KR20070094448A - Method and apparatus for plastic working of hollow rack and hollow rack - Google Patents

Abstract

An improved technology for forming a rack bar used in a steering mechanism of a vehicle from a pipe workpiece by plastic working is provided to realize a substantial reduction in the weight of the product in comparison with the prior art. In an apparatus for performing a method of processing a hollow rack by plastic working using a cylindrical workpiece, the apparatus is characterized in that a plastic working equipment for increasing or decreasing thickness of a workpiece comprises: a mold consisting of a long metal core and a plurality of dies, and a reciprocating drive mechanism for driving the workpiece with respect to the mold such that the reciprocating drive mechanism is operated together with the mold to adjust respective portions of the workpiece to desired thickness values. As a hollow rack formed by performing plastic working of a pipe workpiece used as a steering part of a vehicle, the hollow rack includes a first portion of which a thickness is substantially the same as or slightly increased from a thickness of the pipe workpiece, and a second portion of which a thickness is highly reduced from the thickness of the pipe workpiece and of which a length is elongated, wherein a rack gear is formed on the first portion.

Description

TECHNICAL AND METHOD FOR PLASTIC WORKING AND HOLLOW RACK AND HOLLOW RACK

1 is a schematic view showing the rack bar forming step (A) to (E) of the present invention.

Fig. 2 is a schematic diagram showing a tooth forging process by a shuttle metal core.

3 is a view for explaining diameter reduction steps (A) to (C).

4 is a diagram illustrating thickness increasing steps (A) and (B).

FIG. 5 is a diagram showing steps (C) and (D) following FIG. 4.

FIG. 6 is a diagram showing steps (E) to (G) following FIG. 5.

7 is a diagram showing blank forming steps (A) to (D) in another embodiment.

*** Explanation of symbols for main parts of drawing ***

10 Blank 10-1 Diameter reduction of blank

10-2 Reducing thickness of blank 12 Lower mold for forming rack bar

14 Rack bar forming type 14A rack gear type

16a, 16b Shuttle Type Metal Core 17a, 17b Pressurized Rod

20 Mold holder for diameter reduction 22 Guide

23 reduction die 24 tip deformation die

26 Metal core for diameter reduction 30 Metal core for thickness reduction

32 dice 34 striker

36 Metal core 37 die for diameter reduction

40 Holder 42 1st guide

44 Dice 46

48 diameter reduction die 50 barrel shape metal core

52 rod-shaped metal core

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a rack bar used for steering mechanism of a vehicle by plastic processing using a pipe material, and the conventional processing method of this kind. In particular, the present invention relates to an improved technology capable of realizing a significant weight reduction.

The rack bar, which is a major part of the vehicle steering system, has been conventionally cut by a hobbing machine based on a solid round bar, but has been recently cut by a broach. However, cutting round rods increases the weight of the product. Therefore, in order to reduce the weight, drilling by a hollow drill is used. Compared with cold round bars, it was only a waste of 20-30% weight reduction.

Therefore, in order to reduce the weight of the rack bar, that is, to save resources and to improve the performance of the vehicle, a plastic processing (forging) using a pipe is proposed by the applicant and the like. In this type of forging technique, a pipe is supported by a split mold having teeth on opposite surfaces of the pipe, and the pipe supported by the metal is press-fitted with a metal core. Thereby, the tooth shape which conforms to the tooth shape of a metal mold | die is shape | molded by the transfer type (patent documents 1-3). Moreover, the improvement by the shuttle metal core is also proposed (patent document 4).

(Patent Document 1) Japanese Patent No. 3547378

(Patent Document 2) Japanese Patent No. 3607204

(Patent Document 3) Japanese Patent No. 3607205

Patent Document 4: Japanese Unexamined Patent Publication No. 2006-026703

In the techniques, such as patent documents 1-4 which forge-form a rack bar using a pipe material, the pipe material had a predetermined thickness of about 4 mm as it was supplied from the material maker. The thickness is determined by the height of the gear required for the rack bar as a product. However, when the height of the required gear is high, the thickness of the pipe is also increased, and the thickness is unnecessary at the portions other than the teeth. Conventionally, by leaving the thickness of such functionally unnecessary parts, the result is that the weight of the product becomes larger than the required function, and thus the weight is not sufficiently reduced, and the use efficiency of the material is deteriorated, resulting in cost and resource saving. And it has been required to improve the performance of the car.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and aims to efficiently utilize the thickness over the entire length of the material, while ensuring the necessary performance as a rack bar, while achieving maximum weight reduction, low cost, resource saving, and improved performance of the car. It is aimed at realization.

