SCREW FOR DIRECT SCREWING INTO A COMPONENT

Description

[0001] The invention relates to a screw for direct screwing into a component, in particular a component made of a light metal material.

[0002] EP 1 053 405 B1 discloses a self-tapping screw with a holding section and a penetration section, with which the screw thread displaces the nut material to form a thread. The end of the penetration section facing the screw head forms a calibration section that penetrates only slightly into the nut and is intended to calibrate the formed thread. The lowest level between the calibration ridges in this area lies on the same thread radius as that found in the cylindrical bearing area. The calibration ridges form two opposing support points that are equidistant from the screw's central axis. Only a minimal projection beyond the bearing diameter is intended.

[0003] A similar design is disclosed in WO 95 / 14863 A1, which teaches a thread-forming screw with shaped elements that are placed on the thread. This screw is intended to reduce the screw-in torque, which generally increases with increasing screw-in depth during thread formation in the parent material. Document FR 1 337 952 A shows another screw from the prior art.

[0004] The screw has shaped areas in its front region that extend radially beyond a base thread running essentially from the shank to the tip and are limited in the circumferential direction and relatively short. The aforementioned screw also features a calibration raised section in the bearing area that projects only very slightly beyond the bearing thread, in particular less than 0.08 mm.

[0005] The aforementioned screws reduce friction during the grooving process while still achieving good fastening performance. Reliable production of such calibration ridges, especially using a rolling process, is difficult because the material required to form the calibration ridge is not sufficiently supplied during the rolling process. Therefore, a defined shape of the calibration ridge cannot be reliably guaranteed.

[0006] The object of the invention is to further improve the fastening performance of the screw while maintaining a low forming torque and to facilitate its manufacture.

[0007] The problem is solved by the characterizing features of claim 1 in conjunction with its preamble features.

[0008] In a known manner, a screw for direct fastening into a component, particularly a component made of a light metal material, comprises a head with a drive and a shank, the shank being provided with a thread. The thread's outer radius decreases from a cylindrical bearing area, through a tip area, to the screw tip, such that the thread at the end furthest from the head has a smaller outer radius than in the bearing area. The tip area begins at the position of the screw closest to the bearing area, where the thread's outer radius is smaller than the bearing area radius, and extends to the screw tip.

[0009] The thread in the tip area creates a nut thread in the base material of the component, into which the thread in the load-bearing area is screwed.

[0010] The thread has at least five radially extending projections at its tip. These projections are circumferentially limited, meaning that a local minimum exists between them.

[0011] The thread's outer radius follows a basic thread profile in certain sections along the helix. This basic thread profile is interpolated over the tip area using the local minima located between the ridges. In the area where the thread matches the interpolated basic thread profile, it is referred to as a basic thread, exhibiting a base thread outer radius that increases from the screw tip to the bearing area radius.

[0012] The base thread runs, so to speak, as a thread without protrusions would. The outer radius of the base thread preferably decreases strictly monotonically, particularly linearly, over the tip area and corresponds to the radius of the bearing area within the load-bearing region.

[0013] The base thread outer radius in the bearing area is determined by the outer diameter of the cylindrical envelope in the bearing area. The bearing area radius is constant over the entire area where the thread of the bearing area engages the thread pre-grooved by the projections in the tip area. In this way, according to the invention, no projections are provided in the cylindrical part of the external thread, since these could negatively affect the screw-in behavior in this area due to their unreliable manufacturability.

[0014] In the tip area, the thread exhibits a changing outer radius in the region of the raised sections, which is correspondingly larger than the base thread radius. Each raised section thus has a maximum outer radius along the helix, corresponding to the maximum radius of the raised section itself. This results in a rise and fall in the thread radius across the raised section along the helix.

[0015] According to the invention, at least two protrusions are designed as calibration protrusions, in which the maximum radius of the calibration protrusions is the same size and simultaneously larger than the carrying area radius. The maximum radius of the calibration protrusions defines the calibration radius.

[0016] The presence of at least two calibration ridges ensures that initially only the ridge closest to the screw tip performs the thread cutting action. The at least one more distant ridge performs no or significantly reduced thread cutting action until the ridge closer to the screw tip is worn down. The next ridge further along the bearing surface then takes over the thread cutting function to the extent of the wear on the ridge closer to the screw tip. This allows the bearing thread to engage in a pre-formed thread in the component, even with a longer screw-in length and the associated higher thread cutting action, provided the pre-formed thread is as precisely defined as possible. This results in a reduced screw-in torque.

[0017] Furthermore, the screw according to the invention keeps the screw-in torque low and within narrow limits, since the calibration protrusions only provide additional cutting power when the calibration protrusions located closer to the screw tip are worn.

