JP4937214B2 - nut - Google Patents

Description

  The present invention relates to a nut having a female screw for fastening another member to a metal plate with a bolt, and more particularly to a nut formed integrally with the metal plate.

  Patent Document 1 describes that a bolt is fastened to a nut integrated with a washer and two metal plates of a member to be fastened are fixed. In this case, the nut is separate from the metal plate, and it is necessary to make a hole in the metal plate and temporarily fix the nut to the hole.

  On the other hand, when manufacturing a vehicle, a nut may be welded to bolt fastening parts, such as a door hinge part of a frame. In such a nut welding, accurate positioning is difficult, and the welding operation is complicated.

  Patent Document 2 proposes an apparatus capable of forming various internal threads on a workpiece, but is unsuitable for a thin plate such as an automobile frame.

  In the patent document 3, the present applicant has proposed an internal thread machining apparatus that does not require welding of a nut. In this processing apparatus, the processing tool is pressed against the metal plate while rotating, and a hole is formed in the metal plate by the reduced diameter portion. Further, while the processing tool is inserted into the hole, the processing tool is further rotated and inserted into the hole by the tap portion. Form an internal thread. In addition, by overlaying with a filler, the present invention can be applied to a thin plate such as an automobile frame, and a bush having an internal thread can be formed in one step, which is preferable.

Japanese Patent Laid-Open No. 8-200333 JP-A-1-306124 JP 2005-329528 A

  By the way, when a nut is welded to a metal plate, the nut originally has a sufficient strength and a sufficient fastening strength can be obtained with respect to a bolt. The formed female screw does not necessarily have sufficient strength, and sufficient experimentation and inspection are required.

  In addition, when a nut integrally formed with such a metal plate is applied to a vehicle, vibration is applied to the nut for a long time, and there is a concern that the bolt may loosen, and the fastening torque is particularly increased. Alternatively, it is necessary to provide predetermined locking means.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a nut capable of preventing loosening of a bolt.

  The nut according to the present invention is a nut integrally formed with a metal plate, and has a metal structure different from the screw portion between a base material portion constituting the metal plate and a screw portion having a female screw, and the screw It has a hardness slope part whose hardness is lower than the part and whose hardness decreases from the screw part toward the base material part.

  By providing such a hardness inclined portion, the screw portion has sufficient strength so that the bolt can be reliably screwed together, and even if vibration is applied to the base material portion or the screw portion, the hardness inclined portion The vibration can be absorbed by elasticity, and the bolt can be prevented from loosening.

  The thread portion is composed mainly of bainite, the base material portion is composed mainly of cementite and ferrite, and the hardness inclined portion is refined as the structure approaches the cementite and the base material portion. The main component may be ferrite. Here, the main component means that the component contains approximately 95% or more.

  At least an inner diameter side portion of the hardness inclined portion may have a convex shape toward the protruding direction of the screw portion. Thereby, the effect | action as a spring of a hardness inclination part is further exhibited.

  The hardness inclined portion may be smoothly connected to the metal plate, and the screw portion may protrude from the hardness inclined portion.

  According to the nut according to the present invention, by providing the hardness inclined portion, the screw portion has sufficient strength and the bolt is reliably screwed together, and vibration is applied to the base material portion or the screw portion. In addition, vibration can be absorbed by the elasticity of the hardness inclined portion, and loosening of the bolt can be prevented.

  Hereinafter, embodiments of the nut according to the present invention will be described with reference to FIGS. The bush 14 as a nut according to the present embodiment is obtained by a female thread machining apparatus 10 and a female thread machining method using the female thread machining apparatus 10. First, the internal thread processing apparatus 10 and the internal thread processing method will be described.

  As shown in FIG. 1, the internal thread processing device 10 is a unit type device for forming a bush 14 at a predetermined position in a frame (metal plate) 12 before the main coating, and is detachable from the tip of the robot 16. Is provided. A female screw 15 (see FIG. 12) is formed in the bush 14. The robot 16 is an industrial articulated type, and the internal thread machining apparatus 10 can be set at an arbitrary position and at an arbitrary position within the operation range of the robot 16. Thereby, the internal thread processing apparatus 10 is arrange | positioned so that the door hinge part 12a and the bumper beam part 12b in the flame | frame 12 may be opposed, for example, and the bush 14 can be formed in these locations.

