JP4876897B2 - Method for manufacturing universal joint yoke - Google Patents

Description

  The present invention relates to a universal joint yoke manufacturing method in which a universal joint yoke is manufactured by performing a cold forging step and a plate forming step.

As a manufacturing method of this type of universal joint yoke, for example, a universal joint can be obtained by performing so-called plate forming for performing a process that can be performed easily and in a short time by pressing work such as punching, deep drawing, and punching on a metal plate. The yoke for manufacturing is manufactured (for example, refer patent documents 1 and 2).
JP-A-9-14282 (first page, FIG. 12) JP 2002-66677 A (Page 2, FIGS. 1 to 15)

  However, in particular, in the case where the strength of the yoke is required to increase with the popularization of the electric power steering device capable of high torque as in recent years, and the thickness of the arm base is required, the above Patent Document 1 In the described conventional example, a universal joint yoke is manufactured by bending a metal plate having no level difference as a raw material, so that the connecting portion 100 in the central portion as shown in FIG. And the arm portion 101 bent upward from both sides thereof, the base portion of the arm portion 101 that requires the thickened portion 102 is drawn as shown in the alternate long and short dash line, and the thickness is reduced. There is an unsolved problem that the strength cannot be secured.

Although it is conceivable to form a round bar material by hot forging, since hot forging has poor processing accuracy, there is an unresolved problem that finishing cutting increases and manufacturing costs increase.
Accordingly, the present invention has been made paying attention to the unsolved problems of the above conventional example, and provides a universal joint yoke manufacturing method capable of manufacturing a universal joint yoke with high accuracy while ensuring strength. The purpose is to do.

In order to achieve the above object, a universal joint yoke manufacturing method according to claim 1 forms a universal joint yoke by sequentially performing a cold forging step and a plate forming step on a round bar material . A universal joint yoke manufacturing method, wherein the cold forging step includes a base portion at a central portion and a pair of arm portions extending symmetrically outward from the base portion, and the arm portions are arranged on the base side. A flat part and a link part formed on the front end side connected to the flat part to have a thickened link part protruding from the inner surface in the plate forming step are formed, and at least the base part and the pair of arm parts the thickness of the boundary portion and step you molded cold forged product of step plate shape thicker than the thickness of the arm portion, the plate as molded Engineering, said undercut portion by a flat portion at the base side of the link portion between the cold by a two-step molding as but is formed Both the pair of arm portions of the stepped plate shape formed by granulation process is characterized in that the higher the Engineering of Ru bent to face.

The universal joint yoke manufacturing method according to claim 2 is the invention according to claim 1, wherein, in the cold forging step, two-stage cold forging is performed so as to reduce generation of burrs. It is characterized by.
Furthermore, the manufacturing method of the universal joint yoke according to claim 3 is the invention according to claim 2, wherein in the cold forging step, a cold bar forging is performed by cold forging a round bar material from a direction orthogonal to the axial direction. A first cold forging step for forming an intermediate product, and a cold forging molded product having the stepped plate shape by forging the cold forging intermediate product forged in the first cold forging step from the axial direction It has the 2nd cold forging process which obtains.

Still further, a universal joint yoke manufacturing method according to claim 4 is the invention according to any one of claims 1 to 3, wherein, in the plate forming step, the flat portion is formed so as to form the undercut portion. The first plate forming step for bending the plate and the second plate forming step for bending the link portion connected to the flat portion are performed.

According to the present invention, the round bar material has a base portion at the center and a pair of arm portions extending symmetrically outward from the base portion, and at least the thickness of the boundary portion between the base portion and the pair of arm portions By performing a cold forging process for forming a stepped plate shape that is thicker than the thickness of the arm part, and a plate forming process for bending a pair of stepped plate shaped arm parts formed in the cold forging process in the same direction. Since the universal joint yoke is formed, it is possible to easily form any stepped plate shape having a different thickness in the cold forging process, and at least the thickness of the boundary between the base and the arm is greater than the thickness of the arm. By increasing the thickness, it is possible to prevent the shrinkage from being formed at the base of the arm part when forming the plate for bending the arm part, and to obtain the effect of accurately manufacturing the universal joint yoke while ensuring the strength. .
In addition, when the plate forming process is divided into two stages, the first link is formed when a relatively thick link part protruding inward is formed at the tip of the arm part of the universal joint yoke. Only the flat part of the arm part that does not include the part can be bent, and then the link part can be bent, and the arm part with the undercut part formed on the lower side of the link part can be easily plate-formed, and the thickness is different. The effect that the universal joint yoke having the arm portion can be easily manufactured is obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 is an overall configuration diagram showing a steering apparatus having a universal joint yoke to which the present invention is applied, FIG. 2 is an enlarged longitudinal sectional view of an intermediate shaft, FIG. 3 is a perspective view showing a round bar material, and FIG. FIG. 5 is an explanatory diagram for explaining the start of forging in the second cold forging process, and FIG. 6 is an explanatory diagram for explaining the end of forging in the second cold forging process. FIG. 7 is a partially enlarged cross-sectional view of the second upper die for cold forging, FIG. 8 is a view showing a finished cold forging product and a finished plate forming product, and FIG. (B) is a bottom view of the finished cold forged product, (c) is a front view of the finished plate-formed product, (d) is a bottom view of the finished plate-formed product, and FIG. FIG. 10 is an explanatory diagram for explaining the second plate forming process, FIG. 10 is an explanatory diagram for explaining the second plate forming process, and FIG. It is a surface view.