[0018] Because the calibration protrusions are located in the area of ​​the decreasing outer radius of the base thread, the difference to the outer radius of the base thread is greater than to the bearing area radius. Even with a very small difference between the calibration radius (the maximum radius of the calibration protrusions) and the bearing area radius, the calibration protrusions can be manufactured more reliably, as this provides sufficient material for shaping the calibration protrusions. This difference between the maximum radius of the calibration protrusions (i.e., the calibration radius) and the bearing area radius is preferably very small, and in particular less than 0.1 mm.

[0019] Preferably, at least three calibration ridges with the same maximum radius can be provided. This includes one calibration ridge closest to the screw tip, which still provides a small amount of thread cutting, and two further calibration ridges located further away from the screw tip. After the calibration ridges closest to the screw tip have worn down, the more widely spaced ridges enable precise thread forming in the component. This design becomes increasingly advantageous the harder the component material, and thus the mating material, is.

[0020] Furthermore, at least three preforming protrusions are arranged between the calibration protrusions and the foremost screw tip, each with a maximum protrusion radius smaller than the calibration radius of the calibration protrusions. Additionally, the maximum protrusion radius of each preforming protrusion decreases towards the screw tip. This allows the core material to be progressively formed. The difference in the maximum protrusion radius between successive protrusions is preferably selected such that each preforming protrusion must achieve approximately the same forming capacity.

[0021] According to a preferred embodiment, the base thread outer radius increases from the screw tip over the tip region in the same way as the maximum radii of the preform protrusions increase. The interpolated progression of the maximum protrusion radius is, in particular, parallel to the interpolated progression of the local minima.

[0022] Preferably, a local minimum in the thread's outer radius exists between the bearing area radius and the first maximum radius of the raised section in the direction of the screw tip, where the outer radius of the thread is smaller than the bearing area radius. This means that the raised section also slopes down to the level of the base thread in the direction of the head, in front of the bearing area, where the outer diameter of the thread is smaller than the bearing area radius. As a result, the first raised section extending from the bearing area towards the screw tip lies entirely within the tip region.

[0023] The ratio of the thread outer radius at this first local minimum to the bearing area radius is preferably less than 0.996. This ensures a sufficiently large difference in the outer thread radius so that enough material is available to form the protrusion.

[0024] According to a further advantageous embodiment, the thread is designed such that the ratio of the percentage projection of the calibration radius to a minimum mean value to the percentage projection of the calibration radius to the bearing area radius is greater than 1.4.

[0025] The minimum mean value is the mean of the thread outer radius at the first local minimum and the thread outer radius at the second local minimum. The first local minimum lies between the bearing area and the first elevation closest to the bearing area in the direction of the tip; the second local minimum lies between this first elevation and the elevation closest in the direction of the tip.

[0026] As an alternative to a linear increase in the progression of maximum radii of elevation, the progression of the increase in maximum radii of elevation towards the head can also be degressive. This allows for adaptation to the grooving behavior and the hardness of the component material.

[0027] The local minima between the elevations can correspond to the base thread outer radius and decrease continuously, in particular linearly, towards the screw tip over a groove area that extends at least partially over the tip area.

[0028] If the local minima of the thread outer radius between the protrusions correspond to the base thread outer radius, this leads to simplified manufacturing of the screw and improved pull-out forces, since the threads in the thread-forming tip area can also contribute to the pull-out strength.

[0029] The thread is bounded radially by a thread crest. As usual, the thread extends with its thread crest along the thread helix, whereby the position of the points at the thread crest, where the thread's outer radius is determined, changes in angle in the normal plane (plan view); this angle is called the rotation angle.

[0030] The rotation angle is therefore the angle that the thread's outer radius, which is orthogonal to the screw axis and forms a line on the thread helix, forms with a starting orthogonal defined at the free end of the screw, particularly at the beginning of the thread. Starting from the starting orthogonal at the beginning of the thread, the rotation angle increases by 360° with each full revolution.

[0031] According to a preferred embodiment of a projection, at a first position of the projection's rotation angle, the thread's outer radius can correspond to the base thread's outer radius. As the rotation angle increases, the thread's outer radius then corresponds to the projection's maximum radius at a position at the projection's maximum rotation angle. With a further increase in the rotation angle, at a position at the projection's end, the thread's outer radius corresponds to the base thread's outer radius. This results in a gradual increase and decrease of the thread's outer radius to the base thread's outer radius. In this way, improved load-bearing capacity can be achieved even in the range where the base thread's outer radius is still increasing.