  The frame 12 is carried on the transfer line 18 and temporarily stopped in the vicinity of the robot 16, and an accurate position is confirmed by the camera 19. The frame 12 is processed to form the bush 14 by the female thread processing device 10, and then transferred to the next process station along the transfer line. Thereafter, the unprocessed next frame 12 is placed near the robot 16. Is brought in.

  The robot 16 and the female thread machining apparatus 10 are controlled by a controller 20. The controller 20 controls a robot drive unit 22 that operates the robot 16 based on predetermined teaching data, and a motor control that drives a lift motor (advance / retreat drive unit) 36 and a spindle motor (rotation drive unit) 52 in the internal thread machining apparatus 10. Unit 24, filler feeding control unit 26 for feeding filler 48 (see FIG. 2), arc current control unit 28 for radiating an arc from TIG torch (arc heater 46), and female thread processing device And a cooling control unit 29 for cooling 10 predetermined portions. Further, the controller 20 can confirm the position of the frame 12 and the bushing processing position P based on the image obtained from the camera 19.

  As shown in FIG. 2, the female thread machining apparatus 10 is configured with a base unit 30 and a lifting unit 32 that moves up and down with respect to the base unit 30 as a base. The robot 16 is connected to the side surface of the base unit 30.

  The base unit 30 includes a base body 34, a lifting motor 36, a ball screw 38, a ball nut 40, a guide rail 42, a filler feeder 44, and an arc heater (heating unit) 46 (for example, a TIG torch). ). The base body 34 is a vertically long structure and is provided with a lifting motor 36 at the upper end. The ball screw 38 is connected to the elevating motor 36 and extends downward, and is held rotatably. The guide rail 42 is provided at the end of the base body 34 so as to face the lifting unit 32 and extend in the vertical direction. The guide rail 42 and the ball screw 38 are parallel.

  The ball nut 40 is screwed into the ball screw 38 and connected to the lifting unit 32, and the lifting unit 32 can be lifted and lowered under the rotating action of the lifting motor 36. The amount of lifting of the lifting unit 32 is fed back using a sensor (not shown).

  The filler feeder 44 is directed to the bushing processing position P. The filler feeder 44 feeds the filler 48 toward the bushing processing position P under the action of the filler feeding control unit 26. The arc heater 46 is fixed to the lower end portion of the base body 34 by a bracket 47, performs an arc discharge to the bush machining position P under the action of the arc current control unit 28, and heats the bush machining position P. The bracket 47 is provided with a slide mechanism 47 a that moves the arc heater 46.

  The elevating unit 32 includes an elevating base body 50, a spindle motor 52, a rail engaging portion 54, a rotating rod 56, a chuck 58, a processing tool 60, and a cooling unit (cooling portion) 62. Fins may be provided in the portion cooled by the cooling unit 62 so as to increase the area and enhance the air cooling effect.

  The elevating base body 50 is engaged with the guide rail 42 so as to be movable up and down by two upper and lower rail engaging portions 54, and a predetermined portion is connected to the ball nut 40. A spindle motor 52 is provided at the upper end of the elevating base body 50 so as to face downward. The spindle motor 52 is configured to be able to control the rotation speed under the action of the motor control unit 24, and can rotate in synchronization with the elevating motor 36.

  The rotating rod 56 is connected to the spindle motor 52 and extends downward, and is held rotatably. A chuck 58 for holding the processing tool 60 is provided at the lower end of the rotating rod 56.

  The cooling unit 62 is provided at an intermediate portion of the rotating rod 56, and includes a bearing block 64 that supports the rotating rod 56. The cooling unit 62 is supplied with compressed air from the air supply port 66, and can cool the rotating unit 56 and the bearing block 64 by spraying the compressed air. The compressed air sprayed is discharged to the outside as it is. The air supply port 66 has a plurality of nozzles, for example. The air supply port 66 is provided with an adjustment valve 67 capable of adjusting the air supply amount and opening and closing the flow path. Cooled compressed air is supplied to the regulating valve 67.

  According to such an air cooling type cooling unit 62, a supply line for a cooling medium, a recovery line, and the like are unnecessary and simple.