In the figure, SD is a steering device, and this steering device SD has a steering shaft 2 with a steering wheel 1 mounted at the rear end (right end in FIG. 1), and this steering shaft 2 can freely rotate to a steering column 3. Is held in.
At the front end (left end in FIG. 1) of the steering shaft 2 is connected to the steering shaft 2 and applies a steering assist torque, and an electric motor that generates the steering assist torque connected to the worm reducer 11. A steering assist mechanism (electric power steering) 4 is connected.

An intermediate shaft 18 is connected to the output shaft 14 of the worm reducer 11 via a universal joint 17A, and this intermediate shaft 18 is connected to a pinion shaft 19 of the rack and pinion type steering gear mechanism 6 via a universal joint 17B. ing.
A rack shaft (not shown) of the steering gear mechanism 6 is connected to a steered wheel (not shown) via a tie rod 5.

Here, the steering shaft 2 includes an outer shaft 7 and an inner shaft 8, and the front end portion of the outer shaft 7 and the rear end portion of the inner shaft 8 are spline-coupled and are coupled via a synthetic resin. . Therefore, the outer shaft 7 and the inner shaft 8 can shorten the total length by breaking the synthetic resin at the time of collision.
Further, the cylindrical steering column 3 inserted through the steering shaft 2 is formed by combining the outer column 9 and the inner column 10 in a telescope shape, and absorbs energy caused by the impact when an axial impact is applied. However, it has a so-called collapsible structure in which the overall length is reduced.

The front end portion of the inner column 10 is fixed to the rear end surface of the housing 11a of the worm speed reducer 11, the inner shaft 8 is inserted into the housing 11a of the worm speed reducer 11, and the front end portion of the inner shaft 8 is The output shaft 14 protrudes from the front end surface of the housing 11 a of the speed reducer 11.
The outer column 9 of the steering column 3 is supported on the vehicle body side member 16 by the upper bracket 15U so that the tilt and telescopic position can be adjusted, and the housing 11a of the worm speed reducer 11 in the steering assist mechanism 4 is attached to the vehicle body side member 16. A pivot pin 15p pivotally supported by the attached lower bracket 15L is supported so as to be swingable in the vertical direction.

As shown in FIG. 2 showing the longitudinal sectional view of the intermediate shaft 18, a male shaft 21 connected to the universal joint 17A and a female connected serrated to the outer peripheral side of the male shaft 21 and connected to the universal joint 17B. A shaft 22 is provided.
Here, as shown in FIG. 2, the universal joint 17 </ b> A includes a pair of yokes 23 and 24 and a cross shaft 25 that connects the pair of yokes 23 and 24. The yoke 23 is formed in a U shape by a pair of arm portions 23a and 23b and a connecting portion 23c that connects the base portions of the arm portions 23a and 23b.

Further, as shown in FIG. 3 showing a side view of the yoke 23, a connecting hole 23d is formed through the connecting portion 23c at the center position. The connecting shaft portion 21c of the male shaft 21 is connected to the connecting hole 23d. The connecting portion 23c and the connecting shaft portion 21c are integrally connected by fixing means such as welding or caulking.
Further, link portions 23e and 23f for mounting the cross shaft 25 are formed at the tip portions of the arm portions 23a and 23b, and a bearing cup insertion hole 26 for inserting the cross shaft 25 is formed in the link portions 23e and 23f. .

Similarly to the yoke 23, the other yoke 24 is also formed in a U shape by a pair of arm portions 24a and 24b and a connecting portion 24c that connects the base portions of the arm portions 24a and 24b. The output shaft 14 of the worm reducer 11 is clamped by a bolt 27.
Further, as shown in FIG. 2, the cross shaft 25 includes a body portion 25 a and four shaft portions 25 b formed on the body portion in a cross shape. Each shaft portion 25b has a spider pin 25c embedded at the tip thereof at the center axis position, a needle bearing 25d disposed on the outer peripheral surface, and a bearing cup 25e disposed so as to cover the spider pin 25c and the needle bearing 25d. It is installed. Each shaft portion 25b of the cross shaft 25 is inserted into a bearing cup insertion hole 26 formed in the arm portions 23a, 23b and 24a, 24b of the yokes 23 and 24.

