JP2002321034A - Forming method and apparatus for article in the shape of hollow rack bar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable efficient and low cost forging of an article in the shape of a hollow rack bar from a tube material in hollow rack bar forming. SOLUTION: After a tube material 18 is set in metal dies 12, 14 for thread forming, the dies 12, 14 are closed holding halved mandrels 23A, 23B for flattening inserted from left and right respectively in the material 18, forming a flattened surface 18-1 on one side of the material 18. In this state mandrels with expansion heads are pushed into the material 18 several times repeatedly from left and right alternatively, which moves the material uniformly onto the thread, forging to form rack-type thread on the flattened surface. Then pairs of mandrels with head shapes of a different expansion rate are successively exchanged to perform stepwise forging. From the beginning of flattening of the material to the completion of rack bar forming through insertion and exchange of mandrels with expansion heads, the metal dies 12, 14 are not opened, holding the material clamped by the dies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming a hollow rack bar-shaped article for flattening a tube and forming teeth in the flattened portion of the tube.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 3-5892 discloses a method of forming a rack bar or the like, which is a steering component of an automobile, from a tube by rolling. In the rolling forming of a rack bar in Japanese Patent Publication No. 3-5892, first, a flat surface of a rack bar forming surface of a tube material is performed by heating by pressing while holding the tube material. Next, a core metal is press-fitted into the hollow of the tube from one side in the axial direction while a mold having a linear tooth row on the inner periphery is applied to the flat portion of the tube. The cored bar has a tapered head widening, and the tapered portion engages with the head widening on the inner peripheral side, so that the flat portion of the metal flows plastically toward the tooth row of the molding die. The overhang is provided, and a flat portion of the pipe member is provided with a linear tooth row having a shape in accordance with the tooth row of the molding die, so that a rack bar or the like can be obtained.

[0003]

According to the technique disclosed in Japanese Patent Publication No. 3-5892, a flat portion is formed on a pipe prior to rolling of a tooth profile portion. The formation of the plane part in the previous process is hot,
Regardless of cold forming, a large press of several hundred tons is used exclusively for flattening. It requires large equipment costs, large space and maintenance costs, as well as transportation means to the molding equipment and its maintenance costs. Furthermore, since re-clamping is required by the tooth forming mold after transfer to the molding device, there is a problem of adhesion of dust etc. during transfer, and there is also a small dimensional difference in the split part of the split mold and the outer diameter of the round tube due to misalignment. This may cause biting scratches, which may lower productivity and yield.

[0004] The present invention has been made in view of the above problems, and an object of the present invention is to enable efficient and low-cost roll forming of a hollow rack bar shape from a tube material.

[0005]

According to the first aspect of the present invention, the rack forming portion of the tube is flattened, and then the insertion and withdrawal of the core into and from the hollow portion of the tube are performed by using cores having different head-enlarged shapes. In a method of forming a hollow rack bar-shaped product in which tooth formation is performed on a flattened portion of a tube material by repeating a plurality of times while shifting gold, clamping of the tube material by a mold from flattening of the tube material to completion of tooth forming. There is provided a hollow rack bar forming method, wherein a process from forming a tubular material to forming a tooth shape of a hollow rack bar-shaped article is continued without releasing the state.

According to the second aspect of the present invention, a split mold for cold tooth forming and the like which is also used for cold flattening, an opening / closing device for the split die, and a two-part core for cold flattening. Closing the mold while inserting a two-piece core for flattening into the tube from the left and right, including a metal and a core with left and right heads for performing rolling and molding continuously to the flattening process. The insertion and withdrawal of the core with a head into the hollow part of the tube are repeated several times while shifting the core with different heads without releasing the clamp of the mold. An apparatus for forming a hollow rack bar-shaped object, characterized in that teeth are formed in a crushed portion.

