CN114453481A

CN114453481A - Indirect hot stamping forming method and die for variable-strength part

Info

Publication number: CN114453481A
Application number: CN202210157799.XA
Authority: CN
Inventors: 李永丰; 戚宇彤; 岳毓挺; 李淑慧
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2022-02-21
Filing date: 2022-02-21
Publication date: 2022-05-10
Anticipated expiration: 2042-02-21
Also published as: CN114453481B

Abstract

The invention provides a variable-strength part indirect hot stamping forming method and a die, and the method comprises the following steps: determining a blank plate according to a part to be formed; cold forming the plate and finishing trimming and punching; placing the preformed piece and an upper clamping plate and a lower clamping plate with profiling structures into a heating furnace, heating to austenitize the preformed piece, taking out the preformed piece, clamping the low-strength end of the preformed piece by using the upper clamping plate and the lower clamping plate, and transferring the low-strength end to a mold closing mold, wherein the lower surface of an upper mold and the upper surface of a lower mold of the mold closing mold are respectively provided with a clamping plate embedding shallow groove matched with the contour and the thickness of the upper clamping plate and the lower clamping plate; and maintaining the pressure and quenching after die assembly. The high-strength end part of the pre-stamped part is shaped by die pressure and rapidly quenched to form a full martensite structure, the area of the finally formed part is high in strength, the low-strength end part cannot be completely quenched under the protection of a clamping plate and is converted into a diffusion phase structure, the martensite content is reduced, and the area of the finally formed part is low in strength and good in toughness.

Description

Indirect hot stamping forming method and die for variable-strength part

Technical Field

The invention relates to processing and forming of variable-strength stamping parts, in particular to a variable-strength part indirect hot stamping forming method and a die.

Background

The hot stamping process has the advantages of small deformation resistance, small part resilience and the like, and is widely applied to the production and the manufacture of automobile parts. Because the hot stamping part is very high in strength, the traditional cold punching means is difficult to cut edges and punch holes, and the currently adopted laser cutting technology is limited by a laser power device, so that the production efficiency of the hot stamping part is influenced. The indirect hot stamping process comprises the steps of firstly carrying out cold forming on a blank to obtain a preformed piece with the size close to that of a target part, finishing trimming, punching and the like on the preformed piece, then carrying out austenitization by heating, carrying out heat preservation for a period of time, quickly transferring the preformed piece to a die for shaping, and carrying out appropriate pressure-maintaining quenching to directly obtain a high-strength formed part.

In the automobile industry, some parts need high strength to ensure collision safety, and also need low strength and high toughness to ensure good energy absorption effect locally, namely, strength-variable stamping parts, such as B columns of automobiles and the like. The existing forming process aiming at the variable-strength stamping part mainly comprises a steel plate splicing method and a cooling speed changing method, steel plates with different thicknesses or different materials need to be spliced and welded by laser, or a die material or a cooling flow channel needs to be changed, the process cost is high, and the actual production efficiency is influenced.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides the indirect hot stamping forming method and the die for the variable-strength part, solves the problem of obtaining the variable-strength steel plate part by the indirect hot stamping method, and has the advantages of good comprehensive performance of the formed part, reduced cost and improved efficiency.

A variable strength part indirect hot stamping forming method comprises the following steps:

s1, blanking: determining a blank plate according to a part to be formed;

s2, cold forming: cold forming the plate at room temperature to obtain a preformed piece with a size and a shape close to a target size, finishing trimming and punching, wherein the preformed piece is provided with a low-strength end and a high-strength end according to the use requirement;

s3, heating for austenitizing: placing the preformed piece and an upper clamping plate and a lower clamping plate with profiling structures into a heating furnace, wherein the preformed piece is positioned between the upper clamping plate and the lower clamping plate and has a distance from each other, and heating to austenitize the preformed piece;

s4, transferring: taking the preformed piece, the upper clamping plate and the lower clamping plate out of the heating furnace, clamping the low-strength end of the preformed piece by using the upper clamping plate and the lower clamping plate, and transferring the low-strength end to a mold closing mold, wherein the lower surface of an upper mold and the upper surface of a lower mold of the mold closing mold are respectively provided with a clamping plate embedding shallow groove matched with the outline and the thickness of the upper clamping plate and the lower clamping plate;

s5, die assembly and pressure maintaining quenching: and (3) closing the upper die and the lower die to act on the high-strength end of the preformed piece, the upper clamping plate and the lower clamping plate, maintaining the pressure, quenching for a period of time, opening the die, and taking out the part.

