Threaded spindle and method for manufacturing a threaded spindle

Abstract

Threaded spindle (1), with an inner sleeve (2) and an outer part (3) firmly connected to it, having a thread (5), wherein the inner sleeve (2) and the outer part (3) are made of different materials, characterized in that the inner sleeve (2) is formed into the outer part (3) by forming in a form-fitting manner, replicating the thread (5), and the outer part is surface-hardened.

Description

The invention relates to a threaded spindle according to the preamble of claim 1, intended for use in a screw drive, in particular a ball screw drive. Furthermore, the invention relates to a method for producing such a threaded spindle. A ball screw drive comprising a generic threaded spindle is known, for example, from DE 10 2016 222 894 B4. The threaded spindle of the known ball screw drive is designed as a hollow spindle. An outer part, which has a thread, is assembled with an inner sleeve without additional components. In the case of DE 10 2016 222 894 B4, the inner sleeve has a collar projecting beyond the outer part at the end face, onto which a stop element is formed, which is intended to interact with a stop contour of a ball screw nut of the ball screw drive. A ball screw drive disclosed in DE 33 08 149 A1 also has a threaded spindle designed as a hollow shaft. The balls rolling in the threads of the threaded spindle are mounted in a ball cage that is significantly wider than the nut of the ball screw drive. Thinner-walled sleeves are attached to the two ends of the nut compared to the nut, preventing the balls from falling out. Thanks to the two sleeves rigidly connected to the nut, no ball return is required given the inherently limited adjustment range of the ball screw drive. DE 10 2009 045 857 A1 describes a method for manufacturing a spindle for a spindle drive. The described method involves arranging a coil with a flat, rectangular annular cross-section on a thin-walled tube, and then molding the tube to a base area of the coil by applying high pressure from the inside. The hollow spindle produced in this way is intended to be usable, for example, in an electromechanical brake booster or an electromechanical power steering system. Another method for producing a threaded part for a roller screw drive, i.e., a roller screw drive intended for use in an electromechanical brake booster, is described in WO 2013 / 029842 A1. In this case, threads are formed from metal by forming and overmolded with tubular plastic support parts. Documents DE 10 2019 114 276 A1 and DE 10 2019 120 812 A1 deal with threaded nuts for ball screws. In both cases, thread-like profiled sleeves are formed from sheet steel. On one end of the sleeve, designed as a threaded nut, there is a flange that can be connected to another tubular machine element by welding. The invention is based on the object of further developing threaded spindles designed as hollow shafts compared to the cited prior art, in particular with regard to manufacturing technology, whereby good possibilities for connecting the threaded spindle to another, also hollow machine element should be provided. This object is achieved according to the invention by a threaded spindle having the features of claim 1. The object is also achieved by a method for producing a threaded spindle for a screw drive according to claim 6. The embodiments and advantages of the invention explained below in connection with the manufacturing method also apply mutatis mutandis to the devices, i.e. the threaded spindle and the entire screw drive, and vice versa. The threaded spindle comprises, in a basic concept known per se, an inner sleeve and an outer part which is firmly connected to the inner sleeve and is also sleeve-shaped and has a thread, whereby the two nested parts, i.e. the inner sleeve and the outer part, are made of different materials, in both cases metallic. According to claim 1, the inner sleeve is formed into the outer part in a form-fitting manner, replicating the thread pitch. The fact that the thread pitch of the sleeve-shaped outer part is reproduced by at least one surface of the inner sleeve, in any case by its outer surface, generally means that the respective surface of the inner sleeve is also structured three-dimensionally in the manner of a thread, wherein, compared to the thread of the outer part, the embossing depth of the thread-like structure can be reduced and transitions can be rounded. In addition to the outer surface, the inner surface of the inner sleeve can also have a fundamentally similar thread-like structure, wherein in this case the embossing depth, measured in the radial direction of the inner sleeve and the outer part and achieved by forming, is again reduced compared to the depth of the structure embossed into the outer surface of the inner sleeve. The threaded spindle is a component of a ball screw or other rolling screw drive, according to