JP2009063075A - Ball screw and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw whose heat treatment quality is stable and its manufacturing method. <P>SOLUTION: A nut 5 of the ball screw 1 comprising a screw shaft 3, the nut 5, and balls 9 is manufactured in the following processes: First, thread grooves 5a are formed on the inside circumferential surface of a cylindrical member and machined into a shape of the nut 5. After fixing a steel piece made of the same steel constituting the nut 5 near the thread groove surface of the nut 5, heat treatment is provided on the nut 5. When fixing, the steel piece is brought into contact with the nut 5 and integrated. When heat treated, the steel piece is separated from the nut 5 to analyze hardness, metallographic structure, etc. and to check the result of heat treatment provided on the steel piece. Since the result of the heat treatment of the steel piece and the thread groove surface of the nut 5 can be regarded as identical, the result of heat treatment provided on the thread groove surface can be checked. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ball screw having stable heat treatment quality and a method for manufacturing the same.

Ball screws used in injection molding machines, machine tools, and the like have been used more severely in recent years. Therefore, the ball screw used for these applications is required to have a more stable life.
Carburizing and quenching is generally used as the heat treatment applied to ball screw nuts, but the contents of the heat treatment applied to the surface of the thread groove of the nut (hereinafter referred to as the thread groove surface) include rolling peeling life and wear. It is very important for the life and performance of ball screws such as.

However, since the thread groove surface of the nut of the ball screw is formed on the inner peripheral surface of the cylindrical nut, and the flow of the carburizing atmosphere entering the inside of the nut is not constant, it is difficult to manage the heat treatment conditions. In addition, since the nut has many kinds of sizes and shapes, and it is necessary to increase the quenching depth, it is not easy to perform heat treatment with stable contents without variation.
As a method for managing the heat treatment quality, for example, a method for reliably managing heat treatment conditions such as atmosphere, treatment time, cooling gradient, etc. (see Patent Document 1), and non-destructive inspection of products after heat treatment using ultrasonic waves There is a method (see Patent Document 2).
Japanese Patent Laid-Open No. 10-8136 JP 2006-242580 A

However, although the methods of Patent Documents 1 and 2 can prevent a complete heat treatment failure (almost not hardened or the like), there is a possibility that a slight lack of hardness and the quality control of the metal structure cannot be sufficiently performed.
After heat-treating the nut, it may be possible to inspect the hardness and metal structure and inspect the result of the heat treatment, but in these investigations it is necessary to destroy the nut. It was difficult to investigate.

For this reason, the dummy sample for quality inspection is usually heat-treated with the product and the content of the heat treatment applied to the nut is estimated by investigating this, but the dummy sample has the same shape and size as the nut. Therefore, the result of the heat treatment was not exactly the same as the nut. In addition, the atmosphere in the heat treatment furnace is not necessarily uniform, and the content of the heat treatment may vary depending on the location, so the result of the heat treatment of the product may differ from the above estimation. Therefore, it is not easy to uniformly manage the heat treatment quality of a large number of nuts.
Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a ball screw with stable heat treatment quality and a method for manufacturing the same.

  In order to solve the above problems, the present invention has the following configuration. That is, in the ball screw manufacturing method according to the first aspect of the present invention, a steel piece made of the same steel as the steel constituting the nut is fixed in the vicinity of the thread groove surface of the nut, and then the heat treatment is performed on the nut. A heat treatment step to be performed; an analysis step for confirming a result of the heat treatment applied to the thread groove surface of the nut by analyzing the steel piece separated from the nut; and the nut for confirming the result of the heat treatment; An assembly step for assembling the screw shaft and the ball is provided.

A ball screw manufacturing method according to a second aspect of the present invention is the ball screw manufacturing method according to the first aspect, wherein the steel slab is placed in a recess or a through-hole opened in the inner peripheral surface of the nut. It is characterized by being fixed.
Furthermore, the ball screw manufacturing method according to claim 3 of the present invention is the ball screw manufacturing method according to claim 2, wherein the recess or the through hole is a ball of the screw groove on the inner peripheral surface of the nut. It is characterized by opening in the part which does not run.