The protruding roll type forging molding according to the present invention supports a cylindrical workpiece to a mold, presses a metal core into the inner diameter of the workpiece, and plastically protrudes the flesh of the material toward the mold located at the outer diameter. Although the work is carried out by transferring and molding (rolling), according to the present invention, the primary cross-sectional area adjustment is performed by increasing or decreasing the thickness before the forming process of the rack gear by the protruding rolling. That is, in the primary cross-sectional area adjustment, the workpiece may be plastically processed to increase or decrease each part to a desired thickness along the longitudinal direction, thereby providing a cross-sectional area corresponding to the required function for each part along the longitudinal direction.

Thickness increase and decrease of each part of a workpiece | work is made by dividing | segmenting into one process or several processes by diameter reduction by so-called swaging or thickness reduction by ironing.

The apparatus for adjusting the cross-sectional area in the present invention can be constituted by a combination die consisting of a long metal core and several dies, and a vertical or horizontal hydraulic cylinder mechanism as a mechanism for driving the combination die. The hydraulic cylinder mechanism and the mold work together to increase and decrease each part of the pipe to a desired thickness. Instead of the hydraulic cylinder mechanism, a suitable reciprocating drive mechanism such as one consisting of a servomotor and a linear motion converter mechanism such as a ball screw type can be adopted.

(Example)

Fig. 1 shows a series of processes for forming the rack bar of the present invention. In the first step (A), 10 is a bonderbebe treatment (phosphate film forming treatment) after the tube supplied from the material maker. A blank (intermediate product) or a work is shown, and the thickness of the blank is represented by To, and the length is represented by Lo. The value of the thickness to is 4 mm in this embodiment, and this part of the thickness protrudes to the outer diameter side due to plastic flow, so that a gear part having a desired height and strength of the gear is formed. Can be formed.

In the second step (B), diameter reduction of the first step of only the tooth forming portion in the blank obtained in (A) is performed. By reducing the diameter represented by the portion 10 'of the predetermined length from the left end of the figure in the blank, a thickness t1 which is somewhat increased from the thickness to of the material is obtained. Diameter reduction can be performed by swaging, as will be described later. The length of this diameter reducing portion 10 'corresponds to the length of the gear portion 11 (Fig. 1E) of the rack bar as a product. The remaining part which is not reduced in diameter is represented by 10 ''.

In the third step (C), in the blank after the diameter reduction in the step (B), the thickness reduction step of the portion that becomes the connecting portion (shaft portion) of the rack bar after molding is shown. In other words, the thickness of the pipe is 4 mm as described above to obtain the required height and strength of the gear bar after rack bar forging, but since the shaft part of the rack bar does not take as much force as the gear part, it is 4 mm. The thickness of is unnecessary from the viewpoint of securing the function as the shaft portion. Therefore, in the present invention, the thickness of the portion of the rack bar as a forged product is reduced to a thickness t2 (≒ 0.5 × to (= 2mm)) of about half of the thickness to of the tube by plastic working. Let's do it. This thickness reduction can be achieved by ironing, but by ironing the length of the blank increases and the length of the blank increases from Lo to L1. Therefore, the thickness reduction part 10-2 of thickness t2 is formed in the blank following the diameter reduction part 10-1 corresponding to the part 10 'of (B). In order to correspond to the length of the rack bar as a product, the length L1 required the length corresponding to the minimum L1 also as the length of a blank conventionally. On the other hand, in the present invention, since the length L1 corresponding to the product length is obtained by the stretching through the thickness reduction, the length of the blank can be shortened by the stretching obtained by the diameter reduction processing. That is, compared with the conventional one, the length of the tube can be basically shortened from L1 to Lo, so that the material cost and the running cost can be reduced by reducing the material and the weight of the product.

