JPH11304677A - Method and device for analyzing strength of joined product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a period for product development, to reduce cost, and to improve joining strength by converting welding energy obtained by computations into the joining strength of a joined part and obtaining the strength of a joined product. SOLUTION: Analytical model data in which the shape of each injection-molded component is divided into microelements is created. In addition to this microelement data, molding conditions such as injection pressure, mold temperature and the property values of a resin in use such as viscosity, a specific heat ratio are inputted to obtain the state of deformation in each vibration-welded component by injection-molding CAE software. Then stress generated in each microelement at the time of the forceful joining of a welded part is obtained, and further stress generated in each microelement at the time of the addition of load such as internal pressure assumed at the time of use is obtained. Next, the conditions of vibration welding are inputted to compute welding energy generated with the progress of vibration welding by numerical analytical techniques such as finite element method. Then the welding energy is converted into welding strength through the use of a specific equation to obtain welding strength in each microelement of the welded part. Furthermore, the degree of safety in each microelement is obtained by the welding strength and the above-obtained generated stress.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, but not limited to, a joining process for a component, more preferably, but not exclusively, to a vibration welding process for a resin component, using a joining strength analyzing apparatus, an analyzing method, and an analyzing method. It relates to a method for determining a shape, a material, and joining conditions.

[0002]

2. Description of the Related Art Injection molding, blow molding, extrusion molding, compression molding, and the like are used as molding methods for resin products. There are restrictions on the shapes that can be molded. For example, in the injection molding method, it is difficult to produce a hollow product such as a bent pipe or a tank due to the restriction of the mold structure. In such a case, a complicated shape such as a hollow part can be formed by forming a plurality of parts in advance by a normal forming method and joining them in combination. As a joining method, for example, the vibration welding method divides the product shape into a plurality of parts in advance and forms them by injection molding, blow molding, extrusion molding, compression molding, etc., and then vibrates while pressing each part in combination. Then, there is a processing method capable of forming a complicated shape such as a hollow product by melt-joining by frictional heat.

[0003] In the design of the shape of the vibration welding portion and the setting of the welding conditions, there is no known setting method in accordance with the shape of the product and the resin to be used. If the product is broken by a strength test, the condition is determined by trial and error, such as changing the conditions. For example, JP-A-7-809
No. 38, as a method of manufacturing a resin pipe, the divided body is inclined with respect to the compression direction, thereby shortening the length of the inclined portion of the dividing line to secure the surface pressure of the inclined portion during vibration welding. Although it is known to increase the welding strength, it is difficult to obtain a guide as to how many tilts are required for a complicated product shape.

At the product design stage, for example, the thickness and the reinforcing structure are determined by predicting the presence or absence of breakage when an internal pressure is applied to a hollow portion when the product is used. Since the strength cannot be accurately predicted, a design change is required again by a strength test after actually producing a prototype, which leads to an increase in labor, cost, and a product development period.

[0005] Each component before vibration welding is often obtained by injection molding, but in an injection molded product, warpage often occurs, and the shape of the vibration welded portion does not match the original design. On the other hand, the injection molding CAE is used as a technique for predicting the process of the injection molding by computer simulation with respect to the warpage and preventing molding defects. Here, the injection molded product shape is divided into minute elements, and the injection molding conditions and the resin material properties are input, and the resin pressure is calculated by a numerical analysis method such as the difference method, boundary element method, finite element method, and finite volume method. , Temperature, warped state, etc. According to injection molding CAE, the pressure, temperature, shear stress, etc. of the molten resin flowing in the mold are calculated on a computer, and finally the shrinkage / warpage of the molded product can be obtained, and the product shape and injection By changing molding conditions, resin properties, and the like, conditions under which warpage is reduced can be examined in advance on a computer. But conventional injection molding
CAE can predict the warpage of each part,
It is not possible to predict the effect of residual stress generated when combining a plurality of warped shapes on product strength. For this reason, the influence on the welding strength cannot be considered in the design of the mold during injection molding or the setting of molding conditions during production, which influences the warpage, and trial and error is repeated when setting the molding conditions.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to develop a product by setting optimal shapes, materials, and molding conditions for each product. An object of the present invention is to provide a method and an apparatus capable of predicting a joining strength according to each product such as a product shape, a material, and molding processing conditions in order to shorten a period, reduce a cost, and improve a joining strength.

