WO2024167448A1

WO2024167448A1 - Chainsaw guide bar and method of manufacturing the same

Info

Publication number: WO2024167448A1
Application number: PCT/SE2024/050023
Authority: WO
Inventors: Christian LILIEGÅRD; Axel Jahn; Dirk Dittrich; Jens LIEBSCHER; Robert Drexler
Original assignee: Husqvarna Ab; Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2023-02-10
Filing date: 2024-01-12
Publication date: 2024-08-15

Abstract

A method of manufacturing a guide bar (18) for a handheld chainsaw (10) comprises: arranging a core plate (43) between first and second side plates (42, 44) to form a stacked sandwich structure (61 ) having a first side (40a) and a second side (40b); welding a first weld seam (46a) on the first side (40a), the first weld seam (46a) extending along a first weld line (48a) and penetrating the first side plate (42), the core plate (43), and into the second side plate (44); and welding a second weld seam (46b) on the second side (40b), along a second weld line (48b) offset from the first weld line (48a), and penetrating the second side plate (44), the core plate (43), and into the first side plate (42), both weld seams (46a, 46b) thereby joining the core plate (43) to each of the first and second side plates (42, 44).

Description

CHAINSAW GUIDE BAR AND METHOD OF MANUFACTURING THE SAME

Field of the invention

The present invention relates to a guide bar for guiding the saw chain of a handheld chainsaw, and to a method of manufacturing the same.

A handheld chainsaw comprises a moving saw chain, which is guided in a guide track along the periphery of a generally flat, elongate guide bar. Chainsaws are exposed to rough handling and high wear. For this reason, components of a chainsaw, including the guide bar, need to be rugged and robust. At the same time, the operation of a handheld chainsaw is physically demanding. Therefore, a conflicting requirement is that the chainsaw should be as light as possible.

US 11 ,230,028 B2 relates to a light-weight guide bar for a handheld chainsaw. There is however an incessant strive to increase the durability of the guide bar and to improve the work environment of the chainsaw operator.

It is an object of the present invention to solve, or at least mitigate, parts or all of the above mentioned problems. To this end, there is provided a method of manufacturing a guide bar for a handheld chainsaw, the method comprising: providing a first side plate, a second side plate and a core plate; arranging the core plate between the first and second side plates to form a stacked sandwich structure extending in a longitudinal direction along a guide bar plane and having a first side formed by an outer face of the first side plate and a second side formed by an outer face of the second side plate; welding a first weld seam on the first side, the first weld seam extending along a first weld line and penetrating the first side plate, the core plate, and into the second side plate, the first weld seam thereby joining the core plate to each of the first and second side plates; and welding a second weld seam on the second side, the second weld seam extending along a second weld line and penetrating the second side plate, the core plate, and into the first side plate, also the second weld seam thereby joining the core plate to each of the first and second side plates. By welding the stacked sandwich structure together via said first and second weld seams, each weld seam penetrating all three plates, from both the first side and the second side, the stress generated by the second weld seam will counteract the stress generated by the first weld seam, thereby reducing the stress-induced warp of the guide bar. Reduced warp reduces the wear on the saw chain and the guide bar. It also results in a more accurate shape and uniform width of the guide track along the guide bar, which reduces any sideways meandering tendencies of the chain motion, resulting in an improved user experience and a more precise cut. This may be of particular value especially for long guide bars, for example guide bars having a length of more than 43 cm (18-inch guide bars and above). The weld lines are defined as the centre lines of the respective weld seams. The weld seams may extend along their respective weld lines in an intermittent or continuous manner, wherein the latter is preferred in order to minimize stress concentrations at starts and stops of the respective welds, and to maximize the torsion resistance of the guide bar. Typically, the side plates and core plate may be made of various alloys of steel. According to embodiments, the first and second weld seams may be made by fullpenetration welding, i.e. welding to such a depth that the fused region of the first weld seam reaches all the way through the second side plate to the second side of the stacked sandwich structure, and the fused region of the second weld seam reaches all the way through the first side plate to the first side of the stacked sandwich structure. This even further reduces warp, since the fused region of each weld seam affects both sides of the guide bar to a more similar extent. The guide bar may be provided by a nose wheel, which may preferably be applied after welding, for example by riveting.

