JP7059665B2 - Material property data calculation method, material property data calculation program, and material property data calculation device - Google Patents

Description

The present invention relates to the calculation of material property data in a spot welding simulation, and more particularly to the calculation of material property data that enables appropriate analysis simulation in spot welding in which different materials are combined.

Spot welding is widely used for joining metal materials together in various industrial parts such as automobile bodies. In recent years, for example, steel sheets used for automobile bodies include mild steel sheets, high-strength steel sheets, hot-stamped steel sheets, and the like, and welding is often performed by combining different types of steel sheets of various strengths.

In such spot welding, it is possible to determine the optimum value while confirming the welding conditions and joint strength by actually welding, but doing so takes time and effort. Therefore, in recent years, FEM analysis simulation has been effectively used for studying welding conditions and joint strength.

For example, Non-Patent Document 1 discloses a spot welding analysis system based on an incremental coupled analysis method of an electric field-temperature field-stress field. According to this, it is possible to accurately estimate the weld nugget formation for the plated steel sheet and further predict the occurrence of spatter in which the molten metal is scattered outside the steel sheet.

Non-Patent Document 2 discloses a method of deriving material property data set in a room temperature tensile strength analysis of a spot welded joint by using a melted portion mixing ratio calculated by a spot weld simulation. According to this, the fracture of the spot welded joint can be predicted with high accuracy.

Patent Document 1 discloses a technique for predicting spatter generation from the pressure applied to a steel sheet and the contact pressure of the pressure contact portion at the interface of the steel sheet. According to this, it is possible to predict the occurrence of spatter, and it is possible to obtain welding conditions that improve the energy efficiency required for welding while maximizing the strength of the welded portion.

Fukumoto, Okamura, Fukui, "Development of High-precision Spot Welding CAE Technology for Steel Sheets for Automobiles", Preprints of the 2006 Spring Academic Lecture Meeting of the Society of Automotive Engineers of Japan, No. 74-06, (2006) Ueda, Fukumoto, Nakayama, "Development of Fracture Prediction Technology for Different Thick Plates Using Welding Simulation", Proceedings of the Society of Automotive Engineers of Japan, Vol. 46, No. 3, (2015)

Japanese Unexamined Patent Publication No. 2007-283328

However, Non-Patent Document 1 and Patent Document 1 do not consider sharing of material property data of molten nuggets for the case of welding by combining dissimilar steel materials.

As described above, Non-Patent Document 2 discloses a method of deriving material property data set in the room temperature tensile strength analysis of a spot welded joint by using the melted portion mixing ratio calculated by the spot weld simulation.
Here, the spot welding simulation is a temperature-dependent FEM analysis simulating the energization heating process and the cooling process of spot welding by an electric field-temperature field-stress field coupled analysis. On the other hand, the room temperature tensile strength analysis of a spot welded joint is an FEM analysis under normal temperature conditions simulating a tensile test of a spot welded joint after welding.
Therefore, Non-Patent Document 2 does not describe a method of using the melted portion mixing ratio in the spot welding simulation.

Since the material is melted almost uniformly in the molten nugget, it is originally desirable to use one shared material property data as the molten nugget. However, in the conventional technique, such sharing is not achieved, so that the inside of the molten nugget is analyzed with the material property data of each different type of steel sheet constituting the welded portion, which may cause a difference from the actual situation. be.

Therefore, in view of the above problems, it is an object of the present invention to provide a material property data calculation method capable of obtaining an appropriate analysis result even when a spot welding simulation is performed on materials of different materials. Further, a material property data calculation program for that purpose and a material property data calculation device are provided.

The ratio of the steel plate constituting the welded portion in the molten nugget (melted portion mixing ratio) varies depending on the type of combined material and welding conditions, and is not simply determined by the plate thickness ratio of the steel plate. For example, as described in Non-Patent Document 2, it is known that a high-strength material has a higher electrical resistivity than a mild steel material, a faster growth of a molten nugget, and a higher melting portion mixing ratio.
Therefore, as a result of diligent studies, the inventor derived material property data of the molten nugget from the molten volume ratio calculated in the analysis of the energization heating process of spot welding, and utilized it for temperature-dependent stress analysis in the cooling process of spot welding. The present invention was completed by embodying this idea. Hereinafter, the present invention will be described.

