Tool combination having a chisel holder and two chisels

Abstract

The invention relates to a tool combination consisting of a chisel holder, which can be fastened to a milling drum of a soil tillage machine, and at least one leading and one trailing chisel, which are retained on the chisel holder, wherein the trailing chisel is arranged after the leading chisel, based on a working movement of the tool combination in use in the soil tillage machine, and wherein each chisel has a chisel tip having a cutter. According to the invention the trailing chisel tip of the trailing chisel has, at least in some areas, a greater hardness than the leading chisel tip of the leading chisel. Thus stoppage times of the soil tillage machine for maintenance can be reduced and the loss of chisels can at least be decreased.

Claims

1. A tool combination, comprising: a milling drum for a soil working machine; a chisel holder fastened to the milling drum; at least one leading chisel mounted on the chisel holder, and including a leading chisel tip and a leading cutting edge; at least one trailing chisel mounted on the chisel holder, and including a trailing chisel tip and a trailing cutting edge; the at least one trailing chisel being arranged after the at least one leading chisel with reference to a working movement of the chisels as the milling drum rotates so that the trailing chisel is arranged to rework a milling performed by the leading chisel; the trailing chisel tip having at least in some areas a greater hardness than the leading chisel tip; wherein the leading chisel and the trailing chisel are configured and arranged on the chisel holder such that the leading cutting edge of the leading chisel tip is arranged on a larger radius from a rotational axis of the milling drum and the trailing cutting edge of the trailing chisel tip is arranged on a smaller radius from the rotational axis of the milling drum wherein the leading chisel is rotatably mounted within the chisel holder, and the leading chisel is configured and arranged on the chisel holder such that as the milling drum rotates the leading chisel penetrates obliquely relative to a central longitudinal axis of the leading chisel into soil material to be removed, so that the leading chisel rotates about its center longitudinal axis; wherein the trailing chisel is fixedly mounted within the chisel holder, and the trailing chisel is configured and arranged on the chisel holder such that the trailing chisel follows the path of the leading chisel as the milling drum rotates; and wherein the leading chisel protrudes beyond the trailing chisel transversely to the working movement of the tool combination on both sides of the trailing chisel.

2. The tool combination of claim 1, wherein: the trailing chisel tip is formed, at least in some areas, of a superhard material.

3. The tool combination of claim 2, wherein the superhard material is selected from the group consisting of: a diamond material; a diamond-reinforced material; a silicon carbide material; cubic boron nitride; and combinations of at least two of the aforementioned materials.

4. The tool combination of claim 2, wherein the superhard material includes at least in part a diamond material selected from the group consisting of: a monocrystalline diamond; a polycrystalline diamond; a chemically separated diamond; a physically separated diamond; a natural diamond; an infiltrated diamond; a diamond layer; successive diamond layers; a thermally stable diamond; and a silicon-bonded diamond.

5. The tool combination of claim 2, wherein: the trailing chisel tip includes a base support formed of a carbide material, the base support facing toward the trailing cutting edge being covered by the superhard material.

6. The tool combination of claim 2, wherein: the superhard material is configured as a layer.

7. The tool combination of claim 1, wherein: the trailing chisel is connected to the chisel holder such that the trailing chisel is fixed axially and is fixed in a peripheral direction of the trailing chisel.

8. The tool combination of claim 7, wherein: the leading chisel is connected to the chisel holder such that the leading chisel is held axially and is rotatable in a peripheral direction of the leading chisel.

9. The tool combination of claim 1, wherein: the leading chisel is connected to the chisel holder such that the leading chisel is held axially and is rotatable in a peripheral direction of the leading chisel.

10. The tool combination of claim 1, wherein: the trailing chisel is connected to the chisel holder in a non-exchangeable manner.

11. The tool combination of claim 10, wherein: the leading chisel is exchangeably connected to the chisel holder.

12. The tool combination of claim 1, wherein: the leading chisel is exchangeably connected to the chisel holder.

13. The tool combination of claim 1, wherein: the trailing chisel tip is soldered to the chisel holder so that the trailing chisel tip is directly and non-detachably connected to the chisel holder.

