METHOD AND APPARATUS FOR FORMING ULTRAHIGH TENSILE STEEL

Abstract

Disclosed is an apparatus and a method for forming an ultrahigh tensile steel. The method may include: (a) preparing a blank from a steel plate sheet; (b) cold-forming the blank into a shape corresponding to a desired end-product; (c) fixing the cold-formed materials to a plurality of pallets; (d) moving the pallets into a heating chamber, and heating the materials to a set temperature in the heating chamber; (e) moving the pallets into a cooling chamber, and cooling the materials in the cooling chamber; and (f) straightening dimensions of the materials which have been transformed in the heat treatment process and cooling process.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0119948 filed in the Korean Intellectual Property Office on Oct. 26, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method and an apparatus for forming ultrahigh tensile steel. More particularly, the present invention relates to a method and an apparatus for forming ultrahigh tensile steel in which a material is formed through a cold-forming process, followed by heating and cooling the cold-formed material, thereby manufacturing a ultrahigh tensile steel product.

(b) Description of the Related Art

Recently, applications for ultrahigh tensile steel in the vehicle industry have increased to make the vehicle body more lightweight and improve vehicle safety. The method for forming ultrahigh strength steel generally includes hot stamping, particularly for the formation of ultrahigh strength steel having tensile strength of over 1500 MPa.

In particular, hot stamping is used to manufacture ultrahigh strength steel components with boron steel, which has excellent heat treatability. In general, boron steel is heated to a temperature range at which a phase change to austenite occurs, and then the austenite formed by heating the boron steel is cooled and simultaneously formed such that it changes to a martensite phase.

The hot stamping process is applied, in particular, to impart strength. For example, to ensure strength of a center pillar, a roof rail, a bumper, and an impact beam of a vehicle. By forming these components of high strength materials, reinforcements which are typically added to the components may be removed. As a result, the weight of the vehicle body can be decreased.

However, using the hot stamping process, the entire component is formed of the martensite phase and is adapted to have ultrahigh strength. As a result, it is difficult to perform subsequent forming and contouring steps and the like on these ultrahigh strength components. For example, it becomes difficult to trim a metallic pattern to form an edge and flange of the components by shearing so as to form a contour. Further, in the hot stamping process, time spent in the hot forming and cooling stages may be increased and, thus, productivity may be deteriorated. Further, mass production and cross production of vehicle body products may be difficult, and quality of the vehicle body product may be not ensured because a constant temperature of the material is not easily maintained.

Alternatively, laser trimming without using the metallic pattern can be applied. However, manufacturing costs and processing time increase as a result.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The present invention provides a method and an apparatus for forming ultrahigh tensile steel. In particular, the present invention provides a method and an apparatus that makes it possible to eliminate laser trimming, enables mass production and cross production of products, and improves the quality of the products formed.

According to one aspect, the present invention provides a method for forming an ultrahigh tensile steel that includes: (a) preparing a blank cut from a steel plate sheet; (b) cold-forming the blank to a shape corresponding to a desired end product (“cold-formed material”); (c) fixing the cold-formed shape into a plurality of pallets; (d) disposing the pallets within a heating chamber, and heating the cold-formed materials to a set temperature in the heating chamber (“heated material”); (e) moving the pallets into a cooling chamber, and cooling the heated material in the cooling chamber (cooled material); and (f) straightening and adjusting one or more dimensions of the cooled material which have been transformed in the heat treatment process and cooling process.

According to various embodiments, the blank is formed by to draw pressing, primary trimming, restriking, piercing, and secondary trimming, which are sequentially performed through a plurality of molds in step (b).

According to various embodiments, the blank is cold-formed to a shape corresponding to the desired end product by the plurality of molds in a time frame of within about 6 seconds.

According to various embodiments, the cold-formed shape is fixed by a clamping unit disposed at the pallet instep (c).

According to various embodiments, the cold-formed shape is heated until a temperature thereof reaches about 750-1000° C. in the heating chamber at the step (d).

According to various embodiments, the heated materials are cooled under a nitrogen atmosphere in the cooling chamber in step (e).

According to various embodiments, a coolant is injected by a coolant injecting unit disposed at the pallet, and the heated material is cooled by the coolant in step (e).

According to various embodiments, the cooled material is fixed to the straightening machine, and torsion straightening and cross-section straightening of the cooled material are performed at the step (f).

According to another aspect, the present invention provides an apparatus for forming ultrahigh tensile steel comprising: a cold forming unit configured for cold-forming a blank cut from a steel plate sheet to a shape corresponding to a desired end product (“cold-formed material”); a plurality of pallets configured for fixing the cold-formed material formed by the cold forming unit; a heating chamber adapted to heat the cold-formed material fixed to the pallets to a set temperature (“heated material”); a cooling chamber adapted to cool the heated material heated in the heating chamber (“cooled material”); and a plurality of straightening machines configured for straightening and adjusting one or more dimensions of the cooled materials after performing heat treatment in the heating chamber and cooling in the cooling chamber.

