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Cristovao, Luis
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Publications (10 of 20) Show all publications
Guo, X., Li, R., Cao, P., Ekevad, M., Cristovao, L., Marklund, B. & Grönlund, A. (2015). Effect of average chip thickness and cutting speed on cutting forces and surface roughness during peripheral up milling of wood flour/polyvenyl chloride composite (ed.). Wood research, 60(1), 147-156
Open this publication in new window or tab >>Effect of average chip thickness and cutting speed on cutting forces and surface roughness during peripheral up milling of wood flour/polyvenyl chloride composite
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2015 (English)In: Wood research, ISSN 1336-4561, Vol. 60, no 1, p. 147-156Article in journal (Refereed) Published
Abstract [en]

Wood flour/polyvinyl chloride composite (WFPVCC) is a kind of composite material that, over the years, is becoming more popular in constructions applications. In this work, cutting forces and machined surface roughness were studied during peripheral up milling of WFPVCC under different average chip thickness which was obtained by adjusting rotation speed and feed rate at both high and low speed cutting conditions. The results indicated that cutting forces components, parallel force (F-x) and normal force (F-y) greatly varied during the cutting process. Maximum F-x, maximum F-y and surface roughness increased with the increase of average chip thickness. Maximum F-x and maximum F-y at high speed cutting conditions were lower than that at low speed cutting conditions at a same average chip thickness. The machined surface roughness at high speed cutting conditions was better than that at low speed cutting conditions at a same average chip thickness. When meeting the requirement of certain surface roughness, higher cutting speed can allow higher chip thickness and then decrease the tool wear than lower speed cutting condition. Maximum negative F-y had great impact in machined surface roughness. Machined surface roughness increased with the increase of maximum negative F-y. Thus, high speed cutting conditions not only increase the machining productivity, but also decrease machined surface roughness during the peripheral up milling of WFPVCC

National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-8970 (URN)7863da3d-6e30-4ff2-9909-941a81f4f331 (Local ID)7863da3d-6e30-4ff2-9909-941a81f4f331 (Archive number)7863da3d-6e30-4ff2-9909-941a81f4f331 (OAI)
Note

Validerad; 2015; Nivå 2; 20150410 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Ekevad, M., Cristovao, L., Grönlund, A. & Öhman, M. (2014). Geometry of kerf when curve sawing with a circular rip-saw (ed.). Paper presented at . European Journal of Wood and Wood Products, 72(6), 809-814
Open this publication in new window or tab >>Geometry of kerf when curve sawing with a circular rip-saw
2014 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 72, no 6, p. 809-814Article in journal (Refereed) Published
Abstract [en]

Rip-sawing following the curvature of a crooked log means advantages for yield. However, the possibility to saw in a narrow curve with a circular saw blade is limited because of the inherently flat geometry of circular saw blades. For a double arbour circular saw the situation is even more problematic because the two blades have a certain overlap and thus, the two arbours are not positioned in the same horizontal position. In this study, a theoretical geometrical study of the creation of a kerf with a single circular saw blade and with a double arbour circular saw with two saw blades was examined. Results for stiff saw blades show that the kerfs become in general curved and inclined (tilted) in the vertical direction and also that the width of the kerfs for double arbour saws becomes wider at the top and bottom of the cant than in the middle. Additionally, the sawn boards obtain varying thickness along their width because of the varying kerf width. A comparison with experimental thickness data from four test sawings at a sawmill indicates that the theoretical results are valid and that curve sawn boards become thinner than straight sawn boards.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-2796 (URN)10.1007/s00107-014-0832-6 (DOI)000343877800011 ()2-s2.0-84920710494 (Scopus ID)07eca113-84d7-496c-b1a7-08a88b00e9e3 (Local ID)07eca113-84d7-496c-b1a7-08a88b00e9e3 (Archive number)07eca113-84d7-496c-b1a7-08a88b00e9e3 (OAI)
Note
Validerad; 2014; 20140806 (matse)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Ah Shenga, P., Cristovao, L. & Broman, O. (2013). A review of Mozambican wood exploitation: map of the processing chain (ed.). In: (Ed.), Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan. Paper presented at International Wood Machining Seminar : 04/08/2013 - 07/08/2013 (pp. 293-301).
Open this publication in new window or tab >>A review of Mozambican wood exploitation: map of the processing chain
2013 (English)In: Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan, 2013, p. 293-301Conference paper, Published paper (Other academic)
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-37624 (URN)bb18932b-4467-4bfc-990c-fbf94fea646b (Local ID)978-4-9903467-9-9 (ISBN)bb18932b-4467-4bfc-990c-fbf94fea646b (Archive number)bb18932b-4467-4bfc-990c-fbf94fea646b (OAI)
Conference
International Wood Machining Seminar : 04/08/2013 - 07/08/2013
Note

