Evaluation method for friction stir welding

Abstract

To accurately evaluate deformation of a member to be joined in a friction agitation joining for a short time.SOLUTION: An evaluation method of friction agitation joining evaluating through CAE analysis deformation of respective members to be joined when two members to be joined are joined by the friction agitation joining comprises: a step S2 which defines an agitation section that is a sectional form of a part agitated in the friction agitation joining; a step S3 which defines agitation temperature generated in the member to be joined caused by heat of agitation; and a deformation calculation step S7 which calculates deformation of respective CAE models when inputs the defined agitation temperature of the defined agitation section into a portion to be joined of the CAE model in which the deformation calculation step S7 is executed while heat input portion is changed in order along the portion to be joined until completing heat input into all of the portion to be joined.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed herein belongs to the technical field of a method for evaluating friction stir welding. [Background technology]

[0002] Friction stir welding, which involves stirring and joining the solid workpieces by using plastic flow induced by the rotation of a probe, has been known as a conventional method for joining two workpieces. A known method for evaluating the quality of friction stir welding is to perform image analysis of the welded joint after the friction stir welding.

[0003] For example, Patent Document 1 discloses a method of acquiring color image information of a joint, calculating RGB values ​​of the color image information, converting the RGB values ​​to grayscale to calculate grayscale values, and binarizing the image information based on the grayscale values ​​to determine the area where burrs exist at the joint and the level of burr existence. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-62924 Summary of the Invention [Problem to be solved by the invention]

[0005] One of the items that must be evaluated in friction stir welding is the amount of deformation of the workpieces. In other words, since the workpieces deform to some extent due to the influence of heat during friction stir welding, it is necessary to minimize the amount of deformation of the workpieces. To minimize the amount of deformation of the workpieces, it is necessary to appropriately set welding conditions such as the rotation speed and translation speed of the probe.

[0006] In order to set the joining conditions, it was necessary to actually weld together the workpieces by friction stir welding and evaluate the amount of deformation of the workpieces, as in Patent Document 1. However, in such verification using an actual machine, it is necessary to constantly monitor the temperature during welding in order to verify parameters that affect the deformation of the workpieces, which makes the verification itself quite large-scale, and also takes a considerable amount of time to perform friction stir welding under many different welding conditions.

[0007] Therefore, the present inventors attempted to theoretically evaluate the deformation of the workpieces by fluid analysis. However, their investigations revealed that evaluation using fluid analysis requires an extremely long analysis time of several hundred hours. Therefore, there is a need for a method for evaluating the deformation of the workpieces during friction stir welding in a shorter time.

[0008] The technology disclosed herein has been made in view of the above points, and its purpose is to enable evaluation of deformation of workpieces during friction stir welding to be performed in a short time and with high accuracy. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the technology disclosed herein targets a friction stir welding evaluation method in which deformation of each workpiece when two workpieces are joined by friction stir welding using a rotating probe is evaluated by CAE analysis, and includes a model setting step of setting a CAE model of each workpiece, a cross-section definition step of defining a stir cross-section, which is the cross-sectional shape of the part stirred in friction stir welding, a stir temperature definition step of defining a stir temperature generated in the workpieces by heat caused by the stirring, and a deformation calculation step of calculating the deformation of each CAE model when heat is input at the defined stir cross-section to a joint joined by friction stir welding in each CAE model, and the heat input location is changed sequentially along the workpieces, and the deformation calculation step is executed sequentially until heat input to the entire joint is complete.

[0010] With this configuration, since the stir cross section and stir temperature are defined, there is no need to calculate the fluid deformation at the welded area during friction stir welding or the temperature distribution at the deformed area. Furthermore, since the stir cross section and stir temperature are constant, the deformation of the CAE model due to the heat generated by stirring can be calculated relatively easily. Furthermore, since the deformation of the CAE model is calculated until heat input to the entire welded part is complete, the deformation of each CAE model when friction stir welding is complete can be calculated. This makes it possible to simply and quickly evaluate the deformation of the welded parts during friction stir welding.

