JP2007125583A - Method for forming hollow cylindrical material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a hollow cylindrical material with which the deformation and the breakage of an outer mold and a core or the development of distortion in a formed product can be restrained and further, the development of burr can be restrained. <P>SOLUTION: In the case of performing a die casting while arranging a gap Δ with a first core 3 by using a second core 14, the thicker wall W of the thickness in a surroundings than the thickness Δ in a center part, is formed. Therein, when the cutting work is performed by using an inner diameter working tool T, in the case of developing a center lag δ between the second core 4 and the inner diameter working tool T, a wall W at far side from the inner diameter working tool T can not be perfectly removed. However, since the wall W which can not be removed, is the thicker portion of the surrounding thickness, this wall is not the burr but is remained as comparatively long protruded part P in the axial direction. Therefore, when a rack shaft RS is inserted into the inner part after forming a solidified aluminum blank as a gear box GB, even if the tip end part of the rack shaft RS is hit to the protruded part P, it is restrained from being fallen out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a hollow cylindrical object, and more particularly to a method for forming a hollow cylindrical object suitable for forming a housing of a rack and pinion type steering apparatus.

  As one type of vehicle steering device, a rack-and-pinion type steering device that converts the rotational force and rotational amount of the pinion into the axial thrust and stroke of the rack shaft by engaging a pinion with the rack teeth of the rack shaft is known. ing.

Here, the housing of the rack and pinion type steering device has a shape that is long in the axial direction in order to insert the rack shaft, and is generally formed by aluminum die casting. Patent Document 1 discloses a technique in which a pair of cores are arranged opposite to each other inside an outer mold, molten aluminum is poured into the outer mold, and the core is pulled out in both directions after solidifying.
JP 2000-6823 A

  By the way, the outer mold can be cooled sufficiently with cooling water, etc., but the core is difficult to cool and wrapped in an aluminum material, so the temperature easily rises during molding. There is a problem that it is easy to do. In particular, in the case of a long cylinder like the housing of a rack and pinion type steering device, the difference in thermal expansion between the core and the outer mold tends to increase. If this is done, there will be no escape of the difference in thermal expansion, and there will be a burden on the outer mold and core, which may cause deformation and breakage of the outer mold and core, and distortion of the molded product.

  The present invention has been made in view of the problems of the prior art, and can suppress the deformation and breakage of the outer mold and the core and the distortion of the molded product, and further suppress the generation of burrs. An object of the present invention is to provide a method for forming a hollow cylindrical product.

The method for forming the hollow cylindrical body of the present invention is as follows:
Inserting a first core from one side of the outer mold;
Inserting a second core from the other side of the outer mold, and making its tip face the tip of the first core at a predetermined interval;
Injecting molten material between the outer mold and the first and second cores;
Releasing the outer mold from the first core and the second core after the material has solidified;
The solidified material includes a step of deleting a wall formed between the first core and the second core.

  According to the present invention, since the tip of the second core inserted from the other of the outer molds is opposed to the tip of the first core at a predetermined interval, the outer mold And even if a difference in thermal expansion occurs between the first core and the second core, the tension between the two is avoided, so that the outer mold is deformed or broken, and the molded product is distorted. Can be suppressed.

  The material melted at the time of die-casting flows into the gap between the tips of the first core and the second core, and a wall having a predetermined thickness is formed. Therefore, after the core is solidified, the core is released, and the wall is removed by machining or the like using an inner diameter machining tool, thereby obtaining a hollow cylindrical product.

  By the way, when the thickness of the wall generated at the gap between the tips of the first core and the second core is thin, the first core or When the second core and the inner diameter machining tool are relatively misaligned, the wall cannot be completely removed and may remain as burrs protruding from the inner peripheral surface. When such a hollow cylindrical object is used as a housing of a rack and pinion type steering device, when the rack shaft inserted into the housing hits a burr at the time of assembly and falls into the housing, the rack and pinion There is a risk of problems such as biting into the meshing part. On the other hand, if post-processing of burr removal is performed in a separate process, the cost increases.

