SCREW, USE, METHOD AND SYSTEM

Description

[0001] The invention relates to a screw with a screw head and a screw shank, wherein the screw head is provided with a drive element and the screw shank is provided with a thread at least partially, wherein the screw shank has a cylindrical retaining section and an end section tapering towards one end of the screw, wherein the thread in the retaining section is a standard thread, in particular a metric thread, and wherein the retaining section has a circular cross-section. The invention also relates to the use of a screw according to the invention. The invention further relates to a system and a method for screwing in a screw according to the invention.

[0002] Screws for screwing into existing internal threads are known. Such screws have a screw head and a screw shank, the screw head being provided with a drive element and the screw shank being provided with a thread at least partially, wherein the screw shank has a cylindrical holding section and an end section tapering towards one end of the screw, wherein the thread in the holding section is a standard thread, in particular a metric thread. The tapered end section facilitates insertion into an existing internal thread.

[0003] In addition, so-called self-tapping screws are known. Self-tapping screws are used to tap a thread into an existing hole, for example, a sheet metal opening. For this purpose, a tapered end section of the screw is provided with a self-tapping thread. A retaining thread is then provided in the cylindrical holding section, which is optimized for a secure hold of the screw in the workpiece.

[0004] German patent application DE 10 2014 211 093 A1 discloses a hole- and thread-forming screw with a cross-section of the screw shank that runs the entire length of the shaft in the form of a triangle with rounded corners and convex sides. The thread of the screw is designed as a round thread.

[0005] The ESKA publication "Thread-forming screws for cost-effective direct fastening" describes an ESKA TriloMET screw which is said to have a circular cross-section in the area below the screw head and a trilobular cross-section in the area of ​​a thread-forming tip. The screw thread is trapezoidal along the entire length of the shank.

[0006] From the Spanish publication of a translation ES 2 224 727 T3, a self-tapping screw with a sectionwise polygonal and sectionwise circular cross-section is known. The thread of the screw is said to be a trapezoidal thread over the entire length of the shaft.

[0007] German patent DE 39 09 725 C1 discloses a hole- and thread-forming screw with a polygonal cross-section. The screw has a threadless, rounded tip.

[0008] A method for measuring the angle of rotation and the torque is known from US patent US 4,102,182.

[0009] A method for controlling the torque when screwing in a screw is known from Chinese patent application CN 109 227 104 A.

[0010] The invention aims to improve a screw, a use of a screw, a system for screwing in a screw and a method for screwing in a screw.

[0011] According to the invention, a screw with the features of claim 1, a use of a screw according to the invention with the features of claim 12, a system for screwing in a screw according to the invention with the features of claim 13 and a method with the features of claim 14 are provided for this purpose.

[0012] The invention is based on the surprising finding that it is possible to use the same screws in both holes with and without internal threads. This results in significant advantages in terms of inventory management, documentation, and the process reliability of screw-in operations. Specifically, a screw is provided that is suitable as a self-tapping screw and has a tapered end section extending from the holding section. This end section is provided with at least two threads designed as self-tapping threads, has a polylobular cross-section at least in the area of ​​the self-tapping thread, and the screw shank is hardened in both the holding and end sections.The hardened end section, which has a polylobular cross-section and features at least two threads of a self-tapping thread, and which tapers from the cylindrical holding section, makes the screw suitable as a self-tapping screw. It is possible to use this screw to tap a thread into an existing hole without an internal thread. Within the scope of the invention, it is advantageous if two to six threads of a self-tapping thread are provided. Since the thread in the cylindrical holding section, which has a circular cross-section, is a standard thread, the screw can also be screwed into an existing standard internal thread. Therefore, the same screws can be used regardless of whether a hole has no internal thread and consequently a thread must be tapped with the screw, or whether a hole has an internal thread.

[0013] This initially simplifies inventory management, as the same screws can be used in both threaded and unthreaded holes. A disadvantage, of course, is that the screws according to the invention are more expensive to manufacture than conventional standard threaded screws. Surprisingly, however, these cost disadvantages can be offset and even more than compensated for by the simplified inventory management, the ability to produce the screws according to the invention in very large quantities, and the simplified documentation required for screwing-in processes. Above all, process reliability during screwing is significantly improved. This is because using the same screws for screwing into both threaded and unthreaded holes prevents mix-ups.Screws are generally relatively small components, and while conventional screws with standard threads differ significantly from thread-cutting screws in technical terms, they differ only slightly in appearance. Confusion is therefore possible, as both types of screws have very similar external dimensions. This can even lead to a screw-in machine designed for thread-cutting screws failing to recognize that it is loaded with conventional screws with standard threads. The error might only occur during the production process, i.e., when screwing in the screws, where the standard-threaded screws break off while cutting a thread. However, the situation would be far more critical if the screws did not break during thread cutting, resulting in a workpiece being produced with screws of insufficient strength.Documenting the screwing-in process is also simplified, as the same screws are always used. Since confusion between different screws is no longer possible, process reliability is significantly improved.

[0014] In a further development of the invention, the end section is designed as an ogival tip, wherein the ogival tip is in particular flattened or rounded.