14. The tool combination of claim 1, wherein: the trailing chisel includes a shank connected indirectly or directly to the trailing chisel tip; and the chisel holder includes a trailing chisel receiving fixture, the shank being held in the trailing chisel receiving fixture.

15. The tool combination of claim 14, wherein: the shank is held in the trailing chisel receiving fixture by a connection selected from the group consisting of: an integrally bonded connection; a non-positive connection; and a positive connection.

16. The tool combination of claim 1, wherein: the trailing chisel is configured and arranged to cut a smaller chip volume than is the leading chisel.

17. The tool combination of claim 1, wherein: the smaller radius of the trailing cutting edge of the trailing chisel tip from the rotational axis of the milling drum is no more than 3 mm smaller than the larger radius of the leading cutting edge of the leading chisel tip from the rotational axis of the milling drum.

18. The tool combination of claim 1, wherein: the larger radius, the smaller radius and a distance between the leading cutting edge and the trailing cutting edge are such that given a predefined speed of advancement of the soil working machine and a predefined rotation speed of the milling drum, the trailing chisel has a predefined depth of penetration into a material to be milled.

19. The tool combination of claim 1, wherein: a distance between the leading cutting edge and the trailing cutting edge is in a range of from 45 mm to 75 mm; and the leading chisel and the trailing chisel are configured and arranged on the chisel holder such that the smaller radius is from 1 mm to 7 mm smaller than the larger radius.

20. The tool combination of claim 19, wherein: the distance between the leading cutting edge and the trailing cutting edge is in a range of from 50 mm to 60 mm.

21. The tool combination of claim 19, wherein: the smaller radius is from 2 mm to 5 mm smaller than the larger radius.

22. The tool combination of claim 1, wherein: the leading chisel and the trailing chisel are configured and arranged on the chisel holder such that a setting angle of the trailing chisel relative to a radial line running from the rotational axis of the milling drum through the trailing cutting edge is smaller than a setting angle of the leading chisel relative to a radial line running through the leading cutting edge.

23. The tool combination of claim 22, wherein: the setting angle of the trailing chisel is between 25° and 35°; and the setting angle of the leading chisel is between 35° and 45°.

24. The tool combination of claim 1, wherein: the chisel holder includes a joining zone where the trailing chisel is joined to the chisel holder, and the joining zone is at least partially covered by the leading chisel in a direction of the working movement of the tool combination from the trailing chisel.

Description

(1) The invention is explained in greater detail below on the basis of an illustrative embodiment represented in the drawings, wherein:

(2) FIG. 1 shows in schematic representation and side view a soil tillage machine in the form of a road milling machine,

(3) FIG. 2 shows in a side view a tool combination comprising a chisel holder, a leading chisel and a first trailing chisel,

(4) FIG. 3 shows in a side view the tool combination shown in FIG. 2, fitted on a base part,

(5) FIG. 4 shows in a side view a tool combination comprising a chisel holder, a leading chisel and a second trailing chisel,

(6) FIG. 5 shows in a top view the tool combination shown in FIG. 4, and

(7) FIG. 6 shows in a lateral sectional representation the tool combination shown in FIGS. 4 and 5.

(8) FIG. 1 shows in schematic representation and side view a soil tillage machine 10 in the form of a road milling machine. The soil tillage machine 10 may also be referred to as a soil working machine. A machine frame 12 is supported by running gears 11.1, 11.2, for instance chain drive assemblies, such that it is height-adjustable via four lifting columns 16.1, 16.2. The soil tillage machine 10 can be operated from a control station 13 via a control system 17 arranged in the control station 13. In a concealed milling drum box, a milling drum 15, which is likewise arranged in a concealed manner and in the illustration is drawn in dashed representation, is mounted rotatably about a rotational axis 15.1. A conveying device 14 serves for the evacuation of the milled material.

(9) During use, the machine frame 12 is moved over the subsoil to be tilled at a speed of advancement inputted via the control system 17. Chisels 20, 30, 31 arranged on the rotating milling drum 15 and shown in FIGS. 2 to 6 hereupon remove the subsoil. The height position, and the rotation speed of the milling drum 15, can be set from the control system 17. Via the height position of the milling drum 15, the milling depth is set. The height position of the milling drum can here be realized, according to the machine type, via the height-adjustable lifting columns 16.1, 16.2. Alternatively, the milling drum 15 can be adjustable in height relative to the machine frame 12.

