KR101028647B1 - Method for manufacturing stainless engine cradle using hydroforming process - Google Patents

Abstract

The present invention relates to a method for producing an engine cradle by hydroforming a 204M high strength stainless steel, the process of cutting a 204M stainless steel sheet to a predetermined size, and a tube for forming the cut stainless steel sheet in a tube shape in a predetermined manner The tubing process, bending the tubing tube by a predetermined press to almost match the shape of the engine cradle, placing the bent tube on a mold having a cavity corresponding to the appearance of the engine cradle, and A hydroforming process is applied that applies a high pressure fluid to expand the tube to correspond with the cavity of the mold.

Engine Cradle, 204M Stainless Steel, Hydroforming, Bending, Welding

Description

Manufacturing method of high strength stainless steel engine cradle using hydroforming {METHOD FOR MANUFACTURING STAINLESS ENGINE CRADLE USING HYDROFORMING PROCESS}             

1 is a 5-stage tube forming example using a press brake method,

Figure 2 is a laser welding JIG Layout for tube laser welding of 63.5mm diameter,

Figure 3 is a mid-sized sedan engine cradle tube bending and hydroforming shape diagram,

4 shows the expansion capacity of a 204M tube for engine cradle manufacture;

5 is a comparison of the bending shape of the conventional material and 204M stainless steel,

6 is an exemplary view of a preforming mold equipped with a ended tube,

7 is a perspective view of the engine cradle hydroforming mold of the present invention,

8 illustrates an example engine cradle final assembled using a 1,6 mmt 204M material, and

9 is a setting example for buckling strength test of 1.6mm stainless engine cradle.

The present invention relates to a method for producing engine cradles of a semi-mid-sized vehicle using a hydroforming method using STS204M, which is a 200 series high-strength structural steel. It is about.

Hydroforming technology is not new at all, and it has been applied and mass-produced for T-fitting molding since the 1960s, and it was only mass-produced in automobile chassis and body parts since the early 1990s. To date, all hydroforming automotive parts have been mass produced using materials such as carbon steel and aluminum, and parts production using high-strength stainless steel is difficult to find.

While automakers are constantly working to increase fuel efficiency through lighter vehicles, they are having trouble securing passenger safety when using lightweight materials such as aluminum and magnesium. Despite the demands of the automotive industry such as light weight, improved safety, and increased warranty, the application of stainless steel structural materials with excellent strength and ductility has not found a starting point other than exhaust system components. The high strength and high ductility of the structural material is particularly represented by austenitic stainless steel, and due to the expensive Ni component, it has several times the material cost compared to general steel used for automobile structural members. At this time, as the research on economical 200-based stainless steels replacing Ni, which is expensive raw material, with Mn and N has been actively conducted, the application of stainless steels in automobile structural materials has been realized.

 Accordingly, the present invention intends to reveal a method of manufacturing engine cradles of semi-medium class vehicles using actual hydroforming method using STS204M material among 200 series stainless steels.

Table 1 shows the components of the 204M material used in the present study, and it can be seen that Mn and N contents are much higher than 301L, which is a representative steel grade of 300-based structural materials. <Table 2> summarizes the mechanical properties of these materials by Gauge variation, and in the case of 204M, it can be seen that the mechanical properties are not significantly different according to the thickness change.

Type C Mn Cr Si S Ni N Md30 301L 0.023 1.68 17.48 0.46 0.004 7.16 0.123 10.3 204M 0.038 9.03 16.28 0.5 0.001 2.97 0.236 32.5

Material Material thickness YS (Kg / mm ² ) TS (Kg / mm ² ) YS / TS El (%) n



204M 1.2 mm 38.6 82.3 0.47 54.7 0.282 1.4mm 38.6 81.6 0.47 54.9 0.281 1.6mm 38.8 81.7 0.47 53.3 0.300 2.0mm 38.0 80.1 0.47 53.8 0.301 2.0mm
(TIG welding) 40.1 83.4 0.48 53.8 0.265 2.0mm
(FCAW welding) 40.5 81.0 0.50 35.9 0.305 2.0mm
(Laser welding) 39.5 81.2 0.49 54.8 0.301


301L 2.0mm 34.4 73.7 0.47 46.5 0.310 2.0mm
(TIG welding) 35.2 74.8 0.47 50.7 0.269 2.0mm
(FCAW welding) 34.4 71.9 0.48 33.8 0.345 2.0mm
(Laser welding) 33.4 73.6 0.45 51.4 0.341

The present invention relates to a method for manufacturing the engine cradle of a semi-mid-size vehicle of the automotive structural parts using such a material, which is usually manufactured using carbon steel, the engine cradle parts using stainless materials generally Nothing has been produced. The production of engine cradle using stainless steel has various differences compared to carbon steel materials, such as the difference of springback degree due to the strength increase, the change of welding characteristics, and the optimization of the hydroforming process. 204M used in the present invention is more than twice the strength of the 38Kg grade steel tensile strength can be reduced in weight and high elongation is a material suitable for hydroforming processing.