  Further, in the ball screw manufacturing method according to claim 4 of the present invention, the cylindrical member that is a material of the nut is formed with a recess or a through hole that opens to the inner peripheral surface, and the cylindrical member is configured therein. After fixing a steel piece made of the same steel as the steel to be processed, a processing step of forming a screw groove on the inner peripheral surface of the cylindrical member to form a nut so that the concave portion or the through hole opens on the screw groove surface A heat treatment step for heat-treating the nut, an analysis step for confirming a result of the heat treatment performed on the thread groove surface of the nut by analyzing the steel piece separated from the nut, and the heat treatment An assembly step of assembling the nut, the screw shaft, and the ball, the results of which are confirmed.

Furthermore, the manufacturing method of the ball screw of Claim 5 which concerns on this invention is a manufacturing method of the ball screw as described in any one of Claims 1-4. WHEREIN: Thermal conductivity is provided between the said nut and the said steel piece. It is characterized by interposing a substance.
Furthermore, the ball screw according to claim 6 of the present invention has a screw shaft having a helical screw groove on the outer peripheral surface, and a screw groove facing the screw groove of the screw shaft on the inner peripheral surface. A ball screw comprising: a nut screwed to the screw shaft via a plurality of balls that are movably loaded in a spiral ball rolling path formed by a groove. It is manufactured by the method for manufacturing a ball screw according to claim 1.

  The ball screw of the present invention has a stable heat treatment quality and a long life. In addition, the ball screw manufacturing method of the present invention can manufacture a ball screw having a stable heat treatment quality and a long life.

  DESCRIPTION OF EMBODIMENTS Embodiments of a ball screw and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view of a ball screw according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA of the ball screw of FIG. FIG. 3 is a cross-sectional view of the main part showing the peripheral portion of the end portion of the return tube. In the following drawings, the same or corresponding parts are denoted by the same reference numerals.

  As shown in FIGS. 1 to 3, the ball screw 1 includes a screw shaft 3 having a helical screw groove 3 a on the outer peripheral surface, and a helical screw groove 5 a facing the screw groove 3 a of the screw shaft 3 on the inner peripheral surface. And a plurality of balls 9 loaded in a freely rolling manner on a spiral ball rolling path 7 formed by both screw grooves 3a, 5a. Then, when the nut 5 and the screw shaft 3 screwed to the screw shaft 3 through the ball 9 are relatively rotated, the screw shaft 3 and the nut 5 are relatively moved in the axial direction through the rolling of the ball 9. It is supposed to move. The cross-sectional shape of the thread grooves 3a, 5a may be an arc shape or a gothic arc shape.

  A part of the outer peripheral surface of the nut 5 is cut flat, and a return tube 15 bent in a substantially U shape is fixed on a flat portion 13 parallel to the axial direction by a tube presser 17. That is, the nut 5 is provided with a pair of through holes 19, 19 that open to the flat portion 13 and communicate with the screw groove 5 a of the nut 5 (open to the screw groove surface). Are inserted into the through-holes 19, 19 from the plane portion 13 side. A central portion of the return tube 15 located outside the through holes 19 and 19 is disposed on the flat portion 13. Two or more return tubes may be attached to one nut, and in that case, two or more pairs of through holes 19 are provided.

  The ball 9 rolling in the ball rolling path 7 is circulated through the return tube 15. That is, the ball 9 moves in the ball rolling path 7 and turns around the screw shaft 3 a plurality of times, and then returns at the end point of the ball rolling path 7 (intersection of the return tube 15 and the ball rolling path 7). The tube 15 is scooped into the return tube 15 from one end (opening) of the tube 15. The scooped up ball 9 passes through the return tube 15 and is returned to the starting point of the ball rolling path 7 from the other end (opening) of the return tube 15. In this way, the ball 9 rolling in the ball rolling path 7 is infinitely circulated by the return tube 15 that connects the starting point and the end point of the ball rolling path 7, so that the screw shaft 3 And the nut 5 can continuously move relative to each other.

  The nut 5 of the ball screw 1 is manufactured as follows. First, the thread groove 5 a is formed on the inner peripheral surface of the cylindrical member that is the material of the nut 5, and the nut 5 is processed. A steel piece (not shown in FIGS. 1 to 3) made of the same steel as the nut 5 is fixed in the vicinity of the thread groove surface of the nut 5 (the surface of the thread groove 5a), and then the nut 5 Is subjected to heat treatment. Since a heat treatment must be applied to the thread groove surface, a steel piece cannot be fixed to the thread groove surface. Therefore, the steel piece is fixed as close to the thread groove surface as possible. When fixing, it is preferable that the steel piece is brought into close contact with the nut 5 and integrated so that the result of the heat treatment between the steel piece and the thread groove surface is as identical as possible.