According to embodiments, a projection of the second weld line on the guide bar plane may be offset from a projection of the first weld line on said guide bar plane. Since the first and second weld seams are thereby both at least partly welded in previously un-welded material parts of the respective plates, the stress generated by the second weld seam will be of a magnitude more similar to that of the first weld seam. Preferably, the offset exceeds the width of the weld seam. This makes the stress generated by the respective weld seams even more equal. Even more preferred, the offset exceeds the width of the heat-affected zone within the core plate. According to embodiments, the projection of the second weld line may be offset from the projection of the first weld line along the full length of the second weld line; alternatively, though somewhat less preferred, one or several subsegments of the second weld line may be allowed to coincide with the first weld line.

According to embodiments, said offset may be e.g. between 0,5 mm and 30 mm. The offset may vary along the length of the weld lines. Alternatively, and somewhat more preferred, the offset may be substantially uniform along the second weld line, such that the first and second weld lines extend substantially parallel. According to embodiments, the offset may exceed 1 mm, or even 1 ,5 mm. Thereby, any tendency of the heat-affected zone of the first weld seam to affect the stress generated by the second weld seam will be minimized, which further reduces the stress-induced warp of the guide bar. According to further embodiments, the offset may be less than 15 mm, or less than 7 mm. As the first and second weld lines extend close to each other, the stress generated by the second weld seam will counteract the stress generated by the first weld seam within the local area of the first weld seam, which even further reduces stress-induced warp. Preferably, the first and second weld seams are made using the same welding technology, for example energy beam welding. Thereby, the counteracting stress generated by the respective weld seams will be of similar magnitude and character.

According to embodiments, the offset may exceed a width of the heat-affected zone of the first weld seam.

According to embodiments, welding said first weld seam on the first side may comprise applying an energy beam to said first side to weld said first weld seam, and welding said second weld seam on the second side may comprise applying an energy beam to said second side to weld said second weld seam. Energy beam welding, such as electron beam welding and laser beam welding, generally enables a high energy density, which minimizes the width of the heat-affected zone. Thereby, the second weld seam can be welded closer to the first weld seam without the heat- affected zones of the respective weld seams overlapping.

According to embodiments, welding said first and second weld seams may comprise laser beam welding. The method facilitates obtaining a deep and narrow weld in combination with a narrow heat-affected zone, which reduces warp.

According to embodiments, the first weld seam may be formed to have a width in the guide bar plane, at the interface between the first side plate and the core plate, of between 0,3 mm and 0,7 mm, and the second weld seam may be formed to have a width in the guide bar plane, at the interface between the second side plate and the core plate, of between 0,3 mm and 0,7 mm. It has been found that, compared to a broader weld seam, a narrow weld seam tends to get a less tapering shape as a function of depth, which results in further reduction of stress-induced warp.

According to embodiments, the first weld seam may be formed to have a width in the guide bar plane, at the interface between the core plate and the second side plate, of between 0,2 mm and 0,6 mm, and the second weld seam may be formed to have a width in the guide bar plane, at the interface between the core plate and the first side plate, of between 0,2 mm and 0,6 mm.

According to embodiments, the first and second weld lines may follow a first longitudinal edge of the stacked sandwich structure, wherein the method may further comprise welding a third weld seam on the first side, the third weld seam extending along a third weld line and penetrating the first side plate, the core plate, and into the second side plate, the third weld seam thereby joining the core plate to each of the first and second side plates; and welding a fourth weld seam on the second side, the fourth weld seam extending along a fourth weld line and penetrating the second side plate, the core plate, and into the first side plate, the fourth weld seam thereby joining the core plate to each of the first and second side plates, wherein the third and fourth weld lines follow a second longitudinal edge of the stacked sandwich structure.