According to various embodiments, the cold forming unit includes: a first mold configured for performing draw pressing of the blank, a second mold configured for primarily trimming edges of the blank after the draw pressing, a third mold configured for performing restriking of the blank after the primary trimming, and a fourth mold configured for performing piercing and secondary trimming of the blank after the restriking.

According to various embodiments, the pallet includes: a supporting frame; a plurality of storage plates mounted at the supporting frame and including a plurality of layers, and being configured for supporting the cold-formed material; and clamp rods disposed to move along upward and downward directions by a plurality of clamping cylinders fixed to the supporting frame, wherein a plurality of clamp fingers supporting edges of the cold-formed material may be integrally formed with the clamp rod.

According to various embodiments, the pallet further includes a coolant injecting unit disposed at the supporting frame, and configured for injecting a coolant to the cold-formed material so as to cool the cold-formed material.

According to various embodiments, the supporting frame includes a plurality of vertical shafts configured for supporting each edge of the storage plate, and a plurality of horizontal shafts configured for connecting the vertical shafts between each other in a horizontal direction.

According to various embodiments, the coolant injecting unit includes a coolant supply passage formed in the vertical shaft and the horizontal shaft, and configured to provide communication between the vertical shaft and the horizontal shaft, and injection nozzles mounted at the vertical shaft and the horizontal shaft, and being in connection with the coolant supply passage so as to allow injection of a coolant to the cold-formed material.

According to various embodiments, the straightening machine includes: a frame; a clamping unit mounted at the frame, and configured for clamping the cold-formed material; a torsion straightening unit rotatably mounted at the frame in a state of gripping one end of the cold-formed material, and configured for performing torsion straightening of the cold-formed material; and a plurality of cross-section straightening units disposed at both sides with reference to the cold-formed material at the frame, and rotatably mounted at the frame in a state of gripping flange portions formed at both sides of the cold-formed material, and configured for straightening a cross-section of flange portions of the cold-formed material.

According to various embodiments, the clamping unit includes at least one clamping body mounted movably thereon in upward and downward directions by a clamping cylinder.

According to various embodiments, the torsion straightening unit includes a rotating block rotatably mounted at the frame and corresponding to the one end of the material, and a first gripper connected to the rotating block, the first gripper being movably mounted to move along upward and downward directions by a first operating cylinder, and configured for gripping the one end of the cold-formed material.

According to various embodiments, the torsion straightening unit includes a driving unit configured for rotating the rotating block. The driving unit may include a pinion gear coupled with a rotating shaft of the rotating block, a pair of rack bars coupled at an upper side and a lower side of the pinion gear, and a pair of second operating cylinders in connection with the rack bars.

According to various embodiments, the cross-section straightening unit includes: a rotating body rotatably mounted at the frame at both sides with reference to the cold-formed material; a third operating cylinder fixed to the frame, and hingedly coupled with the rotating body; and a second gripper connected to the rotating body, and configured or gripping the flange portion of the cold-formed material with the second gripper.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an apparatus for forming ultrahigh tensile steel according to an exemplary embodiment of the present invention.

FIG. 2 is a perspective view of a pallet according to an exemplary embodiment of the present invention.

FIG. 3 is a perspective view of a straightening machine according to an exemplary embodiment of the present invention.

FIG. 4 is a perspective view of a clamping unit of a straightening machine according to an exemplary embodiment of the present invention.

FIG. 5 and FIG. 6 are drawings showing a torsion straightening unit according to an exemplary embodiment of the present invention.

FIG. 7 is a perspective view of a cross-section of a straightening unit of a straightening machine according to an exemplary embodiment of the present invention.

FIG. 8 is a partial perspective view of the cross-section straightening unit of FIG. 7.

FIG. 9 is a perspective view showing an operational condition of the cross-section straightening unit.

FIG. 10 is a flowchart of a method for forming ultrahigh tensile steel according to an exemplary embodiment of the present invention.

FIG. 11 is a perspective view showing a pallet of an apparatus for forming ultrahigh tensile steel according to another exemplary embodiment of the present invention.

<Description of Symbols>
1	blank	2	steel plate sheet
3	cold-formed material	10	cold forming unit
11	first mold	12	second mold
13	third mold	14	fourth mold
50, 810	pallet	53	supporting frame
61	clamp rod	69	clamp finger
70	heating chamber	80	cooling chamber
200	straightening machine	210	clamping unit
310	torsion straightening unit
410	cross-section straightening unit
871	coolant injecting unit

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings such that a person skilled in the art can easily accomplish it.

As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Components unrelated to the description will be omitted in order to obviously describe the present invention, and like reference numerals will be used to describe like components throughout the present specification.

Further, in the drawings, the sizes and thicknesses of the components are exemplarily provided for the convenience of description, the present invention is not limited to those shown in the drawings, and the thicknesses are exaggerated to clearly show several parts and regions.

Terms used in the specification, giving the names of the components in ‘first’, ‘second’, ‘third’, etc., is for discrimination of them because the names are the same and they are not limited to the order.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about”.

FIG. 1 is a schematic diagram of an apparatus for forming ultrahigh tensile steel according to an exemplary embodiment of the present invention.

