Patent Publication Number: US-2022221003-A1

Title: Method for machining a bearing ring and for producing a rolling bearing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States National Phase of PCT Appln. No. PCT/DE2020/100297 filed Apr 15, 2020, which claims priority to German Application No. DE102019112061.6 filed May 9, 2019, the entire disclosures of Which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a method for machining a rolling bearing ring. The disclosure further relates to a method for producing a rolling bearing as well as a rolling bearing, e.g., a wheel bearing. 
     BACKGROUND 
     U.S. 2010/0052262 A1 describes a sealing device provided for a wheel bearing, including an elastic sealing element and a metallic stop element. The stop element here has a surface machined by shot blasting treatment. 
     SUMMARY 
     The method according to the disclosure for machining a bearing ring of a rolling bearing includes the following features: clamping a blank provided for the production of the bearing ring in a machine tool, structuring an annular surface of the bearing ring that forms a sealing face by high-feed milling. 
     An annular blank provided for the production of the bearing ring is clamped in a machine tool, for example a milling machine, but a non-rotating arrangement of the blank is also possible as an alternative to rotating the blank. An annular surface of the bearing ring that forms a sealing face is strictured by high-feed milling. 
     High-feed milling, also known as HFM (high-feed milling), enables high cutting performance at the same time having high-feed rates and cutting speeds. The high-performance milling cutters used here have a special cutting edge geometry with several cutting edges. They are available with and without indexable inserts. The use of high-feed milling to generate the sealing face enables a specific adjustment of the surface structure and surface roughness, so that friction between the seal and the sealing face can be specifically adjusted and minimized. 
     The publication “High-feed milling for structuring tool surfaces for sheet metal forming,” Dennis Freiberg, ISBN 978-3-8027-8912-0, Vulkan Verlag, 03/2019, shows the possibilities of high-feed milling to influence the surfaces formed therewith. 
     Different processing parameters during high-feed milling are responsible for the appearance and the respective roughness depths achieved for each surface structuring. Machining parameters include, for example, a feed direction of the high-feed milling cutter, a feed or cutting speed of the high-feed milling cutter, an angle of incidence of an axis of rotation of the high-feed milling cutter with respect to the surface to be machined, and a cutting depth of the high-feed milling cutter. Another optional machining parameter here is a speed of rotation of the workpiece or bearing ring to be machined by high-feed milling. 
     An example cutting speed for metals is about 50 to 300 m/min, depending on the type of metal (brittle or tough). The setting of a cutting depth (axial infeed) for the high-feed milling cutter may be in the range from 1 to 500 μm. 
     The sealing face formed by the structured surface of the bearing ring and the elastic sealing element has low friction and low susceptibility to wear while at the same time having a good sealing effect. The sealing effect relates both to the retention in the rolling bearing of lubricant, i.e., grease or oil, and to keeping dirt away from the interior of the rolling bearing. 
     The high-feed milling may be carried out by means of a face of a high-feed milling cutter (=face milling). This makes it possible to set the high-feed milling cutter at an angle or setting angle with regard to the surface to be machined. The face may be guided in an aligned manner at an angle β f  of 0 to 10° with respect to the surface of the bearing ring forming the sealing face. 
     In the same clamping in which the surface of the bearing ring forming a sealing face is structured, a track of the bearing ring may be produced by cutting, and the blank may rotate during the two mentioned machining steps. Alternatively, however, it is of course also possible to process the bearing ring separately to form the track and the sealing face(s), that is to say in different clamping. In this case, spatially separate and/or different machine tools can also be used to form the track and to form the sealing face(s). 
     If the structuring and consolidating of the sealing face takes place while the workpiece is rotating, at least one roller body track of the bearing ring is machined, i.e., by turning and/or grinding in an example method in the same setting with a rotating blank, i.e., workpiece. An example rotation speed for the workpiece to be machined, here a bearing ring, depends on the diameter of the workpiece to be machined, the milling cutter position and the surface structure to be achieved. 
