During the primary transformation of wood, logs are faced with slabber heads. Chips produced are raw materials for pulp paper and particleboard industries. Efficiency of these industries is partly due to particle size distribution. Command of this distribution is no easy matter because of great dependence on cutting conditions and variability in material. This study aimed a better understanding and predictionof chip fragmentation. It starts with a detailed description of cutting kinematic and interaction between knife and log. This leads to the numerical development of a generic slabber head. Chip fragmentation phenomena were studied through experiments in dynamic conditions. These experiments were carried out thanks to a pendulum (Vc = 400 m/min). It was instrumented with piezoelectric force sensors and high speed camera. Obtained results agreed very well with previous quasi-static experiments

COLLET, Robert

DENAUD, Louis

FROMENTIN, Guillaume

LORONG, Philippe

PFEIFFER, Renaud

English

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Analysis and modeling of green wood milling: Chip production by slabber

SAM : Science Arts et Métiers

Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTechresearchers and makes it freely available over the web where possible.This is an author-deposited version published in: http://sam.ensam.euHandle ID: .http://hdl.handle.net/10985/8497To cite this version :Renaud PFEIFFER, Robert COLLET, Louis DENAUD, Guillaume FROMENTIN, PhilippeLORONG - Analysis and modeling of green wood milling: Chip production by slabber - In:Congrès Français de la Mécanique 21, France, 2013-08-30 - CFM 21 - 2013Any correspondence concerning this service should be sent to the repositoryAdministrator : archiveouverte@ensam.eu21e`me Congre`s Franc¸ais de Me´canique Bordeaux, 26 au 30 aouˆt 2013Analysis and modeling of green wood milling:Chip production by slabber.R. Pfeiffera, R. Colleta, L. Denauda, G. Fromentina , P. Lorongba. Arts et Me´tiers ParisTech, LaBoMaP (EA3633), 71250 Clunyb. Arts et Metiers ParisTech, PIMM (UMR CNRS 8006), 75013 ParisRe´sume´ :En scierie, les grumes sont surface´es a` l’aide de teˆtes de fraisage (slabbers). Les copeaux fragmente´s is-sus de cette ope´ration sont valorise´s principalement dans les industries de paˆte a` papier et de panneauxde particules. Le rendement de ces industries de´pend en partie de la dispersion de la granulome´trie descopeaux. La maˆıtrise de cette dispersion n’est pas une chose aise´e car elle est fortement de´pendante desconditions de coupe et de la variabilite´ du mate´riau. Cette e´tude vise a` mieux comprendre et pre´direla fragmentation des copeaux. Elle de´bute par une description de´taille´e de la cine´matique de coupeainsi que l’interaction outil-matie`re. Ensuite, le phe´nome`ne de formation du copeau a pu eˆtre e´tudie´a` l’aide d’essais expe´rimentaux en conditions dynamiques. Ces essais ont e´te´ re´alise´s sur un pendule(Vc = 400 m/min), instrumente´ avec une platine pie´zo-e´lectrique et une came´ra rapide. Les re´sultatsont permis de valider un grand nombre de phe´nome`nes observe´s en quasi-statique.Abstract :During the primary transformation of wood, logs are faced with slabber heads. Chips produced are rawmaterials for pulp paper and particleboard industries. Efficiency of these industries is partly due to par-ticle size distribution. Command of this distribution is no easy matter because of great dependence oncutting conditions and variability in material. This study aimed a better understanding and predictionof chip fragmentation. It starts with a detailed description of cutting kinematic and interaction betweenknife and log. This leads to the numerical development of a generic slabber head. Chip fragmentationphenomena were studied through experiments in dynamic conditions. These experiments were carriedout thanks to a pendulum (Vc = 400 m/min). It was instrumented with piezoelectric force sensors andhigh speed camera. Obtained results agreed very well with previous quasi-static experiments.Mots clefs : Green wood ; wood chip ; slabber1 IntroductionThe aim of sawmills consists in promoting the maximal wood volume from logs in primary transforma-tion. After cross cutting and debarking, logs are squared by slabber heads. During this operation, upto 30% of logs initial volume is reduced in chips. Produced chips are mainly used as raw materials inpulp industries for paper and fiberboards. But using these chips as energy source is another importantoutlet. Defibration process represents the heart of pulp industry. It can be mechanical, chemical orboth. Chip size distribution affects directly the efficiency of this process [6]. For example, in