CN111054880A

CN111054880A - Rack bar manufacturing device

Info

Publication number: CN111054880A
Application number: CN201811286798.5A
Authority: CN
Inventors: 山胁崇; 野村圣人
Original assignee: Neturen Co Ltd
Current assignee: Neturen Co Ltd
Priority date: 2018-10-17
Filing date: 2018-10-31
Publication date: 2020-04-24
Also published as: WO2020080166A1; CN209349453U; JP2020062662A; JP7149157B2

Abstract

The invention aims to improve the durability of a rack bar manufacturing device and realize miniaturization. A rack bar manufacturing device (100) that forms a flat portion on a shaft of a rack bar obtained by forming a rack on the flat portion provided on the hollow shaft, the rack bar manufacturing device (100) comprising: a flat-pressing punch (101) that presses the outer peripheral surface of the shaft member (2); a pair of dies (110, 111) that are openable and closable in a direction perpendicular to a pressing direction of the platen punch with respect to the shaft, and that hold the outer periphery of the shaft over a length equal to or longer than a processing range of the platen punch; a cam (103) having a pair of engaging portions (122) that sandwich the pair of dies in the opening/closing direction of the pair of dies, and that closes the pair of dies by pressing the flat punch in the pressing direction relative to the shaft member to engage the pair of engaging portions with the pair of dies; and a ring-shaped holder (104) having a fitting hole (130) that fits the cam in the pressing direction of the platen punch with respect to the shaft member, the cam being divided into two parts, a first cam piece (120) and a second cam piece (121), with the abutting surfaces of the pair of dies serving as boundaries, the first cam piece and the second cam piece being cylindrical in a state of being combined with each other.

Description

Rack bar manufacturing device

Technical Field

The present invention relates to a rack bar manufacturing apparatus.

Background

As a rack bar used for a rack-and-pinion steering apparatus or the like, for example, a so-called solid rack bar in which a rack is formed on a solid shaft member is known. In addition, a so-called hollow rack bar is also known in which a rack is formed on a hollow shaft member to achieve weight reduction.

The hollow rack bar 1 is manufactured, for example, by the following method. First, the hollow shaft member is pressed by a flat press punch, so that a flat portion is formed on the outer peripheral surface of the hollow shaft member. Next, the core rod is pushed into the flat portion with the rack teeth die pressed against the flat outer surface of the flat portion, and the size of the pushed core rod is gradually increased and the pushing of the core rod is repeated, thereby forming a rack on the outer surface of the flat portion. In addition, the rack is quenched to increase the hardness of the rack.

The press working apparatus described in patent document 1 is an apparatus that forms a flat portion on an outer peripheral surface of a hollow shaft member that is a material of a hollow rack bar. This stamping device includes: left and right molds opened and closed in the horizontal direction; a flat press punch for pressing the upper part of the shaft member held by the left and right dies; and a support block configured to close the left and right molds by pushing downward.

The lower surface of the support block is provided with a recess for accommodating the left and right molds, and tapered surfaces that engage with each other are provided on the left and right side surfaces of the recess and the side surfaces of the left and right molds that face the side surfaces of the recess. The downward pressing force applied to the support block is converted into a horizontal pressing force for closing the left and right molds by engagement of the tapered surfaces of the concave portions with the tapered surfaces of the left and right molds. Then, the left and right molds are closed and held in the closed state by the converted pressing force in the horizontal direction.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2009-262694

Disclosure of Invention

Technical problem to be solved by the invention

In the press working apparatus described in patent document 1, tapered surfaces for closing the left and right dies in correspondence with the depression of the support block are provided on the concave portion of the support block and the left and right dies accommodated in the concave portion. Therefore, in a cross section perpendicular to the up-down direction, the concave portion and the left and right molds are formed in a rectangular shape. When the flat-pressing punch is pressed against the upper portion of the hollow shaft member, a force in the horizontal direction for opening the left and right dies holding the shaft member acts on the left and right dies, and is forced by the support block. Here, if the cross-sectional shape of the recess is rectangular, stress concentration occurs at, for example, four corners of the recess, which may cause breakage of the supporting block. Although breakage of the support block can be suppressed by increasing the thickness of the frame portion surrounding the recess, the weight of the support block increases, possibly resulting in an increase in the size of the equipment required for lifting and lowering the support block.