[0032] According to a preferred embodiment of a raised section, the thread's outer radius increases monotonically from the base thread's outer radius over a raised section rotation angle and then decreases monotonically again until it returns to the base thread's outer radius. This allows for simple manufacturing and defined groove properties of the raised section. In particular, the increase and decrease follow a parabola whose vertex lies at the raised section's maximum radius.

[0033] The base thread outer radius preferably increases linearly between two parabolic elevations along the helix towards the head.

[0034] According to a further advantageous embodiment of the invention, the maximum radius of elevation of a preform elevation is larger than the nearest thread outer radius at the beginning of the elevation closest to the screw head. At the beginning of an elevation, the increase in the thread outer radius can have a steeper slope than the slope of the base thread. This arrangement of the elevations ensures that all preform elevations only have to perform forming work over a partial area, which reduces the forming torque and the wear of the elevations.

[0035] According to a further advantageous embodiment of the invention, the angular displacement angle, in the plane normal to the screw's central axis, between two adjacent maximum radii of displacement corresponds to an angular distance α, where 360° / n -10° < α < 360° / n +10°, where n is between 2, 3, or 4, and the angular distance between a displacement is less than 210° / n. This defines a relatively short displacement with respect to the angular displacement angle, which reduces friction in the region of the maximum radius of displacement. This, in turn, allows the tightening torque to be reduced.

[0036] The protrusions can extend not only outwards in the direction of the outer radius, but also exhibit a longitudinal extent along the screw that is greater than the longitudinal extent of the base thread. This can be the case on both sides, in particular.

[0037] This allows the width of the nut thread to be progressively increased by means of the preform protrusions.

[0038] In particular, the thread length across the tip area is less than five turns. This allows a large portion of the screw length to contribute to the load-bearing function, especially when screwing into a blind hole.

[0039] According to a further advantageous embodiment, the core diameter increases from the tip through the tip region until it corresponds to the core diameter in the bearing area. This improves the manufacturability of the screw according to the invention.

[0040] The relative increase in the core diameter can be less than the increase in the base thread radius.

[0041] The pitch of the thread line can preferably be approximately 5°–7°, which corresponds to an increase in the base thread's outer radius of 3% to 5% per turn. This gradual increase allows for a gradual forming of the nut thread into the mating material, particularly when the maximum projection radius increases proportionally.

[0042] In a further advantageous embodiment, the thread flank width is narrow in the axial direction. The thread has a guide flank facing the screw tip and a load flank facing the screw head. The guide flank and the load flank form a basic flank angle. The basic flank angle is preferably between 25° and 45°. This allows for improved screw-in behavior, especially in high-strength light metal materials.

[0043] It is further preferred that the thread projections above the screw tip are designed in cross-section such that they have an elliptical shape at the thread tip.

[0044] According to a particularly preferred embodiment, the guide flank and the load flank are connected in the area of ​​the raised section via a thread tip, the contour line of which follows an ellipse in cross-section. The ellipse has a numerical eccentricity ε between 0.5 and 1.

[0045] The elliptical shape of the thread crest in the area of ​​the raised section provides a robust structure at the outermost thread tip, resulting in good thread-cutting properties. Furthermore, the displaced material encounters progressively less resistance from the outermost thread crest towards the thread root and flank with increasing distance from the apex. This reduces the radial forces required to deform the workpiece material, leading to easier thread penetration. This also reduces wear on the raised sections, which, particularly with regard to calibration features, improves the defined thread formation in the workpiece material.

[0046] In addition to the elliptical shape of the thread crests of the raised sections, the thread crests of the base thread in the bearing area can also have an elliptical shape. By adapting the shape of the base thread in the bearing area, improved engagement of the base thread with the grooved nut thread can be achieved. According to a particularly preferred embodiment, the thread is designed such that two tangents to the ellipse defining the thread crest intersect and form an angle of intersection, namely a basic flank angle of less than 60°, and in particular less than 45°.

[0047] Each of the two tangents lies at a point of contact on the ellipse, which is located at the transition from the elliptical region defining the thread tip to the thread flank adjoining the thread tip, namely a load flank and a guide flank, with each tangent enclosing a half-flank angle with the major semi-axis.

[0048] The distance of the two contact points from the major semi-axis is greater than 1 / 3 * tan (half-flank angle) * thread height. The thread height is the difference between the base thread's outer radius and half the core diameter. This design results in relatively narrow thread flanks.

[0049] Preferably, the thread crest in the area of ​​the protrusion can be further developed such that the line connecting the respective point of contact with the vertex of the major semi-axis at the thread crest forms a vertex angle with the major semi-axis that is less than 55°. This ensures a correspondingly slender profile of the thread crest, thus achieving improved penetration into the parent material.