[0007]

According to the present invention, there is provided a method for analyzing the strength of a joined product in which a plurality of members are joined by welding. Calculating the welding energy applied to at least a part of the part by converting the obtained welding energy into the bonding strength of the bonding part, and obtaining the strength of the bonded part; Is provided.

According to another aspect of the present invention, there is provided a method for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein a joining strength of at least a part of a joint portion of the plurality of members is obtained. Calculating the stress generated at the time of loading the joint by calculating, and calculating the strength safety of the joint based on the obtained joint strength and load stress of the joint; analyzing the joint strength. A method is provided.

According to another aspect of the present invention, there is provided a method of analyzing the strength of a joined product in which a plurality of members are joined by welding. The warpage deformation shape at the time of molding of the member is obtained by calculation, the residual stress at the time of forcibly joining the plurality of members subjected to the warpage is obtained by calculation, and the stress generated at the time of loading of the joined product is calculated by calculation. A method for analyzing the strength of a joint product is provided, wherein the strength safety of the joint part is obtained based on the obtained and obtained joint strength, residual stress and load stress of the joint part.

According to another aspect of the present invention, there is provided an apparatus for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein the welding is applied to at least a part of a joint portion of the plurality of members. Means for calculating energy by calculation;
An apparatus for analyzing the strength of a joined article is provided, which has means for converting the obtained welding energy into the joining strength of the joining portion and determining the strength of the joined article.

According to another aspect of the present invention, there is provided an apparatus for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein a joining strength of at least a part of a joining portion of the plurality of members is obtained. Means, means for calculating the stress generated at the time of loading of the joint product by calculation, and means for calculating the strength safety of the joint part based on the obtained joint strength and load stress of the joint part. And an analyzer for analyzing the strength of the bonded product.

According to another aspect of the present invention, there is provided an apparatus for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein the means for determining the joining strength of at least a part of the joint portion; Means for calculating a warp deformation shape during molding of a plurality of members, means for calculating a residual stress when the plurality of members subjected to the warp deformation are forcibly joined, and And a means for calculating the strength safety of the joint portion based on the obtained joint strength, residual stress, and load stress of the joint portion. An analysis device is provided.

According to another aspect of the present invention, the joint strength is predicted by the joint strength analyzing method, joining conditions satisfying the strength specifications are determined, and joining is performed based on the conditions. A method for manufacturing a bonded article is provided.

Further, according to the storage medium of the present invention, there is provided a storage medium storing software for operating a computer so that each procedure of the above-described joint strength analysis method can be performed by the computer.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to vibration welding of a bent pipe will be described below. FIG. 1 is a block diagram for explaining a device configuration of an embodiment of the analysis device of the present invention. (101) is a condition input device, (102) is a minute element dividing device, (103) is a data storage device 1, (10)
4) is a warpage deformation analyzer, (105) is a residual stress analyzer, (106) is a load stress analyzer, (107) is a welding strength analyzer, (108) is a data storage device 2, (10)
9) is a safety analysis device, (110) is a data storage device 3, and (111) is an output device. (103), (10
8) and (110) may be different memory areas in the same hard disk, for example. Also, (101)
(102) (103) (105) (106) (107)
(109) may be realized as a function on the memory of the same or a separate computer.

Next, the outline of the operation of this embodiment will be described with reference to the flowchart of FIG.

In step 1, two-dimensional or three-dimensional analysis model data in which each injection-molded part shape is divided into minute elements such as a square, a triangle, a hexahedron, a tetrahedron, a pentahedron, and a beam element is created. The analysis model data is created using software called a preprocessor of the finite element method, and the data is composed of vertex coordinate values of minute elements and vertex numbers constituting the elements. FIG. 3 shows a state in which the bent hollow molded article is divided into square minute elements. FIG. 4 shows the microelements of FIG. 3 divided into upper and lower parts.

