Abstract
A tool for producing an internal thread in a workpiece pilot hole having a thread major diameter and a thread minor diameter, which tool has a thread-forming section, by which an internal thread profile can be produced in a pilot hole wall. The internal thread profile having the thread major diameter and a thread inner diameter. The tool has a drilling section, by which the thread inner diameter of the internal thread profile can be expanded to the thread minor diameter by machining. At least one, in particular exactly one chip groove is associated with the drilling section of the tool, by which chip groove the chips produced as the thread inner diameter is expanded to the thread minor diameter can be transported away.
Claims
1-14. (canceled)
15. A tool for producing an internal thread in a workpiece pilot hole comprising: a thread major diameter and a thread minor diameter, the tool includes a thread shaping section with which an internal thread profile is produced in a pilot hole wall, which profile has the thread major diameter and a thread inner diameter, wherein the tool includes a drilling section with which the thread inner diameter of the internal thread profile is expanded in a chip machining operation to the thread minor diameter, wherein at least one chip groove is associated with said drilling section of the tool by which chips produced during the expansion of the thread inner diameter to the thread minor diameter are transported away, wherein the drilling section includes at least one longitudinal cutter with a radially outer longitudinal cutting edge, wherein the longitudinal cutting edge extends in the direction of the tool axis between two cutting corners and the longitudinal cutting edge has a radially inwardly bent edge profile by which cut surface edges on the internal thread produced are deburred.
16. The tool according to claim 15, wherein the chip groove extends with a groove length helically or linearly along a tool axis through the thread shaping section and beyond towards a tool clamping shaft.
17. The tool according to claim 15, wherein the thread shaping section includes at least one profile cog having a radially outer profile cog crest crest and a radially inner profile cog base spaced apart from said crest by a cog height, and the profile cog crest is located on a circular line whose diameter is greater than a pilot hole diameter, and in that the profile cog base is located on a circular line whose diameter is smaller than the pilot hole diameter.
18. The tool according to claim 15, wherein the thread shaping section, when viewed in a tool circumference direction, includes circumferentially distributed profile cogs, which are spaced apart from each other by at least one axially extending lubricating groove via which lubricant and/or coolant can be conducted to the profile cogs during thread shaping, and that a chip groove depth is greater than a lubricating groove depth.
19. The tool according to claim 16, wherein the drilling section is formed on a tool tip and transitions into the thread shaping section in a direction of a tool clamping shaft, and said drilling section is inserted stress-free into the workpiece pilot hole in a thread shaping stroke and said drilling section expands the internal thread profile by drilling to the thread minor diameter in a subsequent reversing stroke, whereby the internal thread is completed.
20. The tool according to claim 19, wherein the longitudinal cutting edge transitions into a cross cutter at a cutting corner which faces away from the tool tip, and the material is removed in the reversing stroke by the cross cutter and the longitudinal cutter.
21. The tool according to claim 15, wherein the thread shaping section is formed directly on a tool tip and the drilling section is offset from the tool tip by an axial offset, and the drilling section expands the internal thread profile by drilling to the thread minor diameter during a thread shaping stroke and is guided stress-free out of the internal thread in a subsequent reversing stroke.
22. The tool according to claim 15, wherein the thread producing section includes at least two profile cogs in an axial direction, whose cog flanks which face each other form a shaping chamber into which the workpiece material is displaced during shaping of the thread, and said forming chamber transitions radially inwardly into a pocket-shaped recess on a profile bottom, whereby a displacement space for workpiece material that is available during thread shaping is enlarged and the thread inner diameter of the shaped internal thread profile is reduced.
23. The tool according to claim 15, wherein the chip groove at the drilling section includes a chip guiding step, which at least partially closes the chip groove in an axial direction and by said chip guiding step discharge of chips towards the pilot hole in the machining process is prevented and transport of the chips out of the pilot hole is supported.
24. The tool according to claim 23, wherien the chip guiding step is formed directly on a tool tip, and/or the chip guiding step is formed while reducing a chip groove depth to a reduced chip groove depth.