various possible designs. The threaded spindle functions either as a rotating drive element or as a rotationally secured, movable output element of the ball screw or other rolling screw drive. Alternatively, the threaded spindle can be designed as the input or output element of a simple linear motion thread. Regardless of the type of the entire screw drive, the inner sleeve is preferably made of a weldable material in order to enable a welded connection with another metallic machine element, in particular designed as a tube, sleeve or disc. In the case of the outer part, however, the criterion of weldability typically plays no role. In many cases, hardening of the outer part is provided. For example, the outer part can be hardened conductively or inductively. In the latter case, i.e., with high-frequency hardening, the high frequency at the induction coil ensures that the induced current density is particularly high in the areas close to the surface of the workpiece, thus primarily resulting in surface hardening. Laser or electron beam hardening can also be considered. If hardening is carried out in a furnace, austenitizing can be carried out in a protective gas or vacuum atmosphere. This step can be followed, in a conventional manner, by quenching with a suitable quenching medium. In a conventional manner, tempering of the threaded spindle can also be provided as part of the heat treatment. In any case, the outer sleeve, i.e. the sleeve-shaped outer part, is only hardened after the final shape of the threaded spindle, including the thread of the outer part, has been produced by forming, whereby the thread can basically be a single-start or multi-start thread, for example a two-start or three-start thread. In general, a threaded spindle can be produced in the following steps:- Providing a tool which has an inner surface structured in the manner of a thread,- Providing a blank of an inner sleeve and a sleeve-shaped outer part, wherein the outer part is made of a different material than the inner sleeve,- Forming the inner sleeve and the outer part in the tool in such a way that the outer peripheral surface of the outer part takes on the contour of the thread and the inner peripheral surface of the outer part is brought into positive engagement with the outer peripheral surface of the inner sleeve, reproducing the thread contour in a weakened form,- Separating the threaded spindle formed in the previous step from the tool and formed from the inner sleeve and the outer part. For linguistic simplification, in this case the blanks from which the inner sleeve and the sleeve-shaped outer part of the final threaded spindle are to be formed are referred to as inner sleeve and outer part. The sleeve-shaped outer part of the threaded spindle is also referred to as the outer layer. In an alternative embodiment, instead of a pair of different sleeve-shaped elements that are nested and connected to one another, a roll-clad sheet can also be used as the starting product for producing the threaded spindle. Regarding roll-clad sheets, reference is made to EP 4 067 525 A1 for background information. Whether using a roll-clad sheet or two separate, initially separated, sleeve-shaped elements, namely the inner sleeve and the sleeve-shaped outer part, the forming can occur either by pressure acting from the inside outwards or by pressure acting from the outside. In the latter case, for example, a smooth mandrel is used to hold the inner sleeve. The workpiece is then formed using a tool that has at least one radially adjustable roller that has the thread contour to be created as a negative contour. In a typical design, an arrangement of several profiled rollers, for example three rollers, is used that surround the workpiece, i.e. the threaded spindle being machined, in a star shape. The machining can involve one or more radial feeding and axial movement of the rollers.During machining, the assembly of all rollers—in extreme cases, just a single roller—rotates around the workpiece's central axis, with each roller simultaneously rotating around its own axis. Axial and rotary movements are synchronized to produce the desired thread pitch. After the forming process, the workpiece is removed from the mandrel. Deep drawing is a particularly suitable technology for the non-cutting production of the inner sleeve and the sleeve-shaped outer part, regardless of the subsequent formation of the thread. The inner sleeve and / or sleeve-shaped outer part can also be in the form of drawn tubes. In the case of the inner sleeve, a rolled version is also possible. In this case, the ends of the sheet metal strip bent into a sleeve are joined together, particularly by welding. The weld seam can run either diagonally or parallel to the central axis of the inner sleeve and thus also of the subsequent threaded spindle. Optionally, the inner sleeve blank already has a flange. Such a flange, i.e. an outward-facing