(In step 2, in addition to the microelement data created in step 1, molding conditions such as gate position, resin temperature, injection pressure, and mold temperature during injection molding, and viscosity and specific heat of the resin used, etc.) Enter the physical property values and use the injection molding CA
Using software E, the warped state of each vibration welded part is determined as shown in FIG. FIG. 5 shows the warpage deformation amount 10 times enlarged. For example, according to injection molding CAE such as CAE software using a three-dimensional model described in JP-A-8-99341, a history of material pressure and temperature at the time of injection molding is calculated for an input product shape, Finally, the amount of displacement of the apex of the microelement after molding is output.

In step 3, using structural analysis software using a finite element method or the like, the stress generated in each minute element when the corresponding welded portion of each warped and deformed vibration welded part is forcibly joined is determined. This analysis is realized, for example, by virtually creating a high-rigidity rod element between the vertices of the corresponding minute element between the vibration welding parts and applying a shrinkage load to the rod element so that the length becomes zero. it can. In FIG. 5, reference numeral 503 denotes a part of a rod element generated between the welded portions of the upper and lower parts (501 and 502), and in fact, a part of the rod element generated between all the small elements of the welded part is displayed. It was done.

In step 4, using the structural analysis software using the finite element method or the like to the product forcibly joined in step 3, each minute element when a load such as an internal pressure assumed during use is applied. Find the stress that occurs in
In the initial stage of design, when the injection molding conditions of each vibration welded part are unknown or when there is not enough time for analysis, the injection molding CAE in step 2 is omitted for simplification and the warped shape is reduced. Assuming that the stress due to the forced joining is zero, the product shape after welding is divided into small elements, and a load such as the internal pressure assumed during use was applied using structural analysis software using the finite element method etc. It is also effective as one of the aspects of the present invention to simply find the stress generated in each microelement in this case.

In step 5, as shown in FIG. 6, only the welded portion is divided into minute elements, vibration welding conditions are input, and welding energy generated with the progress of vibration welding is obtained by a numerical analysis method such as a finite element method. The method for calculating the welding energy is shown below.

(1) As the vibration welding condition, a pressing load F
(N), amplitude X (mm), and welding depth D * (mm) are set.

(2) When a pressing load f is applied to the shape of the welded portion 601 divided into minute elements shown in FIG. 6, a minute element portion i (i = 1, 2, N) (N is Pressure Ps (MPa) applied perpendicularly to the welding surface is obtained for the total number of microelements used in. As a method of calculating Ps, a method of calculating using a numerical analysis method such as a finite element method,
Alternatively, a simple calculation method using Expression 1 is conceivable.

Ps = f × sin (θi) / S (1) where S (mm 2) is the area of the welded portion, and θi is the angle (radian) between the welded surface of the microelement portion i and the direction of the pressing load f. It is. This is shown in FIG.

(3) The amount of heat Qi (J) generated in the minute element portion i at the time of vibration welding is obtained from the equation (2).

Qi = F (Ps, X, Si) Equation 2 Here, F is a function determined by experiment, and Si (m
m ² ) is the welding area of the minute element portion i. The function form of F can be determined, for example, by performing a vibration welding experiment on a test piece having a simple shape as shown in FIG. 8, and the inventor has found Expression 3 as a preferred form of F through experiments.

Qi = (A × Ps + B / Si) × Xn × h Formula 3 where h (J / mm ³ ) is the melting energy per unit volume, and A, B, and n are obtained from experiments. H = 3.8 in one example of nylon 6 glass fiber reinforced resin.
It is preferable to use × 10-9, A = 2 × 10-5 to 3 × 10-5, B = 25.0 to 30.0, and n = 1.6. The method of determining A, B, and n is as follows. First, for example, as shown in FIG.
An experiment was conducted in which a 10 mm test piece was applied and welded.
When the welding pressure by pressing in the direction 1 is changed to three or more points, for example, 5, 10, 15 MPa, and the amplitude is changed to three or more points, for example, 1 mm, 1.2 mm, 1.5 mm. For each condition, the welding time required for melting to a certain welding depth is determined. Next, assuming A, B, and n, analysis of the temperature distribution and elution described in (4) and (5) is performed for each welding condition, and fitting such as the least square method is performed so that the welding time matches the actual measurement. By doing so, A, B, and n can be determined.

