Patent Publication Number: US-2019168285-A1

Title: Method for manufacturing ring

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2017/035644, filed Sep. 29, 2017, claiming priority based on Japanese Patent Application No. 2016-193908, filed Sep. 30, 2016. 
    
    
     TECHNICAL FIELD 
     The various aspects of the present disclosure disclosed in the specification relates to methods for manufacturing a ring. 
     BACKGROUND ART 
     Conventionally, methods including a welding step of butt welding ends of a metal strip to form an endless tubular body, a solution treatment step of solution-treating (annealing) the welded tubular body, and a cutting step of cutting the solution-treated tubular body with laser light into ring bodies with a predetermined width have been proposed as methods for manufacturing a ring for a belt-type continuously variable transmission using an annular transmission belt that is formed by binding a multiple elements with the ring (see, e.g., Patent Document 1). 
     Patent Document 1: Japanese Patent Application Publication No. 2002-248522 (JP 2002-248522 A) 
     SUMMARY 
     In the above methods for manufacturing a ring, when the tubular body is cut with laser light, the ring body is structurally changed (heat-affected zones) due to heat of the laser light, which affect plastic workability of the ring body in the subsequent steps. For example, the ring body may break or may not be able to be formed to predetermined dimensions when performing a rolling step of rolling the laser cut ring body and when performing a circumference adjusting step of adjusting the ring bodies to their required circumferences in order to laminate a plurality of the ring bodies in the radial direction to form a laminated ring. Solution treatment needs therefore to be performed again after the laser cutting. 
     It is an aspect of the present disclosure to enhance ring manufacturing efficiency by efficiently removing heat-affected zones formed in a ring body by laser cutting. 
     The embodiments of the present disclosure has taken the following measures in order to achieve the above primary object. 
     A method for manufacturing a ring according to the present disclosure is a method for manufacturing an endless metal ring for a continuously variable transmission using a transmission belt that is formed by binding a plurality of elements with the ring. The method includes: a welding step of butt welding ends of a metal strip to form an endless tubular body; a solution treatment step of solution-treating the welded tubular body; a cutting step of cutting the solution-treated tubular body with laser light into ring bodies with a predetermined width; a lateral end processing step of pressing a grinding wheel against a lateral end of the cut ring body to remove a heat-affected zone formed by the cutting step and form the lateral end into a convex arc shape; and a rolling step of adjusting the ring body with the processed lateral end to a predetermined thickness. 
     In the method for manufacturing a ring according to the present disclosure, after the welding step of forming the endless tubular body, the first solution treatment step of solution-treating the tubular body, and the cutting step of cutting the tubular body into ring bodies by laser cutting are performed, the heat-affected zone formed by the laser cutting is also removed when the lateral end of the ring body is formed into a convex arc shape by the lateral end processing step. No heat-affected zone with high hardness therefore remains in the ring body after the lateral end processing step. This can eliminate the need to subsequently perform the first solution treatment step again and thus can improve ring manufacturing efficiency. After the cutting step is performed with laser light, the heat-affected zone formed in the lateral end of the ring body by the laser cutting is also removed when the lateral end is processed into a convex arc shape by the lateral end processing step. Accordingly, even in the case where a cutting machine that is used in the cutting step is switched from other cutting machine such as a cutter cutting machine to a laser cutting machine, the existing facilities can be effectively used, and additions and changes to manufacturing facilities can be minimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram schematically showing the configuration of a continuously variable transmission  1 . 
         FIG. 2  is a configuration diagram schematically showing the configuration of a transmission belt  10 . 
         FIGS. 3A to 3M  are illustrations showing an example of a manufacturing process of a ring. 
         FIG. 4  is a partial enlarged view showing a laser cut portion in a lateral section of a ring body  23 . 
         FIG. 5  is an illustration showing the relationship between the lateral distance from a laser cut surface of the ring body  23  and the hardness. 
         FIGS. 6A and 6B  are illustration showing a polishing and rounding step. 
         FIG. 7  is a configuration diagram schematically showing the configuration of a polishing apparatus  30 . 
         FIGS. 8A to 8C  are illustrations showing how the outer peripheral side of an end of the ring body  23  is polished and rounded by using an outer peripheral-side polishing roll  41 . 