25. The tool according to claim 23, wherein the chip guiding step includes a chip guiding surface, which at the drilling section converges with a radially outer clearance surface, thereby forming the longitudinal cutter, and/or the chip guiding surface transitions into an end face which forms a tool tip at an end-side transition edge.
26. The tool according to claim 25, wherein the end-side transition edge defines a free chip groove opening region, which leads into the tool end face.
27. The tool according to claim 16, wherein said tool includes a central cooling duct which is conducted from the tool clamping shaft towards a tool tip and the central cooling duct is in fluid communication with an outlet duct which leads into the chip groove, such that in the machining process a coolant is guided in the cooling duct to the tool tip and is guided in the opposite direction in the outlet duct from an orifice into the chip groove to support the chip discharge.
28. The tool according to claim 27, wherein both the central cooling duct and the outlet duct lead into a tool end face, particularly when using said tool in a blind hole, to provide a fluid communication between the central cooling duct and the outlet duct, and a flow cross section of the central cooling duct is greater than an overall cross section of the chip groove opening region and the outlet duct.
Description
[0030] The invention and its advantageous further developments and their advantages will be explained in more detail below with reference to drawings.
Wherein:
[0031] FIG. 1 shows a partial sectional view of a workpiece pilot hole with an internal thread;
[0032] FIGS. 2 and 3 show various views of a thread shaping tool;
[0033] FIGS. 4 to 8 each show views which illustrate the process steps for producing the internal thread shown in FIG. 1;
[0034] FIG. 9 shows a thread shaping tool according to a second embodiment;
[0035] FIG. 10 shows a thread shaping tool according to a third embodiment;
[0036] FIG. 11 shows a sectional view along section plane I-I from FIG. 10;
[0037] FIG. 12 shows a front view onto the tool tip of the thread shaping tool shown in FIG. 10; and
[0038] FIG. 13 shows a view according to FIG. 6.
[0039] FIG. 1 shows a finished threaded blind hole 1. The bottom 3 of the hole 1 is machined into a workpiece 5 to a target hole depth. In addition, the hole 1 comprises an internal thread 7 which extends along a hole axis B to a usable target thread depth t.sub.G. The internal thread 7 has a thread major diameter d.sub.A and a thread minor diameter d.sub.K.
[0040] The internal thread 7 shown in FIG. 1 is executed by means of the thread shaping tool 9 described below with reference to FIGS. 2 and 3. According to these, the tool 9 comprises a thread shaping section 11 and a drilling section 13, whose functions will be explained later. The thread shaping section 11 is implemented with a row of profile cogs 15, each of which comprising a radially outer profile cog crest 17 (FIG. 6) and radially inner profile cog base 19 (FIG. 6), which are spaced apart from each other by a cog height. The profile cog crest 17 is located in FIG. 6 on a circular line whose diameter ds is greater than a pilot hole diameter d.sub.V (FIG. 1 or FIG. 6) of a workpiece pilot hole 1 (FIG. 4). The profile cog base 19, on the contrary, is located on a circular line whose diameter d.sub.G is smaller than the pilot hole diameter d.sub.V. The structure and geometry of the profile cogs 15 of the thread shaping section 11 are of conventional make and known from prior art.
[0041] According to FIG. 2, 4, or 6, the drilling section 13 is formed directly on the tool tip and extends from there towards a tool clamping shaft 21 (FIG. 1) to merge with the thread shaping section 11. In FIG. 3, the drilling section 13 comprises three longitudinal cutters 23, which are evenly distributed across the circumference. Each of the longitudinal cutters 23 has a longitudinal cutting edge 25 (FIG. 6) which is located on an edge diameter d.sub.L which is smaller than the pilot hole diameter d.sub.V and greater than the thread inner diameter d.sub.I of the internal thread profile 27 (FIG. 6) described below.
