KR20190081799A - Die for manufacturing vehicle parts - Google Patents

Abstract

Disclosed is a die (10) for hot stamping with improved cooling performance. The die (10) comprises a plurality of blocks (11) having a molding surface (1), wherein each of the blocks (11) is formed as a plurality of plates (20) are stacked with each other. Grooves (22) which correspond to each other are formed on a contact surface (21) between adjacent plates (20) of the die (10), thereby providing a cooling channel. Moreover, in the cooling channel, a plurality of spot coatings (40) which are spaced apart from each other are formed by a spray coating method.

Description

{DIE FOR MANUFACTURING VEHICLE PARTS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for manufacturing vehicle parts, particularly a hot stamping mold having excellent cooling performance.

One of the biggest buzzwords in the automotive industry is light weight and high strength, and hot stamping technology is at the center of these issues. The hot stamping technique was first introduced in the British patent No. 1490535 of Norrbottens Jarnverk A. B. of Sweden.

Hot stamping is a process in which a steel sheet is heated to a high temperature of 900 ° C or higher in a heating furnace, followed by rapid cooling and molding in a press mold to produce high strength parts. Boron steel containing about 0.2% by weight of carbon, Mn, B and the like is used as the material, and a cooling channel for quenching the steel sheet is provided in the mold.

Such hot stamping is excellent in productivity because molding and heat treatment are performed at the same time. In addition, since the steel sheet is molded at a high temperature, it is excellent in moldability and dimensional accuracy, and also has the advantage that problems such as springback and delayed fracture, which are particularly problematic in high-strength parts, can be reduced.

The quality or productivity of hot stamping parts depends on the cooling rate of the mold. Rapid release of steel sheet heat enables rapid cooling of parts and shortening the waiting time between press strokes. It is necessary to improve the heat transfer coefficient of the mold and the heat transfer efficiency in the cooling channel.

The mold used for hot stamping is made of special mold stainless steel such as SKD11. However, the heat transfer coefficient of SKD11 is not high enough to control the cooling rate. In order to improve the cooling performance, a material having a high heat transfer coefficient is used, but excessive cost increase is a problem.

SUMMARY OF THE INVENTION The present invention is based on the recognition of the prior art as described above, and aims to provide an improved hot stamping mold having excellent cooling performance.

The present invention also provides a hot stamping mold capable of improving cooling performance without using a high-cost material having a high heat transfer coefficient.

The problems to be solved by the present invention are not necessarily limited to those described above, and other tasks not mentioned in the present invention may be understood by the following.

According to an aspect of the present invention, there is provided a hot stamping mold comprising a plurality of blocks each having a molding surface, wherein each block is formed by stacking a plurality of plates.

According to the present invention, a cooling channel is formed by forming grooves corresponding to each other on a contact surface between adjacent plates of the mold, and a plurality of spot coatings spaced from each other are formed in the cooling channel. Many spot coatings are formed by cold spray coating a powder of thermally conductive material.

One of the ways to improve the cooling efficiency of the mold may be to coat the cooling channel of the mold with a material having excellent thermal efficiency. Such a heat dissipation coating can be made entirely in the cooling channel, but according to the invention, the heat dissipation coating is in the form of a spot rather than a continuous form.

A number of spot coatings according to the present invention exhibit excellent cooling performance. These results can provide molds with excellent cooling performance in an economical and productive manner of spot coating.

According to the present invention, it is possible to provide a mold having improved cooling performance while using an existing mold without using a high-cost material having a high heat transfer coefficient.

1 is a schematic view of a hot stamping mold according to an embodiment of the present invention,
2 is a schematic view showing a block of a hot stamped mold according to an embodiment of the present invention,
3 is a schematic view of a plate of a hot stamping mold according to an embodiment of the present invention,
4 is a view showing a cooling channel in a mold block according to an embodiment of the present invention;
5 is a view showing an example where a copper (Cu) plate is spot-coated according to an embodiment of the present invention,
FIG. 6 is a schematic view showing a form of spot coating according to an embodiment of the present invention,
7 is a scanning electron microscope (SEM) photograph of a spot coating according to an embodiment of the present invention,
FIG. 8 is a schematic view illustrating a configuration of a cooling performance test equipment according to an embodiment of the present invention,
9 is a graph showing the results of testing cooling performance for various coating examples using the equipment shown in FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the accompanying drawings, the same or equivalent components or parts are denoted by the same reference numerals as much as possible for convenience of description, and the drawings are exaggerated and schematically shown for clarity and explanation of the features of the present invention. have.

