Patent ID: 12208432

DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present disclosure are described below in more detail with reference to the accompanying drawings. These embodiments are examples of the present disclosure and may be embodied in various other different forms by those of ordinary skill in the art to which the present disclosure pertains. Thus, the present disclosure is not limited to these embodiments.

Referring toFIG.1, a method of drawing an axial tube made of an aluminum (Al) material includes surface etching (S10), surface heat treatment (S20), axial tube drawing (S30), and product completion (S40). An extruded pipe1made of an Al alloy is manufactured as a drawn pipe5through an etched pipe3and a heat treatment pipe4. In this embodiment, the extruded pipe1is an extruded pipe having a diameter of 50 mm. The drawn pipe5of an axial tube is a pipe having different diameters, in which a diameter is varied to 50 mm and 30 mm by drawing the axial tube.

For example, the Al alloy is an A6063-series alloy. Compositional components of the Al alloy include silicon (Si) ranging from 0.2 wt % to 0.6 wt %, iron (Fe) ranging 0.35 wt % or less, copper (Cu) ranging 0.1 wt % or less, magnesium (Mg) ranging from 0.45 wt % to 0.9 wt % or less, chromium (Cr) ranging 0.1 wt % or less, zinc (Zn) ranging 0.1 wt % or less, and titanium (Ti) ranging 0.1 wt % or less, and the remainder thereof includes Al.

For example, in the surface etching (S10), sodium hydroxide (NaOH) etching is applied to a surface of the extruded pipe1. In this case, the NaOH etching removes oxides and foreign materials which are present on the surface of the extruded pipe1made of the Al alloy.

To this end, the NaOH etching treatment is performed at a NaOH concentration ranging from 0.5 normality (N) to 1 N for one to two minutes.

Table 1 shows a relationship between an etching solution and surface roughness of the extruded pipe1, where Ra is average surface roughness.

TABLE 1Etching solutionSurfaceSurface(NaOH)roughnessroughnessconcentrationTime(Ra, μm)(Ra, μm)0 to 0.5One to two1.86.00.5 to 1.0minutes0.151.01 to 1.51.03.0

Table of Relationship Between Etching Solution and Surface Roughness

From Table 1, it is confirmed that, as a result of the NaOH concentration/time condition, the surface roughness as well as the removal of foreign materials on the surface of the extruded pipe1was improved. However, when the NaOH etching concentration is increased, the Al material is etched in addition to the foreign materials being removed, and thus roughness is degraded. In order to prevent the roughness degradation, the NaOH etching concentration is set to a range from 0.5 N to 1.0 N as an optimal NaOH etching concentration.

As a result, the extruded pipe1is manufactured as the etched pipe3The etched pipe3has a surface roughness ranging from 0.15 to 1.0 at a NaOH etching concentration ranging from 0.5 N to 1.0 N.

For example, in the surface heat treatment (S20), high frequency heat treatment is performed on a surface of the etched pipe3. The high frequency heat treatment improves formability of the pipe3and is suitable for solving a problem of cracks which may occur during the axial tube drawing (S30) due to the lack of a stretching rate or ductility of the Al alloy when compared with the steel pipe.

To this end, in the high frequency heat treatment, a heat treatment temperature ranges from 200° C. to 300° C., and a heat treatment time ranges from 5 to 10 seconds.

Table 2 shows a relationship between high frequency heating and a maximum tube reduction ratio of the heat treatment pipe4.

TABLE 2High frequencyMaximum tubeheating temperatureTimereduction ratio100 to 200One to two20%200 to 300minutes40%300 to 40020%

Table of Relationship Between High Frequency Heating and Tube Reduction Ratio

From Table 2, it can be confirmed that the maximum tube reduction ratio of the Al alloy is varied according to the heat treatment time and the high frequency temperature in the high frequency heat treatment. In this case, it was confirmed that, when the high frequency heat treatment temperature was 200° C. or less, a maximum tube reduction ratio was 20% (i.e., a tube reduction ratio when the diameter is reduced from 50 mm to 40 mm). Also, when the high frequency heat treatment temperature ranged from 200° C. to 300° C., the maximum tube reduction ratio was 40% (i.e., a tube reduction ratio when the diameter was reduced from 50 mm to 30 mm). Further, when the high frequency heat treatment temperature was 300° C. or higher, the maximum tube reduction ratio was degraded to 20% (i.e., a tube reduction ratio when the diameter was reduced from 50 mm to 40 mm). In this case, a cause of the degradation of the maximum tube reduction ratio is predicted that a surface temperature of Al rose so that the surface of Al was melted and a friction force was increased.

