Method for producing a threaded nut of a rolling element screw drive.

Abstract

Method for producing a threaded nut (1) of a rolling element screw drive, which has holes (11) distributed over the circumference for receiving deflection pieces (10), which are produced by fluid jet cutting with a cutting tool (12) according to the following steps: - a protective casing (14) is inserted into the threaded nut (1), which is provided over the circumference of its casing surface with a plurality of casing holes (15) which are aligned with respect to the threaded nut (1) at hole positions intended for the formation of the holes (11), - a cutting beam (13) of the cutting tool (12) is directed radially from the outside onto a lateral surface of the threaded nut (1) at the intended hole positions, - the cutting jet (13) penetrates the casing of the threaded nut (1) and the casing hole (15) of the protective casing (14), - after the hole (11) has been formed by means of the cutting jet (13), the protective casing (14) and the threaded nut (1) are separated from each other.

Description

[0001] The present invention relates to a method for producing a threaded nut of a rolling element screw drive, in particular a ball screw drive, and to a rolling element screw drive whose threaded nut is produced according to this method.

[0002] A rolling element screw drive underlying the invention is provided with a threaded nut arranged on a threaded spindle. A screwing relative rotation of the threaded spindle and the threaded nut is converted into a translational displacement of the threaded spindle and the threaded nut relative to each other.

[0003] Rolling elements - for example balls - move along grooves wound helically around the spindle axis - for example ball grooves - which are formed on the inner circumference of the threaded nut and on the outer circumference of the threaded spindle.

[0004] The rolling elements rotate in endless channels, for example, balls in endless ball channels. These channels each have a load section wound helically around a spindle axis and a deflection section connecting the beginning and end of the load section. The load section is formed by the grooves of the threaded nut and the threaded spindle. The deflection sections are each formed on a deflection piece that engages a hole in the threaded nut.

[0005] For example, the publication DE10 2004 004 145 B3 describes a ball screw whose holes are milled into the threaded nut. The burrs resulting from this machining must be removed in an additional step.

[0006] DE 197 11 512 C1 discloses a method for waterjet cutting openings in pipe walls, wherein a core is inserted into the interior of the pipe to protect the inner pipe wall opposite the cutting jet. The materials of the pipe and core must be specifically matched to prevent, for example, an undesired reflection of the water jet from the core when the material is too hard for the core. This prevents the water jet from rebounding against the inside of the pipe wall near the cutting edge, causing unwanted damage to the inside or even an additional, unintended cut.

[0007] The object of the invention was to provide a method which simplifies the production of the holes in the threaded nut.

[0008] According to the invention, this object was achieved by the features of the method according to claim 1. Useful further developments are specified in the subclaims.

[0009] Furthermore, the object is achieved by a ball screw drive according to patent claim 10.

[0010] The threaded nut of the rolling element screw drive has holes distributed around the circumference to accommodate deflection pieces, which are produced by fluid jet cutting using a cutting tool.

[0011] The cutting fluid is a fluid that can be oil. Water is preferred as the cutting medium, to which abrasive additives such as sand or corundum are added.

[0012] Waterjet cutting of materials is a manufacturing process belonging to the main group of cutting processes. It is classified as abrasive processes. Material removal in waterjet cutting is based on the high pressure and resulting high speed of the cutting jet directed at the surface of the workpiece. The fine cutting jet allows for the cutting of very delicate and complex contours.

[0013] Preferably, an abrasive is added to the water to create the holes. In this case, the cutting agent consists of a mixture containing water and an abrasive such as sand, for example, garnet or olive sand, or sometimes corundum. Abrasive cutting, in particular, is preferably used for machining steel workpieces; it is well suited for the present invention.

[0014] The holes can be machined using the cutting jet after a groove has been formed on the inner circumference of the threaded nut, wound helically around a spindle axis of the ball screw. The threaded nut provided with the groove can already be hardened and ground. The inventive production of the holes in the threaded nut's shell using the cutting jet prevents unwanted burr formation on the threaded nut.

[0015] However, it may be appropriate - for example in the case of a milled thread - to form the holes before this groove is formed on the inner circumference of the threaded nut.

[0016] To create the holes, a protective sleeve is first inserted into the threaded nut. This sleeve is provided with a multitude of sleeve holes along its circumference. These holes are aligned with the threaded nut at the positions where the holes are to be drilled into the threaded nut. The threaded nut and the protective sleeve are then positioned relative to each other in the cutting tool.

