KR20130100076A - Method for manufacturing high strength steel shaped body - Google Patents

Abstract

PURPOSE: A method for manufacturing a steel molded body facilitates controlling a heating temperature for molding the molded body and prevents the oxidation or annealing of heated blank materials being transferred to a mold. CONSTITUTION: A method for manufacturing a steel molded body includes the following steps: a step of forming a blank material (140) with cutting a steel sheet coil; a step of directly loading the non-heated blank material on a lower mold (140) of which the upper side has an electrode; a step of allowing the front side of the blank material loaded on the lower mold to function as a resistance; and a step of pressing and molding the blank material heated at a temperature of 680 to 980°C using an upper mold, and then cooling the blank material for 3 to 4 seconds in order to maintain the molded condition of the blank material and in order to secure the desired hardness of the blank material. The steel sheet coil comprises 0.1 to 0.4 wt% of C, below 0.5 wt% of Si, below 0.1 wt% of N, 0.01 to 0.1 wt% of Al, below 0.05 wt% of P, 0.8 to 2 wt% of Mn, 0.002 to 0.01 wt% of B, 0.1 to 0.5 wt% of Mo, 0.1 to 0.5 wt% of Cr, and remnants Fe and other inevitable impurities. The steel sheet coil has a molding temperature of 680 to 980°C.

Description

METHOD FOR MANUFACTURING HIGH STRENGTH STEEL SHAPED BODY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a steel molded body and an apparatus for manufacturing the same, and to a steel molded body capable of improving the strength of the molded body while shortening the process time when manufacturing the steel molded body through a mold.

Recently, the application of high-strength steel sheet in consideration of collision safety in order to secure the safety of passengers and drivers has tended to increase gradually. In addition, the application of the surface-treated steel sheet is increasing in order to meet the increase in the anti-rust warranty.

Conventionally, the high-strength steel sheet described above is generally manufactured by using a press method.

In general, a method of manufacturing automotive parts using a press method is to cut raw materials of cold or hot rolled coils, transfer the materials into press molds, compress them to complete molding, and then cut unnecessary parts and form holes. How to finish the product after finishing the work.

Such a steel plate processing method using a conventional press method is merely to implement the shape of the part by simply processing the strength and physical properties of the steel sheet manufactured by the steel company. Therefore, since the raw material is the property of the component after processing, as the strength of the raw material increases, it becomes more difficult to form a press, so that the precise shape of the product becomes difficult.

On the other hand, among the characteristics of the steel sheet is a phenomenon called spring back (spring back). This means that the steel sheet will return to its original shape even if an external pressure of more than yield strength is applied when the steel sheet is bent at room temperature. That is, the stronger the raw material strength, the greater the property of returning to its original state.

Recently, the automotive industry needs a component that requires high strength and high formability, and thus the molding problem as described above is limited to the application of a strong raw material.

Recently developed 60kg / mm2 trip steel or dual phase steel sheets have been known for their excellent strength and formability. Because it does not come out, it is applied only to the production of parts with a very simple shape, and is rarely applied to the production of complex parts requiring high precision.

Therefore, after cutting the cut raw material (iron plate) at a high temperature, it is molded into a mold, and at the same time, a cooling effect is applied to the mold to increase the strength of the raw material through a quenching effect of drastically lowering the temperature of the raw material. Originally, a mold cooling method was developed that improved the process by two to three times or more.

Since the iron plate is heated to a high temperature during processing by the above-described method, the properties of the iron plate are very soft and the stretching property is excellent, and the formability is excellent. By using the mold cooling method as described above, it is possible to manufacture desired parts with excellent moldability while securing ultra high strength of the steel sheet.

Here, in order to manufacture a high-strength steel molded body for automobiles of 150 kg / mm 2 or more by using a mold cooling method, it is very important to set and control the heat treatment process parameters at the time of material heating and the process variables when rapidly cooling the material in the mold. And such process variables have the greatest impact on component performance. However, there are many difficulties in manufacturing high strength steel molded parts for automobiles because there is no standard data for producing steel molded parts yet.

In addition, the mold cooling method includes a process of cutting a rolling coil, a process of heating a cut material, a process of transferring a heated material, and a process of quenching the pressed material in a mold and quenching the molded body. It is made of a post-treatment process to remove the edge portion, there is a problem that takes a long time in the quenching process.

1 is a schematic view showing a method for manufacturing a steel formed body according to the prior art.

Referring to FIG. 1, first, the blank material 20 cut is passed between heating furnaces 10, and the blank material 20 is heated above a temperature at which the blank material 20 can be processed.

Next, the heated blank material 20 is loaded into the lower mold 40 and then fixed using the holder 30.

Next, the upper die 50 is pressed to change the shape of the blank material 20, and then quenched to form the steel formed body 25.