(10) FIG. 2 shows in a side view a tool combination 50 comprising a chisel holder 40, a leading chisel 20 and a first trailing chisel 30. The leading chisel 20 has a chisel head 21 and a chisel shank 24, integrally molded thereon and shown in FIG. 6. The chisel head 21 bears a leading chisel tip 22, consisting of a hard material, for instance of carbide. On its end, the leading chisel tip 22 forms a leading cutting edge 23.

(11) The leading chisel tip 22 is usually soldered to the chisel head 21 along a contact surface. In the chisel head 21 is incorporated, for this purpose, a receiving fixture 21.2, into which the chisel tip 22 is inserted and soldered.

(12) As shown in FIG. 6, the chisel shank 24 bears a longitudinally slotted, cylindrical clamping sleeve 25. This is held on the chisel shank 24 captively in the direction of the longitudinal extent of the leading chisel 22, yet such that it is freely rotatable in the peripheral direction. In the region between the clamping sleeve 25 and the chisel head 21 is arranged a wear protection disk 26. In the fitted state, the wear protection disk 26 is supported on a counter face of the chisel holder 40 and, facing away from the chisel holder 40, on the bottom side of the chisel head 21, which latter, in this region, is widened in terms of its diameter by a collar 21.1.

(13) The chisel holder 40 is equipped with a leading protrusion 41, in which, as shown in FIG. 6, is incorporated a leading chisel receiving fixture 42 in the form of a cylindrical bore. In this leading chisel receiving fixture 42, the clamping sleeve 25 is held clamped with its outer periphery on the bore inner wall. The leading chisel receiving fixture 42 opens out into an expulsion opening 47. Through this, a drift punch (not shown) can be introduced for the purpose of removing the leading chisel 20. Said drift punch acts on the end of the chisel shank 24 in such a way that, in overcoming the clamping force of the clamping sleeve 25, the leading chisel 20 is ejected from the leading chisel receiving fixture 42.

(14) The leading protrusion 41 is molded onto a base 43 of the chisel holder 40. Laterally offset and opposite to the leading protrusion 41, a plug connector 44 is integrally connected to the base 43. The plug connector 44 can be introduced into a plug socket of a base part 60 shown in FIG. 3 and clamped in place there by means of a clamping screw (not shown). For this, the plug connector 44 has a clamping surface 44.1, shown in FIG. 2, on which the clamping screw acts. To the side of the plug connector 44, the base part 43 has bearing surfaces 43.1, with which, in the fitted state, it is pressed under force action of the clamping screw against the base part 60 shown in FIG. 3. The base part 60 itself is welded via its bottom side 61 onto a milling drum tube of the milling drum 15 indicated in FIG. 1. In the present illustrative embodiment, four bearing surfaces 43.1 are provided on the base part 43. These include two rear bearing surfaces 43.1, which are arranged, at least in some regions, after the plug connector 44. In addition, two front bearing surfaces 43.1, which are arranged, at least in some areas, before the plug connector 44, are used. The two rear bearing surfaces 43.1 lie at an angle to one another. Similarly, the two front bearing surfaces 43.1 lie at an angle to one another. The rear bearing surfaces and the front bearing surfaces 43.1 respectively form a bearing surface pair. Starting from the plug connector side 44, the bearing surfaces 43.1 of a bearing surface pair here diverge in the direction of the machining side defined by the chisels 20, 30. In addition, the front bearing surfaces 43.1 lie at angle to the rear bearing surfaces 43.1.

(15) Alternatively to the four bearing surfaces 43.1, which can be set, in particular, relative to one another in the shape of a pyramid, it is conceivable to use three bearing surfaces 43.1, which lie at an angle to one another and are likewise set relative to one another in a pyramid-like arrangement. It can here be provided that a bearing surface 43.1 is provided, at least in some areas, after the plug connector 44 in the motional direction, and two bearing surfaces 43.1 are provided, at least in some areas, before the plug connector 44 in the motional direction. Conversely, it is also conceivable that two bearing surfaces 43.1 lying at an angle to one another are provided, at least in some areas, in the region after the plug connector 44, and a bearing surface 43.1 is provided, at least in some areas, before the plug connector 44 in the motional direction.

