Patent Publication Number: US-6990738-B2

Title: Process for manufacturing miniature ball bearings

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all rights of priority to Japanese Patent Application No. 2002-044878 filed on Feb. 21, 2002, still pending. 
     FIELD OF THE INVENTION 
     The present invention relates to a process for the manufacturing of ball bearings which are subjected to a radial load. 
     PRIOR ART 
     Ball bearings subjected to radial loads have conventional configurations such that the inner ring is placed on the inner side of the outer ring. A plurality of balls are placed between these orbital rings, and the balls undergo rolling motions and are maintained at an equivalent distance from each other. Since the sliding friction is extremely small, these bearings are frequently used in a rotary section of various types of machines. 
     However, different types of processes for the manufacturing of the inner ring and the outer ring have been utilized over the years. For example,  FIG. 14  and  FIG. 15  show outer rings manufactured by making a hole  2  to accommodate an inner ring formed by a drill. The hole is in the center of the end face of a round rod shape bar thereby making the end section ring-like in shape. The ring section is cut by pushing a drill bit in from the outer side to the outer peripheral section at the deeper side of the ring section while rotating bar material  1  to obtain an outer ring blank  3 . The outer ring is obtained by machining outer ring blank  3 . To make the inner ring, the bar material having a smaller diameter than the bar material for the outer ring is used in the process shown in  FIG. 14 . 
     The manufacturing process shown in  FIG. 15  shows a bit being pushed into a pipe material  4  that is rotated. Pipe material  4  is cut off and an outer ring blank  3  is formed. The outer ring is obtained by machining the outer ring blank  3 . In addition, the inner ring is made of a pipe material having a smaller diameter than the pipe material for the outer ring. The inner ring is formed by the process shown in  FIG. 15 . 
     A disadvantage of the process shown in  FIG. 14  is that as the portion of hole  2  is formed, the cutting margin of the bar material  1  becomes shaves and chips creating a large loss of material. In addition, the amount of cutting oil used is high. Especially in the case of a miniature ball bearing where the diameter of the outer ring is 13 mm or less, the ratio of loss of material for one product is large. For example, in the case of an outer ring with the width of 5 mm or less, the cutting margin may reach about 50% of the width of the outer ring to be obtained in some cases, and thus, the efficiency has been extremely poor. In addition, the shaves and chips of the material are discarded after applying an appropriate treatment process, and the cutting oil, though it might be re-used, leads to environmental contamination when discarded. Therefore, it is beneficial to reduce this waste as much as possible. Furthermore, since an inner ring and an outer ring are made from materials of different sizes, there have been complaints that it is difficult to limit the material cost, and the manufacturing efficiency is poor. 
     In addition, using the process of  FIG. 15  for obtaining the inner ring and the outer ring, where the outer diameter of the outer ring is 13 mm or less, it is difficult to machine and the process lacks practicality. The pipe material of such size is also high in cost or difficult to obtain. Furthermore, it is similar to the process shown in  FIG. 14  in that the ratio of loss of material is high and there arises a problem of environmental contamination from the cutting of the pipe material. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a process for manufacturing miniature ball bearings in which the material loss is greatly reduced. This will limit environmental contamination and reduce the material cost, thereby improving manufacturing efficiency. 
     The first embodiment of the present invention relates to a process for obtaining an outer ring blank and an inner ring blank during the manufacturing process. An outer diameter of the outer ring is 13 mm or less, and an inner ring is placed at the inner side of the outer ring. 
     The steps of this process comprise press cutting a first blank by which the material is mechanically cut. Then, forging the first blank to obtain a final blank. Separating this final blank to obtain the outer ring blank and the inner ring blank. 
     The second embodiment comprises the steps of press cutting a first blank by which the material is mechanically cut and machined. Forging the first blank to obtain a second blank. Then, cutting the second blank into round slices to obtain a plurality of final blanks. The last step is separating these final blanks from each other to form the outer ring blanks and the inner ring blanks. 
     ‘Press-cut’ means use of a cutting device such as one with constrained shearing, for example, by use of a mold die that does not produce shaves and chips. 
     Since the two blanks are obtained simultaneously from the final blank material, the loss in materials can be greatly reduced and the production efficiency is improved. In addition, since press cutting is performed when the first blank is obtained from the material, there is no loss in materials. If we compare this with a cutting by a saw or cutting off with a bit, etc., which requires a cutting margin, it is extremely advantageous for the reduction of the loss in materials. Therefore, the present invention is extremely effective in manufacturing a miniature rolling bearing (where the outer diameter is 13 mm or less and the width is 5 mm or less) for which the material loss ratio has typically been high. The miniature rolling bearings are easier to manufacture. In addition, the material cost can be reduced. 
