JPH04314827A - Production of screw shaft of ball screw - Google Patents

Abstract

PURPOSE:To provide the method, in which rigid ball rolling face in screw thread part of a screw shaft does not melt or its hardness does not lower at the time of quenching the screw shaft of the ball screw by using laser beam. CONSTITUTION:The laser beam 2 is condensed with a lens 3, and after refracting with a reflecting mirror 7, this irradiates one side in one pair of the rigid ball rolling faces 4 at right and left sides of the screw shaft 5 in ball screw. Then, as the screw shaft 5 is rotated on a rotary disk 20 at the constant speed and at the same time, machining head 6 including the reflecting mirror 7 is shafted to vertical direction, the laser beam 11 from the machining head 6 irradiates as spiral along one side of the rigid ball rolling faces 4 of screw shaft 5. After continuously quenching from starting point S to end point E in the screw thread part in the screw shaft 5, in the same way, the other part of the rigid ball rolling face 4 is quenched. In such way, as the quenching is executed under condition of dividing into two times, melting of the screw thread part and lowering of the hardness are avoided.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a thread groove formed in the screw shaft of a ball screw that accommodates a plurality of hard balls in a spiral space defined by opposing the thread groove of a male thread and the thread groove of a female thread. The present invention relates to a method for manufacturing a screw shaft of a ball screw, in which a hard ball rolling surface is hardened by irradiating a high-energy beam.

0002

[Prior Art] Conventionally, carburizing and induction hardening methods have been commonly used to harden the surface of the screw shaft of ball screws, which are used in many positioning mechanisms of machine tools as precision machine elements. There is. However, since these methods involve heat treatment in which the entire ball screw is heated and cooled, large heat treatment distortions such as non-uniform expansion/contraction and bending occur. Therefore, there is a problem in that in order to ensure the required accuracy, it is necessary to correct the bending, and to spend a great deal of effort on grinding and finishing in the subsequent process. Apart from that, a hardening method using a laser beam has recently been attracting attention.

An example of this heat treatment method is ``Screw shaft surface hardening method by laser irradiation'' described in, for example, Japanese Patent Laid-Open No. 59-208022. That is, as shown in FIG. 5, this technique is provided with a beam integrator 10 for averaging the intensity of a laser beam 11 irradiated from a laser beam generator (not shown), and a beam that passes through the beam integrator 10 is provided. The laser beam 11 that has been emitted is split into two directions by a beam splitting mirror 12, and is split into two directions by a first and second reflecting mirror 1, respectively.
It is reflected by 3a and 13b. Beams 11a and 11 reflected by the first and second reflecting mirrors 13a and 13b
The light beams b are focused by the first and second convex lenses 14a and 14b, respectively, and irradiated onto the thread groove formed in the threaded shaft A of the ball screw. The lower half of this screw shaft A is the cooling water 1
5 and is supported so as to rotate and move horizontally.

As shown in FIG. 6, the first convex lens 1
The laser beam 11a focused by 4a is directed to one side (left flank surface) of the hard ball rolling surface of the right thread groove of the thread groove adjacent to both sides of the thread D of the screw shaft A. α) and focused by the second convex lens 14b, the laser beam 11b is applied to the screw shaft of the rigid ball rolling surface of the left-hand thread groove of the thread groove adjacent to both sides of the thread D of the screw shaft A. The other side (right flank surface β) in the axial direction is simultaneously irradiated. By rotating the screw shaft A at the same time as this laser beam irradiation and moving the screw shaft A in synchronization with the screw pitch, the left and right flank surfaces α and β of the screw thread D are simultaneously hardened, and then the adjacent Thread D
The left and right flank surfaces α' and β' of ' are hardened at the same time.

[0005]

However, according to the above method, when it is desired to deeply harden both flank surfaces α and β (rigid ball rolling surfaces) of the thread D, the following problem occurs.