(16) The bearing surfaces 43.1 serve to support the chisel holder 50 on the base part 60. Accordingly, the base part 60 has corresponding support surfaces, on which the bearing surfaces 43.1 of the chisel holder 50 land.

(17) Through the rotation of the milling drum 15 and the advancement of the soil tillage machine 10, the tool combination 50 is moved in accordance with a working movement 76 indicated by an arrow. Based on this working movement 76, after the leading protrusion 41 a first trailing protrusion 45 is molded onto the base 43 of the chisel holder 40. The leading protrusion 41 and the first trailing protrusion 45 are connected to one another along their mutually facing sides. At its end facing away from the base 43, the first trailing protrusion 45 forms a first front side 45.1. Molded into this first front side 45.1 is a solder recess 45.2. In the shown embodiment, the first trailing chisel 30 is formed merely of a trailing chisel tip 32. This has a base support 33. The base support is of cylindrical configuration. It is made of a hard material, in the present case of carbide. To the base support 33 is connected a superhard material 34, in the present case in the form of a polycrystalline diamond. The superhard material 34 forms, facing away from the base support 33, a trailing cutting edge 35. To this end, it is of conical configuration and, facing toward the base support 33, is adapted to the outer cylindrical contour thereof. As a result, the base support 33 is on its end completely covered by the superhard material 34. Opposite to the trailing cutting edge 35, the base support 33 is inserted in the solder recess 45.2 of the first trailing protrusion 45 and soldered to the latter.

(18) FIG. 3 shows in a side view the tool combination 50 shown in FIG. 2, fitted on the base part 60. To this end, as already described with reference to FIG. 2, the chisel holder 40 is plugged with its plug connector 44 into a socket of the base part 60 and fixed therein by means of a clamping screw. The base part 60 is along its bottom side 61 connected, in particular welded, to the milling drum tube (not represented in FIG. 3) of the milling drum 15 shown in FIG. 1.

(19) Starting from the rotational axis 15.1, shown in FIG. 1, of the milling drum 15, a larger radius 70 and a smaller radius 71 are represented by corresponding arrows. The larger radius 70 marks a larger cutting circle 70.1, and the smaller radius 71 a smaller cutting circle 71.1. The leading cutting edge 23 of the leading chisel 20 is arranged on the larger radius 70. The trailing cutting edge 35 of the first trailing chisel 30 lies on the smaller radius 71. Upon rotation of the milling drum 15 along the working movement 76 marked by the arrow, the leading cutting edge 23 of the leading chisel 20 is thus moved along the larger cutting circle 70.1, and the trailing cutting edge 35 of the first trailing chisel 30 along the smaller cutting circle 71.1, without any advancement of the soil tillage machine 10.

(20) Starting from the rotational axis 15.1 of the milling drum 15, two radial lines 72 are respectively run through the leading cutting edge 23 of the leading chisel 20 and the trailing cutting edge 35 of the first trailing chisel 30. They there cross a leading center line 73.1 of the leading chisel 20 or a trailing center line 73.2 of the first trailing chisel 30. The leading center line 73.1 is oriented along the axis of symmetry of the leading chisel 20 in the direction of the longitudinal extent thereof. Correspondingly, the trailing center line 73.2 runs along the axis of symmetry of the first trailing chisel 30. The leading center line 73.1 indicates the orientation of the leading chisel 20, while the trailing center line 73.2 marks the orientation of the first trailing chisel 30. The leading chisel 20 and the first trailing chisel 30 are oriented respectively at a setting angle 74, marked by a double arrow, in relation to the associated radial line 72. The setting angle 74 of the first trailing chisel 30 is here chosen smaller than the setting angle 74 of the leading chisel 20.

(21) In FIG. 4, a tool combination 50 comprising a chisel holder 40, a leading chisel 20 and a second trailing chisel 31 is shown in a side view. The structure of the leading chisel 20 and its fastening to the chisel holder 40 correspond to the previously described structure and the previously described fastening respectively, so that reference is made to this description. The leading protrusion 41, the base 43 and the plug connector 44 also correspond to the description relating to FIGS. 2, 3 and 6.

