JP2004050250A - Ball screw rolling method and shaft with ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for controlling the length of an incomplete threaded portion formed in a rolling starting portion not longer than a permissible value only by the through-feed rolling. <P>SOLUTION: A rolling method of performing through-feed rolling of a ball screw on a columnar stock 18 between roll dies 10, is characterized in that a columnar part 14 and truncated conical parts 12 and 16 continuous to both ends of the columnar part 14 with the diameter thereof reducing outwardly are provided on the roll dies 10. The distance between the roll dies 10 is reduced in a positional relationship in which a columnar part 2 for form rolling the ball screw of the columnar stock 18 for form rolling of the ball screw overlaps the columnar part 14 of the roll dies in a range of 10 to 65% of the length in the axial direction of the columnar part 14 of the roll die. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for rolling a ball screw. In particular, the present invention relates to a technology for rolling a short incomplete thread portion of a ball screw.
[0002]
2. Description of the Related Art FIG. 1 shows an example of a shaft used in a power steering device of an automobile. A small-diameter cylindrical portion A, a ball screw portion B, and a rack tooth portion C are formed on the shaft in order from left to right in FIG. The rack teeth C of the shaft are engaged with a pinion provided at the lower end of the column shaft to form a rack and pinion mechanism. The ball screw portion B is housed in a ball screw nut rotated by a motor. When the driver operates the steering wheel, the column shaft rotates, and the shaft and the pinion mechanism reciprocate the shaft in the axial direction. As the shaft reciprocates, the wheels are steered. When the motor rotates the ball screw nut, the ball screw nut applies an axial force to the ball screw portion B, thereby assisting the reciprocation of the shaft.
[0003]
When a shaft is manufactured, an intermediate material having a small-diameter cylindrical portion A, a cylindrical portion for rolling a ball screw larger in diameter than the small-diameter cylindrical portion A, and a rack tooth portion C is manufactured. Then, the ball screw rolling cylindrical portion of the intermediate material is through-feed rolled from the small-diameter cylindrical portion A side to the rack tooth portion C side by a roll die to complete the ball screw portion B.
The roll dice is provided with a cylindrical portion and, at both ends of the cylindrical portion, a truncated conical portion whose diameter continuously decreases outward. When starting through-feed rolling, the distance between the two roll dies is reduced by the positional relationship in which the ball screw rolling cylindrical portion of the intermediate material overlaps in the axial direction of the roll die cylindrical portion. When the distance between the two roll dies is reduced and the ball screw rolling cylinder is sandwiched between the roll dies, the intermediate material is sent in the axial direction, and the ball screw B is attached to the ball screw rolling cylinder. Rolled.
[0004]
The amount by which the ball screw rolling cylindrical portion overlaps the roll die cylindrical portion (hereinafter, referred to as “overlap amount”) when starting through feed rolling is the axial length of the roll die cylindrical portion. 80% or more.
When the overlap amount is set to 80% or more of the axial length of the roll die cylindrical portion, the rolling start portion (the end portion on the side of the small diameter cylindrical portion A) of the ball screw rolling cylindrical portion becomes a roll die cylindrical portion. The distance that the roll die cylindrical portion moves in the axial direction in contact with the portion is reduced, and the roll die is rolled only by a small portion of the cylindrical portion. Therefore, as shown in FIG. 2, it is inevitable that an incomplete thread portion having a length e + f is formed at the rolling start portion. Therefore, the ball screw rolling cylindrical portion is extended by the length e toward the small-diameter cylindrical portion A side and rolled. After rolling, the range of e is removed by cutting or the like, and a small-diameter cylindrical portion A is finished. In addition, f is the length of the incomplete screw portion allowed for the ball screw portion B.
[0005]
According to the above-mentioned technology, extra rolling must be performed by the length e, and the portion must be removed later by cutting or the like. It takes time and cost to manufacture.