  As shown in FIG. 3, the processing tool 60 includes a reduced diameter portion 70 provided at the tip, a cylindrical portion 72 provided continuously above the reduced diameter portion 70, and a continuous upper portion thereof. A tapped portion 74. The reduced diameter portion 70 has a conical shape with a diameter reduced downward, and the largest diameter portion of the upper end portion of the reduced diameter portion 70 has the same diameter as the cylindrical portion 72. The reduced diameter portion 70 is a portion that forms the hole 100 (see FIG. 7) in the frame 12, and the cylindrical portion 72 acts so that the shape of the hole 100 is stabilized, and these reduced diameter portion 70 and cylindrical portion 72. Are integrated as a lower hole forming portion 76. The tap part 74 is a part for forming a female screw in the hole 100, and is provided with a spiral protrusion 74 a having a diameter larger than that of the cylindrical part 72. Depending on the design conditions and processing conditions, the tap portion 74 may reach the portion directly above the reduced diameter portion 70 or a part of the upper end of the reduced diameter portion 70 without providing the cylindrical portion 72.

  Further, the reduced diameter portion 70 may be formed with a dull process for enhancing the friction effect with the frame 12, a super hard material coating for increasing the strength, or the like.

  The tap part 74 and the pilot hole forming part 76 are configured to be detachable, and either one can be individually replaced depending on the degree of wear. Of course, the tap part 74 and the pilot hole forming part 76 may be integrated. The processing tool 60 is made of metal such as high-speed tool steel, for example.

  The internal thread machining apparatus 10 has a plurality of negative electrode plates 69 (see FIG. 5) arranged around the bush machining position P. Further, instead of the negative electrode plate 69, a ground wire 69a (see FIG. 17) may be provided on a cart, a jig, a processing table or the like that fixes the workpiece.

  Next, a female thread machining method for forming the bush 14 (see FIG. 12) at the bush machining position P of the frame 12 using the female thread machining apparatus 10 configured as described above will be described. In the following description, it is assumed that processing is executed in the order of the indicated step numbers.

  In step S <b> 1 (cooling process) in FIG. 4, under the action of the cooling control unit 29, the cooled compressed air is supplied to the cooling unit 62 to cool the rotating rod 56 and the bearing block 64. This cooling process is continuously performed during a plurality of times of internal thread machining, and the machining tool 60 is indirectly cooled via the chuck 58. Thus, according to indirect cooling via the chuck 58, the machining tool 60 has a simple structure that does not require a cooling means, and the machining tool 60 can be easily replaced.

  Since the processing tool 60 is at room temperature during the first internal thread processing, the cooling step may be omitted and cooling may be started from the second processing.

  This step S1 is a process for appropriately cooling the processing tool 60 heated in step S6 described later, and the processing tool 60 is kept at 600 ° C. or lower, for example, about 500 ° C. This cooling process does not require strict temperature control, and a constant amount of air is continuously blown onto the rotating rod 56 and the bearing block 64 based on experiments or experience, and the processing tool 60 is 600 ° C. or less immediately before step S6. It should be so that.

  According to the results of experiments conducted by the present inventor, even when there is a certain change in room temperature, the cooling unit 62 cools the rotating rod 56 and the bearing block 64 without using feedback control and in accordance with the special room temperature. Even if no adjustment is made, it has been confirmed that a bush 14 having a suitable female screw 15 can be obtained if a constant amount of air is continuously blown onto the rotating rod 56 and the bearing block 64.

  In step S <b> 2, the robot 16 is operated under the action of the robot drive unit 22, the female screw machining apparatus 10 is brought close to the frame 12, and the negative electrode plate 69 is brought into contact. The negative electrode plate 69 is not necessary when a ground is provided on a carriage, a jig, a machining base, etc., for fixing the workpiece. At this time, a preset bushing processing position P is arranged on the axis on which the processing tool 60 advances and retreats.

  In step S3 (heating step), as shown in FIG. 5, the filler 48 is fed from the filler feeder 44 under the action of the filler feeding control unit 26 to build up, and the arc current control unit 28 Under the action, a high voltage is applied to the arc heater 46 to generate an arc A. The arc heater 46 slides to the vicinity of the bushing processing position P, generates an arc at the bushing processing position P, preheats and softens it. The bushing position P is quickly heated by the arc A. After a predetermined time has elapsed, the application of the high voltage is stopped and the arc A is extinguished. The heating of the frame 12 and the filled filler 48 at the bushing processing position P is performed, for example, until reaching 1200 ° C.

  After a predetermined amount of filler 48 has been fed, the remainder is pulled back slightly and retracted into the filler feeder 44. When the plate thickness at the bush processing position P is thick, the build-up by supplying the filler 48 may be omitted.