(22) The second trailing chisel 31 has a pedestal 36, which is integrally connected to a shank 37 shown in FIG. 6. Starting from the cylindrically configured shank 37, the pedestal 36 tapers up to the diameter of the base support 33 of the trailing chisel tip 32. The pedestal 36 is formed of a hard material, in the present case of carbide. The base support 33 of the trailing chisel tip 32 is fitted onto the pedestal 36 and connected, in particular soldered, thereto. Opposite to the pedestal 36, a superhard material 34, in the present case in the form of a polycrystalline diamond, covers the base support 33. The superhard material 34 is here fixedly connected to the base support 33. Facing away from the base support 33, the superhard material 34 forms the trailing cutting edge 35 of the second trailing chisel 31. As represented in FIG. 6, the shank 37 of the second trailing chisel 31 is held in a trailing chisel receiving fixture 46.2. The trailing chisel receiving fixture 46.2 is here configured as a bore in a second trailing protrusion 46 of the interchangeable chisel holder 40. The trailing chisel receiving fixture 46.2, starting from a second front side 46.1 of the second trailing protrusion 46, is here molded into the latter. The shank 37 of the second trailing chisel 31 is fixed, both in the circumferential direction and axially, in the trailing chisel receiving fixture 46.2. The non-positive connection between the shank 37 and the trailing chisel receiving fixture 46.2 is realized in the present case by means of cold-stretching or shrinking. To this end, the shank 37 is produced with an interference fit in relation to the trailing chisel receiving fixture 46.2. For the joining, the shank 37 is cooled to the point where it can be inserted into the trailing chisel receiving fixture 46.2. When the shank 37 is subsequently heated, it expands due to thermal expansion, so that a non-positive connection is formed between the shank 37 and the trailing chisel receiving fixture 46.2. Besides the non-positive connection of the shank 37 to the trailing chisel receiving fixture 46.2 by means of cold-stretching or shrinking, other non-positive, positive or integrally bonded combinations are also conceivable. These can be realized, for instance, as a screwed joint, as a soldered joint, as a welded joint, or as an adhesive joint. Preferably, the shank 37 is also formed of a hard material, in particular of carbide. The screwed joint and the welded joint are examples of positive connections. The soldered joint and the adhesive joint are examples of integrally bonded connections.

(23) The second trailing protrusion 46 is arranged, based on the working movement 76 of the material combination 50, after the leading protrusion 41. Hence also the second trailing chisel 31, based on the working movement 76, is positioned after the leading chisel 20. When the tool combination 50 is fitted, the leading cutting edge 23 is arranged on the larger radius 70, and the trailing cutting edge 35 of the second trailing chisel 31 on the smaller radius 71, as is shown in FIG. 3 for a tool combination 50 comprising a first trailing chisel 30. The second trailing chisel 31 is likewise oriented at a smaller setting angle 74 (see FIG. 3) in relation to an associated radial line 72 than the leading chisel 20.

(24) FIG. 5 shows in a top view the tool combination 50 shown in FIG. 4. Same components are here, as previously adopted, identically labeled.

(25) A center plane 75 of the tool combination 50 is marked by a dashed line. The center plane 75 here relates to the plug connector 44, the base 43 and the leading protrusion 41 of the chisel holder 40, as well as to the leading chisel 20. It hence runs through the center of the leading chisel tip 22. The second trailing chisel 31 is arranged laterally offset from the center plane 75. This enables the tool combination 50 comprising the two chisels 20, 30, 31 to be fastened to the milling drum 15 such that it is obliquely inclined in the direction of the longitudinal extent of this same, wherein the second trailing chisel 31, upon rotation of the milling drum 15, follows the path of the leading chisel 20. As a result of the oblique arrangement, it is achieved that the leading chisel 20 mounted rotatably about its central longitudinal axis penetrates obliquely into the soil material to be removed. This has the effect that the leading chisel 20 rotates about its center longitudinal axis and is hence evenly worn along its periphery.

