WO2016095944A1

WO2016095944A1 - Method for manufacturing a cutter link and cutter link

Info

Publication number: WO2016095944A1
Application number: PCT/EP2014/077726
Authority: WO
Inventors: Adam STAHLKRANTZ
Original assignee: Husqvarna Ab
Priority date: 2014-12-15
Filing date: 2014-12-15
Publication date: 2016-06-23

Abstract

Method for manufacturing a cutter link (2) comprising a first body (4) made of a first material and a second body (6) comprising cutting means made of a second material, whereby the second body (6) comprising the cutting means (8) is inserted in a mounting slot (10) present in the first body (4) in order to form a cutter link assembly (12), the cutter link assembly (12) is heated to a first temperature and is then cooled down with a specific cooling rate from the first temperature to a second temperature. Cutter link (2) for a saw chain (36) comprising at least - a first body (4) made of a first material, and - a second body (6) comprising cutting means (8) made of a second material, - a mounting slot (10) present in a rear section (16) of the first body (4) in which the second body (6) is inserted and form-locking connected with the first body (4), whereby the cutting means (12) of the second body (6) protrude outwardly from the mounting slot (10) in a running direction of the cutter link (2), and - at least one depth gauge (14) positioned forwardly of the cutting means (8) in running direction of the cutter link (2) and protruding outwardly from the first body (4) with lower projection than the cutting means (8).

Description

METHOD FOR MANUFACTURING A CUTTER LINK AND CUTTER LINK

The invention relates to a method for manufacturing a cutter link and a cutter link.

The usual way of manufacturing cutter links is to braze or weld the hard metal piece comprising the cutting means to the main body of the cutter link. However, this has the disadvantage that an extra step is necessary in which the cutter link must be pre- pared and in which the hard metal piece comprising the cutting means is brazed to the cutter link. Further, the brazing results in thermal heating that can affect the structure in the material of the main body of the cutter link and the hard metal piece re^¬ spectively the cutting means. This thermal effect could lead to grain growth or phase changes in the materials what in turn could have a negative effect and impact on the materials proper^¬ ties.

The US 7,836,808 B2 discloses a cutter link comprising a holding link with a holding or key member on which a replaceable cutting tooth can be arranged. Therefore the tooth comprises an inverted L-shaped recess that fits to the correspondingly shaped key mem^¬ ber. To prevent the tooth to be dislodged from the holding link, a safety link comprising a safety lobe is provided.

Also the US 4,497,232 A shows a cutting tool having a cutting tooth that is formed without brazing or welding but by inserting the cutting tooth into a slot provided in the body of the cut^¬ ting tool. For fixing the cutting teeth in the slot, a gripping edge is designed in the slot that provides a substantial re^¬ sistance to inadvertent removal.

From the US 2,852,048 A, a cutter link is known that comprises a body element and a removable cutter element, whereby the body element is formed with a T-shaped edge adapted to be slidably received within a T-shaped slot formed in the base of the cutter element .

It is an object of the present invention to provide a method for manufacturing a cutter link without the use of welding or braz^¬ ing. Another object of the invention is to provide a cutter link .

The first object is achieved by a method for manufacturing a cutter link for a saw chain comprising a first body made of a first material and a second body comprising cutting means made of a second material with the features according to claim 1.

In a first step, the second body comprising the cutting means is inserted in a mounting slot present in the first body in order to form a cutter link assembly. The mounting slot respectively mounting notch or mounting cavity has a geometry that allows to hold the second body in it, for example it is formed by a bent plate, which encloses the second body at least partially when it is inserted in the first body. Therefore the cross section of the second body and the cross section of the bent plate have for example a trapezoidal form, wherein the shorter of the two par^¬ allel sides is present at the bottom side, so that the second body is hold in the mounting slot. The second body is inserted so far that the cutting means protrude outwardly from the mount^¬ ing slot in a running direction of the cutter link.

In a second step the cutter link assembly, hence the cutter link consisting of the first body and the second body comprising the cutting means being inserted in the first body, is heated to a first temperature.