  At the bush processing position P at this time, as shown in FIG. 6, an appropriate built-up portion 110 and a heat-affected portion 112 around the built-up portion 110 are formed. The heat affected zone 112 is a location where the surface color has changed due to the temperature rising due to heating.

  The diameter R1 of the heat-affected zone 112 is preferably about 1.6 to 1.7 times the screw portion upper radius R2 (see FIG. 12) described later.

  In step S4, the process waits until the bushing position P is naturally cooled to an appropriate temperature. At this time, the appropriate temperature at the bushing processing position P is a temperature of the austenite region or higher, for example, about 900 ° C. In step S3 of the previous stage, heating to 900 ° C. may be stopped without heating to 1200 ° C. However, once heating to about 1200 ° C., which is higher than that, and cooling is performed, 900 ° C. in a shorter time. And the heat affected zone 112 can be secured reasonably wide.

  In step S <b> 5, as shown in FIG. 7, the processing tool 60 is advanced without rotation to form the hole 100. Initially, the hole 100 is formed by the distal end portion of the reduced diameter portion 70, and then the diameter is increased by the conical surface of the reduced diameter portion 70, and the cylindrical portion 72 is inserted to stabilize the shape.

  At this time, since the bushing processing position P is about 900 ° C., the processing tool 60 is 600 ° C. or less, for example, 500 ° C., so the bushing processing position P is rapidly cooled and is in the same state as so-called quenching. . If the cooling time is about 0.5 sec, it will be understood that a CCT curve (continuous cooling transformation diagram) 86 is led to the upper part of the bainite region 88 as shown in FIG. FIG. 8 is a continuous cooling state diagram in carbon steel of C0.13% and Mn 0.56%, but when using a metal having a composition other than this, the cooling conditions are set based on the continuous cooling state diagram of the composition. You only have to set it.

  In the rapid cooling process of the frame 12 by the processing tool 60, the temperature of the processing tool 60 rises as the temperature of the frame 12 decreases, and the frame 12 becomes about 600 ° C. to 700 ° C. while both are in contact with each other. In practice, it is continuously performed not only in step S5 but also in the next step S6. A portion of about 600 ° C. to 700 ° C. is a ferrite region, and passes through the bainite region during subsequent air cooling. In rapid cooling to about 600 ° C. to 700 ° C., the cooling equipment is simple.

  Moreover, although a cooling facility enlarges, working efficiency can be improved by making it cool directly to a bainite area at the time of forced cooling.

  During this time, the processing tool 60 receives a heat of the frame 12 and a slight temperature rise occurs. However, since the processing tool 60 is continuously cooled by the cooling unit 62 via the chuck 58, the temperature rises excessively. The thermal expansion is suppressed and high processing accuracy can be maintained.

  In step S <b> 6, after the cylindrical portion 72 is inserted into the hole 100 without rotation, the ball screw 38 and the processing tool 60 are rotated by the spindle motor 52. Further, the number of rotations of the lift motor 36 is controlled, and the processing tool 60 is synchronized so as to advance by the pitch t (see FIG. 7) of the spiral protrusion 74a of the tap portion 74 while the processing tool 60 makes one rotation. As a result, as shown in FIG. 9, tapping is performed so that the spiral protrusion 74 a is screwed into the hole 100, and the bush 14 having the female screw 15 is formed.

  The time during which forced cooling is performed in steps S6 and S7 (that is, the time during which the processing tool 60 is in contact with the work, the time from when the hole is formed and tapping is performed, and the processing tool 60 is removed) For example, about 1.5 sec.

  In addition, after step S5, since the processing tool 60 moves to the next step S6 while being inserted into the hole 100, these steps S5 and S6 can be regarded as substantially one process. Of course, it is not necessary to replace the machining tool 60 between step S5 and step S6.

  In step S <b> 7, the spindle motor 52 and the lifting / lowering motor 36 are rotated in the reverse direction, and the processing tool 60 is extracted from the bush 14. At this time, the spindle motor 52 and the lift motor 36 are synchronized so that the machining tool 60 moves backward by the pitch t while the machining tool 60 makes one rotation. After the tap portion 74 is extracted from the bush 14, the processing tool 60 may be retracted at a high speed.

  By extracting the processing tool 60 from the bush 14, the forced cooling by the processing tool 60 is completed. The processing tool 60 is continuously cooled by the cooling unit 62 thereafter.

