Method and thread forming tap for finishing a thread (inverse thread forming)

Abstract

The invention relates to a method for producing a thread, in which a rough thread is finished with at least one thread-forming profile (3), a forming profile head (7) of the thread-forming profile (3) is spaced apart from the thread base (8) of the rough thread profile (2), and a receiving volume (ΔV) is formed by the resulting intermediate space between the forming profile head (7) of the thread-forming profile (3) and the thread base (8) of the rough thread profile (2), and each forming profile flank (14) and each forming profile transition region (17) of the thread-forming profile (3) is pressed at least partially into an associated rough thread flank (9A, 9B) and an associated transition portion (10) and thereby reshapes and displaces the workpiece material, wherein the displaced workpiece material flows into the receiving volume (ΔV).

Description

[0001] N / EMUGE-353-PCT

[0002] 1

[0003] METHOD AND THREAD DRILL FOR REWORKING A THREAD

[0004] Description

[0005] The invention relates to a method for producing a thread in a workpiece and a thread forming tool, in particular for use in the method.

[0006] A wide variety of machining and non-machining processes and threading tools are known for thread production and thread finishing. An overview of thread production tools and processes in use is provided in the Handbook of Thread Technology and Milling Technology, published by EMUGE-FRANKEN, Publicis Corporate Publishing, 2004 (ISBN 3-89578-232-7), hereinafter referred to as the "EMUGE Handbook".

[0007] Thread forming tools, also known as thread forming tools, are used to create internal threads in pilot holes in workpieces (see EMUGE Handbook, Chapter 9, pages 299 to 324). Thread forming tools feature an arrangement of forming burrs (also called forming wedges or forming teeth) within a working area formed on a tool shank. These burrs encircle a central tool axis along a helical line or thread helix adapted to the thread pitch of the internal thread. The forming burrs project radially outwards from the tool axis and, through plastic deformation, press the thread into the workpiece when the tool is rotated around its axis and fed axially along the same axis.For this purpose, the ejector studs have a thread-forming profile in a cross-section perpendicular to the thread helix or helical line. This profile increases along the length of the ejector stud, viewed in the direction of the thread helix or helical line, initially reaching a maximum profile in a crown or head region that is complementary to the final thread profile of the internal thread, and then decreases again. This results in a more even distribution of the forming force over the length of the ejector stud and reduces friction. In particular, several ejector studs are provided distributed around the circumference, especially in the form of a polygon, with N / EMUGE-353-PCT.

[0008] 2

[0009] Press studs typically have grooves for supplying coolant and / or lubricant.

[0010] Axially to the tool axis, several forming cleats of the thread forming die can also be arranged at intervals equal to the thread pitch, particularly on individual webs. Sufficiently large axial gaps must be provided between the forming cleats of the thread forming die. These gaps must extend significantly further inward radially to the tool axis than the core hole diameter, allowing the workpiece material displaced by the forming cleats during forming to flow into them. The inwardly displaced workpiece material forms a characteristic material protrusion on the core hole wall between the thread turns, also known as a forming claw. This is clearly illustrated in Figure 5, which is taken from the Handbook of Thread Technology, page 318.

[0011] Thread forming tools can also be used for post-processing, for example, hardening or compacting of pre-threads already machined in a core hole, as described, for example, in EP 1 864 740 A2. Here, too, the formed workpiece material is displaced radially inwards into the core hole and forms the forming claw in the space between two axially successive forming burrs.

[0012] The forming claw used in thread forming for the initial production or reworking of a thread does not usually interfere with the insertion of a screw, because the screw also has sufficiently deep gaps between the external thread turns to avoid additional friction, which are adequately spaced away from the forming claw.

[0013] However, if the forming claw is a hindrance in some applications, it can also be removed or ground off in a post-processing step, for example by means of a core hole cutter, thereby restoring a dimensionally accurate core hole.

[0014] In special applications such as motion transmissions, especially ball screw drives, where a drive nut is moved linearly on a drive spindle via rolling bearing balls mounted in the thread, there are high demands on the thread quality. N / EMUGE-353-PCT

[0015] 3

[0016] A ball bearing screw drive of this type is known from DE 10 2013 111 728 A1. The internal thread in the nut of the screw-nut system is produced in two steps. In a first step, an internal thread is produced in a core hole of the nut by material removal, the nominal diameter of which is smaller than a predetermined final nominal diameter. In a second step, the predetermined final diameter is obtained by plastic deformation of the intermediate thread formed in the first step and by material displacement using a thread forming tool. It is described that the material flows out of the intermediate thread in radial, axial, and circumferential directions. In one embodiment of this document (see, for example, DE 10 2013 111 728 A1), the first step can be performed by removing material from the intermediate thread.FIGS. 6 to 8) also show that a groove with a circular arc or rectangular profile can be produced in the thread root or at the bottom of the internal thread, into which material can flow during plastic deformation in the second step. However, as shown and described in FIG. 8, in this case too, the majority of the material of the intermediate thread, especially the material displaced at the flanks, flows (via the chamfer 36 at each thread tip) into the core hole of the nut. This publication DE 10 2013 111 728 A1 deals with the accuracy in the nominal diameter or thread root of the nut thread, but not with the surface finish in the area of ​​the core hole.

[0017] It is now an object of the invention to specify a method for thread production and a thread forming tool, preferably intended for use in the method, in which dimensionally accurate formation of the core hole surface and the subsequent thread areas is possible without a forming claw, in particular and without limiting the generality in the production of the internal thread of a nut of a rolling bearing drive.

[0018] This problem is solved with respect to the method by the features of claim 1 and with respect to the thread forming tool by the features of claim 11. Advantageous embodiments and further developments result from the claims dependent on claim 1 and claim 11, respectively.

[0019] According to claim 1, a method for producing a thread in a workpiece is proposed. N / EMUGE-353-PCT

[0020] 4

[0021] In this process, in a first process step, at least one pre-thread is produced or provided in the workpiece, wherein the pre-thread has a thread pitch, a pre-thread profile with pre-thread flanks and with a thread root connecting the pre-thread flanks, as well as a core hole wall with a core diameter, and wherein the pre-thread flanks transition into the core hole wall in a transition section.

[0022] In a second process step, the at least one pre-thread is reworked or formed with at least one thread forming profile, wherein the thread forming profile has a profile head and two profile flanks, each of which transitions into a core profile surface in an associated profile transition area. In the second process step, the thread forming profile engages with the pre-thread profile, but the profile head of the thread forming profile is at least partially spaced away from the thread root of the pre-thread profile, and a receiving volume (or: a receiving space) is formed by the resulting gap between the profile head of the thread forming profile and the thread root of the pre-thread profile, and optionally additionally by immediately adjacent gaps between the thread forming profile and the pre-thread profile.

[0023] In the second process step, each core profile surface (of the thread forming profile) defines the core diameter or the thread core of the thread produced in the second process step or formed with the thread forming profile (or: final thread, end thread) by equalizing or calibrating (or: smoothing) or forming (or: pressing) the workpiece material on the core hole wall area of ​​the pre-thread.