rim, represents an effective axial safeguard against displacement of the outer part in one direction. Regardless of the form of the starting materials used to manufacture the two-layer threaded spindle, they are formed by applying pressure from the inside, thereby inducing plastic deformation in a tool. The pressure can be applied to the sleeve-shaped blank in a conventional manner, using a tool, rollers, a hydraulic medium, or a rigid or rubber-elastic auxiliary material. By using a one-piece die as a tool, the formation of seams on the workpiece is inherently eliminated. After the forming process, the workpiece, i.e., the threaded spindle, can be unscrewed from the tool. If necessary, the unscrewing process can be facilitated by deliberately changing the temperature of the workpiece and / or the tool. A mechanical change in the tool diameter can also be provided in a production fixture to facilitate the unscrewing process. In principle, the use of a multi-part tool is also possible. Even in cases where the tool is multi-part, the tool can form at least one closed ring. This ring has, in particular, the thread structure on the inside, which is to be transferred to the workpiece. To complete the tool, a further, comparatively small ring can be provided. This ring does not have a thread-like structure and accordingly defines the shape of a section of the workpiece with a smooth wall. The inner sleeve, which is a non-hardened component of the threaded spindle, can be connected to a part attached to the threaded spindle, such as an adapter tube, using any generally known welding process. In cases where the threaded spindle is made of roll-clad sheet metal, the overlay material, i.e., the outer layer, can be partially removed before welding to ensure the desired weldability. Generally, hardening can be performed either before welding the adapter or after manufacturing the spindle assembly, which consists of the threaded spindle and the welded adapter. If the inner sleeve and the sleeve-shaped outer part are initially available as separate individual parts, there are various possibilities for reshaping these individual parts and joining them together. According to a first process variant, the sleeve-shaped outer part is first inserted into the tool and at least partially formed. The inner sleeve is then inserted into the outer part located in the tool and, by applying pressure, pressed against the inner circumferential surface of the outer part, resulting in plastic deformation. This process also gives the outer ring its final shape. This process variant is characterized by the fact that it is also applicable to very thick wall thicknesses of the sleeve-shaped parts to be formed. According to a second process variant, the inner sleeve is inserted into the tool together with the sleeve-shaped outer part. Both parts, i.e., the inner sleeve and the outer part, initially have exclusively smooth inner and outer surfaces. After positioning the aforementioned parts in the tool, the parts are formed simultaneously in the tool according to this variant. In both process variants, the thread structure of the tool is ultimately also imprinted on the inner sleeve, thus creating a permanently stable connection between the inner sleeve and the outer part. The threaded spindle, i.e., a hollow spindle, is particularly suitable for use in an electromechanical actuator of a motor vehicle. This could, for example, be a chassis actuator for leveling. The threaded spindle, designed as a sheet metal composite spindle, could also be used in a linear drive of a stationary system. Several embodiments of the invention are explained in more detail below with reference to a drawing. These show: Fig. 1 in a partially sectioned view of a threaded spindle designed as a sheet metal composite hollow spindle, Fig. 2 a detail of the threaded spindle according to Fig. 1 in a sectional view, Fig. 3 a threaded spindle modified compared to the embodiment according to Fig. 1 in a view analogous to Fig. 2, Fig. 4 a spindle assembly formed from the threaded spindle according to Fig. 1 and a tubular adapter, Fig. 5 a ball screw drive comprising the spindle assembly according to Fig. 4 as the output element and a ball screw nut as the drive element, Fig. 6 the ball screw drive according to Fig. 5 in a perspective view, Fig. 7 an arrangement comprising a one-piece tool for forming a multi-part threaded spindle, Fig. 8 an arrangement provided for forming in the tool according to Fig. 7 and comprising an inner sleeve and a sleeve-shaped outer part, Fig.9 shows an arrangement of two sleeve-shaped parts which is modified compared to the arrangement according to Fig. 8 and which is to be formed into a threaded spindle, Fig. 10 shows the tool according to Fig. 7 with a partially formed outer part inserted therein, Fig. 11 shows the arrangement according to Fig. 10 , supplemented by the inner sleeve which is still undeformed in this