Referring to FIG. 1, an apparatus 100 for forming ultrahigh tensile steel according to an exemplary embodiment of the present invention is configured for forming steel having an initial tensile strength of greater than about 600 MPa to be used in forming vehicle body components having tensile strengths of greater than about 1500 MPa.

For example, as shown and described in the figures, the apparatus 100 for forming ultrahigh tensile steel performs cold forming of a blank 1 (FIG. 10, S12) which has been cut from boron steel, (FIG. 10, S11) which has excellent heat treatment performance. While the exemplary embodiment is described with specific reference to use of boron steel, it is understood that other suitable materials used in forming applicable vehicle body components could also be used. The apparatus then performs heat treatment (FIG. 10, S14) and cooling (FIG. 10m S15) of the cold-formed material 3 (see FIG. 1) so as to manufacture vehicle body components having tensile strength of over 1500 MPa.

Herein, the vehicle body components may be any components that may suitably be formed of ultrahigh tensile steel such as, for example, a center pillar, a roof rail, a bumper, and an impact beam.

The apparatus 100 for forming ultrahigh tensile steel is adapted to eliminate a laser trimming process, decrease production costs, increase manufacturing speed, enable mass production and cross production of the vehicle body components, and improve quality of vehicle body components.

In the forming process of the present invention, the apparatus 100 is used to form a material into a shape corresponding to a desired end-product, followed by trimming, piercing, and further suitable steps through cold forming. Further, according to the present invention, the cold-formed material is heated to a high temperature and is then subsequently quickly cooled thereby improving the strength of the material by about two or three times greater than the strength of the material prior to heating and cooling. Further, after the heating and cooling processes, the dimensions of the complete product can be straightened and adjusted as desired.

As shown in FIG. 1, 1, the apparatus 100 for forming ultrahigh tensile steel includes a cold forming unit 10, pallets 50, a heating chamber 70, a cooling chamber 80, and straightening machines 200.

As shown, the cold forming unit 10 cold-forms the blank 1 cut from a steel plate sheet 2 to a shape corresponding to a desired end-product.

For example, the blank 1 may be cut to have a suitable size from the coiled steel plate sheet 2 such that press forming is possible. In addition, the coiled steel plate sheet 2 may include cold rolled steel, hot rolled steel, sheradizing cold rolled steel, Al—Si boron alloy coating steel, and so on.

The cold forming unit 10 sequentially performs draw pressing, primary trimming, restriking, piercing, and secondary trimming of the blank 1. Therefore, the blank 1 is cold-formed to a shape corresponding to the desired end-product in a short period of time, preferably within about 6 seconds.

In particular, the sequential forming processes are performed en bloc such that the fast manufacturing speed of the cold forming unit 10 is satisfied. In particular the cold forming unit 10 includes a plurality of molds constructed of an upper mold and a lower mold. According to an exemplary embodiment, the plurality of molds include first to fourth molds 11, 12, 13, and 14.

The first mold 11 is adapted to perform the draw pressing to the blank 1, and the second mold 12 is adapted to perform the primary trimming to edges of the blank 1. As such, unnecessary portions besides the shape corresponding to the desired end-product can be removed after the draw pressing of the blank 1.

The third mold 13 is adapted to perform the restriking to the blank 1 after the primary trimming, and the fourth mold 14 is adapted to perform the piercing and the secondary trimming to the blank 1 after the restriking.

The amount of scrap material from the cold forming unit 10 is large and, thus, the scrap trimming is not easily performed if all edges of the blank 1 are trimmed at the second mold 12. Therefore, the primary trimming and the secondary trimming may be separately performed through the second mold 12 and the fourth mold 14 so as to primarily trim a part of the edges and secondarily trim the rest of the edges.

In addition, the restriking of the blank 1 is performed after the primary trimming by the second mold 12 in order to reduce the spring-back of the blank 1 after the draw pressing by the first mold 11.

The pallet 50 is adapted to fix a plurality of cold-formed materials 3 formed with the shape corresponding to the desired end-product in the molds 11, 12, 13, and 14 of the cold forming unit 10 and to deliver the materials 3 to a next process.

FIG. 2 is a perspective view of a pallet 50 according to an exemplary embodiment of the present invention.

Referring to FIG. 1 and FIG. 2, the pallet 50 according to an exemplary embodiment of the present invention is disposed to move in a desired direction by a caster 52 mounted at an edge portion of a lower surface of a base plate 51.

In addition, multiple pallets 50 are preferably provided for mass production of the cold-formed product. The pallets 50 can be delivered to a heating chamber 70 and a cooling chamber 80, which will be described in more detail hereinbelow, by a conveyor (not shown) or other suitable means.

The pallet 50 includes a supporting frame 53, a plurality of storage plates 57, and clamp rods 61 for clamping.

The supporting frame 53 configured to support the storage plates 57, which will be described in more detail hereinbelow.

As shown, the supporting frame 53 is vertically mounted at a base plate 51 which is shown as having a quadrilateral shape, and the supporting frame 53 includes a plurality of vertical shafts 54 supporting each edge portion of the storage plates 57.

