JP6039986B2 - Hollow rack bar manufacturing apparatus and hollow rack bar manufacturing method - Google Patents

Description

  The present invention relates to a hollow rack bar manufacturing apparatus and a hollow rack bar manufacturing method for manufacturing a hollow rack bar used in a power staying device for automobiles, and more particularly to a device capable of uniforming the tooth width in the axial direction.

  As a manufacturing method of a hollow rack bar used for a power steering device of an automobile, there are many conventional methods by cutting from a round bar. However, in order to cope with a complicated shape and weight reduction, what is manufactured from a pipe material by transfer forging is known (for example, refer to Patent Document 1). Specifically, first, the pipe material is pressurized with a cold forging die to form a flat top surface as the first step of the tooth forming process, and in the next step, a mandrel (core metal) is press-fitted into the cavity of the pipe material. Is done. The mandrel has a tapered projection, and the projection engages with the flat portion of the pipe material on the inner peripheral side, so that the meat of the flat portion flows plastically toward the teeth of the mold. Thus, a linear tooth row having a shape corresponding to the tooth row of the mold is applied to the outer peripheral flat portion of the pipe material by a transfer method, and a hollow rack bar can be obtained.

On the other hand, in such a manufacturing method, a phenomenon may occur in which the tooth width becomes small at the end portion in the longitudinal direction of the rack, and at both ends in the axial direction of the rack of the rack forming type, at a height corresponding to the rack tooth base. A method of manufacturing a hollow steering rack shaft that can suppress a phenomenon that the tooth width is reduced by providing a predetermined flat portion is known (for example, see Patent Document 2).
In recent years, as an assist mechanism of a steering mechanism, there is a shift from hydraulic power steering to electric power steering, and the force received by the tooth portion tends to increase. For this reason, it is necessary to form a uniform and sufficient tooth width at both the axial center and the axial end.

Japanese Examined Patent Publication No. 3-5892 JP 2005-28924 A

  The above-described method for manufacturing a hollow rack bar has the following problems. That is, as shown in FIG. 9, in the flattening process for flatly forming the predetermined region K of the pipe material P, the AA cross section and the BB cross section of the processed pipe material P are compared with each other in FIG. As shown, in the BB cross-section corresponding to the center portion, the flat portion fles downward and becomes thick in the radial direction. For this reason, the cross section of the pipe material P is distorted and does not correspond to the shape of the mandrel M.

  When the mandrel M is passed through the pipe material P having the BB cross-section processed in this way using the press-fitting mechanism W, the lower surface Ma of the mandrel M and the pipe material are taken in the A-A cross section as shown in FIG. Although the inner surface of P is in contact, the lower surface Ma of the mandrel M and the inner surface of the pipe material P are not in contact with each other in the BB cross section, and reciprocate in a floating state. That is, as shown in FIG. 11, the mandrel M reciprocates in an arc shape having a convex shape in FIG. In FIG. 11, Ga represents an upper mold, Gb represents a lower mold, and Gc represents a tooth portion. For this reason, the thickness of the pipe material P plastically flowed by the mandrel M increases at the axial center (f2) and decreases at the axial end (f1). As a result, a tooth portion having a uniform tooth width in the axial direction cannot be formed, and there is a possibility that sufficient force cannot be transmitted at the end portion in the axial direction.

  Therefore, an object of the present invention is to provide a hollow rack bar manufacturing apparatus and a hollow rack bar manufacturing method in which a tooth width of a tooth portion forming a rack is formed uniformly and sufficiently in the axial direction.

  In order to solve the above problems and achieve the object, the hollow rack bar manufacturing apparatus and the hollow rack bar manufacturing method of the present invention are configured as follows.