One aspect of the present invention is a method of calculating material property data in a numerical analysis simulation simulating an integrated process from heating, melting, and cooling in spot welding in which materials of different materials are joined, and is a method of calculating material property data. In the melting process, the liquid phase ratio calculation process that calculates the maximum liquid phase ratio from the temperature, solid phase line, and liquid phase line of the material, and the melt nugget volume for each material are calculated from the maximum liquid phase ratio to obtain the melt mixing ratio. A material characteristic data calculation method including a melt mixing ratio calculation process and a melt nugget material characteristic data calculation process for calculating the material characteristic data of the molten nugget used in the cooling process from the melt mixing ratio and the material characteristic data for each material. Is.

Another embodiment of the present invention is a program for calculating material property data in a numerical analysis simulation simulating an integrated process from heating, melting, and cooling in spot welding in which materials of different materials are joined. In the melting process, the liquid phase ratio calculation step to calculate the maximum liquid phase ratio from the temperature, solid phase line, and liquid phase line of the material, and the melt nugget volume for each material are calculated from the maximum liquid phase ratio to obtain the melt mixing ratio. A material property data calculation program including a melt mixing ratio calculation step and a melt nugget material property data calculation step for calculating the material property data of the melt nugget used in the cooling process from the melt mixing rate and the material property data for each material. Is.

Another embodiment of the present invention is a device for calculating material property data when performing a numerical analysis simulation simulating an integrated process from heating, melting, and cooling in spot welding in which materials of different materials are joined, and the program is used. It is provided with a stored storage means, a calculation means that performs a calculation based on a program, and a display means that displays the result calculated by the calculation means. In the calculation means, the temperature of the material in the heating and melting process, The maximum liquid phase ratio is calculated from the solid phase line and the liquid phase line, the melt nugget volume for each material is calculated from the maximum liquid phase ratio, the melt mixing ratio is obtained, and the cooling process is performed from the melt mixing ratio and the material property data for each material. It is a material property data calculation device that calculates the material property data of the molten nugget used in the inside.

According to the present invention, even when a spot welding simulation in which materials of different materials are joined is performed, it is possible to obtain material property data in which the material properties in the molten nugget are shared into one, so that more appropriate analysis results can be obtained. Obtainable.

It is a schematic diagram explaining the scene of spot welding and the molten nugget formed at this time. It is a figure which showed the flow of the spot welding simulation method including the material property data calculation method. It is a figure explaining the structure of the material property data calculation apparatus. It is a figure which shows the result of an Example. It is a figure which shows the result of the comparative example.

FIG. 1 is a cross-sectional view schematically showing a scene of spot welding and a welded portion during spot welding. Here, a scene is shown in which two steel plates 10 and 11 of different types are stacked, sandwiched between two electrodes 1 from one side and the other side, and spot welded. Here, the portion shown by A in FIG. 1 is a molten portion (melted nugget).
Such spot welding itself is known, and a plurality of materials to be welded are stacked, and the material is energized while being sandwiched between two electrodes and pressed. The form shown below relates to the simulation of the spot welding.

FIG. 2 shows the flow of the spot welding simulation method S1. The spot welding simulation method S1 includes a material property data calculation method S10.

The spot welding simulation method S1 includes an energization heating process S2 and a cooling process S3 for performing temperature-dependent stress analysis. Therefore, the spot welding simulation method S1 is a simulation simulating an integrated process of pressing a steel material to heat, melt, and cool it. The simulation is preferably performed by so-called FEM (finite element) analysis, and therefore is performed by an analysis model divided into minute elements (mesh) of appropriate size.
And in this embodiment, the spot welding simulation method S1 is performed by the coupled analysis of the electric field-temperature field-stress field as a whole. Such coupled analysis is known, and for example, the method described in Non-Patent Document 1 can be adopted.

In this embodiment, the spot welding simulation method S1 includes the material property data calculation method S10. By this calculation, the material property data in the molten nugget can be optimized.
As can be seen from FIG. 2, the material property data calculation method S10 includes a liquid phase ratio calculation process S11, a melt mixing rate calculation process S12, and a melt nugget material characteristic data calculation process S13.
Each process will be described below.