The present invention has been made in view of the above-described problem, and provides a technique capable of suppressing the length of an incomplete thread portion formed at a rolling start portion to an allowable value or less only by rolling. The task is to
[0006]
The invention as defined in claim 1 is a method of through-feed rolling a ball screw on a cylindrical material between roll dies. In this manufacturing method, a roll portion is provided with a cylindrical portion, and a truncated conical portion whose diameter is continuously reduced outward at both ends of the cylindrical portion, and a cylindrical material for rolling a ball screw is rolled into a roll die. The distance between the roll dies is reduced, and the roll dies are brought into contact with the cylindrical material in a position relationship that overlaps the roll dies in the range of 10 to 65% of the axial length of the cylinders. It is characterized by starting.
[0007]
Conventionally, when rolling a ball screw through a cylindrical material through feed, the cylindrical material for rolling the ball screw is over the roll die cylindrical portion within a range of 80% or more of the axial length of the roll die cylindrical portion. Due to the positional relationship of wrapping, the distance between the roll dies was reduced, and the roll dies were brought into contact with the cylindrical material to start rolling. If the roll dies cylindrical part does not firmly grip the cylindrical material in such a positional relationship, the cylindrical material swings when starting through feed rolling, and good rolling results cannot be obtained Because it was considered.
The inventor has challenged this common sense and repeatedly conducted various experiments, and as a result, the cylindrical material for rolling the ball screw was found to be in the range of 10 to 65% of the axial length of the roll die cylindrical portion. It has been found that, even when the distance between the roll dies is reduced and the roll dies are brought into contact with the columnar material and the rolling is started, the rolling can be performed satisfactorily due to the positional relationship overlapping the portions.
According to the above rolling method, the rolling start side of the cylindrical material for rolling the ball screw is satisfactorily rolled by the roll die cylindrical portion, and the incomplete thread portion is slightly within the rolling start side. It is only formed. For this reason, the length of the incomplete thread portion formed at the rolling start portion can be suppressed to a value equal to or less than the allowable value. Therefore, it is not necessary to form an extra roll and remove that portion in a subsequent step. For this reason, a good quality ball screw can be easily manufactured at low cost.
[0008]
In the shaft according to the second aspect, the ball screw portion is continuous with the small diameter cylindrical portion, and the non-rolled portion is continuous with the ball screw portion. In the shaft of the present invention, the imperfect thread formed on the small-diameter cylindrical portion side of the ball screw has two grooves or less, and the vicinity of the ball screw portion of the small-diameter cylindrical portion is cut after rolling the ball screw. It is characterized by not having.
In the above-mentioned shaft, the length of the incomplete screw portion formed on the small diameter portion side of the ball screw portion is 2 grooves or less. And. Since the vicinity of the ball screw portion of the small-diameter cylindrical portion is not cut after rolling the ball screw, the number of processing steps is reduced accordingly. Therefore, the shaft can be manufactured at low cost.
[0009]
In the shaft according to claim 2, the non-rolled portion is preferably a rack tooth portion (claim 3).
[0010]
The invention described in claim 4 is a method of through-feed rolling a ball screw on a cylindrical material between roll dies. In this manufacturing method, the roll die is provided with a cylindrical portion and a truncated conical portion whose diameter decreases outward continuously at both ends of the cylindrical portion. The roll die is made of carbon steel and has a Vickers hardness of Hv200 or more and Hv280. A cylindrical material for rolling a ball screw as described below, the distance between the roll dies is reduced in a positional relationship in which the roll dies overlap with the roll dies cylindrical portion in the range of 40 to 50% of the axial length of the roll dies cylindrical portion, The roll die is brought into contact with the cylindrical material to start rolling.
According to the above rolling method, the rolling start side of the cylindrical material for rolling the ball screw is satisfactorily rolled by the roll die cylindrical portion, and the incomplete thread portion is slightly within the rolling start side. It is only formed. Therefore, it is not necessary to perform extra rolling and remove that portion in a subsequent step, and a high-quality ball screw can be easily manufactured at low cost.
[0011]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 schematically illustrates a process of subjecting an intermediate material 18 to a through-feed rolling process with a roll die 10 to complete a ball screw. The intermediate material 18 has, in order from left to right in FIG. 3, a small-diameter cylindrical portion A, a ball screw rolling cylindrical portion 2 having a larger diameter than the small-diameter cylindrical portion A, and a rack tooth portion C.