The storage plates 57 are also shown as quadrilateral plates configured for supporting the cold-formed materials 3. As shown, the supporting frame 53 is mounted at vertical shafts 54 in a plurality of layers along upward and downward directions.

A supporting member 59 having a block-like shape for supporting the cold-formed material 3 is mounted at an upper surface of the storage plates 57. The supporting member 59 has a shape corresponding to the shape of the cold-formed material 3, and is fixed to the upper surface of the storage plate 57 such that the cold-formed material 3 is suitably positioned thereon.

As shown, clamp rods 61 are further provided extending vertically and configured for clamping the cold-formed material 3 that has been positioned on the supporting member 59 of the storage plate 57.

In particular, as shown in FIG. 2, a plurality of clamp rods 61 are mounted at both sides of the supporting frame 53, and are vertically disposed in an arrangement corresponding to the vertical shafts 54. The clamp rods 61 are disposed to be movable along upward and downward directions by a plurality of clamping cylinders 63 fixed to the supporting frame 53.

As shown in FIG. 2, the clamping cylinders 63 are mounted to fixing blocks 65 fixed to a lower outer surface of the lower storage plate 57, and the clamp rod 61 is vertically movable within an operating rod of the clamping cylinder 63.

The clamp rods 61 are mounted to penetrate guide members 67 disposed at outer edges of both sides of the storage plates 57, and the clamp rods 61 are adapted to be movable along upward and downward directions with support of the guide members 67.

Herein, clamp fingers 69 may further be integrally mounted at the clamp rod 61 and configured for supporting edges (flanges) of the cold-formed material 3 positioned on the supporting member 59.

The clamp fingers 69 may be disposed spaced apart from each other by a set distance at the clamp rod 61 along upward and downward directions corresponding to each storage plate 57, and are fixed to the clamp rod 61.

As shown in FIG. 2, the clamp fingers 69 are formed in a shape of an “L” or “F” and are disposed so as to push edges of the cold-formed material 3 positioned on the supporting member 59 by force of the clamping cylinder 63 when the clamp rod 61 is moved downwardly by the clamping cylinder 63.

Meanwhile, the heating chamber 70 is adapted to heat the cold-formed materials 3 fixed to the pallets 50 to a set temperature.

The heating chamber 70, which may be a furnace or the like, is configured to heat a plurality of cold-formed materials 3 fixed to the pallets 50 to a temperature range of from about 750° C. to about 1000° C. within a short period of time, preferably within about 4 to 5 minutes. The cold-formed materials 3 are then delivered from heating chamber 70 to the cooling chamber 80.

The cooling chamber 80 is configured for quickly cooling the plurality of cold-formed materials 3 previously heated in the heating chamber 70.

In particular, the pallets 50 delivered from the heating chamber 70 are inserted into the cooling chamber 80. The cooling chamber 80 can be configured to receive the pallets 50 from the heating chamber 70 and then deliver the pallets 50 to a next process. According to an exemplary embodiment, at the cooling chamber 80, nitrogen gas may be injected into a space in the chamber and the cold-formed materials 3 can be cooled under a nitrogen atmosphere.

Hereinafter, construction of the straightening machine 200 of the apparatus 100 will be described in detail in connection with an exemplary embodiment.

The straightening machine 200 is configured for straightening (adjusting) dimensions of the materials 3 after performing heat treatment in the heating chamber 70 and cooling in the cooling chamber 80.

FIG. 3 is a perspective view of a straightening machine according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the straightening machine 200 includes a frame 110, a clamping unit 210, a torsion straightening unit 310, and a cross-section straightening unit 410.

The frame 110 is configured for supporting various constituent elements of the straightening machine 200, and will be described in more detail hereinbelow.

The clamping unit 210 clamps and fixes the cold-formed material 3 loaded on the frame 110.

FIG. 4 is a perspective view of a clamping unit of a straightening machine 200 according to an exemplary embodiment of the present invention.

Referring to FIG. 3 and FIG. 4, the clamping unit 210 is mounted at the frame 110 so as to be movable along upward and downward directions.

As shown, the clamping unit 210 includes at least one clamping body 213 mounted so as to be movable along upward and downward directions by a clamping cylinder 211.

Multiple clamping bodies 213 may be disposed at the frame 110.

The clamping cylinder 211 is fixedly mounted to a supporting plate 217 disposed at an upper side of the frame 110 by a plurality of supporting rods 215.

A moving plate 221 is further mounted at an operating rod 219 of the clamping cylinder 211. The moving plate 221 is guided by the supporting rods 215, and is adapted to move along upward and downward directions.

The clamping body 213 is mounted at a lower surface of the moving plate 221, and is movable along upward and downward directions by the moving plate 221 so as to fix the cold-formed material 3.

The clamping body 213 is mounted at a connecting member 223 fixed to the lower surface of the moving plate 221. The clamping body 213 has a different shape according to each portion of the material 3, and is formed in a shape corresponding to each portion of the material 3.

The torsion straightening unit 310 rotates in a state of gripping one end of the material 3 so as to perform torsion straightening to the material 3.