At this time, the temperature of the blank material 20 may cause a blank unwinding phenomenon that is naturally cooled while being loaded from the heating furnace 10 to the lower mold 40. In addition, a problem may occur in that an oxide film is formed while the blank material 20 is exposed to air.

Therefore, in view of such a case, it is necessary to heat to a temperature higher than the processable temperature in the heating step. However, in order to overheat, it is necessary to further consume unnecessary energy, and since it is difficult to accurately control the rate of temperature drop between loadings, there is a problem in that the quality of the steel formed body is also not constant.

In addition, repeatedly performing the above-described mold cooling method has a problem that the process time is delayed and productivity is lowered.

The present invention can facilitate the heating temperature control for molding in the method of manufacturing a steel molded body using a hot stamping method, and the steel to prevent the oxidized or loosening phenomenon occurs while the heated blank material is transferred to the mold It aims at providing the manufacturing method of a molded object.

In addition, an object of the present invention is to provide a steel molded body manufacturing apparatus capable of hot stamping and electrical resistance heating in order to perform the above-described method for manufacturing a steel molded body.

Method for manufacturing a steel molded body according to the present invention comprises the steps of (a) cutting a steel coil to form a blank (b) material, (b) loading the blank material into a lower mold provided with a molding part, (c) the (B) heating the blank material to a molding temperature by an electric resistance heating method by contacting an electrode to the blank material and supplying power to the electrode while the blank material is loaded in the lower mold; and (d) In the state heated to a molding temperature, it characterized in that it comprises a step of quenching and simultaneously quenching the blank material with the upper mold having a pressing portion corresponding to the molding portion of the lower mold.

Here, in the step (d), it is characterized in that to cut off the power supplied to the electrode before molding or quenching the blank material.

In addition, the electrode is characterized in that fixed to or separated from the lower mold, the electrode is characterized in that the contact with the blank material when the blank material loading, the electrode is on the upper surface of the lower mold It is characterized in that the arrangement.

Next, the step (b) is characterized in that for loading the blank material in the state of pre-heating the blank material, in the step (c), the blank material is characterized in that it is heated to 680 ~ 980 ℃ And, in the step (d), the time that the blank material is quenched is characterized in that 3 to 4 seconds.

In addition, the mold for manufacturing a steel molded body according to the present invention for carrying out the above-described method is a blank material is loaded, has a lower mold having a molding portion, and a crimping portion corresponding to the molding portion, the blank loaded on the lower mold And an upper mold for crimping the material, an electrode part in contact with the blank material, and a power supply part for supplying power to the electrode part.

Here, the upper mold or lower mold further comprises a temperature measuring unit for measuring the temperature of the blank material, by comparing the temperature value measured by the temperature measuring unit with the moldable temperature of the blank material stored in advance And a control unit for controlling the operation of the power supply unit, wherein the upper mold or the lower mold further includes a cooling unit configured to quench the temperature of the blank material in a state in which the blank material is pressed. .

The method for manufacturing a steel molded body according to the present invention uses a method of directly loading a blank material into a mold after blank forming, and by using a method of heating the blank material by electric resistance heating in a loaded state, the blank material is heated to a furnace. It provides an effect that can be prevented from forming an oxide layer or an annealing phenomenon on the surface of the blank material in the middle of transferring to the molding die after heating in.

Therefore, the method for manufacturing a steel molded body according to the present invention can form a high-strength steel molded body more quickly and easily, and provides an effect of improving the reliability of the product by preventing the degradation of the product strength or the spring back phenomenon.

In addition, the apparatus for manufacturing a steel molded body according to the present invention does not require a heating furnace or a quick transfer device, thereby reducing the overall equipment cost, thereby providing an effect of reducing the manufacturing cost.

1 is a schematic view showing a method for manufacturing a steel formed body according to the prior art.
Figure 2 is a schematic diagram showing the principle of performing a method for producing a steel formed body according to the present invention.
3 and 4 are schematic cross-sectional views showing a mold for producing a steel molded body according to the present invention and a method for manufacturing a steel molded body using the same.

Hereinafter, with reference to the accompanying drawings will be described for the ultra-high strength steel molded body manufacturing method and its manufacturing apparatus according to the present invention.

Advantages and features of the present invention, and methods of accomplishing the same will be apparent with reference to the drawings and embodiments described below in detail. However, the present invention is not limited to the drawings and embodiments disclosed below, but will be implemented in various different forms, and only the drawings and embodiments are intended to complete the disclosure of the present invention, and the present invention belongs to. It is provided in order to fully inform those skilled in the art the scope of the invention, the invention is defined only by the scope of the claims.

Figure 2 is a schematic diagram showing the principle of carrying out a method for producing a steel formed body according to the present invention.