On the other hand, the universal joint 17B has the same configuration as the universal joint 17A. The yoke 23 is connected to the female shaft 22 of the intermediate shaft 18, the yoke 24 is connected to the pinion shaft 19 of the steering gear mechanism 6, and these yokes. And a cross shaft 25 for connecting 23 and 24.
Further, as shown in FIG. 2, the male shaft 21 has a small-diameter central shaft portion 21a, a serration shaft portion 21b formed larger in diameter than the central shaft portion 21a formed at the left end thereof, and a connecting shaft formed at the right end. Part 21c. The serration shaft portion 21b is formed with a relatively long axial length, and the connecting shaft portion 21c is formed with a relatively short axial length.

Further, the female shaft 22 is formed in a cylindrical shape, and a serration hole 22a is formed on the inner peripheral surface thereof over the entire length, and the yoke of the universal joint 17B is formed on the outer peripheral surface of the left end in FIG. 2 as shown in FIG. In a state in which the connection shaft 23b is serrated and connected to the connection hole 23d, the connection shaft portion 22b and the connection portion 23c are connected by fixing means such as welding or caulking as shown in FIG.
The yokes 23 of the universal joints 17A and 17B are, as follows, a circular bar material that is cold-forged and extended outwardly symmetrically from the circular part as a base part having a thick central part and the circular part. A cold forging step for forming a stepped plate-shaped cold forging formed product having a pair of arm portions having a thickness thinner than the circular portion, and subsequently a plate for bending the pair of arm portions in the same direction vertically upward. It is manufactured by performing a molding process.

  In the cold forging process, first, as shown in FIG. 3, the masses of burrs and holes to be cut in the yoke 23 of the universal joints 17A and 17B to be finally formed are cut out during the cold forging process. A round bar made of, for example, carbon steel (S15C to S35c) having a predetermined diameter so as to have an added mass was cut at a predetermined length, and the relationship between the diameter D and the height H was set to H / D ≦ 1. The round bar material 31 is used to improve the yield when forming a final cold forging finished product 35 to be described later.

  And this round bar raw material 31 is heat-processed. In this heat treatment, an annealing method is selected according to the strength requirements of the product and the processing conditions so that S15C to S35C is completely annealed in the annealing furnace, and S25C to S35C is subjected to spheroidizing annealing or complete annealing. did. Furthermore, a surface treatment in which a bonder treatment is added to the shot peening treatment may be performed. Next, the lubricant is applied and then mounted on the press.

  In this press machine, first, as shown in FIG. 4 (a), a flat part 41, and an arcuate concave part 42 having a relatively large radius Rc extending in the front-rear direction formed in the center part of the flat part 41, A pair of first cold forgings that are symmetrical in the vertical direction and formed with an arc 43 having a radius Rd smaller than the radius Rc of the arc-shaped recess 42 formed between the left and right sides of the arc-shaped recess 42 and the flat portion 41. The round bar material 31 is mounted between the upper and lower molds 44U and 44D with the axial direction thereof being, for example, the front-back direction.

Here, the radius Rc of the arc-shaped concave portion 42 of the first cold forging upper die 44U and the lower die 44D is ½ of the diameter D of the round bar material 31, that is, not more than the radius (D / 2) ≧ Rc is selected. The relationship of Rc> Rd and D / 2 ≧ Rc improves the fluidity of the material and has the effect of reducing the load.
Next, as shown in FIG. 4B, the first cold forging upper die 44U and the lower die 44D are moved relative to each other until the distance between the two becomes a predetermined distance t, whereby the round bar material 31 is obtained. The circular portion 32 serving as a base portion that becomes the above-described connecting portion 23c in the central portion by crushing from the vertical direction orthogonal to the axial direction thereof, and the above-described arm portion 23a extending symmetrically outward in the left-right direction from the circular portion 32 The first cold forging intermediate product 34 is obtained in order to obtain a cold forging finished product 35 having a shape with less burr generation in a second cold forging process described later. Perform forging.

  Here, the predetermined interval t between the first cold forging upper die 44U and the lower die 44D is, as shown in FIG. 4B, the first cold forging upper die 44U and the lower die. When the depth of the arc-shaped recess 42 of the die 44D is ΔX and the diameter of the circular portion 32 of the cold forged product 35 ′ is D1 as shown in FIG. 6A, the second cold forging is used. It is selected so that D1 ≦ t + 2ΔX so that it can be stably fixed and placed on the lower mold 45D.