[0024] Furthermore, each profile flank and each profile transition area of ​​the thread forming profile presses at least partially into a corresponding pre-thread flank and a corresponding transition section of the pre-thread profile, preferably to a predetermined indentation depth, and reshapes these outer areas or sections of the pre-thread profile from the thread root. The workpiece material displaced during this forming flows at least predominantly or completely inwards towards the thread root into the receiving volume (or: the receiving space) provided there.

[0025] This means that the workpiece material displaced during forming is mainly directed towards the thread base and the receiving volume provided there between N / EMUGE-353-PCT

[0026] 5

[0027] The material is directed to the root of the pre-thread and the head of the thread forming profile, and little or no workpiece material flows to the core hole wall of the pre-thread. The core profile surface of the thread forming profile or thread cutter, which is matched to the core hole wall of the pre-thread, ensures a defined and dimensionally accurate final thread core wall or core hole surface of the final thread. Forming claws are avoided. Therefore, according to embodiments of the invention, the focus regarding the quality of the finished formed thread, particularly dimensional accuracy, surface finish, and strength, is placed on the thread flanks and the core hole area, and not on the thread root, which is filled with the displaced material. Threads with such requirements are, for example, ball screws for ball screw drives, but the method can also be used to produce threads in other applications.

[0028] In a preferred embodiment, in the second process step the core hole wall of the pre-thread is smoothed or calibrated by the core profile surfaces of the thread forming profile.

[0029] In a preferred first variant, especially for calibration or smoothing, each core profile surface of the thread forming profile has the same radial maximum dimension as the core hole wall of the pre-thread, i.e., half the core diameter.

[0030] Preferably, the core profile surface also guides the thread forming profile on the core hole wall.

[0031] However, in a second variant, the second process step can also involve deformation of the core hole wall by pressing through the core profile surfaces. This can, in particular, achieve a densification or hardening of the thread core wall of the finished or formed thread or end thread, or counteract elastic springback of the workpiece material after removal of the thread forming die. In this second variant for deforming or pressing the core hole wall of the pre-thread, each core profile surface of the thread forming profile of the thread forming die has a radial maximum dimension greater than the core hole wall of the pre-thread by a predetermined forming height, i.e., greater than half the core diameter, whereby this forming height is defined according to N / EMUGE-353-PCT.

[0032] The desired forming process is selected for 6, but is typically less than 10% of the thread forming profile height.

[0033] In one embodiment, in the second process step, no workpiece material flows outwards from the pre-threaded profile through the form profile transition surface pressing into the workpiece material and the adjacent core profile surface, and no forming claw is formed and / or the displaced workpiece material flows completely or exclusively into the receiving volume.

[0034] However, in a third variant, it is also possible to allow only a portion of the displaced workpiece material to flow into the receiving volume at the root of the pre-thread, while still allowing a smaller portion of the displaced material to flow out of the pre-thread profile towards the core hole wall. For this purpose, in the second process step, an additional receiving volume is formed between the core profile surface(s) on the one hand and the core hole wall of the pre-thread on the other. A portion of the displaced workpiece material flows into this volume, preferably by ensuring that the core profile surface(s) has a radial maximum dimension (or inner radius) that is one radial height smaller than the core hole wall of the pre-thread. In particular, this radial height is smaller than half the core diameter of the core hole wall, with this radial height preferably being selected within a range of 0.5% to a maximum of 10% of the thread profile height.Preferably, the core profile surface or each core surface now forms the core surface or core diameter of the formed thread or end thread from the workpiece material that has flowed into this additional receiving volume.

[0035] In one embodiment, each form profile transition surface of the thread form profile, and thus each of the end thread transition areas generated therein between end thread flanks and core hole wall, is concavely curved, preferably with a curvature that reduces notch stresses or keeps them below predetermined limits.

[0036] In one embodiment, the end thread produced in the second process step exhibits higher strength and higher dimensional accuracy in the end thread sections formed with the thread forming profile, at least in the end thread sections formed with the form profile flanks and the form profile transition areas of the thread forming profile, and thus in the end thread sections immediately adjoining the core hole wall, than in the end thread sections formed in the second N / EMUGE-353-PCT

[0037] 7

[0038] Process step: non-formed end thread sections, in particular the thread root.

[0039] In one embodiment, the pre-thread flanks of the pre-thread profile can each be composed of two mutually inclined, preferably straight, pre-thread partial flanks. Preferably, inner pre-thread partial flanks have a smaller flank angle to each other than outer pre-thread partial flanks. Preferably, inner pre-thread flanks transition into the corresponding outer pre-thread partial flanks via a convexly curved transition area, and / or the outer pre-thread partial flanks transition into the core hole wall via the respective transition section of the pre-thread profile. In this embodiment, the receiving space and the receiving volume can be further optimized.

[0040] The forming thread flanks of the thread forming profile preferably enclose the same flank angle to each other as the outer pre-thread flanks, but are radially offset to these and / or have a larger flank diameter or a larger distance from each other and thus extend further outwards than the associated outer pre-thread flanks, so that the material of the workpiece at the outer pre-thread flanks is pressed in and plastically deformed by the thread forming profile by an indentation depth between the outer pre-thread flanks and the forming profile flanks.

[0041] In one embodiment, the thread forming profile with its profile flanks or transition areas intersects at each intersection point a corresponding inner pre-thread flank of the pre-thread profile, and the resulting spaces between the transition areas of the thread forming profile and the inner pre-thread flanks supplement or extend the receiving volume for the flowing workpiece material.

[0042] In one embodiment, the pre-thread has a core hole wall without a forming claw and / or is produced by thread cutting or by thread forming and subsequent removal of the forming claw by core hole cutting or by additive manufacturing.

[0043] In one embodiment, the at least one thread forming profile is on a thread forming die, in particular on a plurality of according to the thread pitch N / EMUGE-353-PCT

[0044] 8 of the pre-thread formed and arranged pressure lug of the thread forming tool.

[0045] The thread forming tool according to claim 11 is preferably intended for use in a method in one embodiment and / or for producing a thread by forming a pre-thread in a workpiece. The pre-thread has a thread pitch, a pre-thread profile with pre-thread flanks and a thread root connecting the pre-thread flanks, and a core hole wall with a core diameter, wherein the pre-thread flanks transition into the core hole wall in a transition section. The thread forming tool is rotatable about a central tool axis. In a working area, the thread forming tool has at least two circumferentially offset rows of several forming teeth (or: forming teeth, forming wedges, forming teeth, forming wedges) arranged axially offset from each other about the tool axis.Circumferentially successive ejector studs of successive rows are arranged and formed along a thread helix around the tool axis, following the thread pitch of the pre-thread. Each ejector stud has a thread forming profile for replicating the pre-thread, in particular the thread forming profile for the second process step. Furthermore, each ejector stud or its thread forming profile has an ejector stud or profile head, the outer radius of which, relative to the tool axis, increases along the associated thread helix or with increasing circumferential angle, initially from a smaller, in particular minimal, outer radius to a maximum outer radius at an ejector stud apex, and then decreases again to a smaller, in particular minimal, outer radius.

[0046] The maximum outer radius of the plunger's crown is smaller than the radius of the thread root of the pre-thread profile (corresponding to the pre-thread profile depth), so that when the plunger's thread forming profile engages the pre-thread profile, a receiving space or receiving volume is formed between the plunger's or forming profile head and the thread root of the pre-thread, and possibly additionally by immediately adjoining spaces between the thread forming profile and the pre-thread profile.