In the energization heating process S2, heating conditions are applied to a plurality of overlapping steel materials of different types so as to reproduce spot welding, and a simulation regarding the formation of a molten nugget is performed.

The liquid phase ratio calculation process S11 is included in the energization heating process S2 and is a process for calculating the maximum liquid phase ratio. The maximum liquid phase ratio is calculated from the temperature of the materials of the steel plates 10 and 11, the solid phase line, and the liquid phase line. In the energization heating process S2, the maximum value is stored for each element (mesh element).

After the analysis of the energization heating process 2 is completed, the melt mixing ratio calculation process S12 calculates the volume of the molten nuggets of the steel plates 10 and 11 from the maximum liquid phase ratio calculated in the liquid phase ratio calculation process S11, and the melt mixing ratio is calculated. Is the process of finding.
For each of the steel plates 10 and 11, the volume is multiplied by the maximum liquid phase ratio for each element (mesh element), and the total of the elements (mesh elements) in the molten nugget portion is taken as the volume of the molten nugget.
Regarding the melt mixing ratio R, when the melt nugget volume on the steel sheet 10 side is V ₁ and the melt nugget volume on the steel plate 11 side is V ₂ , the melt mixing ratio R ₁ on the steel plate 10 side is V ₁ / (V ₁ ). + V ₂ ), the melt mixing ratio R ₂ on the steel sheet 11 side is obtained by V ₂ / (V ₁ + V ₂ ).

The molten nugget material characteristic data calculation process S13 is a process of calculating the material characteristic data of the molten nugget before the stress analysis in the cooling process S3. The material data calculated here is used for stress analysis in the next cooling process S3.
Material property data of the molten nugget include temperature-dependent stress-strain relationship, thermal conductivity, density, specific heat, and coefficient of linear expansion. On the other hand, in the molten nugget material characteristic data calculation process S13, each material characteristic data is obtained by linear mixing approximation from the material characteristic data of each steel sheet using the melt mixing ratio obtained in the melt mixing ratio calculation process S12.
For example, the thermal conductivity λ of the molten nugget is λ ₁ × R ₁ + λ ₂ × R ₂ . Here, λ ₁ is the thermal conductivity of the steel sheet 10, and λ ₂ is the thermal conductivity of the steel sheet 11. Similarly, other material property data such as temperature-dependent stress-strain relationship, density, specific heat, and coefficient of linear expansion are also calculated based on the melt mixing ratio.

In the cooling process S3, a temperature-dependent stress analysis is performed on the molten nugget obtained in the energization heating process S2. At this time, whether or not it is a molten nugget is determined from the maximum liquid phase ratio of the element (mesh element) to be calculated, and the material characteristic data obtained in the molten nugget material characteristic data calculation process S13 is applied as necessary. For example, if the maximum liquid phase ratio is 0.8 or more, it is determined to be a molten nugget, and the element (mesh element) is calculated using the material characteristic data obtained in the molten nugget material characteristic data calculation process S13.

According to the spot welding simulation method S1 as described above, even when a spot welding simulation in which materials of different materials are joined is performed by the material property data calculation method S10 included therein, one material property in the molten nugget is shared. Since the material property data can be obtained, more appropriate analysis results can be obtained.
When performing a spot welding simulation in which materials of different materials are joined, it is desirable to use the material property data shared as the molten nugget because the inside of the molten nugget is melted almost uniformly. If sharing is not achieved, the inside of the weld nugget will be analyzed using the material property data of each steel plate constituting the weld nugget, which may differ from the actual situation. Specifically, the stress distribution differs depending on the element corresponding to each steel plate in the nugget, and the continuity of the stress contour diagram is impaired. On the other hand, according to the above-mentioned material property data calculation method S10, one shared material property data can be used in the molten nugget, and the stress contour diagram in the nugget can be continuously obtained to obtain an appropriate analysis result. ..

