JPH10315051A - Method of improving fatigue strength of screw of tie-bar and roller burnishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a roller burnishing device for improving the fatigue strength of a tie-bar by means of an inexpensive roller burnishing device without requiring an increase in diameter, or an extremely large, expensive rolled thread cutting device. SOLUTION: In the threading method for tie-bars, a specified length from the end face of an end of a tie-bar 2 is first threaded by an NC lathe, and then the roots of an external thread are burnished. Besides, the roller burnishing device is composed of a roller 11, a holder 12 for rotatably holding the roller 11, and a case 13 for supporting the holder 12 turnably around the axis through a compression spring 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of processing a thread portion of a tie bar of an injection molding machine and a roller burnishing apparatus for the processing.

[0002]

2. Description of the Related Art Generally, a mold clamping force of an injection molding machine is supported by a plurality of (typically four) tie bars. Accordingly, a tensile force acts on the tie bar when the mold is closed for molding, and this tensile force is repeatedly applied in each molding cycle. The tie bar has an end threaded at a predetermined length from an end face at one end thereof, and supports the mold clamping force by screw connection with a nut screwed to the external thread. That is, the tensile force repeatedly acts on the male screw of the tie bar. In order to secure the fatigue strength of the screw bottom of the male screw, the thread portion of the tie bar to which the tensile force is repeatedly applied is conventionally subjected to buffing of the screw portion after turning with a lathe. That is, the buffing finish removes the unevenness of the screw processing surface, and secures the fatigue strength by forming a smooth screw shape. Also,
As another means, the male screw is rolled to secure the fatigue strength.

[0003]

Since the conventional method for improving the fatigue strength of the screw of the tie bar is constituted as described above, there are the following problems. In other words, in the buffing process, the fatigue strength is improved by smoothing the surface of the male screw, but it may still be insufficient, and the thickness of the tie bar must be increased in order to increase the strength. is there. Also, when a male screw is rolled, the tie bar is a long bar-shaped member, so the center distance cannot be adjusted, and even if the thread is rolled, there is a possibility that the concentricity of the tie bar outer diameter and the threaded portion will be poor. It is expensive, and in particular, as the diameter increases, the length increases proportionately, necessitating a very large, ie expensive, rolled threading machine.

[0004] The present invention has been made to solve the above-mentioned problems, and does not increase the diameter of a tie bar and uses an inexpensive roller burnishing device.
An object of the present invention is to provide a method and a roller burnishing device for improving the fatigue strength of a tie bar.

[0005]

According to the present invention, there is provided a method for improving the fatigue strength of a screw of a tie bar according to the present invention, wherein the tie bar is machined with an NC lathe for a predetermined length from one end face of the tie bar. This is a method of performing roller burnishing using a roller of a roller burnishing device attached to the NC lathe.

More specifically, there is a method of obtaining a pressing pressure necessary for increasing the fatigue limit of the screw bottom by adjusting a spring force of a compression spring.

[0007] The roller burnishing device has a configuration including a roller, a holder for rotatably holding the roller, and a case for rotatably supporting the holder via a compression spring.

Further, the roller is provided on an annular frame.
And at least one of the rollers is urged by a compression spring.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for improving the fatigue strength of a screw of a tie bar and a roller burnishing apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a front view showing a processing state of the roller burnishing apparatus of the first embodiment, and FIG. 2 is a side sectional view of the roller burnishing apparatus. In the drawing, reference numeral 1 denotes a roller burnishing device having one roller 11, and the roller burnishing device 1 includes a roller 11, a holder 12 for holding the roller 11, and a case 13 for supporting the holder 12. It consists of.

The roller 11 has a substantially cylindrical shape, and a single protrusion 11a is formed on the outer periphery of the middle of the cylinder. The projection 11a has a substantially triangular cross section and is formed in a shape corresponding to the thread bottom of the male screw to be processed. The roller 11 is mounted on a rotary support shaft 15 provided on a forked portion 12 a on the distal end side of the holder 12 by a radial bearing 1.
4 so as to be rotatable.

The holder 12 is formed by the forked portion 12a on the front end side and the cylindrical portion 12b on the rear end side. The case 13 has a first hole 13a at its tip end for accommodating the columnar portion 12b of the holder 12 so as to be pivotable.
And a cylindrical portion having a second hole 13b smaller in diameter than the first hole 13a and formed concentrically and continuously at the rear end side. The cylindrical portion 12b of the holder 12 is inserted into the first hole 13a together with a first thrust bearing 16 and a compression spring 17 composed of a disc spring or the like. Further, the rear end face of the cylindrical portion 12b is provided with a screw portion 12A at the tip end of a shaft 18 inserted through the second hole 13b, the first thrust bearing 16 and the center hole of the disc spring 17. Screwed through. The threaded rear end of the shaft 18 protrudes from the rear end surface of the case 13, and a nut 20 is screwed through a second thrust bearing 19. Furthermore, pins 21 and 22 are provided on the front end side surface of the case 13 and the rear end side surface of the forked shape portion 12a, respectively. The compression spring 17 is compressed by the screwed state of the nut 20, and the pressing force necessary for increasing the fatigue limit of the roller 11 with respect to the case 13 is adjusted.