[0047] The thread forming profiles of the dies each have forming profile flanks and forming profile transition areas for forming an associated N / EMUGE-353-PCT

[0048] 9

[0049] Pre-thread flank and an associated transition section of the pre-thread, particularly in the second process step.

[0050] Finally, in a preferred embodiment, the thread forming tool has side webs that run between axially or in a series of immediately adjacent pressure cleats and have or form core profile surfaces, preferably for contact with the core hole wall of the pre-thread or for forming the material on the core hole wall, in particular the core profile surfaces of the thread forming profile for the second process step.

[0051] In one embodiment, each row of push studs is arranged on an associated push stud web.

[0052] In another embodiment, each row of axially offset pusher studs runs parallel to the tool axis, particularly with regard to the pusher stud apex.

[0053] In another embodiment, each row of axially offset pusher studs, particularly with regard to the pusher stud apex, runs spirally along a spiral helix to the tool axis (pusher studs in the row are offset from each other by a circumferential angle).

[0054] Immediately adjacent rows of thrust blocks are preferably separated from each other by a separating or intermediate groove.

[0055] The total number of rows of push studs is selected from a range of 2 to 12, in particular from 3 to 8, preferably 6.

[0056] In a particularly advantageous embodiment, in particular two, three or four pairs of rows of push studs separated from each other by a separating or intermediate groove are provided.

[0057] In one embodiment, the entire thread profile (including the profile head and flanks) of the tapping lugs increases in a cross-section perpendicular to the thread helix (normal section) in the direction of the thread helix or with increasing circumferential angle, first up to a maximum profile at the tapping lug apex and then decreases again. N / EMUGE-353-PCT

[0058] 10

[0059] In a particular embodiment, the profile head of the die with its constant maximum radius extends in a central area at the die apex over a predetermined circumferential angle range, which is preferably 8% to 35%, typically between 10% and 20%, and in particular 17%, of the total circumferential angle of the die and / or between 0.2° and 8°, preferably between 2° and 4°. Preferably, the die has the maximum profile of the thread forming profile throughout this entire central area. Preferably, this creates a functional surface in this central area which precisely maps the final thread to be produced in an axial section (a section containing the tool axis) and can be accurately measured.

[0060] In one embodiment, the side webs run parallel to the thread helix of the push studs.

[0061] In one embodiment, the core profile surfaces of the side webs follow the rising and falling tread or form profile head along the thread helix, in particular at least approximately parallel.

[0062] In one embodiment, the core profile surfaces of the side webs each increase in their radius, relative to the tool axis, along the thread helix or with increasing circumferential angle, initially from a minimum inner radius to a maximum inner radius at a core profile surface vertex and then decrease again to the minimum inner radius.

[0063] In an advantageous embodiment, a guide rib is arranged between two circumferentially adjacent rows or pairs of rows of pusher studs, or between two circumferentially adjacent pairs of rows of pusher studs, the guide rib having at least at one guide rib a maximum guide rib radius corresponding to half the core diameter of the pre-thread, so that each guide rib is supported at least with its guide rib apex on the free core hole wall of the pre-thread or guides the thread forming tool by sliding, particularly in the second process step.

[0064] Preferably, each guide rib is separated from each immediately adjacent row of thrust cleats by a respective separating groove, which is particularly useful for supplying N / EMUGE-353-PCT.

[0065] 11

[0066] Cooling and / or lubricating agents are separated, preferably via openings in the separating groove.

[0067] In one embodiment, each guide rib has a continuous, preferably round, profile perpendicular to the tool axis.

[0068] The claimable combinations of features and subject matter according to the invention are not limited to the chosen wording and cross-references of the claims. Rather, any feature of one claim category, for example, a method, can also be claimed in another claim category, for example, the thread forming tool or tool. Furthermore, any feature in the claims can be claimed in any combination with one or more other features in the claims, even independently of their cross-references. Moreover, any feature described or disclosed in the description or drawing can be claimed on its own, independently or separately from the context in which it appears, alone or in any combination with one or more other features described or disclosed in the claims or in the description or drawing.

[0069] The invention will be further explained below with reference to exemplary embodiments. Reference will also be made to the drawing, in which

[0070] FIG 1 shows a pre-thread profile with pre-thread core diameter and a thread forming profile with a core radius adapted to the pre-thread core diameter to illustrate a method for producing a thread by re-forming the pre-thread with the thread forming profile.

[0071] FIG 2 a thread forming tool in a perspective view,

[0072] FIG 3 shows the thread forming tool according to FIG 2 in a front view,

[0073] FIG 4 Pressing stud of the thread forming tool according to FIG 2 and FIG 3 in an enlarged perspective view and

[0074] FIG. 5 is an excerpt from the Handbook of Thread Technology, page 318, concerning thread forming according to the prior art, each schematically depicted. Corresponding parts and sizes are designated with the same reference numerals in FIGS. 1 to 5. N / EMUGE-353-PCT

[0075] 12

[0076] FIG. 1 illustrates the inventive principle of forming a pre-thread with a pre-thread profile 2 using a thread forming profile 3 according to the invention, in particular a die profile of a thread forming tool according to the invention. The specific shapes of the pre-thread profile 2 and the thread forming profile 3 shown are exemplary and not limiting.

[0077] The pre-thread with pre-thread profile 2 is pre-produced or pre-fabricated in a first separate process step in a workpiece not shown in detail, which may in particular be a nut of a rolling bearing drive or of another motion screw drive.

[0078] The core diameter of the pre-thread is denoted by D and corresponds to twice the radius or twice the radial dimension of the core hole wall 12 in which the pre-thread is produced, relative to a central thread axis of the pre-thread (not shown), around which the pre-thread runs helically with its thread pitch. Outside the pre-thread section or the axially repeating pre-thread profile 2 (not shown), the core hole wall 12 is therefore cylindrical with respect to the thread axis, with the constant core diameter D being the diameter of the cylinder perpendicular to the thread axis.

[0079] Such a pre-thread with a “clean” constant core diameter and cylindrical core hole wall, i.e. without a forming claw, is preferably produced by thread cutting, especially with a tap, but could also be produced with a thread forming tool and subsequent cleaning or removal of the forming claw by core hole cutting or by additive manufacturing.

[0080] The pre-thread profile 2 of the pre-thread has two pre-thread flanks and a thread root 8 connecting the pre-thread flanks. The pre-thread flanks can be designed according to a desired thread profile, in particular linear as in a metric thread or at least partially circular, but in the present case, without loss of generality, they are each composed of two mutually inclined straight or linear pre-thread partial flanks 9A and 9B. The inner pre-thread partial flanks 9A individually enclose a flank angle α to a central axis of the pre-thread profile 2 and together form a total flank angle of 2α and are connected to each other via the thread root 8. In each case, a N / EMUGE-353-PCT is curved with the curvature KR2.