state, Fig. 12 shows an arrangement resulting from the arrangement according to Fig. 11 and created by applying internal pressure to the inner sleeve with the outer part completely formed on the outside, Fig. 13 , Fig. 14 shows an alternative arrangement for forming a multi-part threaded spindle in various representations, Fig. 15 shows a detail from Fig. 13 . Unless otherwise stated, the following explanations refer to all embodiments. Corresponding or essentially equivalent parts are identified by the same reference numerals in all figures. A threaded spindle, designated overall by the reference numeral 1, is composed of an inner sleeve 2 and a likewise sleeve-shaped outer part 3, which is firmly connected to the inner sleeve 2 without separate connecting elements. The inner sleeve 2 is made of a weldable material and optionally has a flange 4 on one of its end faces, as shown by way of example in Fig. 8 and Fig. 9. A thread 5 is formed on the outer surface of the outer part 3. In all embodiments, the outer part 3 is hardened at least on its outer surface, with possible transitions between a hardened region 6 and an unhardened region 7 being sketched in Fig. 2 and Fig. 3. The geometry of the threaded spindle 1 according to Fig. 3 corresponds to the geometry of the threaded spindle 1 according to Fig. 1 and Fig. 2. In both the embodiment shown in Figs. 1 and 2 and in the embodiment shown in Fig. 3, the inner sleeve 2 has a thread-like contour 8 on its outer circumferential surface, which, with a reduced embossing depth, reproduces in a weakened form the thread contour, designated overall by 9, formed by the thread pitch 5. The inner circumferential surface of the sleeve-shaped outer part 3 is correspondingly deformed, so that a full-surface, positive contact is achieved between the inner sleeve 2 and the likewise sleeve-shaped outer part 3. Deviations from the smooth cylindrical shape of the inner surface of the inner sleeve 2 are not shown in Figs. 2 and 3. The wall thickness of the inner sleeve 2 is significantly greater than the wall thickness of the outer part 3. As can be seen from Fig. 1 as well as from Fig. 4 and Fig. 5, the inner sleeve 2 protrudes beyond the outer part 3 in the form of a smooth cylindrical projection 11. An adapter tube 12 is pushed onto the projection 11. The adapter tube 12 is connected to the threaded spindle 1 by a weld seam 13. The entirety of the threaded spindle 1 and adapter tube 12 is referred to as the spindle assembly 14. The adapter tube 12 has a widened region 15 pushed onto the inner sleeve 2, the inner and outer diameters of which approximately correspond to the inner and outer diameters of the outer part 3. A tubular region 16, which is considerably longer than the widened region 15, has an outer diameter that corresponds to the inner diameter of the inner sleeve 2. The tubular region 16 is connected to the widened region 15 via a conical region 17.Two flattened portions 18 are formed in the tubular region 16, which extend in a strip-like manner in the longitudinal direction of the spindle assembly 14 and extend to the end face of the adapter tube 12 facing away from the projection 11 of the threaded spindle 1. The diametrically opposed flattened portions 18 of the adapter tube 12 can be used, for example, as anti-rotation contours of the spindle assembly 14. In Fig. 5, the spindle assembly 14 is shown as part of a ball screw drive designated overall by 10. The ball screw drive 10, whose central axis is designated MA, further comprises a ball screw nut 19. During operation of the ball screw drive 10, rolling elements, i.e., balls, roll in a conventional manner between the thread contour 9 of the threaded spindle 1, i.e., the ball screw spindle, and an internal thread designated 20 of the ball screw nut 19. Optional means for ball return are not shown. A pulley 21 is firmly connected to the ball screw nut 19, as can also be seen from Fig. 6. The ball screw nut 19 can thus be used as a rotating drive element of the screw drive 10. The pulley 21 represents the output element of a belt drive, in this case a belt drive, which is arranged upstream of the screw drive 10 and designed as a reduction gear. Fig. 7 shows a section of a manufacturing device, designated overall by 22, for forming the threaded spindle 1 from the inner sleeve 2 and the outer part 3. As can be seen from Fig. 7, the still undeformed parts 2, 3, i.e. the inner sleeve 2 and the outer part 3, are inserted together into a tool designated by 23. The tool 23 has an inner surface 24 structured in the manner of a thread, which defines the later thread contour 9 of the outer part 3. After the threaded spindle 1 has been formed in the manufacturing device 22, in the present case, the outer part 3 is surface hardened using a hardening system (not shown), which is also part of the manufacturing device 22. Only after hardening is the threaded spindle 1 connected to the