[0015] The end section preferably has the shape of an ogive, in other words a pointed arch, the tip of which may be flattened or rounded. The transition from the ogive tip to the cylindrical holding section can be tangential, i.e., without a visible or perceptible edge, or it can be such that an edge forms in the contour of the screw, and thus the ogive tip does not enter the cylindrical holding section tangentially.

[0016] In a further development of the invention, the end section is designed as a truncated cone section, in particular with a rounded end.

[0017] In a further development of the invention, the end section terminates at an end surface.

[0018] In the case of the screw according to the invention, it is not necessary to form a tip, since the screw according to the invention is intended for screwing into existing holes in a workpiece.

[0019] In a further development of the invention, the diameter of the end surface, viewed perpendicular to the longitudinal axis of the screw, is between 70% and 80%, in particular 75%, of the diameter of the holding section.

[0020] With such dimensions, especially for the preferably used ogival zone, simplified hole finding is made possible during the automatic processing of the screws according to the invention, and the cutting of a thread can also be carried out in a reliable and process-safe manner.

[0021] In a further development of the invention, the end section has a rounded search tip.

[0022] In this way, the screw can be inserted into existing holes in a very simple way, even if component tolerances are to be expected.

[0023] In a further development of the invention, the search tip is designed without threads.

[0024] This makes it easier to find holes with tolerances.

[0025] In a further development of the invention, the search tip has a circular cross-section.

[0026] This also makes it easier to insert the screw into existing holes. For example, the first few turns can be used to correctly position the screw relative to a smooth hole or a hole with an existing thread before the thread engages.

[0027] In a further development of the invention, the end section has a polylobular cross-section exclusively in the area of ​​the thread.

[0028] In this way, a thread can be formed, making the screw suitable even for smooth bores without internal threads. The retaining section, however, allows for very high pull-out forces. The search section, also round in cross-section—that is, the area located between the threaded section and the free end of the screw—facilitates the insertion of the screw into existing bores, with or without internal threads.

[0029] According to the invention, the thread is designed as a round thread in the end section.

[0030] This facilitates the cutting of a thread, as well as the insertion of the screw. With a round thread, both the thread crest and the thread valleys can be rounded; both the thread sections and the core have a round profile.

[0031] In a further development of the invention, the end section has, in addition to the forming thread, further thread sections which are designed as round threads.

[0032] When screwing the screw into an existing internal thread, finding the thread is made easier. The round thread can also have rounded thread crests and valleys, resulting in a round profile on the threads and in the core.

[0033] According to the invention, the standard thread in the holding section is designed as a trapezoidal thread.

[0034] This design achieves very high pull-out forces. In other words, the retaining thread is designed as a pointed thread with flattened valleys and peaks. The angle between the thread flanks is typically 60°.

[0035] In a further development of the invention, the thread on the screw shaft has a continuous, imaginary envelope extending to the free end of the screw shaft in a side view.

[0036] In other words, the thread does not extend beyond the envelope curve; even in the area of ​​the radially furthest projecting regions of the polylobular cross-section thread, the thread tip merely touches the continuous envelope curve and does not extend beyond it.

[0037] In a further development of the invention, at least the end section is additionally partially hardened, in particular inductively.

[0038] Partial and, in particular, inductive hardening allows at least the end section to be designed in such a way that it withstands the mechanical and thermal stresses during thread cutting. The greatest mechanical and thermal stresses occur in the end section; therefore, it is generally sufficient to partially inductively harden the end section. Specifically, only a portion of the end section, extending from the surface to a predefined depth, is additionally hardened. It is not necessary to partially harden the entire cross-section of the end section, since, according to the invention, the retaining section is already hardened.

[0039] In a further development of the invention, the screw is hardened to strength classes 8.8, 10.9, 12.9 or up to the ultra-high strength range.

[0040] These strength classes have proven to be extremely advantageous for the screw according to the invention. Furthermore, the thread-forming end section can be partially hardened. The hardening process for the screws according to the invention can be bainitic or case-hardened with subsequent tempering. In particular, a bainite microstructure exhibits high strength and very high toughness. A bainite microstructure is formed in carbon steel by a special cooling process in a salt bath. A bainite microstructure has proven to be extremely advantageous for the screw according to the invention.

[0041] In a further development of the invention, the tensile strength of the screw is at least 800 N / mm².

[0042] For example, the screw according to the invention is designed as a so-called 8.8 screw, preferably the screw according to the invention is designed as a 10.9 screw.

[0043] In a further development of the invention, a 0.2% yield strength of the screw is at least 640 N / mm², in particular at least 900 N / mm², and in particular at least 1040 N / mm².

[0044] For example, the screw is designed with a strength of 8.8 or a higher strength, especially up to the ultra-high strength range.

[0045] In a further development of the invention, at least the last complete thread turn of the forming thread before the end of the end section at the transition to the holding section is designed with regard to the thread dimensions like the standard thread in the holding section.

