JP2006090437A - Piece type ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piece type ball screw equipped with a piece member having contradictory characteristics of strength, durability and toughness. <P>SOLUTION: The piece type ball screw is equipped with a screw shaft 1 provided with a spiral thread groove 2 on the outer surface, a nut 3 externally fitted to the screw shaft 1 and provided with a spiral thread groove 4 on the inner surface, a plurality of balls 5 accommodated in a rolling passage formed by two facing thread grooves, an arm 9 fitted to a piece window 6 bored in a barrel part of the nut 3, provided with a coupling groove 8 taking the rolling passage as a revolving passage and positioned by being engaged with the screw groove 4 of the nut 3, and a piece member 7 integrally provided with a guide wall 11 caulked and fixed to both side edges of the piece window 6. The piece member 7 is molded by MIM, formed by precipitation hardening stainless steel having toughness allowing plastic deformation of the guide wall 11, and hardened by solution heat treatment, wherein the surface hardness is set to 30 HRC or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ball screw used in various machine tools such as an electric discharge machine and a tapping center, or an electric power steering or actuator of an automobile, and in particular, improves the strength and durability of a piece member that is a ball circulation component. It relates to the Takoma type ball screw.

  The ball screw is composed of a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, and both opposing screw grooves. It is equipped with a large number of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circuit path, and is used as a motion conversion mechanism that linearly moves the screw shaft by rotating the nut, for example. ing.

  Generally, there are various types of ball screws having different ball circulation mechanisms, one of which is called a piece type. This piece-type ball screw has a threaded groove connection path, and a circulation piece member having a rolling path as a circular path is attached to the nut. This piece type ball screw has an advantage that the configuration is relatively simple and can be configured in a compact manner.

  A typical example of such a piece-type ball screw is shown in FIG. In this piece type ball screw, the nut body 50a of the rotary nut 50 is provided with a piece member fitting opening 51 penetrating the inner and outer peripheral surfaces, and the piece member 52 is fitted into the piece member fitting opening 51 from the inner diameter side. It is.

  The piece member 52 is formed with a connecting groove 52a for connecting adjacent circumferential portions of the inner screw groove 53, and engages with the inner screw groove 53 of the rotary nut 50 so that the piece member 52 is pivoted with respect to the nut body 50a. A pair of arms 54 and 54 for positioning in a direction are integrally provided. The pair of arms 54, 54 are provided at both ends of the piece member 52 in the axial direction so as to protrude opposite to each other in the circumferential direction, and are formed in a semicircular cross-sectional shape that fits into the inner screw groove 53. Here, the portion of the inner screw groove 53 with which the arm 54 is engaged becomes a non-ball circulating portion.

  Both side edges in the circumferential direction of the rotary nut 50 in the piece member 52 are recessed portions 55 whose outer diameter surfaces are recessed relative to other portions, and the side surfaces rising from these recessed portions 55 to the outer diameter side and facing the circumferential direction of the piece member 52. A pair of guide walls 56 are provided along. The opening 51 for fitting the piece member of the nut main body 50a is provided with an engaging step portion 57 at the opening edge of a pair of opposed inner side surfaces, and the width of the opening side portion is slightly wider than the engaging step portion 57. ing.

The piece member 52 is fitted into the piece member fitting opening 51 of the nut main body 50a from the inner diameter side, the pair of arms 54 are engaged with the inner thread groove 53, and the guide wall 56 is plastically deformed to deform the nut main body 50a. Fixed to. The fixing by the plastic deformation is performed by caulking and fixing the guide wall 56 to a pair of opposed inner side surfaces of the piece member fitting opening 51. Specifically, by securing the guide wall 56 to the engagement step portion 57 and engaging, the certainty of fixing the piece member 52 is achieved. The piece member 52 with the arm 54 is used to prevent the piece member 52 from being detached and positioned by the arm 54, to obtain high-precision and high-strength performance, and to easily and reliably fix the piece member 52. Can do.
JP 2001-289301 A

  In this conventional piece type ball screw, the piece member 52 is caulked and fixed to the nut body 50a by plastically deforming a pair of guide walls 56 formed on the outer diameter surface thereof. In general, it is formed of raw material of about 80 to 130 Hv so that cracking does not occur during the caulking operation.