(26) FIG. 6 shows in a lateral sectional representation the tool combination 50 shown in FIGS. 4 and 5. As previously described, the leading chisel 20 is held in the leading chisel receiving fixture 42 of the chisel holder 40 such that it is rotatable on its chisel shank 24 by means of the clamping sleeve 25, but axially blocked. The second trailing chisel 31 is fixed with its shank 37 in the trailing chisel receiving fixture 46.2 of the second trailing protrusion such that it is blocked both in the peripheral direction and axially.

(27) In the tool combinations 50 shown in FIGS. 2 to 6, the leading chisel 20 and the respective trailing chisel 30, 31 are arranged relative to one another such that, when a tool combination 50 is fitted on a milling drum 15, the trailing chisel 30, 31 is moved along the same milling line as the leading chisel 20. The respective trailing chisel 30, 31 is thus, based on the working movement 76 of the tool combination 50, arranged after the leading chisel 20. The trailing chisel 30, 31 is hence arranged protected by the leading chisel 20.

(28) Transversely to the working movement 76, the leading chisel 20 is dimensioned larger than the trailing chisel 30, 31, so that it protrudes beyond the latter on both sides. As a result, the soil material removed by the leading chisel 20 is guided predominantly past the trailing chisel 30, 31. Likewise, the leading chisel 20 and/or the wear protection disk 26 and/or the leading protrusion 41 covers the joining region between the trailing chisel 30, 31 and the trailing protrusion 45, 46 of the chisel holder 40 along the working movement 76. The joining region between the trailing chisel 30, 31 and the trailing protrusion 45, 46 of the chisel holder 40 is thus protected from high abrasive wear. It can thereby reliably be avoided that the trailing protrusion 45, 46 washes out and the joining surface between the trailing chisel 30, 31 and the trailing protrusion 45, 46 is exposed. A situation in which the trailing chisel 30, 31 gets lost due to the wearing of the chisel holder 40 is hence avoided.

(29) The trailing chisel tip 32 of the trailing chisel 30, 31 is at least partially formed of a superhard material. The trailing chisel tip 32 is hence configured harder in comparison to the leading chisel tip 22 of the leading chisel 20, which is preferably made of a carbide. The trailing chisel tip 32, and hence the trailing chisel 30, 31, are thus configured significantly more resistant to abrasively induced wear than the leading chisel tip 22, and hence the leading chisel 20. Combined with the previously described, protected arrangement of the trailing chisel 30, 31, this has a significantly longer service life than the leading chisel 20. Given appropriate design and arrangement of the trailing chisel 30, 31, the service life of the trailing chisel 30, 31 lies in the order of magnitude of the service life of the chisel holder 40. As a result, the trailing chisel 30, 31 cannot be exchangeably connected to the chisel holder 40, in particular cannot be connected to the chisel holder 40 such that it cannot be exchanged in a non-destructive manner. By contrast, the leading chisel 20, which is exposed to heavy mechanical wear, is fastened in an easily exchangeable manner to the chisel holder 40. In the event of a worn leading chisel 20, this can thus be easily exchanged. Since the trailing chisel 30, 31, due to its long service life, no longer has to be exchanged, maintenances involving corresponding stoppage times of the soil tillage machine 10 shall be provided only for the exchange of the leading chisel 20. The operating costs of the soil tillage machine 10 can thereby be kept low.

(30) The superhard material is in the present case realized as a polycrystalline diamond. In accordance with the present invention, it can also be formed as a diamond material, as a diamond-reinforced material, as a silicon carbide material, as a cubic boron nitride, or as combinations of at least two of the aforementioned materials. All these materials or material combinations have a greater hardness than the carbide from which the leading chisel is produced, and hence a greater resistance to wear. Besides the polycrystalline diamond, a monocrystalline diamond, chemically separated diamond, physically separated diamond, natural diamond, infiltrated diamond, one or more successive diamond layers, thermally stable diamond, or silicon-bonded diamond can also be used as the diamond material.