[0046] With the exception of the different cross-sections—the holding section has a circular cross-section and the end section a polylobular cross-section—the last thread of the self-tapping thread corresponds to the standard thread in the holding section with respect to its thread dimensions, i.e., its outer diameter and its core diameter. Unlike conventional self-tapping threads, which have a slightly larger diameter than standard threads, the self-tapping thread of the screw according to the invention is not manufactured with an interference fit compared to the standard thread in the holding section. This has the significant advantage that the screw according to the invention can be screwed into existing internal threads that conform to the standard without any problems.Surprisingly, it has also been found that, even though the self-tapping thread is not manufactured with an interference fit compared to the standard thread in the retaining section, the screw according to the invention can also be screwed into holes without an internal thread, where a thread must first be cut using the self-tapping thread. The maximum insertion torques determined by the material and dimensions can be maintained. The thread dimensions relate to the outer diameter and the core diameter, and in particular the flank diameter, the thread pitch, and the flank angle. Due to the polylobular cross-section of the end section, the outer diameter, the core diameter, and the flank diameter must each be measured as the largest diameter of the last thread turn of the self-tapping thread.Only if the polylobular cross-section is of uniform thickness can the outer diameter, the core diameter, and the pitch diameter of the last thread of the self-tapping thread be measured independently of the angular position. The standard thread in the retaining section can be, for example, a metric or imperial thread. In the case of a metric M5 thread, the outer diameter of the standard thread in the retaining section is between 4.790 mm and 5.0 mm, see DIN 13-20: 2000-08 / M5-4H-6G-6E. A typical self-tapping thread for cutting a metric M5 thread would usually have an outer diameter or a circumference around a polygonal cross-section that is larger than the nominal outer diameter, i.e., larger than 5.0 mm, for at least part of the tolerance range.According to the invention, the thread forming, or at least the last thread of the thread forming, at the transition between the end section and the retaining section is designed with an outer diameter corresponding to the standard thread, i.e., between 4.790 mm and 5.0 mm. 4.790 mm corresponds to the minimum dimension for M5 screws according to tolerance class 6E.

[0047] The invention also relates to the use of a screw according to the invention in a first use case as a thread-forming screw or in a second use case as a screw for screwing into existing internal threads.

[0048] By enabling the screws according to the invention to be used both as thread-forming screws and as screws for insertion into existing internal threads, the same screws can be used for different applications. This simplifies warehousing, allows for large production runs, facilitates documentation of the screw-in process, and, most importantly, avoids manufacturing errors that can arise from confusing different screws. By using the screws according to the invention both as thread-forming screws and as screws for insertion into existing internal threads, potentially safety-relevant errors in workpiece manufacturing can be avoided, and the disadvantage of the higher manufacturing costs of the screws according to the invention compared to conventional screws with standard threads can be offset or even more than compensated for.

[0049] The invention allows for the selection of a maximum tightening torque for a screw according to the invention. First, it is checked whether an internal thread is present in an existing hole in one or more workpieces. If an internal thread is present, a first maximum tightening torque is selected. If no internal thread is present, a second maximum tightening torque is selected, the first being lower than the second. In this way, the screws according to the invention can be used both for cutting an internal thread and for screwing into an existing internal thread. By selecting a lower maximum tightening torque for screwing into an existing internal thread than for cutting a thread, it can be reliably determined whether the screw jams or other irregularities occur when screwing into an existing internal thread.The invention also allows for the reduction of tightening torques in thread-forming screw connections, and this is equally applicable to screw connections with existing nut threads. With an existing nut thread, which is preferably metric, only a very low tightening torque occurs when screwing in a metric screw. When screwing conventional thread-forming screws into an existing nut thread, increased tightening torques can occur because conventional thread-forming screws have an oversize of the outer diameter over the entire thread or at least over a section of the thread. Therefore, the tightening torque can be reduced with the screw according to the invention.Generally, when screwing a self-tapping screw into an existing nut thread, there is a risk of cross-threading, in other words, the risk of creating a second thread, which can damage or destroy the nut thread. This risk of cross-threading is caused by the thread-forming zone on the screw. In practice, when a self-tapping screw is screwed into an existing thread, it is often impossible to distinguish whether increased tightening torques are due to cross-threading or to an oversized screw, resulting in the screw re-tapping the existing thread.The screw according to the invention ensures that when the screw is inserted directly into the existing nut thread—in other words, when the nut thread has been engaged and no cross-threading occurs—the tightening torques are extremely low and generally close to zero. This makes it possible to detect any incorrect tightening in the case of cross-threading with the screw according to the invention, since cross-threading is associated with increased tightening torques. Process reliability is therefore significantly improved when using the screw according to the invention. This can make a substantial contribution to quality improvement when assembling thread-forming screws into existing, preferably metric, nut threads.This allows the strategy of reducing the variety of parts to be implemented much better in practice by using the universal thread-forming screw according to the invention, both for thread-forming screw connections and for screw connections into existing threads.

[0050] The problem underlying the invention is also solved by a system for screwing in a screw according to the invention and comprising a screw according to the invention, in which means are provided for determining whether an existing hole has an internal thread or not, and in which adjusting means are provided to effect the screwing in of the screw with different maximum screwing torque depending on whether an existing hole has an internal thread or not.