[0017] The protective sheath can be arranged in the cutting tool and the threaded nut is pushed onto the protective sheath.

[0018] The jacket holes can define the contour along which the cutting beam will later penetrate the wall thickness of the hole to accommodate the deflector. In this case, the jacket holes can be congruent with the holes in the jacket of the threaded nut.

[0019] The sheath holes can be larger than the holes provided in the sheath of the threaded nut. This can make positioning the protective sheath in the threaded nut easier.

[0020] A particularly advantageous variant provides for the protective sheath to be fixed in the tool and arranged in a stationary manner relative to the cutting nozzle(s) of the tool. The sheath holes can therefore be designed to be small enough that the cutting jet can easily pass through this sheath hole. During cutting, the threaded nut is moved within the tool, i.e. relative to the protective sheath and the cutting jet. During the cutting process, the threaded nut is preferably displaced relative to the cutting jet and the protective sheath. The displacement can comprise an axial shift as well as a change in the angular position of the threaded nut in the cutting tool. This displacement occurs in such a way that enables the cutting jet to cut out the desired hole. This sequence of movements is roughly equivalent to that used in fretsaw work, which also involves displacing the workpiece relative to the tool.

[0021] Preferably, the groove is already formed on the threaded nut before the holes are cut into the threaded nut.

[0022] The outer surface of the protective sheath can rest against the inner circumference of the inner surface of the threaded nut. The protective sheath can be formed by a sleeve with an outer contour adapted to the inner contour of the threaded nut.

[0023] The protective sleeve can be designed as a smooth cylindrical sleeve and rest against the inner surface of the threaded nut. If the ball groove is already formed on the threaded nut, the smooth cylindrical sleeve can only touch the thread crests of the ball groove of the threaded nut.

[0024] The sleeve can be provided with an external thread helically wound around the sleeve axis on its outer circumference, and the threaded nut can be provided with a groove helically wound around the nut axis, into which the external thread of the sleeve engages. The protective cover can therefore be designed as a threaded sleeve whose thread follows the helical groove of the threaded nut. In this case, the threaded sleeve can be screwed into the threaded nut.

[0025] With this threaded sleeve, the grooves of the threaded nut are well protected. In this version, the protective sleeve and the cutting nozzle are not fixed to each other. Rather, the threaded nut and the protective sleeve move relative to the cutting jet. In this case, the cutting jet is moved axially or at an angle to the protective sleeve. This requires either a slot or an enlarged bore in the protective sleeve so that the cutting jet can pass through the protective sleeve unhindered.

[0026] The protective sleeve is positioned inside the threaded nut. A cutting beam from the cutting tool is directed radially from the outside onto the outer surface of the threaded nut at the designated hole positions. The cutting beam cuts through the outer surface of the threaded nut, removing material from the threaded nut and finally penetrating the hole of the protective sleeve unhindered.

[0027] Once the cutting jet has created a hole in the threaded nut's surface, it impacts the opposite surface of the protective sleeve. The protective sleeve prevents the cutting jet from hitting the inner surface of the threaded nut, which could potentially damage the groove already formed there. The holes on the threaded nut are preferably arranged so that one cutting jet does not impact another sleeve hole.

[0028] The protective sheath covers the areas on the inner circumference of the threaded nut that are exposed to the cutting beam when it passes through the outer surface of the threaded nut and hits the opposite side of the inner surface of the threaded nut. This protects any grooves already machined on the inner circumference of the threaded nut.

[0029] After the hole has been created with the cutting jet, the protective sheath and the threaded nut are separated. For example, the threaded nut can be removed from the tool while the protective sheath remains in the tool. Further machining of the holes is eliminated. Any removed material is flushed away with the cutting jet.

[0030] The threaded nut with the protective sheath can also be exposed to a fluid flow, particularly a water flow, flowing through the protective sheath beneath the cutting jet. The cutting jet encounters this water flow, slows it down, and is deflected or fanned out toward one end of the threaded nut. This reliably prevents unwanted stress on the protective sheath caused by the cutting jet. The material removed from the threaded nut is washed away with the fluid flow.