According to embodiments, the method may further comprise: prior to welding said first weld seam, heating the first side plate to a temperature of more than 110°C, and prior to welding said second weld seam, heating the second side plate to a temperature of more than 110°C. Thereby, any risk of crack formation in or adjacent to the weld seams is minimized. This may be particularly useful when the side plates are made of high-carbon steel. For example, the first and second side plates may be made of steel having a carbon content exceeding 0,4% by weight. Thereby, the side plates can be hardened to a high wear resistance. The core plate, on the other hand, may be formed of a mild steel having a carbon content of less than 0,2% by weight. A more preferred temperature range for pre-heating the side plates is between 130°C and 200°C. According to embodiments, both side plates may be heated in a single step, for example by heating the entire stacked sandwich structure.

According to embodiments, the method may further comprise: after welding said weld seams, hardening the guide bar blank defined by the stacked sandwich structure after welding, and tempering the guide bar blank. Hardening may be made by heating the guide bar blank to an exemplary temperature range of between 890°C and 970°C, and thereafter quenching it in e.g. an oil bath. Preferably, prior to tempering, the guide bar blank is clamped in a fixture to assume a flat shape along the guide bar plane. An exemplary suitable tempering temperature is within the range of about 400°C to 550°C, where residual stress of the guide bar may be relieved. After tempering, longitudinal edges of the side plates may be hardened to a small hardening depth, for example less than 2 mm, by e.g. induction hardening. According to embodiments, the core plate may comprise a first longitudinal edge segment extending along the longitudinal direction to define a guide track bottom of a first longitudinal chain guide track segment of the guide bar, a second longitudinal edge segment extending along the longitudinal direction, opposite to said first longitudinal edge segment, to define a guide track bottom of a second longitudinal chain guide track segment of the guide bar, and an aperture arrangement, comprising one or more apertures, positioned between the first and second longitudinal edge segments of the core plate, wherein arranging the core plate between the first and second side plates to form a stacked sandwich structure comprises covering the aperture arrangement with the first and second side plates to define an air compartment arrangement, comprising one or more air compartments, within the guide bar. Thereby, a particularly light guide bar may be obtained. Preferably, a projection of the aperture arrangement on the guide bar plane spans more than 40% of the total area between projections of the respective guide track bottoms on the same plane. The aperture arrangement may comprise one aperture or several apertures separated by walls, resulting in one or several air compartments of the air compartment arrangement. The aperture arrangement may, for example, be punched, laser cut, or waterjet cut.

According to embodiments, an inner face of the first side plate, opposite to said outer face of the first side plate, may comprise a recess arrangement at least partly in register with said aperture arrangement. Similarly, an inner face of the second side plate, opposite to said outer face of the second side plate, may comprise a respective recess arrangement at least partly in register with said aperture arrangement. Similar to the aperture arrangement, the recess arrangement may comprise one recess or several separate recesses. The recess arrangement may, for example, be formed by milling.

According to embodiments, a projection of said first and second weld lines on said guide bar plane may overlap with a projection on said guide bar plane of said first longitudinal edge segment of the core plate. Similarly, a projection of any third and fourth weld lines on said plane may overlap with a projection of said second longitudinal edge segment of the core plate.

According to a second aspect, there is provided a guide bar manufactured using the method of any of the preceding claims.

According to a third aspect, there is provided a guide bar for a handheld chainsaw, comprising: a first side plate, a second side plate and a core plate, wherein the core plate is arranged between the first and second side plates, the guide bar extending in a guide bar plane along a longitudinal direction and having a first side, parallel to said guide bar plane and formed by an outer face of the first side plate, a second side, parallel to said guide bar plane and formed by an outer face of the second side plate, a first longitudinal edge and a second longitudinal edge, wherein the guide bar comprises a first weld seam extending along a first weld line following said first longitudinal edge and penetrating the first side plate, the core plate, and into the second side plate, the first weld seam thereby joining the core plate to each of the first and second side plates; and a second weld seam extending along a second weld line following said first longitudinal edge and penetrating the second side plate, the core plate, and into the first side plate, the second weld seam thereby joining the core plate to each of the first and second side plates. It has been found that two narrow weld seams adjacent to each other tend to cause less stress- induced warp than one broader weld seam of equivalent strength.