[0051] The problem underlying the invention is also solved by a method for screwing in a screw according to the invention, in which the steps of detecting a screwing torque during screwing into an existing nut thread and detecting an incorrect screw connection if the screwing torque exceeds a predefined value are provided.

[0052] Unlike conventional self-tapping screws, the screws according to the invention allow a distinction to be made between whether the screw is correctly screwed into an existing internal thread or whether so-called cross-threading occurs, i.e., whether the screw cuts an additional thread into the existing thread. With conventional self-tapping screws, the insertion torque is very high when screwing into existing internal threads, since, for example, the outer diameter of conventional self-tapping screws is larger than the outer diameter of screws designed for screwing into existing internal threads. For this reason, with conventional self-tapping screws, it is not possible, or at least not always possible, to reliably distinguish between correct insertion into an existing internal thread and cross-threading. The screws according to the invention can now be screwed into an existing internal thread with a comparatively low insertion torque.If cross-threading occurs, this manifests as a significantly higher tightening torque, for example, up to 10 times higher than when correctly tightened. This can be detected, allowing for the identification of an incorrect screw connection and, if necessary, its repair.

[0053] Further features and advantages of the invention will become apparent from the claims and the following description of a preferred embodiment of the invention in conjunction with the drawings. The drawings show: Fig. 1 a side view of a screw according to the invention, Fig. 2 a first workpiece with an existing hole with a partial internal thread, Fig. 3 the screw of the Fig. 1 in the screwed-in state into the workpiece Fig. 2 , Fig. 4 another workpiece with an existing hole without internal thread, Fig. 5 the screw of the Fig. 1 in the screwed-in state into the workpiece Fig. 4 Fig. 6 a schematic representation of a system according to the invention for screwing in a screw, Fig. 7 another workpiece with an existing hole without internal thread, Fig. 8 another workpiece with an existing hole without internal thread, Fig. 9 the workpiece of the Fig. 8 with a screw according to the invention screwed in, Fig. 10 a section view of a screw according to a further embodiment of the invention from a rear oblique angle, wherein the screw is shown without a screw head, Fig. 11 the screw of the Fig. 10 from a frontal oblique view, Fig. 12 the screw of the Fig. 10 Viewed from the front, from the free end, Fig. 13, the screw of the Fig. 10 In a side view, Fig. 14 shows a section view of a screw according to a further embodiment of the invention from a rear oblique angle, wherein the screw is shown without a screw head, Fig. 15 shows the screw of the Fig. 14 from a frontal oblique view, Fig. 16 the screw of the Fig. 14 from the front, with the viewer's gaze directed towards the free end of the screw, Fig. 17 a side view of the screw of the Fig. 14 in a first rotational position about a central longitudinal axis of the screw, Fig. 18 another side view of the screw, wherein the screw is opposite the representation of the Fig. 17 rotated 90° around the central longitudinal axis, Fig. 19 a sectional view of the screw of the Fig. 14 , Fig. 20 another sectional view of the screw of the Fig. 14 , where the sectioning plane is opposite the representation of the Fig. 19 rotated by 90°, Fig. 21 shows a cross-section of the screw. Fig. 14 in the area of ​​the threadless search tip, Fig. 22 the cross-section of the Fig. 21 from the front, Fig. 23 another cross-section of the screw of the Fig. 14 in the area of ​​the threading thread, Fig. 24 the cross-section of the Fig. 23 from the front, Fig. 25 another cross-section of the screw of the Fig. 14 in the area of ​​the retaining thread, Fig. 26 the cross-section of the Fig. 25 from the front and Fig. 27 exemplary torque-angle curves when screwing in a screw according to the invention.

[0054] Fig. 1 Figure 1 shows a screw 10 according to a preferred embodiment of the invention. The screw has a screw head 12 with a Fig. 1 The screw shaft consists of an unrecognizable drive element 14 and a screw shank 16. The screw shank is provided with a thread 18 essentially along its entire length, which is Fig. 1 It is only shown schematically.

[0055] The screw shaft has a cylindrical retaining section 20 and an end section 22 extending away from the screw head 12 in one direction. The end section 22 tapers away from the retaining section 20 in one direction.

[0056] The retaining section 20 is provided with a standard thread, for example, a metric thread. The end section 22 is provided with at least five thread turns of a self-tapping thread. The thread flank height in the end section 22 corresponds at the transition from the retaining section 20 to the end section 22 to the thread height of the standard thread in the retaining section 20 and then decreases towards the free end of the end section 22. The thread height at the free end of the end section 22 is, for example, approximately 50% of the thread height of the end section 22 at the transition to the retaining section 22.