Further, in step S3, the heating temperature of the heating furnace is 900-950 ℃, and the heating and heat preservation time is 3-5 minutes.

Further, in step S4, the preform is conformed to and attached to the contour of the upper and lower clamping plates, and clamping positions are left on the upper and lower clamping plates for clamping by the transfer robot.

Further, in step S4, the lower surface of the lower clamp plate is matched with the upper surface of the lower mold part, and the positioning of the preform is realized by the cooperation of the lower clamp plate and the mold.

Further, in step S5, cooling channels are provided in the upper and lower dies.

Further, in step S5, the upper and lower clamp plates have the same overall thickness.

Further, in step S5, the upper and lower clamping plates are made of high temperature alloy and ceramic material;

the upper clamping plate and the lower clamping plate are manufactured by casting and machining.

Further, in step S5, the upper and lower clamping plates take into account the thermal expansion effect, and the size and shape at high temperature are consistent with the final formed part of the preform.

Further, in step S5, the mold is opened 6 to 12 seconds after the pressure maintaining quenching.

The invention also provides an indirect hot stamping forming die for the variable-strength part, wherein the variable-strength part is provided with a low-strength end and a high-strength end according to the use requirement, the die consists of an upper die and a lower die with pressure maintaining and quenching functions, and the positions of the lower surface of the upper die and the upper surface of the lower die, which correspond to the low-strength end position of the boron steel variable-strength part, are provided with clamping plate embedding shallow grooves;

in the process of closing the hot stamping forming die to carry out hot stamping forming, the upper die and the lower die directly act on the upper end surface and the lower end surface of the high-strength end of the strength-variable part,

and the upper end face and the lower end face of the low-strength end of the variable-strength part are clamped in the middle by an upper clamping plate and a lower clamping plate, and the upper clamping plate and the lower clamping plate are respectively embedded into the clamping plate embedding shallow grooves of the upper die and the lower die.

The invention has the advantages that:

1) the invention reduces the quenching speed of the part by clamping the low-strength end of the preformed piece by the fully heated clamping plate, thereby being beneficial to the good forming of the variable-strength part.

2) The positioning of the plate and the die is easy to realize through the profiling design of the clamping plate, and the strength distribution of the finally formed part is controlled through changing the material and the thickness of the clamping plate.

3) The invention has small deformation resistance in the hot stamping forming process, ensures the product precision and prolongs the service life of the die.

4) The upper clamping plate and the lower clamping plate can be repeatedly recycled, and continuous manufacturing of the variable-strength hot stamping part is realized.

5) The process method has simple flow, is easy to realize, is easy to be applied to large-scale automatic production and has wide prospect.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the embodiments or the prior art description will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings may be obtained according to these drawings without inventive labor.

Fig. 1 is a schematic view illustrating an implementation process of the indirect hot stamping forming method for a boron steel strength-variable part according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of the implementation process of step three in the embodiment of the present invention.

Fig. 3 is a schematic diagram of the implementation process of step four in the embodiment of the present invention.

Fig. 4 is an implementation schematic diagram of step five before mold clamping in the embodiment of the invention.

Fig. 5 is a schematic diagram of the embodiment of step five after mold clamping in the embodiment of the invention.

Fig. 6 is a schematic view of the final parts of an embodiment of the present invention.

FIG. 7 is a schematic diagram of the temperature time profile through different phase regions in a continuous cooling transformation diagram in an embodiment of the present invention, in which A represents an austenite phase region, B represents a bainite phase region, F represents a ferrite phase region, P represents a pearlite phase region, and M represents a martensite phase region.

Description of reference numerals:

1. a preform; 1-1, low strength end; 1-2, high strength end; 2. an upper splint; 3. a lower splint; 4. heating furnace; 5. a manipulator; 6. an upper die; 6-1, embedding the upper clamping plate into the shallow groove; 7. a lower die; 7-1 the lower splint is embedded in the shallow groove.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The following detailed description of the preferred embodiments of the invention, however, the invention is capable of other embodiments in addition to those detailed.

Referring to fig. 1, the invention provides an indirect hot stamping forming method of a boron steel variable strength part, which comprises the following specific steps:

step S1-blanking: determining a blank plate according to a part to be formed;

s2-cold forming: and (3) performing cold forming on the plate at room temperature to obtain a preformed piece 1 with a size and a shape close to a target size, finishing trimming and punching, wherein the preformed piece 1 is provided with a low-strength end and a high-strength end according to the use requirement.