Godkänd; 2013; 20130819 (pedant)

Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
Ekevad, M., Cristovao, L., Grönlund, A. & Öhman, M. (2013). Geometry of Kerf when Curve Sawing with a Circular Rip-Saw (ed.). In: (Ed.), (Ed.), Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan. Paper presented at International Wood Machining Seminar : 04/08/2013 - 07/08/2013 (pp. 206-213).
Open this publication in new window or tab >>Geometry of Kerf when Curve Sawing with a Circular Rip-Saw
2013 (English)In: Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan, 2013, p. 206-213Conference paper, Published paper (Refereed)
Abstract [en]

Rip-sawing following the curvature of a crooked log means advantages for yield. However, the possibility to saw in a narrow curve with a circular saw blade is limited because of the inherent flat geometry of circular sawblades. For a double arbour circular saw the situation is even more problematic because the two blades have a certain overlap and thus the two arbours are not positioned in the same horizontal position. In this study a theoretical geometrical study of the creation of a kerf with a single circular sawblade and with a double arbour circular saw with two sawblades is viewed upon. Input parameters in the study for the double arbour saw are blade diameter, overlap, margin between blades, cant height, curve centre horizontal position and curve radius. Output is the geometry of the kerf that is cut by the teeth. Theoretical results for stiff saw blades show that the kerfs become in general curved and inclined (tilted) in the vertical direction and also that the width of the kerfs for double arbour saws become wider at the top and bottom of the cant than in the middle. Sawing takes place not only in the front part of the blades but also on the back of the blades (back sawing). Parts of the cutting edges of the teeth are cutting when back sawing and not the whole of the width of the teeth. A result is that boards that are cut out of the cant get varying thickness along their width because of the varying kerf width. A comparison with experimental thickness data from four test sawings at a sawmill indicates that the theoretical results are valid and that curve sawn boards become thinner than straight sawn boards.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-30595 (URN)4740d49b-4734-4ae8-a89a-91eb5d10b38d (Local ID)978-4-9903467-9-9 (ISBN)4740d49b-4734-4ae8-a89a-91eb5d10b38d (Archive number)4740d49b-4734-4ae8-a89a-91eb5d10b38d (OAI)
Conference
International Wood Machining Seminar : 04/08/2013 - 07/08/2013
Note
Godkänd; 2013; 20130813 (luicri)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Cristovao, L., Ekevad, M. & Grönlund, A. (2013). Industrial sawing of Pinus Sylvestris L.: power consumption (ed.). In: (Ed.), (Ed.), Proceedings of the 21th International Wood Machining Seminar: August 4th – 7th, 2013, Tsukuba International Congress Center, Japan. Paper presented at International Wood Machining Seminar : 04/08/2013 - 07/08/2013 (pp. 189-198).
Open this publication in new window or tab >>Industrial sawing of Pinus Sylvestris L.: power consumption
2013 (English)In: Proceedings of the 21th International Wood Machining Seminar: August 4th – 7th, 2013, Tsukuba International Congress Center, Japan, 2013, p. 189-198Conference paper, Published paper (Other academic)
Abstract [en]