That is, in that case, the laser beams 11a,
The relative movement speed between the spot 11b and the screw shaft may be slowed down, or the laser beams 11a and 11 with higher output may be used.
It is sufficient to irradiate b. However, since the heat capacity of the thread D is small, the cooling rate necessary for hardening after the spot has moved due to heat accumulation may not be obtained. As a result, the hardening is completed incompletely, and the hardness of the hard ball rolling surface is as low as Hv550 to 600, making it incomplete, and the wear resistance does not improve. Furthermore, when hardening with a high-output beam, the edge portion of the rigid ball rolling surface B may melt, and the hardness may significantly increase or the shape may be deformed at that portion.

The present invention has been made to solve the above-mentioned problems, and it is possible to harden the screw shaft of a ball screw without reducing the hardness, melting, or deforming the ball. An object of the present invention is to provide a method for manufacturing a screw shaft of a screw.

[0008]

[Means for Solving the Problems] In order to achieve this object, the method for manufacturing a screw shaft of a ball screw of the present invention provides a method for manufacturing a screw shaft of a ball screw in which a helical space defined by opposing a thread groove of a male thread and a thread groove of a female thread is provided. A method for manufacturing a screw shaft of a ball screw that accommodates a plurality of hard balls in a screw shaft, the screw shaft having a concave cross-section screw groove having a hard ball rolling surface, one side in the axial direction of the screw shaft from the starting point of the screw groove. After being hardened in a spiral shape with a high-energy beam toward the end point, the other side of the hard ball rolling surface of the thread groove in the axial direction of the screw shaft is hardened in a spiral shape with a high-energy beam. .

[0009]

[Operation] In the present invention having the above configuration, only one side of the thread of the screw shaft of the ball screw is heated with a high-energy beam, and then only the opposite side of the thread is heated with a high-energy beam. Therefore, the amount of heating applied to the thread at one time is reduced, and the cooling rate of the heating portion after the spot of the high-energy beam has moved is increased. Therefore, the hardness of the hard ball rolling surface can be increased, and it will not melt or change its shape.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the screw shaft 5 of the ball screw is parallel to the vertical axis of the chucking device 2 of the rotary disk 20.
01, and the screw shaft 5 is rotated around its axis. A processing head 6 is provided so as to be movable parallel to the axis of the screw shaft 5. This processing head 6 is moved by a well-known moving mechanism 30 by a distance corresponding to the pitch of the thread grooves 51 of the screw shaft 5 per revolution of the screw shaft 5. This moving mechanism 30 moves a vertically moving bracket 301 to which the processing head 6 is fixed onto a guide surface 30.
2, and the vertically movable bracket 30
A feed screw 303 is screwed into the feed screw 1, and the feed screw 303 is rotationally driven by a feed servo motor 304 to move the machining head 6 up and down. This feed servo motor 304 is controlled by a well-known numerical control device 40.

A laser beam 2 as a parallel beam emitted from the laser beam generator 1 is directed to the processing head 6.
After being incident on a lens 3 movably provided within the processing head and condensed, the light is refracted in the horizontal direction by a reflecting mirror 7 within the processing head 6. Laser beam 1 refracted by reflector 7
1 is irradiated onto the thread groove 51 of the screw shaft 5. Screw shaft 5
The irradiation range (spot diameter) of the laser beam 2 irradiated onto the thread groove 51 is set by adjusting the movement of the lens 3.

Further, a nozzle 8 is fixed to the processing head 6 for spraying an assist gas such as nitrogen or argon to the laser beam irradiation part of the screw shaft 5, which cools the laser beam irradiation part and prevents oxidation. There is.

A method of hardening the hard ball rolling surface 4 of the thread groove 51 formed in the screw shaft 5 of the ball screw using the above-mentioned apparatus will be explained.

First, the lens 3 built in the processing head 6 is moved to adjust the irradiation range (spot diameter) of the laser beam 11 refracted by the reflecting mirror 7 to the thread groove 5.
Set to 60% to 75% of the width of 1.