[0011] Furthermore, since the part to which heat is input in actual friction stir welding is the part that is stirred, the situation in which heat is input at a defined stirring temperature to a defined stirring cross section can be said to correspond to the situation in actual friction stir welding. Therefore, according to the above-mentioned configuration, the deformation of the CAE model is calculated taking into consideration the situation that corresponds to actual friction stir welding, so that the deformation of the welded parts in actual friction stir welding can be accurately reproduced in the CAE model.

[0012] In one embodiment of the friction stir welding evaluation method, the method further includes a stir length definition step of defining a stir length, which is the length welded per unit time, and a model addition step of adding a welded joint model to each of the CAE models constituting the welded part at a location of the welded part where the deformation calculation step has been completed, wherein the deformation calculation step is a step of calculating the deformation of the CAE model when heat is input to a region of the welded part having the defined stir cross section and the defined stir length, and when calculating the deformation of the CAE model due to the heat input for the n+1th time (n is a natural number greater than or equal to 1), the deformation of each CAE model is calculated taking into account the joint models added up to the nth time.

[0013] That is, in actual friction stir welding, the probe is translated along the welded parts to gradually weld the parts together. Therefore, the welded part where the welded parts are welded gradually increases. Since the thermal conduction and deformation of this welded part also affect the deformation of the welded parts, the welded part must be taken into account in order to accurately calculate the deformation of the welded parts. In the above-described configuration, a welded part model is added to the part where heat is input, and the deformation of the CAE model when heat is input to the next heat input point is calculated taking the welded part model into account. This makes it possible to calculate the deformation of the CAE model corresponding to the actual deformation of the welded parts. Therefore, the evaluation accuracy of friction stir welding can be improved.

[0014] The friction stir welding evaluation method may further include a clamping condition setting step of defining, for each CAE model, a clamping position at which each of the workpieces is clamped in order to fix the relative positions of the workpieces in actual friction stir welding, and the deformation calculation step may be a step of calculating the deformation of the CAE model taking the clamping position into consideration.

[0015] With this configuration, the deformation of the CAE model is calculated taking into account the conditions corresponding to actual friction stir welding, so the deformation of the workpieces in actual friction stir welding can be accurately reproduced in the CAE model, thereby further improving the evaluation accuracy of friction stir welding.

[0016] In one embodiment of the friction stir welding evaluation method, after calculating the deformation of the CAE model when the entire welded portion is welded in the deformation calculation step, the method further includes a second deformation calculation step of calculating the deformation of the CAE model when heat is released to a predetermined temperature.

[0017] Even with this configuration, the deformation of the CAE model is calculated taking into account the conditions corresponding to actual friction stir welding, so the deformation of the workpieces during actual friction stir welding can be accurately reproduced in the CAE model, thereby further improving the evaluation accuracy of friction stir welding.

[0018] In one embodiment, when there are multiple welded parts, the second deformation calculation step may be a step that is executed after the deformation calculation step has been completed for all of the multiple welded parts.

[0019] That is, in actual friction stir welding, when there are multiple parts to be welded, cooling is performed after the welding of all of the parts to be welded is completed. Therefore, according to the above-mentioned configuration, the deformation of the CAE model is calculated taking into account the situation corresponding to the actual friction stir welding, and the deformation of the welded parts in the actual friction stir welding can be accurately reproduced in the CAE model. This further improves the evaluation accuracy of the friction stir welding.

[0020] In the method for evaluating friction stir welding, the probe may be axially shaped and have a pin portion that contacts the workpieces to be welded, and a shoulder portion that is located on the opposite side of the pin portion in the axial direction from the workpieces to be welded and has a larger diameter than the pin portion, and the cross-section definition step may be a step of defining the stir cross section based on the axial length of the pin portion and at least one of the diameter of the pin portion and the diameter of the shoulder portion.

