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Analysis of Chip Formation Mechanisms and Modelling of Slabber Process Renaud Pfeiffer, Robert Collet, Louis Denaud, Guillaume Fromentin

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Analysis of Chip Formation Mechanisms and Modelling of Slabber Process Renaud Pfeiffer, Robert Collet, Louis Denaud, Guillaume Fromentin Analysis of chip formation mechanisms and modelling of slabber process Renaud Pfeiffer, Robert Collet, Louis Denaud, Guillaume Fromentin To cite this version: Renaud Pfeiffer, Robert Collet, Louis Denaud, Guillaume Fromentin. Analysis of chip formation mechanisms and modelling of slabber process. Wood Science and Technology, Springer Verlag, 2014, pp.1-18. 10.1007/s00226-014-0680-x. hal-01096619 HAL Id: hal-01096619 https://hal.archives-ouvertes.fr/hal-01096619 Submitted on 17 Dec 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Science Arts & Métiers (SAM) is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. This is an author-deposited version published in: http://sam.ensam.eu Handle ID: .http://hdl.handle.net/10985/9114 To cite this version : Renaud PFEIFFER, Robert COLLET, Louis DENAUD, Guillaume FROMENTIN - Analysis of chip formation mechanisms and modelling of slabber process - Wood Science and Technology p.1-18 - 2014 Any correspondence concerning this service should be sent to the repository Administrator : [email protected] Analysis of chip formation mechanisms and modelling of slabber process Renaud Pfeiffer · Robert Collet · Louis Etienne Denaud · Guillaume Fromentin Abstract During the primary transformation in wood Keywords geometrical modelling · chip fragmenta- industry, logs are faced with conical rough milling cut- tion · slabber · wood ters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these 1 Introduction industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling The aim of sawmills consists in valorizing the maximum conditions and material variability. volume of wood from logs during the primary trans- Thus, this study aims at better understanding and formation. After cross cutting and debarking, logs are predicting chips production in wood milling. The differ- squared by rough milling operations with slabber heads ent mechanisms of their formation are studied through i.e. conical milling cutters. During this operation, up to orthogonal cutting experiments at high cutting speed 30% of the logs initial volume is transformed into chips. for beech and Douglas fir. Within these conditions, ejec- These chips are mainly used as raw materials in pulp in- tion of free water inside wood can be observed dur- dustries for paper and fiberboards. Defibration process ing fragmentation, particularly on beech. As previously is a key step for pulp industry. It can be mechanical, seen in quasi-static experiments, chip thickness is pro- chemical or both. The chip size distribution, which af- portional to the nominal cut thickness. Moreover, the fects directly the efficiency of the defibration process grain orientation has a great influence on the cutting (Felber and Lackner, 2005), must be controlled. This mechanisms, so as the nominal cut and the grows circles distribution is greatly dependent on milling conditions widths. This chip fragmentation study finally allows the and on variability in material. This paper aims at pro- improvement of the cutting conditions in rough milling. viding a better understanding of chip fragmentation so as to improve cutting conditions and machine design. In order to optimize machine design as well as cut- In the state of the art, two kinds of experiments ting geometry, a geometrical model of a generic slab- can be performed to study the chip size distribution. ber head is developed. This model allows the study of The first one consists in using industrial slabbers in the effective cutting kinematics, the log-cutting edges real conditions with green wood logs at high cutting interactions and the effective wood grain direction dur- speed (V ' 3600 m/min). An example of this kind of ing cutting. This paper describes the great influence of c experiment is shown in Figure 1a. The parameters to the carriage position on cutting conditions. The results be tested must include cutting kinematics, tool geome- obtained here can be directly used by milling machine try, log positioning and log parameters. Chips produced manufacturers. are then screened and their size distribution carefully observed (Hernandez and Boulanger, 1997; Hernandez and Quirion, 1993; Lagani`ere,2004). R. Pfeiffer · R. Collet · L.E. Denaud · G. Fromentin Arts et Metiers ParisTech, LaBoMaP, Rue porte de Paris The second approach deals with mesoscopic charac- 71250 Cluny - FRANCE teristics. Chipping experiments on wood specimens are E-mail: renaud.pfeiff[email protected] carried out with a compression