  However, when such a piece type ball screw is used for an electric power steering or an actuator of an automobile, a vibration load often acts on the rotary nut 50 or a screw shaft (not shown). When the vibration load acts as a moment load, the load distribution inside the ball screw collapses and the revolution speed of the ball 59 in the rotary nut 50 varies. As a result, when the ball 59 passes through the piece member 52, the connection There is a possibility that a large stress is generated in the groove 52a.

  In such a situation, it is conceivable to increase the surface hardness of the piece member 52 and increase the strength in order to improve the durability of the piece member 52 by improving the pressure resistance and wear resistance, but as described above, It is difficult with the piece member 52 fixed to the nut body 50a by plastic deformation.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a piece-type ball screw provided with a piece member having conflicting characteristics of strength, durability, and toughness.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a spiral thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft and spirally formed on the inner peripheral surface. And a plurality of balls accommodated in a rolling path formed by opposing screw grooves, and a piece window drilled in a body portion of the nut, and the rolling A piece member in which a connecting groove having a circulation path as a circulation path is formed, an arm that engages and positions with a screw groove of the nut, and a guide wall that is clamped and fixed to both side edges of the piece window In the piece-type ball screw, the guide wall of the piece member is plastically deformable and has toughness that can secure the crimped portion strength, and at least the surface hardness of the connecting groove is set to 30 HRC or more by heat treatment. The configuration is adopted.

  In this way, in the piece-type ball screw in which the piece member is crimped and fixed to the nut, the guide wall of the piece member is plastically deformable and has toughness that can secure the strength of the crimped portion, and at least the connecting groove is formed by heat treatment. Since the surface hardness is set to 30 HRC or more, the connecting groove in which a large stress is generated has sufficient pressure resistance and wear resistance, and ensures the toughness of the guide wall serving as a caulking portion. It is possible to prevent cracks and the like from occurring when fixing the nut to the nut. Accordingly, it is possible to provide a piece type ball screw provided with a piece member having conflicting characteristics such as strength, durability and toughness.

  Preferably, as in the invention described in claim 2, if the piece member is a sintered metal formed by MIM, the desired shape can be easily and accurately obtained even if the shape is high and the shape is complicated.・ Can be molded to dimensions.

  In addition, as in the invention described in claim 3, the piece member is formed of a carburized material, the surface is hardened by carburizing and quenching, and the guide wall is annealed to have a surface hardness of 15 to 23 HRC. In addition, as in the invention described in claim 4, it may be formed of precipitation hardened stainless steel and hardened by solution heat treatment.

  Further, as in the invention according to claim 5, the piece member is formed of medium carbon steel, and the surface hardness is set in a range of 15 to 23 HRC by tempering in advance, and at least the connection groove is obtained by induction hardening. The surface hardness may be set to 30 HRC or more.

  The piece ball screw according to the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, A plurality of balls accommodated in a rolling path formed by opposing screw grooves, and a connecting groove that is fitted to a piece window drilled in a body portion of the nut and has the rolling path as a circulation path. In a piece type ball screw comprising: an arm that is formed and positioned by engaging with a screw groove of the nut; and a piece member that is integrally formed with guide walls that are fastened and fixed to both side edges of the piece window. Since the guide wall of the piece member is plastically deformable and has toughness that can secure the caulking portion strength, and at least the surface hardness of the connecting groove is set to 30 HRC or more by heat treatment, a large stress is generated. The connecting groove has sufficient pressure resistance and wear resistance, and To ensure the toughness of the guide wall to be caulked portion, such as cracking and the like when fixing the bridge member to the nut can be prevented from occurring. Accordingly, it is possible to provide a piece type ball screw including a piece member having conflicting characteristics such as strength, durability, and toughness.

  A screw shaft having a spiral thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and a roller formed by both opposing screw grooves. A plurality of balls accommodated in the moving path and a piece window formed in the trunk of the nut, and a connecting groove having the rolling path as a circulation path are formed, and a thread groove of the nut is formed. In a piece type ball screw provided with an arm for engaging and positioning, and a piece member integrally formed with guide walls fixed by crimping on both side edges of the piece window, the piece member is formed by MIM, The guide wall is made of precipitation hardened stainless steel having a toughness capable of plastic deformation and is hardened by a solution heat treatment, and its surface hardness is set to 30 HRC or more.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A and 1B show an embodiment of a piece-type ball screw according to the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a longitudinal sectional view. FIG. 2 is a plan view of a piece member serving as a circulation member, and FIG. 3 is a cross-sectional view.
The screw shaft 1 has a spiral screw groove 2 formed on the outer periphery, and a spiral screw groove 4 corresponding to the screw groove 2 is formed on the inner periphery of a nut 3 fitted on the screw shaft 1. A large number of balls 5 are accommodated between the screw grooves 2 and 4.

