Patent Publication Number: US-10307879-B2

Title: Device and method for the finishing machining of an internal face of a workpiece

Description:
CROSS-REFERENCE TO PRIOR APPLICATION 
     Priority is claimed to German Patent Application No. DE 10 2015 220 319.0, filed on Oct. 19, 2015, the entire disclosure of which is hereby incorporated by reference herein. 
     FIELD 
     The invention relates to a device and method for the finishing machining of an internal face of a workpiece, in particular the track of a ball screw. 
     BACKGROUND 
     Prior art devices and methods regarding the above are known from DE 10 2010 020 814 A1 and DE 40 35 374 A1. In the known devices, the finishing tool is held on a U-shaped tool holder, which can be driven in an oscillating manner about an axis of oscillation. The drawback in the known devices is that a thread length measured along the rotational axis of the workpiece, along which an internal face can be machined in a finishing manner, is limited and predetermined by the length of the U-shaped tool holder. It is furthermore disadvantageous that, depending on an insertion depth of the finishing tool measured along the rotational axis of the workpiece, the maximum possible angles of oscillation of the workpiece holder are limited. 
     Proceeding from this, the present invention is based on the object of providing a device and a method of the type mentioned at the outset, with which the above-mentioned drawbacks are avoided. 
     SUMMARY 
     This object is achieved according to the invention in a device wherein an oscillating drive is provided, by means of which the finishing tool held on the finishing tool holder and the workpiece holder can be driven in an oscillating manner relative to one another in the direction parallel to the rotational axis and that the finishing tool is pivotably held on a finishing tool holder about a pivot axis. 
     In a method of the type mentioned at the outset, the object is achieved according to the invention in that the finishing tool held on the finishing tool holder and the workpiece held on the workpiece holder are driven in an oscillating manner relative to one another in the direction parallel to the rotational axis, superimposed on the rotational movement and the translatory movement, and that the finishing tool is pivoted about a pivot axis relative to the finishing tool holder. 
     According to the invention, an oscillating drive is provided, which serves to move the finishing tool held on the finishing tool holder, on the one hand, and the workpiece holder or the workpiece held on the workpiece holder, on the other hand, relative to one another in an oscillating manner, specifically in a direction parallel to the rotational axis of the workpiece holder or the workpiece. This means that a further linear oscillating movement is superimposed on the translatory movement between the finishing tool and workpiece. The finishing tool is in turn pivotably mounted on the finishing tool holder, so the finishing tool carries out a pivoting movement relative to the internal face to be machined in a finishing manner. 
     In relation to a central rest pivoting position, preferred maximum pivoting angles are between +/−1° (corresponds to a total pivoting angle of 2°) and +/−15° (corresponds to a total pivoting angle of 30°). 
     The device according to the invention and the method according to the invention allow angles of oscillation of the finishing tool that are independent of an insertion depth into the workpiece to be selectable. Moreover, a finishing tool holder extending substantially exclusively parallel to the rotational axis of the workpiece holder can be used, so the machining of workpieces with long threads is substantially simplified. 
     The device according to the invention and the method according to the invention have the further advantage that position errors between the workpiece and finishing tool can be compensated by resting the finishing tool on the internal face of the workpiece and by the pivotability of the finishing tool. 
     In the framework of the present invention, the internal face of a workpiece is taken to mean a groove-shaped indentation in profile, the course of which corresponds to a helix. The internal face is, in particular, a track pointing radially inwardly of a ball screw or the internal thread of a thread pairing. 
     It is possible that the finishing tool, for example a finishing block, is directly pivotably held on the finishing tool holder. In a preferred embodiment, however, a finishing tool receiver is provided, in which the finishing tool, in particular a finishing block, is received, the finishing tool receiver being pivotably held on the finishing tool holder about the pivot axis. 
     The finishing tool receiver preferably comprises a receiving region for the finishing tool, in which the finishing tool is displaceably received. A finishing tool subject to wear can thus be adjusted. 