[0057] The terminal section 22 has the shape of a flattened ogival tip. The in Fig. 1 The visible outer contour of the end section 22 is formed by a circular arc that transitions tangentially into the cylindrical outer contour of the retaining section 20 and terminates at the end surface 26, which is arranged perpendicular to a central longitudinal axis 24 of the screw 10. The end section also has a Fig. 1 The polylobular cross-section 221 is indicated to the right of the end section 22, whereas the retaining section 20 has a cylindrical cross-section 201. In the illustrated embodiment, the cross-section 221 of the end section 22 is provided with three rounded corners 221a, 221b, 221c and three convexly curved side edges 221d, 221e, 221f connecting the rounded corners. This can also be described as trilobularity. In the illustrated embodiment, the cross-section 221 is of uniform thickness. The outer diameter of the cross-section 221 is therefore always the same, regardless of the angular position. However, within the scope of the invention, the polylobular cross-section 221 of the end section 22 can also have an outer diameter that changes depending on the angular position.

[0058] The numbers 10.9 are visible on the upper side of the screw head 12. The numbers 10.9 indicate a screw strength. The tensile strength of the screw is at least 1,000 N / mm² and the yield strength (0.2%) of the screw 10 is at least 900 N / mm². Within the scope of the invention, such so-called 10.9 screws represent the preferred embodiment.

[0059] In end section 22, screw 10 is induction hardened. This is in the Fig. 1 This is schematically indicated by a hardened area 28, shown in a dashed line 28. Through induction hardening, the entire thread forming process is hardened from the surface of the end section 22, as well as an area 28 extending slightly beyond the root of the thread towards the central longitudinal axis 24. An initial section of the retaining section 20 is also induction hardened. This ensures that at least the five threads of the thread forming process in the end section 22 are completely hardened. Specifically, a fully formed thread must lie within the induction-hardened area 28, so that the thread in the retaining section 20 no longer needs to perform a thread forming function.

[0060] Fig. 2 Figure 1 shows a workpiece 30 with a hole 32 in sections. The workpiece consists of a cover plate 34, which is perforated in the area of ​​the hole 32, and a second plate 36, which is provided with a press-fit nut 38. The press-fit nut 38 is shown schematically; in particular, it is not shown how the press-fit nut 38 is pressed into and anchored to the plate 36. By providing the press-fit nut 38, the hole 32 has an internal thread in the area of ​​the press-fit nut 38.

[0061] Fig. 3 The screw 10 of the Fig. 1 When screwed in, the underside of the screw head 12 rests on the top side of the cover plate 34, and the thread 16 in the retaining section 20 engages in the internal thread of the press-fit nut 38. The cover plate 34 and the plate 36 are thus pre-tensioned against each other by means of the screw 10 and the press-fit nut 38.

[0062] When screwing in the screw 10, the tapered end section 22 facilitates the insertion of the screw 10 into the hole 32 and also facilitates the positioning and screwing in of the thread 16 into the internal thread of the press-fit nut 38.

[0063] The screw 10 according to the invention can therefore be easily screwed into existing internal threads, in this case into an existing internal thread of a press-fit nut 38. Since the thread 16 in the retaining section 20 is designed as a standard thread, the thread 16 engages securely in the thread of the press-fit nut 38.

[0064] Fig. 4 Figure 1 shows a second workpiece 40 with a hole 42 that is not provided with an internal thread. The workpiece 40 again has a cover plate 44 and a further plate 46 arranged below the cover plate 44, whereby the cover plate 44 and the further plate 46 are only shown in sections. The further plate 46 is provided with a through-hole 48 that forms an extension of the hole 42.

[0065] Fig. 5 The screw 10 of the Fig. 1 in the screwed-in state into hole 42. After inserting screw 10, so that the end section 22 is inserted section by section into hole 42 and at the Fig. 4 When the screw 10 is seated at the upper end of the through-section 48, it is set in motion and the self-tapping thread in the end section 22 is screwed into the hole 42 in the through-section 48, thereby creating an internal thread in the through-section 48 through its self-tapping action. The end section has at least five thread turns of a self-tapping thread which, as explained, have an increasing thread flank height from the beginning of the end section 22 to the transition into the cylindrical retaining section 20. During the screwing of the end section 22 into the through-section 48, the internal thread in the end section 48 is thus formed to such an extent that it corresponds to a standardized internal thread that matches the standardized thread in the cylindrical retaining section 20.

[0066] The polylobular end section 22 reduces the screw-in torque when the thread is cut, since only the rounded corners of the polylobular cross-section bear against the inner wall of the passage 48, or rather, an increased contact force is exerted outwards on the inner wall of the passage 48 only in the area of ​​these rounded corners. As soon as the insertion section 22 is screwed into the passage 48 up to its end, i.e., the transition to the retaining section 20, the... Fig. 5 At the upper end of the through-hole 48, at least one thread of a fully formed internal thread is available, the dimensions of which conform to the standard and are thus adapted to the standard thread in the retaining section 20. The retaining section 20 can therefore be screwed into the through-hole 48. In the state of Fig. 5 The screw 10 is fully screwed into the passage 48 and thereby pre-tensions the sheet metal 46 and the cover plate 44 against each other.

[0067] The screw 10 according to the invention can therefore also be used to cut a thread into a hole 42 without an existing internal thread.