FIG. 3 is a diagram conceptually showing the configuration of the material property data calculation device 20 according to one form in which a specific calculation is performed according to the spot welding simulation method S1 described above. The material property data calculation device 20 includes an input unit 21, an arithmetic unit 22, and a display unit 28. The arithmetic unit 22 includes an arithmetic unit 23, a RAM 24, a storage unit 25, a receiving unit 26, and an output unit 27. Further, the input means 21 includes a keyboard 21a, a mouse 21b, and an external storage device 21c that functions as one of the storage media.

The arithmetic means 23 is configured by a so-called CPU (central operator), and is a means that can be connected to each of the above-mentioned constituent members and can control them. Further, various programs 25a stored in the storage means 25 or the like functioning as a storage medium are executed, and based on this, data generation for each process of the spot welding simulation method S1 described above and data selection from the steel material database 25b are performed. It is also the calculation means 23 that performs the calculation as a means of performing the calculation.

The RAM 24 is a component that functions as a work area of the arithmetic means 23 and a temporary data storage means. The RAM 24 can be composed of an SRAM, a DRAM, a flash memory, or the like, and is the same as a known RAM.

The storage means 25 is a member that functions as a storage medium for storing programs and data that are the basis of various operations. Further, the storage means 25 may be able to store various intermediate and final results obtained by executing the program. More specifically, the storage means 25 stores (stores) the program 25a and the steel material database 25b. In addition, other information may also be stored.

Here, the stored program includes a welding simulation program that is a basis for calculating each process of the spot welding simulation method S1 described above. That is, the welding simulation program includes an energization heating process calculation step and a cooling process calculation step for performing temperature-dependent stress analysis so as to correspond to the flow of FIG. The specific calculation contents of this program are as described in the above-mentioned spot welding simulation method S1.

The welding simulation program further includes a material property data calculation program that is a basis for specifically calculating the material property data calculation method S10. Therefore, the material property data calculation program corresponds to the liquid phase ratio calculation process S11, the melt mixing rate calculation process S12, and the melt nugget material property data calculation process S13, and corresponds to the liquid phase ratio calculation step, the melt mixing rate calculation step, and the melting. It has a nugget material property data calculation step. The specific calculation contents of this program are as described in the above-mentioned spot welding simulation method S1.

The steel material database 25b is a database in which each characteristic such as a physical property value related to the steel material is stored. This database provides the program with the necessary data as requested by the program.

The receiving means 26 is a component having a function for appropriately incorporating information from the outside into the arithmetic unit 22, and the input means 21 is connected to the receiving means 26. This includes so-called input ports, input connectors, and the like.

The output means 27 is a component having a function of appropriately outputting information to be output to the outside among the obtained results, and a display means 28 such as a monitor and various devices are connected thereto. This includes so-called output ports, output connectors, and the like.

The input device 21 includes, for example, a keyboard 21a, a mouse 21b, an external storage device 21c, and the like. Known keyboards 21a and mice 21b can be used, and the description thereof will be omitted.
The external storage device 21c is a known externally connectable storage means, and also functions as a storage medium. Various required programs and data can be stored here without particular limitation. For example, the same program and data as the above-mentioned storage means 25 may be stored here.
As the external storage device 21c, a known device can be used. Examples thereof include CD-ROMs and CD-ROM drives, DVDs and DVD drives, hard disks, various memories, and the like.

In addition, information may be provided to the arithmetic unit via the receiving means 26 via a network or communication. Similarly, information may be transmitted to an external device via the output means 27 via a network or communication.

According to such a material property data calculation device 20, the spot welding simulation method S1 described above can be performed efficiently and accurately. As the material property data calculation device 20, for example, a computer can be used.

Hereinafter, the material property data calculation method according to the present invention will be described in more detail by way of examples.

As for the combination of steel sheets to be evaluated, the first material is a 980 MPa class steel sheet with a plate thickness of 2.0 mm (hereinafter sometimes referred to as "980 material"), and the second material is a 590 MPa class steel sheet with a plate thickness of 1.0 mm. (Hereinafter, it may be referred to as "590 material".)
The welding conditions were that the pressing force by the electrodes was 4.9 kN, the energizing current for heating was 7 kA, the energizing time was 16 cycles (frequency 60 Hz), and the holding time was 40 cycles. For the simulation, FEM analysis simulation was performed for the integrated process from energization heating to cooling process of spot welding by coupled analysis of electric field-temperature field-stress field. The results are shown in FIGS. 4 and 5.