         FIGS. 9A to 9C  are illustrations showing how the inner peripheral side of the end of the ring body  23  is polished and rounded by using an inner peripheral-side polishing roll  46 . 
         FIGS. 10A to 10D  are illustrations showing how a lateral end of a ring body  23  is polished and rounded by using a polishing roll  41 B of a comparative example. 
         FIG. 11  is a configuration diagram schematically showing the configuration of a polishing apparatus  130  of another embodiment. 
         FIGS. 12A to 12C  are illustrations showing how a lateral end of a ring body  23  is polished and rounded by using a polishing roll  141 . 
     
    
    
     PREFERRED EMBODIMENTS 
     Modes for carrying out the various aspects of the present disclosure will be described below with reference to the accompanying drawings. 
       FIG. 1  is a configuration diagram schematically showing the configuration of a continuously variable transmission  1 . The continuously variable transmission  1  is mounted on a vehicle including a power source such as an engine, and as shown in the figure, includes a primary shaft  2  serving as a drive-side rotary shaft, a primary pulley  3  provided on the primary shaft  2 , a secondary shaft  4  disposed parallel to the primary shaft  2  and serving as a driven-side rotary shaft, a secondary pulley  5  provided on the secondary shaft  4 , and a transmission belt  10  wound around a pulley groove (V-groove) of the primary pulley  3  and a pulley groove (V-groove) of the secondary pulley  5 . The continuously variable transmission  1  changes the groove widths of the primary pulley  3  and the secondary pulley  5  and thus steplessly shifts power of the primary pulley  3  to transmit the shifted power to the secondary pulley  5 . 
       FIG. 2  is a configuration diagram schematically showing the configuration of the transmission belt  10 . As shown in  FIG. 2 , the transmission belt  10  includes a multiple (e.g., several hundreds) elements  11  and a laminated ring  12  and is formed by binding the multiple elements  11  into a ring shape with the laminated ring  12 . For example, the elements  11  are parts punched out from a steel sheet by pressing. The elements  11  are subjected to a clamping force from the pulley (the primary pulley  3 , the secondary pulley  5 ) at their right and left side surfaces, and those elements  11  which are located ahead in the traveling direction of the belt are pushed out by the friction force in a direction tangential to the pulley, whereby power is transmitted. 
     The laminated ring  12  is formed by laminating a plurality of endless metal rings  20  (single rings) having slightly different circumferences from each other in the radial direction. The laminated ring  12  is manufactured by a manufacturing process illustrated in  FIGS. 3A to 3M . 
     As shown in  FIG. 3 , the manufacturing process of the ring  20  is comprised of (A) a strip cutting step (see  FIG. 3A ), (B) a bending step (see  FIG. 3B ), (C) a pre-welding cleaning step (see  FIG. 3C ), (D) a welding step (see  FIG. 3D ), (E) a first solution treatment step (annealing step) (see  FIG. 3E ), (F) a ring cutting step (see  FIG. 3F ), (G) a polishing and rounding step (see  FIG. 3G ), (H) a pre-rolling cleaning step (see  FIG. 3H ), (I) a rolling step (see  FIG. 31 ), (J) a post-rolling cleaning step (see  FIG. 3J ), (K) a second solution treatment step (see  FIG. 3K ), (L) a circumference adjusting step (see  FIG. 3L ), and (M) an aging and nitriding step (see  FIG. 3M ). 
     The strip cutting step (A) is a step of cutting a strip steel (maraging steel) having a predetermined thickness (e.g., 0.4 to 0.5 mm) and wound around a drum in the lateral direction into strips  21  with a predetermined size. The strip cutting step can be performed by using a cutter cutting machine having a cutter edge, a laser cutting machine, etc. The bending step (B) is a step of forming a tubular body  22  by bending the strip  21  into a tubular shape such that the ends of the strip  21  abut on each other. The bending step can be performed by using a roll or a die. 
     The pre-welding cleaning step (C) is a step of degreasing and cleaning the tubular body  22  before welding the abutting portions of the tubular body  22 . The pre-welding cleaning step can be performed by, e.g., shower cleaning, ultrasonic cleaning, etc. The welding step (D) is a step of performing butt welding, namely welding the abutting portions of the tubular body  22 . The welding step can be performed by, e.g., laser welding, plasma welding, etc. The first solution treatment step (annealing step) (E) is a step that is performed in order to level hardness distribution around the weld, which has been changed by the welding step, to improve ductility. 