     On the one hand, efficient and precise machining is favored by the fact that the structured surface of the bearing ring is generated in the same setting in which the machining of the bearing ring also takes place. On the other hand, no separate element is required to produce a sealing contact, for example in the form of a stop disk to be connected to a bearing ring or a thrust ring. Rather, within the rolling bearing, the elastic sealing element fastened to one of the bearing rings makes direct contact with the high-feed milled sealing face of the other bearing ring. This not only minimizes the number of parts compared to conventional solutions, but also tends to minimize the space required by the rolling bearing. 
     In an example embodiment of the method, during the high-feed milling, the high-feed milling cutter used is displaced relative to the bearing ring in the axial direction thereof. Alternatively, during the high-feed milling, the high-feed milling cutter is shifted relative to the bearing ring in the radial direction thereof. 
     This displacement of the machining tool describes, for example, a spiral line, a helical line, or a wavy line that intersects itself multiple times on the machined surface. In any case, at the end of the machining process, depressions that were produced on the machined surface provided as a sealing face are distributed approximately uniformly, expressed as the number of depressions per unit area. 
     Thus it has proven itself in the course of high-feed milling, for the high-feed milling cutter to describe a helical line or a spiral line on the surface to be structured. Alternatively, in the course of high-feed milling, the high-feed milling cutter may describe a multiply intersecting wavy line on the surface to be structured. In this way, a wide variety of surface structures and surface roughness can be set for the sealing face, which can be tailored to the specific application and the requirements thereof. 
     At least one smoothing post-treatment process may be used in the area of the surfaces of the sealing face(s) formed by high-feed milling. Brushing, blasting, etching or the like are suitable as post-treatment methods. As a result, burrs or sharp edges are reduced in the area of the surfaces of the sealing face(s) formed by high-feed milling, which leads to a longer service life of the seal contacting the sealing face. The risk of damage to or roughening of the seal on the contact surface thereof with the sealing face is reduced. 
     The method for producing the rolling bearing includes the following steps: 
     provision of a bearing ring with a surface structured by means of high-feed milling as a sealing face and a further bearing ring, 
     placement of a number of roller bodies between the bearing rings, and 
     installation of a seal between the bearing rings effective in such a way that it is held on the further bearing ring and comes into contact with the structured surface. 
     The sealing face foamed by the structured surface of the bearing ring and the elastic sealing element has low friction and low susceptibility to wear while at the same time having a good sealing effect. The sealing effect relates both to the retention in the rolling bearing of lubricant, i.e., grease or oil, and to keeping dirt away from the interior of the rolling bearing. 
     The rolling bearing according to the disclosure includes at least two bearing rings, between which a number of roller bodies are arranged, and with at least one seal which is held on one of the bearing rings and contacts a high-feed milled surface of the other bearing ring. 
     Balls as well as needles or rollers, for example cylindrical rollers, barrel roller, or tapered rollers, can be provided as roller bodies of the rolling bearing. The rolling bearing can be designed as a single- or multi-row bearing and comprises two bearing rings or a larger number of bearing rings, for example three bearing rings. For example, the rolling bearing may be a wheel bearing for a motor vehicle. 
     For example, the structured surface, that is to say the high-feed milled sealing face, may have depressions with a roughness depth R t  of a maximum of 100 μm. This ensures a sealing effect of the seal is maintained, which runs up against the structured surface or sealing face, and at the same time brings about an optimization with regard to the friction occurring therebetween. A roughness depth R t  of the stnictured surface of a maximum of 10 μm may be selected. A roughness depth R t  in the range from 3 μm to 5 μm, for example, may be selected. 
     While one of the bearing rings of the rolling bearing in the region of the sealing face is machined by high-feed milling, the other bearing ring is generally not provided with such machining. The rolling bearing can be sealed either on one side or on both sides. Each of the bearing rings can either be a one-piece or a split bearing ring. 
