Heat treatment method for metal plates

Abstract

It efficiently raises the temperature of the area to be heated. [Solution] Heat transfer is limited by providing a slit between the frame that grips the metal plate and the molding part.

Description

Technical Field

[0001] The following disclosure relates to a heat treatment method for locally heating a formed metal plate.

Background Art

[0002] [[ID= / / ]] In the forming process of metal plates, classical press forming using dies has been generally used. Dies are generally expensive and require a considerable amount of labor and time to manufacture. Therefore, press forming is inconvenient, for example, in cases where a small quantity is to be produced in a short period of time. One means of overcoming such drawbacks is die-less forming. Die-less forming is a type of sequential forming, in which a tool is pressed vertically against a thin plate fixed in the plane direction by a jig and moved parallel to the plane while gradually forming the thin plate.

[0003] As it is, in the forming process, especially die-less forming, non-uniform and non-negligible stress remains in the metal plate, so heat treatment such as annealing is often additionally performed. Patent Document 1 discloses a heat treatment method for removing residual stress.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a metal plate after die-less forming, the part where residual stress is to be removed is relatively local, and heat treatment is performed using, for example, local heating means using hot air. However, especially for materials with a relatively high thermal conductivity such as steel plates, the heat applied locally quickly dissipates toward the periphery, making it difficult to efficiently raise the temperature of the part to be heated. The technology disclosed below was conceived in view of such problems.

Means for Solving the Problems

[0006] Heat transfer is limited by providing a slit between the frame that grips the metal plate and the molding part. [Effects of the Invention]

[0007] By limiting heat transfer, the desired area can be heated up efficiently. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic perspective view of a blank with slits formed after molding. [Figure 2] Figure 2 is a schematic cross-sectional view showing a heat treatment process applied to a blank with slits. [Figure 3] Figure 3 is a schematic plan view of a blank with slits formed after molding, where (a) represents one embodiment and (b) represents another embodiment. [Figure 4] Figure 4 is a schematic plan view illustrating the relationship between heat and displacement propagation and the slit. [Modes for carrying out the invention]

[0009] Several exemplary embodiments are described below with reference to the attached drawings. Particular attention should be paid to the fact that the drawings are not necessarily to scale, and therefore the dimensional relationships are not limited to those shown. Throughout the following description and the attached claims, and for the sake of explanatory convenience, we will distinguish between top and bottom, but embodiments in which the structure can be arbitrarily inverted, rotated, and reversed are possible.

[0010] Referring mainly to Figure 1, a blank 1 made of a metal such as a steel plate is held by a frame 3 and subjected to forming, and for example, the central part has a formed portion 7 that is recessed downwards. The forming is performed, for example, by die-less forming. The area around the formed portion 7 is usually a flat portion 5 that remains flat, and the blank is subjected to heat treatment while being held by the frame 3 in the flat portion 5. Needless to say, Figure 1 is merely an example, and the formed portion can be of various shapes, and the formed portion is not limited to one, but can be two or more, continuous or discontinuous with respect to each other.

[0011] The blank 1 having the molded portion 7 is subjected to a heat treatment such as annealing together with the frame 3, as shown in Figure 2. Preferably, the frame 3 is the same during molding and heat treatment, or it may be replaced as appropriate during heat treatment. Heating is performed by exposing the blank 1 to a heat flow H from a heating means 13 such as a ceramic heater. Heating may be carried out in an open atmosphere as shown in the figure, or in a suitable furnace. Furthermore, heating does not have to be by thermal radiation or infrared irradiation, but can be done by induction heating, exposure to hot air or flame, contact heating, or a combination of two or more of these.

[0012] Referring to Figure 3, a suitable region 9 surrounding the molded portion 7 is heated exclusively. Prior to the heat treatment, a slit portion 11 is formed by appropriately partially cutting the flat portion 5 along the region 9. The slit portion 11 is, for example, a vertically elongated slit hole that penetrates the blank 1 and is located in the plane direction of the blank 1, and as schematically shown in Figure 2, it limits heat transfer Hc. In particular, by having the slit portion 11 surround the region 9, heat transfer Hc outside the region 9 is limited, thereby improving the heating efficiency of the molded portion 7.

