Monitoring Single Tooth Cutting Forces in Wood Bandsawing

• For economic and environmental benefits, sawmills can reduce their waste by sawing with thinner bandsaw blades. When altering the cutting tooth geometry, it is vital to monitor the sawing process in realistic wood conditions such as frozen (green), non-frozen (green) and dried. The fundamental way to monitor the sawing process is to analyse the cutting forces when single cutting teeth interact with the wood. The three cutting forces acting on a sawtooth are the main, normal, and lateral forces. The main force can be split into two: 1) cutting by the main edge and 2) cutting by the side edges (the side force). The objective of this thesis work was to examine the main, side and normal forces in different wood conditions while cutting with different tooth geometries. In sawing, it is desired for the main and side forces to be minimised, and the normal force should remain close to zero. Two abundant Scandinavian wood species were considered: Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in non-frozen, frozen and dried conditions. The heartwood and sapwood were tested separately for non-frozen and frozen wood. The altered tooth geometries were the cutting width, clearance, band thickness, and the radial and tangential clearance angles.The main force was approximately 75% lower for the narrowest cutting tooth of 1.6 mm compared to the reference 2.87 mm wide tooth used in the industry. Narrow cutting teeth could, however, result in faster tool wear and vibrations. The main force was higher in pine than spruce due to the higher density of pine. Frozen sapwood showed distinctly higher main forces. The radial and tangential clearance angles had a negligible effect on the main force. There was a slight reduction in the main force in frozen sapwood at high radial and tangential clearance angles of 6◦. In frozen sapwood, the normal force was highly negative and self-feeding was observed. The normal force was less negative for narrower cutting teeth and at high radial and tangential clearance angles of 6◦. The cutting width, clearance and radial and tangential clearance angles did not have a notable effect on the normal forces in the remaining wood conditions, and the forces remained close to zero. The elastic spring-back plays an important role in side cutting and can be as high as 4 mm. Frozen wood has less elastic spring-back and, therefore, less side cutting. The percentage of side cutting to the main force was between 55% - 75% for dried wood. Lower clearance and lower radial and tangential clearance angles resulted in more side cutting due to increased contact between the teeth and elastic spring-back.The results show that special consideration needs to be taken when sawing frozen sapwood in the winter. Furthermore, the side cutting force plays a larger role when the cutting width is reduced and in dried wood and needs to be studied in more detail to understand its impact on the cutting process better.v

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Annan maskinteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Other Mechanical Engineering (hsv//eng)

Nyckelord

Träteknik

Wood Science and Engineering

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