  In order to eliminate this burr removal process in another process, in order to completely remove burrs during the inner diameter machining, the misalignment between the first core or the second core and the inner diameter machining tool is completely prevented. Alternatively, it is conceivable to increase the amount of machining by taking into account the amount of misalignment between the first core or the second core and the inner diameter machining tool and relatively thinning the core. However, the former requires a very high part accuracy, and the latter has a problem that the processing time increases as a result of the increased processing removal length.

  On the other hand, the present inventors changed the idea of completely removing burrs, and made the present invention based on a new idea of forming burrs that would not fall even when the insert hits them. . Here, in order to form a burr that does not fall even when the insert hits, the gap between the first core and the second core may be increased, and the wall formed thereby However, as described above, the problem remains that the amount of machining by the inner diameter machining tool increases. In view of this, at least one of the first core and the second core is formed with a convex portion having a smaller outer shape than the outer peripheral surface forming the draft at the tip.

  According to the present invention, since the molten material does not enter the portion where the convex portion is formed, the amount of processing by the inner diameter processing tool can be reduced with respect to the solidified material. In addition, since the melted material flows into the periphery of the convex portion, the wall formed in the gap between the first core and the second core becomes thicker in the periphery, and the core and the inner diameter are increased. Because the machining tool is relatively misaligned, even if a part of the wall remains after machining, the remaining convex part is sufficiently thick and strong, so it may fall off when the insert hits it. It ’s not like that.

  In addition, the “projection having an outer shape smaller than the outer peripheral surface forming the draft angle” means that, in the axial direction of the core, when the outer peripheral surface forming the draft angle is extended in the insertion end direction, the axis line extends from the extension line. The convex part arrange | positioned inside an orthogonal direction shall be said. It is preferable that the convex portion has a tapered surface or a conical surface whose size is reduced toward the insertion end side.

  The first core or the second core that does not have a protrusion is preferably provided with a surface perpendicular to the axis at the tip, but a protrusion may be provided on both.

  The hollow cylindrical object is preferably a housing of a rack and pinion type steering device, but the present invention is not limited to this, and a long hollow cylindrical object can be molded according to the present invention.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a column assist type electric power steering apparatus. In the figure, the lower end of the steering shaft SS with the steering wheel SW attached to the upper end extends in the column tube CT and is connected to the upper end of a torsion bar (not shown) of the assist unit AU. The lower end of the torsion bar is connected to the upper end of the output shaft OS connected to the motor MT via a speed reducer (for example, a worm mechanism). A torque sensor TS that outputs a torque signal corresponding to the received torque is provided based on the twisting of the torsion bar, and the torque signal output from the torque sensor TS is transmitted to the control unit ECU. Since the control device ECU transmits a drive signal to the motor MT based on the input torque signal and information such as the vehicle speed, the motor MT that is drive-controlled based on the drive signal passes through the speed reducer. An auxiliary torque is output to the output shaft OS.

  The output shaft OS is connected to the intermediate shaft IS through the joint JT, and the intermediate shaft IS is connected to the pinion shaft PS through the joint JT.

  FIG. 2 is a view of the configuration of FIG. 1 taken along the line II-II and viewed in the direction of the arrow. In FIG. 2, a pinion shaft PS extending in the vertical direction in a gear box (also referred to as a housing) GB is sealed by a seal SL formed on the inner periphery of a bearing fixture BF screwed into the gear box GB. In addition, the bearing BRG fixed by the bearing fixture BF and the needle bearing NB are rotatably supported in the gear box GB.

  Pinion teeth PN are formed between the bearing BRG of the pinion shaft PS and the needle bearing NB. The pinion teeth PN mesh with the rack teeth RT of the rack shaft RS.