In a third step the cutter link assembly is cooled down with a specific cooling rate from the first temperature to a second temperature. During the cooling of the cutter link assembly, ge- ometry and dimension changes in the first and/or the second body occur, that have different degree for the first and second body consisting of different materials. The idea of the invention is to take advantage of the different behavior during the cooling operation respectively the different material properties of the first and the second material. Thus during the cooling process the different materials of the re^¬ spective different bodies change their volume differently re- suiting in the two bodies being pressed together. Thus the first and the second body are form-fit connected and purely mechanical assembled without the need of any welding or brazing step.

In summary, the method utilizes the differences in the volume of the material and the difference in the thermo-expansion of its different materials in its different phases that occur at dif^¬ ferent temperatures. The method has the advantage that there is no need for brazing or welding the cutter link which certainly represents vulnerability in the cutter link due to thermal heat effects at the weld or braze point. In addition the first and the second body of the cutter link could be designed purly to gain the optimal cutting properties without the need of taking the brazability into account. Further the method reduces the re^¬ quired production steps .

In a preferred embodiment of the invention, the first tempera^¬ ture is selected such that a volume of the first material of the first body is smaller at the first temperature than at the sec^¬ ond temperature. In other words: the first material has a more compact structure at the first temperature, i.e. in the heated state. During the cooling process, the first material undergoes a change in volume so that the first material body would enclose the second body even further, thus the first and the second body are mechanical pressed together. This has the advantage that one is more flexible with regard to the choice of the second materi- al that forms the cutting means and is therefore responsible for the effectivity of the cutter link when it is used, because the mechanical assembling is caused by a volume change of the first material. This also allows the use of one kind of first body made of the first material and then alternating only the second body, thus the second material and the cutting means. The cut^¬ ting means can be adjusted to the different applications but the cutter link stays the same, so that there is no need of changes in the assembling machine.

In particular the first temperature is an austenitic temperature and the first material is in particular steel. Austenitic tem^¬ perature should be defined as a temperature at which the steel is present as austenite or rather as γ-phase. The austenite has a face-centered cubic (FCC) cubic crystal structure that is more compact, and therefore has a lower volume, than a structure that exists for steel at the second temperature.

A further preferred embodiment of the invention is that the spe- cific cooling rate is chosen such that the first material of the first body transforms from austenite structure to a martensitic and/or bainite structure when it is cooled down after the heat^¬ ing process. When the assembled cutter link is heated to a first temperature that is the austenite temperature of steel and therefore the first body having an austenite form is rapidly cooled or guenched to a relatively low second temperature, mar^¬ tensite is formed. The martensitic transformation occurs when the guenching rate is rapid enough to prevent carbon diffusion and only a slight displacement of each atom relative to its neighbors occurs. The martensite has a body-centered tetragonal (BCT) crystal structure. Bainite structure consists of a face- centered-cubic (FCC) a-ferrite phase and cementite phases (or- thorhombic) and is formed when specific cooling-rate is slower than for building the martensite structure, but not rapidly enough for building pearlite. These structural changes, from austenite to martensite (BCT) or bainite comprising cementite and a-ferrite (FCC) are accompanied by changes in the volume, more precisely the volume of the first material respectively the first body made of steel increases during the cooling, because the martensite or bainite structure is less compact than austen^¬ ite. This leads to a volume change with the first material of the first body which would tighten the first material of the first body surrounding the second body even further. It is advantageous, if the first temperature is chosen such that the second material of the second body does not pass through a phase transformation at the first temperature and certainly not before reaching the first temperature. For this purpose the sec^¬ ond material is in particular a hard metal and more preferably a refractory carbide or nitride. For manufacturing the second body and the cutting means, the hard metal respectively the cemented carbide is sintered at a much higher temperature than the first material. The hard metal, especially a refractory carbide or ni^¬ tride or tungsten carbide is stable at high temperatures. There- fore at the first temperature which is e.g. an austenite temper^¬ ature no phase transformation occurs within the second body and the volume of the second body and its internal structure does not change as much as this is the case for the first material. This has the advantage that the second body can be manufactured prior to the assembling because it is unaffected during the man^¬ ufacturing process, thus the heating, cooling and mechanical pressing, and optionally further manufacturing steps at elevated temperatures, e.g. a hardening process, followed after to gain the bainite structure of the cutter link. Rather the second body might recover during the heating step from the plastic defor^¬ mation caused by its prior manufacturing process.