  The cross-sectional shape of each of the thread grooves 2 and 4 may be a circular arc shape or a Gothic arc shape, but here a Gothic arc shape that allows a large contact angle with the ball 5 and a small axial clearance can be set. Is formed. Thereby, the rigidity with respect to an axial load becomes high, and vibration can be suppressed.

  An elliptical piece window 6 that penetrates the inner and outer peripheral surfaces and cuts out a part of the thread groove 4 is formed in the body portion of the cylindrical nut 3. Is fitted. A connecting groove 8 is formed on the inner side of the piece member 7 so as to connect adjacent ones of the screw grooves 4, and the ball 5 rolls between the connecting groove 8 and the substantially one part of the screw groove 4. Constitutes the road. A large number of balls 5 interposed between the inner and outer screw grooves 2 and 4 in the rolling path roll along the screw grooves 2 and 4, and are guided by the connecting grooves 8 of the piece members 7. The mountain passes over the mountain and returns to the adjacent screw groove 4 and rolls along the screw grooves 2 and 4 again.

  As shown in FIG. 2, the connecting groove 8 of the member 7 is formed in an S shape so as to smoothly connect the adjacent thread grooves 4 of the nut 3. Therefore, the connecting groove 8 is connected to the screw groove 4 so that the opening edge 8a at both ends thereof matches the window opening edge 6a of the adjacent screw groove 4 of the nut 3 (see FIG. 1B). Further, the depth of the connecting groove 8 is set to such a depth that the ball 5 can exceed the thread of the screw groove 2 in the screw shaft 1 in the connecting groove 8.

  The piece member 7 is provided with arms 9 formed in a substantially bowl shape on both sides thereof, and is engaged with the thread groove 4 of the nut 3 via a predetermined radial clearance. The arm 9 is provided in order to prevent the piece member 7 from being axially positioned with respect to the nut 3 and to prevent the piece member 7 from coming out of the piece window 6 in the radial direction. Further, both side edges in the circumferential direction of the piece member 7 are formed as recessed portions 10 whose outer diameter surfaces are recessed from the other portions, and a pair of guide walls 11 rising from the recessed portions 10 toward the outer diameter side are provided in the circumferential direction of the piece member 7. It is provided opposite to.

  The ball 5 is assembled by attaching the piece member 7 to the piece window 6 of the nut 3 from the inner diameter side of the nut 3, and then applying the nut 3 from the shaft end of the screw shaft 1. The nut 3 is rotated while being sequentially inserted into the screw shaft 1, and the nut 3 is moved to the screw shaft 1. Besides this, after the piece member 7 is mounted on the piece window 6 of the nut 3, the ball 5 may be similarly inserted using a temporary shaft.

  The piece member 7 is made of a sintered alloy prepared by adjusting a metal powder into a plastic shape and molded by an injection molding machine. In this injection molding, first, metal powder and a binder made of plastic and wax are kneaded with a kneader, and the kneaded product is granulated into pellets. The granulated pellets are molded by so-called MIM (Metal Injection Molding), which is supplied to a hopper of an injection molding machine and pushed into a mold in a heated and melted state. A sintered alloy formed by such an MIM can be easily and accurately formed into a desired shape / dimension even if it has a high workability and a complicated shape.

  In this embodiment, as the metal powder, a material that can be subsequently carburized and quenched, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, and Cr (chromium) is 1.1 wt%. Cu (copper) is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the remainder is Fe (iron). The SCM 415 can be exemplified. In addition to this, it may be a precipitation hardening stainless steel SUS630 in which C is 0.07 wt%, Cr is 17 wt%, Ni is 4 wt%, Cu is 4 wt%, and the remainder is Fe or the like. This SUS630 can appropriately increase the surface hardness by solution heat treatment, and can ensure toughness and high hardness.

  When the piece member 7 is formed of a carburizing material such as SCM415, the piece member 7 is hardened by carburizing and quenching so that the surface hardness is in the range of 30 to 40 HRC, and using a high-frequency temper device, FIG. And the guide wall 11 is annealed, and the surface hardness is set in the range of 15 to 23 HRC.