[0042] As is visible in FIG. 7, the longitudinal cutting edge 25 extends along the tool axis W between two cutting corners 29, 31. The longitudinal cutting edge 25 has a radially inwardly bent profile; the effect of this edge geometry is described below. In addition the longitudinal cutting edge 25 transitions into a cross cutter 33 at the cutting corner 29 that faces away from the tool tip.
[0043] The method for producing the threaded blind hole 1 shown in FIG. 1 is described below with reference to FIGS. 4 to 8. Accordingly, in FIG. 4 the thread shaping tool 9 is inserted during a thread shaping stroke G into the workpiece pilot hole 1 until it reaches the target thread depth t.sub.G, wherein the tool axis W is in coaxial alignment with the drilling axis B. In the thread shaping stroke G, the tool feed f.sub.G and a thread shaping speed n.sub.G are coordinated to each other, such that an internal thread profile 27 (FIG. 5 or FIG. 6) is formed. In FIG. 6, the internal thread 27 has a radially outer thread base 37 and a radially inner crest 39, which are spaced apart by one profile height in the radial direction. As is visible in FIG. 6, material weakenings or defects 41 with molding bulges 40 are formed on the crest 39 of the internal thread profile 27, which bulges project radially inwards from the solid tool material and enclose a cavity 45. During the above thread shaping stroke G, the drilling section 13 formed on the tool tip is inserted stress-free into the workpiece pilot hole 1.
[0044] In the subsequent reversing stroke R (FIG. 7), the thread shaping section 11 on the tool side is guided out of the pilot hole 1 stress-free along the pitch of the internal thread profile 35 by means of an opposing reversing feed f.sub.R and a synchronized opposing reversing speed n.sub.R. The reversing stroke R includes a final processing step in which the drilling section 13 expands the thread inner diameter d.sub.I by drilling to the thread minor diameter d.sub.K. Material removal is selected such that the defects 41 on the crest 39 are completely removed. The cut surface edges 42 (FIG. 8) on the machined crest 39 of the internal thread 7 can at the same time be deburred due to the radially inwardly bent profile of the longitudinal cutting edge 25 outlined in FIG. 6.
[0045] As is apparent from the above description, defects 41 form during the thread shaping stroke G directly on the radially inner crest 39 of the internal thread profile 27. According to FIG. 9, the following action is taken to ensure that the remaining internal thread profile height after the final processing step is sufficient: The pilot hole diameter d.sub.V is reduced compared to conventional thread shaping methods. This means that additional workpiece material is plastically deformed and displaced in the thread shaping process. In addition to the profile cog base 19 of the tool-side thread shaping section 11, pocket-shaped recess 22 (FIG. 6) is provided on the profile cog base of the thread shaping section on the tool side, which enlarges the displacement space available for workpiece material during thread shaping in a radially inward direction. This displacement space which is enlarged radially inwards moves the material weakenings/defects 41 formed on the crest 39 further radially inwards, while at the same time reducing the inner diameter d.sub.I of the internal thread profile 27. As a result, the material weakenings/defects 41 can be completely removed in the final processing step on the one hand, and on the other hand a sufficient internal thread profile height remains to ensure a reliable screwed connection with the screw member.
[0046] FIG. 9 shows the thread shaping tool 9 according to a second embodiment. Unlike the preceding embodiment, the drilling section 13 in FIG. 9 is not formed directly at the tool tip, but offset from the tool tip at an axial spacing. The thread shaping section 11 extends up to the tool tip, however. In this way, it is not just the internal thread profile 27 that is formed in the thread shaping stroke G; at the same time, the drilling section 13 performs the final processing step in which the internal thread profile 27 produced is expanded by drilling to the thread minor diameter d.sub.K.