[0050] This results in a point of contact on the load flank and a point of contact on the guide flank. An orthogonal to the respective tangent through the point of contact intersects the major semi-axis at a point of intersection. The thread crest can preferably be designed such that the distance between the point of contact and the point of intersection is less than the distance of the point of intersection to the vertex of the thread crest. Preferably, the distance between the point of contact and the point of intersection is less than 90% of the distance of the point of intersection to the vertex of the thread crest.

[0051] According to a particularly preferred embodiment, the transition from the elliptical thread crest to the thread flank is tangential. The transition is therefore smooth, and the material displaced by the thread crest can flow along the thread flank with low friction, thereby reducing the forming torque.

[0052] Preferably, the ellipse can transition into a straight section of the guide flank and / or load flank, which is congruent with the tangent.

[0053] In a further development of the invention, the guide flank and / or the load flank can run along an elliptical path, the curvature of which is opposite to the curvature of the ellipse at the thread tip. The curvature can connect directly to the thread tip or to a straight section of the guide flank and / or load flank.

[0054] The eccentricity of the elliptical path of the guide flank and / or load flank is preferably less than the eccentricity of the ellipse defining the thread crest. This results in a significant widening of the thread towards the thread root, thereby increasing the shear strength and stability of the thread.

[0055] According to a further advantageous embodiment of the invention, the major semi-axis of the ellipse defining the thread tip is inclined at an angle of up to 10° towards the guide flank relative to the normal plane to the screw central axis.

[0056] In particular, the distance between adjacent thread flanks at 90% of their thread height is more than 0.7 times the pitch. Furthermore, the flank width at 90% of their thread height can be less than 0.5 times the thread height. This ensures a sufficiently small thread crest width.

[0057] The screw is preferably made of steel.

[0058] Further advantages, features and application possibilities of the present invention will become apparent from the following description in conjunction with the exemplary embodiments shown in the drawings.

[0059] In the drawing, this means: Fig. 1 a side view of the screw in the bearing area and tip area; Fig. 2 a perspective view; Fig. 2 a top view of the tip; Fig. 3 a representation of the thread line and the (interpolated) core diameter; Fig. 3 a partially enlarged view of Fig. 3a ; Fig. 4 a partial sectional view of the thread; Fig. 5 a contour of the support thread in cross-sectional view, and Fig. 6 a contour of the thread of a calibration ridge in cross-sectional view.

[0060] Fig. 1 Figure 1 shows a side view of a screw 10 according to the invention for fastening into a component made of a light metal material. The screw 10 comprises a front end, designated as the screw tip 12, and a head 18 located at the other end of the screw 10. The screw has a thread 20 with a bearing area TB, wherein in the bearing area TB the thread 20 has a constant thread outer radius RA along the helix, namely the bearing area radius RT, which corresponds to half the outer diameter in the bearing area TB. The bearing area radius RT is preferably determined by the nominal outer diameter of the screw. Thus, the bearing area radius RT corresponds to half the nominal outer diameter. Adjoining the bearing area TB in the direction of the screw tip 12 is a tip area SB, over which the thread outer radius RA of the thread 20 varies along the helix and decreases as a result towards the screw tip 12.In the tip region SB, the thread 20 has circumferentially delimited, radially extending projections 14.2, 14.5, 14.8, 16.1, 16.2 (also designated 14.X, 16.X). In the region of these projections 14.X, 16.X, the thread 20 has a changing thread outer radius RA. Starting from the screw tip 12, the thread outer radius RA essentially increases and forms a thread 20 that essentially has a base thread with the base thread outer radius R AB, where the base thread outer radius R AB increases linearly. In addition, the thread has projections 14.X, 16.X whose projection outer radius R AE is larger than that of the base thread outer radius R AB.

[0061] Of the area-specific elevations 14.X, 16.X in the tip area SB, at least two elevations 16.X have a maximum elevation radius R E9max, R E10max, which is the same for both elevations 16.1, 16.2 and corresponds to the calibration radius RK, which is larger than the bearing area radius RT. These elevations are designated as calibration elevations 16.X, since at least those calibration elevations 16.X located further along the helix towards the head do not have to perform excessive forming work to produce the nut thread, but rather are intended to ensure that any inaccuracies of the pre-formed thread, especially in the area of ​​the thread crest, are reduced. In particular, they are intended to reduce inaccuracies that arise from wear of the calibration elevation 16.X located closer to the screw tip 12.This allows the friction of the thread 20 of the load-bearing area TB, which is subsequently screwed into the grooved threads, to be low, so that the screw-in torque can be kept low and within narrow limits.