  After the heat treatment, the steel piece is separated from the nut 5 and the hardness, metal structure, etc. are analyzed to confirm the result of the heat treatment applied to the steel piece. Since the result of the heat treatment of the steel piece and the thread groove surface of the nut 5 can be regarded as the same, the result of the heat treatment applied to the thread groove surface can be confirmed. In general, in heat treatment of nuts, it is not easy to carry out heat treatment with stable contents without any variation, and the heat treatment quality of the obtained nuts may be different one by one. If it manufactures by, the heat processing quality of each nut can be confirmed from the analysis result of a steel piece. A nut 5 having a desired heat treatment quality is selected from the heat-treated nuts, and this, the screw shaft 3 and the ball 9 are assembled to complete the ball screw 1.

  According to such a method, a ball screw having stable heat treatment quality can be manufactured. Therefore, the ball screw 1 obtained by such a method has a long life and a stable life. Therefore, such a ball screw 1 can be suitably used for an injection molding machine or a machine tool. It is also suitable as a ball screw for controlling the raising and lowering of control rods of nuclear power generation facilities that require particularly high quality assurance and the movement of aerospace flaps. However, the use of the ball screw of the present invention is not limited to the above.

The part for fixing the steel piece is not particularly limited as long as it is in the vicinity of the thread groove surface on the inner peripheral surface of the nut 5, but in order to confirm more typical heat treatment quality, the longitudinal direction of the nut 5 is used. It is preferable to arrange in the center. Or you may distribute a steel piece in the several site | part of a longitudinal direction.
Further, in order to make the heat treatment result of the steel slab the same as that of the nut 5, it is necessary to make the heating rate and cooling rate of the steel slab the same as that of the nut 5. It is necessary to make it. Therefore, although a device is required for the method of fixing the steel slab, for example, a method of fixing the steel slab in a recess or a through hole that opens on the inner peripheral surface of the nut 5 is suitable.

  The recessed portion or the through hole may be newly provided to fix the steel piece, but the tapped hole for attaching the through hole 19 for inserting the end portion of the return tube 15 or the tube pressing member 17 for fixing the return tube 15. (Through hole) may be used. The method for circulating the ball 9 is not limited to the return tube method as described above, and other methods may be used. In the case of other methods, the steel piece may be fixed to a through hole into which a circulation part corresponding to the return tube 15 is inserted or a through hole to which a fixing member for fixing the circulation part is attached.

  FIG. 4 shows an example in which a steel piece is fixed to the through hole 19 into which the end of the return tube 15 is inserted. A steel piece 20 having substantially the same shape as the return tube 15 is inserted into the through hole 19 and fixed, and heat treatment is performed. Since the steel pieces 20 and the nuts 5 have different heat capacities, if the steel pieces 20 and the nuts 5 are not sufficiently adhered, the heat treatment results of the two pieces will not be the same. Therefore, it is necessary that the steel piece 20 and the nut 5 be integrated as close as possible. If both are integrated, the portion of the steel piece 20 exposed in the vicinity of the thread groove surface has the same heat treatment quality as the thread groove surface. The steel piece 20 may be fixed using a fixing member having a function similar to that of the tube presser 17 described above.

  Further, the thread groove 5a of the nut 5 is a track on which the ball 9 travels. However, the ball 9 does not travel the whole, and there is a portion where the ball 9 does not travel. For example, in the ball screw 1 provided with two ball rolling paths 7 as shown in FIG. 2, the portion between the start point of one ball rolling path 7 and the end point of the other ball rolling path 7 is This is a portion where the ball 9 does not travel. A steel piece may be fixed to a portion where the ball 9 does not travel.

  FIG. 5 is an example in which a steel piece 20 is fixed in a tap hole 22 (a through hole opened in a thread groove surface of a portion where the ball 9 does not travel) for attaching a tube presser 17 for fixing the return tube 15. . A tap is formed around the steel piece 20 and is fixed to the tap hole 22 by this. Furthermore, you may fix using a volt | bolt. As shown in FIG. 6, the steel piece 20 itself may be formed into a bolt shape. Further, a recess may be provided in a portion where the ball 9 does not travel instead of a through-hole such as the tap hole 22, and the steel piece 20 may be fixed therein.