     The ring cutting step (F) is a step of cutting the tubular body  22  into a plurality of ring bodies  23  with a predetermined width, and this step is performed by using a laser cutting machine.  FIG. 4  is a partial enlarged view showing a laser cut portion in a lateral section of the ring body  23 . As shown in the figure, the laser cut portion includes a solidification structure where metal melted by heat from laser light has solidified and a heat-affected zone (HAZ) where structural changes have occurred due to the heat.  FIG. 5  is an illustration showing the relationship between the lateral distance from a laser cut surface of the ring body  23  and the hardness. As shown in the figure, the hardness of the heat-affected zone is significantly different from the hardnesses of portions far away from the laser cut surface and hardly affected by the heat. If the rolling step (I) is performed with the heat-affected zones remaining in the ring body  23 , the ring body  23  may break from the heat-affected zones with high hardness or may not be able to be formed to intended dimensions due to the difference in deformation resistance. 
     As shown in  FIGS. 6A and 6B , the polishing and rounding step (G) is a step of polishing lateral end (laser cut portions) of the ring body  23  with a polishing roll to remove the heat-affected zones and process the lateral ends of the ring body  23  into a convex arc shape (round shape), and this step is performed by using a polishing apparatus  30  illustrated in  FIG. 7 . As shown in  FIG. 7 , the polishing apparatus  30  includes: a rotating unit  31  having a drive roller  31   a  and a driven roller  31   b  around which the ring body  23  is wound; an inner peripheral-side backup roller  33  that supports the ring body  23  from the inner peripheral side; an outer peripheral-side polishing unit  40  that faces the inner peripheral-side backup roller  33  and polishes the outer peripheral side of a lateral end (the outer peripheral side of an end) of the ring body  23  into a round shape; an outer peripheral-side backup roller  34  that supports the ring body  23  from the outer peripheral side; and an inner peripheral-side polishing unit  45  that faces the outer peripheral-side backup roller  34  and polishes the inner peripheral side of the lateral end (the inner peripheral side of the end) of the ring body  23  into a round shape. The drive roller  31   a  being pressed against the inner peripheral surface of the ring body  23  in a direction away from the driven roller  31   b  is driven to rotate, whereby the rotating unit  31  can rotate (turn) the ring body  23  under tension in the circumferential direction. The rotating unit  31  may include a separate tension roller that tensions the ring body  23 . The outer peripheral-side polishing unit  40  includes: an outer peripheral-side polishing roll  41  having an axis of rotation extending in a direction parallel to the thickness direction of the ring body  23  set on the rotating unit  31 ; and a rotating and moving unit  43  capable of rotating and moving the outer peripheral-side polishing roll  41  in the rotational direction of the outer peripheral-side polishing roll  41 , the axial direction of the axis of rotation of the outer peripheral-side polishing roll  41  (forward and backward in the figure), and a direction perpendicular to this axial direction and parallel to the lateral direction of the ring body  23  (upward and downward in the figure). The inner peripheral-side polishing unit  45  includes an outer peripheral-side polishing roll  46  and a rotating and rotating unit  48  which are similar to those of the outer peripheral-side polishing unit  40 . 