chemicaldefibration, cooking time depends on lignin percentage in wood. Lignin is decomposed by liquor. Inalkaline conditions, liquor uniformly penetrates the chip. So chip thickness will determine the cookingtime [13]. However, unlike chip thickness, chip length and width can be controlled by slabber kinematicparameters. That is why determining the influent parameters on chip thickness is required.This issue can be studied with two points of view. The first one is built on macroscopic considerations.In order to reproduce real conditions, industrial material is used for chipping experiments with full121e`me Congre`s Franc¸ais de Me´canique Bordeaux, 26 au 30 aouˆt 2013logs at high cutting speed (Vc ' 3600 m/min). Tested parameters are cut kinematic, tool geome-try, log positioning and log parameters. Chips produced are screened and observations are done onsize distribution [10, 11, 12, 14] (Fig 1a). The second point of view concerns mesoscopic characteris-tics. Chipping experiments on wood specimens are carried out on specific apparatus in quasi staticconditions (Vc ' 60 mm/min). Tested parameters are the same as in the macroscopic process. Closeattention is paid on area near cutting edge. Chip size distribution, cutting forces, failure modes, strainand stress fields are analyzed in order to understand chipping phenomena. [3, 8, 16, 17] (Fig 1b).(a) Chipping with a slabber head [12] (b) Chipping with Instron testing machine [8]Figure 1 – Experimental devicesOur chip fragmentation analysis starts with a better understanding of cutting kinematic of a slabberhead and of the interactions between knifes and log. Fragmentation phenomena are studied experi-mentally in a second step in dynamic conditions (Vc = 400 m/min). Influent parameters must beidentified in regards to material variability and dynamic behavior of cellular materials [4].This paper will focus only on chip fragmentation analysis.2 Material and methodIn order to get a better physical understanding of the chipping process, we have explored two axis :– Geometric and kinematic studies to correctly define the working context and size of the expe-rimental assembly.– Chip fragmentation experiments in dynamic conditions.2.1 Geometric and kinematic studyA slabber head is a conical milling cutter with special device for finishing (saw blade or finishingknifes). Slabber heads with split knifes like CT700 (Fig 2a) are simple and highly distributed. Theywere used to develop a generic and parameterizable slabber head on Mathematica R© software. Programoutputs consist in animation of cutting kinematic, cutting load, working angles and grain direction(GD) variation during cutting.In order to agree with machining lexicon and to draw easy parallels with experimental devices, toolangles were normalized [1]. The following parameters were introduced (Fig 2b) :Kinematic : Cutting speed Vc, feed fz and cant.Log : Minimal log radius Rlogmin, log tape LogTape, vertical distance between the carriage and theslabber head axis Hcarriage.Slabber head : Head diameter RHeadmin, number of knifes, number of splits, knife length Lknife,tool cutting edge angle κr, tool cutting edge inclination λs, normal rake angle γn, normal wedgeangle βn, normal clearance angle αn.An example of result obtained by this geometric approach is given in section 3.1.221e`me Congre`s Franc¸ais de Me´canique Bordeaux, 26 au 30 aouˆt 2013(a) Slabber CT700 (LBL)Z21Z31 Z12Z32Z22Z13Z23Z33RHeadminWRankZ11RLogminHCarriageCant/2VcVfLog TapeκrλsLKnifeY YZ X(b) Slabber scheme with parameters used in the programFigure 2 – Exemple of a slabber head2.2 Chip fragmentation experimentsChipping experiments were carried out on a Chardin’s pendulum (Fig 3a). It was used to obtaininstrumented orthogonal cutting experiments to characterize cutting forces for dry wood [5]. Thependulum’s arm is 1.2 m long and has a weight of 36 kg. Available kinematic energy is 756 J for amaximum cutting speed Vc of 400 m/min. Specimen holder at the pendulum arm end was 140mmlong. Lexicon of orthogonal cutting was used (f the feed in mm and b the cutting width in mm).According to [7], the delivered energy is high enough to cut chips with f = 30 mm, b = 30 mm on acutting length of 140 mm.Tool holder was designed and machined at LaBoMaP in order to use an industrial knife. Normal rakeangle is set to γn = 45˚ , normal clearance angle to αn = 5˚ and normal wedge angle to βn = 40˚ . Thetool holder is fixed on a piezoelectric force transducer Kistler 9257A (Fig 3b). Amplifier Kistler 5019A,acquisition cards Kistler 9215 and 9234 and software Dasylab 11 record cutting forces. High speedcamera Phantom v9.1 (Maximal resolution at 2000 frames/s, 800*1000 pixels. Exposure time : 6 µs)records cutting films.