S3, heating for austenitizing: and (3) putting the preformed piece 1, the upper clamping plate 2 with the profiling structure and the lower clamping plate 3 into a heating furnace 4 for heating to austenitize the preformed piece 1, wherein the heating temperature of the heating furnace 4 is preferably 900-950 ℃, and the heating and heat preservation time is 3-5 minutes. During the heating process, the preforms 1 are located between the upper clamping plate 2 and the lower clamping plate 3 at a distance from one another.

The upper clamping plate 2 and the lower clamping plate 3 are consistent in thickness, and the quenching degree of each low-strength end of the preformed piece 1 is guaranteed to be the same in the hot stamping process. The materials and the thicknesses of the upper clamping plate 2 and the lower clamping plate 3 are designed and customized according to the requirements of the strength and the toughness of the target part, the thermal expansion effect needs to be considered, and the size and the shape under the high-temperature condition are consistent with those of the finally formed part. For example, the clamping plate can be made of high-temperature alloy and ceramic materials by casting and machining.

S4, transferring: the preformed piece 1, the upper clamping plate 2 and the lower clamping plate 3 are taken out of the heating furnace, the low-strength end of the preformed piece 1 is clamped by the upper clamping plate 2 and the lower clamping plate 3 and is transferred to a mold closing mold, and the lower surface of an upper mold 6 and the upper surface of a lower mold 7 of the mold closing mold are respectively provided with an upper clamping plate embedding shallow groove 6-1 and a lower clamping plate embedding shallow groove 7-1 (shown in figure 4), wherein the profiles and the thicknesses of the upper clamping plate 2 and the lower clamping plate 3 are matched with each other.

S5, die assembly and pressure maintaining quenching: and closing the upper mold and the lower mold to tightly press the upper clamping plate 2 and the lower clamping plate 3, enabling the high-strength end of the preformed piece 1 to be in close contact with the upper mold and the lower mold, opening the molds after pressure maintaining and quenching for a period of time, and taking out the parts. Wherein, the upper die 6 and the lower die 7 are provided with cooling channels, and cooling liquid (such as water or low-temperature cooling liquid) is circulated in the cooling channels for cooling.

The high-strength end part of the pre-stamped part 1, which is directly contacted with the die, is directly shaped by the die pressure and rapidly quenched to form a full martensite structure, and the area of the finally formed part has high strength; the upper end face and the lower end face of the low-strength end part of the pre-stamping part 1 are tightly clamped by the high-temperature upper clamping plate and the high-temperature lower clamping plate, so that the low-strength end part is not quenched and is transformed into a diffusion phase structure, the martensite content is reduced, and the area of the finally formed part is low in strength and good in toughness. Therefore, different parts on one boron steel part have different strengths, and the design requirements are met.

The following is a specific application example of the present invention.

Example one

In the embodiment, the selected part is a T-shaped part made of B1500HS, referring to fig. 1 to 5, the indirect thermoforming method and the mold of the present invention include the following steps:

step one, blanking: determining blank plate materials according to the required forming parts, wherein the size is 400mm multiplied by 280mm, and the thickness is 1.6 mm.

Step two, cold forming: and (3) performing cold forming on the plate stock at room temperature, and trimming and punching to obtain a preformed piece 1 with a shape close to a target size.

Step three, heating and heat preservation: the preform 1 and the upper and

lower clamping plates

2, 3 having a profile structure were placed in a heating furnace 4, the clamping plates having a thickness of 12 mm. Setting the heating temperature to 900 ℃, and keeping the heating temperature for 5min to austenitize the preformed piece 1; the splint material is made of high-temperature alloy consistent with the die material, and is processed by a five-axis milling machine.

Step four, transferring: the preform 1, the upper clamp 2 and the lower clamp 3 are taken out of the heating furnace 4, the low-strength end of the preform 1 is clamped by the upper clamp 1 and the lower clamp 3, and the preform is rapidly transferred onto the mold through the cooperation of the lower clamp 3 and the lower mold 7.

Step five, thermoforming: 1) the press machine drives the upper die 6 to move downwards to complete the stamping. 2) And opening the die after maintaining the pressure and quenching for 10 seconds, and taking out the part.

Referring to fig. 6 and 7, through the steps, the strength-variable T-shaped part of B1500HS is obtained, wherein 1-1 is a low-strength end and 1-2 is a high-strength end. One end of the T-shaped part, which is in direct contact with the die, is shaped by die pressure and rapidly quenched, so that the martensite content is high and the strength is high; the T-shaped part is in close contact with one end of the high-temperature upper clamping plate and the end of the high-temperature lower clamping plate, so that the quenching degree is reduced, the martensite content is reduced, and the strength is low.