[0021] In actual friction stir welding, the pin is pressed against the workpiece and penetrates it. The stirred workpiece expands radially along the shoulder. Therefore, the width of the stir cross section depends not only on the diameter of the pin but also on the diameter of the shoulder. Furthermore, when the shoulder contacts the workpiece, frictional heat is generated between the shoulder and the workpiece, so the range of heat input also depends on the diameter of the shoulder. On the other hand, if the pin penetrates the workpiece only slightly, the contact area between the shoulder and the workpiece is small and can be ignored in calculating the deformation of the workpiece. Therefore, by defining the stir cross section as described above, the deformation of the CAE model can be calculated taking into account the conditions corresponding to actual friction stir welding, allowing the CAE model to accurately reproduce the deformation of the workpiece during actual friction stir welding. Furthermore, the simple shape defined as the stir cross section facilitates the calculation of the deformation of the workpiece. This allows for simpler and more rapid evaluation of the deformation of the workpiece.

[0022] In the method for evaluating friction stir welding, the stir temperature definition step may be configured to set the stir temperature based on the rotation speed and the translation speed of the probe.

[0023] In other words, when the probe's traveling speed is slow, the heat input time is longer, resulting in a higher stirring temperature. Therefore, by defining the stirring temperature taking into account the probe's traveling speed, the deformation of the CAE model is calculated taking into account the conditions corresponding to actual friction stir welding, and the deformation of the welded parts during actual friction stir welding can be accurately reproduced in the CAE model. This further improves the evaluation accuracy of friction stir welding. [Effects of the Invention]

[0024] As described above, according to the technique disclosed herein, deformation of workpieces during friction stir welding can be evaluated in a short time and with high accuracy. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of friction stir welding. [Figure 2] Figure 2 is a flowchart for evaluating friction stir welding using CAE analysis. [Figure 3] FIG. 3 is a flowchart for calculating the deformation of the CAE model. [Figure 4] FIG. 4 is a plan view showing the CAE model. [Figure 5] FIG. 5 is a diagram showing the definition of the stirring cross section. [Figure 6] FIG. 6 is a schematic diagram showing the shape of a probe used to define a stirring cross section. [Figure 7A] FIG. 7A is a diagram showing the temperature distribution when heat is input to the CAE model, and shows the state in which heat is input to the initial stirring position. [Figure 7B] FIG. 7B is a diagram showing the temperature distribution when heat is input to the CAE model, showing the state in which heat is input to the third stirring position. [Figure 8] FIG. 8 is a diagram showing evaluation positions for evaluating the amount of deformation of the workpieces. [Figure 9] FIG. 9 is a graph comparing the amount of deformation in the vertical direction between the CAE analysis according to this embodiment and actual measurement. [Figure 10A] FIG. 10A is a graph comparing the amount of displacement in the front-rear direction of a small diameter hole formed in members to be welded, between the CAE analysis according to this embodiment and actual measurement. [Figure 10B] FIG. 10B is a graph comparing the amount of displacement in the left-right direction of a small diameter hole formed in the workpieces between the CAE analysis according to this embodiment and actual measurements. DETAILED DESCRIPTION OF THE INVENTION

[0026] Exemplary embodiments will now be described in detail with reference to the drawings.

[0027] (Friction stir welding) FIG. 1 schematically illustrates the joining of a first metal workpiece W1 and a second metal workpiece W2 by friction stir welding. In the example shown in FIG. 1, the ends of the first metal workpiece W1 and the second metal workpiece W2 are butted together, and the butted parts are joined by friction stir welding to form a welded portion 101. In friction stir welding, a probe 10 is rotated and brought into contact with the welded portion 101, causing plastic flow in the structures of the first and second metal workpieces W1 and W2, thereby stirring the structures of the first metal workpiece W1 and the second metal workpiece W2, thereby joining the first metal workpiece W1 and the second metal workpiece W2. In friction stir welding, the probe 10 is rotated and translated along the welded portion 101, thereby welding the entire welded portion 101. When friction stir welding is performed, the first workpiece W1 and the second workpiece W2 are clamped together to fix the relative positions of the first workpiece W1 and the second workpiece W2.