In a hollow rack bar manufacturing apparatus that forms a rack in a predetermined region of a steel pipe, a heating unit that heats the upper surface of the predetermined region in the axial center of the steel pipe at a high frequency to 450 ° C. or more and flattening the predetermined region. , a press die for molding the processing wall portion has a tooth die corresponding to the rack, while pressing the tooth die to the predetermined area, and the mold for holding the steel pipe, cooling has been pre Symbol steel A cored bar that is plastically flowed from the inside of the steel pipe to the outside by being press-fitted into the tooth mold to form a rack corresponding to the tooth mold is held by the mold. And a press-fitting mechanism for press-fitting the inside of the steel pipe.

In the hollow rack bar manufacturing method for forming a rack in a predetermined region of a steel pipe, a heating step of high-frequency heating the upper surface of the predetermined region in the axial center of the steel pipe to 450 ° C. or more, and flattening the predetermined region. a pressing step for molding the processing wall portion while pressing the tooth die corresponding to the rack in the predetermined region, a holding step of holding the steel pipe, a cooling step of cooling the steel pipe, a core metal A press-fitting step of press-fitting into the steel pipe and plastically flowing the processed wall portion in contact with the tooth mold from the inside to the outside of the steel pipe to form a rack according to the tooth mold. To do.

  According to the present invention, it is possible to form the tooth width of the tooth portion forming the rack uniformly and sufficiently in the axial direction.

Explanatory drawing which shows the heating process of the hollow rack bar manufacturing method by the hollow rack bar manufacturing apparatus which concerns on one embodiment of this invention. Explanatory drawing which shows the press process of the hollow rack bar manufacturing method. Explanatory drawing which shows the press process of the hollow rack bar manufacturing method. Explanatory drawing which shows the press process of the hollow rack bar manufacturing method. Explanatory drawing which shows the heating range in the heating process of the hollow rack bar manufacturing method. Explanatory drawing which shows the press-fit process of the hollow rack bar manufacturing method. Sectional drawing which shows the steel pipe after the press process in the manufacturing method of the said hollow rack bar. Explanatory drawing which compares the AA cross section and the BB cross section in FIG. 4 of the same steel pipe. The top view which shows the hollow rack bar formed by the hollow rack bar manufacturing method. The perspective view which shows an example of the heating coil of the same hollow rack bar manufacturing apparatus. The perspective view which shows another example of the heating coil of the same hollow rack bar manufacturing apparatus. Sectional drawing which shows the steel pipe after the press process in the conventional hollow rack bar manufacturing process. Explanatory drawing which compares the AA cross section and the BB cross section in FIG. 4 of the same steel pipe. Explanatory drawing which shows the process of pressing-in a mandrel with respect to the steel pipe. The top view which shows the hollow rack bar formed by the conventional hollow rack bar manufacturing method.

  FIG. 1A is an explanatory view showing a heating step of a hollow rack bar manufacturing method by a hollow rack bar manufacturing apparatus according to an embodiment of the present invention, and FIGS. 1B to 1D are explanatory views showing a pressing step of the hollow rack bar manufacturing method, 2 is an explanatory view showing a heating range in the heating process of the hollow rack bar manufacturing method, FIG. 3 is an explanatory view showing a press-fitting process of the hollow rack bar manufacturing method, and FIG. 4 is a view showing a steel pipe after the pressing process in the hollow rack bar manufacturing method. FIG. 5 is an explanatory view for comparing the AA section and the BB section in FIG. 4 of the pipe material P, and FIG. 6 is a plan view showing the hollow rack bar formed by the hollow rack bar manufacturing method. is there.

  In these drawings, P is a pipe material (steel pipe), Pa is a processed wall portion, Pb is a rack, H is a heated portion, and M is a mandrel.

  The hollow rack bar manufacturing apparatus 10 is an apparatus for manufacturing a hollow rack bar by flattening a predetermined region K of the pipe material P, forming a processed wall portion Pa, and forming a rack Pb. The hollow rack bar manufacturing apparatus 10 includes a heating unit 20 that heats a central portion in the axial direction of the pipe material P in a predetermined region K at a high frequency to 450 ° C. or more, and a plastic processing unit 30 that performs plastic processing.