The present invention has been made in order to solve the problems described above, by using a hydroforming method of the engine cradle of a sedan without bars made of high-strength stainless material by using a hydroforming method to provide a lightweight, strength and durability improving parts There is this.

In order to solve the above object, the present invention provides a method for producing an engine cradle by hydroforming 204M high strength stainless steel, the process of cutting a 204M stainless steel sheet to a predetermined size, and the cut stainless A tube tube forming process of forming a steel plate into a tube shape in a predetermined manner, a process of bending the tube tube by a predetermined press to almost match the shape of the engine cradle, and matching the bent tube with the appearance of the engine cradle. It is characterized in that it comprises a hydroforming process that is placed on a mold having a cavity to expand and correspond to the cavity of the mold by applying a high pressure fluid therein.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the case where it is determined that the gist of the present invention may be unnecessarily obscured, the detailed description thereof will be omitted.

The present invention relates to a technique for manufacturing engine cradles of sub-medium class sedans using high-strength stainless steel materials having excellent weight and durability. In order to manufacture such a stainless hydroforming part, several pre-processes are required, such as tube forming, bending, and preforming using a stamping press. In the present invention, a laser welding method was used for the tube tube. The tube tube for laser welding uses the tube molding machine by the press brake method. The advantage of this molding method is that the bending molding is applied to the plate without discontinuously passing the roll as compared to the conventional roll forming method. Since the amount of deformation is imposed and is formed by the round rod-type punch, more uniform deformation can be given with respect to the tube length direction. Hereinafter, with reference to the accompanying drawings, an embodiment of a tube, tube, preforming, hydroforming method of high strength stainless steel according to the present invention will be described in detail.

1 shows a tube tube in a press brake manner over five stages. Material for the present invention is STS204M 1.6mm thick material. The upper and lower molds of the tube were made as shown in Fig. 1 for the 63.5mm tube tube. The interval between the both ends of the tube was set to be around 10mm. Thus, the tube was passed through the laser welding JIG having eight rollers as shown in Figure 2 and passed through the welding speed of 4m / min with a 6Kw laser welder was made of a tube of 63.5mm diameter. At this time, the protective gas used is helium (He), and in the high strength 204M stainless steel, when the welding speed is slow, excessive penetration shows the coarsening of the weld and uneven bead formation. . In addition, weldability is also affected by the flow rate of helium gas. In this regard, the welding of stable key hole formation in the STS204M is He 20 liter / min and the welding speed is 4 to 5 m / min. At this time, the appearance of the tube should be free of any defects or defects.

Figure 3 shows the engine cradle shape produced as described above. As a result of the free buldge test to confirm the expandability of the laser welded tube, as shown in FIG. In Figure 3, the tube was subjected to 7-point bending by using a CNC bending machine, and in the case of high-strength stainless steel, the springback is larger than the general steel, and thus the bending angle is set. At this time, the diameter of the bending part should not exceed 10% of the diameter before bending and there should be no performance problem in parallelism and length. Figure 5 compares the bending degree of the existing material and the STS204M It can be seen that the distance between both ends of the tube in the case of STS204M than the existing material. This is related to the inability to be mounted on the hydroforming mold of FIG. 7 due to the springback when the bent tube is subjected to the preforming process as shown in FIG. Preforming refers to tube stamping forming using a press in advance so that the tube can be more easily formed into the final hydroforming shape. This preforming is inevitable for the production of hydroforming engine cradles using high strength stainless steel. That is, the greater the strength of the material and the greater the difference between the initial tube and the final hydroforming final shape, the preforming process is required.

The preformed material is subjected to a final hydroforming process. Tube hydroforming is a molding method in which a material is deformed in a die shape by forcibly injecting a high pressure fluid into the tube after sealing both ends of the tube. Hereinafter, a method of forming a tube hydroforming of high strength stainless steel will be described in detail.