In the description of the present invention, unless the second element is disposed on the first element or " connected " to each other, unless otherwise specified, it is to be understood that both elements are directly contacted or connected with each other, To allow the first and second elements to relate to each other. Directional expressions such as forward, backward, left and right, and up and down are merely for convenience of explanation.

Fig. 1 shows a mold 10 according to the embodiment, Fig. 2 shows a block 11 constituting a mold 10, and Fig. 3 shows a plate 20 constituting a block 11. Fig.

Referring to FIGS. 1 and 2, the mold 10 includes four blocks 11a, 11b, 11c, and 11d. The upper surface of each block 11 constitutes a forming surface 1 for imparting a shape to the parts, and the lower part can be fixed by the clamp 12.

Referring to FIGS. 2 and 3, each block 11 is manufactured by overlapping a plurality of plates 20. Between each of the plates 20, a fixing member for assembling them may be provided, and the upper surface of each plate 20 forms the molding surface 1.

On one surface 21 of the plate 20, a groove 22 constituting a cooling channel is formed. The groove 22 may be formed as a semicircular concave groove and may be formed as close as possible to the molding surface 1 in order to improve cooling performance.

When the adjacent plate is superimposed on one surface 21 of a plate 20 on which the groove 22 is formed, the groove 22 becomes a semicircular cooling channel. When the grooves 22 are formed in the same pattern on the overlapping surfaces between the adjacent plates 20, the overlapping grooves 22 form a circular cooling channel.

According to the embodiment, the cooling channels are formed with grooves () corresponding to each other so as to form circular cooling channels on the overlapping surfaces between adjacent plates (20). Grooves 22 may be formed on both sides of the plate 20. [ Sealing grooves (not shown) for sealing the cooling channel are provided along both widthwise edges of the groove (), and the ring is inserted into the sealing groove.

2, grooves 22, that is, cooling channels, are not formed on both sides of the block 11, i.e., the side contacting the other block 11. As shown in Fig. In consideration of the assembly convenience between the blocks 11 and the sealing of the cooling channel, cooling channels may not be formed on both side surfaces of the block.

Fig. 4 shows an example of a block 11 'that can be obtained by combining a plurality of plates () formed with grooves () on the surfaces overlapping each other. In the block 11 ', a cooling channel is formed along the face of the plate (i), especially along the edge of the face, in particular close to the molding face (1).

The cooling channel of the block 11 'shown in FIG. 4 is shown in the form of a channel inlet and an outlet provided on each side of the plate. As a more preferred embodiment, each of the inlet and the outlet of the cooling channel provided in the block 11 'may be one each. In other words, the inlet of the cooling channel is provided in the leftmost plate of the block 11 'in FIG. 4, and the outlet of the cooling channel is provided in the rightmost plate. In this case, a connection hole (not shown) may be provided on the plate so that a cooling channel formed on one side of the plate may be connected to a cooling channel formed on the other side of the plate.

Fig. 5 shows an example of spot coating according to an embodiment.

As shown in Fig. 5, a plurality of spot coatings are formed spaced apart from each other. Additional verification and optimization is needed with respect to the extent to which they are spaced apart and the size of the spots that may be associated with them. According to embodiments, spot coatings do not intentionally overlap each other and need not be. Partial overlap may be allowed at the boundary of the spot in order to make the spacing a little tighter, but a continuous coating is not intended to coat the nozzle while moving the nozzle at a constant speed in the form of a path. Continuous coatings as compared to spot coatings are more expensive than the effects, resulting in unintended steps between passes or thermal cracking.

5 (a) to 5 (c) show examples in which a copper plate having a particle diameter of 1 to 3 占 퐉 is used for spot coating on a copper plate by a low temperature spray coating method, wherein (a) (Injection time: 2 seconds) formed at an average height of about 500 mu m, (c) shows an example formed at an average height of about 700 mu m (injection time 3 seconds). Under the coating conditions, the main gas was preheated to 550 ° C, the feed pressure was 4 bar, the distance between the copper plate and the nozzle was 30 mm, and the feed rate of the copper powder was 3 g / min. The coating was sprayed for a few seconds, for 1 to 3 seconds, while the nozzle was being transported at a traverse speed of 30 mm / sec, to form a first spot coating, and then moved and stopped again to form a second spot coating . If the distance between the plate and the nozzle is too close, the impact is too strong and vice versa, so spot coating formation can be difficult.

