JP7149157B2 - Rack bar manufacturing equipment - Google Patents

Description

The present invention relates to a rack bar manufacturing apparatus.

A so-called solid rack bar in which a rack is formed on a solid shaft member, for example, is known as a rack bar used in a rack-and-pinion steering device or the like. Also known is a so-called hollow rack bar in which a rack is formed in a hollow shaft member to reduce weight.

A hollow rack bar is manufactured, for example, as follows. First, a flattened portion is formed on the outer peripheral surface of the hollow shaft member by pressing the flattened punch against the hollow shaft member. Next, while the rack teeth are pressed against the flat outer surface of the flattened portion, the cored bar is press-fitted into the flattened portion. A rack is formed on the outer surface of the flattened portion. Then, the rack is quenched to increase the hardness of the rack.

A press working apparatus described in Patent Document 1 forms a flattened portion on the outer peripheral surface of a hollow shaft member that is a material of a hollow rack bar. This press working device is configured to have left and right dies that are opened and closed in a horizontal direction, a flattening punch that is pressed against the upper portion of the shaft material sandwiched by the left and right dies, and that the left and right dies are closed by being pressed downward. and a support block.

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

JP 2009-262694 A

In the press working apparatus described in Patent Document 1, a tapered surface for closing the left and right dies in accordance with the depression of the support block is provided on the recess of the support block and on the left and right dies accommodated in the recess. Therefore, in a cross section perpendicular to the vertical direction, the recesses and the left and right molds are formed in a rectangular shape. When the flattening punch is pressed against the upper part of the hollow shaft member, a horizontal force that opens the left and right molds holding the shaft member is applied to the left and right molds, and this force is received by the support block. Here, if the cross-sectional shape of the recess is rectangular, stress concentration may occur at the four corners of the recess, for example, and the support block may break. By increasing the thickness of the frame surrounding the recess, breakage of the support block can be suppressed, but the weight of the support block increases, and there is a concern that the equipment required for lifting and lowering the support block will become larger.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the durability and reduce the size of a rack bar manufacturing apparatus.

An apparatus for manufacturing a rack bar according to one aspect of the present invention is a manufacturing apparatus for forming the flattened portion in the shaft member of a rack bar in which a rack is formed in the flattened portion provided in a hollow shaft member. , a flattening punch pressed against the outer peripheral surface of the shaft, and a flattening punch that can be opened and closed in a direction perpendicular to the pressing direction of the flattening punch against the shaft, over a length that is equal to or greater than the processing range of the flattening punch. A pair of dies for holding the outer periphery of the shaft, and a pair of engaging portions sandwiching the pair of dies in an opening/closing direction of the pair of dies, and a direction in which the flattening punch is pressed against the shaft. are pressurized to engage the pair of engaging portions with the pair of molds to close the pair of molds, and the cam moves in the pressing direction of the flattening punch against the shaft member. an annular holder having a fitting hole for fitting, wherein the cam is divided into a first cam block and a second cam block by the abutting surfaces of the pair of molds; The first cam block and the second cam block have a cylindrical shape when combined with each other.

ADVANTAGE OF THE INVENTION According to this invention, the durability improvement and size reduction of the manufacturing apparatus of a rack bar can be achieved.

1 is a perspective view of an example rack bar for describing an embodiment of the present invention; FIG. FIG. 2 is a schematic diagram of a preforming step in manufacturing the rack bar of FIG. 1; FIG. 2 is a schematic diagram of a tooth forming process in manufacturing the rack bar of FIG. 1; FIG. 3 is a plan view of a manufacturing apparatus that performs the preforming step of FIG. 2; 5 is a cross-sectional view of the manufacturing apparatus of FIG. 4 taken along the line VV. FIG. 5 is a schematic diagram showing forces acting on each part of the manufacturing apparatus of FIG. 4. FIG. 5 is a schematic diagram showing forces acting on each part of the manufacturing apparatus of FIG. 4. FIG. FIG. 5 is a cross-sectional view of a modification of the manufacturing apparatus of FIG. 4; FIG. 9 is a cross-sectional view of a rack bar manufactured using the manufacturing apparatus of FIG. 8; FIG. 10 is a cross-sectional view of a steering device using the rack bar of FIG. 9;

FIG. 1 shows an example of a rack bar for describing embodiments of the present invention.