Referring to FIG. 2, in order to perform the method for manufacturing a steel molded body according to the present invention, a blank material 120 is first formed, and then directly loaded onto a lower mold 140 for molding without passing through a heating furnace.

In the present invention, the electrode part 160 for heating the blank material 120 in the mold in an electrical resistance manner is formed in the lower mold 140. At this time, since the heating using the electrical resistance of the blank material 120 itself should be performed, the electrode unit 160 is preferably formed in a form that can be in direct contact with the blank material 120. Therefore, the electrode unit 160 may be formed at a portion where the blank material 120 is loaded into the lower mold 140. In addition, the blank material support of the electrode unit 160 may be formed to be in a shape to be engaged with the holder 130.

When power is applied to the electrode unit 160 in the state in which the blank material 120 is loaded, the blank material 120 is heated by the resistance of the blank material 120. After a certain time, the blank material 120 reaches the moldable temperature of the material.

At a moldable temperature of the blank material 120, the upper mold 150 may be pressed onto the lower mold 140 to perform a hot stamping molding process of forming the blank material 120.

In addition, by simultaneously quenching the blank material 120 through the cooling unit provided in the lower mold 140 or the upper mold 150 at the same time, the molded blank material 120 is formed into a steel molded body as a final product form.

3 and 4 are schematic cross-sectional views showing a mold for producing a steel molded body according to the present invention and a method for manufacturing a steel molded body using the same.

Referring to FIG. 3, the mold for manufacturing a steel molded body includes a lower mold 240, an upper mold 250, and an electrode part 260.

First, the lower mold 240 is loaded with the blank material 220, and includes a molding part for molding the loaded blank material 220 into a desired shape. In this case, the lower mold 240 may include a plate portion for supporting the mold.

In addition, the lower mold 240 may include a region for supporting the holder, and FIG. 3 illustrates a state in which the region for supporting the holder is not included in the lower mold 240.

In the case of the lower mold 140 illustrated in FIG. 2, the area of the molding part is relatively wide, and thus a region for supporting the holder 130 is formed on the lower mold 140. ) Is arranged.

As another embodiment, in FIG. 3, an embodiment for forming an area for supporting the holder 230 on the outer side of the lower mold 240, wherein the electrode part 260 is disposed in this area is illustrated.

As such, the arrangement relationship between the lower mold and the electrode according to the present invention may be changed depending on the embodiments. However, it is preferable to form the electrode so that the electrode can be in contact with the blank material at the same time or immediately after the blank material is loaded.

Next, the upper mold 250 has a crimping portion 252 corresponding to the molding portion of the lower mold 240, and includes an ancillary substrate for pressing the blank material 220 loaded on the lower mold 240. At this time, as a concomitant substrate for pressing the upper mold 250 to the lower mold 240, the pressing spring 256, which can restore the upper mold 250 to its original state when the crimp is released, is formed on the upper end of the pressing part 252. While being provided and fixing the crimping portion 252, the plate portion 258, which can support the crimping spring 256, and the crimping support portion 254 provided under the spring 256 may be provided.

Next, it includes a power supply unit for supplying power to the electrode unit 260. In FIG. 3, the power supply unit is illustrated at the bottom of the lower mold 240, but is not limited thereto.

The apparatus for manufacturing a steel molded body according to the present invention, in addition to the main elements such as the lower mold 240, the upper mold 250, the electrode portion 260, etc., as described above, a temperature measuring unit for measuring the temperature of the blank material as auxiliary devices You can include more.

In addition, the apparatus for manufacturing a steel molded body according to the present invention may further include a controller for controlling the operation of the power supply unit by comparing the temperature value measured by the temperature measuring unit with a moldable temperature of a blank material stored in advance.

For example, when the moldable temperature of the blank material is 700 to 900 ° C., when the temperature of the blank material loaded in the mold is less than 700 ° C., the controller may increase the size of the power supplied from the power supply unit. When the temperature of the blank material loaded in the overheated to more than 900 ℃ can power off the power supply.

In addition, the upper mold or the lower mold may further comprise a cooling unit for quenching the temperature of the blank material in a state in which the blank material is pressed.

As described above, when the mold for manufacturing a steel molded body according to the present invention is prepared, the blank material 220 is loaded on the upper part of the lower mold 240 as a first step as a method for manufacturing a steel molded body therefor. In this case, the first step does not mean the first step of the actual steel molded product manufacturing process, but means the first step in which the mold according to the present invention is used.

The previous step may include the above-described blank material manufacturing step and preheating the blank material, and the present invention may omit the step of preheating the blank material.