     Since a plurality of final blanks are obtained by cutting and separating the second blank, the width of the second blank is set to a width from which the plurality of outer ring blanks and inner ring blanks are respectively obtained. The width of the second blank is naturally wider than the width of the final blank, which is advantageous for handling prior to the separation into the outer ring blanks and the inner ring blanks. 
     In addition, the following steps can be added to the present invention. 
     In the forging step of the first and second embodiment, the inner diameter hole of the inner ring is drilled simultaneously. Drilling the inner diameter hole of the inner ring by forging rather than by cutting, it is beneficial with respect to the reduction in material loss. 
     Prior to the separation step in which the final blank is separated into the inner ring blank and an outer ring blank, the inner diameter hole of the inner ring is drilled in the final blank. The final blank is larger and easier to handle than the inner ring blank after the separation, and it is easier to form the inner diameter hole. 
     After drilling the inner diameter hole of the inner ring, the inner peripheral surface of the inner diameter hole is finished to a pre-determined inner diameter by a machining operation such as cutting or grinding. A larger final blank (the final blank in the first embodiment, and the second blank in the second) is easier to handle than the inner ring blank after the separation, and it is easier to finish the inner diameter hole. In addition, if this finishing of the inner diameter hole is applied to the second embodiment, it is possible to make uniform, with high precision, the inner diameter hole of the inner ring blanks. 
     In addition, it is possible to finish both edge faces of the final blank to a pre-determined width or the outer peripheral face of the final blank to a pre-determined outer diameter prior to the separation step. These finishing steps can be performed by a machining operation such as cutting or grinding, and since the blanks are easier to handle prior to the separation, they are easier to finish. When the width of the final blank is finished, it is possible to manufacture the outer ring blank and the inner ring blank uniformly with high precision. Therefore, it is unnecessary to individually finish the widths or finishing may be achieved only with a slight adjustment. When the widths are individually finished, it is necessary to control the grinding to make the widths uniform, however, that may become unnecessary by finishing the width of the final blank. 
     In addition, the present invention includes a method for providing a groove for separation. The groove allows separation of the final blank into the outer ring blank and the inner ring blank, thereby making the separation of the final blank easier. 
     The above advantages and features are of representative embodiments only. It should be understood that they are not to be considered limitations on the invention as defined by the claims. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a diagram of the manufacturing steps of the first mode of working of the present invention; 
         FIG. 2  shows a schematic side view of processing the bar material to final blanks in the first mode of working; 
         FIG. 3  shows a plane view (A) and a cross sectional view (B) showing separation of the final blank; 
         FIG. 4  shows a plane view (A) and a cross sectional view (B) of an outer ring blank and an inner ring blank obtained from the final blank; 
         FIG. 5  shows a cross sectional view of a bearing assembled in the first mode of working; 
         FIG. 6  shows a diagram of the manufacturing steps of the second mode of working of the present invention; 
         FIG. 7  shows a plane view (A) and a cross sectional view (B) of a final blank on which a pilot groove is formed in the second mode of working; 
         FIG. 8  shows a diagram of the manufacturing steps of the third mode of working of the present invention; 
         FIG. 9  shows a plane view (A) and a cross sectional view (B) of a final blank in which an inner diameter hole is formed in the third mode of working; 
         FIG. 10  shows a diagram of the manufacturing steps in the fourth mode of working of the present invention; 
         FIG. 11  shows a diagram of the manufacturing steps in the fifth mode of working of the present invention; 
         FIG. 12  shows a schematic side view of the initial step to the step in which a second blank is obtained in the fifth mode of working; 
         FIG. 13  shows a schematic side view of the step in which the final blank is cut in round pieces in the fifth mode of working; 
         FIG. 14  shows a partially cut out cross sectional side view showing one example of a conventional process for manufacturing of an outer ring; and 
         FIG. 15  shows a partially cut out cross sectional side view showing another example of a conventional process for manufacturing of an outer ring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following describes the processes of the present invention for the manufacturing of a miniature rolling bearing having an outer diameter of an outer ring of 13 mm or less and a width of 5 mm or less (hereinafter referred to simply as a bearing). 
     A. First Working Mode 
       FIG. 1  shows the manufacturing steps (1) through (7) of the first working mode of the present invention. In the following, we shall explain these steps in sequence. 
     (1) Cutting Out the First Blank 
     As shown in  FIG. 2 , a first blank  10  of a cylindrical pellet form is cut out by press cutting. An ordinary bearing steel material is used for bar  1 , such as a high carbon chrome bearing steel which has been subjected to a predetermined heat treatment. 
