Method for forming vehicle body member

A forming method for a vehicle body member may include a tube making process of forming a steel pipe by welding a steel plate coil; a non-circular tube making process of primary preforming the steel pipe formed in the tube making process so as to have a cross section of a predetermined shape; a bending process of bending and secondarily preforming the steel pipe preformed firstly in the non-circular tube making process; and a hot stamping process of heating the secondarily preformed steel pipe, inserting the heated steel pipe into a mold to form a desired shape, and then, quenching the heated steel pipe to form a vehicle body member, thereby easily forming a vehicle body member having high rigidity.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean Patent Application No. 10-2019-0062651 filed on May 28, 2019 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a vehicle body. More particularly, the present disclosure relates to a method for forming a vehicle body member that forms a roof side member constituting a roof of a vehicle among an upper vehicle body in a tube shape.

BACKGROUND

In general, the upper part of a vehicle body includes a roof forming the roof of the vehicle and at least one pillar which is disposed back and forth along the length direction of the vehicle while supporting the roof.

At least one pillar typically include a front pillar disposed forwardly along the length direction of the vehicle, a rear pillar disposed at the rear, and a center pillar disposed between the front filler and the rear filler.

The opening and closing doors are mounted on the front pillar and the center pillar to be rotatable.

Recently, a vehicle body structure with an upper vehicle body formed by the front and rear fillers without the center filler has been developed and applied to expand the passenger compartment and increase convenience for getting on and off.

However, in such a vehicle body structure, the structural rigidity of the upper vehicle body is inevitably weakened because the center pillar is not used, and various reinforcement structures have been proposed to supplement the weakness of the vehicle body structure, but it was necessary to reinforce the rigidity of the upper vehicle body more effectively with fewer parts without increasing the weight and cost.

Thus, the present applicant has filed “a vehicle body structure” as application numbers of 10-2018-0003192 and 10-2018-0158266, and in the two inventions, a roof side member, which constitutes the upper vehicle body, was made in the form of a tube to increase the stiffness of the upper vehicle body.

The present disclosure relates to a method for forming a roof side member of a tube shape which is applied to the two inventions.

SUMMARY

The present disclosure has been made in an effort to provide a method for forming a vehicle that can be easily manufactured while increasing the stiffness by manufacturing particularly a roof side member among a vehicle body member through a new hot stamping method.

A forming method for a vehicle body member according to an exemplary embodiment of the present disclosure may include, a tube making process of forming a steel pipe by welding a steel plate coil; a non-circular tube making process of primarily preforming the steel pipe formed in the tube making process so as to have a cross section of a predetermined shape; a bending process of bending and secondarily preforming the steel pipe primarily preformed in the non-circular tube making process; and a hot stamping process of heating the secondarily preformed steel pipe in the bending process, inserting the heated steel pipe into a mold to form a desired shape, and then, quenching the heated steel pipe to form the vehicle body member. A post-treatment process post-treating the vehicle body member formed by the hot stamping process may be further included. The post-treatment process may include a shot blasting process that sprays abrasive on the steel pipe to remove scale or casting sand. The post-treatment process may further include a piercing process that makes fastening holes to the vehicle body member through a laser processor after the shot blasting process. The tube making process may include a coil slitting process that unfolds and cuts a spiral-wound coil at a certain, and then, winds in a coil shape again; an uncoiling process of unfolding the spiral-wound again; a levelling process of levelling the uncoiled coil; a roll forming process of roll-forming the levelled coil in a tube shape; a welding process of welding the roll-formed tube; a beads removing process of removing beads generated in the welding process; a cooling process of cooling the tube in which the beads are removed; a sizing and cutting process of sizing and cutting the tube cooled in the cooling process at a predetermined size; a correction and chamfering process of correcting through a calibrator and chamfering through a chamfering machine the tube cut in the cutting process; and an inspection and packing process of inspecting and packing the chamfered steel tube. An electrical resistance welding may be performed in the welding process. An air cooling may be performed in the cooling process. The non-circular tube making process may include a surface treatment process of immersing a bundle of the steel tube packed in the tube making process in a surface treatment tank for surface treatment; a first preforming process of drawing or multi-step roll forming the surface-treated steel tube into a shape having a predetermined cross-section; a correction and cutting process of correcting through a calibrator and cutting the first preformed steel tube at a predetermined size through a cutting machine; an inspection process of nondestructive inspecting the first cut preformed steel tube; and a chamfering process chamfering the steel tube after nondestructive inspection. The first preformed steel tube may have a polygonal closed cross-section. The nondestructive inspection may be performed through ECT (Eddy Current Test). The bending process may include a second preforming process of bending the first preformed steel tube to have various curvatures through a bending machine. The second preforming process may bend the first preformed steel tube so as to have various curvatures on a two-dimensional plane. Bending the steel tube bent to have various curvatures on a two-dimensional plane on a three-dimensional space to have various curvatures again may be further included. In the second preforming process, the first preformed steel tube may be divided into a plurality of sections and bent to have different curvatures for each section. The mold may include an upper die and a lower die; and the lower die may be provided with a forming groove which the second preformed steel tube is seated on and formed in. The lower die may be provided with a slanted surface for inducing the second preformed steel tube into the forming groove; and the upper die may be provided with a slanted surface corresponding to the slanted surface of the lower die.