Next, as shown in FIGS. 5A to 5C, a pair of upper and lower second cold forgings is performed by changing the direction by 90 degrees so that the longitudinal direction of the formed cold forging intermediate product 34 is the vertical direction. Mount on the upper and lower molds 45U and 45D.
Next, as shown in FIGS. 6A to 6C, the second cold forging upper die 45 </ b> U and the lower die 45 </ b> D are moved relative to each other until they approach each other, so that the lower end of the circular portion 32 is moved. A bulging portion 32a bulging downward is formed so as to increase in thickness, and the flat portion 33a is thinner than the circular portion 32 on the circular portion 32 side, and the flat portion is connected to the tip side of the flat portion 33a. A cold forging finished product 35 ′ is obtained in which an arm portion 33 having a link portion 33 b that protrudes in a cylindrical shape upward from the inner surface in a plate forming step described later from the portion 33 a is formed. Perform cold forging.

  Here, in the second cold forging upper die 45U, as shown in FIG. 7, a taper θ1 of 5 to 30 degrees is attached to the portion for pressing the burr to reduce the surface pressure of the burr portion, The increase in load is prevented. However, if the taper angle is increased too much or the relief is made, the surface pressure of the burr portion is lost, and a strong tensile stress is generated in the burr, which may cause cracking. Therefore, the second cold forging upper die 45U The taper angle is preferably 5 to 20 degrees.

Further, in order to improve the mold separation of the material, as shown in FIG. 7, the side surface of the partial mold may be formed with a draft of taper θ2, θ3 (1 to 10 degrees).
In the second cold forging, as shown in FIGS. 6 (a) to 6 (c), a burr 36 extending outward is generated at the outer peripheral edge of the intermediate portion in the vertical direction of the cold forged product 35 '. The burr 36 is punched and removed by punching with a punch having the same shape as the cold forged product 35 in FIG. Finish the forged product 35.

  As shown in FIGS. 8A and 8B, the cold forged finished product 35 has a bulging portion 32a extending outward from the flat surface 32b at the lower end central portion and the outer peripheral edge of the flat surface 32b. The first taper portion 32c having a relatively gentle inclination angle that gradually decreases in thickness according to the angle, and the arm portion 33 with an inclination angle slightly steeper than the inclination angle of the first taper portion 32c from the outer peripheral edge of the first taper portion 32c. The flat portion 33a is formed with a second tapered portion 32d reaching the lower end surface on the circular portion 32 side. The first tapered portion 32c and the second tapered portion 32d do not need to be different tapered portions, and both may be uniform tapered portions.

Further, upon receiving the punch 56 in the plate forming step described later on the upper surface of the circular portion 32 of the cold forged finished product 35, as shown in FIGS. 8 (a) and 8 (b), the punch 56 slides and moves. An engagement recess 32e extending in the front-rear direction when viewed from the plane to be suppressed is formed.
Here, the stepped plate shape to be formed may be formed by making the bending corner portion 32f, which is the base of the arm portion 33 of the circular portion 32, bent in a plate forming step, which will be described later, thicker than the arm portion 33, and the overall shape depends on product requirements. Change the shape arbitrarily.

  In this way, by introducing the first cold forging process, which is a preforming process, in the cold forging process, the generation of burrs can be reduced and the yield is improved. Moreover, since it can be formed into an arbitrary stepped plate shape by crushing the round bar material 31, it is possible to increase the thickness of the bending corner portion 32f that may cause shrinkage when forming a plate described later, It is possible to deal with the production of yokes of various types.

Next, plate forming is performed on the cold forged finished product 35 by bending the arm portion 33 in the same vertical upward direction.
In this plate forming, the arm part 33 of the stepped plate-shaped cold forging finished product 35 is formed by the flat part 33a on the circular part 32 side and the link part 33b protruding inward on the tip part side. Since it cannot be formed by a single bending process using a punch, two-stage forming is performed.

  In this two-stage molding, first, first plate molding is performed by using the first plate molding die 51 to bend the flat portions 33a of the pair of arm portions 33 at a right angle so that they face each other. At this time, as shown in FIG. 9, the first plate forming mold 51 has a lower end portion at the intermediate portion in the width direction of the second tapered portion 32 c of the circular portion 32, that is, the boundary between the circular portion 32 and the arm portion 33. A constricted portion 52 that is opposed to the bent corner portion 32f that is a predetermined distance, a relief portion 53 that is slightly larger in diameter than the constricted portion 52 that communicates below the constricted portion 52, and a constricted portion 52. The first and second plate forming molds 51 are fixedly placed on a pedestal 55. The first and second plate forming molds 51 are fixedly placed on a pedestal 55. As shown in FIG.

  Here, the curved shape of the curved introducing portion 54 is such that when the circular portion 32 of the cold forged finished product 35 is pushed into the narrowed portion 52 with the punch 56 as described later, the outer surface of the arm portion 33, the curved surface, and the contact portion. The gap between the outer surface of the arm portion 33 and the curved surface is surely prevented from being bent locally and tensile stress is prevented from being generated in the gap portion. Like to do.