A case where the tie bar 2 is externally threaded by the roller burnishing apparatus 1 configured as described above will be described below. First, the tie bar 2 on which the male screw processing is performed is placed on a high-precision NC lathe (not shown). This N
A turret tool post 5 of a C lathe is provided with a tooling tool for unthreading and a roller burnishing device 1 (not shown). Next, the NC lathe is driven, and male screw processing is performed by a male screw cutting tool (not shown) from the end face of one end of the tie bar 2 to a predetermined length. Next, the NC lathe is driven and the screw bottom of the male screw after the male screw processing is roller burnished by the roller burnishing device 1. In addition, it can be applied to a general-purpose lathe.

The roller burnishing apparatus 1 adjusts the screwing position of the nut 20 in advance, so that the compression spring 1
7 is set to a predetermined value. Further, the pressing force of the roller burnishing device 1 is reduced by the two pins 21 and
It is determined by measuring the interval between the two and determining the compression force of the compression spring 17. The roller 11 held on the rotation support shaft 15 of the holder 12 via the radial bearing 14 has a protrusion 11
In a state in which the tip of a is pressed against the thread bottom of the male screw of the tie bar 2 with a desired pressing pressure, the tip a rotates without slipping with the rotation of the tie bar 2 and performs roller burnishing. In addition, since the cylindrical portion 12b of the holder 12 is rotatably supported by the case 13 by the first thrust bearing 16 and the second thrust bearing 19, the protrusion 11
“a” can follow the lead angle of the male screw of the tie bar 2.

Although the roller burnishing apparatus 1 having one roller shown in FIGS. 1 and 2 is fixed to the tool rest of the NC lathe, it is used when the pressing force becomes too large or when the rigidity of the NC lathe or the like is reduced. In the case where it is not sufficient, for example, the second embodiment shown in FIG. 3, that is, three roller burnishing apparatuses 1 is used. The three roller burnishing devices 1 are provided on an annular frame 31, and one is provided with a holder 12 (indicated by a forked portion 12a in FIG. 3) via a screw portion 13A so as to be able to enter and exit an adjustment roller support 32. The two are provided on a fixed roller support 33 on which a holder 12 (a forked portion 12a is shown in FIG. 3) is provided on a frame 31. As described above, the roller supports 32 and 33 rotatably hold the roller 11 at the front end, and the frame 31
The frame 31 is rotatably supported as described above so as to face the center from the three directions. The adjusting roller support 32 is configured similarly to the above-described roller burnishing device 1 of the first embodiment, particularly, as shown in a side sectional view of FIG. 4, and further, a case 13 is provided on the frame 31. It is screwed to the adjusting roller support 32 via a screw portion 13A so as to be freely inserted and removed. The fixed roller support 33 is supported by the frame 31 in a state where the case 13 is prevented from moving outward in the axial direction.
In the configuration of FIG. 3, only one roller 11 is built in the adjustment roller support 32 and is pressed by the compression spring 17.
The other rollers 11 were fixed, but the other two rollers 11
The compression spring 17 can also be used to make it freely pressable.

The case where the tie bar 2 is externally threaded by the three roller burnishing apparatuses 1 configured as described above will be described below. First, an external thread is machined from an end face of one end of the tie bar 2 to a predetermined length by a male thread cutting tool. Next, the male screw portion of the tie bar 2 is inserted between the fixed rollers 11 among the three rollers 11 of each roller burnishing device 1. Next, the case 13 of the adjusting roller support 32 is turned to project the tip of the roller 11 toward the center of the frame 31, and the three rollers 11 press the screw bottom of the male screw of the tie bar 2 from three directions with a predetermined pressing force. Set to press. Next, by turning the tie bar 2 while the frame 31 is fixed, the male screw processing and the same roller burnishing of the screw bottom as described above are performed.

[0016]

The method for improving the fatigue strength of a screw of a tie bar and the roller burnishing apparatus according to the present invention are configured as described above, and the following effects can be obtained. In other words, by applying a roller burnishing process to the screw bottom of the male screw of the tie bar with a roller urged by a compression spring, minute irregularities on the screw bottom are crushed and eliminated, the surface is hardened, and the fatigue strength is greatly improved Is done. Therefore, it is not necessary to increase the diameter of the tie bar more than necessary. Also, since the roller burnishing device is a small device, it can be mounted on a normal NC lathe to facilitate roller burnishing, does not require a large and expensive device, and performs a process for improving the fatigue strength of the tie bar. be able to.

[Brief description of the drawings]

FIG. 1 is a front view showing a processing state of a roller burnishing device according to a first embodiment of the present invention.

FIG. 2 is a plan sectional view of a roller burnishing device according to a first embodiment of the present invention.

FIG. 3 is a front view showing a roller burnishing device according to a second embodiment of the present invention.

FIG. 4 is a plan sectional view of a roller burnishing device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Roller burnishing device 11 Roller 12 Holder 13 Case 17 Compression spring 18 Shaft 20 Nut 31 Frame 32 Adjustment roller support 33 Fixed roller support

Claims (4)

[Claims] 1. An NC threading machine is used to machine a predetermined length from one end face of one end of a tie bar (2) by an NC lathe. A method for improving the fatigue strength of a screw of a tie bar, characterized by performing roller burnishing. 2. The method for improving the fatigue strength of a screw of a tie bar according to claim 1, wherein the pressing pressure necessary for increasing the fatigue limit of the screw bottom is obtained by adjusting the spring force of a compression spring. . 3. A roller (11), a holder (12) for rotatably holding the roller (11), and a compression spring for the holder (12).
A roller burnishing device, comprising: a case (13) rotatably supported via (17). 4. An annular frame (31) provided with three rollers (11), and at least one of the rollers (11) is urged by a compression spring (17). Characteristic roller burnishing device.