     The pivot axis of the finishing tool or the assembly, comprised of the finishing tool and finishing tool receiver, preferably runs perpendicular to the rotational axis of the workpiece holder and the workpiece held on the workpiece holder. It is thus possible for the pivot axis and the rotational axis to intersect. These axes may, however, also be arranged in a skew manner, in other words spaced apart from one another. 
     In a preferred embodiment of the invention, a locking mechanism is provided, by means of which a rest pivoting position of the finishing tool is predetermined. The finishing tool can thus be held in a defined position, which is advantageous, in particular, in setting up processes, in other words, for example, when the finishing tool is to be brought with an active face to engage with an internal face of a workpiece to be machined. The locking mechanism cooperates with the finishing tool and/or with the finishing tool receiver and comprises, for example, locking springs supported in the finishing tool holder. 
     The locking mechanism can advantageously be released (in particular without a tool), so a finishing tool or an assembly, consisting of a finishing tool and finishing tool receiver, can be separated from the finishing tool holder without a tool and replaced by a new finishing tool or a new assembly. As a result tool exchanges can be carried out particularly quickly and easily. 
     In a further preferred embodiment of the device, a cooling lubricant supply mechanism is provided. The cooling lubricant provided by a mechanism of this type can be exclusively used in a conventional manner to cool an engagement region between the finishing tool and workpiece and/or to lubricate it. As an alternative or in addition to this it is, however, very advantageous if the cooling lubricant is active as a sliding medium, specifically for a finishing tool displaceably arranged in a finishing tool receiver, in particular a finishing block. 
     It is furthermore particularly preferred if the device comprises a pressing mechanism, which loads the finishing tool with a pressing force to press an active face of the finishing tool against the internal face. 
     It is possible in the framework of the invention for the pressing force to be produced by a mechanical, electrical, hydraulic or pneumatic drive, which loads the tool holder with a pressing force so the pressing force is transmitted by the tool holder, optionally with the interposition of a finishing tool receiver, onto the finishing tool and therefore onto the active face of the finishing tool. 
     It is possible in the framework of the invention for the pressing mechanism to comprise a pressurized fluid for transmitting a pressing force. A fluid of this type has the advantage that a pressing force can also easily be transmitted across complicated geometries. 
     In a particularly preferred embodiment of the invention, the pressurized fluid is a cooling lubricant. The finishing tool can thus be loaded with a pressing force by means of the cooling lubricant, with the cooling lubricant simultaneously being able to have other functions, in particular the cooling and/or lubrication of an engagement region of the finishing tool with the internal face and/or as a sliding medium for a finishing tool displaceably arranged in a finishing tool receiver. 
     In order to be able to load the fluid with a specific pressure, it is preferred if the device comprises a regulating mechanism, with which the pressure of the cooling lubricant of a cooling lubricant supply mechanism can be regulated. 
     One aspect of the invention provides a device for the finishing machining of an internal face of a workpiece, including a workpiece holder and a finishing tool holder. A finishing tool is held on the finishing tool holder. A rotary drive is configured to rotationally drive the workpiece holder and the finishing tool relative to one another about a rotational axis. A linear drive is configured to drive in a translatory movement the finishing tool held on the finishing tool holder and the workpiece holder relative to one another along the rotational axis. An oscillating drive is configured to oscillatingly drive the finishing tool held on the finishing tool holder and the workpiece holder relative to one another in the direction parallel to the rotational axis and the finishing tool is pivotably held on the finishing tool holder about a pivot axis. 
