Tool for machining, and method for manufacturing such a tool

Abstract

The invention relates to a tool for machining a workpiece by removing material, and to a method for manufacturing same. The tool has a shank (1) and a tool head (2) which is designed as a spiral tap and has cutting elements. The cutting elements are formed in the manner of a screw spindle (3). A chip flute (4) extends helically, with a direction of rotation opposite to that of the screw spindle (3), from the distal end of the tool head (2) over at least part of its length. The chip flute (4) is conical at its beginning and merges into a cylindrical core diameter with constant dimensions.

Description

[0001] TOOL FOR MATERIAL PROCESSING

[0002] The invention relates to a tool for material removal from a workpiece, comprising a shank for connecting the tool to a drive and a tool head designed as a spiral tap with cutting elements configured to penetrate the workpiece to be machined and to remove a layer of material from the workpiece, wherein the cutting elements are designed in the form of a screw spindle, and wherein a flute in the form of a screw with a helix angle of non-zero and with a direction of rotation opposite to the screw spindle extends from the distal end of the tool head over at least a part of the length of the tool head, as well as a method for manufacturing such a tool by grinding a flute with a helix angle of non-zero and a conically tapered beginning into at least the distal section of a tool head designed as a spiral tap using a grinding wheel.

[0003] A successful cutting process with a material-removing tool requires good lubrication and effective chip evacuation. When machining blind holes, the chip must be guided backwards, along the tool, and back through the workpiece. When machining through holes, the chip should be guided forwards, as it should not come into contact with the machined thread surface.

[0004] To achieve this, various groove shapes are used, whereby in the following description of the known designs, for the sake of simplicity, a right-hand thread is assumed, i.e., the direction of rotation for screwing in is clockwise.

[0005] The following definitions are used in this application: A cutting edge generally has a cutting angle y, which is defined as the negative of the cutting surface relative to the normal of the material surface, or as the tangent to it at the point of contact. For a rotary tool, the normal is always the straight line that runs from the center of rotation or the longitudinal axis of the tool to the cutting edge. Furthermore, the wedge angle β of the cutting edge and the clearance angle a are important. Here, a + β + y = 90 degrees. At the rear transition of the groove to the outer diameter, i.e., at the edge that becomes the cutting edge when the tool is reversed, a cutting angle or shear angle of approximately 0 degrees should be present. This ensures that, in the case of threads that do not extend completely through the through-hole, the chip is sheared off when the tool is reversed.A positive – and possibly excessively large – cutting angle at this point could lead to the thread being stripped when the tap is unscrewed. A strongly negative cutting angle is highly prone to pinching the chip, which would cause the tool to break.

[0006] The angle of rotation of the grinding wheel during tool manufacturing is defined as the angle between the tool axis of the tool being ground and the normal to the grinding wheel's axis of rotation. For a straight groove parallel to the tool axis, this angle of rotation is 0°, meaning the grinding wheel's axis of rotation is oriented at a 90° angle to the tool.

[0007] For a tool with a spiral flute with a counter-rotation to the thread, i.e., in this case with a left-hand helix, the grinding wheel is guided along the tool with its angle of deflection corresponding to the flute pitch as the tool rotates around its axis. The cutting angle remains constant from front to back, and with a virtually unchanged immersion depth of the grinding wheel, the lip width is constant over the entire length.

[0008] When the tool is used, the groove, which is angled against the direction of rotation, pushes the chip forward. The resulting force increases with increasing helix angle. However, excessive helix angle weakens the tap, which is why, in practice, only a few strongly helixed left-hand spiral flutes are found.

[0009] The resistance to forward chip flow increases with increasing chip length. The chip tends to stall. However, since the tool continues to rotate and penetrate, the chip remains in the flutes. It is no longer pushed forward, or rather, it is pushed backward in the flute. The machining length is thus limited. Shearing off the chip, even with a non-through-hole thread, is not a problem if the flute geometry is well designed.

[0010] In tools with straight grooves and a chamfered (spoon) lead, the front of the straight groove is tapered and widened with a left-hand helix. The straight grooves serve, on the one hand, to supply a suitable lubricant, and on the other hand, to create a clearance angle (rear face) for the cutting wedge.

[0011] There are two common manufacturing methods: Either the grinding wheel is guided conically and obliquely along the tool axis. The cutting angle decreases considerably when viewed from the front, resulting from the shape, the cone, and the helix. Alternatively, the grinding wheel can be guided conically along the tool axis with an angle of entry essentially corresponding to the helix angle, while the tool rotates around its longitudinal axis. This results in a cutting angle that remains almost constant over the chamfering cut length.