(a) Chardin’s pendulum (b) Instrumented tool holder (c) Preliminary results(Beech f = 20 mm, b = 20 mm)Figure 3 – Chipping experiments materialWe setted an experimental design and used the following parameters : feed (f = 6, 10, 14 mm), cuttingdepth (b = 6, 10, 14 mm) and grain direction (GD = 70, 90, 110˚ ). We also selected two species :beech for its homogeneity and douglas fir known for its heterogeneity and bad machinability. MoistureContent (MC) is controlled after experiments by double weight technique. Each set of parameters wasrepeated 5 times. Specimens were machined from fresh beech and douglas fir slabs and put into afridge to limit MC decrease.Preliminary experiments showed higher energy consuming than predicted. Chardin’s pendulum wasnot able to cut wood section of 400 mm2(Fig 3c).321e`me Congre`s Franc¸ais de Me´canique Bordeaux, 26 au 30 aouˆt 20133 Results and discussion3.1 Geometrical resultsThe following parameters were implemented into the program : RHeadmin = 320 mm, Lknife = 60 mm,κR = 45˚ , λS = 0˚ , Hcarriage = 300 mm, Rlogmin = 350 mm, LogTape = 1%, fz = 28 mm, N = 550tr/min, Cant = 50 0mm, γn = 45˚ , βn = 40˚ , αn = 5˚ . We were able to observe cutting kinematicas well as interaction of each knife with the material. The cutting load (section normal to knife pathat cutting edge) was computed at different positions of knifes (Fig 4a). Results of cutting loads werevalidated with a geometrical model on Catia R© software. Differences between these two models are lessthan 5% and are due to circular knife path on Catia R© instead of cycloidal. Due to large feed, cuttingand clearance normal working angles could diverge up to 4˚ with respect to tool angles. Grain directionwas defined as the angle between cutting plane and the longitudinal fibers direction. It decreased quasilinearly during the cut (Fig 4b), starting at 110˚ when knife 2 rank 1 (Z21 on fig 2b) entered intothe wood and finishing at 44˚ . Because of this large evolution, the grain direction was consideredas a parameter during the experimental part. A lack of knowledge and relevance of specific cuttingpressure Kc or even cutting law depending on grain orientation prevents cutting forces computationfrom cutting load.(a) Cutting kinematic (b) Grain direction functions of time for Z21 (Figure 2b)Figure 4 – Results of generic slabber head program3.2 Experimental resultsFragmentation occurs for beech and douglas fir if grain direction is higher than 90˚ (Fig 5a and 5b).Chipping phenomena agree with observations published by McKenzie in [15] (Fig 6). First of all, thecutting edge bends wood fibers (Fig 6a). This bending is due to cell wall buckling. Then, when woodcell are collapsed, fibers are sliced (Fig 6b). The tool follows its cutting motion. Its face induced shearstress on the chip. When stress is higher than shear strength, shearing between fibers occurs, whichejects free water (Fig 6c). This water ejection occurs only when MC is higher than 30%. When thegrain direction is lower than 90˚ , big wood particles are teared by tension on fibers (Fig 5c). Chipwood cells are compressed and free water is ejected. We also observed another cutting phenomenon :shearing between growing rings on douglas fir. It appears only when specimen include few growingring. We assume that shearing between growing rings need less energy than shearing between fibers.So a limit ratio f/b is needed to get a homogeneous material to produce chips.As it could be observed in quasi-static cutting tests [3, 8, 17], average chip thickness is proportionalto the feed and independent of cutting depth. With the same experimental parameters, douglas firchips remain bigger than beech chips. This can be linked among others to the higher density of beech(ρbeech ' 0.7, ρdouglas ' 0.45) which induces higher rigidity.Although specimens were machined from the same slabs at the same time and experiments carried outin consecutive days, large variations on MC appeared and could be measured only after experiments421e`me Congre`s Franc¸ais de Me´canique Bordeaux, 26 au 30 aouˆt 2013(a) Cutting of beech withGD = 110˚ , MC = 66%(b) Cutting of douglas withGD = 90˚ , MC = 34%(c) Cutting of beech withGD = 70˚ , MC = 76%Figure 5 – High speed chipping, Vc = 400 m/min, Frame rate = 2 kHz, b = 10 mm, f = 10 mm.