  Further, as shown in FIG. 9 (b), the punch 56 used for the first plate forming is engaged with the engaging recess 32e of the cold forged finished product 35, and the link portion 33b contacts with the final shape of the left and right side surfaces. A pair of left and right flat portions 56a and 56b for receiving the inner surface of the flat portion 33a are formed at the last position. The distance Lp1 between the flat portions 56a and 56b is 2 from the distance L between the narrowed portions 52 of the first plate forming die 51 to a thickness ΔW1 which is thinner than the thickness ΔW0 of the pair of flat portions 33a of the cold forged finished product 35. When a value obtained by subtracting double (Lp1 = L−2ΔW1) is set and the thickness of the link portion 33b is ΔW2, the relationship between each thickness ΔW0 to ΔW2 is selected as ΔW2> ΔW0> ΔW1.

  Then, with the cold forged finished product 35 placed on the upper end portion of the first plate molding die 51, the punch 56 is placed on the upper surface side of the circular portion 32 of the cold forged finished product 35. The bent corner portion 32f of the bulging portion 32a is bent while being squeezed by the narrowed portion 52 of the mold 51 by being lowered in a state of being engaged with the engaging concave portion 32e. The flat plate portion 33a is erected at a right angle with respect to the circular portion 32 so as to face each other, and the first plate forming is performed to form the plate forming intermediate product 37 with the link portion 33b inclined upward and outward.

Thus, when the bending corner portion 32f of the bulging portion is bent while being squeezed by the squeezing portion 52 of the mold 51, a compressive stress can be applied by sandwiching the side surface of the arm portion 33 between the squeezing portion 52 and the punch 56. Since the yield stress is represented by a value obtained by subtracting the compressive stress from the tensile stress, the tensile stress generated in the bending can be lowered by increasing the compressive stress.
Moreover, since the engagement recessed part 32e which receives the punch 56 is formed in the upper surface of the circular part 32 of the cold forging finished product 35, when the punch 56 engages with the engagement recessed part 32e, the cold forged finished product 35 Can be reduced, and the punch 56 and the cold forged finished product 35 can be accurately centered.

Next, as shown in FIGS. 9A and 9B, the second plate molding die 61 is used to align the link portion 33 b of the plate molding intermediate product 37 with the flat portion 33 a of the arm portion 33. The second plate is bent so that the outer side surfaces of the two become the same vertical surface.
As shown in FIGS. 10 (a) and 10 (b), the second plate forming mold 61 is composed of a divided upper mold 61U and a divided lower mold 61D that are divided vertically. The split upper mold 61U has a symmetric curved introduction portion 62 whose upper end portion engages with the outer surface of the link portion 33b of the plate forming intermediate product 37 and whose opposing length decreases as it goes downward, and this curved introduction portion. A vertical flat portion 63 that engages with the outer surface of the root portion of the arm portion 33 that communicates with the lower end side of the portion 62, and a relief portion 64 that gradually becomes longer than the lower surface of the vertical flat portion 63 and then becomes a vertical surface. And are formed.

On the other hand, the divided lower mold 61D communicates with the lower end of the escape portion 64 of the divided upper mold 61U and has a relief portion 65 whose opposing length becomes shorter as it goes down, and communicates with the escape portion 65 to split the upper portion. A vertical flat portion 63 of the mold 61U and a vertical flat portion 65 having the same vertical surface are provided. Here, the relief portion 65 has an effect of reducing the molding load.
A pedestal 67 for receiving the flat surface 32b of the circular portion 32 and the first tapered portion 32c of the plate forming intermediate product 37 is disposed between the vertical flat portions 66 of the divided lower mold 61D. The pedestal 67 knocks out the finished plate-molded product 38 and prevents deformation and shape correction of the flat surface 32b of the bulging portion 32a and the first tapered portion 32c.

Further, the punch 68 used for the second plate forming is a cylindrical body 68a that engages with the engaging recess 32e of the cold forged finished product 35, as shown in FIG. 11 showing a sectional view perpendicular to the axial direction of the punch. A pair of left and right recesses 68b and 68c for receiving the inner side surface of the link portion 33b are formed on the left and right side surfaces.
The distance Lp2 between the bottom surfaces of the recesses 68b and 68c is the thickness 2 of the pair of link portions 33b of the cold forged finished product 35 from the distance L between the vertical flat portions 63 of the divided upper mold 61U as shown in FIG. A value obtained by subtracting × ΔW2 (Lp2 = L−2ΔW2) is set. For this reason, by receiving the inner surface of the link portion 33b by the recesses 68b and 68c during the second bending process, the front and rear end portions of the link portion 33b are guided by the side surfaces forming the recesses 68a and 68c, and the link portion 33b. The bending in the front-rear direction can be suppressed.