[0012] Both of the tools and manufacturing processes described above ensure excellent chip ejection, with the chip being forced forward. The combination of a left-hand spiral and taper directs the resulting force on the chips even more strongly forward than the spiral flute described earlier. However, these designs significantly reduce the lip width at the front. Therefore, especially with uncut threads, frequent breakage of the cutting lip during chip shearing is observed.

[0013] Tools with only a chamfered lead-in have no clearance angle in their thread profile. Only the conical outer diameter at the lead-in is ground back. This design is rarely used anymore for sheet metal work and short threads. Furthermore, the lack of grooves along the tool prevents lubricant flow.

[0014] CN 104159692 A discloses a spiral tap with a screw section, a primary flute in a screw shape that intersects a screw thread of the screw spindle, and a secondary flute formed in a tip section within the primary flute. A cutting edge is formed along a ridge line between a sidewall surface in the direction of tap rotation, consisting of a pair of sidewall surfaces of the secondary flute and an outer circumferential surface of the screw section, and has a rake angle of -10 to 0 degrees. The secondary flute has a helix angle smaller than that of the primary flute, and the secondary flute has a positive or negative helix angle of 0 to 3 degrees.This tap, primarily intended for machining difficult-to-machine nickel alloys, is not a simple through-hole tap. It also features a right-hand spiral flute, meaning it runs in the same direction as the thread pitch. The chamfered lead-in is almost a straight, tapered flute. There is a distinct kink between the main flute and the chamfered lead-in, and two different helix angles are present.

[0015] The object of the present invention was to overcome the disadvantages of the prior art and to provide a device that ensures safe and trouble-free machining of a workpiece with optimal chip ejection.

[0016] Another task is to find a method for manufacturing such a tool simply, quickly and with minimal effort.

[0017] This problem is solved by a device and a method according to the claims.

[0018] The device according to the invention is characterized in that the chip groove, starting from the distal end of the tool, tapers conically towards the shank over a portion of the length of the screw spindle and then transitions to a cylindrical inner diameter with constant dimensions until its end. Thus, efficient chip evacuation is guaranteed by the conically angled start of the groove, while the spiral groove shape ensures a stable lip width.

[0019] Preferably, the helix angle of the flute is constant on its cut side. However, due to the taper and the varying angle of entry during manufacturing, the helix angle can also be subject to slight variations of up to 4°.

[0020] Another embodiment according to the invention is characterized in that the cutting angle of the cutting elements decreases preferably continuously from the distal end of the tool to at least the end of the conical section of the chip groove.

[0021] Preferably, the cutting angle at the distal beginning of the conical groove section is in the range between 3 and 12 degrees and at the end of the conical section is between -2 and 4 degrees, then abruptly transitions to a cutting angle between 0 and 10 degrees, preferably between 3 and 5 degrees, and preferably remains unchanged until the end of the groove.

[0022] The method for manufacturing a tool according to the preceding paragraphs is characterized according to the invention in that, when the grinding wheel enters the tool at the distal end of the tool head, the angle of entry of the grinding wheel is greater than the helix angle of the chip groove.

[0023] Preferably, the steering angle is between 10° and 2°, preferably about 5°, which is greater than the twist angle of the flute.

[0024] Another embodiment according to the invention provides that during the relative movement of the grinding wheel and the tool, the steering angle of the grinding wheel is preferably continuously reduced to ensure the continued production of the chip groove.

[0025] Advantageously, the deflection angle is approximately equal to the twist angle of the groove at the earliest at the end of the conical section of the clamping groove, particularly in the area of ​​the cylindrical inner diameter.

[0026] To better understand the invention, it is explained in more detail with reference to the following figures.

[0027] They each show, in a highly simplified, schematic representation:

[0028] Fig. 1 shows a side view of a prior art tool with a spiral groove with counter-thread to the thread;

[0029] Fig. 2 shows a front view of the tool in Fig. 1;

[0030] Fig. 3 shows a side view of a tool according to the prior art with straight

[0031] Grooves and peel cut;

[0032] Fig. 4 shows a front view of the tool in Fig. 4;

[0033] Fig. 5 shows a side view of a prior art tool with flat, straight grooves and peeling cut;

[0034] Fig. 6 is a front view of the tool of Fig. 8; Fig. 7 is a perspective view of a tool according to the invention;

[0035] Fig. 8 shows a side view of the tool of Fig. 12;

[0036] Fig. 9 shows a cross-section through the tool of Fig. 12 at the level of plane AA;

[0037] Fig. 10 shows a cross-section through the tool of Fig. 12 at the level of plane BB;

[0038] Fig. 11 shows a cross-section through the tool of Fig. 12 at the level of plane CC;

[0039] Fig. 12 shows a side view of the tool and a grinding wheel during the manufacturing process;

[0040] Fig. 13 shows a perspective view of the tool and the grinding wheel;

[0041] Fig. 14 shows another perspective view of the tool and the grinding wheel.