Next, the feed servo motor 304 is driven by the numerical control device 40 to move the processing head 6 to a position corresponding to the starting point S of the thread groove 51 of the screw shaft 5 of the ball screw. At this time, the processing head 6 is positioned so that the spot of the laser beam 11 is formed on one side of the center of the thread groove 51 (one side in the axial direction of the threaded shaft 5). That is, a spot is formed on one of the right and left rigid ball rolling surfaces 4 of the thread groove 51.

Further, the numerical control device 40 includes data on the amount of movement of the machining head 6 per one rotation (one rotation of the screw shaft 5) of the chucking device 201 of the rotary disk 20, and the feed pitch of the screw groove 51. It is set in advance according to the

When the operator inputs a hardening start command, the numerical control device 40 operates the laser beam generator 1, the rotary disk 20, and the feed servo motor 304. That is, as the screw shaft 5 is rotated, the processing head 6 is moved from the starting point S to the ending point E of the thread groove 51. That is, by moving the spot of the laser beam 11 on one hard ball rolling surface of the thread groove 51 from the starting point S to the ending point E, the corresponding part is continuously hardened. When the spot moves to the end point E, the numerical control device 40 controls the laser beam generator 1, the rotary disk 20, and the feed servo motor 3.
Stop operation with 04.

Thereafter, the numerical control device 40 reverses the feed servo motor 304 to return the machining head 6 to the initial position corresponding to the starting point S of the thread groove 51. At this time, the return position is set such that the spot of the laser beam 11 is formed on the other side of the center of the thread groove 51 (on the other side in the axial direction of the threaded shaft 5). That is, a spot is formed on the other of the right and left rigid ball rolling surfaces 4 of the thread groove 51.

When this return movement is completed, the numerical control device 4
0 operates the laser beam generator 1, rotary disk 20, and feed servo motor 304 again. That is, as the screw shaft 5 is rotated, the processing head 6 moves to the starting point S of the screw groove 51.
is moved from to end point E. In other words, laser beam 1
1 spot is the other hard ball rolling surface of the thread groove 51 as the starting point S
By moving from to end point E, the part concerned is continuously hardened. When the spot moves to the end point E, the numerical control device 40 stops the operation of the laser beam generator 1, the rotary disk 20, and the feed servo motor 304, and ends the machining control.

A screw shaft is hardened by the hardening method detailed above, and a cross section of the hardened portion is shown in a photograph showing a cross section of the metallographic structure in FIG.

Here, the screw shaft of the ball screw is made of material SC
M440, lead 14mm, screw shaft outer diameter 42mm, winding direction left, rigid ball diameter 6mm, thread groove curvature radius 3.
It was created with specifications of 5 mm and thread groove width of 6 mm. Figure 2 shows a laser output of 1.2 kW, a laser beam diameter (spot diameter) of 4.5 mm, and a moving speed of the processing head 6 of 500 mm.
After applying a beam absorbent to the screw shaft manufactured according to the above specifications under processing conditions of This is an enlarged photo.

As is clear from this photograph, it is understood that the quench-hardened layer 10 is formed after the quench-hardened layer 9 is formed (also shown in FIG. 3). The hardening depth is 0.8 to 1.0 mm, and the hard ball rolling surface 4 is not melted.

As shown in FIGS. 2 and 3, the lower part of the thread groove (the lower part of the pair of left and right rigid ball rolling surfaces 4) has an initial hardened layer 9 and a later hardened layer 9. An overlap 11 with layer 10 is formed, and this overlap 11 has been annealed to reduce its hardness.

However, the hard ball 12 makes point contact approximately at the center of the pair of right and left hard ball rolling surfaces 4 of the screw groove of the screw shaft 5 of the ball screw, and does not contact the overlapping portion 11. Therefore, since the hard balls 12 roll on the unannealed portions of the hardened layers 9 and 10, they do not wear out. Generally, the thread groove has a Gothic arch-shaped cross section, so there is a gap between the bottom and the hard ball. Therefore, even if an overlapping portion with low hardness is formed due to annealing, it will not come into contact with the hard ball, so there is no risk of wear.