Wood industry continues to strive to reduce production cost and increase productivity to maintain competiveness. Hence, knowledge of the effect of wood cutting parameters on power consumption would enable increase energy efficiency, thus, reduce operating costs and enhance profitability. Also measurement of power consumption gives knowledge of other specifics such as: tool edge wear, occurrence of catastrophic failures and other parameters which affect the quality of the sawn boards and the momentary efficiency of the break-down process. In this study, power consumption during sawing of Pinus sylvestris L. using double arbour circular saw was investigated. Both climb-sawing and counter-sawing were considered. The experiments were carried out, under normal production, in two Swedish sawmills. The relationship between cutting parameters and calculated power consumption is discussed. The experimental power consumption increased 11-35% during an 8 hour shift mainly due to increase of the tooth radius. Further, this study also showed the climb-sawing had higher power consumption than counter-sawing.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-34831 (URN)922a5ce1-9f2f-4b42-83bd-cbf51def50c1 (Local ID)978-4-9903467-9-9 (ISBN)922a5ce1-9f2f-4b42-83bd-cbf51def50c1 (Archive number)922a5ce1-9f2f-4b42-83bd-cbf51def50c1 (OAI)
Conference
International Wood Machining Seminar : 04/08/2013 - 07/08/2013
Note
Godkänd; 2013; 20130812 (luicri)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Cristovao, L., Ekevad, M. & Grönlund, A. (2013). Industrial Sawing of Pinus Sylvestris L.: Power consumption (ed.). Paper presented at . BioResources, 8(4), 6044-6053
Open this publication in new window or tab >>Industrial Sawing of Pinus Sylvestris L.: Power consumption
2013 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 8, no 4, p. 6044-6053Article in journal (Refereed) Published
Abstract [en]