[0013] The slit portion 11 is formed by appropriate means such as punching, cutting, laser cutting, or waterjet cutting. Waterjet cutting is characterized by not applying heat to the material during cutting. For example, if the blank 1 is made of a material that undergoes an aging effect when heated, it would be appropriate to use a means that avoids heating, such as waterjet cutting.

[0014] Referring mainly to Figure 3(a), heat transfer Hc is directed from the heating region 9 through the flat section 5 towards the frame 3, so the slit sections 11 are positioned and arranged to efficiently restrict this heat transfer. Preferably, the slit sections 11 are within the flat section 5, surrounding the molding section 7 or region 9, and are parallel to the frame 3 (perpendicular to the direction of heat transfer). There can be multiple slit sections 11, and adjacent slit sections 11 can be placed very close together. That is, the group of slit sections 11 can take the form of multiple intermittently arranged line segments (dashed lines). Region 9 and the flat section 5 are connected only between the slit sections 11.

[0015] As schematically shown in Figure 3(b), the molded portion is divided into multiple parts 7a, 7b, and 7c, and if one part 7a is adjacent to another part 7b, a slit portion 11' may also be placed between them. This can limit heat transfer from the heating region 9 to the parts 7a and 7b. The slit portion 11' also limits the propagation of stress between parts 7a and 7b.

[0016] As shown in Figure 4(a), since heat transfer Hc is limited to the connecting portions between the slit portions 11, the heating efficiency of the molded portion 7 is further improved. The slit portions 11 also prevent the restraining force by the frame 3 from extending to the heating region 9, allowing for free displacement D. This is advantageous in preventing large stresses from occurring in the molded portion 7 and preventing secondary deformations such as buckling.

[0017] The slit portion 11 may be left open, but it may be partially or completely closed with an appropriate insulating material 15, for example, as shown in Figure 4(b). The insulating material 15 may be independent for each slit portion 11, or it may be continuous as shown in Figure 4(c). Examples of insulating materials include rock wool, silica, foamed ceramic, and foamed metal. If a sufficiently rigid insulating material is used, the displacement D can be restricted and the restraining force of the frame 3 can be increased. Depending on the shape of the molded portion 7, increasing the restraining force may be more advantageous in preventing secondary deformation.

[0018] According to any of the above embodiments, heat transfer to areas other than the heating area can be restricted, and desired heating can be efficiently realized.

[0019] Although several embodiments have been described, modifications or variations of the embodiments are possible based on the above disclosure.

Industrial Applicability

[0020] A heat treatment method is provided that can efficiently raise the temperature of the part to be heated by restricting heat transfer.

Explanation of Signs

[0021] 1 Blank 3 Frame 5 Flat part 7 Forming part 7a, 7b, 7c Parts 9 Area 11, 11’ Slit part 13 Heating means 15 Heat insulating material H Heat flow Hc Heat transfer

Claims

1. A method for heat-treating a metal plate having a molded portion and a flat portion held by a frame, A slit is formed by partially cutting the flat portion between the molded portion and the frame. The metal plate is heated in at least the region surrounded by the slit portion. A method to prepare for that.

2. The method of claim 1, wherein in the step of forming the slit portion, the slit portion is also formed between one part and another part of the molded portion.

3. The method according to claim 1, wherein in the step of forming the slit portion, the slit portion is formed to be a plurality of intermittently arranged line segments.

4. The method of claim 1, wherein in the step of forming the slit portion, the slit portion is formed along the region.

5. A heat insulating material is inserted into the aforementioned slit. The method of claim 1, further comprising the above.

6. The method of claim 1, wherein, in the step of forming the slit portion, the removal of the flat portion is performed by a water jet.

7. The method according to claim 1, wherein the step of heating the metal plate is one or more selected from the group consisting of hot air heating, infrared heating, induction heating, and contact heating.

8. The method according to claim 1, wherein the molded part is formed by die-less molding.

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