It is noted that embodiments of the invention may be embodied by all possible combinations of features recited in the claims, as well as of the further embodiments defined hereinabove. Moreover, obviously, the various features of the embodiments of the invention according to the first aspect are combinable with the invention as defined in the second and third aspects.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 is a plan view of a handheld chainsaw comprising a saw chain guided by a guide bar;

Fig. 2 is a side view illustrating the interplay between a saw chain drive sprocket, a saw chain, and a guide bar of the chainsaw of Fig. 1 ;

Fig. 3 is a perspective view of the guide bar of Fig. 1 ;

Fig. 4 is a plan view of a pair of side plates, a core plate and a nose wheel of the guide bar of Fig. 3;

Fig. 5 is a section in perspective of the side plates and core plate of Fig. 4 arranged in a stacked sandwich structure; Fig. 6 is a flow chart illustrating a method of manufacturing the guide bar of

Fig. 3;

Fig. 7 is a section of the guide bar of Fig. 3, the section taken along the line VII-VII in Fig. 8; and

Fig. 8 is a plan view of the guide bar of Fig. 3.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

Detailed description of the exemplary embodiments

Fig. 1 illustrates a handheld chainsaw 10. The chainsaw 10 comprises a chainsaw body 12 provided with a pair of handles 14a, 14b, by means of which an operator (not illustrated) may hold and operate the chainsaw 10. The pair of handles comprises a front handle 14a, typically for holding with the left hand, and a rear handle 14b, typically for holding with the right hand. A cutting assembly comprising a saw chain 16, and an elongate guide bar 18 guiding the saw chain 16 in an elongate loop, extends from a front end of the chainsaw body 12 in a longitudinal direction L of the guide bar 18. The guide bar 18 extends in a guide bar plane P defined by the longitudinal direction L and a transversal direction T of the guide bar 18, which transversal direction T is perpendicular to the longitudinal direction L. The chainsaw 10 further comprises a removable battery 20, an electric motor 22 (only schematically indicated by a broken-line circle in Fig. 1 ), and a finger-operated trigger 24 permitting the operator to selectively mobilize the saw chain 16 using the electric motor 22. Even though Fig. 1 illustrates a battery-powered chainsaw 10, the teachings herein are equally applicable to e.g. handheld chainsaws powered by an internal combustion engine, which are well known in the art as such.

Fig. 2 schematically illustrates a saw chain drive sprocket 26, a short section of the saw chain 16, and a proximal end 18a of the guide bar 18 as seen from the side. The saw chain drive sprocket 26 is rotated about a rotation axis A by the motor 22 (Fig. 1 ) via a motor shaft 28, and drivingly engages with the saw chain 16 to move the saw chain 16 along the guide bar 18. The saw chain 16 comprises drive links 16a meshing with drive teeth 30 of the saw chain drive sprocket 26. The drive links 16a ride in a guide track 32 of the guide bar 18, a bottom 33 of which is illustrated by a broken line. Cutter links 16b are provided with cutting teeth adapted to shave off wood chips from the material being cut, and the cutter links 16b and tie straps 16c hold the drive links 16a together. The cutter links 16b and tie straps 16c ride on longitudinal edges 19a, 19b of the guide bar 18.

The perspective view of Fig. 3 illustrates the guide bar 18 in isolation. A plan view of the guide bar 18 is also provided in Fig. 8. Now with reference to Fig. 3, the proximal end 18a of the guide bar 18 comprises a longitudinal slot 34 and a pair of adjustment holes 36a, 36b on either sides of the slot 34. The slot and holes 34, 36a, 36b allow attaching the guide bar 18 to the chainsaw body 12 (Fig. 1) in a manner permitting longitudinal adjustment of the position of the guide bar 18, to allow tensioning the saw chain 16 (Fig. 1 ) in a manner known per se. A distal end 18b of the guide bar 18 comprises a nose wheel 38, of which only the outer tips of its gear teeth are visible in Fig. 3. The guide bar 18 has a first side 40a and a second side 40b opposite to the first side 40a, the sides 40a, 40b extending parallel to the guide bar plane P.

A magnified portion of Fig. 3 more clearly illustrates details of the structure of the guide bar 18. The guide bar 18 comprises a first side plate 42, a second side plate 44, and a core plate (not visible in Fig. 3) which is sandwiched between the first and second side plates 42, 44 and separates the first and second side plates 42, 44 from each other. A guide track 32 is defined by a gap between the first and second side plates 42, 44, and guides the saw chain 16 in the manner elucidated with reference to Fig. 2. The outer faces 45 of the side plates 42, 44 define the first and second sides 40a, 40b of the guide bar 18.