(4) Next, using a numerical analysis method such as the finite element method, the difference method, or the boundary element method, the temperature distribution that changes during the time dt (sec) inside the minute element i when Qi is the heat generation amount Is analyzed by computer. At this time, a part of the inside of the microelement i that has reached the melting point Tm or higher of the material is eluted, and the shape of the microelement is changed by reducing or deleting the microelement size, and the elution of the microelement by elution is performed. With the shape change, the pressure value Ps obtained in (2) is changed with time.

(5) Simultaneously with the analysis of (4), the welding energy Ei shown in the following equation is calculated for each minute element, and integrated until the end of vibration welding.

Ei = {{0.13 × Ps ^m1 × (0.4X × frc) ^m2 · dt} Equation 4 The welding energy Ei defined by Equation 4 is one-to-one with the energy [J] applied to the welded portion. (An energy itself, an amount proportional to the energy itself, or a function not proportional to the energy as in the present embodiment). Is calculated as an index for converting into a welding strength described later.

Here, frc is the frequency (Hz). Ps, X,
[Mpa], [mm], and [sec] are used as units of dt. Further, m1 and m2 are parameters determined by experiments. According to the present inventors, in one example of nylon 6 glass fiber reinforced resin,
It is desirable that m1 = 0.1 and m2 = 1.6. As a method of determining m1 and m2, for example, a welding experiment is performed on a test piece having a size of 30 mm × 10 mm of a welded portion shown at 802 in FIG. The pressure P by pressurizing is, for example, 5 MPa, 10 MPa, 15
MPa, and the welding time t when the amplitude X is changed to three or more points, for example, 1 mm, 1.2 mm, and 1.5 mm, is obtained. ), Ln (1 / t) with respect to ln (X), where
M2 is determined from the slope of.

(6) The length at which the size of the microelements is reduced by elution for all the welded microelements is determined by the welding depth Di (m
m), and the average or minimum value is the set value D
* It is assumed that vibration welding has been completed when
End the analysis.

In step 6, the welding energy Ei is converted into the welding strength Sw (Mpa) using equation 5, and the welding strength at each minute element i of the welded portion is determined.

Sw = α × Ei ² + β × Ei + γ Equation 5 α, β, and γ are parameters obtained by experiments and vary depending on the resin material used. α, β, and γ are, for example, a vibration welding experiment of a test piece having a welded part size of 30 mm × 10 mm of 802 shown in FIG. 8 and a pressing force in the direction of 801 applied to three or more points, for example, 5 MPa, 10 MPa. , 15
MPa, and the amplitude is changed to three or more points, for example, 1 mm, 1.2 mm, and 1.5 mm.
Is determined by obtaining a correlation curve between the welding energy obtained in the above and the measured strength. For example, in the case of nylon 6 glass fiber reinforced resin material, A = −5 × 10−5 to −1 × 10−4, B =
0.07 to 0.09, C = about 20 to 25.

In step 7, the degree of safety of each microelement is determined from the welding strength determined in step 6 and the generated stress determined in step 4. As the degree of safety, for example, a strength safety factor obtained by dividing the welding strength by the generated stress can be used. Alternatively, another index determined from the welding strength and the generated stress can be used as the degree of safety.
Here, when the strength safety factor is equal to or less than a specified value such as 2.0, for example, the process returns to step 5 when the welding condition is changed, and returns to step 1 when the design condition is changed. Search for a condition that is equal to or greater than the default value.

[0036]

Next, an embodiment of the present invention will be described.

FIG. 9 shows an analytical model obtained by dividing a bent hollow product made of nylon 6 glass fiber reinforced resin into square minute elements using a finite element method preprocessor. By using a preprocessor, a pipe-shaped product shape is input, and element shape data including vertex coordinate values of each minute element and vertex numbers constituting each minute element are generated from the product shape. (Step 1) Next, the above-mentioned element shape data was divided into upper and lower two parts before welding and input to the injection molding CAE software. Further, by inputting the injection molding conditions and the physical properties of the resin used, the warped state of the upper and lower parts injection-molded as shown in FIG. 10 was obtained. (Step 2) In FIG. 10, the amount of warpage deformation is enlarged to ten times the calculated value and displayed.