extension piece 12 by welding.Deviating from this, process variants are also possible in which the spindle assembly 14 is heat-treated as a whole, i.e., the adapter tube 12 is welded to the not yet hardened threaded spindle 1. Likewise, a connection between the threaded spindle 1 and the adapter tube 12 by means of a form-fitting connection or by means of combined joining processes is also possible. In the exemplary embodiments, the tool 23 is one-piece, which means that the fully formed threaded spindle 1 must be unscrewed from the tool 23 after the forming process is completed. The forming can be carried out in various ways, in particular by internal high pressure or by a rolling tool. This applies regardless of the form of the inner sleeve 2. In the embodiments according to Fig. 8 and Fig. 9, the inner sleeve 2 is in the form of a wound sheet whose ends are welded together. The weld seam designated 25 has a helical shape according to Fig. 8 and a straight alignment parallel to the central axis MA according to Fig. 9. Fig. 10 outlines the first step of a modified method for manufacturing the threaded spindle 1 compared to Fig. 7. In this case, only the sleeve-shaped outer part 3 is initially inserted into the tool 23. Due to the pressure p acting on the inner circumferential surface of the outer part 3, its outer circumferential surface is at least partially pressed into the thread-like structured inner surface 24 of the tool 23, resulting in a plastic deformation of the outer part 3. In the next process step, as outlined in Fig. 11, the inner sleeve 2 is pushed into the outer part 3 located in the tool 23. The outer part 3 is not yet fully formed at this point. The final shaping of the outer part 3 only occurs when internal pressure is applied to the inner sleeve 2, whereby, as can be seen from Fig. 12, the material of the outer part 3 completely adapts to the shape of the inner surface 24 of the tool 23. In Fig. 12, an idealized completely cylindrical shape of the inner sleeve 2 can be seen. In fact, the outer surface of the inner sleeve 2 adapts to the shape of the inner surface of the outer part 3 with increasing pressure until the state of the threaded spindle 1 shown in Fig. 1 is produced. In both the process variant according to Fig. 7 and the case illustrated in Figs. 10 to 12, the threaded spindle 1 is unscrewed from the tool 23 after the forming process has been completed. To facilitate the unscrewing process, the forming process can take place while the tool 23 is mechanically compressed. Before unscrewing, the externally induced compression of the tool 23 is removed, thus increasing the tool diameter slightly, but to a technically relevant extent. It is also possible to effect diameter changes through targeted temperature changes of the workpiece 1 and / or the tool 23. Figs. 13 to 15 illustrate a manufacturing system 22 for forming the two-part threaded spindle 1, which can be used as an alternative to the device according to Fig. 7. A section line BB (see Fig. 13) is shown in Fig. 14. Fig. 15 shows a detail from Fig. 13. 13 to 15, the assembly comprising inner sleeve 2 and outer part 3 is mounted on a mandrel 26. The thread contour 9 is then created by three profile rollers 27, which are arranged at angular intervals of 120 degrees around the central axis MA of the threaded spindle 1 under manufacture. Each profile roller 27 has a pitchless profiling 28, which has the profiling of the thread 5 to be created, whereby a possible inclination of the profile rollers 27 relative to the central axis MA also plays a role. In any case, the profile rollers 27 are advanced during rolling on the outer part 3, so that the thread contour 9 with the desired pitch is created. Optionally, the mandrel 26 is provided with a central bore so that it can be subjected to hydraulic pressure to clamp the workpiece, i.e. the assembly comprising inner sleeve 2 and outer part 3.In any case, the workpiece is held stably on the mandrel 26 during the formation of the thread contour 9, so that neither relative rotations between the inner sleeve 2 and the outer part 3 nor relative rotations between the entire threaded spindle 1 and the mandrel 26 occur. List of reference symbols 1 Threaded spindle 2 Inner sleeve 3 Outer part 4 Flange 5 Thread 6 Hardened area 7 Unhardened area 8 Thread-like contour 9 Thread contour 10 Ball screw 11 Projection 12 Adapter tube 13 Weld seam between the inner sleeve and the adapter tube 14 Spindle assembly 15 Flared area 16 Tubular area 17 Conical area 18 Flattening 19 Ball screw nut 20 Internal thread of the ball screw nut 21 Pulley 22 Manufacturing device 23 Tool 24 Inner surface of the tool 25 Weld seam connecting the ends of the wound inner sleeve 26 Mandrel 27 Profile roller 28 Pitchless profiling of the profile roller MA Central axis p Print QUOTES CONTAINED IN THE DESCRIPTION This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature DE 102016222894 B4