       FIGS. 8A to 8C  are illustrations showing how the outer peripheral side of an end of the ring body  23  is polished and rounded by using the outer peripheral-side polishing roll  41 .  FIGS. 9A to 9C  are illustrations showing how the inner peripheral side of the end of the ring body  23  is polished and rounded by using the inner peripheral-side polishing roll  46 . In  FIGS. 8A to 8C  and  FIGS. 9A to 9C , L-shaped grooves  42 ,  47  of the outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46  are shown exaggerated for convenience of description. The outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46  are columnar members and have the L-shaped grooves  42 ,  47  formed in the circumferential direction in the distal end portions of their outer peripheral surfaces along the entire circumference. The bottoms of the L-shaped grooves  42 ,  47  are formed by linear portions  42   b,    47   b  extending straight in the axial direction of the outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46 , and corners of the bottoms of the L-shaped grooves  42 ,  47  are formed by concave arc-shaped portions  42   a ,  47   a  having an arc angle θ of about 90 degrees and a radius of curvature r that is about ½ of the thickness t of the ring body  23 . The L-shaped grooves  42 ,  47  have an abrasive grain layer comprised of abrasive grains bonded together. The ring body  23  is polished and rounded by using the outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46  as follows. First, the outer peripheral-side polishing roll  41  is moved in a direction from one lateral end toward the other lateral end of the ring body  23  (downward in the figure) while being rotated, and the inner peripheral-side polishing roll  46  is moved in the direction from the one lateral end toward the other lateral end of the ring body  23  (downward in the figure) while being rotated. The linear portions  42   b,    47   b  are thus pressed against the end face of the one lateral end of the ring body  23  to remove the heat-affected zone in the one lateral end of the ring body  23  (see  FIGS. 8A, 9A ). The outer peripheral-side polishing roll  41  is then moved from the outer peripheral side toward the inner peripheral side in the thickness direction of the ring body  23  (to the left in the figure) while being rotated, so that the concave arc-shaped portion  42   a  is pressed against the outer peripheral side of the one lateral end (the outer peripheral side of the end) of the ring body  23 . The outer peripheral side of the end of the ring body  23  is thus formed into a round shape (see  FIGS. 8B, 8C ). At the same time, the inner peripheral-side polishing roll  46  is moved from the inner peripheral side toward the outer peripheral side in the thickness direction of the ring body  23  (to the right in the figure) while being rotated, so that the concave arc-shaped portion  47   a  is pressed against the inner peripheral side of the one lateral end (the inner peripheral side of the end) of the ring body  23 . The inner peripheral side of the end of the ring body  23  is thus formed into a round shape (see  FIGS. 9B, 9C ). The outer peripheral side and the inner peripheral side of the end of the ring body  23  need not necessarily be processed at the same time, but may be processed at different timings. That is, the inner peripheral side of the end of the ring body  23  may be processed after the outer peripheral side of the end is processed, or the outer peripheral side of the end of the ring body  23  may be processed after the inner peripheral side of the end is processed. The rotational direction of the outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46  at the contact point with the ring body  23  may be either the same as or opposite to the turning direction of the ring body  23 . After the one lateral end of the ring body  23  is thus polished, the ring body  23  is removed from the rotating unit  31  and is mounted again on the rotating unit  31  with its one lateral end and the other lateral end switched, and the other lateral end of the ring body  23  is similarly polished. The heat-affected zones are thus removed from both lateral ends of the ring body  23 , and both lateral ends of the ring body  23  are formed into a semicircular shape with almost no edge. The pair of the outer peripheral-side polishing unit  40  and the inner peripheral-side polishing unit  45  may be provided on each of the one lateral end side and the other lateral end side of the ring body  23  so that each of the one lateral end and the other lateral end of the ring body  23  is polished by a corresponding pair of the outer peripheral-side polishing unit  40  and the inner peripheral-side polishing unit  45 . 
       FIGS. 10A to 10D  are illustrations showing how a lateral end of the ring body  23  is polished and rounded by using a polishing roll  41 B of a comparative example. The polishing roll  41 B of the comparative example has a semicircular groove  42 B formed in the middle in the axial direction of its outer peripheral surface along the entire circumference, and the semicircular groove  42 B has an arc angle θ of about 180 degrees and a radius of curvature r that is about ½of the thickness t of the ring body  23 . In the comparative example, the polishing roll  41 B is moved in the lateral direction of the ring body  23  while being rotated, so that the groove  42 B of the polishing roll  41 B is pressed against the end face of the lateral end of the ring body  23 . The lateral end of the ring body  23  is thus polished and formed into a round shape. In the case where the ring body  23  is polished and rounded by using the polishing roll  41 B of this modification, the lateral end of the ring body  23  can be formed into a semicircular shape with almost no edge if the thickness t of the ring body  23  satisfies the relationship t=2·r for the radius of curvature r of the groove  42 B. However, there is actually a variation in thickness of the ring bodies  23 . If the thickness t of the ring body  23  is t&lt;2·r, edges may remain in both ends in the thickness direction of the end face of the ring body  23  (see  FIGS. 10A, 10B ). If the thickness t of the ring body  23  is t&gt;2·r, both ends in the thickness direction of the end face of the ring body  23  may be polished by the outer peripheral surface of the polishing roll  41 B other than the groove  42 B, which may cause undercuts (see  FIGS. 10C, 10D ). In the present embodiment, the polishing roll is divided into the outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46 , and the outer peripheral side and the inner peripheral side of each lateral end of the ring body  23  are polished into a round shape by the outer peripheral-side polishing roll  41  and the inner peripheral-side polishing roll  46 . This allows both lateral ends of the ring body  23  to be formed into a semicircular shape with almost no edge regardless of the variation in thickness of the ring bodies  23 . 