A 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 section in which the rack 3 is formed (hereinafter referred to as a rack forming section) has a non-circular cross-sectional shape, and a section outside the rack forming section has a circular cross-sectional shape. The hollow rack bar 1 is manufactured, for example, as follows.

2 and 3 show the outline of the manufacturing process of the hollow rack bar 1. FIG.

The shaft member 2, which is a raw material, is a hollow shaft member having a circular cross section made of steel such as JIS-S45C, and both axial ends of the shaft member 2 are open. The shaft member 2 is typically subjected to a zinc phosphate coating treatment or the like for enhancing moldability and corrosion resistance.

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

<Tooth forming process>
Next, as shown in FIG. 3, a rack 3 is formed on the flat outer surface of the flattened portion 4 of the shaft member 2 . A tooth forming device 10 forming the rack 3 includes a tooth forming mold 11, a plurality of core bars 12, a core bar holder 13 for holding the plurality of core bars 12, a first core bar push rod 14, and a second core bar 14. 2 cored bar push rods 15 are provided.

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

One of the plurality of cored bars 12 held by the cored bar holder 13 is inserted into the shaft member 2 from the first opening 5 on one axial end side of the shaft member 2 to form the first cored bar. It is press-fitted inside the flattened portion 4 by a push rod 14 . Then, the press-fitted core bar 12 is pushed back by a second core bar push rod 15 inserted into the shaft member 2 from the second opening 6 on the other axial end side of the shaft member 2 and discharged from the shaft member 2 . be.

While the core metal 12 is reciprocated over the entire length of the flattened portion 4 , the material of the flattened portion 4 is squeezed by the core metal 12 and plastically flows toward the rack teeth 18 . As the core metal 12 is gradually replaced with a larger one and the core metal 12 is repeatedly press-fitted, the material of the flattened portion 4 gradually bites into the tooth spaces of the molding surface 18a of the rack tooth mold 18, and the shape of the molding surface 18a is changed. It is transferred to the flattened portion 4 and the rack 3 is formed on the flattened portion 4 .

The shaft member 2 with the racks 3 formed thereon is subjected, if necessary, to correction of the curvature associated with forming the teeth, grinding of the outer peripheral surface, and quenching to increase the hardness of the racks 3 . Heating for quenching can be performed, for example, by high-frequency induction heating, but is not limited to high-frequency induction heating. Moreover, the heating range during quenching is not particularly limited as long as it includes the rack forming section, and may be the rack forming section alone or the entire length of the shaft member 2 . Further, during quenching, preferably, the rack forming section is restrained from the vertical direction and the lateral direction, so that bending of the shaft member 2 due to quenching is suppressed.

4 and 5 show an example of a rack bar manufacturing apparatus that performs the preforming process shown in FIG.

The manufacturing apparatus 100 includes a flattening punch 101 , a preforming mold 102 , a cam 103 , a holder 104 and a pressure mechanism 105 .

The flattening punch 101 is pressed against the shaft member 2 by a pressing mechanism 105 to form the flattening portion 4 on the outer peripheral surface of the shaft member 2 . In this example, it is pressed against the shaft member 2 from above the shaft member 2 arranged horizontally.

The preforming mold 102 has a first mold 110 and a second mold 111 that form a pair, and the first mold 110 and the second mold 111 are arranged in the pressing direction of the flattening punch 101 against the shaft member 2. is opened and closed in the vertical direction. In this example, a flattening punch 101 is pressed against the shaft member 2 arranged horizontally from above the shaft member 2. The mold 110 and the second mold 111 are opened and closed in the horizontal direction perpendicular to the vertical direction and the front-rear direction. Eject pins 112 are arranged below the first mold 110 and the second mold 111 . The eject pin 112 is inserted between the butted first mold 110 and the second mold 111 to separate the first mold 110 and the second mold 111 .

A retaining groove 113 having a semicircular cross-section is formed in each of the mating surfaces of the first mold 110 and the second mold 111 and crosses the mating surfaces in the front-rear direction. These holding grooves 113 are combined with each other when the first mold 110 and the second mold 111 are closed, and extend over a length equal to or greater than the processing range of the flattening punch 101 to accommodate the shaft material 2 . A shaped molding space is formed, and the outer periphery of the shaft member 2 accommodated in this molding space is held. In addition, communication grooves 114 are formed in the mating surfaces of the first mold 110 and the second mold 111 to reach the holding grooves 113 from the upper surfaces of the first mold 110 and the second mold 111 . The flattening punch 101 is pressed against the outer peripheral surface of the shaft member 2 accommodated in the molding space through the communication hole formed by combining the communication grooves 114 of the first mold 110 and the second mold 111 .