[0042] It should be noted at the outset that in the differently described embodiments, identical parts are provided with the same reference numerals or component designations, and the disclosures contained in the entire description can be applied analogously to identical parts with the same reference numerals or component designations. Furthermore, the positional designations chosen in the description, such as top, bottom, side, etc., refer to the figure directly described and illustrated, and these positional designations must be applied analogously to the new position if the position changes.

[0043] The tool shown in side view in Fig. 1 and in front view in Fig. 2, according to the prior art, consists, as usual, of a shank 1 for connecting the tool to a drive and a tool head 2 designed as a spiral tap with cutting elements for machining the workpiece, which may transition into the shank via a short intermediate section without cutting elements. This intermediate section may have a smaller diameter than the shank and / or the tool head. The cutting elements are typically designed in the form of a screw spindle 3 and penetrate the workpiece during machining to remove a layer of material. At least one helical flute 4 with a helix angle 5 other than 0° runs in the opposite direction of rotation to the screw spindle 3 from the distal end of the tool head 2 over at least a portion of the length of the tool head 2 towards the shank 1.The groove 4 ends with a run-out section 10 at the beginning of the shaft 1 or in the intermediate section.

[0044] Figures 3 and 4 also show, in side view and front view, another tool according to the prior art, wherein straight, i.e., parallel to the longitudinal axis 5 of the tool, flutes 4 are machined into the tool head 2 in the area of ​​the screw spindle 3 with the cutting elements. At the distal end of the tool head 2, a peeling cut 6, also called a spoon cut, is machined by widening the straight flute 4 conically and with a left-hand helix.

[0045] A variant of the tool of Eig. 3 and Fig. 4 with significantly smaller and flatter grooves 4 and also a small peeling cut 6 is shown in Fig. 5 and Fig. 6.

[0046] In order to achieve safe and trouble-free machining of a workpiece with optimal chip ejection, a tool such as the example shown in Figs. 7 to 11 is provided.

[0047] As already known, the tool according to the invention also has a shank 1 for connecting the tool to a drive and a tool head 2 designed as a spiral tap with cutting elements for machining the workpiece, wherein the cutting elements are typically designed in the form of a screw spindle 3. At least one flute 4, preferably several flutes 4, preferably 3 flutes 4, extend in a helical shape and with a helix angle 5 other than 0 with a direction of rotation opposite to the screw spindle 3 from the distal end of the tool head 2 over at least a part of the length of the tool head 2 in the direction of the shank 1.

[0048] Each flute 4 tapers conically from the distal end of the tool over a portion of the length of the screw spindle 3 towards the shank, i.e., it has a distal conical section 7 that ensures efficient chip evacuation. Towards the shank 1, this conical section 7 is followed by a section 9 of the flute 4 with constant dimensions, defined by a narrowly defined, preferably abrupt transition in the region 8. This section 9 of the flute 4 also defines a cylindrical core diameter of the tool up to its end, either before or at the beginning of the shank 1, thus creating a stable lip width for the cutting elements. In a preferred embodiment, the helix angle 5 of the flute 4 is constant on its cutting side and, in the embodiment shown in Fig. 8, is approximately 17°.However, the helix angle 5 may be subject to slight changes of up to 4° due to the conicity and the varying angle of entry of the grinding wheel during manufacturing.

[0049] The cutting angle y of the flute 4, however, preferably decreases continuously, starting from the distal end of the tool along the length of section 7, i.e., at least to its end with the transition region 8. Preferably, the cutting angle y at the distal beginning of the conical flute section 7 is in the range between 3 and 12 degrees and at the end of the conical section 7 is between -2 and 4 degrees. In the transition region 8, there is then a preferably abrupt transition to a cutting angle y between 0 and 10 degrees, preferably to an angle between 3 and 5 degrees. This value then preferably remains unchanged up to the proximal end of the flute 4 in the region of the shank 1 of the tool.

[0050] The cross-sectional shapes shown and described are only valid as long as the outer diameter of the tool head 2 remains constant. At conical (tip) or stepped sections, the cross-sectional shapes may deviate. The cross-sections also change at the grinding wheel exit point, depending on the dimensions of the grinding wheel 12.

[0051] The inventive method for manufacturing such a tool is a further development of the known method in which a flute 4 with a helix angle 5 other than 0 is produced by grinding, preferably with a grinding wheel 11, into at least the tool head 2, which is preferably designed as a spiral tap. In this process, for example, a tapered beginning 7 can also be produced in at least the distal section by controlling the depth of penetration of the grinding wheel.