     The pre-rolling cleaning step (H) is a step of, before rolling the ring body  23 , removing polishing debris etc. that has stuck to the ring body  23  in the polishing and rounding step. The rolling step (I) is a step of rolling the ring body  23  to a required thickness with a rolling roller to produce a ring body  24 . As described above, the heat-affected zones with high hardness have been removed from the ring body  23  by the polishing and rounding step (G) after the ring cutting step. The ring body  23  can therefore be rolled to a desired thickness by the rolling step (I) without breakage. The post-rolling cleaning step (J) is a step of removing rolling oil etc. that has stuck to the ring body  24  by the rolling. The second solution treatment step (K) is a step of heating the ring body  24  produced by the rolling to recrystallize a metallic structure transformed by the rolling. 
     The circumference adjusting step (L) is a step of finely adjusting the circumferences of the ring bodies  24  produced by the rolling so that a plurality of the ring bodies  24  can be laminated in the radial direction. The aging and nitriding step (M) is a step of aging the ring bodies  24  with the adjusted circumferences and then nitriding the ring bodies  24  to strengthen the surfaces of the ring bodies  24 . 
     The method for manufacturing a ring according to the embodiment described above is a method for manufacturing an endless metal ring for a continuously variable transmission using a transmission belt that is formed by binding a plurality of elements with the ring. The method includes the welding step (D) of butt welding the ends of a strip  21  to form an endless tubular body  22 , the first solution treatment step (E) of solution-treating (annealing) the welded tubular body  22 , the ring cutting step (F) of cutting the solution-treated tubular body  22  with laser light into ring bodies  23  with a predetermined width, and the polishing and rounding step (G) of polishing the lateral ends of the cut ring body  23  with a grinding wheel to remove the heat-affected zones formed by the ring cutting step (F) and form the lateral ends of the ring body  23  into a round shape. No heat-affected zone with high hardness therefore remains in the ring body  23  after the polishing and rounding step (G). This can eliminate the need to subsequently perform the first solution treatment step again and thus can improve ring manufacturing efficiency. 
     After the ring cutting step (F) is performed with a laser cutting machine, the heat-affected zones formed in the lateral ends of the ring body  23  by the laser cutting are also removed when the lateral end faces are processed into a round shape by the polishing and rounding step (G). Accordingly, even in the case where a cutting machine that is used in the ring cutting step (F) is switched from other cutting machine such as a cutter cutting machine to a laser cutting machine, a step of removing the heat-affected zones formed by the laser cutting needs only to be added to the polishing and rounding step (G). The existing facilities can therefore be effectively used, and additions and changes to manufacturing facilities can be minimized. That is, in the case where the heat-affected zones formed by the laser cutting are removed by solution treatment, a facility for solution-treating the ring body  23  is required. However, since the heat-affected zones are removed by the polishing and rounding step (G), such a facility need not be added. 