[0081] 13

[0082] In transition area 13, the inner pre-thread flanks 9A each transition into an outer pre-thread flank 9B. The outer pre-thread flanks 9B form a total flank angle of 2β, where β > α. The outer pre-thread flanks 9B of the pre-thread profile 2 transition into the core hole wall 12 with the core diameter D of the pre-thread at both axial sides or exits of the pre-thread profile 2 or pre-thread section in a transition section 10. A pre-thread profile height of the pre-thread profile 2, measured from the lowest point at the thread root 8 to the core hole wall 12, is denoted by t.

[0083] In a second process step, the pre-thread is further processed. Specifically, the pre-thread profile or thread section is further formed or reshaped with a defined geometry in sections of the pre-thread flanks, including the transition areas to the core hole wall, using a thread forming profile inserted into the pre-thread profile. This re-forming does not occur in the area of ​​the thread root. High dimensional accuracy is achieved in the formed thread profile sections.

[0084] The transition areas between the thread flanks of the final thread and the core hole wall or the final thread core at the core diameter are defined by a form profile transition surface, in particular 17, of the thread form profile 3 with the desired curvature (in particular KR1). This achieves defined limits of the notch stresses and high strength in this critical "corner" area, and calibrates and hardens the area around the original, usually cut transition section 10 of the pre-thread, which is subject to tolerances. This also allows the effect of large transmission forces on the final thread flanks to be absorbed during operation, e.g., in a ball bearing drive. The curvature KR1 of the form transition surface 17, and thus of the corresponding transition area between the final thread flank and the core hole wall, is defined by the thread form profile 3.The core hole diameter D in the end thread is therefore set sufficiently large and is typically in the range of a few hundredths to several tenths of a millimeter.

[0085] The thread forming profile 3 with a core profile surface 15 rests against the core hole wall next to the pre-thread. This serves to guide the core hole wall and, under a specific pressing force, may also be used to form and / or calibrate or smooth it. According to FIG. 1, the maximum inner radius RImax of the core profile surface 12 preferably corresponds to half the core diameter D / 2. N / EMUGE-353-PCT

[0086] 14 dh the core profile surface 12 slides on a trajectory on the cylindrical core hole wall between or next to the pilot thread.

[0087] In this preferred embodiment, the forming transition surface (17) pressing into the material and the core profile surface prevent material from flowing outwards from the pre-thread and prevent the formation of a forming claw.

[0088] The material displaced during forming or plastic deformation at the thread flanks flows instead into a space between the thread forming profile and the thread root of the pre-thread and, if applicable, subsequent partial areas of the flanks or transition areas to them.

[0089] In the present embodiment according to FIG. 1, this is implemented as follows: The thread forming profile 3 comprises a profile head 7 which transitions in two opposing transition regions 11 with a convex curvature KR3 into a profile flank 14, which in turn transitions in a profile transition region 17 with a concave curvature KR1 into a core profile surface 15 of the thread forming profile 3. A central axis of the thread forming profile 3 is preferably col-linear with respect to the central axis of the pre-thread profile 2.

[0090] The height of the thread forming profile 3, measured from the highest point at the profile head 7 (located at the maximum outer radius RAmax) to the core profile surface 15 at the maximum inner radius (or core radius) RImax, is denoted by h and is less than the pre-thread profile height t, i.e., h < t and h = RAmax - RImax. In other words, the profile head 7 is spaced from the thread root 8 of the pre-thread profile 2 by the distance th, such that a free space exists or is formed between the thread root 8 of the pre-thread profile 2 and the profile head 7 of the thread forming profile 3, forming a receiving volume (or receiving space) AV for material from the workpiece that flows during the forming process during post-forming.

[0091] The forming thread flanks 14 are preferably inclined to each other by the same flank angle 2β as the outer pre-thread flanks 9B, but are radially offset from them. The forming thread flanks 14 therefore have a larger flank diameter or a greater distance from each other and extend further outwards than the corresponding pre-thread flanks 9B. Thus, the material of the workpiece at the pre-thread flanks 9B is reduced by the thread forming profile 3 by one of the differences or the distance between the N / EMUGE-353-PCT

[0092] 15

[0093] The pre-thread flanks 9B and the form profile flanks 14 are further pressed in and plastically deformed to a corresponding indentation depth As. The indentation volume resulting from the indentation depth As by integrating over the formed surfaces is chosen to be smaller than the receiving volume AV, so that the receiving volume AV can completely accommodate the displaced workpiece material. The forming volume is therefore chosen to be smaller than the receiving volume.

[0094] In the embodiment shown in FIG. 1, the thread forming profile 3, with its profile flanks 14 or transition areas 11, intersects a corresponding inner pre-thread flank 9A at each intersection point Pl or P2. The resulting gaps between the transition areas 11 of the thread forming profile 3 and the inner pre-thread flanks 9B supplement or extend the receiving volume AV for the workpiece material flowing during the forming process.

[0095] In the present embodiment according to FIG. 1, this means specifically, but also generally according to embodiments of the invention, that no plastic deformation by the thread forming profile 3 takes place at the thread root 8 of the pre-thread. The unmachined thread root 8 of the pre-thread therefore also forms the thread root of the final thread or end thread after machining by the thread forming profile 3. The material at the pre-thread is pressed in and deformed only in the pre-thread flanks by the forming profile flanks of the thread forming profile. Due to the closure by the profile transition surface 17 and by the core profile surface 15 of the thread forming profile 3, which abuts the core hole wall 12, the plastically deformed and displaced material cannot flow out of the pre-thread profile 2 and form a forming claw there, as in the prior art.Instead, the displaced material flows into the receiving volume AV, which is formed within the pre-thread or pre-thread section by a gap between the thread root and the profile head and possibly also by additional gaps between adjoining non-engaging sub-areas of the pre-thread flanks and the profile flanks or transition areas to the thread root or profile head.

[0096] In a variant or alternative (not shown), in the second process step each core profile surface presses into the core hole wall 12 of the pre-thread or forms the core hole wall 12 of the pre-thread. Each core profile surface 15 preferably has a radial maximum N / EMUGE-353-PCT that is greater by a forming height AU > 0.

[0097] 16

[0098] The dimension is that of the core hole wall 12 of the pre-thread. Therefore, in this embodiment, the maximum inner radius RImax of the core profile surface 15 of the thread forming tool or thread forming profile 3 is not equal to half the core diameter D / 2 of the core hole wall 12 of the pre-thread, as shown in FIG. 1, but rather RImax > D / 2 or RImax = D / 2 + AU is selected. In particular, it is greater than half the core diameter D / 2 of the core hole wall 12 by the forming height AU, where the forming height AU is preferably less than 10% of the forming profile height h of the thread forming profile 3.