[0068] Fig. 6 Figure 50 shows a system 50 for screwing screws 10 according to the invention into different workpieces 30, 40 and 60. The workpiece 30 has already been prepared based on the Fig. 2 explained, workpiece 40 was already prepared using the Fig. 4 explained. Workpiece 60 differs from workpiece 30. Fig. 2 This is achieved solely by the fact that a plastic plate 64 is provided instead of the cover plate, and the hole 62 is limited by a brass sleeve 66 inserted into the plastic plate 64. The plastic plate 64 is arranged above the plate 36 with the press-fit nut 38.

[0069] System 50 is designed to screw identical screws 10 into different workpieces 30, 40, and 60. The screw 10 is mounted on a schematically depicted screw-in device 70, whose shaft 72 can be rotated in the screw-in direction. A maximum screw-in torque can be preset. The screw-in device 70 can move longitudinally along the screw and perpendicular to it—in other words, in three spatial directions—to insert the screw 10 into one of the holes 32, 42, or 62. The screw-in device is equipped with a camera 74, which is directed at the workpieces 30, 40, or 62 and is connected via at least one data line to a control unit (not shown) within the screw-in device 70. Using the camera 74 or another suitable sensor, it can be determined whether or not an internal thread is present in each hole 32, 42, or 62.Depending on whether it is determined that an internal thread is present or not, a maximum screw-in torque is set for screwing in the screw 10 using the screw-in machine 70.

[0070] The hole 32 of the first workpiece 30 has an internal thread in the area of ​​the press-fit nut 38. Consequently, when the screw 10 is screwed into the hole 32, an initial tightening torque is applied. This initial tightening torque is chosen, for example, to correspond to the usual tightening torque when screwing standard threaded screws into existing internal threads.

[0071] When screw 10 is screwed into hole 42, which has no internal thread, even in the area of ​​the sheet metal opening 48, a second maximum screw-in torque is applied, sufficient to cut a thread in the opening 48. This second maximum screw-in torque is higher than the first maximum screw-in torque.

[0072] In the hole 62 of the third workpiece 60, an internal thread is again present in the area of ​​the press-fit nut 38. Consequently, when screwing the screw 10 into the hole 62, the first maximum screw-in torque is again applied, which is lower than the second maximum screw-in torque.

[0073] When using the system 50 according to the invention for screwing identical screws 10 into different workpieces 30, 40, 60 or into one and the same workpiece, for example a motor vehicle body, with differently shaped holes, confusion between different screw types can be avoided, since the same screws 10 are always used regardless of whether a hole into which a screw is to be screwed has an internal thread or not. This significantly improves the process reliability of the screwing-in process. Documentation of the screwing-in process is also simplified, since the same screws 10 are always used.

[0074] With the in Fig. 6 The same screws 10 shown in system 50 can also be used in the system shown in Fig. 7 und 8 The workpieces shown, 70 and 80, are screwed in. Fig. 7 Figure 1 shows the workpiece 70 with a drilled core hole 72, which is cylindrical in shape. The core hole 72 has no internal thread, and the screw 10 according to the invention can be inserted into the core hole 72, whereby the screw 10, when screwed into the core hole 72, forms a thread on the wall of the core hole 72.

[0075] The in Fig. 8 The workpiece 80 shown has a cast conical core hole 82. The core hole 82 is frustoconical in shape and consequently has a conical shape at its end. Fig. 8 The open end shown above has a larger diameter than at its other end. Fig. 8 The end shown below.

[0076] Fig. 9 Figure 10 shows the screw 10 according to the invention in the screwed-in state in the core hole 82 in the workpiece 80. A further component 90 was fastened to the workpiece 80 using the screw 10. It is in Fig. 9 It can be seen that the screw 10 has cut a thread into the core hole 82. The screw 10 ends before the bottom of the core hole 82, which is designed as a blind hole, so that there is still a gap 84 between the end of the screw 10 and the bottom of the blind hole.

[0077] Fig. 10 Figure 1 shows a further screw 100 according to the invention in a section view from a rear oblique angle. The screw 100 has a screw head (not shown) with a drive element, for example the one shown in Figure 1. Fig. 1 The screw head shown is 12. For the sake of clarity, this screw head is shown in the illustration of the Fig. 10 omitted. The screw head would rest on the in Fig. 10 The end facing the viewer is thus placed on the cut surface 102. According to the invention, a further section of a shaft 116 of the screw 100 can also follow the cut surface 102. The screw 100 has a screw thread 118 along its entire length on the screw shaft 116, which is designed as a standard thread, specifically a trapezoidal thread, in a holding section 120 and as a round thread in an end section 122. This is already shown in the view of the Fig. 10 to recognize that the end section has a groove section 123 with a polylobular cross-section, specifically a trilobular cross-section, and at the free end of the screw 120, i.e., at the end visible to the observer in Fig. 10 At the far end of the end section 122, there is a search section 124 with a circular cross-section. The holding section 120 also has a circular cross-section. A working thread with a total of four threads is arranged in the working section 123.