  The heating unit 20 includes a heating coil 21 and a power unit 22 that applies high-frequency power to the heating coil 21. The power unit 22 heats the central portion (the heated portion H) in the axial direction of the pipe material P in the predetermined region K at a high frequency to 450 ° C. or higher. Specifically, it is preferable to heat to 600 to 650 ° C.

  The plastic working portion 30 has a press die 40 for flattening a predetermined region K of the pipe material P and molding a processing wall portion, and a tooth die 53 corresponding to the rack. While pressing, the mold 50 for holding the pipe material P and the processing wall portion Pa in contact with the tooth mold 53 by being press-fitted into the pipe material P are plastically flowed from the inside to the outside of the pipe material P to form the tooth mold. 53, a mandrel M for forming a rack according to 53, and a press-fitting mechanism 60 for press-fitting the mandrel M into the pipe material P held by the mold 50 are provided.

  The mold 50 includes an upper mold 51 and a lower mold 52 that hold the pipe material P from above and below, and a tooth mold 53 that is pressed against the processing wall portion Pa.

  In the hollow rack bar manufacturing apparatus 10 configured as described above, the hollow rack bar Q is manufactured from the pipe material P as follows. That is, as shown in FIG. 1A, in a predetermined region K of the pipe material P, a high frequency having a predetermined frequency / current is applied to the heated portion H from the power portion 22 to the heating coil 21. As shown in FIG. 2, the heating range at this time is a range where the upper 90 ° to 120 ° press work is performed, and is set based on the tooth specifications. The heating temperature is 600 to 650 ° C. This temperature is 450 ° C. or higher, which is the recrystallization temperature of pure iron, and is an annealing temperature range in which stress can be removed. And as shown to FIG. 1B, the predetermined area | region K is press-processed with the press die 40, flattening is performed, and the process wall part Pa is formed. This suppresses work hardening in the flattening process by allowing to cool and keeps the temperature maintained at 500 ° C. or higher as shown in FIG. 1C. Next, as shown in FIG. 1D, the press die 40 is separated and allowed to cool. By allowing to cool, work hardening in flattening processing is suppressed, power necessary for the press-fitting process of the next process is reduced, and the tooth mold life is improved.

  Next, the mandrel M is press-fitted into the pipe material P, and the processing wall portion Pa in contact with the tooth mold 53 is plastically flowed from the inside to the outside of the pipe material P to form a rack Pb corresponding to the tooth mold 53.

  According to the hollow rack bar manufacturing method using the hollow rack bar manufacturing apparatus 10 as described above, in flattening processing for forming the predetermined region K of the pipe material P flatly, AA of the processed pipe material P shown in FIG. Comparing the cross section with the BB cross section, as shown in FIG. 5, the AA cross section and the BB cross section corresponding to the central portion have substantially the same thickness (t1 = t2). This is because when the heated portion H of the pipe material P is flattened, the meat does not escape to the unheated lower portion, and moves downward, that is, toward the inner diameter side. For this reason, the radial thickness of the lower part of the pipe material P does not increase.

  Therefore, when the mandrel M is allowed to pass through the flattened pipe material P, the lower surface of the mandrel M and the inner surface of the pipe material P come in contact with each other along both the AA and BB cross sections and reciprocate. . That is, as shown in FIG. 3, the mandrel M reciprocates in the horizontal direction. For this reason, the thickness of the pipe material P plastically flowed by the mandrel M is substantially the same at the axially central portion and the end portion. As a result, a tooth portion having a uniform tooth width in the axial direction can be formed, and a force can be sufficiently transmitted even at the axial end portion.

  7 and 8 are perspective views showing an example of the heating coil 21 of the hollow rack bar manufacturing apparatus 10. The shape of the heating coil 21 is appropriately set depending on the shape and range of the heated part H.

  As described above, according to the hollow rack bar manufacturing apparatus and the hollow rack bar manufacturing method according to the present embodiment, the tooth widths of the tooth portions forming the rack are formed uniformly and sufficiently in the axial direction. It is possible.

