JP2006342971A - Worm gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the number of processing steps while ensuring worm gear accuracy satisfactorily. <P>SOLUTION: A work material is positioned between a first rolling die 100 and a second rolling die 101 by rotation of the rolling dies, and a servomotor 76 for feeding the work material. When a lead angle of a worm is large and there is a large difference between a finished diameter and a blank diameter, the lead angle changes during the progress of rolling process, resulting in occurrence of through-feed. As a slide plate 55 is freely slidable on a slide 53, through-feed occurs owing to the lead angles of the first and second rolling dies 100 and 101 and the workpiece. When the through-feed becomes more than a set value, the rotation of the first rolling die 100 and the second rolling die 101 is stopped. Then, the first rolling die 100 and the second rolling die 101 initiate reverse rotation, and at the same time, the slide plate 55 also initiates movement in the reverse direction. Thus, rolling is started. Thereafter, similar processing is repeated to manufacture a worm gear 80 having circular arc-shaped bottom. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a worm gear, and more particularly, to a worm gear obtained by processing a worm gear used for driving a steering wheel of an automobile by a rolling method by a rolling process .

  2. Description of the Related Art As an electric power steering device for a vehicle, there is known a type that decelerates the rotational output of an electric motor through a worm gear mechanism and assists driving an output shaft connected to a steering wheel. In a power steering apparatus for a light vehicle that does not require a large load, a type in which a metal cylindrical worm gear and a resin worm wheel are combined to be used as a worm gear mechanism is known (for example, Patent Document 1).

  Since this metal worm gear is required to be accurate, it is manufactured by turning a hardened steel and then heat-treating it after grinding. When machining with a lathe, it is cut with a cutting tool. To increase productivity, a conical milling cutter is used, and this milling axis is tilted by γ (advance angle in the pitch line of the worm gear) with respect to the worm axis. Cut in the way of threading.

  However, the worm gear manufacturing process requires at least three processes, at least cutting, heat treatment, and grinding. In addition, for this, at least three units of a lathe, a heat treatment facility, and a grinding machine are required. For this reason, the processing cost increased, and the advantages of the worm wheel made of resin could not be fully exhibited.

  Further, when rolling a male screw, a worm gear, or the like, the first rolling die and the second rolling die that are arranged to face each other approach each other and perform push-feed. At this time, when the advance angle of the worm gear is large and the difference between the finished diameter and the material diameter is large, the phenomenon in which the advance angle changes during the rolling process is called “step”. When this step occurs, the contact of the round die differs between the flanking surface of the thread in the moving direction of the workpiece due to the step and the opposite flank surface, and there is a problem that the finished accuracy of the rolling surface is deteriorated. In order to prevent this step, correction may be made by changing the phase position of the first rolling die or the second rolling die in the axial direction, usually by visual observation or the like.

  However, in the case of parts that have male screws or shafts larger than the diameter of the worm gear on both sides of the worm gear, this correction method is not corrected to prevent the rolling die from interfering with this part. Have difficulty. In such a case, rolling is performed by rotating the die forwardly or reversely. However, due to the occurrence of backlash or the like, a product with high product accuracy cannot be obtained, and the productivity is poor. The present applicant has proposed a spindle tilt mechanism that rotates this step around an axis perpendicular to the rotation axis of the first rolling die and the second rolling die (Patent Document 2).

  However, even if this spindle tilt mechanism is used, it is not possible to completely prevent the occurrence of steps in workpieces such as worm gears that have a large change in diameter from the start of machining to the end of machining. Appear.

Japanese Patent Laid-Open No. 9-24855 JP-A-11-285766

An object of the present invention, the gear accuracy a worm gear having reduced sufficiently secured while machining process, and to provide a worm gear obtained by processing the worm gear by rolling method.

Another object of the invention is a worm gear having a reduced cost while sufficiently securing the gear accuracy, and to provide a worm gear obtained by processing the worm gear by rolling method.

In order to achieve the above object, the present invention employs the following means.
The worm gear according to the first aspect of the present invention includes a plurality of cylindrical dies that are formed by rolling a cylindrical material, a die rotation driving unit that synchronously drives the dies, and the material. A worm gear rolled by a worm gear rolling method using a rolling machine provided with a material support means for rotatably supporting and a pushing means for pushing the dies close to each other,
The shape of the tooth bottom between the teeth of the worm gear is such that the top is formed in a cross section including the axis of the worm gear. The top portion is preferably a carbon steel for machine structural use with an angle of 120 to 150 degrees, and the tip of the top portion has a cross-section with a radius of 1.0 to 1.5 mm.

The worm gear according to the second aspect of the present invention includes a plurality of cylindrical dies for forming a rolling process with a cylindrical material as a center, a die rotation driving means for synchronously rotating the dies, and the material. A worm gear rolled by a worm gear rolling method using a rolling machine provided with a material support means for rotatably supporting and a pushing means for pushing the dies close to each other,
The worm gear according to the third aspect of the present invention is the worm gear according to the first or second aspect of the present invention, wherein the tooth bottom between the teeth of the worm gear has an arc formed in a section including the axis of the worm gear. The arc is preferably a carbon steel for machine structural use having an arc shape with a radius of 1.0 to 1.5 mm in cross section.