The present invention has been made in view of the above circumstances, and an object thereof is to improve durability and to achieve downsizing of a rack bar manufacturing apparatus.

Means for solving the problems

One aspect of the present invention is a rack bar manufacturing apparatus configured to form a flat portion in a shaft member of a rack bar, the rack bar being obtained by forming a rack bar in the flat portion provided in the hollow shaft member. The manufacturing apparatus includes: a flat pressing punch configured to press an outer peripheral surface of the shaft; a pair of dies configured to be openable and closable in a direction perpendicular to a pressing direction of the platen punch with respect to the shaft, and configured to hold an outer periphery of the shaft over a length equal to or longer than a processing range of the platen punch; a cam configured to have a pair of engaging portions that sandwich the pair of dies in an opening/closing direction of the pair of dies, and to close the pair of dies by engaging the pair of engaging portions with the pair of dies by pressing the platen in a pressing direction of the shaft member; and an annular holder having an engagement hole configured to engage with the cam in a pressing direction of the platen punch with respect to the shaft member. The cam is divided into a first cam block and a second cam block by using a butt joint surface of the pair of dies as a boundary, and the first cam block and the second cam block are formed into a cylindrical shape in a mutually combined state.

Effects of the invention

According to the present invention, durability of a rack bar manufacturing apparatus can be improved and miniaturization can be achieved.

Drawings

Fig. 1 is a perspective view of one example of a rack bar for explaining an embodiment of the present invention.

Fig. 2 is a schematic view of a preforming process in the manufacturing process of the rack bar of fig. 1.

Fig. 3 is a schematic view of a tooth forming process in the manufacturing process of the rack bar of fig. 1.

Fig. 4 is a plan view of a manufacturing apparatus for performing the preforming step of fig. 2.

Fig. 5 is a cross-sectional view of the manufacturing apparatus of fig. 4 taken along line V-V.

Fig. 6 is a schematic diagram showing forces acting on various parts of the manufacturing apparatus of fig. 4.

Fig. 7 is a schematic diagram showing forces acting on various parts of the manufacturing apparatus of fig. 4.

Fig. 8 is a cross-sectional view of a modification of the manufacturing apparatus of fig. 4.

Fig. 9 is a sectional view of a rack bar manufactured using the manufacturing apparatus of fig. 8.

Fig. 10 is a sectional view of a steering apparatus using the rack bar of fig. 9.

Description of the symbols

1: hollow rack bar

2: shaft member

3: rack bar

4: flat portion

5: first opening

6: second opening

7: plane part

10: tooth forming device

11: tooth forming die

12: core rod

13: core rod holder

14: first mandrel push rod

15: second core rod push rod

16: upper die

17: lower die

18: rack tooth die

100: manufacturing apparatus

101: punch head

102: preforming mold

103: cam wheel

104: holding member

105: pressurizing mechanism

110: first mold

111: second mold

112: ejector pin

113: holding groove

114: communicating groove

115: inclined plane

116: inclined plane

117: plane part

120: first cam block

121: second cam block

122: concave (fastening part)

123: inclined plane

124: inclined plane

130: fitting hole

131: inserting hole

200: steering device

201: shell body

202: pinion gear

203: rack guide

204: spring

Detailed Description

Fig. 1 shows an example of a rack bar for explaining an embodiment of the present invention.

The rack bar 1 shown in fig. 1 is a so-called hollow rack bar made of a hollow shaft member 2 having a circular cross section. A rack 3 is formed on the shaft member 2. A sectional shape of a section where the rack 3 is formed (hereinafter, referred to as a rack forming section) is non-circular, and a sectional shape of a section deviating from the rack forming section is circular. The hollow rack bar 1 is manufactured, for example, by the following method.

Fig. 2 and 3 schematically show a manufacturing process of the hollow rack bar 1.

The shaft member 2 as a base material is, for example, a hollow shaft member having a circular cross section and made of steel such as JIS-S45C, and both ends of the shaft member 2 in the axial direction are opened. In general, zinc phosphate coating treatment or the like is applied to the shaft member 2 to improve formability and corrosion resistance.