In accordance with a forming method for a vehicle body member according to an exemplary embodiment of the present disclosure, among the vehicle body members constituting the vehicle body, a roof side member constituting a roof of a vehicle can be manufactured by a hot stamping method to be combined with other vehicle body members so that it is possible to increase the rigidity of the roof of the vehicle with decreasing the weight and the number of parts of the vehicle body.

Furthermore, the vehicle body member can be easily manufactured with high rigidity.

DETAILED DESCRIPTION

The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

Since size and thickness of each component illustrated in the drawings are arbitrarily represented for convenience in explanation, the present disclosure is not particularly limited to the illustrated size and thickness of each component and the thickness is enlarged and illustrated in order to clearly express various parts and areas.

A method for forming a vehicle body member according to an exemplary embodiment of the present disclosure may include a tube making process, a non-circular tube making process, a bending process, a hot stamping process and a post-treatment process.

The tube making process is intended to manufacture a steel pipe with welding robustness by applying a thin-walled tube buckling control roll forming technique and a high-strength steel welding heat input quantity controlling technology. First, a coil slitting work that unfolds and cuts a spiral-wound coil at a certain width may be performed, and then winds it in a coil shape again.

Subsequently, a levelling work that unfolds the spiral-wound coil again and passes a levelling machine to make flat steel plates may be performed.

Continuously, the flat steel plates may be formed to steel pipes through a roll forming machine, and then welded in a welding machine through electrical resistance welding (ERW). At the same time, the welding beads may be removed through an eliminator.

In the tube making process, preferably, the thin pipe of high strength of 60K grade and 2.0 t thickness may be formed to steel pipes through roll forming control in a stable butt state before welding.

Further, when welding high carbon steel of 0.25 C or more, the quenching organization generation mechanism control and the heat input control may be performed so as to form homogeneous organization.

Next, after removing welding beads, the steel pipe may cooled through appropriate heat treatment such as air cooling, and then sized through a sizing machine and cut through a cutting machine at a predetermined size.

Continuously, the correction through the calibrator and the chamfering through the chamfering machine of the steel pipe may be performed to improve the precision of the steel pipe. For example, after the nondestructive inspection through the inspection machine may be performed and then, steel pipes10may be packed into the appropriate unit.

The steel pipe10manufactured in the tube making process as described above may be formed to have an appropriate cross-sectional shape through the non-circular tube making process. The non-circular tube making process may aim to prevent welding part cracks of the steel pipe10made in tube making process and to design optimal non-circular cross-section that can minimize thickness deviation after processing and form a drawing tube. At first, after the packed steel pipe10bundles may be immersed in a surface treatment tank in order for surface treatment, the surface-treated steel pipe10may be drawn into a steel tube with a predetermined cross-sectional shape in a drawing machine.

Of course, the surface-treated steel pipe10may be formed into a cross-section by a multi-step roll forming method.

The cross-section of the steel pipe formed by drawing or multi-step roll forming, as shown inFIG. 1, may have a polygonal closed cross-section.

The polygonal closed cross-section may be a cross-section of a roof side member, and also, may be formed into other polygonal cross-section when forming other members of the vehicle body.

Next, the steel tube may be calibrated to a predetermined size through a calibrator, cut to the predetermined size with a cutter, and then, subjected to the nondestructive inspection through an ECT (Eddy Current Test) and chamfered through the chamfering machine.

Next, in the bending process, the steel tube formed with a predetermined cross-section may be bent to have a various curvature through a CNC machine.

For example, as shown inFIG. 2, when forming a roof side member11, dividing a roof side member11into a plurality of sections based on the side profile of the finished vehicle and subdividing the curvature R1, R2, R3, R4, R5, . . . in each section and preforming the steel tube by performing a two-dimensional CNC bending process.

Continuously, as shown inFIG. 3, dividing the steel tube into a plurality of sections based on the front profile of the finished vehicle and subdividing the curvature r1, r2, r3, r4, r5, . . . in each section and preforming the steel tube by performing a three-dimensional CNC bending process.

Next, in the hot stamping process, the steel tube preformed to have the required cross-section and curvatures in the non-circular tube making process and bending process may be heated and quenched to have a final layout.

In the hot stamping process, the preformed steel tube may be heated and then, formed by a mold in order to have a final design size. Continuously, coolant may be directly injected to the heated steel tube to increase the rigidity of the steel tube.

When heating and seating the preformed steel tube on the mold, since the preformed steel tube has a three-dimensional shape with a plurality of curvatures in the preceding bending process, it is not ease to seat it on the mold. Thus, in the present disclosure, as shown inFIG. 4, a slanted surface22may be provided at a lower die20and an upper die21of the mold, respectively, so that the preformed and heated steel tube with three-dimensional multi-step curvatures can be easily seated in the lower die20.

That is, the preformed and heated steel tube with three-dimensional multi-step curvatures may move down along the slanted surface22of the lower die20and may be easily inserted into and seated on a final forming groove formed at the lower die.

After the preformed and heated steel tube with three-dimensional multi-step curvatures is seated on the lower die20, the upper die22with the same slanted surface21may be coupled with the lower die20to pressurize the steel tube, so that the steel tube may be formed to have a final design size.

Finally, in the post-treatment process, the abrasive may be sprayed on the steel tube separated from the mold so that the scale or casting sand may be removed (shot blasting). Also, fastening holes may be formed at the steel tube through a laser processor to complete a vehicle body member.

On the other hand, although an exemplary embodiment of the present disclosure describes the molding of a roof side member as an example, it can be applied to other vehicle body members as well.