The guide bar 18 has a first longitudinal edge 19a and, opposite to the first longitudinal edge 19a, a second longitudinal edge 19b, each of which extends along the longitudinal direction L from the proximal end 18a to the distal end 18b of the guide bar 18. The longitudinal edges 19a, 19b of the guide bar 18 are defined by longitudinal edges of the side plates 42, 44. A first longitudinal guide track segment 32a extends along the first longitudinal edge 19a, and a second, opposite, longitudinal guide track segment 32b extends along the second longitudinal edge 19b.

The magnified portion of Fig. 3 further illustrates a first weld seam 46a, which extends along a first weld line 48a, and a second weld seam 46b which extends along a second weld line 48b. The first and second weld lines 48a, 48b follow the first longitudinal edge 19a of the guide bar 18. As apparent from the drawing, each of the weld seams 46a, 46b extends continuously, without interruption, from a first respective weld end adjacent to the proximal end 18a of the guide bar to a second respective weld end adjacent to the distal end 18b of the guide bar. The second weld line 48b follows the first weld line 48a with a lateral offset d, i.e. a separation of the weld lines 48a, 48b as seen in a projection of the weld lines 48a, 48b onto the guide bar plane P, of about 2 mm. The offset d is substantially constant along the length of the guide bar 18. At the proximal end 18a, the weld lines 48a, 48b followed by the weld seams 46a, 46b diverge slightly from each other. The second weld seam 46b is also shorter than the first weld seam 46a. Even though welded under the same process conditions, on the first side 40a of the guide bar 18, the first weld seam 46a is wider than the second weld seam 46b. This is because the first weld seam 46a has been welded from the first side 40a, and the second weld seam 46b has been welded from the second side 40b of the guide bar 18. The guide bar 18 further comprises a third weld seam 46c and a fourth weld seam 46d, which extend along third and fourth weld lines (not illustrated) following the second longitudinal edge 19b of the guide bar 18.

Fig. 4 illustrates the first side plate 42, the core plate 43, and the second side plate 44 prior to stacking and welding to form the guide bar 18 (Fig. 3). The side plates 42, 44 are made of high-carbon steel having a carbon content of about 0,65% by weight, whereas the core plate is made of mild steel having a carbon content of about 0,1 % by weight. Fig. 4 illustrates the outer face 45 of the first side plate 42, and an inner face 47 of the second side plate 44; it will be appreciated that the outer face of the second side plate 44 may be identical to the outer face 45 of the first side plate 42, and that the inner face of the first side plate 42 may be identical to the inner face 47 of the second side plate 44.

The core plate 43 comprises a first longitudinal edge segment 43a and, opposite to the first longitudinal edge segment 43a, a second longitudinal edge segment 43b. The longitudinal edge segments 43a, 43b will, once the guide bar 18 (Fig. 3) is complete, define respective bottoms 33 (Fig. 2) of the longitudinal guide track segments 32a, 32b (Fig. 3). Between the first and second longitudinal edge segments 43a, 43b, the core plate 43 is cut out, for example by laser cutting, to define an aperture arrangement 50, comprising a plurality of apertures 52 which together cover the main part of the area between the longitudinal edge segments 43a, 43b. The apertures 52 are elongate, their direction of elongation extending in the longitudinal direction L (Fig. 3) of the guide bar 18. Aperture separation walls 54 delimit the individual apertures 42, and contribute to the torsional strength of the guide bar 18 (Fig. 1 ). The entire core plate 43 is of uniform thickness in the direction perpendicular to the guide bar plane P (Fig. 3). In the illustrated example, the core plate 43 is cut from steel sheet having a thickness of 1 ,57 mm; a typical suitable thickness may range from 1 ,28 mm to 1 ,65 mm.