[0028] 1, the probe 10 has a pin portion 11 that actually contacts the first and second workpieces W1, W2, a shoulder portion 12 that is located on the axially opposite side of the pin portion 11 from the first and second workpieces W1, W2 and has a larger diameter than the pin portion 11, and a rod portion 13 that is located on the opposite side of the shoulder portion 12 from the pin portion 11. The pin portion 11, shoulder portion 12, and rod portion 13 are coaxial. The pin portion 11, shoulder portion 12, and rod portion 13 are formed from a single member.

[0029] The cross-sectional shape of the friction stir welded joint is determined by the rotation speed and the probe shape. However, the width of the part of the welded part 101 that is stirred by friction stir welding is equal to or greater than the diameter of the pin part 11 and less than the diameter of the shoulder part 12, and the depth of the part that is stirred is slightly greater than the penetration depth of the pin part 11.

[0030] In friction stir welding, the workpieces are deformed to some extent due to the heat generated, so it is necessary to minimize the amount of deformation of the workpieces. To minimize the amount of deformation of the workpieces, it is necessary to appropriately set welding conditions such as the shape of the probe 10, the rotation speed and translation speed of the probe, and the clamping position of the workpieces.

[0031] In the past, when setting welding conditions, it was necessary to actually weld the workpieces together using friction stir welding and evaluate the amount of deformation of the workpieces to set the welding conditions. However, in this kind of verification using actual equipment, it is necessary to constantly monitor the temperature during welding in order to verify the parameters that affect the deformation of the workpieces, making the verification itself quite large-scale, and it also takes a considerable amount of time because it is necessary to perform friction stir welding under many different welding conditions.

[0032] One possible method is to estimate the deformation of the workpieces on a desk using fluid analysis. However, the inventors of the present application have found that verification using fluid analysis is extremely time-consuming, requiring hundreds of hours of analysis time, especially when the workpieces have complex shapes. For this reason, the inventors of the present application have devised a method for evaluating the deformation of each workpiece using CAE analysis, thereby enabling the deformation of the workpieces during friction stir welding to be evaluated quickly and accurately. The evaluation method for friction stir welding according to this embodiment will now be described in detail.

[0033] (Evaluation of friction stir welding using CAE analysis) 2 and 3 are flowcharts showing a process for evaluating deformation of workpieces during friction stir welding by CAE analysis.

[0034] <Step S1> First, in step S1, the process sets up a CAE model for each workpiece, which is a model that imitates the actual workpiece.

[0035] FIG. 4 shows an example of a CAE model 20. The workpieces represented by this CAE model 20 are part of an on-vehicle component. The workpieces are a main body, a first part to be joined to the main body, and a second part. The main body is a flat plate made of an aluminum alloy and is generally L-shaped. The main body has multiple large-diameter holes on its outer periphery and multiple small-diameter holes located closer to the center than the outer periphery. The first part is arranged along the inside of the L-shape of the main body, from the rear left to the front left of the main body. The second part has a smaller area than the first part and is arranged in the front right of the main body. As shown in FIG. 4, the CAE model 20 includes a main body model 21 representing the main body, a first part model 22 representing the first part, and a second part model 23 representing the second part. The main body model 21 reproduces the overall shape of the main body, the position and size of each large-diameter hole, and the position and size of each small-diameter hole. The first part model 22 reproduces the shape and arrangement of the first part. The shape and arrangement of the second part are reproduced in the second part model 23. Note that the front-rear and left-right directions in Fig. 4 are shown for the sake of convenience in order to simplify the explanation, and do not limit the actual state of use.

[0036] The boundary portion between main body model 21 and first part model 22 and the boundary portion between main body model 21 and second part model 23 are each defined as a welded part 24 to be welded by friction stir welding. In other words, this CAE model 20 has a plurality of welded parts 24.

[0037] <Step S2> Next, in step S2, the process defines a stir cross section, which is the cross-sectional shape of the part that is stirred in friction stir welding. This stir cross section corresponds to the cross-sectional shape of the welded part between the first workpiece W1 and the second workpiece W2 in FIG.