  The worm gear of the present invention 4 is the worm gear of the present invention 1 or 2, wherein the dies of the rolling machine are arranged approximately at the center of the four guides, and two rotation axes are arranged in parallel. Those consisting of are preferred.

The worm gear of the present invention 5 is preferably the worm gear according to the first or second aspect of the present invention, wherein the rolling machine includes a spindle tilting means that rotates about an axis orthogonal to the rotation axis of the die.
The worm gear of the present invention 6 is preferably applied to the worm gear according to the first or second aspect of the present invention, wherein the worm gear has a cross section including the axis of the worm gear and the tooth thickness of the worm gear is smaller than the interval between the tooth bottoms.

The effect of the worm gear of the present invention ( advantage of the present invention) is that the roll-shifted thin-tooth worm gear can be machined with high accuracy by rolling, so that the number of machining steps can be reduced compared to the conventional worm gear. The processing cost can be greatly reduced.

  Hereinafter, embodiments embodying the present invention will be described. FIG. 1 is a three-dimensional external view showing the entire rolling machine for rolling a worm gear according to the present invention. FIG. 2 is a partial cross-sectional view of FIG. 1 taken along the line II-II. FIG. 3 is a front view of the rolling machine. FIG. 4 is a cut plan view. The rolling machine 1 is a round die rolling machine in which cylindrical dies are arranged to face each other and a material is plastically deformed to perform plastic working. In an ordinary round die rolling machine, a movable die that is rotationally driven and a stationary die that rotates with the movable die are arranged to face each other so that their rotational axes are parallel to each other, and a material is arranged between them.

  The rolling machine 1 for machining a worm gear according to the present invention is configured to synchronize and rotate two round dies simultaneously in the same rotational direction during machining. Hereinafter, a detailed structure for this purpose will be described. The bed 2 constitutes a main body of the rolling machine 1 and is a structure base having a hollow inside (see FIG. 2). The bed 2 has a generally box shape, and is made by welding a casting or a steel plate. Two first guide rails 3 are fixed and arranged in parallel on the upper surface of the bed 2 with bolts or the like. On the two 1st guide rails 3, the 1st die movement support stand 4 is movably mounted via the linear bearing block 5. As shown in FIG. A first die moving table 6 is integrally fixed and supported on the front surface of the first die moving support table 4. Similarly, the first die moving table 6 is also movably provided on the two first guide rails 3 via the linear bearing block 5.

  On the front surface 7 of the first die moving table 6, a first round die support table 8 is rotatably supported and mounted for reasons described later (see FIG. 3). Two first round die bearings 9 and a second round die bearing 10 are disposed on the first round die support base 8 at an interval. Between the 1st round die bearing 9 and the 2nd round die bearing 10, the 1st round die axis | shaft 11 is arrange | positioned in the horizontal direction, and this both ends are the 1st round die bearing 9 and the 2nd round die bearing. 10 supports each.

  The first round die support base 8 can be rotated around a rotation axis perpendicular to the center axis of the first round die shaft 11 by a first main shaft tilt mechanism (not shown). The first spindle tilting mechanism includes a gear disposed on the side surface of the first die moving table 6 and a servo motor that meshes with the gear. The servo motor 142 that rotationally drives the first round die support base 8 controls the rotational angle position of the first round die support base 8 by a CNC device 120 (see FIG. 9) described later. The first spindle tilting mechanism is a mechanism for preventing a machining error due to a step phenomenon that occurs during machining of a part having a spiral shape such as a screw and a worm gear described later.

  A gear box 12 is disposed at the end of the second round die bearing 10, and a detector 134 (see FIG. 9) is built in the gear box 12. The gear mechanism in the gear box 12 transmits the rotation from the drive shaft 14 to the first round die shaft 11 via the universal joint 13. The drive shaft 14 is further connected to an output shaft (not shown) of the speed reduction mechanism 16 via the universal joint 15. The speed reduction mechanism 16 is supported and fixed by a bracket 18.

  The bracket 18 is mounted on the drive mechanism support base 20. The drive mechanism support 20 is fixedly disposed integrally with the bed 2 adjacent to the central portion of the side surface of the bed 2. An output shaft of the servo motor 17 is connected to an input shaft (not shown) of the speed reduction mechanism 16. Eventually, the rotation output of the servo motor 17 is decelerated by the speed reduction mechanism 16 and further rotates the first round die shaft 11 via the universal joint 15, the drive shaft 14, the universal joint 13, and the gear mechanism in the gear box 12. Drives the rotation according to the speed command. The rotation output of the servo motor 17 is controlled by a CNC device 120 described later.

  In order to transmit the rotational drive of the servo motor 17 to the first round die shaft 11, a rotational drive transmission mechanism composed of two universal joints 15 and a universal joint 13 was adopted. While the servo motor 17 is fixed on the drive mechanism support base 20, the first round die shaft 11 moves on the two first guide rails 3, so that the position of the first die movement base 6 is constant. Therefore, rotation cannot be transmitted smoothly with a normal joint structure. This rotational drive transmission mechanism using the universal joints 13 and 15 fulfills the function of transmitting the rotation of the servo motor 17 to the first round die shaft 11 smoothly and at a constant speed.