The wood industry continues to strive to reduce production costs and increase productivity to remain competitive. Knowledge of the effect of wood cutting parameters on power consumption could increase energy efficiency, reducing operating costs and increasing profitability. Measuring power consumption also provides information about other variables, such as tool edge wear, occurrence of catastrophic failures, and other parameters that affect the quality of the sawn boards and the momentary efficiency of the breakdown process. In this work, power consumption during sawing of Pinus sylvestris L. using a double arbor circular saw was investigated. Both climb-sawing and counter-sawing were considered. The experiments were carried out under normal production circumstances in two Swedish sawmills. The relationship between cutting parameters and theoretical power consumption was investigated. The experimental power consumption increased by 11 to 35% during an 8-h shift, mainly due to an increase in the tooth radius. Additionally, this study showed that climb-sawing consumed more power than counter-sawing.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-4688 (URN)2ab3c4e7-53e4-4b74-afd4-8cecc759793f (Local ID)2ab3c4e7-53e4-4b74-afd4-8cecc759793f (Archive number)2ab3c4e7-53e4-4b74-afd4-8cecc759793f (OAI)
Note
Validerad; 2013; 20131008 (luicri)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Cristovao, L. (2013). Machining properties of wood: Tool wear, cutting force and tensioning of blades (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Machining properties of wood: Tool wear, cutting force and tensioning of blades
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cutting processes, in general, and wood cutting processes, in particular, are complex to explain and describe with many influencing factors. Wood, in contrast to man-made fabricated materials, is not a homogenous and distinct material, but a multifaceted and nonhomogeneous biological material. A fundamental understanding of wood cutting processes and the machining properties of wood can be obtained by investigating the interaction of wood properties, cutting tools and machining parameters. Such an understanding provides possibilities for improving product quality, increasing production efficiency, or otherwise improving the machining processes. The aim of this thesis was to find ways of improving the machining properties of some wood species, focusing on tool wear, cutting forces and the tensioning of circular sawblades. The studied wood species were five Mozambican tropical species, namely: Swartzia Madagascariensis (ironwood); Pseudolachnostylis maprounaefolia (ntholo); Sterculia appendiculata (metil); Acacia nigrescens (namuno); Pericopsis angolensis (muanga) and two main Swedish wood species: Pinus sylvestris L. (Scots pine); and Picea abies (L.) Karst. (Norway spruce). A series of experimental tests were conducted to determine the suitability of different cutting tool materials when machining these wood species. Machining tropical hardwood and Swedish frozen wood under winter conditions is still a challenge when it comes to the choice of which cutting tool material to use. Tool wear was used as a criterion to evaluate the performance of the cutting tool materials. Additionally, the relationship between tool wear and some chemical and physical properties for Mozambican tropical wood species was analysed. Different wear mechanisms were identified using a scanning electron microscope. It was concluded that tool hardness alone was not the only factor affecting tool wear; a certain amount of tool toughness was also needed to obtain low tool wear. The predominant wearing mechanisms for the tropical wood species tested were abrasion and edge-chipping. Furthermore, tropical hardwood species were subjected to cutting force tests. A standard single saw tooth, mounted on a piezoelectric load cell, was used to evaluate cutting forces. The theoretical approach used for the prediction of the main cutting forces was based on surface response methodology. Among the studied variables, chip thickness and cutting direction had the greatest effect on the main cutting force level, while wood density, moisture and rake angle had the least effect.Power consumption using double arbour circular saw machines was investigated. The experiments were carried out, under normal production, in two Swedish sawmills. The climb-sawing model in both sawmills was able to estimate the power consumption better than the counter-sawing model. Climb-sawing had higher power consumption than counter-sawing. The lowest power consumption was found using a higher overlap between circular sawblades. Finally, experimental and theoretical models to improve circular sawblade dynamic lateral stability were developed. Different methods for monitoring flatness and tensioning in circular sawblades for wood cutting were discussed. Additionally, the effects of the magnitude of the roller load, number of grooves and groove positions were tested. The roll-tensioning effects were evaluated by measuring the shift in natural frequencies of several vibration modes. Natural frequencies obtained with the finite element method were in good agreement with the experimental test results. The magnitude of the roller load, number of grooves, and groove positions all affected the natural frequencies.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2013. p. 44
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-26091 (URN)c98ad54d-9908-4da2-b762-0c0aaad0c240 (Local ID)978-91-7439-779-6 (ISBN)978-91-7439-780-2 (ISBN)c98ad54d-9908-4da2-b762-0c0aaad0c240 (Archive number)c98ad54d-9908-4da2-b762-0c0aaad0c240 (OAI)
Note
Godkänd; 2013; 20131108 (luicri); Tillkännagivande disputation 2013-11-18 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Luís Cristóvão Ämne: Träteknik/Wood Technology Avhandling: Machining Properties of Wood: Tool Wear, Cutting Force and Tensioning of Blades Opponent: Professor Frieder Scholz, Hochschule für angewandte Wissenschaften, Fachhochschule Rosenheim, Tyskland Ordförande: Docent Mats Ekevad, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Måndag den 9 december 2013, kl 10.00 Plats: Hörsal A, Campus Skellefteå, Luleå tekniska universitetAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-24Bibliographically approved
Ekevad, M., Cristovao, L. & Marklund, B. (2012). Lateral cutting forces for different tooth geometries and cutting directions (ed.). Paper presented at International Wood Machining Seminar : 07/06/2011 - 10/06/2011. Wood Material Science & Engineering, 7(3), 126-133
Open this publication in new window or tab >>Lateral cutting forces for different tooth geometries and cutting directions
2012 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 126-133Article in journal (Refereed) Published
Abstract [en]

Lateral (sideways) cutting forces were measured for 6 different tooth geometries when cutting green spruce and pine heartwood. The teeth were intended for use on circular saw blades for the rip sawing of logs. The 6 tooth geometries were designated straight, pointed, bevelled, rounded, trapezoidal and hollowed out. Cutting speed was 15 m/s, feed per tooth was 0.3 mm and the cutting directions were 90°–90° (rip sawing) and 90°–0° (milling), with two different variants of growth ring angles for each direction. The tools were tested in sharp conditions, in dull conditions and in a dull condition with a corner broken off. All lateral forces were small when cutting with sharp teeth, except for the rounded and bevelled teeth. Lateral forces increased with wear, except for a period of initial wear where the lateral forces were reduced. High wear resulted in greater lateral forces, most probably due to unsymmetrical wear. Growth ring direction did not generally affect lateral forces. The teeth with acute corners, which were the straight and hollowed out tooth, were most sensitive to a broken off corner. The lateral forces in the cases of wood cutting at 90°–90° increased less with wear compared to the 90°–0° cases.