In the embodiment of Fig. 1C, a relatively short portion 10-3 is left on the rear end side of the thickness reducing portion 10-2 in the blank while remaining at the thickness of the tube. In the inner circumference of the part 10-3, the thread part for connecting the rack bar to the other parts of the steering mechanism is cut and formed so that the thickness part 10-3 is left. In practice, the thread is machined after the diameter reduction to match the diameter of the tap drill hole.

In addition, diameter reduction part 10 'of FIG. 1 (B) is shown as diameter reduction part 10-1 by making additional diameter reduction.

In the fourth step shown in Fig. 1D, the flattening deformation step of the portion of the blank obtained in (C), which becomes the gear part of the rack bar, is shown. That is, the upper surface 10-1A of the diameter reduction part 10-1 in the pipe used as the gear part of the rack bar as a product is deformed so that it may become flat, As a result, the pipe shows a cross-sectional shape of the half moon in this part. .

In the fifth step (E), the forging process of the rack gear in the flattening deformation part 10-1A of the blank is shown, and the teeth of the mold are formed in the flattening deformation part 10-1A by alternating indentation from the left and right sides of the metal core. According to the forging principle of the rack gear 11 according to the transfer molding is made. Fig. 2 schematically shows a forging process, which is basically the same as that of Patent Documents 1 to 3 or a long metal core may be used. In this embodiment, a shuttle-shaped metal core according to Patent Document 4 is used. I use it. That is, in FIG. 2, the combined mold for forming the rack bar is composed of a lower mold 12 and an upper and lower halves of the upper mold 14 so that the rack gear 14A is formed on the lower surface of the upper mold 14, The flattened top surface 10-1A in the diameter reduction part 10-1 of the blank 10 in which the rack gear type 14A completed the primary molding process (cross-sectional adjustment process) by the plastic working of FIGS. 1 (A)-(C) (FIG. 1 (D)). As disclosed in Patent Document 4, shuttle-type metal cores 16a and 16b are disposed on the left and right sides of the mold, and recesses (dashed lines) and end portions of the cross-sections of the shuttle-type metal cores are coupled to the outside of the shuttle-type metal cores 16a and 16b. Pressing rods 17a and 17b are arranged. The diameter reducing portion 10-1 of the blank 10 is disposed between the upper and lower molds 14 and 12, and when the mold closing is completed by combining the upper and lower molds 14 and 12, the upper surface 10-1A of the diameter reducing portion 10-1 of the blank 10 is the upper mold 14 It is substantially flattened by pressurizing by the gear part 14A, and the flattening process of the gear part formation surface demonstrated by FIG. 1D can be completed. The process then proceeds to the forging process for forming the rack gear. That is, the shuttle type metal cores 16a and 16b are alternately moved forward and backward (arrow f) by the pressure rods 17a and 17b, and pressed into the blank supported by the mold, so that the shuttle type cores 16a and 16b are reduced in diameter of the blank. In 10-1, the flesh of the material is projected (baking flow) toward the rack gear 14A of the upper die 14, and the flat gear 10-1A at the reduced diameter portion 10-1 of the blank according to the rack gear die 14A. The teeth 11 are transferred and molded (transfer molding) under the forging principle.

When the tooth rolling is completed as described above, the general process for finishing the product, that is, bending calibration, both ends swaging, flute processing, and two-side width processing 포장 加工, both ends of inner diameter tap, quenching and tempering, outer diameter grinding, gear meshing test, rust-proofing, etc. , shipping, but these processes are not related directly with the subject matter of the present invention a detailed description thereof will be omitted.