[0099] In another variant (not shown), the pre-formed core diameter D of the pre-thread is slightly larger than the core diameter of the thread forming die or thread forming profile to achieve a comparatively small radial height AK > 0. Thus, in this embodiment, the maximum inner radius RImax of the core profile surface 15 of the thread forming die or thread forming profile 3 is not equal to half the core diameter D / 2 of the core hole wall 12 of the pre-thread, as shown in FIG. 1, but rather RImax < D / 2 or RImax = D / 2 - AK. This creates an additional receiving volume AV' with radial extent AK between the core hole wall 12 with radius D / 2 and the core profile surface 15, into which some of the workpiece material displaced during forming also flows.The radial height AK and the resulting receiving volume AV' are preferably selected such that the core profile surface 15 of the thread former or thread forming profile 3 forms or defines the core surface or core wall of the finished formed thread; that is, the exact and dimensionally accurate geometry of the core hole profile 15 of the thread former is again mapped onto or equalized to the core hole wall of the finished thread. The core diameter of the finished thread again corresponds to the core diameter. Thus, when the thread former is used, the material initially flows slightly radially inwards in the core area until it encounters the core of the thread former and is equalized to the core diameter. This radial height AK must not be too large, otherwise claw formation will occur in the core. A suitable value range for AK is from approximately 0.5% to a maximum of 10% of the form profile height h of the thread forming profile 3.The advantage of this design is a reduction in torque, as less pressure is built up in the core area, while still preventing claw formation and creating a defined core area of ​​the finished thread.

[0100] Thus, in the second process step, the core profile surface 15 defines the core surface or core diameter of the thread forming profile N / EMUGE-353-PCT.

[0101] 17 formed end thread. This applies to each of the aforementioned variants by equalizing or calibrating (especially if RImax = D / 2 or Imax = D / 2 - AUK) or forming (especially if RImax = D / 2 + AU) the workpiece material at the core hole wall (12) of the pre-thread. In particular, the core diameter of the end thread in all variants is equal to twice the maximum inner radius 2 RImax of the core profile area 15 of the thread forming tool or thread forming profile 3, i.e., determined or defined by the core geometry or core dimension of the thread forming tool or thread forming profile 3.

[0102] The final thread resulting from the second process step, the forming of the pre-thread using the thread forming profile, is now manufactured and hardened to low tolerances with high dimensional accuracy on the formed flank areas and the transition areas between the flanks and the core hole wall, as well as on the core diameter. This high dimensional accuracy is also guaranteed for long threads. In the unformed thread root of the final thread, the dimensional accuracy is determined by the manufacturing process of the pre-thread.

[0103] The thread forming profile 3 in FIG 1 with the core profile surfaces 12 is preferably the thread forming profile or die profile of a thread forming tool.

[0104] With reference to FIGS. 2 to 4, exemplary embodiments of a thread forming tool that can be used for the method of producing a thread by forming a pre-thread, as explained with reference to FIG. 1, are explained in more detail.

[0105] The thread forming tool 5 comprises a shaft 4 that can be coupled to a machine tool or drive and, at its free end, a working area 6 and an end face 6A. It extends along a central tool axis A about which the thread forming tool 5 can be rotated in one direction DR or in the opposite direction and along which it can be moved axially to enable a screwing motion according to the specified thread pitch. Radial here means radial or perpendicular to the tool axis A, and axial means along or parallel to the tool axis A.

[0106] In the working area 6, the thread forming tool 5 has at least one, preferably several, rows of axially arranged press teeth (or: press teeth, press wedges, forming teeth, forming wedges), which are preferably each arranged on an associated press tooth web 60. In FIG N / EMUGE-353-PCT

[0107] 18

[0108] 2 and 3 each provide pairs of two axial rows of thrusting tunnels 51 and 52, thrusting tunnels 53 and 54, and thrusting tunnels 55 and 56, between which an axial intermediate groove 70 is formed, i.e. a total of six rows of thrusting tunnels or thrusting tunnel webs.

[0109] The cutting lugs 51 to 56 are arranged along a helix or helical path around the tool axis A according to the thread(s) to be produced and their thread pitch. Along the helix or helical path, cutting lugs 51, 52, 53, 54, 55, and 56 follow one another, operating sequentially or simultaneously in the same pre-thread.

[0110] Each of the ejector studs 51 to 56 takes on an outer radius RA relative to the tool axis A at its ejector stud or form profile head 7 along the associated helix or with increasing circumferential angle. <p zunächst von einem minimalen Außenradius RAmin zu einem maximalen Außenradius RAmax bei dem Drückstollenscheitel DSmax zu und dann wieder auf den minimalen Außenradius RAmin ab. In einem Querschnitt senkrecht zur Gewindehelix oder Schraubenlinie weisen die Drückstollen ein Gewindeformprofil auf, das in Richtung der Gewindehelix oder Schraubenlinie des Drückstollens zunächst bis auf ein dem Endgewindeprofil des Innengewindes komplementäres Maximalprofil bei dem Drückstollenscheitel DSmax zunimmt und dann wieder abnimmt. Dadurch wird die Umformkraft über die Drückstollen gleichmäßiger verteilt und die Reibung verringert. Insbesondere wird das gesamte Gewindeformprofil 3 einfach über die Länge des Drückstollens radial angehoben und dann wieder abgesenkt.In a central area 26 at the apex DSmax of the ejector stud, the profile head 7 can also extend over a wider circumferential angle range with a fixed or constant radius RAmax to increase the outermost pressing surface at the apex DSmax; the flanks 14 are adapted accordingly. The circumferential angle range for the central area 26 is preferably selected from an interval of 8% to 35%, typically between 10% and 20%, particularly 17%, of the total circumferential angle of the ejector stud, or from an interval of 0.2° to 8°, preferably between 2° and 4°. This creates a functional surface in this central area 26 that can precisely map the internal thread to be produced in an axial section (a section containing the tool axis A) and can be accurately measured. The geometry of the thread profile is slightly distorted in the ascent and descent by the preferred thread grinding process.However, tolerances caused by this distortion can be N / EMUGE-353-PCT.

[0111] 19 by measuring the exact effective profile or maximum profile in the flat central area 26 can be avoided.

[0112] The corresponding push studs of the pairs of rows, i.e., the push studs 51 and 53, and likewise the push studs 52 and 54, as well as the push studs 55 and 51 and 56 and 52, are offset in the illustrated embodiment without loss of generality by a circumferential angle q>= 125°, while the push studs 51 and 52, and likewise 53 and 54, as well as 55 and 56 of the same pairs are offset from each other by a circumferential angle q>= 40°.

[0113] The core profile surfaces 15 of the thread forming profile 3 are formed on the radial outer surfaces of lateral side webs 25 of the tapping lugs, which run between axially or in a row immediately adjacent tapping lugs, as can best be seen in FIGS. 2 and 4, where, for example, they are shown between the tapping lugs 51 and between the tapping lugs 52 and 53 and 54 of the corresponding rows. The side webs 25 generally run longitudinally parallel to the helix of the associated tapping lugs and preferably follow the tapping lug or forming profile head 7, which rises along the helix from the minimum outer radius RAmin to the maximum outer radius RAmax and then descends again to the minimum outer radius RAmin, preferably even at least approximately parallel or at a constant distance.Preferably, the thread forming profile 3 of the pusher stud is raised radially along its length together with the core profile surface 15 and then lowered again.

[0114] The core profile surfaces 15 of the side webs 25 take on, as can best be seen in FIG. 3 and FIG. 4, their radius, here referred to as inner radius RI, relative to the tool axis A along the associated helix or with increasing circumferential angle. <p oder entlang ihrer Länge zunächst von einem minimalen Innenradius RImin zu einem maximalen Innenradius RImax bei einem Kernprofilflächenscheitel KFmax zu und dann wieder auf den minimalen Innenradius RImin ab.