(31) During a milling process, the tool combination 50, due to the rotation of the milling drum 15 and the advancement of the soil tillage machine 10, is moved through the soil material to be removed. The trailing cutting edge 35 of the trailing chisel 30, 31 is arranged, based on the rotational axis 15.1 of the milling drum 15, on a smaller radius 71, or a same radius as the leading cutting edge 23 of the leading chisel 20. Hence, and as a result of the diminished geometry of the trailing chisel 30, 31 in relation to the leading chisel 20, the leading chisel 20 cuts a larger volume than the trailing chisel 30, 31. According to the invention, the trailing chisel 30, 31 is designed and arranged to rework the milling of the leading chisel 20. In particular, a coarser milling is performed by the leading chisel 20, and a finer milling by the trailing chisel 30, 31. Correspondingly, the trailing cutting edge 32 of the trailing chisel 30, 31 is spatially arranged in such a way in relation to the leading cutting edge 23 of the leading chisel 20 that, given predefined operating parameters of the soil tillage machine 10, each of the chisels 20, 30, 31 has a customized depth of penetration into the soil material.

(32) For the performance of a fine milling, a depth of penetration of less than 15 mm, for instance, is suitable for the trailing chisel 30, 31. Typical operating parameters of the soil tillage machine 10 for such a milling process are a rotation speed of the milling drum 15 of 130 r.p.m., a speed of advancement of the soil tillage machine 10 of 20 m/min, and a milling depth of 100 mm. The larger cutting circle 70.1 of the leading cutting edge 23 measures, for instance, around 980 mm. From the milling depth of 100 mm and the larger cutting circle 70.1, a milling angle of 37.25°, within which the chisels 20, 30, 31, when the soil tillage machine 10 is operated with forward travel, engage in the soil material. From the engagement of the tool combination into the soil through to its exit from the soil, the soil tillage machine 10 moves forward about 15 mm. In order to obtain the desired fine-finishing with the trailing chisel 30, 31, as is suitable for the performance of a precision-milling, the smaller radius 71 on which the trailing cutting edge 35 of the trailing chisel 30, 31 is arranged must hence be chosen approximately no more than 3 mm smaller than the larger radius 70 on which the leading cutting edge 23 of the leading chisel 20 is arranged. Through the suitable arrangement of the trailing cutting edge 35 of the trailing chisel 30, 31, based on the leading cutting edge 23 of the leading chisel 20, the depth of penetration of the trailing chisel into the soil material can thus be set and predefined for predefined operating parameters of the soil tillage machine 10. It thereby becomes possible for the leading chisel 20 to execute, for example, a coarse milling task, for instance roughing, while the trailing chisel 30, 31 is designed for a precision milling, for instance finishing. The trailing chisel 30, 31 thus reworks the milling of the leading chisel 20. It hence determines the obtained milled surface pattern. Due to the very low wearing of the trailing chisel 30, 31, this milled surface pattern remains at least broadly the same, even after lengthy period of use of the tool combination 50 and high wearing of the leading chisel 20. When the leading chisel 20 becomes somewhat worn, then the trailing chisel 30 additionally assumes a part of the work function of the leading chisel 20, while a milled surface pattern with high surface quality is maintained.

(33) It is also conceivable to design the system such that, under the adopted machine parameters, the trailing chisel 30, at the start of the assignment, possesses a depth of cut of 0. Only once the leading chisel 20 starts to wear does the trailing chisel 30 enter into action and perform a material removal. Just as described above, it then reworks the milling of the leading chisel 20. A perfect milled surface pattern is hence obtained again.

(34) The leading chisel 20 is held in the leading chisel receiving fixture 42 of the chisel holder 40 such that it is rotatable about its center longitudinal axis. When the leading chisel 20 engages in the removed soil material, it is rotated about its center longitudinal axis. The leading chisel 20 hence becomes evenly worn over its periphery, whereby its service life is significantly extended. By contrast, the trailing chisel 30, 31 is non-rotatably connected to the chisel holder 40. Due to the extreme hardness of the trailing chisel tip 32, only minor wearing of the trailing chisel 30, 31 occurs, so that no rotatable mounting of the trailing chisel 30, 31 is necessary. As a result of the rigid connection of the trailing chisel 30, 31 to the chisel holder 40, vibrations in the trailing chisel tip 32 can be avoided. Such vibrations can lead to the fracture of the superhard material 34.