     Another aspect of the invention provides a method for the finishing machining of an internal face including holding a workpiece on a workpiece holder and holding a finishing tool on a finishing tool holder. The workpiece and the finishing tool are driven rotationally relative to one another about a rotational axis. The finishing tool and the workpiece are driven in a translatory movement relative to one another along the rotational axis. The finishing tool and the workpiece are driven in an oscillating movement relative to one another in the direction parallel to the rotational axis, the oscillating movement superimposed on the rotational movement and the translatory movement. The finishing tool is pivoted relative to the finishing tool holder about a pivot axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  is a perspective view of an embodiment of a device for the finishing machining of an internal face of a workpiece; 
         FIG. 2  is a perspective longitudinal section of the device according to  FIG. 1 ; 
         FIG. 3  is a perspective view of a finishing tool holder, a finishing tool receiver and a finishing tool of the device according to  FIG. 1 ; 
         FIG. 4  is a perspective view of the finishing tool receiver and the finishing tool; 
         FIG. 5  is a schematic view of a cooling lubricant supply mechanism of the device according to  FIG. 1 ; 
         FIG. 6  is the longitudinal section of the finishing tool holder, the finishing tool receiver and the finishing tool of the device according to  FIG. 1 , wherein the finishing tool adopts a rest pivoting position; 
         FIG. 7  is a longitudinal section corresponding to  FIG. 5 , wherein the finishing tool adopts a pivoting position deflected from the rest pivoting position; 
         FIG. 8  is a perspective view of a further embodiment of a device for the finishing machining of an internal face of a workpiece; and 
         FIG. 9  is a perspective longitudinal section of the device according to  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an embodiment of a device  10  for the finishing machining of an internal face  12  of a workpiece  14 . 
     The internal face  12  is, in particular, the track of a ball screw. The internal face  12  is pitch circle-like or arcuate in profile. The internal face  12  extends in a helix-like manner (helically) at least along a part of a length of the workpiece  14  measured parallel to a workpiece axis  16 . 
     The device  10  comprises a workpiece holder  18 , which may be configured, for example, as a chuck  20 . The workpiece holder  18  is connected to a rotary drive  22 , by means of which the workpiece holder  18  and the workpiece  14  can be rotationally driven about a rotational axis  24 . 
     The device  10  furthermore comprises a linear drive  26 , which serves to drive a slide  28  in the direction parallel to the rotational axis  24 , for example in a direction  30  in the direction of the workpiece holder  18  and opposite thereto. 
     The slide  28  is used for fastening an oscillating drive  32 , which, relative to the slide  28 , produces an oscillating movement  34  also running parallel to the rotational axis  24 . The oscillating drive  32  is connected to a finishing tool holder  36 . The finishing tool holder  36  comprises a connecting portion  38  for connection to a housing of the oscillating drive  32 . Furthermore, the finishing tool holder  36  comprises an arm  40  extending parallel to the rotational axis  24 . The arm  40  has a straight course and is slim enough to be able to be inserted in a space of the workpiece  14  surrounded by the internal face  12 . 
     The finishing tool holder  40  has a pivot bearing  42  (cf.  FIG. 3 ), which defines a pivot axis  44 . The pivot axis  44  runs perpendicular to the rotational axis  24  (cf.  FIG. 2 ). 
     The device  10  furthermore comprises a finishing tool  46  in the form of a finishing block  48 . The finishing tool  46  has an active face  50 , which is preferably curved and can be brought into engagement with the internal face  12  of the workpiece  14  (cf.  FIG. 2 ). In this case, the active face  50  is oriented inclined in accordance with the thread pitch of the internal face  12 . 
     A finishing tool receiver  52  is provided for mounting the finishing tool  46  on the arm  40  of the finishing tool holder  36 . The finishing tool receiver  52  has bearing bolts  54 , which cooperate with the pivot bearing  42  of the arm  40 . The finishing tool  46  is thus pivotably mounted on the finishing tool holder  36  about the pivot axis  44 . The finishing tool receiver  52  is arranged in a central recess  56  of the arm  40 . 
     The tool holder  36  is preferably hollow so cooling lubricant can be supplied from an access  58  to the finishing tool  46 . 
     The access  58  cooperates with a channel  60 , which runs in the radial direction and opens on a central channel  62 . The central channel  62  extends within the arm  40  to a limitation  64 , which is arranged adjacent to the recess  56 . 