[0115] Between each pair of rows of push studs or push stud ribs, a guide rib is arranged, separated from each row or push stud rib by a respective intermediate or separating groove 71 for supplying coolant and / or lubricant via openings 78 in the intermediate grooves 71. In FIGS. 2 and 3, a first guide rib 61 is shown circumferentially between the N / EMUGE-353-PCT

[0116] 20

[0117] Pushing tunnels 52 and 53 are arranged separately from each pushing tunnel 52 and 53 by an intermediate groove 71, a second guide web 62 is arranged between the pushing tunnels 54 and 55, each separated from each pushing tunnel 54 and 55 by an intermediate groove 71, and a third guide web 63 is arranged between the pushing tunnels 56 and 51, each separated from each pushing tunnel 56 and 51 by an intermediate groove 71.

[0118] The guide webs 61, 62, and 63 are axially formed with a continuous, preferably round, profile perpendicular to the axial direction and have a radially outward-projecting guide web apex FSmax in the center, which has a radial height or a maximum guide web radius RF that preferably corresponds to half the core diameter D / 2, but can also be made slightly smaller than D / 2, for example, in the case of a workpiece with a thin wall that can expand elastically radially during thread forming and then spring back. In this case, the guide web can again contact the formed, but springing back, core diameter and compress it slightly. The resulting deviations are small, but high-precision thread profiles are the focus here. This effect can be avoided by incorporating a small undersize to compensate for the elastic springback. This typically involves values ​​for D / 2 - RF of 0.005 to 0.025 mm.

[0119] As a result, the guide webs 61 to 63, with their guide web apexes FSmax, slide on the free core hole wall during the process, thus supporting and guiding the thread forming die 5. In the illustrated embodiment, without loss of generality, the guide webs 61, 62, and 63 are offset by a circumferential angle of q ≥ 40° relative to the immediately adjacent die shanks 52 and 53, 54 and 55, and 56 and 51, respectively. However, the guide webs can also be omitted in an embodiment not shown.

[0120] The circumferential angles <p werden dabei bevorzugt an den radial äußersten oder höchsten Positionen der Drückstollen oder Führungsstege angesetzt oder gemessen, also den Drückstollenscheiteln DSmax und den Führungsstegscheiteln FSmax.

[0121] Instead of an axial orientation of the push-stud rows and corresponding grooves, a helical or spiral orientation of the rows can also be chosen, whereby the axial offset of the push-studs is complemented by an offset in the circumferential direction according to the spiral. Furthermore, more or fewer than 6 push-stud rows can be provided, typically between 2 and 12 rows. N / EMUGE-353-PCT

[0122] 21

[0123] Rows with or without guide rib(s). However, only one row of thrust bolts may also be provided, particularly in combination with an opposing guide rib or two or more than two guide ribs.

[0124] The thread forming tool shown is specifically designed for a three-start thread, i.e., three parallel threads with the same pitch. For this purpose, in each axial row, every third forming block belongs to the same thread, or the thread pitch corresponds to the axial distance of a forming block to the next forming block in the row or axially two blocks ahead, with the same circumferential angle and two forming blocks in between. The thread forming tool thus processes three threads (turns) simultaneously or engages three parallel pilot threads. However, the thread forming tool can also be designed in a standard version for a single-start thread, in which all forming blocks produce the same thread, or in which forming blocks are arranged in a row or axially adjacent or consecutive positions at an axial distance corresponding to the thread pitch.Furthermore, the thread forming tool can also be designed for a double-start thread, in which a pressing stud is arranged at an axial distance corresponding to the thread pitch from the pressing stud next in the row or axially.

[0125] Furthermore, a grouting area can also be provided in a manner known per se, in which the tunnel height, i.e. the maximum outer radius RAmax at the tunnel crown DSmax seen axially from the front face 6A to the rear, increases from an initially smaller value to the final maximum value.

[0126] Although the thread forming tool and the method for producing a thread were shown and described in the exemplary embodiments for an internal thread, the measures according to the invention are equally applicable to forming an external thread. The thread root of the internal thread then corresponds to the thread head or thread crown region of the external thread.

[0127] According to the invention, the pre-thread is not formed in the thread root (8) and the adjoining inner areas (9A) of the pre-thread flanks of the pre-thread profile (2), but rather the pre-thread is formed in reverse or inverted and unlike in the prior art in the outer transition sections (10) immediately adjoining the core hole wall and the adjoining outer pre-thread flank areas (9B), wherein N / EMUGE-353-PCT

[0128] 22 The core hole wall (12) is closed off by the post-forming thread profile (3). The displaced material of the workpiece is not, or only to a small extent, guided outwards into the core hole from the pre-thread profile or its thread root, as in the prior art, but instead flows in the opposite direction into the pre-thread profile into the inner receiving space left open by the thread forming profile. The method according to the invention can therefore also be described as inverse thread forming.

[0129] The method and the thread forming tool in the preferred embodiments according to the invention combine in particular three measures:

[0130] 1. A pre-thread with a predetermined core diameter (D), i.e., a core hole wall (12) without a forming claw, is provided or produced, in particular by thread cutting or, when using thread forming, by cleaning the core hole wall by core cutting or also by 3D printing. By providing or producing a pre-thread, the essential proportion or volume of the workpiece material is already removed from the thread, and only small volumes of the workpiece material need to be formed for the subsequent thread forming.

[0131] 2. Now, by inverse thread forming, the pre-thread is formed in the areas adjacent to the core hole wall (12) that are outer with respect to the thread profile (radially inner with respect to the thread axis), namely the outer pre-thread flank areas (9B) and a transition section (10) up to the core hole wall (12), thereby hardening and bringing it precisely to a predetermined contour or profile dimensions. The resulting surface exhibits low dimensional tolerances or high dimensional accuracy and high load-bearing capacity.

[0132] 3. In contrast, no post-forming takes place in the thread root (8) of the pre-thread and the inner areas (9A) of the pre-thread profile (2) adjoining the thread root. This is achieved by making the thread forming profile for post-forming shorter than, or not as deep as, the pre-thread profile and thus not extending to the thread root. Therefore, a receiving space or volume is formed between the thread forming profile and the thread root and inner area of ​​the pre-thread profile, into which the workpiece material displaced during the forming of the outer pre-thread profile areas can flow. Unlike in the prior art, the workpiece material does not flow outwards from the pre-thread profile, or only to a (smaller) extent. Rather, the formed and displaced material is at least predominantly contained within the N / EMUGE-353-PCT

[0133] 23

[0134] The receiving space is located in the inner area of ​​the pre-thread profile, which is left free by the thread forming profile. The pre-thread profile is therefore generally produced to a sufficient depth so that the workpiece material in the receiving space does not obstruct the mating thread engaging with the final thread in the application. The indentation depth, and thus the forming volume on the flanks and in the transition section of the pre-thread profile, is chosen to be smaller than the receiving volume so that the displaced material can be completely contained within the receiving volume.

