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SAWING STRATEGIES FOR TROPICAL HARDWOOD SPECIES: Simulation studies based on industrial conditions of Mozambique
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Luleå University of Technology.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The harvesting of Mozambique tropical hardwood species is considerable higher than the natural regrowth in the forest and the stock is decreasing drastically. Therefore, it is important to improve the material recovery when the wood is refined (i.e., in sawing and further refinement to products such as joineries, furniture etc.) to reduce the waste and to re-utilize efficiently the by-products to increase the added value. The wood processing industry is an important means to boost the industries in the rural areas and also to generate incomes for the local communities by creating jobs and business opportunities.

The majority of the logging that can be used for sawmilling in Mozambique is exported as roundwood due to the inability of companies to meet the product standards set for export and to generate profit. The lack of capabilities of the local sawmills to generate profit, also foments the illegal logging because of the higher price of roundwood for export which contributes to increase the number of unlicensed individuals in harvesting. This threatens the law enforcement and thus the degradation of the local wood industry. An alternative to increase the profit and empower the local community could be to export more refined wood products such as sawn timber, parquet, and veneer instead of the roundwood.

The objective of the work was to investigate alternative sawing strategies of tropical hardwood species that could increase the profitability of the Mozambique wood industry in general and at sawmill in particular. The subject was approached using a database of virtual logs and together with a sawing simulator. The thesis has two main focus areas: (1) creating the log database with the corresponding algorithms for sawing simulation, and (2) investigations of alternative sawing strategies.

The first focus was to build the database of surface-scanned logs and develop the algorithm for the saw simulation. The results are a database of 15 logs models describing the logs outer shape in which 10 jambirre (Millettia stuhlmannii Taub.) and 5 umbila (Pterocarpus angolensis DC.), and the algorithm for the sawing simulation. The algorithm use “brute force” i.e., determines all volume yields of sawn timber from the combination of all settings of log-positioning parameters (offset, skew and rotation) and selects the maximum value of volume yield. From simulation, using three sawing patterns (cant-sawing, through-and-through sawing and square-sawing) combined with two positioning parameters (offset and rotation) it was found that the sawing pattern has great impact on volume yield and that the square-sawing gave higher yield followed by through-and-through sawing pattern.

The second focus was on alternative sawing strategies; having in mind that the optimal volume yield is achieved by aid of computerized production systems and that these resources are not yet in use in Mozambique. Hence, the objective was to find the positioning parameters that can be set manually and improve the volume yield. The result have shown that the rotation is the most affecting parameter followed by offset and skew, and that the volume yield can decrease by between 7.7% and 12.5% from the optimal positioning when the logs are manually positioned with the knowledge about the optimal log position. In another study, using crook-up or horns-down positioning as alternative to the optimal positioning, the volume yield decreases by between 10% and 13% from the optimal positioning. By using bucked logs , the optimal volume yield increased by between 8% and 13% in relation to full lengths logs, and the volume yield of bucked logs when using crook up positioning decreases 2% in relation to optimal positioning of full length logs.

It is concluded that there is an unexploited value potential in the wood chain which can be reached using alternative positioning and modern measurement techniques and that the grading of wood will facilitate and improve the sawing process.

Place, publisher, year, edition, pages
Luleå University of Technology, 2016.
Keyword [en]
sawing strategies, tropical hardwood species, simulation, volume yield, log grading, umbila, jambirre.
National Category
Engineering and Technology
Research subject
Wood Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-38902ISBN: 978-91-7583-717-8ISBN: 978-91-7583-718-5 (pdf)OAI: oai:DiVA.org:ltu-38902DiVA: diva2:1033354
Public defence
2016-12-02, Hörsal A193, Forskargatan N 1, Skelleftea, 10:00 (English)
Opponent
Supervisors
Available from: 2016-10-12 Created: 2016-10-03 Last updated: 2016-11-16Bibliographically approved
List of papers
1. 3D Phase-shift Laser Scanning of Log Shape
Open this publication in new window or tab >>3D Phase-shift Laser Scanning of Log Shape
2014 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 9, no 4, 7593-7605 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a portable scanner to determine the 3D shape of logs was evaluated and compared with the measurement result of a computer tomography scanner. Focus was on the accuracy of the shape geometry representation. The objective is to find a feasible method to use for future data collection in Mozambique in order to build up a database of logs of tropical species for sawing simulations. The method chosen here was a 3D phase-shift laser scanner. Two logs, a birch log with bark and a Scots pine log without bark, were scanned, resulting in 450 cross sectional “images” of the pine log and 300 of the birch log. The areas of each point cloud cross section were calculated and compared to that of the corresponding computer tomography cross section. The average area difference between the two methods was 2.23% and 3.73%, with standard deviations of 1.54 and 0.91, for the Scots pine and birch logs, respectively. The differences in results between the two logs are discussed and had mainly to do with presence of bark and mantle surface evenness. Results show that the shape measurements derived from these methods were well correlated, which indicates the applicability of a 3D phase-shift laser scanning technology for gathering log data.