It is advantageous, when the cutter link assembly is heated again to a third temperature after cooling down the cutter link assembly to the second temperature. Martensite is very hard, but brittle, as there are internal stresses that have been intro^¬ duced during guenching. Therefore tempering the cutter link at a third temperature below the eutectoid temperature for a specific time period allows diffusion process and the formation of tem- pered martensite comprising an a-ferrite-phase and a cementite phase. As using refractory carbides and/or nitrides due to their higher temperature tolerance it is uncomplicated to perform a normal hardening process after assembling the cutter link as described above.

The second object is achieved with a cutter link with the fea^¬ tures according to claim 8 . A cutter link for a saw chain comprises at least a first body or main body made of a first mate^¬ rial and a second body comprising the cutting means made of a second material. The first material and the second material are different from each other. Further the cutter link comprises a mounting slot present in a rear section, related to the running direction of the cutter link, of the first body in which the second body is inserted and form-locking connected with the first body. Thereby the cutting means of the second body pro^¬ trude outwardly from the mounting slot in a running direction of the cutter link. The cutter link also comprises at least one depth gauge positioned forwardly of the cutting means in running direction of the cutter link, respectively related to the direc- tion of rotation of the saw chain, and protruding outwardly from the first body with lower projection than the cutting means.

The cutter link can be manufactured by the method described above. After heating the cutter link assembly, thus the first body and the second body that is inserted in the mounting slot, to a first temperature, and cooling it down to a second tempera^¬ ture, the second body is form-locking connected with the first body. In other words: the first body is pressed around the sec^¬ ond body. In a preferred embodiment the rear section of the first body of the cutter link comprises a bent plate that forms the mounting slot respectively mounting notch or mounting cavity in between. Therefore the bent plate has a geometry respectively form or shape whose inner surface is adapted to an outer surface of the second body, so that the second body is fitted in the mounting slot and at least partially enclosed by it when inserted in the second body. At least the cutting means protrude outwardly from the mounting slot in a running direction of the cutter link.

Particularly the first body comprises a base body that is formed by two, thus a pair of oppositely disposed and spaced apart side plates. Each of the side plates may have a depth gauge posi^¬ tioned at the front end of the base body and at least two rivet holes for connecting the cutter link with a driving link via a connecting link. For forming a saw chain, the driving link is disposed between the two oppositely disposed and spaced apart side plates. It is particularly preferred, if the bent plate has a base side and two shank sides that run towards each other related to the direction of the base body of the first body and whereby each of the shank sides is connected to one side plate of the base body. The bent plate with its base side and the two shank sides, the two side plates and the depth gauge may be integrally formed. The two side plates are at least nearly parallel spaced apart plates each comprising at least two rivet holes. In other words: the mounting slot formed by the bent plate has a trapezoidal cross section, wherein the shorter of the two parallel sides that is present at the bottom side, thus at the side where the two shank sides merge into the side plates. The second body is likewise formed with a trapezoidal cross section so that it can be inserted in the mounting slot and form-fit connected with the first body. In a preferred embodiment of the invention, the cutting means protrude laterally and/or above from the first body. In other words: the cutting means that protrude outwardly from the mount^¬ ing slot have a side and a top cutting edge. Especially when the cutting means protrude laterally on both sides of the first body, there is the advantage that there is no need, to arrange the cutting edge alternately to the left and the right between adjacent cutter links. Thus it is possible to make the saw chain thinner as the cutting force will be distributed on both sides of the saw chain during cutting operation and therefore the force acting on the saw chain will be reduced.

In a further preferred embodiment an inner surface of the first body comprises at least one recess in the rear section that fits with at least one projection available at an outer surface of the second body. The recess is in particular present in the rear section of the first body that is forming the mounting slot, so for example in the bent plate or respectively in a shank side of the plate. Thereby the second body is additionally fixed in the mounting slot of the first body, especially during assembling of the cutter link.

Particularly the first material of the first body is made of steel and the second body is made of a hard metal, in particular a refractory carbide or nitride. The use of refractory carbides or nitrides has the advantage that these materials are stable at high temperatures. Further a saw chain comprising cutting means made of these materials has a more stable sharpness so that there is no need to sharpen the cutting means. This may also lead to longer periods of use because the battery of electrical chain saws is conserved.