[0135] N / EMUGE-353-PCT

[0136] 24

[0137] Reference symbol list

[0138] 2 Pre-thread profile

[0139] 3 Thread forming profile (pull stud profile)

[0140] 4 Furcherschaft

[0141] 5 thread forming tools

[0142] 6 Work area

[0143] 6A Front

[0144] 7 Profile head

[0145] 8 Pre-thread base

[0146] 9 A, 9B Pre-threaded part flanks

[0147] 10 Transition section

[0148] 11 Transition area

[0149] 12 Core hole wall

[0150] 13 Transition area

[0151] 14 Form profile flank

[0152] 15 core profile area

[0153] 16 cylindrical area

[0154] 17 Shape profile transition surface

[0155] 25 sidebar

[0156] 26 Central area

[0157] 51 to 56 Push tunnels

[0158] 60 Push tunnel bridge

[0159] 61, 62, 63 Management walkway

[0160] 70, 71 Intermediate groove

[0161] 77 Opening

[0162] 78 openings

[0163] A tool axis

[0164] D core diameter

[0165] DR Direction of rotation

[0166] DSmax push stud apex

[0167] FSmax guide bar apex h profile height

[0168] KFmax core form surface vertex

[0169] KR1 Curvature

[0170] KR2 Curvature N / EMUGE-353-PCT

[0171] 25

[0172] KR3 curvature

[0173] RA outer radius

[0174] RAMax maximum outer radius

[0175] RAmin minimum outer radius RF guide slope radius

[0176] RI inner radius

[0177] RI max maximum inner radius

[0178] RImin minimum inner radius

[0179] As indentation depth t pre-thread profile height

[0180] AV recording volume a flank angle

[0181] 2ß flank angle

Claims

N / EMUGE-353-PCT 26 Patent claims 1. Method for producing a thread, in particular a thread for a ball screw drive, in a workpiece, a) in which, in a first process step, at least a pre-thread is produced or provided in the workpiece, al) wherein the pre-thread has a thread pitch (P), a pre-thread profile (2) comprising pre-thread flanks (9A, 9B) and a thread root (8) connecting the pre-thread flanks (9A, 9B) and a core hole wall (12) with a core diameter (D) and a2) wherein the pre-thread flanks (9A, 9B) each transition into the core hole wall (12) in a transition section (10), and b) wherein in a second process step the at least one pre-thread is post-processed by forming with at least one thread forming profile (3), bl) wherein the thread forming profile (3) comprises a form profile head (7) and two form profile flanks (14) which each transition into a core profile surface (15) in an associated form profile transition area (17),b2) wherein in the second process step the thread forming profile (3) engages in the pre-thread profile (2) and b3) the form profile head (7) of the thread forming profile (3) is at least partially spaced apart from the thread root (8) of the pre-thread profile (2) and a receiving volume (AV) is formed by the space thereby created between the form profile head (7) of the thread forming profile (3) and the thread root (8) of the pre-thread profile (2) and optionally additionally by immediately adjoining spaces between the thread forming profile (3) and the pre-thread profile (2), b4) each form profile flank (14) and each form profile transition area (17) of the thread forming profile (3) is pressed at least partially into an associated pre-thread flank (9A, 9B) and an associated transition section (10) and thereby deforms and displaces the workpiece material, b5) wherein the displaced workpiece material flows at least predominantly into the receiving volume (AV),b6) wherein in the second process step each core profile surface (15) is equalized or calibrated or reshaped by leveling or calibrating the workpiece material at the core hole wall (12) of the pre-thread to the core surface or core diameter (2 RImax) of the core produced in the second process step, N / EMUGE-353-PCT 27 or defined with the thread forming profile of the thread or end thread.

2. The method of claim 1 comprising one or any combination of the following features: (i) in the second process step each core profile surface (15) rests against or slides on the core hole wall area (12) of the pre-thread. (ii) In the second process step, each core profile surface (15) smooths or calibrates the core hole wall (12) of the pre-thread, (iii) each core profile surface (15) has the same radial maximum dimension (RImax) as the core hole wall (12) of the pre-thread, and is therefore in particular equal to half the core diameter (D / 2) of the core hole wall (12), (iv) each core profile surface (15) guides the thread forming profile (3) along the core hole wall (12).

3. The method of claim 1 comprising one or any combination of the following features: (i) in the second process step, each core profile surface (15) presses into the core hole wall (12) of the pre-thread or re-forms the core hole wall (12) of the pre-thread, (iii) Each core profile surface (15) has a radial maximum dimension larger by a forming height than the core hole wall (12) of the pre-thread, and is therefore in particular larger by the forming height than half the core diameter (D / 2) of the core hole wall (12), wherein the forming height is preferably less than 10 % of a forming profile height (h) of the thread forming profile (3).

4. Method according to one of the preceding claims, wherein in the second method step no workpiece material flows outwards from the pre-threaded profile (2) through the form profile transition surface (17) pressing into the workpiece material and the adjacent core profile surface (15) and no forming claw is formed and / or wherein the displaced workpiece material flows completely or exclusively into the receiving volume (AV). N / EMUGE-353-PCT 28 5. The method according to claim 1, wherein in the second method step an additional receiving volume is formed between the core profile surface (15) and the core hole wall (12) of the pre-thread, into which a portion of the displaced workpiece material flows, preferably by the core profile surface (15) having a radial maximum dimension smaller by a radial height (AK) than the core hole wall (12) of the pre-thread, i.e., in particular, being smaller by the radial height (RI-max = D / 2 - AK) than half the core diameter (D / 2) of the core hole wall (12), wherein this radial height (AK) is preferably in a range of 0.5% to a maximum of 10% of a forming profile height (h) of the thread forming profile (3), wherein preferably the core profile surface (15) forms the core surface or the core diameter (2 Imax) of the formed thread or end thread from the workpiece material that has flowed into this additional receiving volume.

6. Method according to one of the preceding claims, wherein each form profile transition surface (17) of the thread forming profile (3) and thus each of the end thread transition areas formed or produced therein between end thread flanks and core hole wall (12) is concavely curved, preferably with a curvature (KR1) that reduces notch stresses or keeps them below predetermined limits.

7. Method according to one of the preceding claims, wherein the end thread produced in the second process step has a higher strength and higher dimensional accuracy in the end thread sections formed with the thread forming profile, at least in the end thread sections formed with the form profile flanks (14) and the form profile transition areas (17) of the thread forming profile (3) and thus in the end thread sections immediately adjoining the core hole wall (12) than in the end thread sections not formed in the second process step, in particular the thread root (8).

8. A method according to any of the preceding claims comprising one or any combination of the following features: (i) the pre-thread flanks (9A, 9B) of the pre-thread profile (2) are each composed of two mutually inclined, preferably straight, pre-thread partial flanks (9A and 9B), N / EMUGE-353-PCT 29 (ii) Inner pre-thread flanks (9A) enclose a smaller flank angle (2a) to each other than outer pre-thread flanks (9B, , 2ß) and / or inner pre-thread flanks (9A) each transition via a convexly curved transition region (13) into the associated outer pre-thread flanks (9B) and / or wherein outer pre-thread flanks (9B) transition via the respective transition section (10) of the pre-thread profile (2) into the core hole wall (12), (iii) the forming thread flanks (14) of the thread forming profile (3) enclose the same flank angle (2β) to each other as the outer pre-thread flanks (9B), but are radially offset to these and / or have a larger flank diameter or a larger distance from each other and thus extend further outwards than the corresponding outer pre-thread flanks (9B), so that the material of the workpiece at the outer pre-thread flanks (9B) is pressed in and plastically deformed by the thread forming profile (3) by an indentation depth (As) between the outer pre-thread flanks (9B) and the forming profile flanks (14), (iv) the thread forming profile (3) intersects with its profile flanks (14) or transition areas (11) at each intersection point (PI or P2) an associated internal pre-thread flank (9A) and the resulting spaces between the transition areas (11) of the thread forming profile (3) and the internal pre-thread flanks (9A) supplement or extend the receiving volume (AV) for the flowing workpiece material.