[0002] DE 3308149 A1

[0003] DE 102009045857 A1

[0004] WO 2013 / 029842 A1

[0005] DE 102019114276 A1

[0006] DE 102019120812 A1

[0006] EP 4067525 A1

[0017]

Claims

Threaded spindle (1), with an inner sleeve (2) and an outer part (3) which is firmly connected to the inner sleeve and has a thread (5), the inner sleeve (2) and the outer part (3) being made of different materials, characterized in that the inner sleeve (2) is formed into the outer part (3) in a form-fitting manner, replicating the thread (5). Threaded spindle (1) according to claim 1, characterized in that the inner sleeve (2) is made of a weldable material. Threaded spindle (1) according to claim 1 or 2, characterized in that the outer part (3) is hardened. Threaded spindle (1) according to one of claims 1 to 3, characterized in that the inner sleeve (2) and the outer part (3) are in the form of a roll-plated sheet. Threaded spindle (1) according to one of claims 1 to 3, characterized in that the inner sleeve (2) is in the form of a wound sheet metal. Method for producing a threaded spindle (1) for a screw drive (10), comprising the following steps:- providing a tool (23) which has an inner surface (24) structured in the manner of a thread,- providing an inner sleeve (2) and a sleeve-shaped outer part (3), wherein the outer part (3) is made of a different material than the inner sleeve (2),- forming the inner sleeve (2) and the outer part (3) in the tool (23) such that the outer peripheral surface of the outer part (3) takes on the contour of the thread (24) and the inner peripheral surface of the outer part (3) is brought into positive engagement with the outer peripheral surface of the inner sleeve (2), reproducing the thread contour of the tool (23) in a weakened form,- separating the threaded spindle (1) formed in the previous step and formed from the inner sleeve (2) and the outer part (3) from the tool (23). Method according to claim 6, characterized in that the outer part (3) is hardened, wherein the hardening takes place as surface hardening according to one of the hardening methods inductive hardening, conductive hardening, laser hardening and electron beam hardening. Method according to claim 6 or 7, characterized in that the forming takes place in a tool (23) by which a closed ring is formed, wherein after the forming the diameter of the tool (23) is changed and then the threaded spindle (1) is unscrewed from the tool (23). Method according to one of claims 6 to 8, characterized in that first the sleeve-shaped outer part (3) is inserted into the tool (23) and at least partially deformed and then the inner sleeve (2) is pushed into the outer part (3) located in the tool (23) and is pressed against the inner circumferential surface of the outer part (3) by exerting pressure under plastic deformation. Method according to one of claims 6 to 8, characterized in that the inner sleeve (2) together with the sleeve-shaped outer part (3), both parts (2, 3) having exclusively smooth inner and outer surfaces, are inserted together into the tool (23) and deformed there simultaneously.

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