  Here, if the surface hardness of the hardened layer by carburizing and quenching is less than 30 HRC, the pressure resistance and wear resistance of the connecting groove 8 are insufficient, and if it exceeds 40 HRC, the heat treatment deformation of the piece member 7 becomes undesirably large. . Further, if the surface hardness of the guide wall 11 by annealing is less than 15 HRC, the strength of the caulking portion is insufficient, and if it exceeds 23 HRC, cracks or the like may occur during caulking, which is not preferable.

  On the other hand, when the piece member 7 is formed of precipitation hardening stainless steel such as SUS630, the surface hardness is set to be 30 HRC or more by the solution heat treatment. This SUS630 has a feature that the alloy element is easily solid-solutioned by heating to a predetermined temperature and then rapidly cooling.

  Since the piece member 7 is made of a sintered alloy formed by molding these carburized materials or precipitation hardened stainless steel by MIM, at least the connecting groove 8 where a large stress is generated has sufficient pressure resistance and wear resistance. Moreover, the toughness of the guide wall 11 serving as the crimping portion is high, and the occurrence of cracks and the like can be prevented when the piece member 7 is fixed to the nut 3. Accordingly, it is possible to provide a piece type ball screw provided with a piece member having conflicting characteristics such as strength, durability and toughness.

  As a material of the piece member 7, medium carbon steel such as S45C may be used other than the above-described sintered alloy formed by MIM. In this case, the surface hardness can be set in a range of 15 to 23 HRC by tempering in advance, and a hardened layer having a surface hardness of 30 HRC or more can be formed on at least the surface of the connecting groove 8 by induction hardening. Thereby, like the above-mentioned material, the contradictory characteristics, such as strength, durability, and toughness, can be ensured.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The piece type ball screw according to the present invention can be applied to various type machine tools such as an electric discharge machine and a tapping center, or a piece type ball screw used for an electric power steering or an actuator of an automobile.

(A) is a top view which shows one Embodiment of the piece-type ball screw which concerns on this invention. (B) is a longitudinal cross-sectional view same as the above. It is a top view which shows the piece member which concerns on this invention. It is sectional drawing of the piece member which concerns on this invention. (A) is a fracture | rupture front view which shows the conceptual structure of the rotation nut in the conventional piece type | formula ball screw. (B) is a broken side view of the above.

Explanation of symbols

1 ... Screw shaft 2, 4 ... Screw groove 3 ... Nut 5 ... Ball 6 ... Frame window 6a ... Window opening edge 7 ... Frame member 8 ...・ Connecting groove 8a ・ ・ ・ ・ ・ ・ ・ ・ ・ Opening edge 9 ・ ・ ・ ・ ・ ・ ・ ・ Arm 10 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Recessed part 11 ・ ・ ・ ・ ・ ・ ・ ・ Guide Wall 50... Rotating nut 50a... Nut body 51... Member 52a ... Connection groove 53 ... Internal thread groove 54 ... Arm 55 ... Recess 56・ ・ ・ ・ ・ ・ ・ ・ Guide wall 57 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ engaging step 58 ・ ・ ・ ・ ・ ・ ・ ・ ・Tricks section 59 ......... ball

Claims (5)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls housed in a rolling path formed by opposing screw grooves;
An arm that is fitted to a piece window formed in the trunk portion of the nut and has a rolling groove that is a circular route, and that engages and positions the screw groove of the nut, and the piece In a piece type ball screw provided with a piece member integrally formed with a guide wall that is caulked and fixed to both side edges of the window,
The piece type is characterized in that the guide wall of the piece member is plastically deformable and has toughness that can secure the crimped portion strength, and at least the surface hardness of the connecting groove is set to 30 HRC or more by heat treatment. Ball screw.   The piece type ball screw according to claim 1, wherein the piece member is made of a sintered metal formed by MIM.   The piece according to claim 1 or 2, wherein the piece member is formed of a carburized material, the surface is hardened by carburizing and quenching, and the guide wall is set to a surface hardness of 15 to 23 HRC by annealing. Ball screw.   The piece type ball screw according to claim 1 or 2, wherein the piece member is formed of precipitation hardening stainless steel and is hardened by a solution heat treatment.   The piece member is formed of medium carbon steel, and the surface hardness is set in a range of 15 to 23 HRC by tempering in advance, and at least the surface hardness of the connecting groove is set to 30 HRC or more by induction hardening. Item 1. The piece type ball screw according to Item 1.

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