  The gear box GB forms a hollow column HP extending leftward in the drawing from the periphery of the rack shaft RS. A rack support device RSD is arranged in the hollow column part HP. The rack support device RSD is a cylindrical holder HD, a shaft SF with both ends mounted in a groove of the holder HD, and a drum-shaped rolling element that is disposed around the shaft SF and contacts the back surface of the rack shaft RS. A cylindrical roller CR, a needle bearing NB that rotatably supports the cylindrical roller CR with respect to the axis SF, a screw member SCR for attaching the holder HD to the hollow column HP, and between the screw member SCR and the holder HD It comprises a disc spring WS for urging the holder HD toward the rack shaft RS, and a lock member LM for the screw member SCR. By adjusting the screwing amount of the screw member SCR, the compression amount of the disc spring WS changes, and the pressing force of the rack shaft RS can be adjusted. After the adjustment, the screw member SCR can be locked and locked by the lock member LM to prevent the looseness.

  In FIG. 1, both ends of the rack shaft RS protrude from the gear box GB and are connected to tie rods TR constituting the steering device via ball joints SJ, and the rack shaft RS moves in the longitudinal direction. A wheel (not shown) is steered. In the present embodiment, the gear box GB is a hollow cylinder.

  The operation of this embodiment will be described. When a steering force is input to the steering wheel SW, the steering force is transmitted to the torsion bar in the assist unit AU via the steering shaft SS. At this time, based on the torque signal output from the torque sensor TS, the auxiliary steering force generated by the motor MT driven and controlled by the control unit ECU is transmitted to the output shaft OS. The steering force to which the auxiliary steering force is added is further transmitted to the pinion shaft PS through the intermediate shaft IS, and the rotational force of the pinion shaft PS is increased in the longitudinal direction of the rack shaft RS through the meshing pinion teeth PN and the rack teeth RT. It is converted into a directional thrust, and a wheel (not shown) is steered through the tie rod TR by the longitudinal thrust. At this time, the cylindrical roller CR rolls on the back surface of the rack shaft RS, and allows the rack shaft RS to move with low friction. Further, when a strong force is transmitted between the pinion shaft PS and the rack shaft RS, a separation force is generated to separate the rack shaft RS from the pinion shaft PS. The cylindrical roller CR supports such a separation force. can do.

  Hereinafter, a method for forming the gear box GB will be described. FIG. 3 is a cross-sectional view of an aluminum die cast mold for molding the gear box GB. FIG. 4 is an enlarged view showing a portion indicated by an arrow IV in the configuration of FIG. First, as for the 1st core 3 and the 2nd core 4 shown as a comparative example, the front end surface which cross | intersects the outer peripheral surface which has a draft is orthogonal to an axis line.

  In FIG. 3, the first core 3 is inserted from the left side in the figure into the cylindrical space formed between the upper mold 1 and the lower mold 2 forming the outer mold, and the second core from the right side in the figure. A core 4 is inserted. Here, as shown in FIG. 4, a predetermined gap Δ is provided between the tip of the first core 3 and the tip of the second core 4. The gap Δ can be obtained by measuring the protruding amounts of the end portions of the first core 3 and the second core 4 from both end surfaces of the upper mold 1 or the lower mold 2.

  In such a state, after the molten aluminum material AL is discharged to a hollow cylindrical space formed by the upper mold 1, the lower mold 2, and the cores 3 and 4 through a gate (not shown), and this is solidified, The upper mold 1 and the lower mold 2 and the cores 3 and 4 are released. According to the present embodiment, the front end of the first core 3 is opposed to the front end 4 of the second core with a predetermined interval Δ. Even when a difference in thermal expansion occurs between the core 2 and the second core 3, the tension between the two is avoided, so that the outer molds 1, 2 and the cores 3, 4 are deformed or damaged, Further, it is possible to suppress the distortion of the gear box GB to be molded.

  By the way, since the wall W having a thickness Δ exists inside the solidified aluminum material AL at the stage of releasing (see FIG. 4), it is necessary to remove this in a subsequent process.