Next, the diameter reduction step outlined in FIG. 1 (B) as the primary forming (cross-section adjustment) step for forging the rack bar in the present invention and the shaft thickness reduction step outlined in FIG. This will be described in more detail. First, the diameter reduction step (step (B) of FIG. 1) will be described with reference to FIG. 3. The plastic processing apparatus for carrying out this step includes a mold holder 20 and a guide 22 which is inserted into the holder 20 in series and reduced. A combination die composed of a die 23 and a tip extrusion die 24, and an integral metal core composed of a metal core large diameter portion 26, a medium diameter portion 28, and a small diameter portion 29. The integral metal core is connected to the hydraulic cylinder mechanism. The length of the small diameter portion 29 is the length corresponding to the length of the gear portion 11 (Fig. 1 (C)) of the rack bar as a product.

Referring to the diameter reduction process performed by the apparatus of Fig. 3, first, as shown in (A), the blank 10 after the Bonderube treatment is mounted on the metal core diameter portion 28 as the first step. The blank 10 has a length Lo as described in Fig. 1A and is constant in the longitudinal direction with a thickness to. The metal core large diameter portion 26, the metal core medium diameter portion 28, and the small diameter portion 29 are moved forward integrally as in the direction of arrow a, and the blank 10 flows into the mold holder 20 and is guided by the tip tapered portion 22A. Flows into. When moving inside the guide 22, the blank is substantially free from plastic deformation and the outer diameter of the blank 10 is maintained (there is a gap between the inner diameter of the blank 10 and the small diameter portion 29 of the tip portion of the metal core middle diameter portion 28).

The metal core is further moved forward so that the blank 10 is introduced into the reduction die 23, and the taper portion 23A of the reduction die 23 causes the blank 10 to have a smaller diameter in order to eliminate the gap with the tip small diameter portion 29 of the middle core portion 28 of the metal core. In this way, the portion of the blank 10 to be reduced in diameter is represented by 10 'in FIG. 3 (B), and the portion of the original diameter that is not reduced in diameter is represented by 10' '. As the length of the diameter reducing portion 10 ', one corresponding to the length of the gear portion of the rack bar as a product is finally obtained. In other words, a blank (intermediate processed product) corresponding to Fig. 1B is obtained.

In this embodiment, the metal core medium diameter portion 28 is advanced together with the metal core diameter portion 26 as a last step, and the blank 10 in contact with the end face of the metal core diameter portion 26 is formed by the metal core diameter portion 26. By pressing forward in the direction of arrow a ', as shown in Fig. 3C, the tip of the diameter reducing portion 10' of the blank 10 is deformed as 10 '' 'by the tip extrusion die 24. This part 10 '' 'is not shown in Fig. 1 (B), but is formed auxiliary for bonding with the metal core in the thickness reduction process and is cut and removed when the use is finished.

4 to 6 show a plastic working process for reducing the thickness and reducing the diameter of the shaft portion of the rack bar as the product outlined in Fig. 1 (C). The plastic working device for reducing the thickness is formed by a metal core for thickness reduction 30 which is reciprocally driven in an axial direction by a long hydraulic cylinder device (not shown), and acts like a metal core 30 to reduce the diameter. Dice 32 for fine reduction and thickness reduction, and striker 34 (striker 34 is a radius in Fig. 4A) that becomes a stopper when the blank 10 is brought into close contact with the metal core 30 by diameter reduction and thickness reduction. The position which retracted to the outer side (arrow b ') is shown in figure. The metal core 30 is connected to the inlet part 30-1, the inner diameter determining part 30-2 subsequent to the thickness reducing part, and the hydraulic piston (not shown) by reducing the diameter to the same outer diameter as the inlet part 30-1. A stepped shape consisting of 30-3 is formed. The inflow portion 30-1 of the metal core 30 has a length corresponding to the length of the gear portion of the rack bar as the product, and the inner diameter determination portion 30-2 has a length corresponding to the length of the shaft portion of the rack bar as the product.

