KR100520213B1 - The Manufacturing Method of Tailed Weld Blank Parts Excellent in Welding Properties for Automobile Door - Google Patents

Abstract

The present invention cuts two or more homogeneous and dissimilar steel sheets into a certain size and welds them according to the purpose to produce tailored weld blanks (TWB, hereinafter referred to as TWB) for automobile doors, which are excellent in welding quality in the manufacturing process of automobile parts processing. A method for manufacturing parts. The present invention through laser welding can produce a tailored welded blank product having a melt width of less than 120% and a penetration rate of 70% or more.

Description

The manufacturing method of Tailed Weld Blank Parts Excellent in Welding Properties for Automobile Door}

The present invention is to cut the steel plates having different materials and thicknesses different from each other according to the characteristics of the parts in order to manufacture the automotive parts, such as cutting the cloth to match and weld using a laser for use in forming automotive parts It relates to a method for producing a tailored welded blank steel sheet for automobiles. In particular, the present invention relates to a method for manufacturing a TWB (Tailored Weld Blank) product having excellent welding quality of a welded part of an automobile part.

Conventionally, laser welding technology is used to improve the quality of welded parts, but there are many variables that need to be controlled in proportion to the effect, and various conditions in cutting and welding process, especially steel grade condition, welding output, welding allowance interval. In the case of welding speed, laser focal radius, melting width after laser welding, penetration rate, etc., the combination of various laser beam conditions and working conditions could not be achieved.

Therefore, the present invention cuts two or more kinds of different and different steel sheets into a certain size, welds according to the purpose, grasps all the physical properties in the manufacturing process of automobile parts, and finds suitable conditions for automobile doors having excellent welding quality. Tailored Weld Blank (TWB) The purpose is to provide a method for manufacturing parts.

Accordingly, the present invention cuts two or more homogeneous and dissimilar steel sheets into a certain size and welds them to a purpose, thereby tailoring welded blanks (TWB) for automobile doors having excellent welding quality in the manufacturing process of automobile parts processing. In particular, the present invention relates to a method for manufacturing parts, in particular, the present invention enables the production of a tailored welded blank product having a melt width of less than 120% and a penetration rate of 70% or more.

The present invention will be described in more detail.

In general, the TWB process is largely divided into a cutting process of cutting a steel sheet manufactured in a thin plate form, a welding process of welding the cut steel sheet, and a blanking process of blanking the welded steel sheet.

The blanked material is molded into parts of the automobile company and assembled into the vehicle body. The cutting process of the TWB process is a simple process but one of the very important processes. The reason for this is that the TWB technology is capable of welding different thicknesses and different types of steels, and also uses laser as a welding source.

The cut surface of the steel plate is largely composed of four. The initial upper face where the cut is applied is plastically deformed and the next cut creates a shear plane and a fracture plane just below the shear plane. And finally, burrs are created when the material is pushed or torn. If the cut surface is not uniform in this way, the welding defects are generated when the laser welding is performed with two different thicknesses of steel sheets. If the laser welding is not good, the cut surface process is very important because the welding part breakage in the part forming process.

Next is the laser welding process. A laser is a beam of intense energy, such as an electron beam. Laser welding has a large welding speed, a deep penetration depth, welding at any part, and a small range of deformation due to heat and a wide range of flexibility. The laser welding power source uses CO ₂ and welds by adjusting welding speed, laser power, laser focal radius and position. Laser welding requires proper parameter adjustment to be applied to sheet steel.

Table 1 shows the welding conditions in general IF steel and high tensile steel. When a laser beam focused on a workpiece by a mirror or lens is irradiated onto the surface of the steel sheet, some beams are absorbed at the surface portion. The absorbed beam is converted into thermal energy, causing localized heating and melting of the steel sheet. At this time, heat is transferred to the inside of the object, and the molten portion is expanded, so that the weld section of the molten portion is affected by thermal conductivity. If the steel sheet has a high output density of the irradiated beam, vaporization and sublimation occur, thereby forming a key hole of 0.2-1 mm. When the keyhole is generated, the penetration depth is larger than the width, and the weld hole is surrounded by the molten metal around the welded portion. In other words, the keyhole is generated as a single tube to weld the steel plate while moving in the welding direction.