Next, with respect to the upper and lower parts after the warp deformation, a bar element having a rigidity at least 10 times higher than that of the upper and lower parts is defined between the vertices of the corresponding minute elements of the welded part, and the bar element shrinks to zero length. The stress generated in the microelements of the upper and lower parts when doing this was obtained by structural analysis using the finite element method. FIG.
FIG. 1 shows the distribution of stress generated in the minute element at the welded portion. This stress value indicates a stress value generated when the warped and deformed upper and lower parts are forcibly joined. (Step 3) Next, deformation and generated stress when an internal pressure of 10 kg / cm2 was applied as a load assumed during use to the upper and lower parts that were forcibly joined were analyzed by a finite element method. FIG. 12 shows the stress generated at the welded portion when a load is applied at 1202, and the stress generated at the time of forced joining obtained at step 4 is shown at 1203. At this time, the stress value σi generated in each minute element of the vibration welding portion was stored in the storage device. (Step 4) Next, as shown in FIG. 13, only the welded portion is divided into minute elements, and the pressure load during vibration welding is set to 100 kg, the amplitude is set to 1.5 mm, and the welding depth is set to 1.5 mm. Based on the welding energy calculation method, parameters m1 = 0.1, m2 =
As 1.6, the welding energy Ei generated in each microelement was determined. (Step 5) Next, the welding energy Ei was converted into the welding strength Sw using Expression 5. At this time, the parameter values are A = -7 × 10-5, B =
0.08 and C = 22. FIG. 14 shows the welding strength at five points. (Step 6) Next, the welding strength Sw was divided by the generated stress σi when a load was applied, and the strength safety factor Ai of each microelement was calculated as shown in FIG. In the case of this product, the strength safety factor is 1.5 in the design specification.
Although the above was required, the strength safety factor of the part C was 1.5
It has been found that: Therefore, the pressure load at the time of vibration welding was changed to 80 kg, and step 5 and the subsequent steps were performed again. As a result, as shown in FIG. There was found. In this embodiment, the safety factor is improved by changing the pressure load at the time of vibration welding. Modification methods such as increasing the projection area of the welded portion in the pressure direction and changing the resin material used are also conceivable. (Step 7)

[0039]

According to the method and the apparatus for analyzing the bonding strength according to the present invention, it is possible to predict the vibration welding strength according to each product such as the shape of the product, the resin and the molding processing conditions, and to study the improvement of the strength on a computer. It is possible to shorten the product development period, reduce costs, and improve welding strength by setting the optimal shape, resin, and molding processing conditions for each joined product such as vibration welding products. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a method of analyzing a bonding strength according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example in which a hollow molded product is divided into rectangular microelements.

FIG. 4 is a view showing a fine element division model of the hollow molded product shown in FIG. 3 divided into upper and lower parts.

FIG. 5 shows the warped shape of the upper and lower parts shown in FIG.
It is a figure which shows the state which part of the corresponding welding part was connected with the rod element.

6 is a view showing a state where only a welded portion of the hollow molded article shown in FIG. 3 is divided into minute elements.

FIG. 7 is a diagram showing a definition of a direction of a pressure applied to a welding portion and an angle of a welding surface.

FIG. 8 is a diagram showing an example of a test piece shape used for a welding experiment.

FIG. 9 is a diagram showing an example in which a hollow molded product is divided into quadrangular microelements.

10 is a diagram showing a result of analyzing warpage deformation generated when upper and lower parts of the hollow molded article shown in FIG. 9 are injection-molded.

11 is a diagram showing stress values generated when the warped shape shown in FIG. 10 is forcibly joined.

12 is a diagram showing stress values generated when an internal pressure is applied after forcibly joining the warped shape shown in FIG. 10;

13 is a view showing a state in which only a welded portion of the hollow molded article shown in FIG. 9 is divided into minute elements.

FIG. 14 is a view showing the result of analyzing the welding strength of the welded portion shown in FIG.

FIG. 15 is a diagram showing a result of obtaining a safety factor from the generated stress shown in FIG. 12 and the strength shown in FIG.