  Then, as shown in FIG. 10A, the plate molding intermediate product 37 is placed on the second plate molding die 61 with the outer surface of the link portion 33 b in contact with the curved portion 62, and the base of the arm portion 33. The punch 68 is lowered with respect to the plate forming intermediate product 37 with the recesses 68b and 68c facing the pair of link portions 33b. . As a result, as shown in FIG. 10B, the flat surfaces 33a of the arm portion 33 and the outer surfaces of the link portions 33b extend in a straight line in the vertically upward direction, and the inner facing surfaces of the link portions 33b are punched. The undercut portion 33c is formed on the lower side of the link portion 33b in contact with the concave portions 68b and 68c of the 68, and a plate molding finished product 38 having a shape corresponding to the yoke 23 of the intended universal joints 17A and 17B is obtained. It is done.

At this time, the concave portions 68b and 68c of the punch 68 do not hit so strongly that the inner surface of the link portion 33b is greatly deformed, and contact the extent that the inner surface of the link portion 33b is prevented from being deformed and corrected.
Then, the connecting hole 23d is formed in the center of the circular portion 32 of the finished plate molding 38, and the bearing cup insertion hole 26 is formed in the link portion 33b, thereby forming the yokes 23 of the universal joints 17A and 17B. To do.

The materials for the cold forging dies 44U, 44D, 45U, 45D, plate forming punches 56, 68 and plate forming dies 51, 61U, 61D described above may be cemented carbide, high speed steel, dies. Tool steel such as steel can be mainly applied.
Next, the operation of the above embodiment will be described.
First, to manufacture the yokes 23 and 24 of the universal joints 17A and 17B, as shown in FIG. 3, a round bar material 31 obtained by cutting a round bar of a predetermined diameter with a predetermined length is prepared. As shown in FIG. 4 (a), the first cold forging as shown in FIG. 4 (b) after the axial direction is horizontal and mounted on the first cold forging upper and lower dies 44U and 44D. The upper die 44U is lowered with respect to the first cold forging lower die 44D until the distance between them becomes a predetermined interval t, whereby the circular portion 32 and the circular portion 32 are symmetrical in the left-right direction. First cold forging is performed to obtain a cold forging intermediate product 34 having an arm portion 33 extending outward.

  Next, as shown in FIGS. 5A to 5C, the cold forging intermediate product 34 is mounted between the second cold forging upper and lower molds 45U and 45D, and is used for the second cold forging. By performing the second cold forging in which the upper and lower molds 45U and 45D are relatively moved as shown in FIGS. 6 (a) to 6 (c), the cold shown in FIGS. 8 (a) and 8 (b) is performed. A forging finished product 35 'is obtained. At this time, a burr 36 extending outward is generated over the entire circumference of the intermediate portion in the vertical direction of the cold forged product 35 ', that is, at the contact position of the upper and lower molds 51U and 51D. And finished to a finished cold forged product 35 having a stepped plate shape.

  Next, as shown in FIG. 9A, the finished cold forging finished product 35 is placed on the upper end portion of the first cold forging where plate forming is performed, and this state is placed. Then, by bringing the punch 56 into contact with the engaging recess 32e at the center of the upper surface of the circular portion 32 and lowering the punch 56, as shown in FIG. 9B, the circular portion 32 and the pair of arm portions 33 are separated. By performing the first plate molding that bends the flat portions 33a of the pair of arm portions 33 at a right angle so that they face each other while the bending corner portion 32f of the boundary portion contacts the flat surfaces 56a and 56b of the punch 56, the link A plate-molding intermediate product 37 is obtained that is inclined obliquely outward so that the inner surface of the portion 33b does not come into contact with each other and has an inverted C shape.

  Next, as shown in FIG. 10A, the plate forming intermediate product 37 is engaged with the second plate forming mold 61 with the outer surface of the base portion of the arm portion 33 engaged with the vertical flat portion 63, and the link. The outer surface of the portion 33b is engaged with the curved portion 62 and placed, and in this state, the punch 68 is brought into contact with the central portion of the upper surface of the circular portion 32 to perform the second plate molding, thereby forming the link portion 33b. 8 (c) and 8 (d) in which the inner side surface is vertical and contacts the recesses 68b and 68c of the punch 68, the undercut portion 33c is formed on the lower side, and the outer side surface is vertical by the vertical flat portion 63. A finished plate molding 38 having a shape corresponding to the yoke 23 shown in FIG.

Thereafter, the connecting hole 23d is formed in the center of the circular portion 32 of the finished plate molding 38, and the bearing cup insertion hole 26 is formed in the link portion 33b, whereby the yokes 23 of the universal joints 17A and 17B are formed. Is done.
Then, the connecting shaft portion 21c of the male shaft 21 is serrated and connected to the connecting hole 23d of the yoke 23 in the formed universal joint 17A, and is connected by fixing means such as welding and caulking, and the yoke 23 in the universal joint 17B is connected. The connecting shaft portion 22b of the female shaft 22 is serrated and connected to the connecting hole 23d by a fixing means such as welding or caulking.