     In the above embodiment, the polishing roll for the polishing and rounding step (G) is divided into the outer peripheral-side polishing roll  41  that polishes the outer peripheral side of an end of the ring body  23  and the inner peripheral-side polishing roll  46  that polishes the inner peripheral side of the end of the ring body  23 . However, a lateral end of the ring body  23  may be polished and rounded by using the polishing roll  41 B of the comparative example shown in  FIG. 10 . Alternatively, as shown in  FIG. 11 , the outer peripheral side and the inner peripheral side of an end of the ring body  23  may be polished and rounded by using an integrated polishing roll  141 .  FIG. 11  is a configuration diagram schematically showing the configuration of a polishing apparatus  130  of another embodiment. As shown in the figure, the polishing apparatus  130  of the another embodiment includes: a rotating unit  31  having a drive roller  31   a  and a driven roller  31   b;  a polishing unit  140  that polishes and rounds the outer peripheral side and the inner peripheral side of an end of the ring body  23 ; inner peripheral-side backup rollers  133   a,    133   b  that are disposed in front of and behind the polishing unit  140  in a direction in which the ring body  23  is fed and support the ring body  23  from the inner peripheral side; and outer peripheral-side backup rollers  134   a,    134   b  that are disposed in front of and behind the polishing unit  140  in the direction in which the ring body  23  is fed and support the ring body  23  from the outer peripheral side. The polishing unit  140  includes: a polishing roll  141  having an axis of rotation extending in a direction parallel to the thickness direction of the ring body  23  set on the rotating unit  31 ; and a rotating and moving unit  143  capable of rotating and moving the polishing roll  141  in the rotational direction of the polishing roll  141 , the axial direction of the axis of rotation of the polishing roll  141  (forward and backward in the figure), and a direction perpendicular to this axial direction and parallel to the lateral direction of the ring body  23  (upward and downward in the figure). 
       FIGS. 12A to 12C  are illustrations showing how a lateral end of the ring body  23  is polished and rounded by using the polishing roll  141 . In  FIG. 12 , a groove  142  of the polishing roll  141  is shown exaggerated for convenience of description. The polishing roll  141  is a columnar member and has the groove  142  formed in the circumferential direction in the middle of its outer peripheral surface in the axial direction along the entire circumference. The bottom of the groove  142  is formed by a linear portion  142   b  extending straight in the axial direction of the roll and both corners of the bottom of the groove  142  are formed by concave arc-shaped portions  142   a,    142   c  having an arc angle θ of about 90 degrees and a radius of curvature r that is about ½ of the thickness t of the ring body  23 . The groove  142  has an abrasive grain layer comprised of abrasive grains bonded together. The ring body  23  is polished and rounded by using the polishing roll  141  as follows. First, the polishing roll  141  is moved in a direction from one lateral end toward the other lateral end of the ring body  23  (downward in the figure) while being rotated, so that the linear portion  142   b  is pressed against the end face of the one lateral end of the ring body  23  to remove the heat-affected zone in the one lateral end of the ring body  23  (see  FIG. 12A ). The polishing roll  141  is then moved from the outer peripheral side toward the inner peripheral side in the thickness direction of the ring body  23  (to the left in the figure) while being rotated, so that the concave arc-shaped portion  142   a  is pressed against the outer peripheral side of the one lateral end (the outer peripheral side of the end) of the ring body  23 . The outer peripheral side of the end of the ring body  23  is thus formed into a round shape (see  FIG. 12B ). The polishing roll  141  is then moved from the inner peripheral side toward the outer peripheral side in the thickness direction of the ring body  23  (to the right in the figure) while being rotated, so that the concave arc-shaped portion  142   c  is pressed against the inner peripheral side of the lateral end (the inner peripheral side of the end) of the ring body  23 . The inner peripheral side of the end of the ring body  23  is thus formed into a round shape (see  FIG. 12C ). After the one lateral end of the ring body  23  is thus polished, the ring body  23  is removed from the rotating unit  31  and is mounted again on the rotating unit  31  with its one lateral end and the other lateral end switched, and the other lateral end of the ring body  23  is similarly polished. The heat-affected zones are thus removed from both lateral ends of the ring body  23 , and both lateral ends of the ring body  23  are formed into a semicircular shape with almost no edge. The polishing unit  140  may be provided on each of the one lateral end side and the other lateral end side of the ring body  23  so that each of the one lateral end and the other lateral end of the ring body  23  is polished by a corresponding one of the polishing units  140 . In that another embodiment, the inner peripheral side of the end of the ring body  23  is processed after the outer peripheral side of the end is processed. However, the outer peripheral side of the end of the ring body  23  may be processed after the inner peripheral side of the end is processed. The outer peripheral side and the inner peripheral side of the end of the ring body  23  may be alternately processed little by little at a time by repeatedly reciprocating the polishing roll  141  in the axial direction. 