Although there is a pair of roll dies 10 on both sides of the intermediate material 18, only one of the roll dies 10 is shown in FIG. The roll die 10 includes a cylindrical portion 14, and truncated conical portions 12 and 16 whose diameters continuously decrease outward at both ends of the cylindrical portion 14. A spiral ridge (not shown) for rolling a ball screw is formed on the outer periphery of the roll die 10.
The roll die 10 is driven by a drive mechanism (not shown) and rotates around its axis. The axial position of the roll die 10 is fixed. One of the roll dies 10 arranged on both sides of the intermediate material 18 is fixed in the direction perpendicular to the axis, while the other roll die 10 is movable in the direction perpendicular to the axis.
[0012]
A series of operations of through feed rolling will be described with reference to the drawings.
As shown in FIG. 4, in the first operation S10 of through feed rolling (hereinafter, “operation” is abbreviated and simply described as S10), the intermediate material 18 moves to a predetermined position ( (A positional relationship of an overlap length j described later). In S12 following S10, the pair of roll dies 10 (hereinafter, referred to as “roll dies R and L” in the description of FIG. 4) is driven, and the rotation is started. The roll die R is movable in the direction perpendicular to the axis, and the roll die L is fixed in the direction perpendicular to the axis. In S14, the roll die R starts to advance with respect to the intermediate material 18. When the roll dice R starts moving forward, the distance between the roll dice R and the roll dice L decreases. Then, in S16, the intermediate material 18 is sandwiched between the roll dice R and the roll dice L, and the rolling of the ball screw is started. When the rolling of the ball screw is started, the intermediate material 18 rotates while being rolled, and is sent out in the axial direction.
[0013]
In S18, the roll die R moves forward to the forward end position. As the roll die R advances to the forward end position, the roll dice R and the roll dice L are arranged so as to keep a predetermined distance. In this state, the rolling of the intermediate material 18 is continued. In S20, it is detected that the intermediate material 18 has been fed to a predetermined position in the axial direction (a position where the roll die 10 is separated from the intermediate material 18 in order to avoid interference with the rack teeth C, which will be described later). For this detection, for example, an optical sensor is used. When it is detected that the intermediate material 18 has been sent to the predetermined position, the retreat of the roll die R is started in S22. When the roll die R moves backward, the roll die R separates from the intermediate material 18. In S24, the roll die R retreats to the retreat end. Then, in S26, the rotation of the roll dies R and L is stopped.
[0014]
3A shows the position of the roll dice 10 when the distance between the roll dice starts approaching. At this time, the length j in which the ball screw rolling cylindrical portion 2 of the intermediate material 18 overlaps the cylindrical portion 14 of the roll die 10 is set to 10 to 65% of the length m of the cylindrical portion 14. When the roll dies 10 are brought closer in this positional relationship, the intermediate material 18 is rolled between the roll dies 10. 3B shows the position of the roll dice 10 when the distance between the roll dice starts to increase.
[0015]
We experimented by changing the overlap length j and how it affects the ball screw shape. Hereinafter, the results will be described.
When the overlap length j is 10% or less of the length m of the cylindrical portion 14 of the roll die 10, the diameter of the screw bottom is small (thin) near the left end (in FIG. 3) of the ball screw rolling cylindrical portion 2. It was confirmed that it became too much. This is because the left end of the ball screw rolling cylindrical portion 2 is easily moved to the small-diameter cylindrical portion A side with the rolling, the overlap length j is set to 10% or less of the cylindrical portion length m, and the cylindrical portion 14 It is thought that when most of the rolls are rolled, the rolls are rolled more.
When the overlap length j is 10% or more of the column length m, the diameter of the screw bottom in the vicinity of the left end of the ball screw rolling column 2 is prevented from becoming too small.
[0016]
On the other hand, if the overlap length j exceeds 65% of the cylindrical portion length m, insufficient rolling occurs at a portion slightly away from the left end of the ball screw rolling cylindrical portion 2, and the diameter of the screw bottom is large (thick). It was confirmed that it became too much.