  FIG. 7 shows an example in which the steel piece 20 is fixed to a portion where the ball 9 does not travel when the tap hole 22 cannot be formed in the nut 5 as shown in FIGS. In the case of FIG. 7, a long steel piece 20 is inserted from a through hole 19 into which a circulation part such as a return tube 15 is inserted, bent near the opening of the through hole 19, and one end of the steel piece 20 is nut 5. Is arranged along the screw groove 5a. In addition, the other end of the flat tube 13 for fixing the return tube 15 is bent so that the steel piece 20 is substantially U-shaped and the steel piece 20 is fixed to the nut 5. Thereby, the one end part of the steel piece 20 is fixed to the part of the thread groove surface of the nut 5 where the ball 9 does not travel.

Furthermore, in order for the steel pieces 20 and the nuts 5 to have the same heat treatment results, it is necessary to bring the steel pieces 20 and the nuts 5 into close contact with each other as much as possible. Examples of methods for strengthening the integration of the steel piece 20 and the nut 5 include the following.
FIG. 8 is a diagram for explaining a method that can be adopted when the steel piece 20 is fixed to the through hole 19 into which the return tube 15 is inserted. Since the edge of the flat portion 13 of the nut 5 is chamfered along the bent return tube 15, when the cylindrical steel piece 20 is inserted into the through hole 19, A space is formed between the chamfered portion. When a wedge-shaped member 24 is inserted there, a force directed radially outward (in the direction indicated by the arrow in FIG. 8) is applied to the steel piece 20, so that the steel piece 20 is brought into close contact with the nut 5 to enhance integration. be able to. The wedge-shaped member 24 may be pressed and fixed from above using a presser 26. The material of the wedge-shaped member 24 is preferably copper.

  FIG. 9 is a diagram for explaining a method suitable for the SRC type (type using resin circulation parts) often used in injection molding machines. In the SRC type ball screw, since the through hole 19 into which the circulating component is inserted has a long cross-sectional shape, the shape of the steel piece 20 is slightly smaller than the through hole 19 and the steel piece 20 is inserted into the through hole 19. A wedge-shaped member 24 may be inserted into the gap formed. Then, as in the case of FIG. 8, the wedge-shaped member 24 applies a force to the steel piece 20 (plan view of the through-hole 19 opening in the flat portion 13 of FIG. 9A from above) (FIG. 9 (). In b), the force in the direction indicated by the arrow) is applied, so that the steel piece 20 can be brought into close contact with the nut 5 to enhance the integration.

  As shown in FIGS. 5 and 6, when the steel piece 20 formed with the tap is screwed into the tap hole 22 and fixed, the steel piece 20 is strongly attached to the nut 5 by adjusting the torque applied to the steel piece 20. Integration can be strengthened by close contact. In addition, as shown in FIG. 7, when the long steel piece 20 is fixed in a substantially U shape, between the other end portion of the steel piece 20 protruding on the flat surface portion 13 and the flat surface portion 13. A wedge-shaped member may be inserted. By doing so, the wedge-shaped member applies a force directed radially outward (upward in FIG. 7) to the steel piece 20, so that the steel piece 20 can be closely attached to the thread groove surface of the nut 5 to enhance the integration. it can.

  Furthermore, you may manufacture the nut 5 of the ball screw 1 of this embodiment as follows. First, a concave portion or a through-hole that opens to the inner peripheral surface is formed in a cylindrical member that is a material of the nut 5, and a steel piece made of the same steel as that constituting the cylindrical member is fixed therein. The recessed portion or the through hole may be newly provided to fix the steel piece, but the tapped hole for attaching the through hole 19 for inserting the end of the return tube 15 or the tube presser for fixing the return tube 15 ( You may divert a through-hole. Moreover, the above-mentioned method shown to FIGS. 4-9 can be used for the fixing method of a steel piece.

  Next, the thread groove 5a is formed in the inner peripheral surface of the cylindrical member to which the steel piece is fixed, and the nut 5 is processed. In that case, the thread groove 5a is formed in the internal peripheral surface of a cylindrical member so that a recessed part or a through-hole may open in a thread groove surface. When the nut 5 is subjected to heat treatment, the steel piece is separated from the nut 5 and the hardness, metal structure, etc. are analyzed to confirm the result of the heat treatment applied to the steel piece. Since the result of the heat treatment of the steel piece and the thread groove surface of the nut 5 can be regarded as the same, the result of the heat treatment applied to the thread groove surface can be confirmed. A nut 5 having a desired heat treatment quality is selected from the heat-treated nuts, and this, the screw shaft 3 and the ball 9 are assembled to complete the ball screw 1.

