KR100993988B1 - Indirect hot stamping - Google Patents

Abstract

PURPOSE: An indirect hot stamping molding method is provided to stabilize molding quality and to reduce the amount of hot-working by previously performing cold-working. CONSTITUTION: An indirect hot stamping molding method is as follows. A material is cut(S-31). The cut material is cold-worked(S-32). The edge of the cold-worked material is trimmed(S-33). The trimmed material is put into a furnace and is heated with 768~1000°C(S-34). A residual mold of the heated material is hot-pressed and is quickly cooled with -20~-100°C/sec(S-35).

Description

Indirect Hot Stamping Forming Method {INDIRECT HOT STAMPING}

The present invention relates to a hot stamping molding method for forming a high-strength component having a complex shape by performing heat treatment simultaneously with molding, and more particularly, indirect hot stamping molding in which a majority of the shape molding is performed in a cold forming process. It is about a method.

Conventionally, automobile parts were manufactured by using a press method.

In general, the manufacturing method of automobile parts using the press method is to cut the raw material of the cold or hot rolled coil, transfer the material into the press mold, press it to complete the molding, and then cut the unnecessary parts and form holes, etc. 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 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 iron plate is a phenomenon called spring back (spring back). This is the property that the iron plate is returned to its original shape even if an external pressure of yield strength or more is applied when the iron plate 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.

The object of the present invention is to break away from the conventional hot stamping method of forming all the shape of the product through the hot forming, most of the shape forming is made through the cold forming process, the minimum forming and dimensional precision improvement in the hot forming process It is to provide an indirect hot stamping molding method to make a correction for the work.

Another object of the present invention is to provide an indirect hot stamping molding method capable of performing the trim and piercing process with minimal or no use of laser equipment applied in trim or hole machining of a product.

The present invention provides a blanking process for cutting a material; A cold forming process of cold forming the cut material into a press mold having a shape corresponding to the finished product; Trimming process for trimming the edge of the cold-formed material (trimming); A heat treatment step of heating the trimmed material in a heating furnace to a temperature range of 768 to 1000 ° C; And a finishing hot forming process of correcting the heated material to a final shape in a press mold having a shape corresponding to the finished product and simultaneously quenching the heated material.

When the finished product has a through hole, it is preferable to perform trimming and piercing in the trimming process.

The trimming process is preferably performed by a press die,

The quenching speed of the finishing hot forming process is preferably -20 ° C / sec to -100 ° C / sec.

Here, the cold forming process and the finishing hot forming process may use the same press mold or may use different press molds.

The present invention also provides a blanking process for cutting a material; Cold forming process for cold forming the cut material to 60 ~ 95% of the amount compared to the shape of the finished product; Trimming process for trimming the edge of the cold-formed material (trimming); A heat treatment step of heating the trimmed material in a heating furnace to a temperature range of 768 to 1000 ° C; And a final hot forming step of quenching and simultaneously quenching the residual molding amount of 5 to 40% of the heated material.

Indirect hot stamping molding method according to the present invention can minimize the use of the laser equipment or in some cases can be used to trim and piercing using the press mold without using at all, thereby reducing the processing costs associated with the laser equipment It can bring an effect. This reduction in processing cost results in a cost savings of about 30% to 50% or more compared to conventional laser equipment.

In addition, trimming and piercing operations using a press die have a shorter process time than processing using a laser, thereby reducing cycle time required for processing. This results in an increase in output per unit time.

In addition, the present invention reduces the amount of hot forming by performing a cold forming in advance and then correcting the shape through hot forming, thereby bringing about a stabilization of molding quality distribution according to the hot forming process.

1 is a process flowchart showing a general hot stamping molding method,
Figure 2 is a process schematic showing a general hot stamping forming method,
3 is a process flow chart showing an indirect hot stamping forming method according to the present invention.
Figure 4 is a process schematic showing the indirect hot stamping forming method according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of a method for manufacturing a steel molded body according to the present invention.

In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of description.

In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or an operator.

Therefore, definitions of these terms should be made based on the contents throughout the specification.

Hot stamping molding method is the quenching effect of cutting the raw material (iron plate) to a high temperature and then forming it into a mold and simultaneously cooling the die to give a cooling effect. Through the method of improving the strength of the raw material to two to three times or more than the original.

In addition, since the iron plate is heated to a high temperature during the hot stamping process, the properties of the iron plate are very soft and the stretching property is excellent, and the formability is excellent. Thus, by using hot stamping to secure the ultra-high strength of the iron plate and at the same time can produce the desired parts with excellent moldability.

First, a general hot stamping molding method will be described.

FIG. 1 is a process flowchart showing a general hot stamping molding method, and FIG. 2 is a process schematic diagram showing a general hot stamping molding method.

