Analysis of chip formation mechanisms and modelling of slabber process

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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 were studied through orthogonal cutting experiments at high cutting speed for beech and Douglas fir. Under these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on 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 growth ring widths. This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling. In order to optimize machine design as well as cutting geometry, a geometrical model of a generic slabber head was developed. This model allows the study of the effective cutting kinematics, the log-cutting edges interactions and the effective wood grain direction during cutting. This paper describes the great influence of the carriage position on cutting conditions. The results obtained here can be directly used by milling machine manufacturers.