According to such a method, since the shape of the end portion of the steel piece facing the opening of the recess or the through hole is formed along the shape of the thread groove surface, the heat treatment conditions of the thread groove surface and the steel piece are The closer the heat treatment results are, the closer the same.
Although the heat treatment quality of the steel slab may be investigated after the heat treatment by this method, the steel slab may be taken out after grinding the thread groove surface simultaneously with the nut (finishing process), and the heat treatment quality may be investigated. By doing in this way, it becomes possible to investigate the heat treatment quality in consideration of the machining allowance after the heat treatment.

When the steel piece 20 is fixed to the nut 5, a heat conductive material may be interposed between the steel piece 20 and the nut 5. By doing so, the heat conduction between the steel slab 20 and the nut 5 becomes good and the heating rate and the cooling rate of both are likely to be the same, so the results of the heat treatment of both are likely to be the same. Although the kind of heat conductive substance is not specifically limited, For example, a soft substance like copper is preferable.
In the present embodiment, the case where the nut 5 is made of steel has been described. However, the present invention is not limited to this, and the screw groove surface is hardened by heat treatment when the nut 5 is made of titanium, for example. Applicable to the case.

It is a top view of one embodiment of a ball screw concerning the present invention. It is AA sectional drawing of the ball screw of FIG. It is principal part sectional drawing which shows the peripheral part of the edge part of a tube. It is sectional drawing which shows the state which fixed the steel piece to the through-hole which inserts a return tube. It is sectional drawing which shows the state which fixed the steel piece in the tap hole. It is sectional drawing which shows the state which fixed the bolt-shaped steel piece in the tap hole. It is sectional drawing which shows the state which fixed the steel piece to the part which a ball | bowl does not drive | work among screw thread surfaces. It is sectional drawing explaining the method of strengthening integration with a steel piece and a nut using a wedge-shaped member. It is sectional drawing explaining another method of strengthening integration with a steel piece and a nut using a wedge-shaped member.

Explanation of symbols

1 Ball screw 3 Screw shaft 3a Screw groove 5 Nut 5a Screw groove 7 Ball rolling path 9 Ball 15 Return tube 19 Through hole 20 Steel piece 22 Tap hole

Claims (6)

In the vicinity of the thread groove surface of the nut, after fixing a steel piece made of the same steel as the steel constituting the nut, a heat treatment step of performing a heat treatment on the nut,
An analysis step of confirming a result of the heat treatment applied to the thread surface of the nut by separating and analyzing the steel piece from the nut;
An assembling process for assembling the nut, the screw shaft, and the ball that have confirmed the result of the heat treatment;
A method of manufacturing a ball screw, comprising:   The ball screw manufacturing method according to claim 1, wherein the steel piece is fixed in a recess or a through-hole that opens on an inner peripheral surface of the nut.   3. The method of manufacturing a ball screw according to claim 2, wherein the recess or the through hole is opened in a portion of the screw groove on the inner peripheral surface of the nut where the ball does not travel. After forming a recess or a through-hole that opens in the inner peripheral surface of the cylindrical member that is a material of the nut, and fixing a steel piece made of the same steel as the steel constituting the cylindrical member, the recess Alternatively, a processing step of forming a screw groove on the inner peripheral surface of the cylindrical member so that the through hole opens on the screw groove surface and forming a nut,
A heat treatment step for heat treating the nut;
An analysis step of confirming a result of the heat treatment applied to the thread surface of the nut by analyzing the steel piece separated from the nut;
An assembling step of assembling the nut, the screw shaft, and the ball that have confirmed the result of the heat treatment;
A method of manufacturing a ball screw, comprising:   The method of manufacturing a ball screw according to any one of claims 1 to 4, wherein a thermally conductive material is interposed between the nut and the steel piece.   A screw shaft having a helical thread groove on the outer peripheral surface, and a thread groove facing the screw groove of the screw shaft on the inner peripheral surface, is transferred to a spiral ball rolling path formed by the both screw grooves. A ball screw comprising: a nut screwed onto the screw shaft via a plurality of balls loaded in a freely movable manner. The ball screw is manufactured by the ball screw manufacturing method according to any one of claims 1 to 5. A ball screw characterized by that.

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