[0038] In this embodiment, the stir cross section is defined as a triangle with a maximum width of W and a depth of D, as shown in Fig. 5. In friction stir welding, the heat input range generated by the surface portion in contact with the pin portion 11 of the probe 10 is the widest, and the heat input range becomes narrower as the distance from the surface increases. For this reason, if the stir cross section is defined as a triangle, the stir cross section in actual friction stir welding can be roughly reproduced.

[0039] The maximum width W and depth D are defined based on the shape of the probe 10. Specifically, as shown in Fig. 6, the maximum width W is set in the range of equal to or greater than the diameter L1 and less than the diameter L2 based on the diameter L1 of the pin portion 11 and the diameter L2 of the shoulder portion 12 of the probe 10. The depth D is set based on the height H of the pin portion 11 to a value equal to or slightly greater than the height H.

[0040] When setting the stir cross section, the cross-sectional shape of the welded portion when actually performing friction stir welding using the same probe 10 may be used as a reference.

[0041] <Step S3> Next, in step S3, the process defines the stirring temperature generated in the workpieces due to the heat generated by stirring. In this embodiment, the stirring temperature is set based on the rotation speed and translation speed of the probe 10. This is because when the translation speed of the probe 10 is slow, the heat input time becomes long and the stirring temperature becomes high. The stirring temperature defined here is the temperature at the contact position between the probe 10 and the workpieces, and the temperature distribution spreading from that contact position is calculated in step S7, which will be described later.

[0042] <Step S4> Next, in step S4, the process defines an agitation length, which is the length to be joined per unit time. The agitation length is defined based on the translation speed of the probe 10. For example, if the translation speed of the probe 10 is 10 mm / s, the agitation length is defined as 10 mm.

[0043] <Step S5> Next, in step S5, the process defines a weld model 25 (see FIG. 7B ) and a stir position. The weld model 25 is a model representing a new member welded to both of the two CAE models constituting the welded parts 24 when heat due to stirring is deemed to have been input in step S7, which will be described later, and corresponds to a welded part in an actual friction stir welding. The shape of the weld model 25 has the stir cross section set in step S2 as a cross section and the stir length set in step S4 as a length along the welded parts 24. The stir position is the position where heat due to stirring is deemed to have been input in step S7, which will be described later, and is the position where the weld model 25 is placed. The stir position is not a position set as a point, but has a certain range. Specifically, the cross-sectional shape of the stir position is the shape of the stir cross section defined in step S2, and the length of the stir position along the welded parts 24 is the stir length defined in step S4.

[0044] <Step S6> Next, in step S6, the process sets boundary conditions for the CAE model 20. The boundary conditions are parameters relating to constraint conditions of the members to be welded and physical properties of the members to be welded.

[0045] As mentioned above, in actual friction stir welding, both workpieces are clamped to fix their relative positions. Therefore, the clamp position and clamp force are set as constraint conditions for the CAE model 20. However, because the external force caused by stirring is not included in the analysis conditions in CAE, only the clamp condition for the main body model 21 is set as a constraint condition here. In cases where the first and second part models 22 and 23 are clamped to prevent deformation, both are set as constraint conditions.

[0046] Furthermore, thermal conductivity and linear expansion coefficient are set as parameters relating to the thermal properties of the members to be joined. In this case, since the members to be joined are aluminum alloys, the thermal conductivity and linear expansion coefficient of the aluminum alloy are set. Furthermore, Young's modulus and the like are set as parameters relating to the stress of the members to be joined. If the materials of the members to be joined are changed, the parameters relating to the physical properties of the members to be joined (hereinafter simply referred to as physical property parameters) are changed to the physical property parameters of the changed material.

[0047] <Step S7> Next, in step S7, the process calculates the deformation of the CAE model 20 when heat due to stirring is input to the parts to be joined 24. Here, "deformation of the CAE model 20" refers to displacement in the up-down, front-back, and left-right directions due to thermal deformation of each part of the CAE model 20. In step S7, the amount of displacement of each part of each CAE model 20, i.e., the amount of deformation of each CAE model 20, is calculated. In other words, calculating "deformation of the CAE model 20" is synonymous with calculating "the amount of deformation of the CAE model 20."