FIG. 4 (A) shows a state in which a blank whose diameter is reduced by the plastic working apparatus of FIG. 3 is mounted on the metal core 30 for the thickness reduction process by ironing. As shown in the figure, the outer circumferential surface of the metal core 30 from the inlet portion 30-1 of the metal core to the inner diameter determining portion 30-2 of the thickness reducing portion is formed from the blank 10 from the portion 10 'to the portion 10' '. It has a shape corresponding to the inner circumferential surface. The tip of the inlet portion 30-1 of the metal core 30 is in contact with the tip deformation portion 10 '' 'of the blank 10 (see Fig. 3C). In this state, when the hydraulic pressure flows into the hydraulic cylinder mechanism (not shown), the metal core 30 connected to the piston is advanced in the direction of the arrow a by the extension of the piston, and the tip of the inlet portion 30-1 of the metal core 30 is advanced. Since it is in contact with the tip deformation portion 10 '' ', the blank 10 moves toward the die 32 in the direction of the arrow a which is the same direction as the metal core 30. As a result, the blank flows into the die 32 from the tip deformation portion 10 '' '. In the region 10 'following the tip deformation portion 10' '' (see Fig. 3 (B)), the outer diameter of the blank is somewhat larger than the inner diameter of the die, but the difference in diameter is the clearance for the inlet portion 30-1. ), The diameter is reduced by that much, but the workpiece is subjected to slight diameter reduction without being affected by the increase or decrease in thickness. In Fig. 4B, the portions 10 '' 'and 10' after passing through the die 32 are not substantially changed in thickness.

The metal core 30 is moved further and the inner diameter determining portion 30-2 is opposed to the thickness reducing die 32 with the portion 10 '' of the blank (the thickness and the outer diameter being the unchanged state before the plastic working). ) The inner diameter of the die 32 is considerably smaller than the outer diameter of the portion 10 '', for example, the difference is about 1/2 of the thickness of the workpiece, and therefore the ironing operation by the die 32 under the forward movement (arrow a) of the blank 10 By this, the part 10 '' of the blank is reduced in thickness and lengthened. The portion where the thickness of the blank on the inner diameter determining portion 30-2 10 '' (Fig. 4 (A)) passed through the dice 32 was reduced to 10-2 in Fig. 4B. In the process of ironing, the portion 10 '' positioned behind the die 32 in the workpiece gradually becomes shorter, and the portion 10 '' on the inner diameter determining portion 30-2 is plastically processed to form the connecting portion 30. With the length increasing toward -3 and the cylinder connecting portion 30-3 of the metal core 30 passing through the die 32, the relatively short portion of the portion 10 '' is the thickness of the tube as shown in Fig. 4 (B). Remains on phase 30-3. As for the foremost end (FIG. 4 (B)) in the forward movement (arrow a) of the metal core 30, the workpiece on the metal core 30 passes through the die 32 completely and the rear end surface of the blank 10 ( The face is located somewhat beyond the front face of the striker 34 in the retracted position.

Fig. 5 shows the next step (C) of the plastic working apparatus, and the striker 34 which has been in the retracted position so far is advanced in the radially inward direction (arrow b) so that the tip of the striker 34 is in contact with the connection part 30-3 of the metal core. do.

The following process is shown in Fig. 5C, in order to retract the metal core 30 in the same direction as the arrow c in the right direction of the drawing, the hydraulic pressure of the hydraulic cylinder for driving the metal core not shown is switched. During the retraction of the metal core 30, the rear end 10 '' of the blank 10 is in contact with the shoulder 30-4 between the joint 30-3 and the inner diameter determining portion 30-2 of the metal core, so that the rear end 10 '' is in contact with the striker 34. Until the blank 10 is interlocked with the metal core 30. However, if the back end 10 '' is retracted in the direction of the arrow c of the metal core 30 until the contact with the striker 34 occurs, the linkage (retraction) of the blank 10 is blocked by the striker 34, while the retraction movement of the metal core 30 is Subsequently, in the process, the inner diameter determining unit 30-2 presses the rear end 10 '' of the blank 10 outward to expand the radius. Therefore, at the rear end of the work, an expansion pipe part 10-3 protruding radially outward from the thickness reducing part 10-2, which is close to the pipe thickness of the work, appears. Accordingly, the right end portion is reduced in diameter by the post process and is given the thickness required to process the tab. 5 (D) shows a state in which the metal core 10 has been removed to the retracted position.