As a result, the etched pipe3is manufactured as the heat treatment pipe4. The high frequency heat treatment temperature ranging from 200° C. to 300° C., at which a maximum tube reduction ratio of 40% (i.e., a tube reduction ratio when the diameter is reduced from 50 mm to 40 mm) was formed, was applied to the heat treatment pipe4.

For example, in the axial tube drawing S30, the heat treatment pipe4is manufactured by being put into and drawn in an axial tube mold100. In the axial tube mold100, when compared with a draw speed in a large diameter section having a length 510 mm, a draw speed ranges between 0.5 m/minute to 1 m/minute in a variable section in which a diameter is 50 mm and a length is 80 mm. A draw speed ranges between 1 m/minute to 3 m/minute in a small diameter section in which a diameter of a reduced tube is 30 mm and a length thereof is 870 mm.

As a result, the heat treatment pipe4is manufactured as the reduced drawn pipe5. The reduced drawn pipe5is manufactured to have a diameter reduction section7, in which a diameter do of 50 mm is reduced to a diameter d1of 30 mm, between a large diameter section6having the diameter do of 50 mm and a small diameter section8having the diameter d1of 30 mm. In other words, the axial tube drawn pipe5is formed to have a tube reduction ratio of 40% between the large diameter section6and the small diameter section8.

For example, the product completion (S40) is in a state in which the drawn pipe5is manufactured by being drawn in the axial tube mold100.

Meanwhile,FIG.2illustrates an example in which the extruded pipe1is manufactured as a cowl cross bar10by the drawing method of an axial tube made of an Al material through the etched pipe3, the heat treatment pipe4, and the drawn pipe5.

As shown in the drawing, the cowl cross bar10includes a driver seat section11and a passenger seat section13. In this case, since the cowl cross bar10is the reduced drawn pipe5drawn by the axial tube mold100(seeFIG.1), the driver seat section11is equal to the large diameter section6having the diameter d0of 50 mm and the passenger seat section13is equal to the small diameter section8having the diameter d1of 30 mm A connection portion between the driver seat section11and the passenger seat section13is equal to the diameter reduction section7in which the diameter d0of 50 mm is reduced to the diameter d1of 30 mm.

Therefore, a cowl panel20is formed using the drawn pipe5(seeFIG.1) as the cowl cross bar10. The drawn pipe5(seeFIG.1) is a component of a cockpit module of a vehicle, such as the role of the cowl cross bar10, and may guide and support electronic components of the cockpit, such as a steering shaft, an instrument panel, an air conditioning system, an airbag, and an audio system. The cowl cross bar10may constitute a frame for preventing the vehicle from being bent or distorted in a left-right direction and for increasing durability of a vehicle body. Thereby, the cowl cross bar10may provide a guide surface on which the electronic components of the cockpit are installed and safely protect passengers in the case of a head-on collision.

As described above, the drawing method of an axial tube made of an Al material for the cowl cross bar10according to the present embodiment performs NaOH etching on the extruded pipe1having a single diameter and made of an Al alloy. Subsequently, the drawing method includes high frequency heat treatment on the extruded pipe1to increase a tube reduction ratio of the extruded pipe1and manufacturing the cowl cross bar10. The large diameter section6and the small diameter section8of the cowl cross bar10have a difference in diameter due to a tube reduction ratio of 40% of the diameter reduction section7, through the drawing of the extruded pipe1using the axial tube mold100. Therefore, even when an A6063 aluminum alloy series, which is an Al material, is manufactured as an axial tube having different diameters, the occurrence of cracks is prevented. In particular, the tube reduction ratio is increased due to surface treatment of an Al extruded material for reducing a frictional force on an entire surface of the axial tube as well as high frequency heating so that occurrence of cracks of the Al material is prevented during the tube reduction process.

A drawing method of an axial tube made of an aluminum (Al) material, which is applied to manufacturing of a cowl cross bar of the present disclosure implements the following actions and effects.

First, it is possible to manufacture a cowl cross bar with no cracks using an Al material. Second, all disadvantages of the existing steel pipe welding product with a welding quality problem using the Al material are solved. Third, when compared with the existing room temperature axial tube without surface treatment and high frequency application, a tube expansion ratio of the Al material can be increased twice or more (about 40%) and a salty water spray evaluation (about 480 hours) can be satisfied so that improvement in corrosion resistance of the cowl cross bar can be achieved.

While the present disclosure has been described with reference to the accompanying drawings and the disclosed embodiments, it should be apparent to those of ordinary skill in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. The present disclosure is not limited to the embodiments disclosed herein. Accordingly, it should be noted that such alternations or modifications fall within the scope of the claims of the present disclosure, and that the scope of the present disclosure should be construed on the basis of the appended claims.