     For the active fluid connection between the channel  62  and the recess  56 , in which the finishing tool receiver  52  is arranged, the channel  62  has, adjacent to or in the region of the limitation  64 , a passage  66 , through which fluid can be guided out of the channel  62  onto the outside of the arm  40 . An overflow region  68  leading up to the recess  56  is preferably provided on the outside of the arm  40 . 
     As the finishing tool receiver  52  is spaced apart from the edging of the recess  56 , cooling lubricant can flow past the finishing tool receiver  52  to the active face  50 , so the workpiece surface to be machined, in other words the internal face  12 , can be supplied with cooling lubricant. 
     Reference will be made below to  FIGS. 6 to 7 . The finishing tool receiver  52  has a receiving region  70 , in which the finishing tool  46  is slidingly displaceably arranged. The receiving region  70 , at least at the level of an approximately centrally arranged opening region  72 , is open toward the outside of the finishing tool holder  52  so cooling lubricant, which is arranged in the recess  56 , can arrive at the receiving region  70  through the opening region  72 . The cooling lubricant can thus serve as a sliding medium for the finishing tool  46  received in the receiving region  70 . 
     The finishing tool receiver  52  furthermore has a pressure chamber  73 , which is fed with cooling lubricant from the recess  56  via connecting channels  74 . When the cooling lubricant present in the pressure chamber  73  is loaded with pressure, the pressure acts on a head face  76  of the finishing tool  46 . The head face  76  is arranged on the end of the finishing tool  46  that is spaced apart from the active face  50 . 
     The finishing tool receiver  52 , at its end remote from the pressure chamber  73 , has overflow lines  78 . These are flooded with cooling lubricant from the pressure chamber  73  when the finishing tool  46  has shortened to such an extent that the head face  76  is arranged below a level  80  defined by the overflow lines  78 . 
     An active fluid coupling of the pressure chamber  73  and the overflow lines  78  leads to a pressure drop of the cooling lubricant, which can easily be detected by means of a sensor. This allows the easy detection of a state of a worn-out finishing tool  46 , which has to be exchanged for a new finishing tool  46 . 
     In order to be able to supply the pressure chamber  73  with pressurized cooling lubricant, the device  10  comprises a cooling lubricant supply mechanism  82  shown schematically in  FIG. 5 . This comprises a reservoir  84 , a filter mechanism  86  and a pump  88 , furthermore a pressure-control valve  90 , a check valve  92  and a 3/2-way valve  94 . The valve  94  communicates with a line  96  leading to the supply line  58  of the finishing tool holder  36 . The cooling lubricant then arrives in the manner described above in the recess  56  and from there via the connecting channels  74  into the pressure chamber  73 . 
     The cooling lubricant supply mechanism  82 , together with the pressure chamber  73 , forms a pressing mechanism  98  for producing a pressing force, with which the active face  50  of the finishing tool  46  is pressed against the internal face  12  of the workpiece  14 . 
     To define a rest pivoting position of the finishing tool holder  52  about the pivot axis  44 , the device  10  comprises a locking mechanism designated in total by the reference numeral  100  (cf.  FIG. 6 ). Said locking mechanism comprises at least one, preferably two, spring-loaded pins  102 ,  104 , which are supported on one end of the arm  40  and project into the recess  56  and are in contact there with an outer face  106  of the finishing tool receiver  52 . 
     Proceeding from the rest pivoting position (cf.  FIG. 6 ) the finishing tool receiver  52  can be pivoted into deflected positions (cf.  FIG. 7 ). This is accompanied by a relaxation of one of the spring pins  102 ,  104  and a compression of another of the spring pins  102 ,  104 . 
     For a rapid exchange of a finishing tool  46 , it is possible to displace a finishing tool receiver  52  together with a worn-out finishing tool  46  out of the pivot bearing  52 , counter to the action of the spring pins  102 ,  104 . Then a fresh finishing tool  46  held on a further finishing tool receiver  52  can be guided into the pivot bearing  42 . In this case, the finishing tool receiver  52  is inclined in accordance with the shape of the pivot bearing  42  (cf.  FIGS. 3 and 7 ). The locking mechanism  100  fixes the finishing tool receiver  52  in the recess  56  and transfers the finishing tool receiver  52  into the rest pivoting position (cf.  FIG. 6 ). 