From the above experimental results, assuming that the overlap length j is 10 to 65% of the length m of the cylindrical portion, the intended screw bottom diameter is set on the right side from a portion slightly away from the left end of the cylindrical portion 2 for ball screw rolling. It was confirmed that the completely threaded part having a good roll was formed.
The axial length of the imperfect thread portion of the ball screw rolled in this way is within two thread grooves.
[0017]
The desired overlap length j has a correlation with the hardness of the cylindrical portion 14 of the intermediate material 18. The intermediate material 18 made of carbon steel equivalent to S35 to S45 having a Vickers hardness of Hv200 to Hv280 has an overlap. It was confirmed that the length j is more preferably 40 to 50% of the column length m.
[0018]
According to the present invention, when rolling is started from a state in which only a distance corresponding to 10 to 65% of the axial length of the cylindrical portion 14 of the roll die 10 is overlapped, it is very close to the left end of the ball screw rolling cylindrical portion 2. A complete thread can be formed from the position. For this reason, unlike the conventional case, there is no need to perform extra rolling and remove that portion later. Therefore, it is possible to manufacture a shaft having no removal portion near the ball screw portion B of the small diameter cylindrical portion A.
After rolling the ball screw rolling cylindrical portion 2, the roll die 10 separates from the intermediate material 18 in order to avoid interference with the rack teeth C.
[0019]
In the present embodiment, the present technology is applied to a shaft for power steering, but an object to which the present invention can be applied is not limited to this. For example, a shaft having a small-diameter cylindrical portion on both sides of the ball screw portion is also included. Further, the cylindrical portion for rolling a ball screw referred to in the present invention means that the rolling surface is a cylinder, and includes a cylindrical member having a shaft hole formed in a material. The technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.
[Brief description of the drawings]
FIG. 1 illustrates an example of a shaft to which the present invention is suitably used.
FIG. 2 is a diagram illustrating ball screw dimensions of a shaft.
FIG. 3 shows a rolling start position and a rolling end position of a roll die with respect to an intermediate material.
FIG. 4 shows a series of operations of through-feed rolling.
[Explanation of symbols]
A: small diameter cylindrical part B: ball screw part C: rack tooth part e: (removed) imperfect screw part length f: imperfect screw part length j: overlap length m: cylindrical part length 2: ball screw rolling Cylinder section 10: roll die, 10A: approach start position, 10B: separation start position 12: truncated cone section 14: cylinder section 16: truncated cone section 18: intermediate material

Claims (4)

In the method of through-feed rolling a ball screw into a cylindrical material between roll dies,
The roll dice is provided with a cylindrical portion and a truncated cone portion whose diameter continuously decreases outward at both ends of the cylindrical portion,
The distance between the roll dies is reduced by overlapping the cylindrical material into which the ball screw is to be rolled in such a manner that the cylindrical material overlaps the roll dies in the range of 10 to 65% of the axial length of the roll dies. A method for rolling a ball screw, comprising rolling a portion by contacting a portion with a cylindrical material. A shaft in which a ball screw portion is continuous with a small-diameter cylindrical portion and a non-rolled portion is continuous with the ball screw portion, and an incomplete screw portion formed on the small-diameter cylindrical portion side of the ball screw has two grooves or less; A shaft, wherein the vicinity of the ball screw portion of the small-diameter cylindrical portion is not cut after rolling the ball screw. The shaft according to claim 2, wherein the non-rolled portion is a rack tooth portion. In the method of through-feed rolling a ball screw into a cylindrical material between roll dies,
The roll dice is provided with a cylindrical portion and a truncated cone portion whose diameter continuously decreases outward at both ends of the cylindrical portion,
A cylindrical material for rolling a ball screw made of carbon steel and having a Vickers hardness of Hv200 or more and Hv280 or less is overlaid on the roll die cylindrical portion within a range of 40 to 50% of the axial length of the roll die cylindrical portion. A method of rolling a ball screw, comprising: bringing a distance between roll dies closer in relation to a wrapping position; and starting rolling by bringing a cylindrical portion of the roll die into contact with a cylindrical material.

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