FIG. 16 corrects the welding conditions of the hollow molded article shown in FIG. 9,
It is a figure which shows the result of having calculated | required the safety factor of the welding part intensity | strength.

[Explanation of symbols]

 101 ... condition input device 102 ... minute element dividing device 103 ... data storage device 1 104 ... warpage deformation analysis device 105 ... residual stress analysis device 106 ... load stress analysis device 107 ...・ Welding strength analyzer 108 ・ ・ ・ Data storage device 2 109 ・ ・ ・ Safety factor analyzer 110 ・ ・ ・ Data storage device 3 111 ・ ・ ・ Output device 301 ・ ・ ・ Microelement 302 ・ ・ ・ Welding part 401 ・ ・-Upper part 402 ... Lower part 403 ... Welding part 501 ... Upper part 502 ... Lower part 503 ... Bar element 601 ... Micro element 701 ... Pressing direction 702 ... Welding surface 703: angle between pressing direction and welding surface 801: pressing direction 802: welding surface 901: minute element 902: welding part 1001: upper part 1002: Lower part 1201: Stress output position 1202: Stress generated by internal pressure load 1203: Stress generated by forced joining 1301: Small element 1501: Safety factor lower limit of design specification 1601 ...・ Lower safety factor of design specification

Claims (12)

[Claims] 1. A method of analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein a welding energy applied to at least a part of a joint portion of the plurality of members is obtained by calculation. A method for analyzing the strength of a joined product, wherein welding energy is converted into the joining strength of the joining portion, and the strength of the joined product is obtained. 2. A method for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein a joint strength of at least a part of a joining portion of the plurality of members is obtained, and the joint strength is generated when the joined product is loaded. A method for analyzing the strength of a joined product, wherein a stress is obtained by calculation, and a strength safety level of the joint is obtained based on the obtained joint strength and load stress of the joint. 3. A method for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein a joining strength of at least a part of the joining portion is obtained, and a warp deformation shape at the time of molding of the plurality of members is determined. Obtained by calculation, the residual stress at the time of forcibly joining the plurality of members subjected to the warp deformation is obtained by calculation, the stress generated at the time of loading of the joined product is obtained by calculation, and the obtained joint part is obtained. A method for analyzing the strength of a joint product, wherein a strength safety of the joint portion is obtained based on a joint strength, a residual stress, and a load stress. 4. An apparatus for analyzing the strength of a joined product in which a plurality of members are joined by welding, comprising: means for calculating welding energy applied to at least a part of a joint portion of the plurality of members; An apparatus for analyzing the strength of a bonded product, comprising means for converting the obtained welding energy into the bonding strength at the bonding site and determining the strength of the bonded product. 5. An apparatus for analyzing the strength of a joined product in which a plurality of members are joined by welding, comprising: means for determining a joining strength of at least a part of a joining portion of the plurality of members; And a means for calculating the strength safety of the joint based on the obtained joint strength and load stress of the joint. 6. An apparatus for analyzing the strength of a joined product in which a plurality of members are joined by welding, wherein a means for determining the joining strength of at least a part of the joining portion, and a warp deformation during molding of the plurality of members. Means for calculating a shape, means for calculating a residual stress when the plurality of members subjected to the warp deformation are forcibly joined, and means for calculating a stress generated when a load is applied to the joined product. And a means for determining the strength safety of the joint portion based on the obtained joint strength, residual stress, and load stress of the joint portion. 7. The method according to claim 1, wherein a model including a large number of minute elements is used for calculating the welding energy. 8. The method according to claim 1, wherein the welding is based on frictional heat during vibration. 9. The method for analyzing joint strength according to claim 1, wherein a positive curve is used when converting welding energy into joint strength. 10. The method according to claim 9, wherein a quadratic curve using welding energy as a variable is used as the positive curve. 11. The method according to claim 1, wherein the strength of the joint product or the strength safety is predicted, the joining condition satisfying the strength specification is determined, and the joining process is performed based on the condition. The manufacturing method of the joined article. 12. A storage medium storing software for operating a computer so that each procedure of the method for analyzing joint strength according to claim 1, 2 or 3 can be performed using the computer.