< preforming step >

As shown in fig. 2, on the outer peripheral surface of the shaft member 2, a flat portion 4 extending in the axial direction of the shaft member 2 is formed. The rack 3 is formed on the flat outer surface of the flat portion 4 by a tooth forming process shown in fig. 3. The flat portion 4 is formed by flattening the outer peripheral surface of the shaft member 2 flat to the vicinity of the tooth bottom height of the rack 3.

< teeth Forming Process >

Next, as shown in fig. 3, a rack 3 is formed on the flat outer surface of the flat portion 4 of the shaft member 2. The tooth forming device 10 forming the rack 3 includes: a tooth forming die 11, a plurality of mandrels 12, a mandrel holder 13 that holds the plurality of mandrels 12, a first mandrel bar 14, and a second mandrel bar 15.

The tooth forming die 11 has an upper die 16 and a lower die 17 which are opened and closed in the up-down direction by a clamping mechanism (not shown). The upper die 16 and the lower die 17 vertically hold the shaft 2 therebetween and hold the outer periphery of the shaft 2. The rack and pinion die 18 is detachably attached to the upper die 16, and the rack and pinion die 18 is fixed in contact with the substantially flat outer surface of the flat portion 4. A plurality of tooth grooves for forming the rack 3 are provided on a forming surface 18a of the rack and pinion die 18 which is in contact with the outer surface of the flat portion 4.

One of the plurality of mandrels 12 held by the mandrel holder 13 is inserted into the shaft 2 from the first opening 5 on the one axial end side of the shaft 2, and is pushed into the flat portion 4 by the first mandrel pusher 14. The pushed-in mandrel 12 is pushed back by a second mandrel pusher 15 inserted into the shaft member 2 from the second opening 6 on the other end side in the axial direction of the shaft member 2, and is discharged from the shaft member 2.

During the reciprocating movement of the core rod 12 over the entire length of the flat portion 4, the material of the flat portion 4 is pressed by the core rod 12 and plastically flows toward the rack and pinion die 18. By gradually changing to the larger-sized plug 12 and repeating the pushing-in of the plug 12, the material of the flat portion 4 gradually penetrates into the tooth grooves of the forming surface 18 of the rack and pinion die 18, and the shape of the forming surface 18a is transferred to the flat portion 4, thereby forming the rack 3 on the flat portion 4.

The shaft member 2 formed with the rack 3 corrects the curvature accompanying the formation of the teeth and grinds the outer peripheral surface as necessary, and is quenched to increase the hardness of the rack 3. The heating at the time of quenching may be performed by, for example, high-frequency induction heating, but is not limited to high-frequency induction heating. Further, the heating range at the time of quenching is not particularly limited as long as it includes the rack forming section, and may be only the rack forming section or the entire length of the shaft member 2. Further, at the time of quenching, the rack forming section is preferably restrained from the up-down direction and the left-right direction to suppress bending of the shaft member 2 caused by quenching.

Fig. 4 and 5 show one example of a manufacturing apparatus of a rack bar for performing the preforming process shown in fig. 2.

The manufacturing apparatus 100 includes a flat-pressing punch 101, a preforming die 102, a cam 103, a holder 104, and a pressing mechanism 105.

The flat punch 101 presses the shaft 2 by a pressing mechanism 105, and forms a flat portion 4 on the outer peripheral surface of the shaft 2. In this example, the shaft member 2 is pressed from above the horizontally arranged shaft member 2.

The preforming die 102 has a pair of a first die 110 and a second die 111, and the first die 110 and the second die 111 are opened and closed in a direction perpendicular to a pressing direction of the flat-pressing punch 101 with respect to the shaft 2. In this example, the flat punch 101 presses the shaft member 2 from the upper side of the shaft member 2 horizontally disposed, sets the axial direction of the shaft member 2 to the front-rear direction, and opens and closes the first die 110 and the second die 111 in the left-right direction perpendicular to the up-down direction and the front-rear direction. An ejector pin 112 is disposed below the first mold 110 and the second mold 111. The ejector pins 112 are inserted between the butted first mold 110 and second mold 111 to separate the first mold 110 and second mold 111.