1 and 2, the general hot stamping molding method is a blanking step (S-11) for cutting the coil material, a heat treatment step (S-12) for heating the blanked material to a predetermined temperature range, and Hot forming and quenching process (S-13) for forming a material and quenching at the same time, and a laser trimming process (S-14) for precisely cutting the cured material using a laser equipment.

In the case of a general hot stamping molding method, all the molding is performed in hot forming, and thus, a trimming process for precisely cutting the outline of the product cannot be performed before hot forming. Since press-molding requires a part to be fixed to the holder, it cannot be cut to this part in the blanking step before molding, so that the trimming operation is inevitably performed after the molding is completed and the material is cured.

By the way, hardened | cured material was high in intensity | strength, and trimming cannot be performed by a general press die, and laser equipment was used. However, the laser equipment has a disadvantage that the cost of the equipment is higher than the press mold, and the process time takes a lot due to the nature of the operation is performed by moving the laser beam along the cut portion.

In addition, since all the molding is made by hot forming, the distribution of molding quality distribution has a disadvantage.

Next, an indirect hot stamping molding method according to the present invention will be described.

3 is a process flowchart showing an indirect hot stamping molding method according to the present invention, Figure 4 is a process schematic diagram showing an indirect hot stamping molding method according to the present invention.

3 and 4, the indirect hot stamping molding method according to the present invention is a blanking step (S-31) for cutting the material, and cold forming step (S) for cold forming the cut material into a press mold (S) -32), a trimming process (S-33) for trimming the edges of the cold-formed material, and a heat treatment process for heating the trimmed material in a heating furnace in a temperature range of 768 to 1000 ° C. 34) and a finishing hot forming process (S-35) for quenching the heated material to the final shape and quenching the same.

The indirect hot stamping molding method according to the present invention is characterized by forming the largest possible shape by cold forming, and then performing trimming. As described above with reference to FIGS. 1 and 2, in the case of a general hot stamping molding method, trimming is performed after the hot forming and quenching process (S-13). There was a problem requiring laser equipment because it could not be performed. On the other hand, the indirect hot stamping molding method according to the present invention can perform the trimming process with the press mold by performing the trimming process (S-33) before the material is cured, thereby reducing the cost and time required for laser equipment can do.

Although it may seem that the process will take more time due to the addition of a cold forming process to the process step, in fact, the cold forming process using the press die is very short and the process time does not increase significantly. On the other hand, by replacing the conventional laser trimming process (S-14) with a trimming process (S-33) using a press mold, it is possible to shorten a lot of processing time, thereby reducing the overall process cycle time.

Indirect hot stamping molding method according to the present invention has two embodiments.

In the first embodiment, all of the molds used in the cold forming process (S-32) and the finish hot forming process (S-35) correspond to the finished product shape.

In the second embodiment, 60-95% of the total molding is performed in the cold forming process (S-32), and the finished product is formed by molding the remaining portion in the finishing hot forming process (S-35).

Each process is explained in full detail below.

The blanking step S-31 is a step of cutting the coil-shaped material to enable press molding. Materials that can be used include cold rolled steel sheet, hot rolled steel sheet, galvanized cold rolled steel sheet, Al-Si Boron coated steel sheet. If the net weight of the final part is 100 by cutting into the shape of the plate, the weight of the blanked material is about 120 to 150.

If the blanking is less than the above range, when forming the blanked material in the press device may be insufficient due to the part fixed by the blanking holder may not be completely formed, if exceeding the above range, the waste of the material is severe and cost It acts as a synergistic factor.

The blanking step (S-31) is the same without showing any difference in the first embodiment and the second embodiment.

Cold forming process (S-32) is a process for processing the shape of the blanked material through cold molding. In the first embodiment, the cold molding is performed using a press mold corresponding to the shape of the finished product, and in the second embodiment, the cold molding is performed using a press mold having a shape close to the shape of the finished product.

The second embodiment is applied to a case where the shape is complicated or the molding depth is deep, and the cold forming is performed at a level of 60 to 95% of the molding amount compared to the finished product shape. Since the molding of the product is three-dimensional and difficult to calculate numerically, the molding amount in the present invention means the ratio of the height of the molded article to the height of the finished product. In other words, the height of the finished part is the height of the finished product of the finished product finished by processing the plate material, the height of the molded part is the height of the molded part in the middle part of the molded product.

For example, if the molding depth of the finished product is 5cm and the molding depth of the cold-formed molded article is 4.7cm, the molding amount is 94%.