Keyword
Outer shape, Log measurement, 3D scanner, CT scanner, Information technology - Other information technology, Informationsteknik - Övrig informationsteknik
Research subject
Wood Technology; Wood Products Engineering
Identifiers
urn:nbn:se:ltu:diva-5940 (URN)421b96bb-ab34-4037-9af4-7557868effb8 (Local ID)421b96bb-ab34-4037-9af4-7557868effb8 (Archive number)421b96bb-ab34-4037-9af4-7557868effb8 (OAI)
Note
Validerad; 2014; 20141031 (pedant)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-10-06Bibliographically approved
2. Simulation of Tropical Hardwood Processing: Sawing Methods, Log Positioning, and Outer Shape
Open this publication in new window or tab >>Simulation of Tropical Hardwood Processing: Sawing Methods, Log Positioning, and Outer Shape
2015 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 10, no 4, 7640-7652 p.Article in journal (Refereed) Published
Abstract [en]

To increase understanding of breakdown strategies for Mozambican timber, simulations were carried out using different sawing patterns that can be alternatives to the low degree of refinement performed for export today. For the simulations, 3D models of 10 Jambirre and 5 Umbila logs were used. The log shape was described as a point cloud and was acquired by 3D-laser scanning of real logs. Three sawing patterns (cant-sawing, through-and-through sawing, and square-sawing) were studied in combination with the log positioning variables skew and rotation. The results showed that both positioning and choice of sawing pattern had a great influence on the volume yield. The results also showed that the log grade had an impact on the sawing pattern that should be used for a high volume yield. The volume yield could be increased by 3 percentage points by choosing alternative sawing patterns for fairly straight logs and by 6 percentage points for crooked logs, compared to the worst choice of sawing pattern.

Keyword
Simulation, Tropical hardwood processing, Sawing Methods, Log Positioning, Materials science - Other processing/assembly, Teknisk materialvetenskap - Övrig bearbetning/sammanfogning
Research subject
Wood Technology
Identifiers
urn:nbn:se:ltu:diva-14760 (URN)e2e93312-1e42-4e11-b23a-31002fb45f7e (Local ID)e2e93312-1e42-4e11-b23a-31002fb45f7e (Archive number)e2e93312-1e42-4e11-b23a-31002fb45f7e (OAI)
Note
Validerad; 2015; Nivå 2; 20150925 (pedant)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-10-06Bibliographically approved
3. The Effect of Log Position Accuracy on the Volume Yield in Sawmilling of Tropical Hardwood
Open this publication in new window or tab >>The Effect of Log Position Accuracy on the Volume Yield in Sawmilling of Tropical Hardwood
2016 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 11, no 4, 9560-9571 p.Article in journal (Refereed) Published
Abstract [en]

This study investigated the effect of the positioning of the log before sawing on the volume yield of sawn timber from tropical hardwood species. Three positioning parameters were studied, the offset, skew, and rotation, combined with two sawing patterns of cant-sawing and through-and-through sawing. A database consisting of two tropical hardwood species with very different outer shapes, jambirre (Millettia stuhllmannii Taub.) and umbila (Pterocarpus angolensis DC.), was used to simulate the sawing process. The result of the simulation revealed that, according to the combined effect of offset, skew, and rotation positioning, the positioning of the log before sawing is extremely important to achieve a high volume yield of sawn timber. The positioning parameter that has the highest effect on the volume yield is the rotation, and the variation in the volume yield associated with a deviation in the positioning can reduce the volume yield of sawn timber by between 7.7% and 12.5%.

Keyword
Log positioning error; Tropical species; Skew; Offset; Rotation
National Category
Other Mechanical Engineering
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-37010 (URN)10.15376/biores.11.4.9560-9571 (DOI)
Note

Validerad; 2016; Nivå 2; 2016-11-23 (andbra)

Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2016-11-30Bibliographically approved
4. A review of Mozambican wood exploitation: map of the processing chain
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, 293-301 p.Conference paper (Other academic)
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: 2016-10-06Bibliographically approved

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