9. Method according to one of the preceding claims, wherein the pre-thread has a core hole wall (12) without a forming claw and / or is produced by thread cutting or by thread forming and subsequent removal of the forming claw by core hole cutting or by additive manufacturing.

10. Method according to one of the preceding claims, wherein the at least one thread forming profile (3) is formed on a thread forming tool (5), in particular on a plurality of pressure lugs of the thread forming tool formed and arranged according to the thread pitch of the pre-thread. N / EMUGE-353-PCT 30 11. Thread forming tool (5), in particular for use in a method according to one of the preceding claims, for producing a thread by forming a pre-thread in a workpiece, a) wherein the pre-thread has a thread pitch, a pre-thread profile (2) with pre-thread flanks (9A, 9B) and with a thread root (8) connecting the pre-thread flanks (9A, 9B) and a core hole wall (12) with a core diameter (D), wherein the pre-thread flanks (9A, 9B) each transition into the core hole wall (12) in a transition section (10), b) wherein the thread forming tool (5) is rotatable about a central tool axis (A) and c) wherein the thread forming tool (5) has at least one, preferably at least two, row(s) of several press studs (51, 52, 53, 54) arranged axially offset from each other in the circumferential direction about the tool axis in a working area (6). 55 and 56) shows,d) wherein successive press studs (51 to 56) of successive rows are arranged and formed circumferentially along a thread helix following the thread pitch of the pre-thread around the tool axis (A), e) wherein each of the press studs (51 to 56) has a thread forming profile (3) for re-forming the pre-thread, in particular the thread forming profile (3) for the second process step, f) wherein each of the press studs (51 to 56) or its thread forming profile (3) has a press stud or forming profile head (7) which in its outer radius (RA) with respect to the tool axis (A) is formed along the associated thread helix or with increasing circumferential angle ( <p) zunächst von einem kleineren, insbesondere minimalen, Außenradius (RAmin) zu einem maximalen Außenradius (RAmax) bei einem Drückstollenscheitel (DSmax) zunimmt und dann wieder auf einen kleineren, insbesondere minimalen, Außenradius (RAmin) abnimmt,wherein the maximum outer radius (RAmax) at the pusher stud apex (DSmax) is smaller than the radius of the thread root (8) of the pre-thread profile (2), so that when the thread forming profile (3) of the pusher stud engages in the pre-thread profile (2), a receiving space or receiving volume (AV) is formed between the pusher stud or forming profile head (7) and the thread root (8) of the pre-thread, and optionally additionally by immediately adjoining spaces, N / EMUGE-353-PCT 31 between the thread forming profile (3) and the pre-thread profile (2), g) wherein the thread forming profiles (3) of the dies each have form profile flanks (14) and form profile transition areas (17) for forming an associated pre-thread flank (9A, 9B) and an associated transition section (10) of the pre-thread, in particular in the second process step, and h) wherein the thread forming tool (5) preferably has side webs (25) which run between axially or in a series immediately adjacent dies and have or form the core profile surfaces (15), in particular the core profile surfaces (15) of the thread forming profile (3) for the second process step.

12. Thread forming tool according to claim 11 with one or more of the following features: (i) each row of thrust tunnels (51 to 56) is arranged on an associated thrust tunnel bridge (60), (ii) each row of axially offset pusher studs, in particular with respect to the pusher stud apex, runs parallel to the tool axis or in which each row of axially offset pusher studs, in particular with respect to the pusher stud apex, runs helically along a helical helix to the tool axis, (iii) immediately adjacent rows of thrust tunnels are separated from each other by a separating or intermediate groove (70), (iv) in particular two, three or four pairs of rows of thrusting tunnels (51 and 52, 53 and 54, 55 and 56) separated from each other by a separating or intermediate groove (70) are provided, (v) the total number of rows of push studs is selected from a range of 2 to 12, in particular from 3 to 8, preferably 6.

13. Thread forming tool according to claim 11 or claim 12, wherein the thread forming profile (3) of the press studs (51 to 56) in a cross-section perpendicular to the thread helix (normal section) in the direction of the thread helix or with increasing circumferential angle first increases to a maximum profile at the press stud apex (DSmax) and then decreases again.

14. Thread forming tool according to one of claims 11 to 13, wherein the form profile head is located in a central area (26) at the thrust pin apex (DSmax). N / EMUGE-353-PCT 32 (7) of the ejector stud has the constant maximum radius (Amax) over a predetermined circumferential angle range, which is preferably 8% to 35%, typically between 10% and 20%, in particular 17%, of the total circumferential angle of the ejector stud and / or between 0.2° and 8°, preferably between 2° and 4°, wherein preferably the ejector stud has the maximum profile of the thread forming profile (3) in the central area (26), wherein preferably a functional surface is generated in this central area (26) which exactly maps the end thread to be produced in an axial section (a section containing the tool axis A) and can be precisely measured.

15. Thread forming tool according to one of claims 11 to 14, wherein (i) the side webs (25) run parallel to the thread helix of the push studs and / or (ii) the core profile surfaces (15) of the side webs (25) follow the rising and falling push-stud or form profile head (7) along the thread helix, in particular at least approximately parallel, and / or (iii) the core profile surfaces (15) of the side webs (25) each in their radius (RI), with reference to the tool axis (A), along the thread helix or with increasing circumferential angle ( <p) zunächst von einem minimalen Innenradius (RImin) zu einem maximalen Innenradius (RImax) bei einem Kernprofilflächenscheitel (KFmax) zunehmen und dann wieder auf den minimalen Innenradius (RImin) abnehmen.

16. Thread forming tool according to one of claims 11 to 15, in which a guide web (61, 62, 63) is arranged between two circumferentially adjacent rows or pairs of rows of pusher studs or between two circumferentially adjacent pairs of rows of pusher studs, the guide web having at least at one guide web apex (FSmax) a maximum guide web radius (RF) which is equal to or slightly less than half the core diameter (D / 2) of the pre-thread, so that preferably each of the guide webs (61 to 63) is supported at least with its guide web apex (FSmax) on the free core hole wall (12) of the pre-thread or guides the thread forming tool (5) by sliding, preferably in the second process step, wherein in particular each guide web is separated from each immediately adjacent row of pusher studs by a respective separating groove (71), which N / EMUGE-353-PCT is provided in particular for supplying coolant and / or lubricant, preferably via openings (78) in the parting groove (71), is separated and / or wherein in particular each guide web (61, 62, 63) has a continuous, preferably round, profile perpendicular to the tool axis (A).

Images