  On the other hand, a second die moving table 25 is arranged at a position on the bed 2 facing the first die moving table 6. Two second guide rails 26 are fixedly disposed on the upper surface of the bed 2 with bolts or the like. The 2nd guide rail 26 is arrange | positioned in the position which extended the two 1st guide rails 3 which guide the 1st dice moving stand 6 on the straight line (refer FIG. 4). On the two 2nd guide rails 26, the 2nd die movement stand 25 is movably mounted via the linear bearing block 27 (refer FIG. 3).

  On the front surface 28 of the second die moving table 25, a second round die support table 29 is mounted so as to be rotatable about the center 0 for reasons described later (see FIG. 5). On the second round die support base 29, two third round die bearings 30 and a fourth round die bearing 31 are arranged at intervals (see FIG. 2). Between the 3rd round die bearing 30 and the 4th round die bearing 31, the 2nd round die axis | shaft 32 is arrange | positioned in the horizontal direction, and this both ends are the 3rd round die bearing 30 and the 4th round die. The die bearings 31 are rotatably supported.

  The second round die support base 29 is rotated by an angle + α or −α about a rotation axis O perpendicular to the central axis of the second round die shaft 32 by a second main shaft tilt mechanism (not shown). (See FIG. 5). The second spindle tilting mechanism is composed of a gear disposed on the side surface of the second die moving table 25 and a servo motor that meshes with the gear. The servo motor 147 that drives the second round die support base 29 controls the position of the second round die support base 29 by a CNC device 120 described later (see FIG. 9). The second spindle tilting mechanism is a mechanism for preventing an error due to a step phenomenon that affects the shape accuracy of a part having a helical structure such as a screw and a worm described later.

  A gear box 33 is disposed at the end of the fourth round die bearing 31, and a rotation detection mechanism (not shown) is built in the gear box 33. The gear mechanism in the gear box 33 transmits the rotation from the drive shaft 35 to the second round die shaft 32 via the universal joint 34. The drive shaft 35 is further connected to an output shaft (not shown) of the speed reduction mechanism 37 via a universal joint 36. The speed reduction mechanism 37 is supported and fixed by the bracket 18 described above.

  The output shaft of the servo motor 38 is connected to the input shaft of the speed reduction mechanism 37. Eventually, the rotation output of the servo motor 38 is decelerated by the reduction mechanism 37, and the second round die shaft 32 is connected to the CNC device via the universal joint 36, the drive shaft 35, the universal joint 34, and the gear mechanism in the gear box 33. Control is performed according to a command 120 (see FIG. 9).

  The shaft fixing portions 41 are arranged at the four corners of the outer periphery of the first die moving support base 4 and the first die moving base 6. One end of the four connecting shafts 40 is fixed to the shaft fixing portion 41. The four connecting shafts 40 are arranged so as to be parallel to each other, and are arranged so as to be parallel to the first guide rail 3 and the second guide rail 26. The four connecting shafts 40 are provided with guide portions 42 at the four corners of the outer periphery of the second die moving table 25, and support the second die moving table 25 movably through bearings incorporated in the guide unit 42. is doing.

[Die feeder 49]
FIG. 6 is a schematic plan view of a rolling machine showing a schematic mechanism of the die feeding device. As can be understood from the above description, the second die moving table 25 is guided by the second guide rail 26 and the four connecting shafts 40 so as to be relatively close to the first die moving table 6, or Separate movement is possible. The other end of the connecting shaft 40 is connected and fixed to the pressure plate 45. A hydraulic cylinder 50 composed of a hydraulic cylinder is fixed to the pressure plate 45. The hydraulic cylinder 50 includes a servo valve that can control the extension position of the piston with high accuracy. The tip of the piston rod 51 that is the output shaft of the hydraulic cylinder 50 is fixed to the back surface 52 of the second die moving table 25.

  When hydraulic pressure is introduced into the hydraulic cylinder 50 and driven, the piston rod 51 extends. The hydraulic cylinder 50 is fixed to the pressure plate 45, and the pressure plate 45 and the first die moving table 6 are connected to each other by the connecting shaft 40, so that the extension of the piston rod 51 causes the first die moving table 6 and the second die moving table 6 to be connected to each other. The dice moving table 25 approaches each other.

  As shown in FIG. 6, a rack 91 is arranged in the same direction as the moving direction of the second die moving table 25, and the second die moving table 25 is fixed to one end of the rack 91. One end of a rack 90 is fixed to the pressure plate 45. The rack 90 and the rack 91 are arranged so as to be parallel to each other.

  The rack 90 and the rack 91 are engaged with the pinion 93. A pinion shaft 94 of the pinion 93 is rotatably provided on the bed 2. Eventually, when the hydraulic cylinder 50 is driven, the piston rod 51 extends. The hydraulic cylinder 50 is fixed to the pressure plate 45, and the pressure plate 45 and the first die moving table 6 are connected to each other by the connecting shaft 40, so that the extension of the piston rod 51 causes the first die moving table 6 and the second die moving table 6 to be connected to each other. The die moving table 25 approaches or separates from each other.