A holding groove 113 having a semicircular cross section is formed on the abutting surface of each of the first mold 110 and the second mold 111 so as to traverse the abutting surface in the front-rear direction. These holding grooves 113 are combined with each other when the first die 110 and the second die 111 are closed, form a cylindrical molding space for accommodating the shaft element 2 over a length equal to or longer than the working range of the flat punch 101, and hold the outer periphery of the shaft element 2 accommodated in the molding space. Further, a communication groove 114 reaching the holding groove 113 from the upper surface of each of the first mold 110 and the second mold 111 is formed in the abutting surface of each of the first mold 110 and the second mold 111. The flat punch 101 is pressed against the outer peripheral surface of the shaft element 2 accommodated in the molding space through a communication hole formed by combining the communication grooves 114 of the first die 110 and the second die 111.

An inclined surface 115 inclined in the vertical direction is provided on the outer surface of the first mold 110 on the side opposite to the butting surface, and the inclined surface 115 extends from the upper surface of the first mold 110 to at least the position of the lower end of the holding groove 113. The same inclined surface 116 is also provided on the outer side surface of the second mold 111.

The cam 103 has a first cam piece 120 and a second cam piece 121. The first cam block 120 and the second cam block 121 are disposed opposite to each other so as to sandwich the first mold 110 and the second mold 111 in the opening and closing direction of the first mold 110 and the second mold 111. The cam 103 has a substantially cylindrical shape as a whole, and the first cam block 120 and the second cam block are formed in a semi-cylindrical shape obtained by dividing the cylinder into two with the abutting faces of the first die 110 and the second die 111 as boundaries.

A recess (engaging portion) 122 is formed on each of the opposing surfaces of the first cam piece 120 and the second cam piece 121. In the concave portion 122 of the first cam block 120, the first die 110 is accommodated and an inclined surface 123 which can be brought into sliding contact with the inclined surface 115 of the first die 110 is provided. In the recess 122 of the second cam block 121, the second mold 111 is accommodated and an inclined surface 124 that can be brought into sliding contact with the inclined surface 116 of the second mold 111 is provided.

The holder 104 is formed of a rectangular parallelepiped block, and has a fitting hole 130 having a circular cross section penetrating the block in the up-down direction. The retainer 104 is formed in a ring shape surrounding the outer periphery of the fitting hole 130. The first die 110 and the second die 111 are disposed at the center of the fitting hole 130, the first cam block 120 is disposed between the first die 110 and the inner circumferential surface of the fitting hole 130, and the second cam block 121 is disposed between the second die 111 and the inner circumferential surface of the fitting hole 130. The first cam piece 120 and the second cam piece 121 are fitted in the fitting hole 130 movably in the up-down direction. Further, in the first cam block 120, the second cam block 121, and the holder 104, an insertion hole 131 communicating with the above-described molding space formed by the first die 110 and the second die 111 is formed.

The first cam block 120 and the second cam block 121 are pressed downward by the pressing mechanism 105 independently of the flat press punch 101. By pressing the first cam block 120 and the second cam block 121 downward, the inclined surface 123 of the first cam block 120 engages with the inclined surface 115 of the first mold 110, and the inclined surface 124 of the second cam block 121 engages with the inclined surface 116 of the second mold 111. By the engagement of these inclined surfaces, the downward pressing force acting on the first cam block 120 and the second cam block 121 is converted into a pressing force in the left-right direction, and acts on the first die 110 and the second die 111. Thereby, the first mold 110 and the second mold 111 are closed and firmly held in the closed state.

In the preforming process, first, the flat-pressing punch 101, the first cam block 120, and the second cam block 121 are lifted by the pressing mechanism 105, and the shaft member 2 is disposed at a predetermined position between the holding groove 113 of the first die 110 and the holding groove 113 of the second die 111 through the insertion hole 131 in a state where the first die 110 and the second die 111 are opened. Next, the first cam block 120 and the second cam block 121 are pressed downward, so that the first mold 110 and the second mold 111 are closed. Then, the flat punch 101 is pressed downward against the outer peripheral surface of the shaft member 2. Thereby, the flat portion 4 is formed on the outer peripheral surface of the shaft member 2.

Fig. 6 and 7 schematically show forces acting on respective portions of the manufacturing apparatus 100 in the preforming step.