FIG. 4 is the result of the example, and is the stress distribution after the completion of the cooling process as a result of the analysis using the material property data calculation method S10. From the analysis result of the energization heating process, the melt mixing ratio was R ₁ : 590 material R ₂ = 0.749: 0.251 of 980 material. Using this melt mixing ratio, each material property data of temperature-dependent stress-strain relationship, thermal conductivity, density, specific heat, and linear expansion coefficient is calculated, and these are used as material property data in the melt nugget for stress analysis of the cooling process. And obtained the contour shown in FIG. This contour shows that the stress increases as the density increases.
As a result, as can be seen from FIG. 4, the stress contours in the molten nugget are continuous, and an appropriate analysis result can be obtained.

On the other hand, FIG. 5 is a result of a comparative example, and is a contour of the stress distribution after the completion of the cooling process as a result of analysis without using the material property data calculation method S10.
As a result, as can be seen from FIG. 5, although the inside of the molten nugget is melted almost uniformly, the stress contours appearing in the molten nugget become discontinuous, and the analysis result is different from the actual one.

1 Electrode 10 Steel 11 Steel 20 Material characteristic data calculation device 21 Input means 22 Calculation device 23 Calculation means 25 Storage means 28 Display means A Molten nugget S1 Spot welding simulation method S2 Energization heating process S3 Cooling process S10 Material characteristic data calculation method S11 Liquid Phase ratio calculation processing S12 Melting mixing ratio calculation processing S13 Melting nugget material characteristic data calculation processing

Claims (3)

It is a method to calculate material property data when performing temperature-dependent numerical analysis simulation simulating an integrated process from heating, melting, and cooling in spot welding where materials of different materials are joined.
The liquid phase ratio calculation process for calculating the maximum liquid phase ratio from the temperature of the material, the solid phase line, and the liquid phase line in the heating and melting processes, and
The melt mixing ratio calculation process for calculating the melt nugget volume for each material from the maximum liquid phase ratio and obtaining the melt mixing ratio,
From the melt mixing ratio and the temperature-dependent stress-strain relationship, heat conductivity, density, specific heat, and linear expansion coefficient for each material, the temperature-dependent stress-strain relationship and heat conduction of the melt nugget used in the cooling process. Including molten nugget material property data calculation processing to calculate rate, density, specific heat, linear expansion coefficient ,
Material property data calculation method. It is a program that calculates material property data when performing temperature-dependent numerical analysis simulation that simulates the integrated process from heating, melting, and cooling in spot welding that joins materials of different materials.
The liquid phase ratio calculation step of calculating the maximum liquid phase ratio from the temperature of the material, the solid phase line, and the liquid phase line in the heating and melting processes, and
The melt mixing ratio calculation step of calculating the melt nugget volume for each material from the maximum liquid phase ratio and obtaining the melt mixing ratio,
From the melt mixing ratio and the temperature-dependent stress-strain relationship, heat conductivity, density, specific heat, and linear expansion coefficient for each material, the temperature-dependent stress-strain relationship and heat conduction of the melt nugget used in the cooling process. Includes a molten nugget material property data calculation step to calculate the rate, density, specific heat, and linear expansion coefficient .
Material property data calculation program. It is a device that calculates material property data when performing temperature-dependent numerical analysis simulation that simulates the integrated process from heating, melting, and cooling in spot welding that joins materials of different materials.
The storage means in which the program was stored and
An arithmetic means that performs an operation based on the program and
A display means for displaying the result calculated by the calculation means is provided.
In the calculation means,
The maximum liquid phase ratio is calculated from the temperature of the material, the solid phase line, and the liquid phase line in the heating and melting processes.
The melt nugget volume for each material was calculated from the maximum liquid phase ratio to obtain the melt mixing ratio.
From the melt mixing ratio and the temperature-dependent stress-strain relationship, thermal conductivity, density, specific heat, and coefficient of linear expansion of each material, the temperature-dependent stress-strain relationship and heat conduction of the molten nugget used in the cooling process. Calculate rate, density, specific heat, coefficient of linear expansion ,
Material property data calculator.

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