Further, the yoke 24 connected to the output shaft 14 of the worm speed reducer 11 in the steering assist mechanism 4 is connected to the yoke 23 of the universal joint 17A via the cross shaft 25, and the cross shaft 25 is connected to the yoke 23 of the universal joint 17B. By connecting the yoke 24 connected to the pinion shaft 19 of the steering gear mechanism 6 via the steering gear SD, the steering device SD can be configured.
When the driver steers the steering wheel 1 with the steering device SD, the steering torque is detected by a steering torque sensor (not shown) built in the steering assist mechanism 4, and the steering assist according to the steering torque is detected. The electric motor 12 is driven and controlled to generate a force. The steering assist torque generated by the electric motor 12 is transmitted to the output shaft 14 connected to the steering shaft 2 via the worm speed reducer 11, and the steering torque acting on the steering shaft 2 and the steering assist torque are intermediate. This is transmitted to the steering gear mechanism 6 via the shaft 18, and the steered wheels are steered from the steering gear mechanism 6 via the tie rod 5. For this reason, the steering wheel 1 can be steered with a light steering torque.

In the present embodiment, as described above, when the yoke 23 of the universal joints 17A and 17B is manufactured, the round bar material 31 is cold forged to form the stepped plate-shaped cold forged finished product 35. Compared to hot forging of the rod material, the cold forged finished product 35 can be formed with high accuracy, the finishing cutting can be minimized, and the manufacturing cost can be greatly reduced.
Moreover, since the material in the cold forging process only needs to remove the burrs 36 generated in the second cold forging process, the metal after punching by punching a metal plate as in the case of using a plate material is used. The board is not wasted, and the yield can be greatly improved as compared with the case of using the board material.

Then, by forming the cold forged finished product 35 by plate forming, a U-shaped plate formed finished product 38 is obtained as viewed from the side surface serving as the yoke, so that the manufacturing cost is greatly reduced without the need for finish cutting. Can do.
Further, the stepped plate shape formed by cold forging is used to form the connecting portion 23c of the yoke 23 by increasing the thickness of the circular portion 32 and the bending corner portion 32f serving as the boundary portion between the circular portion 32 and the arm portion 33. The mechanical strength at the circular portion 32 can be sufficiently secured, and when the arm portion 33 is bent at the bending corner portion 32f in the plate forming process, it is ensured that the bending corner portion 32f is contracted outside. Accordingly, the bending corner portion 32f can be made thick, and the mechanical strength of the base portion of the arm portion 33 can be sufficiently secured.

  Furthermore, when the plate forming process is divided into two steps, a relatively thick link portion 33b protruding inward is formed at the tip of the arm portion 33 of the universal joint yoke. It is possible to bend only the flat portion 33a of the arm portion 33 not including the link portion 33b, and then bend the link portion 33b, and easily form the arm portion 33 having the undercut portion 33c formed on the lower side of the link portion 33b. The universal joint yoke 23 that can be molded and has the arm portions 33 having different thicknesses can be easily manufactured.

  Also, in the cold forging process, the first cold forging is performed by pressing the round bar material 31 from the direction orthogonal to the axial direction, and the circular portion and the arm portion extending symmetrically outward from the circular portion 32 are provided. 33, and the cold forging intermediate product is subjected to the second cold forging from the vertical direction to form the cold forging finished product 35, thereby reducing the burrs and the yield. Can be improved.

  In the above embodiment, the case where the yokes 23 of the universal joints 17A and 17B are formed has been described. However, the present invention is not limited to this, and the yoke 23 and the male shaft 21 connected thereto are integrally formed. You can also. For this purpose, the second cold forging lower die 45D in the cold forging step is provided with a through hole for penetrating the male shaft 21, and the base for receiving the first plate forming die 51 in the plate forming step. A through hole that allows the male shaft 21 to pass through may also be formed in the pedestal 67 of 56 and the second plate forming die 61. In this case, since the male shaft 21 is supported by the through-hole, there is no need to prevent tilting or centering, and therefore the engagement recess 32e that receives the punch 56 formed in the circular portion 32 may be omitted. In this way, since the yoke 23 and the male shaft 21 can be integrally formed, the cost can be reduced and the mechanical strength at the joint between the yoke 23 and the male shaft 21 can be improved. Can do.

  Moreover, in the said embodiment, although the case where the connection hole 23d was drilled in the circular part 32 after shape | molding the plate molding completion product 38 was demonstrated, it is not limited to this, The cold forging completion product 35 is used. When forming, a hole is formed in one of the second cold forging upper and lower molds 45U and 45D at a position facing the central portion of the circular portion 32, and the other is punched to engage with the hole. By forming the convex portion, the connection hole 23d can be formed at the same time during the second cold forging, and the manufacturing cost and manufacturing man-hour of the yoke 23 can be further reduced.