In the next step, the diameter of the second stage of the portion that becomes the gear part of the rack bar as a product by passing through the steps (E) to (G) of FIG. 6 with respect to the blank of FIG. Reduce. The diameter reduction device is composed of a metal core 36 and a die 37. In step (E) of FIG. 6, the metal core 36 for diameter reduction is inserted into the workpiece of FIG. 5D. The metal core 36 includes a tip portion 36-1, a tapered portion 36-2, and a base portion 36-3 having a reduced outer diameter, and the base portion 36-3 is connected to a hydraulic cylinder not shown in the drawing.

The metal core 36 is advanced by flowing hydraulic pressure into the hydraulic cylinder, and the work on the metal core 36 flows into the die 37. By flowing into the die 37, the portions 10 " 'and 10' of the blank 10 are smaller in diameter by the clearance of the outer diameter of the tip portion 36-1 of the metal core 36. Fig. 6 (F) shows the most advanced state of the metal core 36 in which the tapered portion 36-2 of the metal core 36 is in contact with the die 37 from the front, and the portion 10 '(Fig. 6 (E)) of the blank 10 is its entire length. The thickness is reduced while the thickness remains as it is, resulting in a diameter reduction portion 10-1, and the tip portion thereof is indicated by 10-1 '. In this state, the metal core retreats in the direction of the arrow in (G), and as a result, the tip diameter reducing portion 10-1 (Fig. 1 (C)) which becomes the gear portion in the rack bar product is formed. The tip 10-1 ′ is finally cut off as an unnecessary portion, and basically, a blank for gear roll forming as described in FIG. 1C can be obtained. The blank undergoes forging of the rack gear with respect to the diameter reduction part 10-1 by going through the steps 1 (D) and (E).

Fig. 7 and the following shows a second embodiment of the present invention. The work for forming the gear portion shown in Figs. 1 (B) and (C) is shown at a glance using a blank pre-processed only at the tip deformation portion after the Bonderube treatment. Preliminary plastic processing (reduction of the diameter of the portion that becomes the gear part of the rack bar and reduction of the thickness and length extension of the portion that becomes the shaft portion of the rack bar). The plastic working apparatus of this embodiment includes a holder 40, in which a combination die as a series of structures of a first guide cylinder 42, a die 44, a second guide cylinder 46, and a diameter reduction die 48 is inserted. The diameter reducing die 48 is in contact with the inner projection 40-1 of the holder 40, and the pressure tool 49 is fastened to the rear end with a screw so as to be in contact with the first guide cylinder 42, whereby the guide cylinder and the die are fixed in the holder 40. The first guide cylinder 42 is tapered in its inlet end 40A in order to facilitate the inflow of the blank by the metal core 52, but the remaining portion has a uniform inner diameter. The die 44 has a step 44A, and acts like a metal core 52, thereby reducing the thickness of the blank. The die 44 is connected to the diameter reduction die 48 with a second guide cylinder 46 having a constant internal diameter therebetween, and the diameter reduction die 48 only reduces the diameter while substantially maintaining the thickness of the blank tip by the tapered portion 48A. The combination die is processed by acting in combination with a combined metal core composed of a large metal core diameter portion 50 and a metal core medium diameter portion 52. The metal core (punch) large diameter portion 50 and the metal core medium diameter portion 52 are connected to a hydraulic cylinder (not shown in the drawing) and stretchable. In addition, the metal core medium diameter portion 52 includes a small diameter portion 52-2 for diameter reduction protrusion that protrudes forward with the taper portion 52-1 interposed therebetween. 54 is a blank knockout pin after completion of the process.

Next, the operation of the second embodiment will be described. As for the blank 10, as described in Fig. 1 (A), the Bonderube treatment is performed on the tube supplied from the manufacturer, and only the tip portion is deformed and the other portion is straight and has a constant thickness. Will have. The blank 10 is introduced into the apparatus by the metal core medium diameter portion 52 and the small diameter portion 52-2 which are turned to the left in the direction of the arrow a in the figure. In other words, the blank 10 is bonded to the metal core medium diameter portion 52 substantially without space, but since the tip of the metal core small diameter portion 52-2 is in contact with the deformation portion of the tip portion, the blank 10 is moved by advancing the entire metal core in the direction of arrow a. Are interlocked in the same direction. And until the front end of the blank 10 reaches the state of FIG. 7 (A) which contact | abuts the step part 44A of the die 44, processing with respect to the blank 10 is not substantially made but the diameter and thickness of the blank 10 remain as it is.