When the flat punch 101 is pressed against the shaft element 2, a force F1 in the left-right direction for opening the first die 110 and the second die 111 acts on the first die 110 and the second die 111 that hold the shaft element 2. The force F1 is applied to the first cam piece 120 and the second cam piece 121, but is decomposed into a vertical force F2 and a horizontal force F3 by the engagement between the inclined surface 123 of the first cam piece 120 and the inclined surface 115 of the first mold 110 and the engagement between the inclined surface 124 of the second cam piece 121 and the inclined surface 116 of the second mold 111. The vertical force F2 is applied by the pressing mechanism 105.

The left-right direction force F3 acts on the first cam piece 120 and the second cam piece 121 so that the first cam piece 120 and the second cam piece 121 are pushed open in the left-right direction, transmitted to the holder 104 through the first cam piece 120 and the second cam piece 121, and forced by the holder 104. Here, since the first cam piece 120 and the second cam piece 121 are originally separated in the left-right direction, the first cam piece 120 and the second cam piece 121 are not broken by the force F3. Also, since the first cam piece 120 and the second cam piece 121 are formed in the semi-cylindrical shape, the force F3 in the left-right direction becomes a radially dispersed force F4 acting on the retainer 104. Therefore, the holder 104 can be prevented from being damaged by the force F3, and the durability of the manufacturing apparatus 100 can be improved.

Further, since the holder 104 receiving the force F3 in the right-left direction is fixed in the preforming step, the first cam piece 120 and the second cam piece 121, which are not damaged by the force F3, can be made smaller than the holder 104. Therefore, the pressing mechanism 105 for lifting and lowering the first cam block 120 and the second cam block 121 can also be miniaturized. This can reduce the size of the manufacturing apparatus 100.

Preferably, A ≧ B ≧ C, where A is the hardness of the material forming the first mold 110 and the second mold 111, B is the hardness of the material forming the first cam block 120 and the second cam block 121, and C is the hardness of the material forming the retainer 104. For example, the first mold 110 and the second mold 111 may be made of cold-work mold steel having a Rockwell hardness of 58 to 62HRC, the first cam block 120 and the second cam block 121 may be made of cold-work mold steel having a Rockwell hardness of 54 to 58HRC, and the holder 104 may be made of hot-work mold steel having a Rockwell hardness of 48 to 54 HRC. Note that the rockwell hardness of each material was as defined in JIS 2245: 2016 in the Rockwell hardness test.

Generally, the hardness and toughness of steel are tradeoffs, with the higher the hardness, the lower the toughness. If the toughness of the material forming the first mold 110 and the second mold 111 is a, the toughness of the material forming the first cam piece 120 and the second cam piece 121 is B, and the toughness of the material forming the retainer 104 is C, the above-mentioned hardness relational expression A.gtoreq.B.gtoreq.C is converted into the toughness relational expression, and a.gtoreq.b.gtoreq.c. By making the material of the first mold 110 and the second mold 111 relatively high in hardness, abrasion of the first mold 110 and the second mold 111 contacting the shaft element 2 can be suppressed, and by making the material of the retainer 104 relatively high in toughness, breakage of the retainer 104 receiving the force F3 in the left-right direction can be prevented, and the durability of the manufacturing apparatus 100 can be further improved.

Fig. 8 shows a modification of the manufacturing apparatus 100.

In the example shown in fig. 8, a flat portion 117 is provided at the bottom of the holding groove 113 having a semicircular cross section of each of the first die 110 and the second die 111. The flat surface portion 117 extends over a length equal to or longer than the processing range of the flat punch 101.

Fig. 9 shows a sectional shape of a rack forming section of the hollow rack bar 1 manufactured by using the manufacturing apparatus 100 shown in fig. 8, in which flat surface portions 7 formed by flat surface portions 117 are formed on both left and right sides of the rack 3.

Fig. 10 shows an example of a steering apparatus using the hollow rack bar 1 of fig. 9, the steering apparatus 200 including: a housing 201 for supporting the hollow rack bar 1 to be movable in the axial direction; a pinion 202 that meshes with the rack 3 of the hollow rack bar 1; a rack guide 203 that slidably supports the hollow rack bar 1 by sandwiching the hollow rack bar 1 between the rack guide and the pinion 202; and a spring 204 that urges the rack guide 203 toward the hollow rack bar 1.