  At this time, since the pinion shaft 94 is rotatably supported by the bed 2, it rotates but does not move. As a result, the center position of the interval between the first die moving table 6 and the second die moving table 25 is always located at a fixed position on the bed 2. When the center axis of the workpiece (workpiece) is made coincident with the fixed position, the workpiece machining accuracy is improved, and the workpiece is easily supplied to and removed from the rolling machine 1.

  The distance between the first die moving table 6 and the second die moving table 25 is measured by moving table interval measuring means (described later) arranged on the second die moving table 25. The moving table interval measuring means includes a linear scale 111 fixed to the upper part of the second die moving table 25, a sensor (not shown) for reading the magnetic scale of the linear scale 111, a rod-shaped sensor table 110 to which the sensor is fixed, and the like. (See FIG. 4).

  One end of the sensor table 110 is fixed to the first die moving table 6. Therefore, if the first dice moving table 6 and the second dice moving table 25 move relative to each other, the sensor can read the magnetic scale of the linear scale 111 and read the interval therebetween. The rotational drive of the first round die shaft 11 and the second round die shaft 32 of the rolling machine 1 and the movement of each rolling die are controlled synchronously or asynchronously by the CNC device 120 described later.

[Work feeding device 59]
FIG. 7 is a side view of a workpiece feeding device 59 for supporting and feeding a workpiece W that is a workpiece. A first rolling die 100 and a second rolling die 101 are key-fixed to the first round die shaft 11 and the second round die shaft 32 described above. One linear rail 58 is fixed on the substrate 61 with bolts. The two linear blocks 57 are movably mounted on the linear rail 58.

  Work length adjusting plates 89 are respectively hung on both side surfaces of the two linear blocks 57 and are connected and fixed to each other by bolts. Further, the slide pressers 54 are fixed to the upper surface of the work length adjusting plate 89 by bolts. A slide plate 55 is slidably provided between the two slide pressers 54 while being guided by the slide presser 54. The moving range of the slide plate 55 guided and moved by the slide press 54 moves during the rolling process and is only the set moving range.

  After all, the linear block 57, the work length adjusting plate 89, the slide press 54, and the slide plate 55 constitute the feed base 53. A tailstock 60 is fixed to the upper surface of the slide plate 55. A center 62 for rotatably supporting a worm gear material or a workpiece W is inserted and fixed to the tailstock 60. A sensor dog 63 that determines the moving range of the slide plate 55 is fixed to the tailstock 60 with bolts 64. An advance position detection sensor 79 that detects the movement of the sensor dog 63 is fixed on the substrate 61.

  A chuck base 65 is disposed and fixed on the slide plate 55 so as to face the tailstock 60. The chuck base 65 is provided with a center support shaft 67, and a rotation center 66 is rotatably supported on the center support shaft 67 via a bearing 68. On the other hand, a chuck pneumatic cylinder 69 for driving the center support shaft 67 movably in the axial direction is fixed to the back surface of the chuck base 65 by bolts 70. The piston rod of the pneumatic cylinder 69 for chuck that operates by air pressure is connected to the center support shaft 67.

  Accordingly, when the chuck pneumatic cylinder 69 is operated, the center support shaft 67 and the rotation center 66 are driven to expand or contract in the axial direction, and the material or workpiece W is moved between the rotation center 66 and the center 62. Can be attached or removed. A nut 72 is fixed to the linear block 57. A feed screw 73 is screwed into the nut 72. One end of the feed screw 73 is connected to the output shaft 77 of the servo motor 76 via a coupling 74 which is a rotary joint.

  Therefore, when the servo motor 76 is driven, the feed screw 73 is rotationally driven, the feed base 53 moves on the linear rail 58, and its position is controlled. A sensor dog 71 is fixed on the chuck base 65 with bolts 78. A reverse position detection sensor 75 that detects the movement of the sensor dog 71 is fixed to the substrate 61. Accordingly, the forward position detection sensor 79 detects the forward position of the workpiece W, and the backward position detection sensor 75 detects the backward position of the workpiece W.

  A linear scale 99 that is a magnetic scale is disposed and fixed on the side surface of the chuck base 65. The movement of the linear scale 99 is read by a fixed reading device (not shown), and the movement is detected. Therefore, the movement of the workpiece W is detected by detecting the movement of the linear scale 99.

  As the rolling process progresses, the advance angle of the workpiece W, which is the worm gear, changes, resulting in an error. Without this error, the workpiece W theoretically does not move in the axial direction as will be described later. This error occurs as the amount of step by which the workpiece moves in the axial direction. The movement of the linear scale 99 is read by a sensor, and this data is calculated as a step amount by a step amount detection program 160 (see FIG. 9).

  That is, when rolling the spiral groove on the workpiece W, the first rolling die 100 and the second rolling die 101 are gradually pushed toward the workpiece W so as to approach each other gradually. The diameter becomes smaller. For this reason, the circumferential length of the valley portion of the workpiece W is shortened when the pushing is completed, compared to when the workpiece W is pushed. In other words, the relationship between the circumferential length and the pitch of the workpiece W is different at the start of rolling and at the end of rolling.