The cutter link can be used in a saw chain for a chain saw that comprises in addition to several cutter links, driving links and connecting links. As the second material of the second body re- spectively the cutting means can be varied without the need of using another first body or another connecting link, costs are reduced and time would be saved as there is no need of different tools for making cutter links with different cutting means mate- rials respectively different cutting tips.

The invention will be described more fully hereinafter with reference to the accompanying drawings, in which Fig. 1 is a flowchart of the method for manufacturing a cutter link,

Fig. 2 is a first body of the cutter link, Fig. 3 is a second body of the cutter link comprising the cut ting means,

Fig. 4 is a cutter link comprising the first body and the sec^¬ ond body inserted in a mounting slot of the first body,

Fig. 5 is a part of a saw chain,

Fig. 1 shows a flowchart for a method for manufacturing a cutter link 2 for a saw chain. The cutter link 2 comprises a first body 4 made of steel and a second body 6 whereby the second body com^¬ prises cutting means 8 respectively a cutting tip or cutting tooth made of a hard metal especially made of a refractory car^¬ bide (Fig. 2 - 4) . In a first step 100 the second body 6 comprising the cutting means 8 is inserted in the mounting slot 10 present in the first body 4 in order to form the cutter link assembly 2, 12, comprising the first body 4 and the second body 6 with the cutting means 8. In the next step 200 the cutter link assembly 2, 12 is heated to an austenitic temperature of the steel, e.g. about 900°C, where^¬ by only a deformation of the first body 4 made of steel takes place. The second body 6 and the cutting means 8 made of the re- fractory carbide show no phase transformation before and at this temperature, but result in a constant volume. Only the normal thermal expansion occurs in both materials, thus in the first body 4 as well as in the second body 6. In a third step 300 the assembled cutter link 2 is cooled down with a specific cooling rate from the first, austenitic tempera^¬ ture to a second temperature, for instance room temperature. The specific cooling rate is chosen such that from the austenitic structure a martensite and a bainite structure is formed, there- fore the cutter link 2 is guenched.

In a fourth step 400 the cutter link assembly 12 is heated again to a third temperature, between 250°C and 650°C for tempering the cutter link assembly 12, especially the first body 4 made of steel after the cooling respectively guenching step.

Fig. 2 shows the first body 4 of the cutter link 2 made of steel. In its rear section 16, the first body 4 comprises a mounting slot 10 that is formed by a bent plate 18. The bent plate 18 is formed nearly trapezoidal in cross section and com^¬ prises a base side plate 24 and two shank side plates 26 that run towards each other and merge into two oppositely disposed and spaced apart side plates 22 that form a base body 20 of the first body 4. In other words: the mounting slot 10 formed by the bent plate 18 has approximately the shape of a trapezoidal prism. According to Fig. 2 the two side plates 22 and the bent plate 18 with its base side 24 and the two shank sides 26 are formed integrally. The first body 4 comprises two depth gauges 14. Each of the depth gauge 14 is positioned forwardly of the cutting means 8 in running direction R of the cutter link 2 at one side plate 22. Each of the side plates 22 comprises two riv^¬ et holes 46. The inner surface 28 of the first body 4 respec^¬ tively the rear section 16 or the mounting slot 10 comprises a recess 30, which has for example the form of a rectangle.

Fig. 3 shows a second body 6 of the cutter link 2 that comprises cutting means 8 made of refractory carbide. The second body 6 has a geometry that fits with the mounting slot 10 and shows an trapezoidal cross section, respectively has approximately the form of a trapezoidal prism. In general the geometry of the sec^¬ ond body 6 should be designed in order to accommodate the stresses created during the cooling for the chosen material of the second body 6 and the cutting means 8 and to fit in the pro^¬ duction process. The cutting means 8 comprises cutting surfaces 44. An opposite side of the cutting means 8 forms a stop 48 that prevents the cutting means 8 from being inserted in the mounting slot 10. The second body 6 comprises a projection 34 on its out^¬ er surface 32 that fits with the recess 30 of the mounting slot 10.