[0078] Fig. 11 shows a view of screw 100 of the Fig. 10 from a slightly angled front view, again omitting the screw head. It is in the view of the Fig. 11 It can be seen that in search section 124, the single thread found there has a circular cross-section and is designed as a round thread. The four threads in the punching section 123 are formed on a trilobular cross-section of the shank 116 and are also designed as round threads. In the holding section 120, which follows the punching section 123, the standard thread, which is designed as a 60° trapezoidal thread, is again formed on a circular cross-section of the shank 116. It can be seen that in the holding section 120, the thread has flattened thread tips. Search section 124 and punching section 123 together form the end section 122.

[0079] In the presentation of the Fig. 11 Areas 126 can be seen on the last thread of the forming section 123 and on the first thread of the holding section 120, in which the thread is formed slightly differently. These areas are not designed with flattened, but with rounded thread tips and serve only to ensure a smooth transition from the trilobular cross-section of the forming thread 123 to the thread of the holding section with a circular cross-section.

[0080] Fig. 12 The screw shows 100 of the Fig. 10 in a front view, again omitting the screw head. The view goes into Fig. 12 to the final section 122. In Fig. 12 It can be seen that the first thread 128 of the end section 122 still has an approximately circular cross-section. This first thread 128 is followed by four threads of the self-tapping thread 123 with a trilobular cross-section. Behind the self-tapping thread 123, the retaining section 120 with a standard thread and circular cross-section can be seen. Fig. 12 This clearly shows that the thread 123 does not project beyond the cross-section of the retaining thread in the retaining section 120. In other words, even the outermost radial areas of the thread 123 do not extend beyond the contour of the retaining thread in the retaining section 120.

[0081] Fig. 13 shows a side view of screw 100 of the Fig. 10 , again omitting the screw head. It is clearly visible that in the end section 122, the thread is designed as a round thread with rounded thread crests. Within the scope of the invention, the thread valleys can also be rounded. In the retaining section 120, however, the thread is designed as a trapezoidal thread with flattened thread crests and flattened thread valleys.

[0082] Fig. 14 Figure 1 shows a further embodiment of a screw 200 according to the invention. The screw 200 has a screw shank 216 and is shown only in section. Specifically, a screw head that would be placed on a cut surface 202 is not shown. The screw shank 216 can also extend beyond the cut surface 202. For example, the screw head can be attached to the cut surface 202. Fig. 1 The screw head shown (12) is to be attached.

[0083] The screw 200 has a retaining section 220 and an end section 222. The end section 222 has four threads of a self-tapping thread 223 and a threadless probe tip 224. The threadless probe tip 224 is rounded at its free end and gradually increases in diameter until it reaches the first thread of the self-tapping thread. The probe tip 224 has a circular cross-section. In the area of ​​the self-tapping thread 223, the shank 216 has a trilobular cross-section. In the retaining section 220, the thread is designed as a standard thread and specifically as a 60° trapezoidal thread with flattened thread crests and flattened thread valleys.

[0084] Fig. 15 The screw 200 shows the Fig. 14 In a front view, the circular cross-section of the search tip 224 and the trilobular cross-section of the threading thread 223 are clearly visible. The circular cross-section of the thread in the holding section 220 is also visible.

[0085] Fig. 16 The figure shows screw 200 in a front view, with the screw head omitted. Clearly visible are the circular cross-section of the search tip 224, the trilobular cross-section of the threads of the cutting thread 223, and the circular cross-section of the thread in the holding section 220. Fig. 16 It can be seen that the threads of the forming thread 223 do not extend beyond the contour of the retaining thread in the retaining section 220.

[0086] Fig. 17 shows a side view of screw 200 of the Fig. 14 in a first rotational position about the central longitudinal axis. In the area of ​​the thread 123, the thread tips are rounded. This differs from the illustration in Fig. 17 The thread valleys can also be rounded.

[0087] Fig. 18 shows another side view of screw 200, with the screw opposite the illustration of the Fig. 17 was rotated 90° around the central longitudinal axis.

[0088] Fig. 19 shows a sectional view of screw 200 and Fig. 20 shows another sectional view of screw 200, where the section plane of the Fig. 20 opposite the cutting plane of the Fig. 19 rotated 90° around the central longitudinal axis.

[0089] Fig. 21 shows a sectional view of screw 200 in the area of ​​the search tip 224. Fig. 22 shows the sectional view of the Fig. 21 From the front. The circular cross-section of the search tip is clearly visible; it is smooth, unthreaded, and rounded at its free end.

[0090] Fig. 23 Figure 1 shows another sectional view of screw 200, with the section plane placed in the area of ​​the thread 223. The polylobular cross-section with three maxima, in other words a trilobular cross-section, is clearly visible. Fig. 24 shows the sectional view of the Fig. 23 from the front.

[0091] Fig. 25 Figure 2 shows another sectional view of screw 200 in the area of ​​the retaining section 220. The circular cross-section of the screw shank in the retaining section 220 is clearly visible. It should also be taken into account that... Fig. 26 , which reflects the view of Fig. 25 From the front, it shows that the cutting plane in Fig. 25 und Fig. 26 The cutting plane runs perpendicular to the central longitudinal axis of the screw, while the threads of the retaining thread have a pitch. For this reason, the cutting plane runs in Fig. 25 und Fig. 26 On the one hand, the thread is formed by a trough, and on the other hand by a ridge. This explains the slight deviations from a perfectly circular shape.