The operation and effect of the present invention will be described. In order to obtain a predetermined flattened shape, two flat cores for flattening are inserted from the left and right ends of the tube. When the molding die is closed after the insertion of the cored bar, and the tube material is clamped by the split mold, the tube material is crushed at the same time. That is, the flattening die is not a dedicated die, but a tooth rolling die is also used as the flattening die. After the flattening, the two-part flat metal core is pulled out from the left and right, and the tooth mold clamp is not released. In other words, the clamped state of the tube material by the tooth mold for flattening formation is maintained, that is, flat. Subsequently, while maintaining the force that can withstand the tooth forming shape that receives a greater reaction force than the crushing, the core with a head for the tooth forming shape is alternately inserted and withdrawn from the left and right alternately, and the tube material is inserted into the flattened surface of the tube. The tooth profile is roll formed.
The right and left metal core pairs are different in head-enlarged shape and shifted according to the required number of steps, and the tooth forming step is performed stepwise. However, from the start of flattening of the tooth profile to the completion of rolling by press-fitting and shifting of the core metal, the split mold for the tooth forming shape is not opened or closed at all, and the tube material is kept clamped between the split dies. The process of forming the tubing into a hollow rack bar is completed. Since the mold for forming and rolling is also used as a flattening mold, the process moves from the flattening process to roll forming by press-fitting of the core metal as it is, eliminating the need for a special press mold for flattening. No need for transfer means to the tooth forming process, equipment costs can be reduced, installation space can be greatly reduced, and the total hollow rack bar manufacturing cost can be significantly reduced. Can be. In addition, since the process moves from the flattening process to the tooth forming process while maintaining the clamped state, the problem of dust adhesion that can occur in the related art during the transfer from the flattening process to the tooth mold forming process will not occur, In addition, since the clamp is kept in the clamped state, there is no danger of a small dimensional difference at the split part of the split mold that may occur when the clamp is opened and closed, and there is no risk of biting damage at the maximum diameter part of the round tube due to misalignment. It is possible to realize a great improvement in both the performance and the yield.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a mold 10 as a split mold comprises an upper mold 12 and a lower mold 14. The upper mold (split mold for rolling forming) 12 is a lower mold (split mold for reaction force support)
The lower die 14 has a semicircular cross section on the upper surface facing the upper die 12, while the lower die 14 has a tooth portion 12-1 such as a rack tooth shape in a longitudinal concave portion on the inner peripheral surface facing the upper die 12. A longitudinal groove 14-1 is formed. Cross-section semi-circular longitudinal groove 14-1 of lower mold 14
The tube material 18 is placed on the tube. Reference numeral 19 denotes a pressure head (opening / closing device for a split die according to the present invention), and the upper die 12 is fixed to a lower surface thereof. Reference numeral 21 denotes a reaction force receiving base on which the lower mold 14 is fixed.

In FIG. 1, two divided metal cores 23A and 23B for maintaining a flat shape are arranged on the left and right sides of a mold 10. Core metal 23A, 2
3B functions to secure a predetermined flattened shape when flattening the tooth forming surface of the tube. The metal cores 23A and 23B are held by left and right metal core holders (not shown), and the metal cores 23A and 23B extend from the metal core holder in a cantilever manner. As will be described later, the left and right core metal holders are provided with head-enlarged metal cores 24A-1, 24B-1; 24A-2, 24B for forming a tooth profile on the flattened surface of the tube 18 by rolling.
-2, 24A-3, and 24B-3 (Fig. 5).

Next, a method of roll-forming a hollow rack bar-shaped article of a tube material 18 according to the present invention will be described.
In FIG. 1, the mold opening / closing head 19 is supplied with hydraulic pressure to its cylinder (not shown) so as to move upward.
As shown in (B), the upper mold 12 is located away from the lower mold 14. And the tube material 18 to be roll-formed is the lower mold 1
4 is placed in the semicircular arc-shaped longitudinal groove 14-1. The flat metal core bars 23A and 23B are mounted on the left and right metal core holders in a cantilever manner.

Next, the left and right metal core holders are driven forward toward the mold 10, and as shown in FIG.
3B is inserted into the hollow portion of the tube 18 at the same time as the left and right. The metal cores 23A and 23B are directly opposed to each other in the pipe 18 with a slight space therebetween. The metal cores 23A, 23B are provided with shoulders 23A ', 23B' at the end and flat surfaces 23A ", 2 in front of the shoulders 23A ', 23B'.
3B ", and the distance between the shoulders 23A 'and 23B' is
The length corresponds to the length L of the flattened surface to be formed in FIG.

Next, the opening / closing head 19 is lowered as shown in FIG. 3, and the upper and lower dies 12, 14 are completely closed as shown in FIG. 3 (B). At this time, the upper surface of the tube 18 is pressed by the rack-shaped teeth 12-1 of the upper mold 12, and a part of the cores 23A and 23B has a flat portion corresponding to the length L in FIG. Crushed. FIG. 6A shows the length on the upper surface of the tube material 12.
The L flattened portion 18-1 is shown. The flattened portion 18-1 is connected to the round cross-section of the tube via the shoulders 18-2 at both ends.