National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-32650 (URN)10.1080/17480272.2012.662699 (DOI)2-s2.0-84866855032 (Scopus ID)734f1613-7514-4d5d-9393-8de34d000886 (Local ID)734f1613-7514-4d5d-9393-8de34d000886 (Archive number)734f1613-7514-4d5d-9393-8de34d000886 (OAI)
Conference
International Wood Machining Seminar : 07/06/2011 - 10/06/2011
Note
Validerad; 2012; 20120607 (matse); Konferensartikel i tidskriftAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-07-10Bibliographically approved
Cristovao, L., Broman, O., Grönlund, A., Ekevad, M. & Sitoe, R. (2012). Main cutting force models for two species of tropical wood (ed.). Paper presented at International Wood Machining Seminar : 07/06/2011 - 10/06/2011. Wood Material Science & Engineering, 7(3), 143-149
Open this publication in new window or tab >>Main cutting force models for two species of tropical wood
Show others...
2012 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 143-149Article in journal (Refereed) Published
Abstract [en]

The aim of the study was to evaluate the main cutting force for two species of tropical Mozambican wood and to develop predictive models. Cutting these hardwoods is difficult. Determination of cutting parameters is required to optimize cutting processes, machines and tools in the cutting operations. This determination would enable the forestry and wood sector to achieve higher financial results. Samples of a lesser-known wood species Pseudolachnostylis maprounaefolia (ntholo) and a well-known wood species Swartzia madagascariensis (ironwood) were machined in a test apparatus. A standard single saw tooth mounted on a piezoelectric load cell was used to evaluate the main cutting force. Data were captured using an A/D converter integrated with National Instruments LabVIEW software. The measured signals were recorded at a sampling frequency of 25 kHz. The experimental set-up used response surface methodology for developing predictive models. The experimental clearly determined the relationship between the main cutting force and edge radius, wood density, rake angle, chip thickness, moisture content (MC) and cutting direction (CD). Among the studied variables, chip thickness and CD had the highest effect on the main cutting force level while wood density, MC and rake angle had the lowest effect.

Keywords
Engineering mechanics - Other engineering mechanics, Cutting force, Pseudolachnostylis maprounaefolia, Swartzia madagascariensis, Teknisk mekanik - Övrig teknisk mekanik
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-34845 (URN)10.1080/17480272.2012.662996 (DOI)2-s2.0-84866854152 (Scopus ID)9255db02-0236-4f8e-a988-62b2f0cab656 (Local ID)9255db02-0236-4f8e-a988-62b2f0cab656 (Archive number)9255db02-0236-4f8e-a988-62b2f0cab656 (OAI)
Conference
International Wood Machining Seminar : 07/06/2011 - 10/06/2011
Note
Validerad; 2012; 20120418 (ysko); Konferensartikel i tidskriftAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-07-10Bibliographically approved
Cristovao, L., Ekevad, M. & Grönlund, A. (2012). Natural frequencies of roll-tensioned circular sawblades: Effects of roller loads, number of grooves and groove positions (ed.). Paper presented at . BioResources, 7(2), 2209-2219
Open this publication in new window or tab >>Natural frequencies of roll-tensioned circular sawblades: Effects of roller loads, number of grooves and groove positions
2012 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 7, no 2, p. 2209-2219Article in journal (Refereed) Published
National Category
Other Mechanical Engineering
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-15536 (URN)f110d569-94dc-4374-9f32-6ed5397a5d04 (Local ID)f110d569-94dc-4374-9f32-6ed5397a5d04 (Archive number)f110d569-94dc-4374-9f32-6ed5397a5d04 (OAI)
Note
Validerad; 2012; 20120328 (luicri)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
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