  In step S8 (heat radiation step), the bush 14 is naturally air-cooled. As a result, the cooling gradually proceeds like the portion below the bending point 90 in the CCT curve 86 in FIG. 8, and the frame 12 is cooled through the bainite region 88. Thereby, bainite precipitates on the frame 12 and a sufficiently high internal thread is obtained. Bainite is a structure in which fine cementite is dispersed in ferrite and has high hardness and toughness. It does not matter whether the CCT curve 86 passes through the pearlite region 96 or not.

  In addition, since the metal plate is once heated to the austenite region, it is possible to respond flexibly and depending on the design conditions, various heat treatments can be performed on the metal structure. In FIG. 8, reference numerals 92, 94, 96, and 98 denote an austenite region, a ferrite region, a pearlite region, and a martensite region in this order.

  In step S8, heat dissipation of the bush 14 may be promoted by heat absorption means other than the processing tool 60 (heat dissipation process).

  Thereafter, the internal thread machining apparatus 10 is separated from the frame by operating the robot 16.

  In step S9 (which may be parallel to step S8), it is confirmed whether or not an unprocessed bush remains. If there is an unprocessed bush, the female thread processing apparatus 10 is moved to the next bush processing position P. Then, the process returns to step S2, and the machining is continued by the same procedure.

  If all the bushings 14 have been processed, the cooling unit 62 is stopped (step S10), and the processing shown in FIG.

  As described above, in the female thread machining apparatus 10 and the female thread machining method, by providing the arc heater 46 and the cooling unit 62, when the machining tool 60 is inserted into the heated bush machining position P, the bush machining position P is rapidly cooled. As a result, the tissue becomes hard and a high-strength female screw 15 can be formed.

  Further, the processing tool 60 is pressed to the bush processing position P without rotation, and the hole 100 is formed at the bush processing position P by the reduced diameter portion 70. Thereafter, the processing tool 60 is rotated, and the processing tool 60 is moved to the hole 100. Further, the internal thread 15 is formed in the hole 100 by the tap portion 74. Thereby, the bush 14 can be formed substantially in one step, and the working efficiency can be improved.

  The cooling unit 62 is not limited to the air cooling type, but may be a liquid cooling type like a cooling unit 62a shown in FIG. The cooling unit 62a absorbs heat of the rotating rod 56 by flowing liquid (water, oil, etc.) through a flow path 180 provided in the rotating rod 56 through a rotating joint (not shown), and dissipates heat with a radiator (not shown). And circulating. According to such a liquid cooling type cooling unit 62a, a high cooling effect can be obtained.

  As the processing tool 60, for example, a processing tool 60a shown in FIG. 11 may be used. The cylindrical portion 72 and the tap portion 74 in the processing tool 60a are the same as the processing tool 60, and are different in that a tip portion 80 is provided in a portion corresponding to the reduced diameter portion 70. The distal end portion 80 is obtained by adding a spiral protrusion 80 a to the reduced diameter portion 70.

  The spiral direction of the spiral protrusion 80a and the spiral direction of the spiral protrusion 74a in the tap portion 74 are the same direction, but may be reversed depending on the design conditions.

  Next, the bush 14 that is formed by the female thread machining apparatus 10 and the female thread machining method and has the female thread 15 in the inner cavity will be described.

  FIG. 12 is a cross-sectional cut model of the bush 14. As shown in FIG. 12, the bush 14 has a threaded portion 150 and a heat affected zone 112. The outer side of the heat affected zone 112 is a base material portion 114. The screw part 150, the heat-affected part 112, and the base material part 114 have different structures, and can be identified by the difference in cross-sectional color. A female screw 15 is formed on the inner surface of the screw portion 150.

  The threaded portion 150 is a structure based mainly on the filler 48 that has been built up, and is considered to be a portion that has a considerably large thermal effect, and contains a large amount of bainite (containing 95% or more of bainite as a main component). ) The threaded portion 150 has a shape protruding downward, and the boundary with the heat-affected zone 112 is substantially bent at the upper connecting portion 150a and the lower connecting portion 150b.

  The heat-affected zone 112 is considered to be a portion in which some filler 48 is mixed with the frame 12 as a base material and is further affected by heat to some extent, and spherical ferrite is mixed in fine ferrite ( 95% or more is contained as a main component of cementite and ferrite whose structure becomes finer as it approaches the base material part). In the heat-affected zone 112, the metal structure of the ferrite becomes finer as the inner screw portion 150 is approached.