In the present invention, the molds 12 and 14 for tooth formation are also used as flattening molds, and the mold 10 is continuously moved to the next step without opening the mold. I have. Thus, there is an advantage that the process can be continued from flattening to the tooth formation shape, and the clamping operation can be performed only once at the first time, so that the chance of scratching caused by the clamping can be eliminated. The accuracy of the flattening used for flattening the tooth form rolling mold does not cause any strength problem because the pressing force of the flattening is lower than the tooth form rolling force. Further, in terms of accuracy, since there is no mismatch between the shoulder portion 18-2 in FIG. 6 between the conventional flat type and the tooth rolled type, higher accuracy is expected.

The flattening of the upper surface of the tube 18 by the tooth forming molds 12 and 14 can be performed in any of a cold state, a warm state and a hot state.

FIG. 4 shows a tube material 1 formed by the tooth forming molds 12 and 14.
After the flattening of the upper surface of the tube 8 is completed, the core metals 23A and 23B are
FIG.

FIG. 5 illustrates the rolling process of the present invention by repeatedly press-fitting, pulling back, and shifting the cored bar after flattening the upper surface of the tube 18.

In this embodiment, three pairs of cores are provided: a pair of 24A-1, 24B-1, a pair of 24A-2, 24B-2, and a pair of 24A-3, 24B-3. Are sequentially shifted in the direction of the arrow a so that the processing is advanced in a stepwise manner. Each core metal basically has a common structure.
1 and serves as a guide for introduction into the tube 18. Behind the guide part 241, the enlarged diameter part via the tapered part 242
243 continues, the tapered part 242 at the time of press-fitting of the core metal, then the enlarged diameter part
243 engages the flat portion 18-1 of the tube material 18 to project the wall of the tube material from inside to outside toward the irregularities of the rack toothed portion 12-1 of the mold by plastic flow. 18-1
Then, a rack-shaped tooth portion complementary to the uneven shape is rolled.
In FIG. 6, the core metal has a concave portion 2 slightly reduced in diameter following the enlarged diameter portion 243.
44 is formed, and this portion can function as a lubricating oil reservoir. The round section 246 is connected to the concave section 244, and this section is adapted to be fitted to the round sections at both ends of the tube 18.

FIG. 6 shows a state in which the press-fitting of the left core metal 24A-2 is performed to the root. After this, core metal 24A-
2 is moved to the left until it is completely removed from the tube 18.

The right-hand core (core 24B-2 in the state of FIG. 5) is pulled out of FIG.
Starts moving to the left, and the core 24B-2 on the right
Is introduced into the internal cavity, and the enlarged diameter portion causes metal plastic flow in the overhanging direction for forming the tooth shape in the same manner as described for the left core metal.

The press-in / pull-out of the left mandrel 24A-1, 24A-2, 24A-3 and the subsequent press-in / pull-out of the right mandrel 24B-1, 24B-2, 24B-3 are repeated about ten times. . That is, the press-fitting of the left and right cores into the tube 18 is alternately repeated a plurality of times.
The repetitive press-fitting of each core into the internal cavity of the tube 18 can successively promote a reliable flow of meat into the recess of the mold. That is, although the flow of the meat is insufficient by only one press-fitting of the core metal, the highly accurate rolling cannot be performed, but the highly accurate rolling of the tooth profile can be performed by the repeated press-fitting. Further, by alternately performing the press-fitting of the left and right cores a plurality of times, the metal flow to the concave portion of the mold can be made uniform without segregation, and there is an effect that highly accurate rolling can be realized. If the cored bar is installed on only one side, the flow of the meat is likely to be biased or entangled, and such uneven flow of the meat may be caused by uneven stress residual after the completion of molding of rack teeth and the like. This causes a return of elastic strain, that is, a non-uniformity of the amount of springback, which causes a decrease in strength as well as the precision of the product. Problems are resolved.

Next, the vertical shift of the cored bar will be described. A plurality of pairs of left and right cored bars are provided vertically. In FIG. 5, the pair of cored bars is the pair of 24A-1, 24B-1, 24A-2, 24B
Although three pairs, such as the pair of -2 and the pair of 24A-3 and 24B-3, are visible, the number of stages is not limited to three, and the required number of metal core pairs are arranged vertically. The shape of the enlarged metal core, such as the working diameter, is gradually changed in the shift direction so that the processing proceeds step by step with each shift. The holders of the plurality of cored bar pairs are stacked on left and right stackers (not shown), and processing is performed while shifting the cored bar holders in the stacker. That is, after the first stage of processing is performed by alternately press-fitting the metal cores 24A-1 and 24B-1 of the first processing stage, the core metal holders (not shown) in the left and right stackers (not shown) are the cores after the drawing is completed. At the time of waiting for gold, it is shifted upward as indicated by an arrow a, and the second-stage metal cores 24A-2 and 24B-2 are made to match with the tube material 18, and the metal cores 24A-2 and 24B-2 are alternately placed in the tube material 18. Is press-fitted into the internal cavity, and the second stage of processing is performed (FIG. 5 shows this state). Next, the third stage core bar 24A-
3 and 24B-3 are shifted in the direction of arrow a so as to coincide with the tube 18, and the cores 24A-3 and 24B-3 are alternately left and right.
The third stage of processing is carried out by press-fitting into the internal cavity of the metal pipe, and thereafter, the same procedure is required. There is an effect that the rolling of the deep unevenness can be realized with high accuracy.