  The circumferential length of the workpiece W can be determined by assuming that the circumferential length at the start of pushing is L and the advance angle (twisting angle) of the worm gear is constant at β. It will be shortened by the smaller amount. However, in the conventional rolling machine, the lead angle (twist angle) β of the round die does not change during this pushing operation. For this reason, a pitch deviation δP occurs between the pitch P of the workpiece W at the start of pressing and the pitch P1 of the workpiece W at the completion of pressing.

  A phenomenon occurs in which the workpiece W moves in the direction of the central axis during rolling by the pitch deviation δP. The phenomenon in which the workpiece W moves during the rolling is called “walking” of the workpiece W. In particular, this phenomenon appears remarkably in the case of a workpiece W such as a worm gear or screw having a large outer diameter and valley diameter. When the step occurs, the worm gear in the moving direction of the workpiece W due to the step, the first rolling die 100 and the second rolling die 101 in which the flank surface of the thread is a round die come into strong contact. As a result, the shape accuracy, which is the processing accuracy of the rolled processed part, is deteriorated.

  The first main spindle tilting mechanism and the second main spindle tilting mechanism described above are mechanisms for preventing steps that affect the shape accuracy of products such as worm gears and screws, and the lead angle is set to the circumferential length of the workpiece during pushing. Correct by. Although the advance angle of the workpiece to be machined changes due to the correction, the shape accuracy is not greatly affected by a small amount, and there is less error than in the case where correction is not performed, and it is well within the tolerance range.

[CNC device 120]
FIG. 9 is a block diagram showing the configuration of the CNC device 120 and each control motor. The CNC device 120 is equipped with an NC board for performing servo motor control, sequence control, etc. in an expansion slot of an NC dedicated machine or a small personal computer (hereinafter referred to as a personal computer), and has a numerical control function and a personal computer function. A so-called personal computer NC device can be used. The CNC device 120 is provided with a CPU 121 as information processing means for performing various data processing. A flash memory 123 and a RAM 124 are connected to the CPU 121 as a main storage device via a bus 122.

  The CPU 121 operates in accordance with the system program and data stored in the flash memory 123 and the program and data loaded into the RAM 124 (read into the memory). The programs loaded into the RAM 124 in this way include an OS (operating system) that is a basic program, an NC command processing program that performs processing according to each NC command of a number of NC commands, and a tool / workpiece data setting program. Measurement dimension calculation program 125, tilt angle calculation program 126, measurement data setting program 127, step amount detection program 160, display control program for displaying characters and figures on the display unit 130, and the like.

  The measurement dimension calculation program 125 is used for the rolling process based on the distance between the first rolling die 100 and the second rolling die 101 obtained by reading the linear scale 111 with a sensor, data of the detector 134, the detector 137, and the like. It is a program that calculates every moment to determine the indentation speed. This calculation result is instructed and executed by the NC interval control unit 150 by the NC machining program in the NC machining program memory 129.

  The tilt angle calculation program 126 is based on the step amount measured by the step amount detection program 160, the interval between the first rolling die 100 and the second rolling die 101 measured by the measurement dimension calculation program 125, and the like. This is a program for calculating the tilt angles of the main shaft tilt mechanism and the second main shaft tilt mechanism from time to time. This calculation result is commanded to the tilt control unit 140 of the first spindle tilt mechanism and the tilt control unit 145 of the second spindle tilt mechanism by the NC machining program in the NC machining program memory 129. The measurement data setting program 127 is a program for storing setting data for setting the dimensions of the first rolling die 100 and the second rolling die 101, the dimensions of the workpiece W, and the like in the memory.

  The step amount detection program 160 is a program for measuring the step amount from data obtained by reading the linear scale 99. A parameter memory 128 is connected to the CPU 121 via a bus 122. The parameter memory 128 stores various parameters necessary for the rolling process. The parameter memory 128 can retain the stored contents even when the power of the CNC device 120 is turned off by using a nonvolatile memory.

  Further, an NC machining program memory 129 and the like are connected to the CPU 121 via a bus 122. In the NC machining program memory 129, the workpiece W is moved to the machining position or the retracted position, the rotation speed and the rotation amount of the first rolling die 100 and the second rolling die 101 when machining the workpiece W, the first An NC machining program for performing rolling machining by sequentially controlling the tilt angle of the first spindle tilt mechanism and the second spindle tilt mechanism, the distance between both dies, and the like is stored. The NC machining program is a program in which an operator programs machining conditions, the rotational speed of each die, the moving speed, the feed amount, and the like according to the type, material, and shape of the workpiece W.

  In addition, input / output devices are connected to the CPU 121 via a bus 122. As input / output devices, a display unit 130 for displaying characters and graphics, and an input unit 131 for an operator to input data are connected to the bus 122 via an interface circuit. As the display unit 130, a CRT, an EL display panel, a liquid crystal display, or the like can be used. As the input unit 131, a keyboard, a touch panel combined with the display unit 130, or the like can be used.

  Further, a fixed disk device as an auxiliary storage device may be connected to the CPU 121 via the bus 122. In that case, various programs to be executed by the CPU 121 are stored in the fixed disk device, and these programs and the like may be loaded from the fixed disk device to the RAM 124 and the NC machining program memory 129 as appropriate.