The laser beam radius and the focal radius are inversely related to each other. The larger the laser beam radius, the lower the energy density at the focal radius. The smaller the laser beam radius, the higher the energy density at the focal point. The basis for judging the weld weld goodness in the welding using a laser beam includes weld weld shape (depth of penetration, weld cross section, front and rear weld beads), weld defect, steel sheet weld microstructure, and the like. The variables affecting these judgments are greatly influenced by the laser's own variables, process variables generated in the work lamp, and the welding materials used. Laser itself parameters include laser beam power, focal radius, and beam mode. Divergence angle. Process variables generated during operation include welding speed, focus position, and plasma gas. In welding materials, the state of the cut surface, the surface state, and the shape of the joint are important factors in preparation of the joint of the used material.

The laser focal radius is related to the focusing intensity of the laser beam. The smaller the focal radius, the better, but it is related to the allowable spacing of the two steel plates, which should generally be larger than the allowable spacing.In consideration of the welding quality, the laser beam focal radius is better than the allowable spacing of the two steel sheets because welding quality is excellent under the allowable spacing of 1.5mm or less. Increase the upper limit to 1.5mm and work. In addition, the allowable spacing between the two steel sheets is 0.5mm or less, especially 0.2mm or less. If the welding allowance interval is larger than 0.5mm, the penetration amount is small, and the weld bead top and bottom bend sag, which reduces the weld quality. An object of the present invention is to develop a TWB product having excellent welded quality. In order to improve the quality of the weld, the various factors described above must be optimally controlled.

When welding different thicknesses and steel grades with a laser to be applied to a car door, the welding part is the most sensitive area to be broken in the pressing process. Therefore, the TWB technology that manufactures the weld width and penetration rate within a standard value is a laser beam radius and a focal radius. It is a technology that can be molded without breaking the car body part door by adjusting the.

1 is a diagram showing the melt width and penetration rate in the present invention.

Welding conditions must be optimized to meet the requirements of melt width and penetration rate. Since TWB is a technology for welding different thicknesses and different types of steels, it is possible to obtain excellent weldability only by setting welding conditions according to each thickness and steel type.

( Example

An embodiment of the present invention will be described with reference to the accompanying drawings and Tables 1-3.

In general, the weld evaluation items are evaluated according to the following Table 1. According to the present invention, the welding part evaluation items are set in Table 1 below according to the conventional standard, and accordingly, the welding conditions as shown in Table 2 were given and tested.

In addition, in the present invention, the welding conditions were set, tested, and evaluated as shown in Tables 2 and 3 to control the melt width and penetration rate of the welded portion.

Here, the melt width ratio is expressed as a percentage by dividing the maximum width of the melted portion by the thickness of the sheet, and the unmelted portion is the portion where the butt face is not melted. The penetration rate is expressed as a percentage by dividing the minimum thickness of the melted portion by the sheet thickness. The plate strain is expressed as a percentage by dividing the step difference between the thicknesses. The maximum load is expressed as the product of thickness and width multiplied by the tensile strength obtained after the tensile test. In other words, the contents described above are expressed as follows.

Melt width ratio = (melt width / thickness) x 100

Penetration rate = (melt thickness / sheet thickness) x 100

Sheet strain rate = (step / sheet thickness) x 100

Maximum load = tensile strength obtained after tensile test x thickness x test width

Ericsson punch height = the maximum punch height from the Ericsson test to material determination

2 illustrates a tailored weld blank apparatus in one embodiment. First, when the steel sheet cut into the desired shape enters the direction of the arrow, the SOUKA seam roller is driven and adjusted to the welding allowance interval, and the allowable gap between the different thicknesses is used in the SOUVIS1 surface detector. Check the condition. The entering steel sheet is inspected by the laser beam and the welded part in Subvis 2, the vertical weld state, and finally the weld bead and the final weld state in Subvis 3. The laser head is stationary so that the height of the beam scanned is 200 mm.

X, Y, Z three axes are used to control the scan center at the center of different thickness. The welding line and X axis are parallel, the laser beam and Z axis are parallel, and the welding line and Y axis are vertical. Therefore, the Z-axis moves up and down to adjust the focal radius of the actual laser beam scanned to the weld. The Z-axis depends on the thickness of the material. Set it to 0.2 ~ 1.5mm in consideration of the welding quality. In general, the laser output, welding speed, laser focal radius and welding allowance have the most influence on the welding quality in the laser self and process variables. When the laser output was lower than the lower limit of 5.2kW, the welding efficiency decreased, and the welding was not performed. If the upper limit was higher than 6.8kW, the weld was over welded and the welding bead became large. The welding speed is related to the efficiency of thermal energy reaching the welding part during welding, such as the laser output. It was also confirmed that the welding speed was less than 6mpm and the laser beam scanned in the welding part stayed for a long time to increase the penetration amount of the welding part, and when the welding speed was faster than 9mpm, the penetration amount was small and the welding was not good.