FIG. 5 and FIG. 6 are drawings showing a torsion straightening unit according to an exemplary embodiment of the present invention.

Referring to FIG. 5 and FIG. 6, the torsion straightening unit 310 is rotatably disposed at the frame 110. In addition, the torsion straightening unit 310 may rotate in right and left directions.

The torsion straightening unit 310 includes a rotating block 311, a first gripper 331, and a driving unit 351.

The rotating block 311 is rotatably mounted at the frame 110 corresponding to the one end of the cold-formed material 3. In addition, the rotating block 311 may rotate in right and left directions. As shown, the rotating block 311 may be disposed to rotate in right and left directions by a rotating shaft 313.

The first gripper 331 grips the one end of the cold-formed material 3. In addition, the first gripper 331 is fixedly mounted at the rotating block 311 by a mounting bracket 333, and is disposed to move along upward and downward directions by a first operating cylinder 335.

The first gripper 331 includes a gripping pad 337 configured for pushing and gripping the cold-formed material 3. As shown, and the gripping pad 337 is mounted at an operating rod 336 of the first operating cylinder 335.

The driving unit 351 is configured for rotating the rotating block 311 in right and left directions around the rotating shaft 313.

As shown, the driving unit 351 includes a pinion gear 353 coupled with the rotating shaft 313 of the rotating block 311, a pair of rack bars 355 coupled at an upper side and a lower side of the pinion gear 353, and a pair of second operating cylinders 357 connected with the rack bars 355.

According to the depicted exemplary embodiment, the rack bars 355 change a rectilinear motion of the second operating cylinder 357 to a rotary motion of the pinion gear 353.

The second operating cylinder 357 is fixedly mounted at the frame 110, and the rack bar 355 is coupled with an operating rod 358 of the second operating cylinder 357. Each operating rod 358 of the pair of operating cylinders 357 are movable in opposite directions from each other.

In particular, each rack bar 355 is movable in an opposite direction from the other so as to rotate the pinion gear 353 in both directions based on each operating rod 358 of the second operating cylinder 357 which move in opposite directions from each other. Thus, the rotating shaft 313 may be rotated in the reverse (backward) direction, and the rotating block 311 may be rotated in right and left directions.

The cross-section straightening unit 410, which is shown in FIG. 3 and in further detail in FIGS. 7 and 8, rotates in a state of gripping flange portions formed at both sides of the cold-formed material 3 so as to straighten the cross-section of the flange portions of the cold-formed material 3.

FIG. 7 is a perspective view of a cross-section straightening unit 410 of a straightening machine 200 according to an exemplary embodiment of the present invention. Further, FIG. 8 is a partial perspective view of the cross-section straightening unit 410.

Referring to FIG. 7 and FIG. 8 together with FIG. 3, the cross-section straightening unit 410 is plurally disposed at both sides with reference to the cold-formed material 3 at the frame 110, and is rotatably mounted at the frame 110 in a state of gripping the flange portions formed at both sides of the cold-formed material 3.

As shown in FIGS. 7 and 8, the cross-section straightening unit 410 includes a rotating body 411, a third operating cylinder 431, and a second gripper 451.

In particular, the rotating body 411 is mounted to rotate in upward and downward directions at the frame 110 at both sides with reference to the material cold-formed 3, and is supported by a supporting block 471 disposed at the frame 110 so as to rotate in upward and downward directions.

According to the depicted exemplary embodiment, the rotating body 411 is guided by a guide hole 473 disposed at both sides of the supporting block 471 so as to rotate in upward and downward directions. The guide hole 473 is formed according to a pivot trajectory of the rotating body 411. As shown in FIG. 8, the guide hole 473 is coupled with a pair of rollers 415 disposed at both sides the rotating body 411.

The third operating cylinder 431 is fixedly mounted at the frame 110, and is hingedly connected with the rotating body 411 by a hinge pin 433.

The second gripper 451 is adapted to grip edges (flanges) of the cold-formed material 3, and is connected with the rotating body 411.

As shown in FIG. 9, the second gripper 451 performs cross-section straightening of the flange portion of the cold-formed material 3 according to the rotating body 411 as it rotates in upward and downward directions by operation of the third operating cylinder 431 in a state of gripping the flange portion of the cold-formed material 3.

Hereinafter, a method for forming ultrahigh tensile steel according to an exemplary embodiment of the present invention using the apparatus 100 for forming ultrahigh tensile steel will be described in detail referring to the above-mentioned drawings and accompanying drawings.

FIG. 10 is a flowchart of a method for forming ultrahigh tensile steel according to an exemplary embodiment of the present invention.

Referring to FIG. 1 and FIG. 10, the blank 1 is cut to have a suitable size from the coiled steel plate sheet 2 at a process S11.

Herein, the steel plate sheet 2 may include cold rolled steel, hot rolled steel, sheradizing cold rolled steel, Al—Si boron alloy coating steel, and so on.

In the process S11, the blank 1 is prepared having a predetermined weight that is higher than a weight of the desired end-product.