From the state of FIG. 7A, the hydraulic pressure is continuously supplied to the hydraulic cylinder for driving the metal core, and the entire metal core until the taper portion 52-1 reaches the state of FIG. 7B facing the taper portion 44A of the dice 44 Will move forward. The entire metal core is further advanced from the state shown in Fig. 7B, and the blank 10 is advanced while the tip of the small diameter portion 52-2 is in contact with the deformation portion of the tip, and blank 10 passes through the die 44 in the process. The taper portion 44A decreases the diameter, and the diameter reduction portion 10 '' '' of the blank after diameter reduction is in contact with the outer circumferential surface of the diameter reduction protrusion 52-2 of the metal core medium diameter portion 52, The thickness is slightly increased or substantially the same as the tube. In the advancement of the metal core, the portion of the blank on the rear side of the die 44 is not reduced in diameter and the outer diameter is intact, but the length portion 10-3 of the portion having the outer diameter as it is is extruded to the rear and the thickness is reduced. So-called back extrusion molding.

When the metal core medium diameter portion 52 is further advanced from the state of Fig. 7 (B) as shown in Fig. 7C, the metal core medium diameter portion 52 acts like the taper portion 44A of the die 44, and the blank is reduced in thickness and is extruded backward. A thickness reducing portion 10 " '" is formed and the blank is elongated by that thickness reduction. If it continues, the diameter reduction part 10-1 will pass through the diameter reduction die 48, and since the diameter of the metal core 52-2 is small even if it is influenced by the diameter reduction, it will remain the thickness and diameter reduction die as shown in FIG.7 (D). Protrudes from 48. As a result, the diameter reducing portion 10-1 (the portion that becomes the gear portion of the rack bar as a product) and the thickness reducing portion 10-2 reduced to, for example, 1/2 of the thickness of the tube, substantially as the thickness of the tube. Substantially the same as that described in Fig. 1 (C), which consists of an end portion 10-3 (a screw for connecting to other parts is formed on the inner circumference) having a cross-sectional area adapted for tapping, and a portion which becomes a connecting shaft of a rack bar as a product This completes the blank forging of the rack gear.

In the second embodiment, it is possible to make the blank for roll bar rolling substantially in one step by using a straight pipe which has been pre-processed only in the tip deformation portion of the universal machine.

In the above embodiment, the hydraulic cylinder device for driving the metal core is assumed to be horizontal in the example shown in the drawing, but may be vertical. In addition, in order to improve productivity and ease of use, instead of a hydraulic cylinder device, a long ball screw driven by a variable speed servomotor can be used.