[0062] Between the calibration protrusions 16.X and the foremost tip 12, at least three preforming protrusions 14.X are arranged for thread forming purposes. Their respective maximum protrusion radii RE1max,..., RE8max are smaller than the calibration radius RK. In the present embodiment, eight preforming protrusions 14.X are provided. The increase in the maximum protrusion radii RE1max, up to RE8max, i.e., the thread outer radius RA at the local maximum of the protrusion 14.X, across the tip area SB towards the bearing area TB, forms the nut thread into the nut material with increasing depth. This increase in the maximum protrusion radii RE1max is particularly evident in the illustration according to... Fig. 3a , in which the course of the increase of the respective maximum elevation radius R E1max , up to RE 8max , which is denoted by the interpolated course R AEMax, can be clearly seen.

[0063] Fig. 2a shows a perspective view of the screw tip 12 of screw 10. Analogous to the execution according to Fig.1 The thread 20 begins at the screw tip 12 and extends towards the head along its screw line.

[0064] Starting at a starting point S on the thread 20, for example at the beginning of the thread 20, the angle of the thread radius at the angular position WP E2max, where the maximum radius of the second preform elevation 14.2 is located, forms a rotational angle U with the radius at the starting point when projected onto the normal plane to the screw's central axis MA. The rotational angle U increases by 360° with each full rotation, whereby the position of the outer thread radius at the respective angular position shifts along the screw's central axis towards the head with increasing rotational angle U. The top view of the normal plane is shown in Fig. 2b depicted.

[0065] The rotational angular distance alpha Max between the maxima of two adjacent elevations, for example between the angular positions WP E2max and WP E3max, is 120° in this case, so that there is no circumferential offset between the axially superimposed elevations. Alternatively, the rotational angular distance alpha Max between the maxima of two adjacent elevations 14.X,16.X can also be, for example, 125°, resulting in a circumferential offset of the elevations.

[0066] Furthermore, each elevation extends over a rotational angular distance beta. Each elevation 14.X, 16.X thus has an angular position WP at which the elevation 14.X, 16.X begins and another angular position WP at which the elevation ends. For example, the third elevation 14.3 begins at the angular position WP E3start and extends to the end of the third elevation 14.3 at the angular position WP E3ende.

[0067] Preferably, the rotational angular distance alpha between two adjacent elevations is more than twice as large as the rotational angular distance beta of the elevation.

[0068] Fig. 3a Figure 1 schematically shows an example of the path of a thread line GL at the outermost point of the thread crest, along the helix and its development over the helix angle. The general increase of the thread's outer radius RA towards the bearing area TB is visible over the crest area SB. The general increase of the base thread's outer radius is represented as the base thread line BL, shown as a short dashed line. This shows the path of a "base thread" as the thread 20 would proceed without the area-specific elevations 14.X and 16.X.

[0069] The solid line shows the course of the actual thread line GL along the base thread and across the projections that extend beyond the base thread line in their outer thread radius. The projections reach their local maximum at their maximum projection radius R AEmax. In this example, the increase of R AEmax across the peak area runs parallel to the base thread line.

[0070] This illustration shows that the elevations are short in the circumferential direction and only extend over a short angular range of up to approximately π / 3 (60°). The circumferential angular distance between two elevations, for example between WP E2ende and WP E3start, is approximately π / 3 (60°).

[0071] The thread has three calibration elevations 16.X in the tip area SB of the screw 10, namely in the area in which, in particular, the outer thread radius RA of the base thread increases continuously, in this case linearly.

[0072] The three calibration protrusions 16.X have the same maximum protrusion radius R E9Max, R E10 Max, R E11Max, which corresponds to the calibration radius RK. The calibration radius RK, and thus the maximum protrusion radius R E9Max, R E10Max, R E11Max, of the calibration protrusions 16.X is larger than the bearing thread radius RT of the thread in the bearing area TB of the screw.

[0073] Since the calibration ridges 16.X are located in the radius increase area at the tip (SB), there is a greater difference between the base thread radius R AB and the calibration radius RK compared to the bearing area (TB). This allows the calibration ridges 16.X to be reliably and precisely manufactured even using a rolling process. This then leads to a more reliable reduction of the forming torque of such a screw when directly screwed into light metal.

[0074] The overall extent of the protrusion corresponds approximately to, or is preferably less than, a rotational angle of 60°. This results in friction being generated only over a small screw angle, thus keeping the screw-in torque low.

[0075] Fig. 3b shows a partial enlargement of the illustration from Fig. 3a , with a focus on the calibration elevations 16.X. In this enlarged representation, it becomes clear that the difference in the outer radius to the base thread BL is still significantly larger even at the elevation closest to the bearing area TB than would be the case in the bearing area TB, where the difference would only be RK -RT and which, according to the invention, is preferably less than 0.1 mm.