If the weight of the blank 1 is lower than the predetermined weight, a holding portion of the press is insufficient, and thus complete forming is not adequately performed. Further, if the weight is higher than the predetermined weight, then material is wasted and costs increase.

The blank 1 is cold-formed to the shape corresponding to the desired end-product by the cold forming unit 10 at a process S12.

At the process S12, the blank 1 is preferably formed according to the draw pressing, the primary trimming, the restriking, the piercing, and the secondary trimming processes that are sequentially performed through the first to fourth molds 11, 12, 13, and 14.

Herein, the first mold 11 performs the draw pressing of the blank 1, the second mold 12 performs the primary trimming to edges of the blank 1 after the draw pressing, the third mold 13 performs the restriking of the blank 1 after the primary trimming, and the fourth mold 14 performs the piercing and the secondary trimming of the blank 1 after the restriking.

According to the depicted exemplary embodiment, the draw pressing, primary trimming, restriking, piercing, and secondary trimming of the blank 1 are sequentially performed through the first to fourth molds 11, 12, 13, and 14 in the cold forming unit 10. Further, the blank 1 is cold-formed to the shape corresponding to the desired end-product within a short time, preferably within about 6 seconds during which the sequential forming processes are performed en bloc.

If the cold forming of the blank 1 formed by the cold forming unit 10 is completed, then the cold-formed materials 3 formed to the shape corresponding to the desired end-product is loaded on the pallets 50, and the cold-formed materials 3 are clamped and fixed at a process S13.

In further detail, the cold-formed materials 3 which are cold-formed at the cold forming unit 10 may be provided on the supporting member 59 on each storage plate 57 of the pallets 50 through a robotic or shuttle system.

Then, the clamp rods 61 are moved downwardly by operation of the clamping cylinders 63. Thus, the clamp rods 61 are guided by the guide member 67, and are moved in the lower position.

Therefore, the clamp fingers 69 of the clamp rods 61 are adapted to push edges (flanges) of the cold-formed material 3 which is provided on the supporting member 59 disposed on each storage plate 57 by force of the clamping cylinder 63 so as to fix the flanges of the material 3.

The pallets 50 are then moved into the heating chamber 70 with the cold-formed materials 3 fixed to the pallets 50.

In the heating chamber 70, the materials 3 are heated to temperature range of from about 750° C. to about 1000° C. for a short period of time (e.g. for about 4 to 5 minutes) at a process S14.

Herein, the temperature range from about 750° C. to about 1000° C. is a stabilizing/transition temperature of austenite. In a case in which steel heated by the stabilizing/transition temperature of austenite is quickly cooled, a high strength required of the products of the invention can be ensured. Further, higher temperatures may be undesirable because a coating layer of the cold-formed material 3 may be vaporized if the heating temperature is higher than about 1000° C.

On the other hand, it is difficult if not impossible to gain a uniform and stable austenite structure if the heating temperature is lower than about 750° C.

In addition, the heating time of the cold-formed materials 3 is short, preferably about 4 to 5 minutes, to provide a uniform structure by removing stress of the material 3 and ensuring uniform processing ability in a process after heating. According to several experimental results, the amount of generated austenite is insufficient in a case that the heating time is shorter than about 4 minutes. Further, austenite crystal grains undesirably grow in a case that the heating time is longer than about 5 minutes. This growth of the austenite crystal grain results in a deterioration in the strength of the product.

The pallets 50 are then moved into the cooling chamber 80. According to preferred embodiments, a nitrogen atmosphere is formed in the cooling chamber 80, and the cold-formed materials 3 fixed to the pallets 50 are cooled for about 3 seconds by the nitrogen gas at a process S15.

That is, the cold-formed materials 3 that were previously heated to a set temperature are subsequently quickly cooled by the nitrogen gas in the cooling chamber 80 such that the cold-formed materials 3 are transformed to a martensite structure. This provides the cold-formed materials 3 with sufficient strength and high tension.

If the heat treatment process and the cooling process of the materials 3 are completed, dimensions of the materials 3 transformed during the heat treatment process and the cooling process are straightened/adjusted as desired by the straightening machine 200 at a process S16.

According to the method and the apparatus 100 for forming ultrahigh tensile steel, the laser trimming process may be eliminated so as to reduce production cost.

In addition, productivity may be improved, and mass production and cross production of the vehicle body components are possible as the forming processes may be automatically performed, and the time of the heat treatment and the cooling are short.

Further, the forming quality of the vehicle body components is improved as the temperature of the material can be constantly maintained at a set temperature.

FIG. 11 is a perspective view showing a pallet of an apparatus for forming ultrahigh tensile steel according to another exemplary embodiment of the present invention.

Referring to FIG. 1 and FIG. 11, the apparatus 100 for forming ultrahigh tensile steel according to this exemplary embodiment of the present invention does not cool the cold-formed materials 3 by using nitrogen gas in the cooling chamber 80. Rather, in this embodiment a pallet 810 is included for cooling the materials 3 by using a coolant.

As shown in FIG. 11, the pallet 810 includes a supporting frame 811, a plurality of quadrangular storage plates 813, a plurality of clampers 851, and a coolant injecting unit 871.