The outer surface of the first mold 110 opposite to the abutment surface is provided with an inclined surface 115 that is inclined in the vertical direction. It extends to the lower end position. A similar inclined surface 116 is also provided on the outer surface of the second mold 111 .

Cam 103 has a first cam block 120 and a second cam block 121 . The first cam block 120 and the second cam block 121 are arranged to face each other with the first mold 110 and the second mold 111 sandwiched in the opening/closing direction of the first mold 110 and the second mold 111 . there is The cam 103 has a substantially columnar shape as a whole, and the first cam block 120 and the second cam block are semicircles formed by dividing the column into two with the abutting surfaces of the first mold 110 and the second mold 111 as boundaries. It is formed in a columnar shape.

A concave portion (engagement portion) 122 is formed in each of the facing surfaces of the first cam block 120 and the second cam block 121 . The recess 122 of the first cam block 120 accommodates the first mold 110 and is provided with an inclined surface 123 that makes sliding contact with the inclined surface 115 of the first mold 110 . A recess 122 of the second cam block 121 accommodates the second mold 111 and is provided with an inclined surface 124 that makes sliding contact with the inclined surface 116 of the second mold 111 .

The holder 104 is composed of a rectangular parallelepiped block, and has a fitting hole 130 having a circular cross section penetrating the block in the vertical direction. The holder 104 is formed in an annular shape surrounding the outer periphery of the fitting hole 130 . The first mold 110 and the second mold 111 are arranged in the center of the fitting hole 130 , and the first cam block 120 is positioned between the first mold 110 and the inner peripheral surface of the fitting hole 130 . The second cam block 121 is arranged between the second mold 111 and the inner peripheral surface of the fitting hole 130 . The first cam block 120 and the second cam block 121 are fitted in the fitting hole 130 so as to be vertically movable. The first cam block 120 and the second cam block 121 and the holder 104 are formed with an insertion hole 131 communicating with the molding space formed by the first mold 110 and the second mold 111 .

The first cam block 120 and the second cam block 121 are pushed down by the pressing mechanism 105 independently of the flattening punch 101 . By pushing down the first cam block 120 and the second cam block 121, the inclined surface 123 of the first cam block 120 and the inclined surface 115 of the first mold 110 are engaged, and the inclined surface of the second cam block 121 is engaged. 124 and the inclined surface 116 of the second mold 111 are engaged. Due to 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 lateral pressing force, thereby forming the first mold 110 and the second mold. 111. As a result, the first mold 110 and the second mold 111 are closed and firmly held in the closed state.

In the preforming process, first, the flattening punch 101, the first cam block 120 and the second cam block 121 are lifted by the pressure mechanism 105, and the first mold 110 and the second mold 111 are opened. In this state, the shaft member 2 is arranged at a predetermined position between the holding groove 113 of the first mold 110 and the holding groove 113 of the second mold 111 through the insertion hole 131 . Next, the first cam block 120 and the second cam block 121 are pushed down, and the first mold 110 and the second mold 111 are closed. Then, the flattening punch 101 is pushed down and pressed against the outer peripheral surface of the shaft member 2 . Thereby, the flattened portion 4 is formed on the outer peripheral surface of the shaft member 2 .

6 and 7 schematically show forces acting on each part of the manufacturing apparatus 100 in the preforming process.

When the flattening punch 101 is pressed against the shaft member 2, the first mold 110 and the second mold 111 that hold the shaft member 2 are provided with the left-right direction to open the first mold 110 and the second mold 111. of force F1 acts. This force F1 is applied to the first cam block 120 and the second cam block 121, and the engagement between the inclined surface 123 of the first cam block 120 and the inclined surface 115 of the first die 110 and the engagement of the second cam block. Due to the engagement between the inclined surface 124 of 121 and the inclined surface 116 of the second mold 111, the force is decomposed into a vertical force F2 and a horizontal force F3. Of these forces, the vertical force F2 is received by the pressurizing mechanism 105 .