testing machine with a specific experimental setup (Fig. 1b). For these exper- 2 Experimental analysis in orthogonal cutting iments in quasi static conditions (Vc ' 60 mm/min), close attention is paid to the area near the cutting edge. 2.1 Local grain direction definition Tested parameters are unchanged with respect to the previous macroscopic process. Chip size distribution, Although the experimental work is carried out in or- cutting forces, failure modes, strain and stress fields thogonal cutting conditions, it is necessary to define are analysed in order to understand chipping phenom- locally the grain direction in complex 3D cases. This ena (Buchanan and Duchnicki, 1963; Hellstr¨om,2008b; notion was tackled by Kivimaa (1950) and McKenzie Twaddle, 1997; Uhmeier, 1995). (1960) with the cutting modes defined by two angles. However these two angles were not well defined for com- plex 3D cases. In Figure 2, a new definition is proposed. Locally, the grain direction is defined with two angles: the Grain Edge Inclination angle GEI and the Grain Direction angle GD. The GEI angle is measured in the grain cutting edge plane PsGD, containing the cutting edge and the grain direction. This angle is chosen to vary between 0 and 90°. The GD angle is measured in the grain working plane PfGD, containing the resultant cutting and the grain directions. The resultant cutting direction contains the cutting direction, as well as the (a) Chipping experiment with a slabber head (Forintek Canada feed direction (ISO, 1982). GD is an oriented angle from Corp, Quebec) the resulting cutting edge direction and the grain di- rection oriented towards the cutting face. So GD varies between 0 and 180°. In Figure 2 appears the working cutting edge plane Pse defined in (ISO, 1982). Resultant Cutting cutting direction face P fGD GD (b) Chipping experiment with compression testing machine (Hellstr¨om,2008b) P se Fig. 1: Chipping experimental setups GEI So as to offer a better understanding of the phys- P sGD ical chipping processes, this paper focuses on two ap- Grain Direction proaches of chip production. The first one refers to the observation of fragmentation phenomena with a spe- Fig. 2: Definitions of the Grain Edge Inclination angle GEI cific experimental setup in dynamic conditions (Vc = and the Grain Direction angle GD. GEI is measured in the 400 m/min), which allows the extraction of influent pa- grain cutting edge plane PsGD, containing the cutting edge and the grain direction. GD is measured in the grain rameters like grain direction and nominal cut thickness. working plane PfGD, containing the resultant cutting and The second one consists of a geometrical and kine- the grain directions. Pse is the working cutting edge plane, matic study of the milling process in order to analyse defined in (ISO, 1982). the effect of cutting geometrical and kinematic parame- ters on the local cutting conditions. This study will give guidelines to milling machine manufacturers to help then to improve machine design and optimize chips for- 2.2 Experimental method mation. In the whole paper, except for grain direction, all Chipping observations are carried out on a Chardin's geometric and kinematic abbreviations are taken ac- pendulum, similar to a Charpy's pendulum, but de- cording to ISO 3002 standard (ISO, 1982, 1984). signed to measure cutting forces in sawing (Chardin, 1958). It was used to obtain instrumented orthogonal green beech section on a 140 mm cutting length. Fig- cutting experiments to characterize cutting forces on ure 4 shows an uncompleted cut of a 400 mm2 section of dry wood (Eyma et al, 2005). The arm of the pendu- beech and the definitions of the nominal cut thickness lum is 1:2 m long and weighs 36 kg. So the available hD and the nominal cut width bD. As a consequence, kinematic energy reaches 756 J and the cutting speed an experimental design is set and uses the following pa- Vc 400 m/min. rameters: nominal cut thicknesses hD = 6; 10; 14 mm, Contrary to its usual practice, the specimen holder nominal cut widths bD = 6; 10; 14 mm and Grain Di- is placed at the arm extremity. The specimen holder is rection angles GD = 70; 90; 110°. The GEI angle is 140 mm long and is equal to the specimen and the cut- kept at 90°. Two wood species are selected: beech for its ting lengths. A tooth coming from an industrial milling homogeneity and Douglas fir known for its heterogene- cutter is used for these experiments. The normal rake ity and bad machinability. The Moisture Content (MC) angle is set to γn = 45°, the normal clearance angle is controlled after the experiments by a double weight to αn = 5°. The tool holder, in green in Figure 3, technique (Eq 1) (ASTM, 1994). Each set of parame- is attached to a Kistler piezo-electric force transducer ters is repeated 5 times.
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