Fig. 4 shows the cutter link 2 after the manufacturing process. The second body 6 is inserted in the mounting slot 10 of the first body 4 and form-locking connected with the first body 4 after the heating and cooling operation. The cutting means 8 protrude outwardly from the mounting slot 10 in a running direc^¬ tion R of the cutter link 2. The two depth gauges 14 protrude outwardly from the base body 20 of the first body 4 with lower projection than the cutting means 8. Further the cutting means 8 protrude laterally on both sides (direction x and -x) and above (direction z) from the first body 4, respectively from the rear section 16 of the first body 4 formed by the bent plate 18.

Fig. 5 shows a part of a saw chain comprising a cutter link 2, a driving link 38 and connecting link 40 (represented by dashed lines) . The cutter link 2 is attached to the driving link 38 via the connecting link 40 by rivets (not shown) , which engage into the rivet holes 46.

List of reference numerals

2 cutter link

4 first body

6 second body

8 cutting means

10 mounting slot

12 cutter link assembly

14 depth gauge

16 rear section

18 bent plate

20 base body

22 side plate

24 base side

26 shank side

28 inner surface

30 recess

32 outer surface

34 projection

38 driving link

40 connecting link

42 stop

44 cutting surface

46 rivet hole

Claims

1. Method for manufacturing a cutter link (2) comprising a

first body (4) made of a first material and a second body (6) comprising cutting means made of a second material, whereby the second body (6) comprising the cutting means (8) is inserted in a mounting slot (10) present in the first body (4) in order to form a cutter link assembly (12), the cutter link assembly (12) is heated to a first temperature and is then cooled down with a specific cooling rate from the first temperature to a second temperature.

2. Method according to claim 1, whereby the first temperature is selected such, that a volume of the first material of the first body (4) is smaller at the first temperature than at the second temperature.

3. Method according to one of the claims 1 or 2, whereby the first temperature is an austenitic temperature.

4. Method according to one of the previous claims, whereby the specific cooling rate is chosen such that the first material transforms to martensitic and/or bainite structure.

5. Method according to one of the previous claims, whereby the first temperature is chosen such that the second material of the second body (6) does not pass through a phase transfor^¬ mation .

6. Method according to one of the previous claims, whereby the second material is a refractory carbide or nitride.

7. Method according to one of the previous claims, whereby the cutter link assembly (12) is heated to a third temperature after cooling down the cutter link assembly (12) to the second temperature.

8. Cutter link (2) for a saw chain (36) comprising at least

- a first body (4) made of a first material, and

- a second body (6) comprising cutting means (8) made of a second material,

- a mounting slot (10) present in a rear section (16) of the first body (4) in which the second body (6) is in^¬ serted and form-locking connected with the first body (4), whereby the cutting means (12) of the second body (6) protrude outwardly from the mounting slot (10) in a running direction of the cutter link (2), and

- at least one depth gauge (14) positioned forwardly of the cutting means (8) in running direction of the cutter link (2) and protruding outwardly from the first body (4) with lower projection than the cutting means (8) .

9. Cutter link (2) according to claim 8, whereby the rear section (16) of the first body (4) comprises a bent plate (18) that forms the mounting slot (10) in between.

10. Cutter link (2) according to claim 8 or 9, whereby the first body (4) comprises a base body (20) that is formed by two oppositely disposed and spaced apart side plates (22).

11. Cutter link (2) according to one of the claims 8 to 10,

whereby the bent plate (18) has a base side (24) and two shank sides (26) that run towards each other and each of the shank sides (26) is connected to one side plate (22) of the base body (20) .

12. Cutter link (2) according to one of the claims 8 to 11, whereby the cutting means (12) protrude laterally and/or above from the first body (4) .

13. Cutter link (2) according to one of the claims 8 to 12,

whereby an inner surface (28) of the first body (4) compris^¬ es at least one recess (30) in the rear section (16) that fits with at least one projection (34) available at an outer surface (32) of the second body (6) .

14. Cutter link (2) according to one of the claims 8 to 13,

whereby the first material of the first body (4) is made of steel and the second material of the second body (6) is made of a hard metal.

15. Cutter link according to claim 14, whereby the hard metal is a refractory carbide or nitride or tungsten carbide.