[0047] FIG. 10 shows a thread shaping tool 9 according to a third embodiment, which is substantially of an identical construction as the thread shaping tool 9 according to the first embodiment as described in FIGS. 1 to 8. The thread shaping tool 9 comprises circumferentially distributed profile cogs 15 in the thread shaping section 13, as is also visible in FIG. 3. These cogs are spaced apart from each other by axially extending lubricating grooves 16. The lubricating grooves 16 extend linearly in the axial direction from the tool tip to the tool shaft 21 in the FIGS. 2 to 7 or in the FIGS. 11 and 12. Their lubricating groove depth t.sub.S (FIG. 2, 11, or 12) is dimensioned such that lubricant and/or coolant can reliably be supplied to the profile cogs 15 in the machining process to ensure sufficient lubricant and/or coolant supply to the profile cogs 15 while the thread is shaped. In addition to the lubricating grooves 16, the thread shaping tool 9 has a total of three chip grooves 43 in FIG. 3, which grooves are machined into the tool with a chip groove depth t.sub.N. The chip groove depth t.sub.N is much greater dimensioned than the lubricating groove depth t.sub.S. The chips produced when expanding the thread inner diameter d.sub.I to the thread minor diameter d.sub.K are transported out of the pilot hole 1 via the chip grooves 43.
[0048] In FIG. 3, each of the chip grooves 43 is defined by a chip surface 44, which merges with a radially outer tool clearance surface 45 at the longitudinal cutter 23 of the drilling section 13. The total of three circumferentially distributed chip grooves 43 shown in FIG. 3 extend in the axial direction at a much reduced groove length I.sub.N only between the tool tip and the thread shaping section 3, without passing axially through it.
[0049] Unlike that, just a single chip groove 43 is configured in the tool in the third embodiment of FIGS. 10 to 13. This groove extends linearly along the tool axis W and has a groove length I.sub.N such that it passes through the thread shaping section 3 and runs up to the tool clamping shaft 21. This results in a considerably improved chip discharge compared to the first embodiment.
[0050] As can also be seen in FIGS. 10 to 13, the chip groove 43 in the drilling section 13 additionally comprises a chip guiding step 47 which partially closes the chip groove 43 in the axial direction. The chip guiding step 47 is used to hold the chips produced in the machining process back from the pilot hole base 3 and to support the chip discharge out of the pilot hole 1. The chip guiding step 47 is formed directly at the tool tip in the FIGS. 10 to 13. Furthermore, the chip guiding step 47 has an end-side chip guiding surface 49, which has a reduced groove depth t.sub.L compared to the groove depth t.sub.N of the chip groove 43 and is radially offset into the tool (FIG. 13).
[0051] The chip guiding surface 49 of the chip guiding step 47 converges with a radially outer clearance surface 45 (FIG. 11) to form the longitudinal cutter 23. Viewed in the axial direction, the chip guiding surface 49 transitions at an end-side transition edge 51 into a tool end face 53 (FIG. 12 or 13) which forms the tool tip of the thread shaping tool 9. The end-side transition edge 51 defines a free chip groove opening region 55 (FIGS. 10 to 13) which leads into the tool end face 53.
[0052] The thread shaping tool 9 shown in the FIGS. 10 to 13 can be connected to a coolant system. For this purpose, the tool 9 comprises a central cooling duct 57 which extends from the tool clamping shaft 21 towards the tool tip. An outlet duct 59 which has an orifice 61 into the chip groove 43 extends axially parallel to said cooling duct in the tool 9. Both the central cooling duct 57 and the outlet duct 59 lead into the tool end face 53. When shaping a thread in a blind hole, this results in a coolant path K (FIG. 13) where the coolant first flows via the central cooling duct 57 into a space 48 which is formed between the tool tip and the bottom 3 of the hole. Further downstream, the coolant K flows in the opposite direction through the outlet duct 59 into the chip groove 43 to support the chip discharge. In addition, the coolant K flows from the space 58 via the free chip groove opening region 55 into the chip groove 43 to further support the chip discharge. It is of relevance for an effective chip discharge that the flow cross section of the central cooling duct 57 is greater than the overall cross section of the chip groove opening region 55 and the outlet duct 59. In this way, the chips are transported out of the chip groove 43 at a high flow rate by creating a Venturi effect.