[0031] The cutting beam can be directed into different beam positions relative to the threaded nut to create hole walls in the threaded nut that are inclined to the threaded nut axis. This allows complex hole walls to be created. These different beam positions can be achieved, for example, by changing the angular position of the threaded nut in the cutting tool.

[0032] Depending on the number of hole positions, an equal number of cutting beams can be set up. This allows all holes to be produced simultaneously.

[0033] The shape and size of the jacket holes in the protective jacket can be dependent, as described, on the desired shape of the holes in the threaded nut and on the arrangement of the workpiece and the protective jacket in the tool.

[0034] A ball screw drive provided according to the method according to the invention is provided with a threaded nut arranged on a threaded spindle and with balls that rotate in endless ball channels, each of which has a load section wound helically around a spindle axis and a deflection section connecting a beginning and an end of the load section. The load section is formed by ball grooves wound helically around the spindle axis on the inner circumference of the threaded nut and on the outer circumference of the threaded spindle. The deflection section is formed on a deflection piece that is inserted into one of the holes in the threaded nut, which are manufactured according to the method according to the invention and its expedient developments.

[0035] The invention is explained in more detail below using an exemplary embodiment illustrated in a total of five figures. They show: Fig. 1 a schematic representation of a cutting tool with an inserted threaded nut of a ball screw drive, Fig. 2 an enlarged section of the Fig. 1, Fig. 3 a section of a ball screw in perspective view, Fig. 4 a longitudinal section through a threaded nut of the ball screw drive of the Fig. 3, and Fig. 5 a perspective view of the threaded nut of the ball screw of the Fig. 3.

[0036] Fig. 1 shows a schematic representation of a method for producing a threaded nut 1 of a rolling element screw drive designed as a ball screw drive, the essential components of which are initially shown on the basis of the Fig. 3 to 5 are explained.

[0037] The ball screw drive is provided with a threaded nut 1 arranged on a threaded spindle 2. Rolling elements 20, designed as balls 4, rotate in endless channels 21, which are designed as ball channels 5. The ball channels 5 each have a load section 6 wound helically around a spindle axis, as well as a deflection section 7, which connects a beginning to an end of the load section 6. The load section 6 is formed by grooves 22, 23 wound helically around the spindle axis, which are designed as ball grooves 8, 9 on the inner circumference of the threaded nut 1 and on the outer circumference of the threaded spindle 2. The deflection section 7 is formed on a deflection piece 10. The threaded nut 1 has holes 11 distributed over the circumference to accommodate the deflection pieces 10. A deflection piece 10 is inserted into each of the holes 11.

[0038] The holes 11 are produced by waterjet cutting. In the exemplary embodiment, a cutting tool 12 is used, whose cutting jet 13 is provided by a water jet with added abrasive such as sand or corundum.

[0039] Before the cutting process begins, the threaded nut 1, which is already provided with the ball groove 8, is inserted into a holder of the cutting tool 12 (not shown) and held therein.

[0040] A protective sheath 14 is inserted into the threaded nut 1. The protective sheath 14 is provided with a plurality of sheath holes 15 around its circumference, which are aligned with respect to the threaded nut 1 at hole positions where the holes 11 are to be made in the threaded nut 1. The protective sheath 14 is arranged in a fixed position relative to the cutting jet 13 in the cutting tool 12. The threaded nut 1 is moved in the cutting tool 12 relative to the protective sheath 14 both in the axial direction and in its angular position. The advantage of this variant is that only a small hole is required in the protective sheath 14 for the cutting jet 13.

[0041] In the exemplary embodiment, the protective casing 14 is provided with a sleeve 17 with an outer contour adapted to the inner contour of the threaded nut 1. The sleeve 17 can either be provided with an external thread wound helically around the sleeve axis, which engages the helically wound ball groove 8 of the threaded nut 1, or it can be designed as a smooth cylinder.

[0042] Cutting nozzles 16 of the cutting tool 12 are directed radially from the outside onto a circumferential surface of the threaded nut 1 at the designated hole positions where the holes 11 are to be created. An equal number of cutting nozzles 16 is provided according to the number of hole positions.

[0043] The cutting beam 13 penetrates the jacket of the threaded nut 1 and the jacket hole 15. The jacket hole 15 can be so large that the hole to be cut in the jacket of the threaded nut 1 lies completely within the jacket hole 15. The cutting beam 13 impacts the opposite jacket surface of the protective jacket 14 and is deflected.