FIG. 6B shows an example of a completed state of a rack bar or the like, in which a tooth profile 18A corresponding to the tooth profile 12-1 of the mold is rolled on a flat surface 18-1 formed by flattening. It is built. The pattern applied to the mold may have any shape, such as normal teeth, bevel teeth, mountain teeth, serrations, square teeth, and round teeth.

An important point in the present invention is that the two-part flat metal cores 23A and 23B are inserted into the tube material, the mold 10 is closed, and the mold is not opened even after the flattening. While the tube 18 is being clamped, the process is continuously shifted to the formation of a tooth profile, and the cores 24A-1, 24B-1; 24A-2, 24B-2; 24A-3, 24B-
Repeated insertion / withdrawal of 3, and core metal 24A-1, 24B-
1; 24A-2, 24B-2; 24A-3, 24B-3 to obtain a rack bar-shaped object by performing a shift. The tooth formation by press-fitting / pulling-back and shifting of the metal core is continuously performed without releasing the clamping of the tube 18 by the mold 10 for flattening. Such continuous molding with the mold closed from the flattening process to the tooth forming process eliminates the equipment cost and maintenance cost and space cost of the installation of the press machine when the flattening is performed as the previous process, In addition, it is possible to eliminate the transfer means from the flattening process to the tooth mold forming process and the maintenance cost thereof, and also to attach the dust during the transfer when the flattening is performed as a separate process and to reduce the minute cracks in the split mold. Troubles such as the occurrence of biting scratches due to dimensional tolerances can be eliminated in advance, thereby improving productivity and yield, thereby achieving a significant reduction in the manufacturing cost of rack bars. Is played.

[Brief description of the drawings]

1A is a longitudinal sectional view of a rack bar forming and rolling apparatus according to the present invention, and FIG. 1B is a transverse sectional view of the apparatus (a sectional view taken along line AA in FIG. 1). Figure).

FIG. 2 is the same as FIG. 1, but showing the state of insertion of a two-piece core for flattening.

FIG. 3 is similar to FIG. 1, but shows a flattened state by closing the mold.

FIG. 4 is the same as FIG. 3, but showing a state in which the flattening core has been removed.

FIG. 5 is similar to FIG. 1, but illustrates alternate insertion and shifting from the left and right of the tooth forming core, which is carried out directly after the flattening step.

FIG. 6 is a perspective view showing a flat state of the tube material (a) and a hollow rack bar formed by forming a tooth on the flat surface (b).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Die 12 ... Upper mold 14 ... Lower mold 18 ... Tube material 19 ... Pressing head 21 ... Reaction force receiving stand 23A, 23B ... Two-piece core metal 24A-1, 24B-1; 24A- 2, 24B-2, 24A-3, 24B-3… Core metal with head

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B21J 13/02 B21J 13/02 B

Claims (2)

[Claims] The flattening of a pipe material is performed by flattening a rack-formed portion of the pipe material, and then repeating the insertion and withdrawal of a core metal into the hollow portion of the pipe material a plurality of times while shifting core metals having different head-enlarged shapes. In the method of forming a hollow rack bar-shaped article, which performs tooth shaping on the formed portion, from the flattening of the pipe to the completion of the tooth forming, the hollow rack bar-shaped article can be removed from the tube without releasing the clamped state of the tube by the mold. A method of forming a hollow rack bar, wherein the steps up to forming teeth are made continuous. 2. A split mold for cold tooth forming and the like which is also used for cold flattening, an opening and closing device for the split die, a two-part core metal for cold flattening, and a continuous flattening process. A metal core with left and right heads for carrying out roll forming is provided, and a two-piece core metal for flattening is inserted into the tube material from the left and right, and the mold is closed to flatten the metal. Inserting and pulling out the cored bar into the hollow part of the tube without releasing the clamp of the mold is repeated a plurality of times while shifting the cored bar having a widened head shape to form teeth in the flattened part of the tube. An apparatus for forming a hollow rack bar-shaped object.