     In typical configurations, the bearing ring of the rolling bearing, which is machined through high-feed milling, is the inner ring. Either the inner ring or the outer ring can be provided as the rotating bearing ring. Accordingly, the bearing ring with the high-feed milled sealing face can in principle be both an inner ring and an outer ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, two exemplary embodiments of the disclosure are explained in more detail through a drawing. In the figures: 
         FIG. 1  shows a schematic representation of the machining of a surface of a bearing ring through high-feed milling, 
         FIG. 2  shows a perspective view of the bearing ring machined with the method according to  FIG. 1 , 
         FIG. 3  shows a rolling bearing designed as a deep groove ball bearing including the bearing ring according to  FIG. 2 , 
         FIG. 4  shows a section of a rolling bearing designed as a wheel bearing with a bearing ring to be machined according to  FIG. 1 , and 
         FIG. 5  shows different surface structurings formed by means of high-feed milling on surfaces made of a metallic material. 
     
    
    
     DETAILED DESCRIPTION 
     Unless otherwise stated, the following explanations relate to all exemplary embodiments. Parts or structures that correspond to each other or have basically the same effect are marked with the same reference symbols in all figures. 
     A rolling bearing identified overall with the reference number 1 is designed as a ball bearing and comprises an inner ring  2  and an outer ring  3  (compare  FIG. 3 ). The rolling bearing  1  shown in  FIG. 3  is a deep groove ball bearing, while the rolling bearing  1 , only partially sketched in  FIG. 4 , is a two-row angular ball bearing, namely a wheel bearing for a motor vehicle. In this case, a flange of the inner ring  2  is denoted by 4. 
     In both cases, balls roll as roller bodies  5  between the bearing rings  2 ,  3 . The roller bodies  5  can be guided in a cage, not shown. A track  6  of the inner ring  2  contacting the roller bodies  5  and a track  7  of the outer ring  3  contacting the roller bodies  5  can be seen. 
     A seal  8 , which has a sealing lip  9 , is held on the outer ring  3 . The sealing lip  9  comes into contact with a surface  10  of the inner ring  2  which, in the case of  FIG. 3 , describes a concentric cylinder which is parallel to the central axis M of the rolling bearing  1 . In the case of  FIG. 4 , on the other hand, the surface  10  lies on a plane which is oriented to be normal to the central axis M. In both cases, the seal  8  is a contact seal. In a manner not shown, the seal  8  can have more than one sealing lip  9 . 
     The surface  10 , which is contacted by the sealing lip  9 , is structured by means of high-feed milling which is illustrated in  FIG. 1  and provides a surface structuring  11 . This method is used in the production of the inner ring  2  of the rolling bearing  1  according to 
       FIG. 3  as well as in the production of the inner ring  2  of the rolling bearing  1  according to  FIG. 4 , A smooth finishing of the surface  10  provided as a sealing face after the high-feed milling does not take place. 
     To produce the inner ring  2 , a blank, the basic shape of which corresponds to the shape of the later inner ring  2 , is clamped into a machine tool, not shown, e.g., a milling machine. During the following processing, the blank, that is to say the later inner ring  2 , rotates about the central axis M thereof at a cutting speed v e . The machining of the blank while it is clamped in the machine tool includes machining of the roller body track  6 . 
     In the example sketched out in  FIGS. 1 to 3 , the rolling bearing  1  is only sealed on one side. Accordingly, the rolling bearing  1  has only a single cylindrical surface  10 , Which functions as a sealing face within the fully assembled rolling bearing  1  ( FIG. 3 ). The surface structuring  11  of the surface  10  indicated in  FIG. 2  is also given in the exemplary embodiment according to  FIG. 4 . The surface structuring  11  has the form of numerous depressions  12 . The roughness depth R t  of the structured surface  10  here is in the range from 3 to 5 μm. 
     A tool  13  in the form of a high-feed milling cutter  14  is used to produce the depressions  12 . The tool  13  is installed on the machine tool. 
     The high-feed milling cutter  14  can be oriented in an XYZ coordinate system (see  FIG. 1 ) in relation to the central axis M in the XY plane and/or in an angled manner, seen in the YZ plane. The high-feed milling cutter  14  is advanced axially in the direction of the Y-axis, that is, material is removed by being advanced in the direction of the axis of rotation M. 
