Analysis of green wood chip formation mechanisms at high cutting speed

Abstract

During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability. Thus, this study aims at better understanding and predicting chips production in wood milling. The different mechanisms of their formation are studied through orthogonal cutting experiments at high cutting speed. Chipping observations are carried out on a Chardin's pendulum. This experimental setup, similar to a Charpy's pendulum, was designed to measure cutting forces in sawing. A piezoelectric force transducer records the cutting forces. It is synchronized with a high speed camera to observe the formation of chips. In this experimental campaign, wood specimens are machined with fresh and saturated beech and Douglas fir. Within these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on saturated beech. As previously seen in quasi-static experiments, chip thickness is proportional to the nominal cut thickness. Moreover, the grain orientation has a great influence on the cutting mechanisms, so as the nominal cut and the grow circles widths. Digital image correlation is carried out in order to observe the strains fields during the cut for different cutting mechanisms. This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling for slabber manufacturers.