  The CNC device 120 is connected to a servo motor 17 that rotationally drives the first rolling die 100 via a main shaft rotation control unit 132 of the first rolling die 100 and an amplifier 133. The rotation speed of the servo motor 17 is fed back to the amplifier 133 via the detector 134, and a predetermined rotation speed is maintained. Accordingly, the angular position around the axis of the first rolling die 100 is fed back from the detector 134 to the main shaft rotation control unit 132, and the desired rotational speed and angular position of the first rolling die 100 can be controlled.

  Similarly, the CNC device 120 is connected to a servo motor 38 that rotationally drives the first rolling die 100 via a rotation control unit 135 and an amplifier 136 of the second rolling die 101. The rotation speed of the servo motor 38 is fed back to the amplifier 136 via the detector 137 and controlled to a predetermined rotation speed. Therefore, the angular position around the axis of the second rolling die 101 is fed back from the detector 137 to the spindle rotation control unit 132, and the second rolling die 101 is controlled to be controlled to a desired rotational speed and angular position.

  Further, the CNC device 120 is connected to the servo motor 142 of the first spindle tilt mechanism and the servo motor 147 of the second spindle tilt mechanism for tilting the first rolling die 100 and the second rolling die 101. , Control each. That is, the CNC device 120 is connected to the servo motor 142 that controls the rotation of the first rolling die 100 through the inclination control unit 140 and the amplifier 141 of the first rolling die 100. The rotation of the servo motor 142 is fed back to the amplifier 141 via the detector 143, and a predetermined inclination angle is maintained. Therefore, the rotation angle position for inclining the first rolling die 100 is fed back from the detector 143 to the inclination control unit 140, and the first rolling die 100 is positioned at a desired rotation angle position for inclination. Is possible.

  Similarly, the CNC device 120 is connected to a servo motor 147 that controls the rotation angle position for tilting the second rolling die 101 via the tilt control unit 145 and the amplifier 146 of the second rolling die 101. Yes. The rotation of the servo motor 147 is fed back to the amplifier 146 via the detector 148 and controlled to a predetermined tilt angle. Therefore, the rotation angle position of the second rolling die 101 is fed back from the detector 148 to the tilt control unit 145, and the second rolling die 101 can be positioned at a desired rotation angle position for tilting. It is.

  Further, the CNC device 120 controls the interval between the first rolling die 100 and the second rolling die 101 by performing on / off control of the opening / closing of the servo valve 152 of the hydraulic cylinder 50. For this purpose, the CNC device 120 is connected to a servo valve 152 that controls the hydraulic cylinder 50 via a die interval controller 150 and an amplifier 151. In this example, this positioning accuracy is about 4 to 5 μm at a load of 100 KN.

The CNC device 120 is connected to a servo motor 76 that controls the position of the workpiece W via a positioning control unit 153 and an amplifier 154 of the workpiece feeding device 59. The rotation of the servo motor 76 is fed back to the amplifier 154 via the detector 155 and sent to a predetermined rolling start position. The backward position detection sensor 75 is for detecting the last backward position when the workpiece W is rolled. The advance position detection sensor 79 is for detecting the most advanced position when the workpiece W is rolled. Each drive shaft described above is controlled independently except for the synchronous rotation of the first rolling die 100 and the second rolling die 101. However, when the control function reserve capacity there Ru may be used to control synchronization.

  The linear scale 99 is arranged on the side surface of the tailstock 60 as described above. The step amount detection program 160 is a program for calculating the step amount after the start of rolling by reading the linear scale 99. The amount-of-step detection program 160 calculates the amount of deflection of the work W after the start of rolling while the work W is clamped between the tailstock 60 and the chuck base 65.

[Worm gear rolling method 1]
In the rolling machine 1 and the workpiece feeding device as described above, a rolling method of the worm gear used in the worm gear mechanism for assisting the electric power steering device of the vehicle will be described as an example. Fig.8 (a) is sectional drawing of a worm gear tooth when cut | disconnecting in the surface containing the centerline of a worm gear. The worm gear 80 has a tooth thickness 82 that is thinner than the tooth gap 83 as compared with a normal worm gear when viewed at the circumferential position of the cross section 81 including the pitch line.

  This is because the worm wheel (not shown) that meshes with the worm gear 80 is made of synthetic resin and therefore has a low mechanical strength, so that the tooth thickness of the worm wheel is increased. The tooth bottom is formed at an angle α so that two spiral inclined surfaces 84 cross each other in cross section. In this example, the angle α is 150 degrees. In the worm gear rolling method of the present invention, the pitch circle is 18 to 20 mm, the module is 1.5 to 2.0, and the number of worms is 2 or 3, and the angle α is the carbon steel for machine structure ( For example, if it is S45C etc., the range of 120 to 150 degrees is preferable from the viewpoint of smooth plastic flow. The tooth height is preferably 6 mm or less and the valley diameter is preferably 10 mm or more. If the value is out of the numerical range, a phenomenon such as the material peeling off from the surface occurs.