  In addition, about each apparatus of a heating, flattening, and a tooth shaping | molding, you may be an integrated apparatus or another apparatus, respectively.

The present invention is not limited to the above embodiments, the addition, it is given Ru course der various modifications may be implemented without departing from the scope of the present invention. Hereinafter, the invention described in the scope of claims of the present application will be appended.
[1] In a hollow rack bar manufacturing apparatus that forms a rack in a predetermined region of a steel pipe, a heating unit that heats the central portion in the axial direction of the steel pipe in the predetermined region at a high frequency to 450 ° C. or more, and flattening the predetermined region And a press die that molds the processing wall portion and a tooth die corresponding to the rack, and a die that holds the steel pipe while pressing the tooth die against the predetermined region, and is press-fitted into the steel pipe. A core metal that forms a rack according to the tooth mold by plastically flowing the processed wall portion in contact with the tooth mold from the inside to the outside of the steel pipe is press-fitted into the steel pipe held by the mold. A hollow rack bar manufacturing apparatus including a press-fitting mechanism.
[2] The hollow rack bar manufacturing apparatus according to [1], wherein the heating unit heats the central portion to 600 to 650 ° C.
[3] In a hollow rack bar manufacturing method for forming a rack in a predetermined region of a steel pipe, a heating step of high-frequency heating the axial central portion of the steel pipe in the predetermined region to 450 ° C. or more, and flattening of the predetermined region And pressing the tooth mold corresponding to the rack against the predetermined area while holding the steel pipe, press-fitting a metal core into the steel pipe, and the tooth mold A hollow rack bar manufacturing method comprising: a press-fitting step of plastically flowing the processed wall portion in contact with the steel pipe from the inside to the outside of the steel pipe to form a rack according to the tooth shape.
[4] The hollow rack bar manufacturing method according to [3], wherein the heating step heats the central portion to 600 to 650 ° C.

  DESCRIPTION OF SYMBOLS 10 ... Hollow rack bar manufacturing apparatus, 20 ... Heating part, 21 ... Heating coil 30, ... Plastic processing part, 40 ... Press die, 50 ... Mold, 53 ... Tooth type, 60 ... Press-fit mechanism, P ... Pipe material (steel pipe) ), Pa ... work wall, Pb ... rack, H ... heated part, M ... mandrel.

Claims (4)

In a hollow rack bar manufacturing apparatus that forms a rack in a predetermined region of a steel pipe,
A heating unit for heating the upper surface of the steel pipe in the axial direction in the predetermined region at a high frequency to 450 ° C. or higher;
A pressing die for flattening the predetermined region and molding a processing wall;
A mold having a tooth mold corresponding to the rack, and holding the steel pipe while pressing the tooth mold against the predetermined region;
The metal core to form a rack corresponding to the tooth die by plastically flow outwardly of the processing wall portion from the inside of the steel pipe in contact with the tooth die by being pressed into cool been pre Symbol the steel pipe, A hollow rack bar manufacturing apparatus comprising: a press-fitting mechanism for press-fitting into a steel pipe held by the mold. The hollow rack bar manufacturing apparatus according to claim 1, wherein the heating unit heats an upper surface of the central portion to 600 to 650 ° C. In a method for producing a hollow rack bar for forming a rack in a predetermined region of a steel pipe,
A heating step of high-frequency heating the upper surface of the predetermined region in the axial central portion of the steel pipe to 450 ° C. or higher;
A pressing step of flattening the predetermined region and molding a processed wall;
A holding step of holding the steel pipe while pressing a tooth mold corresponding to the rack against the predetermined region ;
A cooling process for cooling the steel pipe;
The core metal is pressed into the interior of the steel pipe, that said processing wall portion in contact with the tooth die by plastically flow from the inside to the outside of the steel pipe and a press-fitting step of forming a rack corresponding to the tooth die A method for producing a hollow rack bar. The method for producing a hollow rack bar according to claim 3, wherein the heating step heats the upper surface of the central portion to 600 to 650 ° C.

Images