The relationship between the hardness and the depth from the hard ball rolling surface 4 at the contact point C of the hard ball (at a 45 degree angle with respect to the center of the hard ball) at this time is shown in the graph of FIG. Hardness is H on average
v700-730, hardened layer depth is 0.8-1 on average
．． It was 0 mm.

For comparison, a beam absorbing agent was applied to the screw shaft 5 of a ball screw manufactured according to the above specifications, and then a beam absorbing agent was applied to the screw shaft 5 of the ball screw manufactured according to the above-mentioned specifications.
FIG. 7 shows a graph corresponding to FIG. 4 when quenching was performed by the conventional method described in Publication No. 22. As is clear from comparing both figures, it is understood that the quench-hardened layer can be formed deeper when the present invention is applied.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention. For example, in the above embodiment, after the first hardening process, the processing head was moved back to the start point S side of the thread groove and then the second hardening process was performed. After processing, a second hardening process may be performed from the end point E side of the thread groove after a predetermined period of time has elapsed. Furthermore, instead of moving the processing head, the screw shaft may be moved along its axis.

[0029]

As described in detail above, according to the present invention, one side in the axial direction of the screw shaft of the hard ball rolling surface of the screw groove having a concave cross-section of the screw shaft can be moved from the starting point of the screw groove. After being hardened in a spiral shape with a high-energy beam toward the end point, the other side of the hard ball rolling surface of the thread groove in the axial direction of the screw shaft is hardened in a spiral shape with a high-energy beam. As a result, the amount of heat received by the irradiated part of the high-energy beam is smaller than in the past, and a hardened layer that does not melt the threads or reduce its hardness is obtained, resulting in a wear-resistant layer. It has the advantage of good properties.

[0030] Also, there is an advantage that there is little thermal distortion during hardening and that no post-processing is required, resulting in lower manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is an explanatory view showing a method of hardening a screw shaft of a ball screw according to the present invention.

FIG. 2 is a photograph showing an enlarged cross section of the metal structure of the screw shaft when the screw groove is hardened.

FIG. 3 is an explanatory diagram showing the arrangement of a pair of left and right hard ball rolling surfaces of the screw groove of the screw shaft and the hard balls.

FIG. 4 is a graph showing the relationship (hardness distribution curve) between the depth from the rigid ball rolling surface and the Vickers hardness of a screw shaft processed by the hardening method of the present invention.

FIG. 5 is an explanatory diagram showing a conventional method.

6 is a detailed explanatory diagram of the laser hardening portion in the conventional method of FIG. 5; FIG.

7 is a graph showing the relationship (hardness distribution curve) between the depth from the rigid ball rolling surface and the Vickers hardness of the screw shaft machined by the conventional method shown in FIG. 5; FIG.

[Explanation of symbols]

1 Laser beam generator 1 4 Rigid ball rolling surface 5 Screw shaft of ball screw 6 Processing head 9 Quenched hardened layer 10 Quenched hardened layer 11 Laser beam 20 Turntable 30 Moving mechanism 40 Numerical control device 51 Thread groove

Claims (1)

[Claims] 1. A method for manufacturing a screw shaft of a ball screw in which a plurality of hard balls are accommodated in a spiral space defined by opposing thread grooves of a male thread and a thread groove of a female thread, the screw shaft having a concave cross-section. One side in the axial direction of the screw shaft of the hard ball rolling surface of the screw groove is hardened in a spiral shape from the start point to the end point of the screw groove using a high energy beam, and then the hard ball rolling surface of the screw groove is hardened. A method for manufacturing a screw shaft of a ball screw, characterized in that the other side of the moving surface in the axial direction of the screw shaft is hardened in a spiral shape using a high-energy beam.