Sealing is important for hydraulic leakage at both ends of the tube, and the thinning area of the material by axial feeding of both ends of the tube as the molding progresses to prevent material thinning due to hydroforming molding. To prevent breakage. In summary, in the case of fixing the both ends of the tube with a mold and injecting a high pressure fluid into the inside of the bent tube to perform high pressure hydraulic molding to the same shape as the mold, punches are inserted at both ends of the tube to expand the inner diameter. And the step of pressing the edges of both ends of the expanded tube to fix it between the mold and the punch, and injecting fluid into the bent tube to reach the final shape. First, in order to fix both ends of the tube with a mold includes a lower mold and another upper mold of FIG. The lower mold is fastened to the bed of the press and the upper mold is fastened to the lower part of the press ram so that the blank pressing force is set to 4000 tons or more for molding. At both ends of upper and lower molds, it is necessary to dig a semicircle groove in the same shape as the punch so that a punch can be inserted for sealing from the press, and the length of the semicircle groove should be at least 150mm. The lubricant should be prepared so that the coefficient of friction between the tube and the mold is at most 0.1 and below. The punch is operated by a hydraulic system and there is a hollow inside the punch, through which fluid is injected into the material tube.

With the raw material tube mounted in the semi-circular groove of the lower die and the upper die moved downward to clamp the raw material tube, the stroke of the hydraulic system is elongated so that the punch moves toward the end of the raw material tube. The end of the punch is inserted into the end of the raw material tube. In this state, if the punch continues to move in the middle direction of the raw material tube, the end of the raw material tube is expanded and the mold and the tube end are bitten and fixed. In this state, the high pressure fluid is continuously injected into the material tube through the hollow of the punch. The tube internal pressure for forming the STS204M is in the range of 1600 ~ 1800bar. At this time, both ends of the tube should be minimized through thinning of the tube by axial feeding. In this state, the high pressure fluid through the hollow causes the material tube to swell and to be molded until the material adheres to the upper and lower molds (Calibration). At this time, the press reaches the maximum pressure. The pressure is then removed and the press is operated to raise the upper die. The product is taken out and cleaned for assembly for the final part. High pressure method with axial material supply is important for manufacturing stainless steel engine cradle. In this case, stainless steel material with large springback phenomenon can maintain the final part shape through high pressure molding. Important consideration in the hydroforming design is the radius of the bending portion (radius) when manufacturing the engine cradle of the present invention the minimum radius should be at least four times the material thickness 1.6mm.

8 is an example of a final part assembled using a tube manufactured by hydroforming as described above. The attached JIG was assembled by welding the SAPH370 jig to the STS204M tube using MAG welding using Ar (80%) and CO2 (20%) protective gases. In this case, the welding condition is 180A, 20V, and the protective gas flow rate is 18 liter / min. Using the final parts manufactured as described above, the buckling strength was measured as shown in FIG. 9 and compared with the parts using 2mm general steel materials. As for the SAPH370 2mm thick material, the buckling strength was 4066Kgf and the STS204M 1.6mm material In the case of 20% weight reduction, the buckling strength was not significantly different to 3704kgf.                     

Apparently, there are many ways to modify these embodiments while remaining within the scope of the claims. In other words, there may be many other ways in which the invention may be practiced without departing from the scope of the following claims.

The engine cradle of the semi-medium size sedan using the high-strength austenitic stainless steel of the present invention is excellent in bending property, weldability, and buckling strength, and can be lightened at the same time, thereby showing the possibility of using high strength stainless steel as an automobile structural component. In addition, the high-strength STS204M of the present invention is rich in ductility, there is an advantage that the engine cradle of the desired shape can be safely manufactured with less resistance to breakage due to lower molding limit during hydroforming in the existing materials.

Claims (2)

A method for hydroforming a 204M high strength stainless steel to make an engine cradle, Cutting the 204M stainless steel sheet to a certain size; A tube tube forming step of forming the cut stainless steel sheet into a tube shape by a press brake method; Forming a tube by welding both ends of the formed tube shape with a protective gas at a content of 20 liter / min and a welding speed of 4-5 m / min; Bending the formed tube by a predetermined press to match the shape of the engine cradle; And And placing the bent tube on a mold having a cavity corresponding to the appearance of the engine cradle and applying a high pressure fluid therein to expand the tube to correspond with the cavity of the mold. The internal pressure of the tube is 1600 ~ 1800bar, wherein both ends of the tube is 25mm high strength stainless steel engine cradle manufacturing method using hydroforming, characterized in that to minimize the thinning of the tube through the axial forced supply by 25mm. delete

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