     To produce the surface structuring  11  of the inner ring  2  according to  FIG. 4 , the tool  13  is, for example, moved slowly and evenly radially from the inside to the outside or from the outside to the inside, The depressions  12  thus generated theoretically lie on a spiral line. If, on the other hand, the tool  13  is moved with a comparatively high frequency between a first extreme point, which lies radially inward, and a second extreme point, which represents the radially outer boundary of the surface  10 , then those waveforms of the surface structuring  11  arise first which lie in a single plane, namely the plane of the surface  10 . In the course of several revolutions of the inner ring  2 , these waves overlap several times, in principle comparable to the exemplary embodiment according to  FIG. 1 , so that also in this case a high uniformity is achieved in the distribution of the depressions  12  within the surface  10 . 
       FIG. 5  shows in the representations 5 a)-5 e) five different surface structurings  11   a  to  11   e  formed by means of high-feed milling on flat surfaces made of metallic material, in particular steel. Different machining parameters during high-feed milling are responsible for the appearance and the respective roughness depths achieved of each surface structuring  11   a  to  11   e . For each surface structuring  11   a  to  11   e , the parameters cutting speed v e , axial infeed a c , radial infeed a p , feed per tooth f z  and setting angle β f  are given below, which were used to form them with identical milling cutters. 
       FIG. 5 a   ):
         v c =100 m/min   a e =1 mm   a p =100 μm   f z =0.05 mm   β f =0.1°       
       FIG. 5 b   ):
         v c =100 m/min   a e =3 mm   a p =100 μm   f z =0.3 mm   β f =5°       
       FIG. 5 c   ):
         v c =100 m/min   a e =1 mm   a p =100 μm   f z =0.1 mm   β f =0.1°       
       FIG. 5 d   ):
         v c =100 m/min   a e =1 mm   a p =100 μm   f z =0.15 mm   β f =0.1°       
       FIG. 5 e   ):
         v c =100 m/min   a e =1 mm   a p =100 μm   f z =0.3 mm   β f =0.5°       
     The appearance of a sealing face can be designed in such a way that parallel processing tracks  110  of a high-feed milling cutter  14  are shown in a longitudinal structure that runs in the direction of the feed direction, with arc-shaped or partially circular milling tracks  111  within such a processing track  110  as a transverse structure, which essentially is formed perpendicular to the longitudinal structure, can be seen [compare  FIGS. 5 a   ),  5   b ), and  5   e )]. However, more uniform surface structurings that do not show a pronounced longitudinal structure can also be produced [compare  FIGS. 5 c   ),  5   d )]. 
     The XYZ coordinate system, which is shown as an example for illustration  5 e), is intended to clarify the machining parameters. The cutting speed v c  is given in the cutting direction along the Z-axis, the axial infeed a e  is given in the direction of the Y-axis, the radial infeed a p  is given in the direction of the X-axis, the feed per tooth is f z  indicated in the direction of the Z-axis, and the angle of incidence β f  of the axis of rotation R of the high-feed milling cutter  14  (see  FIG. 1 ) is indicated with respect to the XZ plane. 
     Through a few experiments with variation of the machining parameters during high-feed milling, different surfaces that are suitable for use as surface structuring for a sealing face can be generated. It should be noted, however, that different designs of the milling cutter used with regard to the number of cutting edges (or number of teeth) and cutting edge arrangement also have an influence on the surface structure achieved. Using the same processing parameters, but different milling cutter geometries, different surface structures are achieved. However, the average person skilled in the art is easily able to find suitable surface structures for sealing faces of bearing rings with the aid of a few experiments while changing the machining parameters during high-feed milling with a given milling cutter. 
     REFERENCE NUMERALS 
       1  Rolling bearing 
       2  Inner ring 
       3  Outer ring 
       4  Flange 
       5  Roller body 
       6  Track of the inner ring 
       7  Track of the outer ring 
       8  Seal 
       9  Sealing lip 
       10  Surface 
       11 ,  11   a - e  Surface structuring 
       110  Processing track 
       111  Milling track 
       12  Depression 
       13  Tool 
       14  High-feed milling cutter 
     M Central axis 
     R Axis of rotation 
     X X coordinate 
     Y Y coordinate 
     Z Z coordinate