[0076] In this way, according to the invention, the calibration elevations 16.X. can also be precisely produced using the rolling process in order to achieve the most defined possible shaping of the nut thread.

[0077] Between the calibration elevation 16.3 closest to the carrying area and the carrying area, the thread outer radius RA at the rotation angle position WP E12end has a local minimum with the thread outer radius RA (WP E12end ).

[0078] The ratio of the thread outer radius RA (WP E12ende ) at this local minimum to the bearing area radius RT is preferably less than 0.996.

[0079] Furthermore, at the end of the second calibration survey 16.2, i.e. at the rotation angle position WP E11end, another local minimum with the thread outer radius RA (WP E11end) is obtained.

[0080] The thread is designed in such a way that the ratio of the percentage protrusion of the calibration radius RK over a minimum mean value to the percentage protrusion of the calibration radius RK over the bearing area radius RT is greater than 1.4.

[0081] The minimum mean value is the mean value of the thread outer radius RA (WP E12end ) at the first local minimum and the thread outer radius RA (WP E11end ) at the second local minimum.

[0082] The design of the thread therefore satisfies the formula: R K / R A WP E 12 ende + R A WP E 11 ende / 2 − 1 / R K / R T − 1 > 1 , 4

[0083] The extent of the elevation in the axial direction is in Fig. 4 depicted.

[0084] Fig. 4 Figure AA shows a schematic sectional view through a thread 20 at the transition from the bearing area TB to the tip area SB. Starting from its baseline GG, the thread 20 has a load flank 52 facing the head in the area of ​​the calibration protrusion, which transitions into a thread crest 54 with an elliptical contour. Subsequently, in the direction of the screw tip, the thread crest 54 transitions again into a thread flank, namely a guide flank 56. The contour of the base thread, as it would be in the section plane if there were no protrusion, is shown with a dashed line. In the bearing area TB, the actual path then corresponds to that of the base thread, which has a load flank 42, a thread crest 44, and a guide flank 46.

[0085] In the circumferential direction, a calibration protrusion 54 projects beyond the course of the base thread. At its local maximum, the calibration protrusion has a maximum radius R AEmax, which in this case corresponds to the calibration radius RK. Fig. 4 It is evident that, in contrast to the base thread profile shown in the form of a dashed line, the protrusion also extends in the axial direction beyond the base thread, preferably being rolled along with the protrusion during a rolling process.

[0086] As well as Fig. 3b As can be seen, at the angular position WP E12max, i.e., in the area where the base thread height still increases, there is a significantly larger difference between the base thread and the calibration height RK than would be the case in the load-bearing area TB compared to the load-bearing area radius RT. This allows the elevation 54 to be produced more reliably.

[0087] The base thread has an elliptically shaped thread tip 44 in the bearing area. The design of the thread tip is in Fig. 5 described in more detail.

[0088] The thread tip 54 has an elliptical cross-section, the design and effect of which are described in the context of Fig. 6 will be described in more detail.

[0089] The improved resistance of the elliptical thread tip to wear, combined with the inventive design of the calibration area in the tip region, enables a particularly reliable and precise forming of the nut thread.

[0090] The elliptical contour of the thread tip in the bearing area is particularly suitable for adapting to the cross-sectional shape of the protrusion, thereby increasing the contact area when tightened and thus potentially increasing the pull-out forces. The shape of the thread tip of the protrusion is similar to that of the base thread, as shown below with regard to Fig. 6 is described in detail.

[0091] Fig. 5 Figure 1 shows a cross-section of the thread in the bearing area TB with the thread tip 44 having an elliptical cross-section. This thread shape is essentially also present in the base thread over the tip area SB of the screw, i.e., in the area between the protrusions.

[0092] The cross-sectional contour of the thread tip 44 follows an ellipse SE. The thread tip 44 transitions into a guide flank 46 towards the screw tip and into a load flank 42 towards the screw head. The vertex SP of the thread tip lies at the vertex of the ellipse SE at its intersection with its major semi-axis HA.

[0093] The thread tip 44 transitions into the load flank 42 at transition point UP1 and into the guide flank 46 at transition point UP2. Transition points UP1 and UP2 are the points where the thread contour leaves the elliptical path SE that defines the thread tip 44.

[0094] At the transition points UP1 and UP2, a tangent T1, T2 can be drawn, which defines the flank angle.

[0095] The tangent T1 lies at the transition point UP1, enclosing the load flank angle LF with the major semi-axis HA.