[0044] During the process described, in this embodiment, a relative movement occurs between the cutting nozzles 16 and the threaded nut 1, forming the holes. For this purpose, the threaded nut 1 can be moved in the tool holder (not shown).

[0045] In addition, the threaded nut 1 is exposed to a water flow 18 that flows axially through the threaded nut 1 and thus through the protective sheath 14. The protective sheath 14 can be arranged so close to the inner circumference of the threaded nut 1 that this water flow 18 flows exclusively through the protective sheath 14. The water flow 18 assists in deflecting the cutting jet 13, which strikes the water flow 18 and is deflected toward a front side of the threaded nut 1.

[0046] After the holes 11 have been formed by means of the cutting jet 13, the protective casing 14 and the threaded nut 1 are separated from each other. List of reference symbols 1 threaded nut 2 threaded spindles 3 ---- 4 balls 5 ball channel 6 Load section 7 Deflection section 8 ball groove 9 ball groove 10 deflection piece 11 holes 12 cutting tools 13 Cutting beam 14 Protective sheath 15 jacket hole 16 Cutting nozzle 17 sleeve 18 Water flow 19 ---- 20 rolling elements 21 channel 22 grooves 23 grooves

Claims

[1] Method for producing a threaded nut (1) of a rolling element screw drive, which has holes (11) distributed over the circumference for receiving deflection pieces (10), which are produced by fluid jet cutting with a cutting tool (12) according to the following steps: - a protective casing (14) is inserted into the threaded nut (1), which is provided over the circumference of its casing surface with a plurality of casing holes (15) which are aligned with respect to the threaded nut (1) at hole positions intended for the formation of the holes (11), - a cutting beam (13) of the cutting tool (12) is directed radially from the outside onto a lateral surface of the threaded nut (1) at the intended hole positions, - the cutting jet (13) penetrates the casing of the threaded nut (1) and the casing hole (15) of the protective casing (14), - after the hole (11) has been formed by means of the cutting jet (13), the protective casing (14) and the threaded nut (1) are separated from each other. [2] Method according to claim 1, wherein the threaded nut (1) is exposed to a fluid flow (18) which flows in the axial direction through the threaded nut (1) and deflects the cutting jet (13) in the direction of an end face of the threaded nut (1). [3] Method according to claim 1 or 2, the cutting beam (13) is brought into different beam positions in its beam direction to form hole walls of the threaded nut (1) which are inclined to the threaded nut axis. [4] Method according to one of claims 1 to 3, characterized in that an equal number of cutting nozzles (16) of the cutting tool (12) are set up according to the number of hole positions. [5] Method according to one of claims 1 to 4, the jacket holes (15) of which are congruent with or larger than the associated holes (11) of the threaded nut (1). [6] Method according to one of claims 1 to 4, the jacket holes (15) of which are smaller than the associated holes (11) of the threaded nut (1). [7] Method according to one of claims 1 to 5, the threaded nut (1) is provided with a groove (8) formed on the inner circumference and wound helically around a longitudinal axis of the threaded nut (1) before the protective sheath (14) is inserted into the threaded nut (1), wherein the protective sheath (14) covers the inner surface of the threaded nut (1) at points which are detected by the cutting beam (13) after penetrating the sheath of the threaded nut (1). [8] Method according to one of claims 1 to 7, the protective casing (14) of which is provided by a sleeve (17) with an external thread wound helically around the sleeve axis, and the threaded nut (1) of which is provided with a groove (8) wound helically around the nut axis, into which the external thread of the sleeve (17) engages. [9] Method according to one of claims 1 to 8, in which the cutting means is formed from a mixture containing water and an abrasive substance such as sand or corundum. [10] Ball screw drive, with a threaded nut (1) arranged on a threaded spindle (2), and with balls (4) which rotate in endless ball channels (5), each having a load section (6) wound helically around a spindle axis and a deflection section (7) which connects a start to an end of the load section (6), wherein the load section (7) is formed by ball grooves (8, 9) wound helically around the spindle axis on the inner circumference of the threaded nut (1) and on the outer circumference of the threaded spindle (2), and wherein the deflection section (7) is formed on a deflection piece (10) which is inserted into one of the holes (11) of the threaded nut (1), which are produced according to the method of at least one of claims 1 to 9.

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