[0092] Screws 100 and 200 of the Fig. 10 bis 26 Furthermore, they are hardened and exhibit a bainite microstructure. This allows for high strength and, above all, very high toughness of the screw.

[0093] Fig. 27 This shows exemplary torque-angle curves when screwing screws of the invention into existing threads. A [missing information] was used for this purpose. Fig. 14 bis 26 The corresponding screw, naturally with a screw head featuring a drive mechanism, had a diameter of 6 mm and thus an M6 thread in the holding section. As described, the end section 122 has a round thread. When correctly screwed into an existing M6 nut thread, a torque of no more than 0.1 Nm is achieved over a rotation angle of more than 2,000°, according to curves CRV001, CRV002, and CRV003. The screw according to the invention can therefore be easily and quickly screwed into an existing nut thread.

[0094] In contrast, the two curves CRV0004 and CRV0005 show the screw being inserted into an M6 nut thread, where the screw was deliberately inserted at an angle to provoke cross-threading, i.e., the cutting of an additional thread on top of the existing nut thread. It can be seen that the torque required increases to a value significantly greater than 1 Nm within the first turn, i.e., within the rotational angle range of 0 to 360°. Therefore, when cross-threading occurs, the screw according to the invention requires at least ten times the torque needed for correct insertion. With the screw according to the invention, it is thus possible to detect very easily whether the screw has been correctly inserted into an existing thread or whether cross-threading has occurred.This can be easily achieved by measuring the torque required for screwing in the screw and detecting when predefined torque limits are exceeded. In the case of... Fig. 27 A limit value could be set, for example, at 0.2 Nm in the torque-angle curves shown. If the torque required to screw the screw according to the invention into an existing thread exceeds 0.2 Nm, so-called cross-threading occurs. The component and screw must then be inspected and, if necessary, repaired. As already explained, with conventional self-tapping screws, the torque required to screw into an existing nut thread is in the same order of magnitude, both when screwing in correctly and when cross-threading occurs. A comparable detection of incorrect tightening or the occurrence of cross-threading is therefore not possible with conventional self-tapping screws.

Claims

1. Screw (10) having a screw head (12) and a screw shaft (16), wherein the screw head is provided with a drive formation (14) and the screw shaft is at least partially provided with a thread (18), wherein the screw shaft has a cylindrical retention portion (20) and an end portion (22) which tapers toward a screw end, wherein in the retention portion the thread is in the form of a standard thread, in particular a metric thread, wherein the retention portion has a circular cross section, wherein the end portion tapers from the retention portion, wherein the end portion is provided with at least two thread turns which are in the form of tapping threads, wherein the end portion has a polylobulated cross section at least in the region of the tapping thread and wherein the screw shaft is hardened in the retention portion and in the end portion, characterized in that the tapping thread is in the form of a round thread in the end portion and wherein the standard thread is in the form of a trapezoidal thread in the retention portion.

2. Screw according to Claim 1, characterized in that the end portion has a rounded searching tip (224).

3. Screw according to Claim 2, characterized in that the searching tip is constructed without a thread.

4. Screw according to Claim 2 or 3, characterized in that the searching tip has a circular cross section.

5. Screw according to at least one of the preceding claims, characterized in that the end portion has a polylobulated cross section exclusively in the region of the tapping thread.

6. Screw according to one of the preceding claims, characterized in that the end portion has additional thread turns which are in the form of round threads in addition to the tapping thread.

7. Screw according to at least one of the preceding claims, characterized in that the thread has, when viewed from the side, on the screw shaft a continuous notional generating curve as far as the free end of the screw shaft.

8. Screw according to one of the preceding claims, characterized in that at least the end portion is further partially hardened.

9. Screw according to at least one of the preceding claims, characterized in that a tensile strength of the screw is at least 800 N / mm2, in particular at least 1040 N / mm2.

10. Screw according to at least one of the preceding claims, characterized in that a 0.2% permanent elongation limit of the screw is at least 640 N / mm2, in particular at least 900 N / mm2.

11. Screw according to at least one of the preceding claims, characterized in that at least the last complete thread turn of the tapping thread is constructed before the end of the end portion at the transition to the retention portion with respect to the thread dimensions in the same manner as the standard thread in the retention portion.

12. Use of a screw according to at least one of the preceding Claims 1 to 11 in a first application as a thread-tapping screw or in a second application as a screw for being screwed into provided internal threads.

13. System (50) for screwing in a screw according to one of the preceding Claims 1 to 11, comprising a screw according to one of the preceding Claims 1 to 11, characterized by means for establishing whether or not a provided hole has an internal thread, and, in accordance therewith, screwing in the screw with a different maximum screwing-in torque.

14. Method for screwing in a screw according to one of the preceding Claims 1 to 11, characterized by detecting a screwing-in torque during the screwing action into a provided nut thread and detecting an incorrect screwing arrangement if the screwing-in torque exceeds a predefined value.