Also the side plates 42, 44 are cut from steel sheet. An exemplary suitable thickness is between 1 ,0 mm and 1 ,8 mm; in the illustrated example, steel sheet having a thickness of 1 ,5 mm is used. The outer faces 45 of the side plates 42, 44 are flat, whereas the inner faces 47 each have a respective recess arrangement 56 milled therein. The recess arrangement 56 comprises a plurality of recesses 58 where the side plates 42, 44 have a reduced thickness. The recesses 58 are separated by recess separation walls 60 along which the side plates have the full, nominal thickness of the steel sheet, i.e., in the illustrated case, 1 ,5 mm. Fig. 4 also illustrates the position of the nose wheel 38 in relation to the core plate 43 in the guide bar 18 (Fig. 3).

Now with reference to the section of Fig. 5 and the flow chart 100 of Fig. 6, the guide bar 18 is assembled and welded as follows:

In a stacking step 101 , the core plate 43 is arranged between the first and second side plates 42, 44, such that the inner faces 47 (Fig. 4) of the side plates 42, 44 face and abut the core plate 43, thereby forming a stacked sandwich structure 61 . A broken line 62 in Fig. 4 illustrates the position of the outer perimeter of the side plates 42, 44 in relation to the core plate 43. The side plates 42, 44 cover the apertures 52 (Fig. 4) of the aperture arrangement 50 to define air compartments 64. Moreover, the recesses 58 (Fig. 4) of the side plates 42, 44 are in register with the apertures 52 (Fig. 4) of the core plate 43, such that a subset 60a (Fig. 4) of the recess separation walls 60 of the side plates 42, 44 meet a subset 54a (Fig. 4) of the aperture separation walls 54 of the core plate 43.

Then, in step 102, the stacked sandwich structure 60 pre-heated to a temperature of about 160 degrees, and thereafter welded together. In a first welding step 103, the stacked sandwich structure 61 is welded from the first side 40a, by laser beam welding the first weld seam 46a and the third weld seam 46c (Fig. 3) along respective weld lines 48a, 48c (Fig. 3). The first and third weld seams 46a, 46c are welded such that the fused region of the respective welds 46a, 46c penetrate the first side plate 42, the core plate 43, and into the second side plate 44, thereby joining the core plate 43 to each of the first and second side plates 42, 44 to form a welded guide bar blank. In a second welding step 104, the welded guide bar blank is welded from the second side 40b, by laser beam welding the second weld seam 46b and the fourth weld seam 46d (Fig. 3) along respective weld lines 48b, 48d (Fig. 3). The second and fourth weld seams 46b, 46d are welded such that the fused region of the respective welds penetrate the second side plate 44, the core plate 43, and into the first side plate 42, thereby even further joining the core plate 43 to each of the first and second side plates 42, 44.

Fig. 4 illustrates a projection of the positions and trajectories of the weld lines 48a, 48b, 48c, 48d on the first side plate 42 and the core plate 43, respectively. As seen in a projection on the guide bar plane P (Fig. 3), the first and second weld lines 48a, 48b extend within the first longitudinal edge segment 43a, and the third and fourth weld lines 48c, 48d extend within the second longitudinal edge segment 43b, of the core plate 43.

Fig. 7 illustrates a section of the guide bar 18. The section shows the weld seams of the welded guide bar blank 63 after welding. Referring to the magnified portion of Fig. 7, at the interface between the first side plate 42 and the core plate 43, the first weld seam 46a has a width W1 , in the guide bar plane P, of about 0,45 mm. The second weld seam 46b has a similar width W1 , of about 0,45 mm, at the interface between the second side plate 44 and the core plate 43. At the interface between the core plate 43 and the second side plate 44, the first weld seam 46a has a width W2 in the guide bar plane P of about 0,3 mm. Similarly, the second weld seam 46b has a similar width W2 of about 0,3 mm at the interface between the core plate 43 and the first side plate 42. The welds 46a, 46b are full-penetration welds, i.e. the first weld seam 46a extends all the way to the second side 40b of the guide bar 18, and the second weld seam 46b extends all the way to the first side 40a of the guide bar 18.