     (2) Forming a Final Blank by Forging 
     By forging first blank  10  and compressing it in an axial direction, a disk shaped final blank  20  shown in  FIG. 2  is formed. The outer diameter and the width of final blank  20  is approximate to that of the bearing which will be finally obtained. 
     (3) Grinding of the Width 
     Final blank  20  is subjected to width grinding by which both edge faces of final blank  20  are ground, and the width of final blank  20  is finished to the width of the bearing being produced. 
     (4) Grinding of the Outer Peripheral Face 
     The outer peripheral face of final blank  20  is subjected to grinding, and the outer diameter of final blank  20  is finished to the outer diameter of the bearing being produced. 
     (5) Manufacturing of the Outer Ring Blank and the Inner Ring Blank by the Separation of the Final Blank 
     As shown in  FIG. 3 , final blank  20  is cut and separated along the concentric circle at a pre-determined distance from the center by cutting. The ring on the outer peripheral side is obtained as an outer ring blank  30 , and the disk at the inner peripheral side as an inner ring blank  40 . 
     (6) Post-Processing of the Outer Ring Blank and the Inner Ring Blank 
     The inner peripheral face of outer ring blank  30  is ground, and the inner diameter is finished to the inner diameter dimension of the outer ring. As shown in  FIG. 5 , a groove  32  for the running of balls, a groove  33  for seal ring installation and a step section  34  for seal ring installation, and a groove  35  for snap ring installation are formed respectively at the center in the width direction of the inner peripheral face, at the one end side, and at the other end side. Outer ring blank  30  is finished as outer ring  30 A. 
     On the other hand, as shown in  FIG. 4 , the center of inner ring blank  40  is cut, by drilling an inner diameter hole  41  on the inner ring, and thus, the inner ring blank  40  is made into a ring shape. The outer peripheral face of inner ring blank  40  is ground, and the outer diameter is finished to the size of the outer diameter of the inner ring. Following this, the inner peripheral face of inner ring blank  40  is ground, simultaneously finishing the inner diameter to the size of the inner diameter of the inner ring, as shown in  FIG. 5 . A groove  42  for the running of balls is formed at the center in the width direction of the outer peripheral face. Inner ring blank  40  is finished as inner ring  40 A. 
     (7) Assembly of Bearing 
     When outer ring  30 A and the inner ring  40 A have been obtained as described above, inner ring  40 A is placed at the inner side of outer ring  30 A as shown in  FIG. 5 . A pre-determined number of balls  50  are inserted into grooves  32  and  42  such that they face each other. A retainer  51  is fitted to each of balls  50 , thereby holding balls  50  at equal intervals in a freely rolling manner. After washing and rinsing, lubricating oil is applied in between retainer  51  and balls  50 . Finally, a seal ring  52  is fitted into groove  33  of outer ring  30 A, and another seal ring  53  is fitted into stepped section  34  on the opposite side. Snap ring  54  is fitted into groove  35 . In this case, seal ring  52  is the one obtained by coating a core bar  52   a  with rubber  52   b , and is maintained in its position by fitting it into groove  33  by utilizing the elasticity of rubber  52   b . In addition, seal ring  53  is made of a metal, and its position is maintained by snap ring  54 . The bearing shown in  FIG. 5  is assembled in the above-mentioned procedure. 
     Since the two rings, outer ring blank  30  and inner ring blank  40 , are obtained at the same time from final blank  20 , the loss in material is greatly reduced, and the manufacturing efficiency is improved. In addition, since press cutting is used at the time when first blank  10  is obtained from bar material  1 , there is very little loss of material. Compared with cutting by means of a saw or cutting off by means of a bit, which requires a cutting margin, this process is extremely advantageous in reducing material loss. Therefore, for manufacturing a miniature ball bearing having an outer diameter of 13 mm or less and a width of 5 mm or less, this process is extremely effective, and the manufacturing is simple and easy. In addition, a reduction in material costs can be achieved as the reduction of the loss in materials is accomplished. This also limits environmental contamination. 
     In addition, prior to step (5) in which final blank  20  is separated into outer ring blank  30  and inner ring blank  40 , the width of final blank  20  is finished by grinding the width thereof in step (3), and the outer diameter thereof is finished by grinding the outer peripheral face of final blank  20  in step (4). In any of these cases, since a work piece can be more easily handled when compared to prior to the separation, the finishing is more easily accomplished. Especially, when the width is cut in step (3), it is possible to obtain a uniform width of outer ring blank  30  and inner ring blank  40  at high precision, and thus it becomes unnecessary to perform individual finishing of the widths of outer ring blank  30  and inner ring blank  40  after the separation. Therefore, the manufacturing efficiency is improved. 