  The heat affected zone 112 has a shape inclined slightly downward toward the inner screw portion 150, and is connected to the base material portion 114 smoothly and substantially horizontally.

  That is, at least the inner diameter side portion of the heat affected zone 112 has a convex shape toward the protruding direction of the screw portion 150 (downward in FIG. 12), and the effect of the spring of the heat affected zone 112 is further exhibited. Is done. This can be easily understood from the fact that, for example, the bellows-shaped member is easier to bend than the linear member.

  The base material portion 114 is a portion in which the structure is hardly changed from the original frame 12, and spherical cementite is mixed in coarse ferrite (containing 95% or more of cementite and ferrite as main components).

  The screw portion upper diameter R2 and the screw length L of the screw portion 150 are in an inversely proportional relationship, and when one becomes longer, the other becomes shorter. As for the strength of the threaded portion 150, it is preferable to make the thread length L longer than increasing the threaded portion upper diameter R2. Therefore, the threaded portion upper diameter R2 does not need to be excessively thick, and is preferably about 1.3 to 1.5 times the diameter R3 (see FIG. 3) of the processing tool 60. It is good to adjust by.

  Further, the heat affected zone 112 is a portion connecting the base material portion 114 and the screw portion 150 and desirably has appropriate toughness and elasticity. As described above, the diameter R1 of the heat affected zone 112 is the upper portion of the screw portion. About 1.6 to 1.7 times the diameter R2 is preferable.

  As will be described later, the heat-affected zone 112 has a tenacious property, and exerts a spring action when the bolt 168 is fastened to the screw portion 150. In addition, the heat affected zone 112 is harder than the base material portion 114, and the base material portion 114 is deformed so as to follow the elastic deformation of the heat affected zone 112.

  Here, as shown in FIG. 13, when the heat-affected zone 112 is excessively wide, the base material portion 114 is pushed downward, and a sufficient contact area between the upper plate 170 and the frame 12 can be secured. Disappear.

  On the other hand, when the diameter R1 of the heat affected zone 112 is about 1.6 to 1.7 times the upper diameter R2 of the screw portion, the base material portion 114 is pushed downward as shown in FIG. Is suppressed, and a sufficient contact area between the upper plate 170 and the frame 12 can be secured.

  The inventor conducted a Vickers hardness test on the hardness of the bush 14 at a pitch of 0.5 mm along the test path 154. The test path 154 is a radial direction linear path from the innermost part 154 a of the screw part 150 in the bush 14 to the part 154 b sufficiently separated from the heat affected part 112 in the base material part 114. The boundaries of the screw part 150, the heat affected part 112, and the base material part 114 are defined as a boundary 154c and a boundary 154d. The test results are shown in FIG.

  As understood from FIG. 15, the hardness is extremely high in the section from the inner side 154 a to the boundary 154 c corresponding to the screw part 150. This is because the screw part 150 is composed mainly of bainite. In the vicinity of the boundary 154c, a steeply inclined line 156 is shown, and the hardness rapidly decreases to about 60%.

  In the section from the boundary 154c to the boundary 154d corresponding to the heat affected zone 112, a gentle slope line 158 is shown, and the hardness is further increased to about 60% from the threaded portion 150 toward the base material portion 114 with reference to the boundary 154c. Without increasing at a continuous and moderate rate.

  In the section after the boundary 154d corresponding to the base material portion 114, the hardness tends to decrease slightly, but is almost constant.

  Thus, while the hardness of the screw portion 150 is high and the hardness of the base material portion 114 is low, the hardness of the heat-affected zone 112 having an appropriate width therebetween shows a gradual change depending on the distance. This is considered to be based on the fact that the metal structure of the ferrite becomes finer toward the inner side in the heat affected zone 112.

  According to such a composition, the screw portion 150 has sufficient strength, and the bolt can be reliably screwed together. Even if vibration is applied to the base material portion 114 or the screw portion 150, the heat-affected zone 112 is obtained. Vibration can be absorbed by this elasticity, and the effect of preventing loosening between the bolt and the female screw 15 can be obtained. In particular, the heat-affected zone 112 is lower in hardness than the screw portion 150 and has a hardness that decreases from the screw portion 150 toward the base material portion 114. Therefore, the heat-affected zone 112 has a characteristic in which a plurality of elastic springs are combined. In addition, vibrations of various frequencies can be absorbed. Further, since the heat affected zone 112 is gently connected to the hardness of the threaded portion 150 and the base material portion 114, there is no local stress concentration.