In an electric power steering mechanism or the like, a variable pitch rack bar is often employed. In this kind of mechanism, it is necessary to change the pitch and the inclination angle as the teeth, and it is suitable to plasticize the pipe material because it is difficult to manufacture by cutting. In addition, in electric power steering, the bending strength in the gear portion is required to be higher than in the hydraulic type. Therefore, although the teeth are larger and require a thicker thickness, the present invention can realize the maximum reduction in the weight of the rack bar while satisfying this requirement. That is, the gear part molding of this invention protrudes radially under the plastic flow, ie, non-cutting of a metal fiber, of a pipe material. Under such a molding principle, the management of the cross-sectional area of the raw material was originally necessary, but in the conventional method, it was performed by simple polishing. In the present invention, on the other hand, the workpiece is subjected to plastic working so as to increase or decrease the thickness of each part as desired along the longitudinal direction, thereby providing a cross-sectional area corresponding to the required function for each part. In the tooth shaping portion, the thickness of the tube is basically maintained so that the required teeth are obtained by the plastic flow, but when the thickness needs to be increased somewhat, the thickness is increased by reducing the diameter. On the other hand, in the parts other than the tooth-molded part, since the required strength is achieved even if it is thinner than the thickness of the tube, the present invention reduces the thickness within the allowable range of the required strength. Reducing the thickness is effected by ironing and the shaft length is extended by that amount. In other words, the present invention manages the final product length by calculating the extension length of the shaft length due to the reduction of the thickness of the pipe. In other words, the shorter length of the pipe material can be adopted as the extension length of the shaft length. Can also be reduced. For example, in the prior arts of Patent Documents 1 to 4 and the like, in the case of using a material having a thickness of 4 mm, a diameter of 25 mm, and a length of 615 mm as a starting material (tube), the weight of the tube is a large error as the weight of the product. It is about 1,236g without. On the other hand, according to the present invention, even if the thickness of the tube is equal to 4 mm in the gear portion, even if the thickness of the long shaft portion other than the gear portion is 2 mm, which is about half, it is possible to sufficiently secure the rigid function even by ironing. I knew there was. In this case, a short one can be used for the extension by ironing, and the length of the gear is the same as the thickness of the tube. However, by reducing the required length of the tube, the material weight (= product weight) is 920 g. There was no problem. In this case, the weight reduction is also reduced by 25.6% in comparison with the conventional forging methods such as Patent Documents 1 to 4, and in fact, the reduction ratio is more than 60% in comparison with the round bar as a material. Cost reduction can be realized even if additional processing by swaging or ironing is required to manage the cross-sectional area by plastic working. For example, if the material cost is 1 kg = 170 yen, the material cost reduction in the above example is (1.236-0.920) x 170 = 53.7 yen / piece, while the depreciation cost of the mold including the hydraulic cylinder device is 10 yen / piece at most. Material costs can be reduced by as much as 48 yen per piece. In addition, since the weight of the rack bar is reduced, the weight of the vehicle is reduced, and as a result, the acceleration performance of the vehicle is improved and the fuel consumption is reduced. The fuel economy reduction effect is insignificant for one-to-one, but it is also desirable from the point of view of resource savings considering the vast global automobile market, which reaches 70 million vehicles annually.

In addition, thinning the thickness by ironing after swaging causes surface roughness to be mirrored on both inside and outside, so that the size can be managed by the size of micron unit, thereby ensuring high quality and high precision easily. can do.

Claims (6)

In the method of processing a hollow rack by plastic working using a cylindrical work, the angle along the longitudinal direction as the hollow rack prior to the provision of teeth to the work In order to give a cross-sectional area corresponding to the required function for each site, each process in the longitudinal direction of the workpiece is increased or decreased to a desired thickness by plastic working to reduce the weight. In the plastic working method of the hollow rack which clamps a cylindrical workpiece | work by a metal mold | die, and presses a metal core into the inside diameter of a workpiece | work, and gives a tooth | die shape by a metal mold | die to the predetermined | prescribed part of a workpiece | work, Prior to the provision of the tooth to the workpiece, the portion of the workpiece in the non-imparted region of the tooth by the mold is stretched in the longitudinal direction by reducing the thickness by plastic working, thereby reducing the weight. Way. The method according to claim 1 or 2, The plastic working process for reducing the thickness or increasing the thickness in one step. The method according to claim 1 or 2, The plastic processing for reducing or increasing the thickness is made by dividing into several processes. The apparatus for carrying out the method of claim 1 or 2, wherein the plastic processing apparatus for increasing or decreasing the thickness of the workpiece comprises a mold consisting of a long metal core and several dies, and works in the same manner as the mold. And a reciprocating drive mechanism for driving the workpiece relative to the mold to increase and decrease each portion of the mold to a desired thickness. Hollow racks used as steering parts of vehicles and formed by plastic working using pipes, which have the thickness of the pipes as they are or are increased to some extent, and which are greatly reduced from the existing thickness of the pipes and are elongated. A hollow rack having a portion and having a rack gear shape formed at a portion where the thickness is substantially the same as the existing thickness of the tube or is increased to some extent.

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