  FIG. 5 is a diagram illustrating a cutting process after die casting. In FIG. 5, when the inner diameter machining tool T such as a drill is inserted into the solidified aluminum material AL while being rotated, the wall W is perforated and deleted (part indicated by a dotted line). Here, in order to suppress the processing amount in the cutting process, it is necessary not to make the outer diameter of the inner diameter processing tool T excessively larger than the inner diameter of the solidified aluminum material AL (= the outer diameter of the core). is there.

  However, for example, when cutting is performed using an inner diameter machining tool T having an outer diameter substantially equal to the minimum outer diameter of the second core 4, a misalignment δ between the second core 4 and the inner diameter machining tool T is performed. If this occurs, the wall W on the side far from the inner diameter machining tool T cannot be completely removed, and this may remain as burrs B. If the wall W has a small thickness Δ, after forming the gear box GB, as shown in FIG. 6, when the rack shaft RS is inserted therein, the tip of the rack shaft RS hits the burr B and drops off. There is a fear.

  In order to prevent this burr B from being generated, a measure to bring the misalignment amount δ closer to zero or a measure to increase the outer diameter of the inner diameter machining tool T can be considered. However, the former countermeasure is difficult in terms of accuracy, and the latter countermeasure increases the machining amount of the inner diameter machining tool T.

  Therefore, in the following embodiment, the burrs B are prevented from falling off as follows. FIG. 7 is a cross-sectional view similar to FIG. 4 according to the first embodiment. In the present embodiment, only the shape of the core is different. More specifically, a truncated cone portion 14a as a convex portion is formed at the tip of the second core 14, and the angle of the outer peripheral conical surface of the truncated cone portion 14a is determined by the second core. 14, the angle of the draft angle of the outer peripheral surface 14b of the main body 14 is larger. Therefore, as apparent from FIG. 7, the frustoconical portion 14a has a smaller outer diameter than the outer peripheral surface 14b forming the draft angle. . The shapes of the first core 3 and the upper mold 1 and the lower mold 2 are the same as those shown in FIGS.

  When die casting is performed using the second core 14 as described above while the gap between the first core 3 and the first core 3 is Δ, as shown in FIG. A wall W having a thicker periphery is formed. Here, as shown in FIG. 8, when cutting is performed using the inner diameter machining tool T, if a misalignment δ occurs between the second core 4 and the inner diameter machining tool T, the inner diameter The wall W far from the processing tool T cannot be completely removed. However, since the wall W that could not be deleted is a thick portion around the periphery, the wall W remains as a raised portion P that is relatively long in the axial direction, not a burr (see FIG. 8).

  Therefore, after the solidified aluminum material is formed as the gearbox GB, as shown in FIG. 9, when the rack shaft RS is inserted into the gearbox GB, even if the tip of the rack shaft RS hits the raised portion P, it will fall off. Is suppressed. Note that when the rack shaft RS is inserted from the second core 14 side, the tip of the rack shaft RS faces the tapered surface of the raised portion P formed by the truncated cone portion 14a, so that the rack shaft RS can be inserted smoothly. There are benefits.

  FIG. 10 is a cross-sectional view similar to FIG. 7 according to the second embodiment. In FIG. 10, a small cylindrical portion 24c is formed at the tip of the second core 24 at the tip of the truncated cone portion 24a, and functions as a convex portion. The outer diameters of the truncated cone portion 24 a and the small cylindrical portion 24 c are smaller than the minimum outer diameter of the main body outer peripheral surface 24 b of the second core 24. Other configurations are the same as those of the embodiment shown in FIG.

  FIG. 11 is a cross-sectional view similar to FIG. 7 according to the third embodiment. In FIG. 11, similarly to the second core 14 shown in FIG. 7, a truncated cone portion 13 a as a convex portion is formed at the tip of the first core 13. The outer diameter of the truncated conical portion 13 a is smaller than the minimum outer diameter of the main body outer peripheral surface 13 b of the first core 13. Other configurations are the same as those of the embodiment shown in FIG.