The left-right force F3 acts on the first cam block 120 and the second cam block 121 so as to spread the first cam block 120 and the second cam block 121 in the left-right direction. It is transmitted to the holder 104 via the block 121 and received by the holder 104 . Here, since the first cam block 120 and the second cam block 121 are originally separated in the horizontal direction, the first cam block 120 and the second cam block 121 are not broken due to the force F3. Since the first cam block 120 and the second cam block 121 are formed in a semi-cylindrical shape, the lateral force F3 acts on the holder 104 as a radially dispersed force F4. Thereby, it is possible to suppress breakage of the holder 104 due to the force F3, and the durability of the manufacturing apparatus 100 can be enhanced.

In addition, the holder 104 that receives the force F3 in the left-right direction is fixed through the preforming process, and the first cam block 120 and the second cam block 121 that are not broken due to the force F3 are more flexible than the holder 104. can be made smaller. Therefore, the pressure mechanism 105 for raising and lowering the first cam block 120 and the second cam block 121 can also be made compact. Thereby, the manufacturing apparatus 100 can be miniaturized.

Preferably, the hardness of the material forming the first mold 110 and the second mold 111 is A, the hardness of the material forming the first cam block 120 and the second cam block 121 is B, and the holder A≧B≧C, where C is the hardness of the material forming 104 . For example, the material of the first mold 110 and the second mold 111 is cold work tool steel with a Rockwell hardness of 58 to 62 HRC, and the material of the first cam block 120 and the second cam block 121 is Rockwell hardness. 54-58 HRC cold work tool steel, and the holder 104 material can be hot work tool steel with a Rockwell hardness of 48-54 HRC. The Rockwell hardness of each material is a value measured by the Rockwell hardness test specified in JIS2245:2016.

In general, there is a trade-off between hardness and toughness of steel, the higher the hardness the lower the toughness. 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 block 120 and the second cam block 121 is b, and the holder 104 is formed. Assuming that the toughness of the material used is c, the hardness relational expression A≧B≧C can be converted into the toughness relational expression as a≦b≦c. By making the material of the first mold 110 and the second mold 111 relatively hard, the wear of the first mold 110 and the second mold 111 in contact with the shaft member 2 can be suppressed, and the material of the holder 104 can be reduced. is relatively tough, the breakage of the holder 104 that receives the lateral force F3 can be suppressed, and the durability of the manufacturing apparatus 100 can be further enhanced.

FIG. 8 shows a modification of the manufacturing apparatus 100. As shown in FIG.

In the example shown in FIG. 8 , flat portions 117 are provided at the bottoms of holding grooves 113 each having a semicircular cross section in the first mold 110 and the second mold 111 . The flat portion 117 extends over a length equal to or longer than the working range of the flattening punch 101 .

FIG. 9 shows the cross-sectional shape of the rack forming section of the hollow rack bar 1 manufactured using the manufacturing apparatus 100 shown in FIG. formed.

FIG. 10 shows an example of a steering device using the hollow rack bar 1 of FIG. A hollow rack bar 1 is sandwiched between pinion gears 202 meshing with the pinion gear 202, a rack guide 203 slidably supporting the hollow rack bar 1, and the rack guide 203 is pressed toward the hollow rack bar 1. and a spring 204 .

Since the flat portion 7 of the hollow rack bar 1 forms a portion that makes plane contact with the rack guide 203, the support of the hollow rack bar 1 by the rack guide 203 is stabilized.

The width W of the flat portion 7 and the width W of the flat portion 117 of the holding groove 113 forming the flat portion 7 are preferably 0.3 mm or more and 10 mm or less. Further, when the outer diameter D of the hollow rack bar 1 is used as a reference, the width W is given by the following formula, where α° is the center angle of the arcuate portion sandwiched between the left and right flat portions 7 on the side opposite to the rack 3. preferably fulfilled.
W≦D×sin[(180°−α°)/2]

As described above, the rack bar manufacturing apparatus disclosed in the present specification is a rack bar in which a rack is formed in a flattened portion provided in a hollow shaft member. An apparatus for manufacturing a rack bar to be formed, comprising: a flattening punch pressed against the outer peripheral surface of the shaft member; a pair of dies for holding the outer periphery of the shaft over a length equal to or longer than the processing range of the pair of dies; By applying pressure in the pressing direction of the flattening punch against the shaft member, the pair of engaging portions are engaged with the pair of molds to close the pair of molds, and the cam for closing the pair of molds and the an annular holder having a fitting hole into which the cam is fitted in the pressing direction of the flattening punch, wherein the cam is positioned between a first cam block and a second The first cam block and the second cam block have a columnar shape when combined with each other.