  Two inclined surfaces 84 intersecting at this angle α intersect, and the middle of the tooth bottom is formed with the smallest diameter. The tooth surface 88 and the inclined surface 84 are connected by a curved surface 85. Two inclined surfaces 84, that is, conical surfaces are also connected by a curved surface 86. The curved surface 86 of the worm gear having the specifications described above is preferable from the viewpoint that a radius of 1.0 to 1.5 mm in the cross section smoothes the plastic flow. The tooth bottom has a tapered convex portion when viewed from the tool side, and the plastic flow is likely to occur evenly and the rolling is smooth. In other words, since the inclined surfaces 84 whose tooth bottoms are two conical surfaces intersect each other, that is, the tip has an angle, the plastic flow of the metal distributed on both sides of the tip tends to occur and becomes uniform.

  FIG. 8B is a cross-sectional view of another worm gear tooth having a different tooth gap shape from that of FIG. The tooth bottom 87 of the tooth gap 83 shown in FIG. 8B has a shape that forms an arc of radius R1 in cross section. The shape of the tooth bottom 87 shown in FIG. 8B is formed in a circular arc on the tooth bottom 87, and a convex arc on the rolling die side, so that it is a material compared to the shape of the tooth bottom in FIG. 8A. There is an advantage that a natural plastic flow is likely to occur. The radius R1 of the root 87 of the carbon steel for machine structure is preferably 1.0 to 1.5 mm in cross section from the viewpoint of smooth plastic flow.

  FIG. 10A to FIG. 12F show the process sequence of the worm gear rolling process. At the chucking position of the material M of the solid and cylindrical workpiece W, the chuck pneumatic cylinder 69 is operated to hold the material M between the center 62 and the rotation center 66. While the rotation of the first rolling die 100 and the second rolling die 101 is stopped, the servo motor 76 is activated, the feed screw 73 is rotated to drive the slide plate 55, and the first rolling die 100 is driven. And to the second rolling die 101 side (see FIG. 10A), and further to the machining start position (see FIG. 10B).

  The first rolling die 100 and the second rolling die 101 are positioned at predetermined positions. The first rolling die 100 and the second rolling die 101 are activated so as to rotate in the same rotational direction and are rotated synchronously with each other. While the first rolling die 100 and the second rolling die 101 rotate synchronously with each other, the hydraulic cylinder 50 is driven to push in close to each other. By this pushing, the rolling process is started.

  At this time, when the lead angle of the worm gear to be processed (usually, the lead angle at the pitch point) is strong and the difference between the finished diameter and the material diameter is large, the rolling start position and the rolling end position are During the rolling process, the lead angle changes and an error occurs. This error is the process described above. When the rolling process is started, this step occurs and the slide plate 55 moves. Since the slide plate 55 is freely slidable on the feed base 53, the workpiece W being rolled is rotated in synchronism with the rotation of the first rolling die 100 and the second rolling die 101. Even if controlled, since the lead angles of the first rolling die 100 and the second rolling die 101 are constant, the lead angle of the worm gear and the amount of movement corresponding to the number of rotations, that is, the step amount, Move in the axial direction.

  When the rolling process proceeds and the slide plate 55 is fed by a predetermined amount by walking, the sensor dog 63 is detected by the advance position detection sensor 79. Alternatively, the advance position of the workpiece W by walking may be detected by the linear scale 99. When this is detected, the first rolling die 100 and the second rolling die 101 stop rotating and the pushing operation by the hydraulic cylinder 50 is stopped. Further, the first rolling die 100 and the second rolling die 101 are retracted in the direction opposite to the pushing direction. In this example, it is released by retreating about 0.05 to 0.2 mm, that is, retreating to such an extent that the rolling pressing pressure is removed.

  This retraction releases the elastic deformation of the material M and the elastic deformation of the mechanical system of the rolling machine so as to prevent the first rolling die 100 and the second rolling die 101 and the material M from contacting each other. Operation (hereinafter also referred to as “springback”). Then, the 1st rolling die 100 and the 2nd rolling die 101 are pushed in again to a rolling processing position (cutting operation), and reverse rotation is started (refer to Drawing 11 (d)). Pushing (cutting operation) is a worm gear having the specifications described above, and adopts a method of cutting while changing stepwise in 5 to 30 steps. As will be described later, rolling is performed by intermittently inserting a dwell described later at this stage as necessary.

  This rolling process by reverse rotation also corrects machining errors due to steps. Although the detailed mechanism of this error correction principle is unknown, it is estimated to make the contact between the workpiece W and the die uniform. By this rolling process, the workpiece W is moved in the axial direction opposite to the above-described rolling by the lead of the first rolling die 100 and the second rolling die 101, and the sensor dog 71 is moved backward. 75. Alternatively, the detection of the backward position of the workpiece W due to walking may be detected by the linear scale 99.

  Next, the rotation of the first rolling die 100 and the second rolling die 101 is stopped, and the hydraulic cylinder 50 is driven to start the first rolling die 100 and the second rolling die 101 from the workpiece W. Are pulled back to the retracted position (see FIG. 12E). The servo motor 76 is activated, the feed screw 73 is rotated in the reverse direction to drive the feed base 53, and the feed screw 53 is fed away from the first rolling die 100 and the second rolling die 101, and sent to the original machining start position. (Refer FIG.10 (f)). Thereafter, the same process is repeated to perform rolling. In the case of the worm gear having the specifications described above, the rotation speed of the first rolling die 100 and the second rolling die 101 is 10 to 40 rev / min, and the number of forward / reverse rotations is 15 to 50 times.