[0096] An orthogonal line to the tangent T1 at transition point UP1 intersects the major semi-axis at intersection point BP1. The thread crest is preferably designed such that the distance between intersection point BP1 and transition point UP1 is less than 90% of the distance between the vertex SP and intersection point BP1. This ensures sufficient curvature of the thread crest for good material flow during displacement, thus reducing wear on the thread crest during the forging process.

[0097] Furthermore, the thread tip is preferably shaped such that the line connecting VL1 of the transition point UP1 with the vertex SP forms a vertex angle VL1 - HA with the major semi-axis HA. This vertex angle VL1-HA is particularly less than 45°; in the present embodiment, it is approximately 22°.

[0098] The thread tip 44 is designed so that the relationships applicable to UP1 also apply to UP2 of the guide flank.

[0099] The tangent T2 lies at the transition point UP2, enclosing a guide flank angle FF with the major semi-axis HA.

[0100] An orthogonal line to the tangent T2 at transition point UP2 intersects the major semi-axis at intersection point BP2. The thread crest is preferably designed such that the distance between intersection point BP2 and transition point UP2 is less than 90% of the distance between the vertex SP and intersection point BP2. This ensures sufficient curvature of the thread crest for good material flow during displacement, thus reducing wear on the thread crest during the forging process.

[0101] Furthermore, the thread tip is preferably shaped such that the connecting line VL2 of the transition point UP2 with the vertex SP forms a vertex angle VL2 - HA with the major semi-axis HA. This vertex angle VL2-HA is particularly less than 45°; in the present embodiment, it is approximately 22°.

[0102] Furthermore, a basic flank angle can be determined, which results from the sum of the load flank angle LF and the guide flank angle FF. In the present embodiment, this is 35°.

[0103] The thread is preferably designed such that a line parallel to the tangent T1 through the vertex intersects the thread baseline at a foot point FP1. According to the invention, the distance A1 of the foot point FP1 to the major semi-axis is at most three times greater than the distance A2 of the transition point UP1 to the major semi-axis.

[0104] In the described embodiment, the thread is designed such that the distance A1 is approximately twice as large as the distance A2 of the transition point to the major semi-axis HA. This allows for a slim thread form.

[0105] In the present embodiment, the flank profile of both the guide flank 46 and the load flank 42 is at least partially determined by elliptical contours. These flank ellipses FE1, FE2 have a significantly lower eccentricity than the ellipse SE that defines the thread crest.

[0106] Fig. 6 Figure 1 shows a thread cross-section of another thread form in the tip region SB of screw 10, where the thread crest 54 of the groove area is shown in the region of a protrusion. An elliptical thread crest 54 leads to improved groove properties and thus reduces the wear of the calibration protrusions designed in this way. Furthermore, the thread cross-section of the base thread with its thread crest 34 is shown opposite the protrusion contour, as it would be at the intersection line through the thread with the protrusion if the base thread had a uniformly increasing profile at this point.

[0107] The vertex SP lies here at the maximum elevation radius R E8max away from the screw center axis.

[0108] The course along the apex ellipse is similar to the course of the apex ellipse according to Fig. 5 .

[0109] Since the thread in the bearing area has the same contour as the base thread, the tangent T1 to the load flank lies parallel to the ellipse defining the thread crest at the transition point UP1 to the load flank in the area of ​​the protrusion, and parallel to the tangent T1 to the ellipse at the transition to the load flank in the bearing area TB. Both thus enclose the same load flank angle with the major semi-axis HA. The same applies analogously to the tangent T2 with respect to the guide flank.

[0110] In this respect, the cross-sectional contour of the raised section essentially corresponds to the contour in the bearing area. Only the area where the thread flank follows the tangents T1 and T2 is longer in the raised section. This results in a pre-grooved thread that is larger than that in the bearing area, into which the thread in the bearing area can engage with flank areas lying parallel to the pre-grooved nut thread.

[0111] The calibration ridge closest to the bearing area is designed in the same way, with the difference between the base thread and the ridge being greater than the difference between the thread in the bearing area and the ridge. This ensures reliable manufacturing of the ridges while still producing a slightly larger pre-formed nut thread.

