus sylvatica L.). Several cutting regimes were tested by combining different values of rotation speed, feed speed, and cutting depth. The cutting power and the processing roughness were assessed and compared. The results clearly showed that the cutting power involved in the milling of heat-treated beech wood was up to 50% lower than that of untreated wood, but the processing roughness was slightly higher. PEER-REVIEWED ARTICLE Ispas et al. (2016) . "Milling of heat-treated beech," BioResources 11(4), 9095-9111. 9096 hard, brittle hardwoods. The sharpness of the cutters is important, in order to avoid tearing, especially when milling across the grain. The greatest problems with tearing, as well as enhanced and uneven, accidental, vibrational waviness, occur at the beginning and the end of the milling path, when the cutter gets into and comes out of the wood. Previous studies on the machinability of heat-treated beech wood have shown that the most important factors that affect the cutting power during the milling of heat-treated wood as compared to untreated wood are the cutting speed, the rake angle of the cutter, and the feed speed (Kubs et al. 2016) . The cutting power represents the mechanical work at processing released per second. It is determined by measuring the electric power absorbed by the machine motor during processing as well as at idle run (Eq. 1) Mandic et al. (2010) investigated the influence of the temperature (170, 190, and 210 °C) used during the heat-treatment of beech samples on the cutting power during milling. Only the samples treated at 190 °C and 210 °C were cut with a significantly lower cutting power than the untreated ones, and the cutting power increased significantly at feed speeds above 8 m/min. However, none of the previously published works found a clear correlation between the cutting power and the cutting parameters used during the processing of heattreated wood. This lack of a correlation might be the result of variability of the wood samples, failure to observe the importance of preparing the samples with strictly oriented fibers, or the sensors' performance and limitations. Some authors have compared the surface roughness of heat-treated wood with that of untreated wood, where the samples were planed prior to the heat treatment, but not afterwards. The measurements of surface roughness after heat treatment indicated slightly lower roughness for Turkish river red gum wood, Eucalyptus camaldulensis (Unsal and Ayrilmis 2005), red-but maple, Acer trautvetteri Medw. (Korkut and Guller 2008), Turkish hazel, Corylus colurna L. (Korkut et al. 2008), European Hophornbeam, Ostrya carpinifolia Scop. (Korkut et al. 2009), and Rowan wood, Sorbus aucuparia L. (Korkut and Budakci 2010). However, evaluating the surface roughness of heat-treated wood after machining is more interesting because in real practice the heat treatment precedes processing (milling, drilling, turning, sanding, etc.). The modifications that wood undergoes during a heat treatment, such as mass loss, might have an important impact on the surface roughness, seen as the result of wood-tool interactions, in a different way than in the above studies. Budakci et al. (2013) determined the roughness (Ra) perpendicular to the grain of Eastern beech wood (Fagus orientalis L) heat-treated at 140 C and 160 C (for 3, 5, and 7 h), after milling at a rotation speed of 6000 rpm, with a 4-m/min feed speed and a 1-mm cutting depth, using two types of cutters (star blade and razor blade). The roughness values (Ra), as measured by a stylus with a 5-m tip radius, for heat-treated wood were slightly higher (up to 8%) than those for untreated wood, and they increased with increasing duration of the heat-treatment. Kvietkova et al. (2015) investigated the roughness (Ra), measured along the feed direction by the stylus method, after milling beech wood (Fagus sylvatica L.). After varying the rotation speed, feed speed, clearance angle, rake angle, and cutting angle of the milling cutter, the authors concluded that the thermal treatment had no significant influence upon the average roughness of the milled surfaces. There was, however, a significant effect of the cutting speed and feed speed. The lowest value of Ra was found with a clearance angle of 20° and the highest value of cutting speed (40 m/s). The heat
doi:10.15376/biores.11.4.9095-9111 fatcat:qfq44dxiprdy7j2f7w73k4hmuy