Trimming process (S-33) is a process to precisely cut the edge of the cold-formed material. Piercing is also made in the trimming process (S-33) if a hole is required for the finished product shape. In the case of general hot stamping, the press mold cannot be used because the trimming is performed using a laser after the molding and curing of the material are completed. Therefore, the laser or waterjet is used. Was consumed, and the process time was long, resulting in a decrease in productivity.

The present invention, in order to improve this problem, by trimming the material formed through the cold forming process (S-32) using a press die brings the effect of reducing the process time and equipment costs.

In the trimming process (S-33), the tolerance of the trim line is preferably ± 0.75.

Since the product is already trimmed or holed during cold forming, the product expands in all directions during heat treatment and shrinkage occurs during transfer to the mold and during molding by the mold. It is not easy to manufacture a product. Therefore, it is reasonable to consider the margin of tolerance more than the conventional press cold forming tolerance.

Heat treatment step (S-34) is a process of heating the temperature range of 768 ~ 1000 ℃ by inserting the trimmed material in the heating furnace.

Here, the final heating temperature of the material in the heat treatment furnace (furnace) is more than the austenite stabilization temperature 1000 ℃ or less, the holding time is 4 to 6 minutes. The reason is that the steel is usually heated to the austenite stabilization temperature to obtain a structural state that can secure the strength required by the component after quenching, while the temperature above 1000 ℃ is the temperature at which the coating layer starts to evaporate. Because.

In the heat treatment furnace to obtain a uniform structure by stress relief of the material and to ensure uniform processability in the post-heating process, if the retention time of the material is less than 4 minutes in a number of experiments, the amount of residual austenite is insufficient. Even if it exceeds minutes, since the effect of further austenite structure is saturated, it is preferable to set the holding time as 4-6 minutes. In general, the relationship between the martensite transformation start temperature and the cooling rate is very important for obtaining martensite structure. That is, molding should start at a temperature above the martensite transformation start, and parts should be taken out of the mold below the martensite transformation end temperature.

Finishing hot rolling process (S-35) is a process of quenching and simultaneously molding the material heated in the heat treatment process (S-34) in a press die.

In the case of the first embodiment, even if cold forming is performed using a mold corresponding to the shape of the finished product, the spring back shape does not have a desired final product shape. The shape of the product is corrected and the material is hardened.

In the second embodiment, the remaining molding amount is further molded and simultaneously quenched to form and harden the final product.

In the first embodiment, both the mold used in cold forming and the mold used in hot forming correspond to the finished product shape. The cold forming process (S-32) and the finish hot forming process (S-35) are performed using the same mold. Can be done. Of course, you can also provide and use a separate metal mold | die.

It is preferable that the cooling rate at the time of quench is -20 degreeC / sec--100 degreeC / sec.

The reason why the cooling rate is maintained at −20 ° C./sec or more is to facilitate phase transformation into martensite tissue.

That is, when the material heated to a high temperature is cooled at a cooling rate of -20 ° C / sec or less, the structure may have pearlite or bainite structure, and thus may not have sufficient strength. Therefore, it is desirable to maintain the quenching speed so that the base iron portion can undergo phase transformation into a fully martensite structure.

As described above, the indirect hot stamping molding method according to the present invention performs cold forming before hot forming and performs a trimming process after cold forming, thereby minimizing the use of expensive equipment such as a laser or a water jet, or not at all. The trimming process can be carried out using a press mold without use, which greatly reduces the process time required for the trimming process and improves productivity.

Although embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to the above embodiments and can be modified in various forms, and a person of ordinary skill in the art to which the present invention belongs. It will be appreciated that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

S-31: Blanking Process
S-32: Cold Forming Process
S-33: Trimming Process
S-34: Heat Treatment Process
S-35: Finishing Hot Forming Process

Claims (14)

delete delete delete delete delete delete delete delete A blanking process of cutting the material;
Cold forming process for cold forming the cut material to 60 ~ 95% of the amount compared to the shape of the finished product;
Trimming process for trimming the edge of the cold-formed material (trimming);
A heat treatment step of heating the trimmed material in a heating furnace to a temperature range of 768 to 1000 ° C; And
And hot-press molding the remaining molding amount of the heated material and at the same time, finishing hot forming step of rapidly cooling at a cooling rate of -20 ° C / sec to -100 ° C / sec.
The trimming process is performed in a tolerance range of ± 0.75mm with respect to the outline of the finished product, when the finished product has a through hole, trimming and piercing is performed in the trimming process,
The trimming process is hot stamping molding method, characterized in that performed by a press die.
delete delete delete delete The method of claim 9,
Indirect hot stamping molding method characterized in that the material used in the blanking process is one of a cold rolled steel sheet, hot rolled steel sheet, galvanized cold rolled steel sheet and Al-Si Boron-coated steel sheet.

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