The embodiment shows that the method provided by the invention can well realize the hot stamping forming of the boron steel variable-strength part and simultaneously meet different strength requirements of different parts.

The above description is of the preferred embodiment of the invention. It is to be understood that the invention is not limited to the particular embodiments described above, in that devices and structures not described in detail are understood to be implemented in a manner common in the art; those skilled in the art can make many possible variations and modifications to the disclosed embodiments, or modify equivalent embodiments to equivalent variations, without departing from the spirit of the invention, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims

1. The indirect hot stamping forming method for the variable-strength part is characterized by comprising the following steps of:

s1, blanking: determining a blank plate according to a part to be formed;

s2, cold forming: performing cold forming on a plate at room temperature to obtain a preformed piece (1) with a size and a shape close to a target size and finish trimming and punching, wherein the preformed piece (1) is provided with a low-strength end and a high-strength end according to use requirements;

s3, heating for austenitizing: placing the preformed piece (1), an upper clamping plate (2) with a profiling structure and a lower clamping plate (3) into a heating furnace (4), wherein the preformed piece (1), the upper clamping plate (2) and the lower clamping plate (3) are spaced from each other, and heating to austenitize the preformed piece (1);

s4, transferring: taking the preformed piece (1), the upper clamping plate (2) and the lower clamping plate (3) out of the heating furnace, clamping the low-strength end of the preformed piece (1) by using the upper clamping plate (2) and the lower clamping plate (3) and transferring the low-strength end to a mold closing die, wherein clamp plate embedding shallow grooves matched with the contour and the thickness of the upper clamping plate (2) and the lower clamping plate (3) are respectively arranged on the lower surface of an upper die (6) and the upper surface of a lower die (7) of the mold closing die;

s5, die assembly and pressure maintaining quenching: and (3) closing the upper die and the lower die to act on the high-strength end of the preformed piece (1), the upper clamping plate (2) and the lower clamping plate (3), maintaining the pressure, quenching for a period of time, opening the die, and taking out the part.

2. The indirect hot stamping forming method for the parts with variable strength according to claim 1, wherein in step S3, the heating temperature of the heating furnace (4) is 900 ℃ to 950 ℃, and the heating and heat preservation time is 3 minutes to 5 minutes.

3. The method for indirectly hot stamping and forming the strength-variable part according to claim 1, wherein in step S4, the pre-formed part (1) is consistent with and attached to the contour of the upper clamping plate (2) and the lower clamping plate (3), and clamping positions are reserved on the upper clamping plate (2) and the lower clamping plate (3) for clamping by a transfer manipulator (5).

4. The indirect hot stamping method for strength-variable parts according to claim 1, wherein the upper die (6) and the lower die (7) are provided with cooling channels.

5. The indirect hot press forming method of a strength-modified part according to claim 1, wherein in step S5, the upper clamping plate (2) and the lower clamping plate (3) have the same thickness as one another.

6. The indirect hot stamping forming method for the strength-variable part according to claim 1 or 5, wherein the upper clamping plate (2) and the lower clamping plate (3) are made of high-temperature alloy and ceramic materials;

the upper clamping plate (2) and the lower clamping plate (3) are manufactured by casting and machining.

7. The indirect hot press forming method for the strength-variable parts according to claim 1 or 5, wherein in step S5, the upper clamping plate (2) and the lower clamping plate (3) take the thermal expansion effect into consideration, and the size and shape at high temperature are consistent with the final formed parts of the preformed member (1).

8. The indirect hot stamping method for a part with variable strength according to claim 1, wherein in step S5, the die is opened 6 to 12 seconds after the pressure maintaining quenching.

9. The indirect hot stamping forming die for the variable-strength part is provided with a low-strength end and a high-strength end according to the use requirement, and is characterized in that the die consists of an upper die (6) and a lower die (7) with pressure maintaining and quenching functions, and clamping plate embedding shallow grooves are formed in the positions, corresponding to the low-strength end of the variable-strength part, of the lower surface of the upper die (6) and the upper surface of the lower die (7);

in the process of closing the hot stamping forming die to carry out hot stamping forming, the upper die (6) and the lower die (7) directly act on the upper end surface and the lower end surface of the high-strength end of the strength-variable part,

and the upper end face and the lower end face of the low-strength end of the variable-strength part are clamped in the middle by an upper clamping plate (2) and a lower clamping plate (3), and the upper clamping plate (2) and the lower clamping plate (3) are respectively embedded into the clamping plate embedding shallow grooves of the upper die (6) and the lower die (7).