Broken lines 48a’, 48b’ in Fig. 7 illustrate the positions of the weld lines 48a, 48b (Fig. 4) in the guide bar plane P. The offset d between the first and second weld lines 48a, 48b is about 2,5 mm, and the first weld line extends at a distance D from the bottom 33 of the guide track 32a of about 1 ,8 mm. The heat-affected zone 66 of each weld 46a, 46b extends about 0,3 mm from the respective weld 46a, 46b. This means that, for example for the first weld 46a, the heat-affected zone extends, at the interface between the first side plate 42 and the core plate 43, about 0,5 mm from the respective weld line 48a. The third and fourth weld seams 46c, 46d have a size and shape which, as seen in a section perpendicular to the guide bar plane P, is similar to those of the first and second weld seams 46a, 46b.

After welding, and still with reference to the flow chart of Fig. 6, the weld seams 46a-d are machined, in a machining step 105, to be level with the outer faces 47 of the side plates 42, 44. Then, in step 106, the welded guide bar blank 63 is hardened at a temperature of about 900°C and quenched in an oil bath; in step 107, the welded guide bar blank 63 is placed in a fixture and clamped to assume a flat shape, and in step 108 the welded guide bar blank 63 is tempered at a temperature of about 500°C to alleviate any residual stress in the welded guide bar blank 63, and in particular, in the weld seams 46a-d. In step 108, the longitudinal edges 19a, 19b of the welded guide bar blank 63 are induction hardened to a depth of about 1 mm. Lastly, in step 109, the nose wheel 38 is riveted to the welded guide bar blank 63 to form the final guide bar 18 illustrated in Figs 3 and 8.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, it is possible to use other weld methods than laser welding. The weld seams do not need to fully penetrate the entire guide bar; it may be sufficient that they reach to a certain depth of the respective opposite side plate. The sandwich structure of the guide bar is not limited to three plates; it may comprise additional plates, which may be interposed between the core plate and the side plates. While the invention has been described with reference to a chainsaw driving a saw chain having cutting teeth adapted to cut wood, it is equally applicable to chainsaws driving saw chains provided with abrasive elements for cutting rock, concrete, and the like.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

1 . A method of manufacturing a guide bar (18) for a handheld chainsaw (10), the method comprising providing a first side plate (42), a second side plate (44) and a core plate (43); arranging the core plate (43) between the first and second side plates (42, 44) to form a stacked sandwich structure (61 ) extending in a longitudinal direction (L) along a guide bar plane (P) and having a first side (40a) formed by an outer face (45) of the first side plate (42) and a second side (40b) formed by an outer face (45) of the second side plate (44); welding a first weld seam (46a) on the first side (40a), the first weld seam (46a) extending along a first weld line (48a) and penetrating the first side plate (42), the core plate (43), and into the second side plate (44), the first weld seam (46a) thereby joining the core plate (43) to each of the first and second side plates (42, 44); and welding a second weld seam (46b) on the second side (40b), the second weld seam (46b) extending along a second weld line (48b) and penetrating the second side plate (44), the core plate (43), and into the first side plate (42), the second weld seam (46b) thereby joining the core plate (43) to each of the first and second side plates (42, 44).

2. The method according to claim 1 , wherein a projection of the second weld line (48b) on the guide bar plane (P) is offset from a projection of the first weld line (48a) on said guide bar plane (P).

3. The method according to claim 2, wherein said offset is between 0,5 mm and 30 mm.

4. The method according to any of the claims 2-3, wherein the offset exceeds a width of the heat-affected zone (65) of the first weld seam (46a).

5. The method according to any of the preceding claims, wherein welding said first weld seam (46a) on the first side (40a) comprises applying an energy beam to said first side (40a) to weld said first weld seam (46a), and welding said second weld seam (46b) on the second side (40b) comprises applying an energy beam to said second side (40b) to weld said second weld seam (46b).

6. The method according to claim 5, wherein welding said first and second weld seams (46a, 46b) comprises laser beam welding.

7. The method according to any of the preceding claims, wherein the first weld seam (46a) is formed to have a width (W1 ) in the guide bar plane (P), at the interface between the first side plate (42) and the core plate (43), of between 0,3 mm and 0,7 mm, and the second weld seam (46b) is formed to have a width (W1 ) in the guide bar plane (P), at the interface between the second side plate (44) and the core plate (43), of between 0,3 mm and 0,7 mm.