The supporting frame 811 is configured for supporting the storage plates 813. In addition, the supporting frame 811 includes a plurality of vertical shafts 815 configured for supporting each edge of the storage plates 813, and horizontal shafts 817 for connecting the vertical shafts 815 with each other in a horizontal direction.

Herein, the vertical shafts 815 support and connect each edge of the quadrangular storage plates 813, and are vertically disposed. The vertical shafts 815 may be formed in a shape of a pipe of which an upper end thereof is closed and a lower end is opened.

As shown, the horizontal shafts 817 support the vertical shafts 815. In addition, the horizontal shafts 817 correspond to each storage plate 813, and connect the vertical shafts 815 with each other in width and height directions.

The horizontal shafts 817 may be formed in a shape of a pipe of which both ends thereof are opened. In addition, both ends are respectively connected with each of the vertical shafts 815, and an interior of the horizontal shaft 817 is in communication with an interior of the vertical shaft 815.

As shown, the storage plates 813 are quadrilateral plates configured for supporting the cold-formed materials 3, and the supporting frame 811 is mounted at the vertical shafts 815 in a plurality of layers along upward and downward directions.

Edges of each storage plate 813 are connected with the vertical shafts 815. The vertical shafts 815 respectively penetrate edges of each storage plate 813, and are connected (such as by welding or the like) at edges of each storage plate 813.

The clampers 851 are configured for clamping and fixing edges (flanges) of the cold-formed materials 3 provided on each storage plate 813.

The clampers 851 are mounted at the storage plates 813 so as to correspond to edges of the cold-formed materials 3 provided on the storage plates 813.

Each clamper 851 can include a locater (not shown) configured for properly locating edges of the cold-formed material 3, a clamp body 853 configured for restricting edges of the cold-formed material 3, and a clamping cylinder 855 hingedly coupled with the locater and the clamp body 853 and configured for rotating the clamp body 853 by a reciprocating motion of an operating rod.

The clamper 851 may be in the form of a conventional clamping device which clamps and restricts a component. Therefore, a detailed description of the clamper will be omitted.

The coolant injecting unit 871 is configured to inject a coolant to the cold-formed materials 3 which have previously undergone heat treatment in a state of clamping by the clampers 851 in the heating chamber 70, to thereby quickly cool the cold-formed materials 3.

The coolant injecting unit 871 is disposed at the supporting frame 811 of the pallet 810. In addition, the coolant injecting unit 871 includes a coolant supply passage 881 formed in the vertical shafts 815 and the horizontal shafts 817 of the supporting frame 811. A plurality of injection nozzles 883 are further mounted at the vertical shafts 815 and the horizontal shafts 817.

According to the exemplary embodiment, the vertical shafts 815 and the horizontal shafts 817 are formed in a shape of a pipe and the coolant supply passage 881 is an internal space of the vertical shafts 815 and the horizontal shafts 817.

The coolant supply passages 881 which are formed in the vertical shafts 815 and horizontal shafts 817 communicate with each other. In embodiments in which the vertical shaft 815 is formed in a shape of a pipe with a closed upper end and an open lower end, a coolant flows in the coolant supply passage 881 through the open lower end.

That is, a coolant inflow portion 885 is formed at the lower end of the vertical shaft 815 such that a coolant flows into the coolant supply passage 881.

Therefore, a coolant having flowed into the coolant supply passage 881 through the coolant inflow portion 885 may flow along the coolant supply passage 881 in the vertical shafts 815 and the horizontal shafts 817.

The injection nozzles 883 are configured for injecting a coolant to the material 3 on the storage plate 813, after the coolant has flowed along the coolant supply passage 881 in the vertical shafts 815 and the horizontal shafts 817.

The injection nozzles 883 are mounted spaced apart along length directions of the vertical shafts 815 and the horizontal shafts 817, and are configured to communicate with the coolant supply passage 881 in the vertical shafts 815 and the horizontal shafts 817.

In particular, a coolant flowing in the vertical shafts 815 through the coolant inflow portions 885 of the vertical shafts 815 flows along the coolant supply passage 881, and is injected to the cold-formed material 3 on the storage plate 813 through the injection nozzles 883.

According to an exemplary embodiment of the present invention, in the state that the pallets 810 are moved into the cooling chamber 80, a coolant is injected to the cold-formed materials 3 through the coolant injecting unit 871 of the pallets 810 from the cooling chamber 80 so as to quickly cool the materials 3.

In addition, in this exemplary embodiment, a coolant such as nitrogen gas is not used. Rather, a coolant such as cooling water is injected through the coolant injecting unit 871 disposed at the pallets 810 so as to cool the materials 3. Therefore, construction of the entire system can be simplified, and an initial investment cost may be saved.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for forming an ultrahigh tensile steel comprising:

(a) preparing a blank cut from a steel plate sheet;

(b) cold-forming the blank to a shape corresponding to a desired end-product, to thereby form cold-formed materials;

(c) fixing the cold-formed materials to a plurality of pallets;

(d) moving the pallets into a heating chamber, and heating the cold-formed materials to a set temperature in the heating chamber, to thereby form heated materials;

(e) moving the pallets into a cooling chamber, and cooling the heated materials in the cooling chamber, to thereby form cooled materials; and

(f) straightening dimensions of the cooled materials.