Since the flat surface portion 7 of the hollow rack bar 1 forms a portion in flat contact with the rack guide 203, the support of the hollow rack bar 1 by the rack guide 203 is stable.

The width W of the flat surface portion 7 and the width W of the flat surface portion 117 of the holding groove 113 for forming the flat surface portion 7 are preferably 0.3mm or more and 10mm or less, and further, when the center angle of the arc surface portion sandwiched between the left and right flat surface portions 7 on the side opposite to the rack 3 is α ° with reference to the outer diameter D of the hollow rack bar 1, the width W preferably satisfies the following formula:

W≤D×sin[(180°－α°)/2]

as described above, the present specification discloses a rack bar manufacturing apparatus for forming a flat portion in a shaft member of a rack bar obtained by forming a rack bar in the flat portion provided in the hollow shaft member, the rack bar manufacturing apparatus comprising: a flat press punch that presses an outer peripheral surface of the shaft; a pair of dies that are openable and closable in a direction perpendicular to a pressing direction of the platen punch with respect to the shaft, and that hold an outer periphery of the shaft over a length equal to or longer than a processing range of the platen punch; a cam having a pair of engaging portions that sandwich the pair of dies in an opening/closing direction of the pair of dies, the pair of engaging portions being engaged with the pair of dies by pressing the platen punch in a pressing direction of the shaft member, and the pair of dies being closed; and an annular holder having a fitting hole that fits the cam in a pressing direction of the platen punch with respect to the shaft member, wherein the cam is divided into two parts, namely a first cam piece and a second cam piece, with a butting surface of the pair of dies serving as a boundary, and the first cam piece and the second cam piece are cylindrical in a state of being combined with each other.

In the rack bar manufacturing apparatus disclosed in the present specification, when the hardness of the material forming the pair of dies is A, the hardness of the material forming the first cam piece and the second cam piece is B, and the hardness of the material forming the retainer is C, A.gtoreq.B.gtoreq.C.

In the rack bar manufacturing apparatus disclosed in the present specification, each of the pair of dies has a groove having a semicircular cross section for accommodating the shaft member, and the groove has a flat surface portion extending over a length equal to or longer than a working range of the flat punch at a bottom portion of the groove.

In the rack bar manufacturing apparatus disclosed in the present specification, the width of the flat surface portion is 0.3mm to 10 mm.

Claims

1. A rack bar manufacturing device is configured to form a flat portion on a shaft member of a rack bar, wherein the rack bar is obtained by forming a rack on the flat portion provided on the hollow shaft member,

the manufacturing device of the rack bar comprises:

a flat pressing punch configured to press an outer peripheral surface of the shaft;

a pair of dies configured to be openable and closable in a direction perpendicular to a pressing direction of the platen punch with respect to the shaft, and configured to continuously hold an outer periphery of the shaft over a length equal to or longer than a processing range of the platen punch;

a cam configured to have a pair of engaging portions that sandwich the pair of dies in an opening/closing direction of the pair of dies, and to close the pair of dies by engaging the pair of engaging portions with the pair of dies by pressing the platen in a pressing direction of the shaft member; and

an annular holder having an engagement hole configured to engage with the cam in a pressing direction of the platen punch with respect to the shaft member,

the cam is divided into a first cam block and a second cam block by taking the butt joint surface of the pair of dies as a boundary,

the first cam piece and the second cam piece are configured to be cylindrical in a combined state with each other.

2. The manufacturing apparatus according to claim 1,

the hardness of the material forming the pair of molds is set to a,

setting the hardness of a material forming the first cam block and the second cam block to be B,

the hardness of the material forming the holder is set to C,

then A is more than or equal to B and more than or equal to C.

3. The manufacturing apparatus according to claim 1 or 2,

the pair of molds respectively have a groove having a semicircular cross section configured to receive the shaft member,

the groove has a flat surface portion extending continuously over a length equal to or longer than a processing range of the flat-pressing punch at a bottom portion of the groove.

4. The manufacturing apparatus according to claim 3,

the width of the plane part is more than 0.3mm and less than 10 mm.