(a) Fiber bending (b) Fiber slicing (c) Shearing and freewater ejectionFigure 6 – Chip fragmentation mechanism(20 to 60% for douglas fir and 30 to 90% for beech). This can be explained by the fast drying of thethinest specimens (a couple of hours).Motion of Chardin’s pendulum induces a grain direction variation of 7˚ during the cutting. Study ofchip thickness evolution during the cutting on high speed film shows that grain direction evolutionis negligible at this scale. As the pendulum falls freely, Vc decreases about 20% during the cutting.Measurement of chip thickness variation during cutting shows no influence of speed decrease at thisscale.Average cutting forces measurements were done with piezoelectric forces transducers. However, chip-ping frequency was higher than transducers bandwidth. As a consequence, we could not confirm resultsof [15] and [17]. The obtained signals were close to results of [9] with appearance of peaks correspondingto chipping frequencies.4 Conclusion and perspectivesPulp industry needs to control chips size distribution to improve efficiency. To get a better understan-ding of the green wood chipping process in dynamic conditions, two axis were explored.A generic parameterizable slabber head was developed to observe the influence of geometric andkinematic parameters on cutting load and working angles. An experimental device was sized withthese results and used in dynamic chipping experiments. Results from experimental design agree withthe ones from quasi-static conditions. Cutting films allow us to observe ejection of free water duringchip fragmentation. Other cutting phenomena were observed like shearing between growing circles.521e`me Congre`s Franc¸ais de Me´canique Bordeaux, 26 au 30 aouˆt 2013Following works will improve our methodology. A new experimental design must be set to find otherinfluent parameters on chip thickness. New force transducer with higher bandwidth should be usedand coupled to high speed camera. Simulate chip fragmentation with Discrete Element Method [2]will be used to predict and understand cutting phenomena.AcknowledgementsThis work was carried out at LaBoMaP at Arts et Me´tiers ParisTech Cluny. We acknowledge MathieuMartin, LE2I lecturer, for his technical support in high speed motions and LaBoMaP technicians fortheir availability and advice.Re´fe´rences[1] AFNOR 1993 Grandeurs de base pour la coupe et la rectification. Norme NF ISO 3002-1[2] Andre´ Damien 2012 Mode´lisation par e´le´ments discrets des phases d’e´bauche et de doucissage dela silice. Universite´ de Bordeaux PhD Thesis[3] Buchanan J.G. and Duchnicki T.S. 1963 Some Experiments in Low-Speed Chipping. Pulp andPaper Magazine of Canada 5 May p. 235-245[4] Chakravarty U.K. 2010 An investigation on the dynamic response of polymeric, metallic, andbiomaterial foams. Composite structures 92 10 Sep p. 2339-2344[5] Eyma Florent 2002 Caracte´risation des efforts de coupe de diffe´rentes essences de bois a` l’aide deleurs parame`tres me´caniques. Universite´ Henry Poincare´, Nancy 1 PhD Thesis[6] Felber, G. and Lackner R. 2005 Optimization of the production process of sawmill chips for thepulp and paper industry. Proceding IWMS 17 p. 225-240[7] Goli G., Fioravanti M., Marchal R., Uzielli L., Busoni S. 2010 Up-milling and down-milling woodwith different grain orientations - The cutting forces behaviour. European journal of wood and woodproducts 68 4 Nov p. 385-395[8] Hellstro¨m L.M. 2008 A Method for Experimental Investigation of the Wood Chipping Process.Nordic Pulp and Paper Research Journal 23 3, p. 339-342[9] Hellstro¨m, L.M., Gradin P. A., Gulliksson M., Carlberg T. 2008 A Laboratory Wood Chipper forChipping Under Realistic Conditions Experimental mechanics 51 8, p. 1309-1316[10] Hernandez R.E. and Quirion B. 1993 Effect of a chipper-canter knife clamp on the quality ofchips produced from black spruce. Forest Products Journal 43 9, p. 8-14[11] Hernandez R.E. and Boulanger J. 1997 Effect of the rotation speed on the size distribution ofblack spruce pulp chips produced by a chipper-canter. Forest Products Journal 47, 4, p. 43-49[12] Houziaux Gaspard 2008 Analyse de la fragmentation des plaquettes par Slabber. Arts et MetiersParisTech Cluny Master Thesis[13] Lachenal Dominique Advance Courses on Alkaline Pulping. INP Pagora[14] Laganie`re Benoit 2004 Effect of canter head rotation speed, log feed speed and vertical positionof logs on lumber surface and chip quality. Forintek Canada Corp. Technical repport[15] McKenzie W.M. 1960 Fundamental analysis of the wood cutting process. University of MichiganPhD Thesis[16] Twaddle A. 1997 The influence of species, chip length, and ring orientation on chip thickness.Tappi Journal 80 6, p. 123-131[17] Uhmeier A. 1995 Some fundametal aspects of wood chipping. Tappi 78 10 p. 79-86[18] Uhmeier A. and Persson K. 1997 Numerical analysis of wood chipping. Holzforschung 51 1 p.83-906

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Analysis and modeling of green wood milling: Chip production by slabber

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