Claims

1. Screw (10) for direct screwing into a component, in particular made of a light metal material, comprising a head and a shank, which shank has a thread (20), the outer thread radius (RA) of which decreases from a cylindrical load-bearing region (TB) of a constant load-bearing region radius (RT) through a tip region (SB) toward the screw tip (12), which thread (20) has at least five elevations (14.X, 16.X) in the tip region, i.e. the region in which the thread outer radius (RA) decreases toward the screw tip (12), which elevations (14.X, 16.X) are delimited in the circumferential direction and extend in the radial direction, with the thread outer radius (RA) changing in the region of the elevations (14.X, 16.X) in such a way that a maximum elevation radius (RE1max, RE2max, RE8max) associated with an elevation is obtained, characterized in that the respective maximum elevation radius (RE10max, RE11max, RE12max) of at least two elevations - calibration elevations (16.X) - is the same and corresponds to a calibration radius (RK) which is greater than the load-bearing region radius (RT), with at least three preforming elevations (14.X) being arranged between the calibration elevations (16.X) and the foremost screw tip (12), which preforming elevations (14.X) have a smaller respective maximum elevation radius (RE1max, RE2max, RE8max) than the maximum elevation radius (RE10max, RE11max, RE12max) of the calibration elevations (16.X), and moreover the maximum elevation radius (RE1max, RE2max, RE8max) of the preforming elevations (14.X) decreases in the direction of the screw tip (12).

2. Screw according to claim 1, characterized in that, between the load-bearing region radius (RT) and the first elevation in the direction of the screw tip (12), there is a local minimum in the thread outer radius (RA), which is smaller than the load-bearing region radius (RT).

3. Screw according to claim 2, characterized in that, at the first local minimum, the ratio of the thread outer radius (RA(WPE12end)) to the load-bearing region radius (RT) is less than 0.996.

4. Screw according to any one of claims 2 or 3 above, characterized in that the thread is designed such that a ratio of the percentage protrusion of the calibration radius (RK) to a minimum mean value (((RA(WPE12end) +RA(WPE11end)) / 2) to the percentage protrusion of the calibration radius (RK) to the load-bearing region radius (RT) is greater than 1.4, which minimum mean value is formed by the mean value of the thread outer radius (RA(WPE12end)) at the first local minimum between the load-bearing region and the first calibration elevation (16.3) and the thread outer radius (RA(WPE11end)) at the second local minimum between the first calibration elevation (16.3) and the second elevation (16.2).

5. Screw according to any one of the preceding claims, characterized in that, starting from the tip (12), over the tip region, the increase in the respective maximum elevation radius (RAEmax) of the preforming elevations (14.X) occurs in the same way as the increase in the thread outer radius (RA) at the local minima between the preforming elevations (14.X).

6. Screw according to any one of the preceding claims, characterized in that, in an elevation (14.X, 16.X) at a first rotation angle position (WPEXstart) of a rotation angle (U), the thread outer radius (RA) is at the level of the base thread outer radius (RAB), corresponds to the elevation maximum radius (RAEmax) on further increase, and, on further increase, corresponds again to the base thread outer radius (RAB) at the corresponding rotation angle position (WPEXend) of the rotation angle (U) at the end of the elevation.

7. Screw according to claim 6, characterized in that, in an elevation (14.X, 16.X), the thread outer radius (RA) increases continuously over a rotation angle distance (beta) starting from the base thread outer radius (RAB) and then decreases again until it again corresponds to the base thread outer radius (RAB), in particular follows a parabolic course.

8. Screw according to claim 7, characterized in that, in the thread (20), the base thread outer radius (RAB) increases linearly between two adjacent preforming elevations (14.X), starting from the screw tip.

9. Screw according to any one of the preceding claims, characterized in that the load-bearing region radius (RT) is more than 90% of the calibration radius (RK).

10. Screw according to any one of the preceding claims, characterized in that the calibration radius (RK) is at most 0.1 mm larger than the load-bearing region radius (RT).

11. Screw according to any one of the preceding claims, characterized in that the maximum elevation radius (RAEmax) of a preforming elevations is larger than the nearest thread outer radius (RA) at the beginning of the nearest elevation in the direction of the head (18).

12. Screw according to any one of the preceding claims, characterized in that the rotation angle (U) in the normal plane to the screw center axis between two adjacent elevation maxima corresponds to a rotation angle distance (alphamax), with 360° / n-10° < alphamax < 360° / n+10°, with n being between 2, 3 or 4, and the angular distance (beta) of an elevation being less than 210° / n.

13. Screw according to any one of the preceding claims, characterized in that the elevations (14.X, 16.X) also extend beyond the base thread in the axial direction, in particular on both sides.

14. Screw according to any one of the preceding claims, characterized in that the slope of the thread line is between approx. 5° and 7°, which corresponds to an increase of the base thread outer radius per turn of between 3% and 5%.

15. Screw according to any one of the preceding claims, characterized in that, starting from the tip (12), the core diameter (DK) increases over the tip region (SB), and that, starting from the screw tip (12) in the direction of the head, the relative increase of the core diameter (DK) is less than the increase in the base thread outer radius (RAB).