2. The method of claim 1, wherein

in (b),

the blank is formed by s draw pressing, primary trimming, restriking, piercing, and secondary trimming sequentially through a plurality of molds.

3. The method of claim 2, wherein the blank is cold-formed to the shape corresponding to the desired end-product by the plurality of molds within about 6 seconds.

4. The method of claim 1, wherein

in (c),

the cold-formed materials are fixed by a clamping unit disposed at the pallet.

5. The method of claim 1, wherein

in (d),

the cold-formed materials are heated until a temperature thereof reaches about 750-1000° C. in the heating chamber.

6. The method of claim 1, wherein

in (e),

the heated materials are cooled under a nitrogen atmosphere in the cooling chamber.

7. The method of claim 1, wherein

in (e),

a coolant is injected by a coolant injecting unit disposed at the pallet, and the heated materials are cooled by the coolant.

8. The method of claim 1, wherein

in (f),

the cooled materials are fixed to the straightening machine, and torsion straightening and cross-section straightening of the material are performed.

9. An apparatus for forming ultrahigh tensile steel, comprising:

a cold forming unit configured for cold-forming a blank cut from a steel plate sheet to a shape corresponding to a desired end-product, to thereby form cold-formed materials;

a plurality of pallets configured for fixing the cold-formed materials formed by the cold forming unit;

a heating chamber adapted to heat the cold-formed materials fixed to the pallets to a set temperature, to thereby form heated materials;

the cooling chamber adapted to cool the heated materials heated in the heating chamber, to thereby form cooled materials; and

a plurality of straightening machines configured for straightening one or more dimensions of the cooled materials after heating in the heating chamber and cooling in the cooling chamber.

10. The apparatus of claim 9, wherein the cold forming unit comprises:

a first mold configured for performing draw pressing of the blank,

a second mold configured for primarily trimming edges of the blank after the draw pressing,

a third mold configured for performing restriking of the blank after the primary trimming, and

a fourth mold configured for performing piercing and secondary trimming of the blank after the restriking.

11. The apparatus of claim 9, wherein the pallet comprises:

a supporting frame;

a plurality of storage plates mounted at the supporting frame and including a plurality of layers, and being configured for supporting the material; and

a plurality of clamp rods movably disposed to move along upward and downward directions by a plurality of clamping cylinders fixed to the supporting frame,

wherein a plurality of clamp fingers configured for supporting edges of the cold-formed material are integrally formed with the clamp rod.

12. The apparatus of claim 11, wherein the pallet further comprises

a coolant injecting unit disposed at the supporting frame, and configured for injecting a coolant to the cold-formed materials so as to cool the materials.

13. The apparatus of claim 12, wherein the supporting frame comprises

a plurality of vertical shafts configured for supporting each edge of the storage plate, and

a plurality of horizontal shafts connecting the vertical shafts to each other in a horizontal direction.

14. The apparatus of claim 13, wherein the coolant injecting unit comprises:

a coolant supply passage formed in the vertical shaft and the horizontal shaft, and providing communication between the vertical shaft and the horizontal shaft; and

injection nozzles mounted at the vertical shaft and the horizontal shaft, and in connection with the coolant supply passage so as to inject a coolant to the cold-formed material.

15. The apparatus of claim 9, wherein the straightening machine comprises:

a frame;

a clamping unit mounted at the frame, and configured for clamping the material;

a torsion straightening unit rotatably mounted at the frame in a state of gripping one end of the cold-formed material, and configured for performing torsion straightening to the cold-formed material; and

a plurality of cross-section straightening units at opposing sides with reference to the cold-formed material at the frame, and being rotatably mounted at the frame in a state of gripping flange portions formed at both sides of the cold-formed material, and configured for straightening a cross-section of flange portions of the cold-formed material.

16. The apparatus of claim 15, wherein the clamping unit comprises at least one clamping body movably mounted along upward and downward directions by a clamping cylinder.

17. The apparatus of claim 15, wherein the torsion straightening unit comprises:

a rotating block rotatably mounted at the frame corresponding to the one end of the cold-formed material; and

a first gripper connected with the rotating block and movably mounted along upward and downward directions by a first operating cylinder, and configured for gripping the one end of the cold-formed material.

18. The apparatus of claim 17, wherein the torsion straightening unit comprises a driving unit configured for rotating the rotating block, and

the driving unit comprises a pinion gear coupled with a rotating shaft of the rotating block, a pair of rack bars coupled at an upper side and a lower side of the pinion gear, and a pair of second operating cylinders connected with the rack bars.

19. The apparatus of claim 15, wherein the cross-section straightening unit comprises:

a rotating body rotatably mounted at the frame at both sides with reference to the cold-formed material;

a third operating cylinder fixed to the frame, and hingedly coupled with the rotating body; and

a second gripper connected with the rotating body, and configured for gripping the flange portion of the cold-formed material.