Next, the electrode unit 260 is connected to the blank material 220. In this case, the electrode unit 260 may be connected to both edge portions of the blank material 220. By connecting the electrodes to both edge portions of the blank material 220 as described above, the entire surface of the blank material 220 can act as a resistance, and heat generated by the resistance is accumulated so that the blank material 220 is heated.

In this case, the blank material 220 may be heated by using the holder 230, and the blank material 220 may be heated without driving the holder 230.

In addition, the heating temperature of the blank material 220 by the electrode may be 680 ~ 980 ℃, which is different for each material. Such a heating temperature means a possible temperature at which the blank material 220 may be formed by hot stamping.

Conventionally, the temperature of the blank material should be heated to 1000 ° C. or higher in consideration of the temperature drop during the time of transfer from the furnace to the mold. However, in the present invention, since there is no energy loss during the transfer, the temperature of 680 to 980 ° C. The temperature range can lower the overall heating temperature range.

Therefore, the energy consumption for heating can be reduced, and the problem of oxidizing the surface of the blank material while being exposed to air during transport in the heated state can be reduced.

Next, referring to FIG. 4, as described above, during the heating of the blank material, the temperature measuring device transmits the current temperature to the controller, and the controller compares the previously determined moldable temperature of the blank material to the electrode unit 260. Adjust the power supply.

Next, the upper mold 250 is pressed onto the blank material to form a steel molded body 225 in the form of a final product. In this case, the lower mold 240 or the upper mold 250 may be further provided with a cooling unit so that a product having a desired strength can be easily obtained.

In addition, it is preferable to control the time for which the blank material is quenched to within 3 to 4 seconds, which is also an optimum time range for obtaining a product having a desired strength. If the cooling time is less than 3 seconds is not enough cooling is not possible to maintain the molding state, and if the quenching for more than 4 seconds may not achieve the desired hardness.

Power supplied to the electrode unit 260 is cut off before molding or quenching. At this time, considering that the quenching is performed almost simultaneously with the molding of the blank material, preferably, the power is completely cut off before the molding of the blank material, but a method of turning off the power before the quenching after the molding is started may be used. .

In this case, the blank material is carbon (C) 0.1 to 0.4wt%, silicon (Si) 0.5wt% or less, nitrogen (N) 0.1wt% or less, aluminum (Al) 0.01 to 0.1wt%, phosphorus (P) 0.05wt% Hereinafter, manganese (Mn) 0.8 to 2wt%, boron (B) 0.002 to 0.01wt%, molybdenum (Mo) 0.1 to 0.5wt%, chromium (Cr) 0.1 to 0.5wt% and the remaining iron (Fe) and other unavoidable impurities It can be used to include. This is a combination of composition ranges in which the properties of electric resistance heating and the strength of the final molded product are more prominent than other materials.

As described above, the method for manufacturing a steel molded body according to the present invention can be formed by combining a hot stamping method and an electrical resistance method, and can form a high-strength steel molded body more quickly and easily, and prevent the product strength degradation or spring back phenomenon There is an advantage to improve the reliability.

While the present 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, It is to be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (1)

(a) 0.1 to 0.4 wt% of carbon (C), 0.5 wt% or less of silicon (Si), 0.1 wt% or less of nitrogen (N), 0.01 to 0.1 wt% of aluminum (Al), 0.05 wt% or less of phosphorus (P), Manganese (Mn) 0.8 to 2wt%, boron (B) 0.002 to 0.01wt%, molybdenum (Mo) 0.1 to 0.5wt%, chromium (Cr) 0.1 to 0.5wt% and the remaining iron (Fe) and other unavoidable impurities Forming a blank material by cutting a steel coil having a forming temperature of 680 to 980 ° C .;
(b) directly loading the blank material into a lower mold having a molding part and having an electrode disposed on an upper surface thereof, without being heated;
(c) an electrode is brought into contact with both edges of the blank material so that the blank material front surface acts as a resistance while the blank material is loaded in the lower mold, and the electric power is supplied to the electrode from the power supply to heat the electric resistance. The blank material is heated by the self-resistance of the blank material in a manner, and a temperature measuring part measuring the temperature of the blank material and a temperature value measured by the temperature measuring part are compared with a moldable temperature of the blank material previously stored. Heating the blank material to 680 to 980 ° C. by using a control unit controlling the operation of the power supply unit; And
(d) a pressing portion corresponding to the molding portion of the lower mold, a pressing spring for restoring the upper mold to its original state when the pressing is released, and the pressing spring in the state where the blank material is heated to 680 to 980 ° C. While pressing and molding the blank material with an upper mold having a plate portion for supporting the pressure and a crimping support provided on the lower portion of the crimping spring, while cooling for 3 to 4 seconds while maintaining a molding state, Cutting off the power supplied to the electrode before the forming or cooling of the blank material.

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