[0052] According to the invention, this method, schematically illustrated in Figures 12 to 14, is further improved in that, when a grinding wheel 11 preferably enters the tool at the distal end of the tool head 2, the angle of entry 8 of the grinding wheel 11, i.e., the angle between the tool axis 5 of the tool to be ground and the normal to the grinding wheel's axis of rotation 12, is greater than the helix angle 5 of the flute 4. In particular, the angle of entry 8 is between 10° and 2°, preferably about 5°, greater than the helix angle of the flute 4. In the embodiment shown in Figure 12, the angle of entry 8 is about 19°.

[0053] The method can be advantageously extended by continuously reducing the deflection angle 8 of the grinding wheel 11 during the relative movement of the grinding wheel and the tool, i.e., the feed of the grinding wheel relative to the tool in its axial direction while the tool rotates about its longitudinal axis 5, in order to continue producing the chip groove 4. At the earliest towards the end of the conical section 7 of the chip groove 4, but particularly in the region of the cylindrical inner diameter, the deflection angle 8 is then approximately equal to the helix angle 5 of the chip groove 4.

[0054] The exemplary embodiments show possible embodiment variants, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiment variants, but rather various combinations of the individual embodiment variants are also possible and this possibility of variation lies within the skill of the person skilled in this technical field due to the teaching on technical action by the present invention.

[0055] All references to value ranges in this description are to be understood as encompassing any and all sub-ranges thereof, e.g., the reference 1 to 10 is to be understood as including all sub-ranges, starting from the lower limit 1 and the upper limit 10, i.e., all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g., 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0056] For the sake of clarity, it should be noted that, for better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced in size. Reference symbols list

[0057] 1 tool shaft

[0058] 2 Tool head

[0059] 3 screw spindles

[0060] 4 clamping groove

[0061] 5 Tool longitudinal axis

[0062] 6. Peel cut

[0063] 7 Conical groove section

[0064] 8 Transition area

[0065] 9 Groove section with constant dimensions

[0066] 10. Grinding wheel exit

[0067] 11 grinding wheel

[0068] 12 Axis of the grinding wheel a Clearance angle ß Wedge angle

[0069] Y angle of intersection

[0070] 5 twist angles

[0071] E Steering angle

Claims

P a t e n t a n s p r ü c h e 1. Tool for material removal from a workpiece, comprising a shank (1) for connecting the tool to a drive and a tool head (2) designed as a spiral tap with cutting elements designed to penetrate the workpiece to be machined and to remove a layer of material from the workpiece, wherein the cutting elements are designed in the form of a screw spindle (3), and wherein a flute (4) in the form of a screw with a helix angle (5) other than 0 and with a direction of rotation opposite to the screw spindle (3) extends from the distal end of the tool head (2) over at least a part of the length of the tool head, characterized in that the flute (4) is designed to taper conically from the distal end of the tool over a part (7) of the length of the screw spindle (3) towards the shank (1) and then transitions to a cylindrical inner diameter with constant dimensions up to its end.

2. Tool according to claim 1, characterized in that the cutting angle (y) of the cutting elements decreases preferably continuously from the distal end of the tool to at least the end of the conical section (7) of the flute (4).

3. Tool according to claim 2, characterized in that the cutting angle (y) at the distal beginning of the conical flute section (7) is in the range between 3 and 12 degrees and at the end of the conical section (7) is between -2 and 4 degrees, then abruptly transitions to a cutting angle (y) between 0 and 10 degrees, preferably between 3 and 5 degrees, and preferably remains unchanged until the end of the flute (4).

4. Method for manufacturing a tool according to claims 1 to 3 by grinding a flute (4) with a helix angle (5) other than 0 and a conically tapered beginning into at least the distal section of a tool head (2) designed as a spiral tap by means of a grinding wheel, characterized in that when the grinding wheel enters the tool at the distal end of the tool head (2) the angle of entry (s) of the grinding wheel is greater than the helix angle (5) of the flute (4).

5. Method according to claim 4, characterized in that the steering angle (s) is between 10° and 2°, preferably about 5°, greater than the twist angle (5) of the clamping groove (4).

6. Method according to claim 4 or 5, characterized in that during the relative movement of the grinding wheel and the tool for the continued production of the chip groove (4) the steering angle (s) of the grinding wheel (12) is preferably continuously reduced.

7. Method according to claim 6, characterized in that the deflection angle (s) is approximately equal to the twist angle (5) of the clamping groove at the earliest at the end of the conical section of the clamping groove, in particular in the region of the cylindrical inner diameter.

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