     As described above, a method for manufacturing a ring according to the present disclosure is a method for manufacturing an endless metal ring ( 20 ) for a continuously variable transmission ( 1 ) using a transmission belt that is formed by binding a plurality of elements ( 11 ) with the ring. The method includes: a welding step (D) of butt welding ends of a metal strip ( 21 ) to form an endless tubular body ( 22 ); a solution treatment step (E) of solution-treating the welded tubular body ( 22 ); a cutting step (F) of cutting the solution-treated tubular body ( 22 ) with laser light into ring bodies ( 23 ) with a predetermined width; a lateral end processing step (G) of pressing a grinding wheel ( 41 ,  46 ) against a lateral end of the cut ring body ( 23 ) to remove a heat-affected zone formed by the cutting step (F) and form the lateral end into a convex arc shape; and a rolling step (I) of processing the lateral end to adjust the ring body ( 23 ) to a predetermined thickness. 
     In the method for manufacturing a ring according to the present disclosure, after the welding step (D) of forming the endless tubular body ( 22 ), the first solution treatment step (E) of solution-treating the tubular body ( 22 ), and the cutting step (F) of cutting the tubular body ( 22 ) into ring bodies ( 23 ) by laser cutting are performed, the heat-affected zone formed by the laser cutting is also removed when the lateral end of the ring body ( 23 ) is formed into a convex arc shape by the lateral end processing step (G). No heat-affected zone with high hardness therefore remains in the ring body ( 23 ) after the lateral end processing step (G). This can eliminate the need to subsequently perform the first solution treatment step (E) again and thus can improve ring manufacturing efficiency. After the cutting step (F) is performed with laser light, the heat-affected zone formed in the lateral end of the ring body ( 23 ) by the laser cutting is also removed when the lateral end is processed into a convex arc shape by the lateral end processing step (G). Accordingly, even in the case where a cutting machine that is used in the cutting step (F) is switched from other cutting machine such as a cutter cutting machine to a laser cutting machine, the existing facilities can be effectively used, and additions and changes to manufacturing facilities can be minimized. 
     The method for manufacturing a ring according to the present disclosure may further include: a second solution treatment step (K) of solution-treating the ring body ( 24 ) adjusted to the predetermined thickness; a circumference adjusting step (L) of adjusting a circumference of the solution-treated ring body ( 24 ); and an aging and nitriding step (M) of aging and nitriding the ring body ( 24 ) with the adjusted circumference. The heat-affected zone formed in the cutting step (F) described above is removed by the polishing step (G). Accordingly, the solution treatment step (E) is not subsequently performed again, and the ring body ( 23 ) can be restrained from breaking when the ring body ( 23 ) is rolled in the rolling step (I) or the circumference of the ring body ( 23 ) is adjusted in the circumference adjusting step (L). Satisfactory processing accuracy can thus be achieved. 
     In the method for manufacturing a ring according to the present disclosure, the lateral end processing step (G) may be a step in which the ring body ( 23 ) under tension is rotated in a circumferential direction, and a concave arc-shaped grinding wheel ( 42   a,    142   a ) is pressed against the lateral end of the ring body ( 23 ) from an outer peripheral side toward an inner peripheral side in a thickness direction of the ring body ( 23 ) to form the outer peripheral side of the lateral end of the ring body ( 23 ) into a convex arc shape, and a concave arc-shaped grinding wheel ( 47   a,    142   c ) is pressed against the lateral end of the ring body ( 23 ) from the inner peripheral side toward the outer peripheral side in the thickness direction of the ring body ( 23 ) to form the inner peripheral side of the lateral end of the ring body ( 23 ) into a convex arc shape. The lateral end (the outer peripheral side and the inner peripheral side of the end) of the ring body ( 23 ) can thus be formed into a semicircular shape with almost no edge even if there is a variation in thickness of the ring bodies ( 23 ). 
     Although the embodiments of the invention of the present disclosure are described above, it is to be understood that the invention of the present disclosure is not limited in any way to the embodiments and may be carried out in various forms without departing from the spirit and scope of the invention of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The various aspects of the present disclosure can be utilized in manufacturing industries of transmission belts for use in continuously variable transmissions.