8. The method according to any of the preceding claims, wherein the first weld seam (46a) is formed to have a width (W2) in the guide bar plane (P), at the interface between the core plate (43) and the second side plate (44), of between 0,2 mm and 0,6 mm, and the second weld seam (46b) is formed to have a width (W2) in the guide bar plane (P), at the interface between the core plate (43) and the first side plate (42), of between 0,2 mm and 0,6 mm.

9. The method according to any of the preceding claims, wherein the first and second weld lines (48a, 48b) follow a first longitudinal edge (19a) of the stacked sandwich structure (61 ), the method further comprising welding a third weld seam (46c) on the first side (40a), the third weld seam (46c) extending along a third weld line (48c) and penetrating the first side plate (42), the core plate (43), and into the second side plate (44), the third weld seam (46c) thereby joining the core plate (43) to each of the first and second side plates (42, 44); and welding a fourth weld seam (46d) on the second side (40b), the fourth weld seam (46d) extending along a fourth weld line (48d) and penetrating the second side plate (44), the core plate (43), and into the first side plate (42), the fourth weld seam (46d) thereby joining the core plate (43) to each of the first and second side plates (42, 44), wherein the third and fourth weld lines (48c, 48d) follow a second longitudinal edge (19b) of the stacked sandwich structure (61 ).

10. The method according to any of the preceding claims, comprising prior to welding said first weld seam (46a), heating the first side plate (42) to a temperature of more than 110°C, and prior to welding said second weld seam (46b), heating the second side plate (44) to a temperature of more than 110°C.

11 . The method according to any of the preceding claims, comprising: after welding said weld seams (46a, 46b, 46c, 46d), hardening the stacked sandwich structure (61), and tempering the stacked sandwich structure (61).

12. The method according to any of the preceding claims, wherein the core plate (43) comprises a first longitudinal edge segment (43a) extending along the longitudinal direction (L) to define a guide track bottom (33) of a first longitudinal chain guide track segment (32a) of the guide bar (18), a second longitudinal edge segment (43b) extending along the longitudinal direction (L), opposite to said first longitudinal edge segment (43a), to define a guide track bottom (33) of a second longitudinal chain guide track segment (32b) of the guide bar (18), and an aperture arrangement (50), comprising one or more apertures (52), positioned between the first and second longitudinal edge segments (43a, 43b) of the core plate (43), wherein arranging the core plate (43) between the first and second side plates (42, 44) to form a stacked sandwich structure (61 ) comprises covering the aperture arrangement (50) with the first and second side plates (42, 44) to define an air compartment arrangement, comprising one or more air compartments (64), within the guide bar (18).

13. The method according to claim 12, wherein an inner face (47) of the first side plate (42), opposite to said outer face (45) of the first side plate (42), comprises a recess arrangement (56) at least partly in register with said aperture arrangement (50).

14. The method according to any of the claims 12-13, wherein a projection of said first and second weld lines (48a, 48b) on said guide bar plane (P) overlaps with a projection on said guide bar plane (P) of said first longitudinal edge segment of the core plate (43).

15. A guide bar (18) manufactured using the method of any of the preceding claims.

16. A guide bar (18) for a handheld chainsaw (10), comprising a first side plate (42), a second side plate (44) and a core plate (43), wherein the core plate (43) is arranged between the first and second side plates (42, 44), the guide bar (18) extending in a guide bar plane (P) along a longitudinal direction (L) and having a first side (40a), parallel to said guide bar plane (P) and formed by an outer face (45) of the first side plate (42), a second side (40b), parallel to said guide bar plane (P) and formed by an outer face (45) of the second side plate (44), a first longitudinal edge (19a) and a second longitudinal edge (19b), wherein the guide bar (18) comprises a first weld seam (46a) extending along a first weld line (48a) following said first longitudinal edge (19a) and penetrating the first side plate (42), the core plate (43), and into the second side plate (44), the first weld seam (46a) thereby joining the core plate (43) to each of the first and second side plates (42, 44); and a second weld seam (46b) extending along a second weld line (48b) following said first longitudinal edge (19a) and penetrating the second side plate (44), the core plate (43), and into the first side plate (42), the second weld seam (46b) thereby joining the core plate (43) to each of the first and second side plates (42, 44).