  When the first rolling die 100 and the second rolling die 101 start rolling the material M, the contact with the material M is not uniform at all the outer peripheral positions of the material M. That is, the worm gear is usually formed with two or three teeth, but the number of sets of the first rolling die 100 and the second rolling die 101 that mesh simultaneously with each other is the angular position of the outer periphery. Different. In other words, since the force with which the first rolling die 100 and the second rolling die 101 press the outer periphery of the material M is constant, the plastic flow is different at the angular position of the outer periphery, and the cross-sectional shape in the case of two teeth In the case of an ellipse or three, it is easy to form a substantially triangle.

  In order to correct this shape, the pushing operation (feeding operation) by the hydraulic cylinder 50 is stopped, and the pushing operation by the operation in which the first rolling die 100 and the second rolling die 101 approach each other is stopped ( Dwell), when the number of forward / reverse rotations is 2 to 5 times, the pitch cylinder diameter and outer diameter that are about to become elliptical and substantially triangular in the cross-sectional shape described above are rolled into a perfect circle. The With this rolling method, if the worm gear with the specifications described above is not put into the dwell process, an error of 0.2 to 0.3 mm due to an error in pitch cylinder diameter and outer diameter will be within 0.02 mm. It was possible to roll with the error of. These two to three dwell operations are intermittently placed at any stage of pushing (cutting operation) to perform rolling.

[Worm gear rolling method 2]
In the worm gear rolling method 1 described above, the error due to the workpiece step is corrected by reversing the first rolling die 100 and the second rolling die 101. However, according to the calculation result of the tilt angle calculation program 126, the servo motor 142 and the servo motor 147 are controlled to control the tilt of the first rolling die 100 and the second rolling die 101, thereby correcting the step. As described above, a method may be used in which rolling is performed while control is performed so that no step occurs or the step amount is a certain value or less.

  The present invention is not limited to the worm gear used in the electric power steering apparatus for automobiles described above and the rolling method thereof, but is also a metal worm gear and its rolling process for power transmission for other industrial machines and consumer machines. Applicable to the method.

FIG. 1 is a three-dimensional external view showing the entire rolling machine for rolling a worm gear according to the present invention. FIG. 2 is a partial cross-sectional view of FIG. 1 taken along the line II-II. FIG. 3 is a front view of the rolling machine. FIG. 4 is a plan view of the rolling machine. FIG. 5 is a left side view of the second die moving table. FIG. 6 is a plan view of a rolling machine showing a schematic mechanism of the die feeding device. FIG. 7 is a side view of a workpiece feeding device for supporting and feeding a workpiece as a workpiece. FIG. 8A is a cross-sectional view of the tooth profile of the worm gear, and FIG. 8B is a cross-sectional view of another worm gear tooth having a different tooth groove shape in FIG. 8A. FIG. 9 is a block diagram showing the configuration of the CNC device, each control motor, and the like. FIGS. 10A to 10B are process diagrams showing processes when the worm gear is rolled. FIG.11 (c)-(d) is process drawing which shows a process when rolling a worm gear. FIGS. 12E to 12F are process diagrams showing processes when the worm gear is rolled.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rolling machine 2 ... Bed 3 ... 1st guide rail 4 ... 1st dice movement support stand 6 ... 1st die move stand 8 ... 1st round die support stand 20 ... Drive mechanism support stand 25 ... 2nd dice move stand 26 ... 2nd guide rail 29 ... 2nd round die support base 40 ... Connecting shaft 59 ... Work feed device 100 ... 1st rolling die 101 ... 2nd rolling die 142 ... Servo motor 120 ... CNC device 100 ... 1st rolling Dice 101 ... Second rolling die

Claims (5)

A plurality of cylindrical dies for rolling and processing with a cylindrical material at the center;
Die rotation driving means for synchronously rotating the dice with each other;
Material support means for rotatably supporting the material;
A worm gear rolled by a worm gear rolling method by a rolling machine provided with pushing means for pushing the dies close to each other,
The worm gear is characterized in that the shape of the tooth bottom between the teeth of the worm gear is such that a top portion in which an arc is formed in a cross section including the axis of the worm gear is formed. A plurality of cylindrical dies for rolling and processing with a cylindrical material at the center;
Die rotation driving means for synchronously rotating the dice with each other;
Material support means for rotatably supporting the material;
A worm gear rolled by a worm gear rolling method by a rolling machine provided with pushing means for pushing the dies close to each other,
The shape of the tooth bottom between the teeth of the worm gear is such that an arc is formed in a cross section including the axis of the worm gear. In claim 1 or 2,
The die of the rolling machine is
A worm gear characterized in that the worm gear is composed of two units arranged substantially at the center of the four guides and arranged in parallel with the rotation axis. In claim 1 or 2,
The rolling machine is provided with a main shaft tilting means that rotates around an axis perpendicular to the rotation axis of the die. In claim 1 or 2,
The worm gear has a cross section including the axis of the worm gear, and the tooth thickness of the worm gear is smaller than the interval between the tooth bottoms.

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