Table 2 shows the welding conditions by steel type and steel plate thickness in the TWB process. Table 3 shows the results of evaluation of melt width and penetration rate by steel type and steel plate thickness after laser welding in TWB process.

Based on the results of the long-term test according to the above welding conditions and the welding results of the following Table 3, the welding method for manufacturing the TWB parts is welded. The welding allowable spacing during the laser welding is 0.2 mm or less, especially 0.03 mm or less. The welding power is 5.2 ~ 6.8Kw, the focal laser focal radius is 1.5mm or less, and the welding speed is accelerated slowly as the thickness difference of the two steel sheets to be welded is increased, but it is adjusted to 6 ~ 9mpm, so that the melting width is 120% or less, We found that penetration rate of 70% or more and sheet deformation rate of 10% or less can be satisfied. Especially, in the case of homogeneous steel sheet, welding allowance gap 0.03mm or less, welding power 6.0Kw or less, and laser focal radius 0.35mm or less are the best results. It was revealed. In addition, the welding speed is slower according to the thickness difference between the two steel plates as described above, but the welding speed is 7.7-8.8mpm when the thickness difference between the two steel sheets to be opposed to less than 0.3mm, the welding speed 7.5 when the thickness difference is more than 0.3mm and less than 0.5mm Welding speed 7.2 ~ 8.0mpm when thickness difference is more than 0.5mm and less than 0.7mm, welding speed 6.5 ~ 7.3mpm when thickness difference is more than 0.7mm and less than 0.9mm, and welding speed is generally 6.0 when thickness difference is more than 0.9mm It was confirmed that setting to ~ 6.5mpm yields the best results.

If the welding speed is lower than the lower limit, the productivity will be lowered. If the welding speed is lower than the upper limit, welding failure will result. Moreover, these ranges could achieve 120% or less of the melt width rate, 90% or more of penetration rate, and 1% or less of sheet strain.

The molten part of the weld part should be minimized since it has a higher hardness than the base metal and degrades moldability. Material Nos. 1 to 6 are comparative materials of the present invention and are materials that will cause deterioration in workability because the melt width does not satisfy the prescribed condition of 120% or less. Material No. 7 to No. 10, which is the material of the present invention, satisfies all of the regulatory conditions, and thus the weld quality is excellent, and thus, the workability is advantageous.

Figure 3 shows an enlarged photograph of the welded section of the test material Nos. 7 to 10 of the present invention tested according to the laser welding conditions of Table 2. As can be seen here, it can be seen that the welding state of the weld shown in the weld photograph is very uniform and good.

According to the present invention, by adjusting the laser welding conditions for each steel type in the TWB facility and appropriately adjusting the cutting surface and other processes, the manufacturing of the tapered welded parts having excellent weldable quality can be processed without deterioration of the welded part quality during the molding process of the automobile company. A method could be provided.

1 is an explanatory view of the melt width and penetration rate calculation according to the present invention

2 is an explanatory diagram of a tailor weld related device through laser welding of different steel sheets;

3 is a cross-sectional photograph of a welded part according to laser welding conditions.

Claims (2)

In the laser welding method for manufacturing a tailored welded blank (TWB) component for an automobile door, the welding allowable spacing between two steel sheets to be welded during the laser welding is 0.2mm or less, welding output 5.2 ~ 6.8Kw, laser focal radius 1.5mm The welding conditions are set below. In particular, in case of homogeneous steel, the welding allowance interval is 0.03mm or less, welding power is 6.0Kw or less, laser focal radius is 0.35mm or less, and the welding speed is welded. The larger the method, the slower the welding speed but the 6 ~ 9mpm to adjust the melt width rate 120% or less, melt rate 70% or more, sheet strain 10% or less to satisfy the TWB manufacturing method characterized in that According to claim 1, The welding speed according to the difference between the two steel plate thickness is less than 0.3mm welding speed 7.7 ~ 8.8mpm, the thickness difference is greater than 0.3mm welding speed 7.5 ~ 8.5mpm, 0.3mm or less Welding speed is 7.2 ~ 8.0mpm when more than 0.5mm and less than 0.7mm, thickness difference is more than 0.7mm and less than 0.9mm, welding speed is 6.5 ~ 7.3mpm, and thickness difference is more than 0.9mm when welding speed is set to 6.0 ~ 6.5mpm. Method for manufacturing a TWB part characterized in that