Further, in the rack bar manufacturing apparatus disclosed in this specification, the hardness of the material forming the pair of molds is set to A, and the material forming the first cam block and the second cam block where B is the hardness of the holder and C is the hardness of the material forming the holder, A≧B≧C.

Further, in the rack bar manufacturing apparatus disclosed in this specification, each of the pair of molds has a groove with a semicircular cross-section for accommodating the shaft member, and the groove is processed by the flattening punch. A flat portion at the bottom of the groove extends over a length of more than the range.

Further, in the rack bar manufacturing apparatus disclosed in this specification, the width of the flat portion is 0.3 mm or more and 10 mm or less.

1 Hollow rack bar 2 Shaft member 3 Rack 4 Flattened portion 5 First opening 6 Second opening 7 Plane portion 10 Tooth forming device 11 Tooth forming mold 12 Mandrel 13 Mandrel holder 14 First mandrel push rod 15 Second core push rod 16 Upper die 17 Lower die 18 Rack tooth die 100 Manufacturing device 101 Punch 102 Preforming die 103 Cam 104 Holder 105 Pressure mechanism 110 First die 111 Second die 112 Eject pin 113 Holding groove 114 Communication groove 115 Inclined surface 116 Inclined surface 117 Flat portion 120 First cam block 121 Second cam block 122 Concave portion (engagement portion)
123 Inclined surface 124 Inclined surface 130 Fitting hole 131 Insertion hole 200 Steering device 201 Casing 202 Pinion gear 203 Rack guide 204 Spring

Claims (4)

A rack bar manufacturing apparatus for forming the flattened portion in the shaft member of a rack bar in which the rack is formed in the flattened portion provided in the hollow shaft member,
a flattening punch pressed against the outer peripheral surface of the shaft;
a pair of dies that can be opened and closed in a direction perpendicular to the direction in which the flattening punch is pressed against the shaft, and hold the outer periphery of the shaft over a length that is equal to or greater than the working range of the flattening punch;
It has a pair of engaging portions that sandwich the pair of molds in the opening and closing direction of the pair of molds, and the pair of engaging portions is pressurized in the pressing direction of the flattening punch against the shaft member. a cam that engages the pair of molds and closes the pair of molds;
an annular holder having a fitting hole into which the cam is fitted in the pressing direction of the flattening punch against the shaft;
with
The cam is divided into a first cam block and a second cam block by the abutting surfaces of the pair of molds, and
the first cam block and the second cam block have a columnar shape when combined with each other ;
Let A be the hardness of the material forming the pair of molds,
Let B be the hardness of the material forming the first cam block and the second cam block,
Assuming that the hardness of the material forming the holder is C,
Manufacturing equipment where A≧B≧C . The manufacturing apparatus according to claim 1,
The pair of molds each have a groove with a semicircular cross section for accommodating the shaft member,
A manufacturing apparatus in which the groove has a flat portion extending over a length equal to or longer than the processing range of the flattening punch at the bottom of the groove. A rack bar manufacturing apparatus for forming the flattened portion in the shaft member of a rack bar in which the rack is formed in the flattened portion provided in the hollow shaft member,
a flattening punch pressed against the outer peripheral surface of the shaft;
a pair of dies that can be opened and closed in a direction perpendicular to the direction in which the flattening punch is pressed against the shaft, and hold the outer periphery of the shaft over a length that is equal to or greater than the processing range of the flattening punch;
It has a pair of engaging portions that sandwich the pair of molds in the opening and closing direction of the pair of molds, and the pair of engaging portions is pressurized in the pressing direction of the flattening punch against the shaft member. a cam that engages the pair of molds and closes the pair of molds;
an annular holder having a fitting hole into which the cam is fitted in the pressing direction of the flattening punch against the shaft;
with
The cam is divided into a first cam block and a second cam block by the abutting surfaces of the pair of molds, and
the first cam block and the second cam block have a columnar shape when combined with each other;
The pair of molds each have a groove with a semicircular cross section for accommodating the shaft member,
A manufacturing apparatus in which the groove has a flat portion extending over a length equal to or longer than the processing range of the flattening punch at the bottom of the groove. The manufacturing apparatus according to claim 2 or 3,
The manufacturing apparatus, wherein the width of the flat portion is 0.3 mm or more and 10 mm or less.

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