     For the finishing machining of the internal face  12 , the workpiece  14  is rotationally driven by means of the rotary drive  22  about the rotational axis  24  in the rotational direction  108  (cf.  FIGS. 1 and 2 ). This rotational movement, in accordance with the pitch of the internal face  12 , is superimposed by a translatory movement, with which the slide  28  is displaced parallel to the rotational axis  24  by means of the linear drive  26 . Superimposed on these two movements, the finishing tool holder  36  is driven in an oscillating manner by means of the oscillating drive  32 . The finishing tool holder  36 , together with the finishing tool receiver  52  and the finishing tool  46 , moves here in the direction parallel to the rotational axis  24 . An oscillating frequency is typically between about 0.5 and 35 Hz. A typical amplitude of the oscillating movement is, for example, between about 0.2 and 5 mm. 
     Owing to the oscillating movement of the tool holder  36 , the pivot axis  44  of the finishing tool  46  moves in the direction parallel to the rotational axis  24  relative to a portion of the internal face  12  that is about to be machined. A pivoting movement, in which the finishing tool and the finishing tool receiver  52  pivot back and forth about the pivot axis  44 , is superimposed on this translatory movement as a result of the engagement of the curved active face  50  in the profile of the internal face  12 . 
     The pressing force, with which the active face  50  of the finishing tool presses against the internal face  12 , is determined by the pressure of the cooling lubricant, which is supplied to the pressure chamber  73  in the manner described above. 
     An angle, at which the finishing tool receiver  52  together with the finishing tool  46  is pivoted back and forth in the course of the machining of the internal face  12 , is determined by the amplitude of the oscillating movement, which is in turn determined by the oscillating drive  32 . The pivoting angle is freely selectable and can be set by setting the oscillating amplitude. This setting possibility is regardless of how deeply the arm  40  is inserted into the workpiece  40 . 
     A further embodiment of a device  10  for the finishing machining of an internal face  12  of a workpiece  14  will be described below. In this case, reference is made to the above description of the device  10  according to  FIG. 1 to 7 . Only the differences between the devices  10  according to  FIGS. 8 and 9  and according to  FIG. 1 to 7  will be dealt with below. 
     A pressing mechanism  98 , which is active between the oscillating drive  32  and the finishing tool holder  36 , is provided in the device  10  according to  FIGS. 8 and 9 . The pressing mechanism  98  comprises a bearing unit  110 , which is connected to the fastening portion  38  of the finishing tool holder  36  and can be displaced along a bearing axis  111  relative to a housing of the oscillating drive  32  (cf.  FIG. 9 ). 
     The pressing mechanism  98  moreover comprises a pressing drive  112 , schematically shown in  FIG. 9 , for producing a pressing force  114  also indicated in  FIG. 8 . The pressing drive  112  may, for example, be formed by a pneumatic cylinder. 
     The pressing force  114  runs perpendicular to a respective portion of the internal face  12  to be machined, in other words radially outwardly in relation to the workpiece axis  16  of a workpiece. 
     By means of the fastening portion  38  and the arm  40  and by means of the finishing tool receiver  52 , the pressing force  114  is transmitted to the finishing tool  46  and therefore to the active face  50 . It is therefore unnecessary in this case for the finishing tool  46  to be received in a sliding manner within the finishing tool receiver  52 . Accordingly, the finishing tool receiver  52  may be configured as a simple clamping body (cf.  FIG. 9 ). 
     To improve the supply of the machining point with cooling lubricant, it is preferred if the passage  66  at the end of the channel  62  (differing from the configuration according to  FIG. 1 to 7 ) is arranged adjacent to the active face  50  of the finishing tool  46 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.