  FIG. 12 is a cross-sectional view similar to FIG. 7 according to the fourth embodiment. In FIG. 12, the second core 24 shown in FIG. 10 and the first core 13 shown in FIG. 11 are used in combination. Other configurations are the same as those of the embodiment shown in FIG.

  FIG. 13 is a cross-sectional view similar to FIG. 7 according to the fifth embodiment. In FIG. 13, a truncated conical portion 34a as a convex portion is formed discontinuously with the main body outer peripheral surface 34b on the end surface of the main body outer peripheral surface 34b of the second core 34. The maximum outer diameter of the truncated conical portion 34a is smaller than the minimum outer diameter of the main body outer peripheral surface 34b forming the draft angle. Other configurations are the same as those of the embodiment shown in FIG.

  FIG. 14 is a cross-sectional view similar to FIG. 7 according to the sixth embodiment. In FIG. 14, a conical portion 44 a as a convex portion is formed on the end surface of the main body outer peripheral surface 44 b of the second core 44. The tip of the conical portion 44a is sharp. Other configurations are the same as those of the embodiment shown in FIG.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the present invention can be used for manufacturing a hollow cylinder other than a gear box of a steering device.

1 is a schematic configuration diagram of a column assist type electric power steering apparatus according to a first embodiment. FIG. It is the figure which cut | disconnected the structure of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is sectional drawing of the aluminum die-casting type | mold which shape | molds the gear box GB. FIG. 4 is an enlarged view showing a part indicated by an arrow IV in the configuration of FIG. 3. It is a figure which shows the cutting process after die-casting. It is sectional drawing which shows the state at the time of incorporating the rack axis | shaft RB in the gear box GB of a comparative example. It is sectional drawing similar to FIG. 4 concerning 1st Embodiment. In 1st Embodiment, it is a figure which shows the cutting process after die-casting. It is sectional drawing which shows the state at the time of incorporating the rack axis | shaft RB in the gear box GB of 1st Embodiment. It is sectional drawing similar to FIG. 7 concerning 2nd Embodiment. It is sectional drawing similar to FIG. 7 concerning 3rd Embodiment. It is sectional drawing similar to FIG. 7 concerning 4th Embodiment. It is sectional drawing similar to FIG. 7 concerning 5th Embodiment. It is sectional drawing similar to FIG. 7 concerning 6th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper mold | type 2 Lower mold | type 3,13 1st core 4,14,24,34 2nd core 13a A truncated cone part 13b Main body outer peripheral surface 14a, 24a, 34a, 44a A truncated cone part 14b, 24b, 34b Main body outer peripheral surface AL Aluminum material AU Assist unit B Burr BF Bearing fixture BRG Bearing CR Cylindrical roller CT Column tube ECU Controller GB Gear box HD Holder HP Hollow column part IS Intermediate shaft JT Joint LM Lock member MT Motor NB Needle bearing OS Output shaft P Raised portion PN Pinion tooth PS Pinion shaft RB Rack shaft RS Rack shaft RSD Rack support device RT Rack tooth SCR Screw member SF Shaft SJ Joint SL Seal SS Steering shaft SW Steering wheel T Inner diameter machining tool TR Tie rod TS Torque sensor W Wall WS disc spring

Claims (4)

Inserting a first core from one side of the outer mold;
Inserting a second core from the other side of the outer mold, and making its tip face the tip of the first core at a predetermined interval;
Injecting molten material between the outer mold and the first and second cores;
Releasing the outer mold from the first core and the second core after the material has solidified;
A step of removing a wall formed between the first core and the second core in the solidified material.   2. The hollow according to claim 1, wherein at least one of the first core and the second core is formed with a convex portion having a smaller outer shape than an outer peripheral surface forming a draft at the tip. A method for forming a cylindrical object.   The method of forming a hollow cylindrical object according to claim 2, wherein the first core or the second core has a surface perpendicular to the axis at the tip. The method for forming a hollow cylindrical object according to any one of claims 1 to 3, wherein the hollow cylindrical object is a housing of a rack and pinion type steering device.

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