Referring to FIG. 6, it is preferable that the spot coating by low-temperature spray coating as described above is formed into a cylindrical shape having a broad bottom surface and a narrow upper side. The bottom surface of the spot coating has a width of about 1.2 mm, and the height of the spot coating may be varied up to a height of 700 to 800 탆 although a difference may occur depending on the coating time and the supply flow rate of the powder. However, when the thickness of the spot coating is increased, the top surface of the spot coating becomes sharp in a conical shape, and it is difficult to obtain a uniform shape, and a phenomenon in which the upper part falls off due to cracking occurs and adversely affects the heat transfer performance. According to the embodiment, the optimum height of the spot coating is 500 mu m.

FIG. 7 is a SEM photograph of the spot coating shown in FIG. 5 (b). As a result of observing the spot coating, coarse cracks and micropores were observed when the height of the spot coating was 300 탆, which was better than no coating, but the cooling efficiency was not improved satisfactorily, and the height of the spot coating was 500 탆 The micropore is observed and the cooling efficiency is also good. On the other hand, when the height of the spot coating is 700 mu m as shown in FIG. 5C, a defect such as a part of the upper part of the coating is removed, and a cooling performance is improved by a spot having a height of 500 mu m The result is lower than that of the coating. According to the embodiment, the height of the spot coating is about 400 to 650 μm, more preferably about 450 to 600 μm.

8 is a schematic view of a test equipment for confirming the cooling performance of the spot coating according to the embodiment.

The heat sink 100 is formed so that the cooling water can flow through the spot-coated copper plate as shown in FIG. 5 by simulating the hot stamping mold, and heat is generated at the bottom of the heat sink 100 using the heater 200 Supply. Cooling water is supplied to the heat sink 100 from the cooling water supply device 300. Current is supplied to the heater 200 from the power supply device 400 and a sensor for detecting temperature is installed at the center of the copper plate do. The detected temperature is recorded in the temperature recorder 500.

FIG. 9 shows some of the results of various test data using the test equipment as shown in FIG.

In Fig. 9, Bare shows the temperature profile when a copper plate with no coating is used.

Example 1 is a temperature profile in the case where copper is electroplated on a copper plate and nanowires having good heat transfer characteristics are continuously coated thereon. The heat transfer performance is better than the bare case, but the cooling performance is only marginal.

Example 5 is a temperature profile when a copper plate is subjected to spot coating (low-temperature spray coating) at a height of 500 mu m using copper powder. As can be seen from the graph, the cooling performance is the most outstanding.

Example 2 is a temperature profile in which a copper plate is continuously coated with a copper powder (coating can be performed in a continuous spraying manner along the pass once coated with a pass, low temperature spray coating). While the continuous coating of metal is more difficult and takes longer to coat than the coating of materials such as nanowires, the achievable cooling efficiency is somewhat worse than that of spot coating. It is believed that spot coating in a cylindrical form with a height of 500 μm higher than the continuous coating, which is difficult to obtain uniform shape or structure as desired, is more beneficial for increasing the surface area and cooling performance.

Example 3 was the same as Example 5 except that the copper plate was subjected to spot coating (low-temperature spray coating, the same conditions as in Example 5) at a height of 500 μm on the copper plate using copper powder, Profile. As can be seen from Fig. 9, the cooling performance is not so good. This is probably because the coating of different materials increases the contact resistance between materials and thus the cooling performance is degraded.

Example 4 is a temperature profile when copper is electroplated on a copper plate. It is difficult to expect a significant improvement in cooling performance by plating.

Example 6 is a temperature profile of a copper foil with continuous coating of silver nano wire. Only intermediate cooling performance was observed with Example 5 where bare and copper were spot coated.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention as set forth in the following claims.

10: mold 11: block
20: plate 22: groove (cooling channel)
30: copper plate 40: spot coating
100: Heatsink 200: Heater
300: Cooling water supply 400: Power supply
500: Temperature recorder

Claims (2)

A hot stamping mold comprising a plurality of blocks each having a forming surface, wherein each block is formed by superimposing a plurality of plates,
A cooling channel is provided by forming grooves corresponding to each other on a contact surface between adjacent plates, a plurality of spot coatings spaced from each other are formed in the cooling channel,
Wherein the plurality of spot coatings are formed by low temperature spray coating of the thermally conductive material powder. The hot stamping mold according to claim 1, wherein the spot coating is formed to a height or a thickness of 450 to 700 탆, and the material is metal.

Images