  As described above, according to the bush 14 as a nut according to the present embodiment, the threaded portion 150 has sufficient strength by providing the heat-affected portion 112 as the hardness inclined portion, and the screw 168 is screwed. As a result, the vibration can be absorbed by the elasticity of the heat-affected zone 112 and the bolt 168 can be prevented from loosening even if the base material portion 114 or the screw portion 150 is vibrated.

  Instead of the cooling unit 62 described above, a cooling unit 300 shown in FIG. 16 may be applied. The periphery of the bearing block 64 is covered with a box 302, and compressed air cooled from an inlet pipe 304 is supplied to the box 302 to cool the bearing block 64 and the rotating rod 56, thereby indirectly cooling the processing tool 60. Can do. By covering the bearing block 64 with the box 302, the cooled compressed air does not diffuse unnecessarily and contacts the object to be cooled with high density, so that efficient cooling is performed. The air that has cooled the bearing block 64 and the like in the box 302 is discharged from an outlet pipe 306 provided on the opposite side of the inlet pipe 304. Thereby, the compressed air is not discharged into the air, and the sound is quiet. In the box 302, a guide wall that appropriately sets a path through which the compressed air passes may be provided so that efficient cooling is performed. As shown in FIG. 17, instead of the negative electrode plate 69, the ground wire 69 a may be provided on a processing table 310, a jig, a carriage, or the like that fixes the frame 12 or a part including the bush processing position P. As a result, the frame 12 is electrically connected to the negative electrode, and the negative electrode plate 69 is not required on the processing machine side, and facilities and work are simplified.

  Of course, the nut according to the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.

It is an abbreviated functional block diagram of a robot provided with a female thread processing device and a controller. It is a cross-sectional side view of an internal thread processing apparatus. It is a disassembled perspective view of a processing tool. It is a flowchart which shows the procedure of the internal thread processing method. It is explanatory drawing which shows a mode that it heats with an arc. It is a perspective view of the build-up part and heat influence part provided in the bush processing position. It is explanatory drawing which shows a mode that a hole is formed in a bush processing position. It is a continuous cooling state figure in carbon steel of C0.13% and Mn0.56%. It is explanatory drawing which shows a mode that an internal thread is formed by a tap part. It is a schematic cross section of a liquid cooling type cooling unit. It is a side view of the processing tool which concerns on a modification. It is a cross-section cut model of a bush. It is a figure which shows a deformation | transformation of a heat influence part and a base material part when a volt | bolt is screwed together to a thread part, when a heat influence part is excessively wide. It is a figure which shows the deformation | transformation of a heat affected zone and a base material part when a volt | bolt is screwed together in a thread part when a heat affected zone is moderately wide. It is a graph which shows the test result of the Vickers hardness test done about the bush. It is a side view of the cooling unit which concerns on a modification. It is a schematic diagram of the processing stand provided with the earth wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Female thread processing apparatus 12 ... Frame 14 ... Bush (nut) 15 ... Female screw 30 ... Base unit 32 ... Lifting unit 34 ... Base body 36 ... Lifting motor 38 ... Ball screw 40 ... Ball nut 44 ... Filler feeder 46 ... Arc heating Machine 52 ... Spindle motor 54 ... Rail engaging part 56 ... Rotating rod 58 ... Chuck 60, 60a ... Processing tool 62, 62a, 300 ... Cooling unit 70 ... Reduced diameter part 72 ... Cylindrical part 74 ... Tap part 88 ... Bainite area

Claims (4)

In the nut formed integrally with the metal plate,
Between the base material part constituting the metal plate and the screw part having the female screw, the metal part has a metal structure different from that of the screw part, the hardness is lower than that of the screw part, and the direction from the screw part toward the base material part. A nut having a hardness inclined portion that decreases in hardness. The nut according to claim 1,
The threaded portion is composed mainly of bainite,
The base material part is composed mainly of cementite and ferrite,
The said hardness inclination part is comprised as a main component the cementite and the ferrite which a structure | tissue refines | miniaturizes so that the said base material part is approached. The nut according to claim 1 or 2,
At least an inner diameter side portion of the hardness inclined portion has a convex shape toward a protruding direction of the screw portion. In the nut according to any one of claims 1 to 3,
The hardness inclined portion is smoothly connected to the metal plate,
The nut, wherein the threaded portion protrudes from the hardness inclined portion.

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