     Additionally, inner diameter hole  41  of inner ring  40 A may be formed at the time of forging in step (2). Since inner diameter hole  41  may be formed by forging, its dimension is not entirely precise. Therefore, it is finished to the desired dimension of the inner diameter as described above at the time of post-machining in step (6). If the inner diameter hole is formed in the forging step in this manner, it further reduces the loss of materials. 
     The first mode described above is just one example embodying the process of the present invention. Additional modes of working are modifications of the first mode. 
     B. Second Mode of Working 
     The process shown in  FIG. 6  has an additional step (4)b, “formation of a pilot groove” between the above-mentioned step (4) and the above-mentioned step (5), of the first mode of working. In this step (4)b, as shown in  FIG. 7 , a pilot groove  22  (groove for separation) of a pre-determined width is used to separate final block  20  into outer ring blank  30  and inner ring blank  40 . Pilot Groove  22  is formed on both faces of final blank  20 . Pilot groove  22  can be formed by cutting or forging. By forming pilot groove  22  in this manner, the pressure on a cutting tool during separation is reduced. Separation can be accomplished by cutting in the next step (5), or the separation can be achieved by punching out by means of a press in place of cutting. In either case, the separation of final blank  20  becomes easier. 
     C. Third Mode of Working 
     The process for the manufacturing in the third mode of working shown in  FIG. 8  has an additional step (4)c, “formation of an inner hole of an inner ring” between the step (4) and step (5), of the first mode of working. As shown in  FIG. 9 , in step 4(c) an inner diameter hole  41  is formed in advance by cutting out the center of final blank  20  prior to the separation of final blank  20 . Therefore, the formation of inner diameter hole  41  in step (6) is omitted. If inner diameter hole  41  is formed prior to the separation of final blank  20 , that is, final blank  20  is larger than inner ring blank  40 , and there are advantages in that final blank  20  is easier to handle and inner diameter hole  41  and it is more easily formed. 
     D. Fourth Mode of Working 
     The process for manufacturing in the fourth mode of working shown in  FIG. 10  has an additional step (4)-b of the second mode of working between step (4)c and step (5), of the third mode of working. After forming inner diameter hole  41  of the inner ring at the center of final blank  20  in step (4)c, pilot groove  22  as shown in  FIG. 7  is formed on both faces of final block  20 . Then, in step (5), final blank  20  is separated. 
     E. Fifth Mode of Working 
     In the manufacturing process of the fifth mode of working shown in  FIG. 11 , a first blank  10  B of a cylindrical form is cut out from bar material  1  by press cutting, as shown in  FIG. 12 . The length of first blank  10  B is set to the length which makes it possible to obtain pluralities of sets of outer ring blanks  30  and inner ring blanks  40 , respectively. In next step (2), forging to compress first blank  10  B in the axial direction is performed, thereby forming second blank  20  B of a cylindrical shape as shown in  FIG. 12 . The width of this second blank  20  B is set to the width which makes it possible to obtain pluralities of sets of outer ring blanks  30  and inner ring blanks  40 , respectively. In step (2)b, second blank  20  B is cut into round pieces, as shown in  FIG. 13 , thereby forming a plurality (2 in the case shown in the drawing) of final blanks  20 . Second blank  20 B may be cut into many round pieces. After this, similarly to the above-mentioned first mode of working, outer ring blanks  30  and inner ring blanks  40  are obtained from final blanks  20  in step (3) through step (7). Step (3) through Step (7) may be performed in accordance with any of the above described modes of working. 
     When second blank  20  B is obtained in the stage prior to final blank  20  it is made thick in advance, this provides an advantage in the handling prior to the separation of outer ring blanks  30  and inner ring blanks  40 . It is possible to add step (4)b or step (4)c with respect to the plurality of final blanks obtained by cutting round pieces in this fifth mode of working. 
     Here each of the above-mentioned modes of working is applied to a miniature ball bearing in which rolling elements are balls, and the present invention can be applied to all types of miniature ball bearings which utilize needles and rollers, etc. as rolling elements. 
     For the convenience of the reader, the above description has focused on a representative sample of all possible embodiments, a sample that teaches the principles of the invention and conveys the best mode contemplated for carrying it out. The description has not attempted to exhaustively enumerate all possible variations. Other undescribed alternative embodiments may be possible, and fall within the claims. For example, where multiple alternative embodiments are described, in many cases it will be possible to combine elements or steps of different embodiments, or to combine elements of the embodiments described here with elements of other embodiments that are not expressly described. It will be appreciated that many of those undescribed embodiments are within the literal scope of the following claims, and others are equivalent.