Furthermore, although the case where the base is formed in a circular shape has been described in the above embodiment, the present invention is not limited to this, and the base can be formed in an arbitrary shape such as a square or a polygon.
Furthermore, in the above-described embodiment, the case where the two-stage cold forging is performed in the cold forging process has been described. However, the present invention is not limited to this, and three-stage or more multi-stage cold forging is performed. In this case, the same effect as that of the above embodiment can be obtained.

Furthermore, in the above embodiment, the case where the plate forming process is also performed in two stages has been described. However, the present invention is not limited to this and may be used for performing three or more stages. Even in this case, the same effect as that of the above embodiment can be obtained.
Moreover, in the said embodiment, although the case where a pair of arm part 33 was bent at right angle so that both might oppose, it is not limited to this, A bending angle can be set arbitrarily.

In the above embodiment, the case where the present invention is applied to the steering device SD having the steering assist mechanism 4 has been described. However, the present invention is not limited to this, and the steering device SD without the steering assist mechanism 4 is also applicable. The present invention can be applied.
Furthermore, in the above-described embodiment, the case where the present invention is applied to the yoke 23 of the universal joints 17A and 17B used in the steering device SD has been described. However, the present invention is not limited to this. The present invention can be applied to any applicable universal joint yoke.

1 is an overall configuration diagram showing an embodiment in which a universal joint yoke according to the present invention is applied to a steering device. It is sectional drawing which shows the structure of the intermediate shaft to which the yoke for universal joints by this invention is applied. It is a perspective view which shows a round bar raw material. It is explanatory drawing which shows a 1st cold forging process. It is explanatory drawing which shows the state before the start of a 2nd cold forging process. It is explanatory drawing which shows the completion | finish state of a 2nd cold forging process. It is an expanded sectional view of the 2nd cold forging up-and-down metal mold | die. It is the top view and front view which show a cold forging completion product and a plate molding completion product. It is explanatory drawing which shows a 1st board formation process. It is explanatory drawing which shows a 2nd board formation process. It is sectional drawing which shows the punch used for a 2nd plate formation process. It is a front view which shows the yoke shape | molded using the conventional board | plate raw material.

Explanation of symbols

  SD: Steering device, 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering column, 4 ... Steering assist mechanism, 6 ... Steering gear mechanism, 17A, 17B ... Universal joint, 18 ... Intermediate shaft, 21 ... Male shaft, 22 ... Female shaft, 23, 24 ... Yoke, 23a, 23b ... Arm part, 23c ... Connection part, 31 ... Round bar material, 32 ... Circular part, 33 ... Arm part, 33a ... Link part, 34 ... Cold forging intermediate product 35 ... Finished cold forging product, 36 ... Burr, 37 ... Intermediate plate product, 38 ... Finished plate molding product, 44U ... First upper die for forging, 44D ... First lower forging die, 45U ... second upper forging die, 45D ... second lower forging die, 51 ... first plate forming die, 51U ... upper die, 51D ... lower die, 56 ... punch, 61U ... Second plate molding die, 61D ... second plate molding die 68 ... punch

Claims (4)

Relative round bar material, a cold forging step, sequentially performs a plate forming step, a method for producing a universal joint yoke which forms a yoke for a universal joint, the cold forging process, the base of the central portion A pair of arm portions that extend symmetrically outward from the base portion, and the arm portion has a flat portion on the base portion side and a surface that is inward in the plate forming step on a distal end side connected to the flat portion. A step-shaped cold forging molded product formed so as to have a protruding and thick link portion, and at least the boundary portion between the base portion and the pair of arm portions is thicker than the thickness of the arm portion. a process that be molded in, as the plate forming Engineering is stepped plate shape formed by the cold forging process by a two-step molding as the undercut portion by the flat portion is formed on the base side of the link portion bending a pair of arm portions so as both to face Method for producing a universal joint yoke, characterized in that the about Engineering.   2. The method for manufacturing a universal joint yoke according to claim 1, wherein in the cold forging step, two-stage cold forging is performed so as to reduce generation of burrs.   In the cold forging process, a first cold forging process in which a round bar material is cold forged from a direction orthogonal to the axial direction to form a cold forging intermediate product, and forging in the first cold forging process. 3. The second cold forging step according to claim 2, further comprising: a second cold forging step of forging the cold forged intermediate product obtained from the axial direction to obtain a cold forged molded product having the stepped plate shape. A method of manufacturing a joint yoke. In the plate forming step, a first plate forming step of bending the flat portion so as to form the undercut portion, and a second plate forming step of bending the link portion connected to the flat portion, The method for manufacturing a universal joint yoke according to any one of claims 1 to 3, wherein:

Images