[0048] Step S7 will be described in detail below with reference to FIG.

[0049] <Step S70> First, in the initial stage of step S7, as shown in Figures 7A and 7B, members are removed from the to-be-welded portion 24 of the CAE model 20 set in step S1. The cross-sectional shape of the removed portion corresponds to the stir cross section defined in step S2. After heat due to stirring is input to the to-be-welded portion 24 from which the members have been removed, a weld model 25 (see Figure 7B) is sequentially added in step S74, which will be described later.

[0050] <Step S71> Next, in step S71, the process assigns a stirring temperature to the first stirring position. That is, it is assumed that heat due to stirring is input to the stirring position set in step S5. FIG. 7A shows the state in which a stirring temperature has been assigned to the first stirring position. The first stirring position is the position of the part to be joined 24 between the main body model 21 and the first part model 22. At this stage, no joining part model 25 is placed at the part to be joined 24.

[0051] <Step S72> Next, in step S72, the process calculates the heat conduction from the stirring position and the deformation of each CAE model 20. The physical property parameters set in step S6 are taken into consideration when calculating the heat conduction and deformation of each CAE model 20. Furthermore, the deformation of each CAE model 20 is calculated assuming that the CAE model 20, particularly the main body model 21, is fixed at the clamp position set in step S6.

[0052] In this step S72, a temperature distribution that spreads substantially radially from the stirring position as shown in Fig. 7A is calculated. Then, the deformation of each CAE model 20 due to thermal expansion according to the calculated temperature distribution is calculated. As described above, the range of the stirring position is defined by the stirring cross section defined in step S2 and the stirring length defined in step S4. Therefore, in this step S72, the deformation of each CAE model 20 when heat is input at the stirring temperature defined in step S3 to a region having the defined stirring cross section and the defined stirring length is calculated.

[0053] <Step S73> Next, in step S73, the process determines whether or not the allocation of the stirring temperature has been completed for the entire part to be joined 24. In this embodiment, the part to be joined 24 is located between the main body model 21 and the first part model 22, and between the main body model 21 and the second part model 23. Here, "the entire part to be joined 24" means that when there are multiple parts to be joined 24, the stirring temperature has been allocated to the entire part of each of the parts to be joined 24.

[0054] The process proceeds to step S76 if the answer is YES, meaning that the allocation of the stirring temperature has been completed for the entire to-be-joined portion 24, and proceeds to step S74 if the answer is NO, meaning that the allocation of the stirring temperature has not been completed for at least a portion of the to-be-joined portion 24.

[0055] <Step S74> In step S74, the process adds the joint model 25 to the stirring position to which the stirring temperature has been assigned. As a result, the joint model 25 is added to the position where the heat input by stirring is completed, as shown in Fig. 7B. The position where the joint model 25 is added is considered to be the position where a member integrated with the two CAE models 20 (here, the main body model 21 and the first part model 22) that make up the part to be welded 24 exists.

[0056] <Step S75> Next, in step S75, the process assigns a stirring temperature to a stirring position adjacent to the position where the weld model was added in step S74 in the extension direction of the welded part 24.

[0057] After step S75, the process returns to step S72. When returning from step S75 and executing step S72, the deformation of each CAE model 20 is calculated taking into account the bond models 25 added to the stirring positions up to the nth (n is a natural number of 1 or more) position. In other words, when calculating the deformation of the CAE model 20 due to the (n+1)th (n is a natural number of 1 or more) heat input, the bond models 25 added up to the nth are taken into account.

[0058] 7B shows a state in which a stirring temperature is assigned to the third stirring position and heat conduction (i.e., temperature distribution) is calculated. At this time, a joint model 25 is added to each of the first two stirring positions. In step S72, heat conduction also occurs to each of these joint models 25, which is considered to contribute to the deformation of each CAE model 20, and the deformation of each CAE model 20 is calculated.

[0059] Furthermore, when returning from step S75 and executing step S72, the deformation of each CAE model 20 is calculated based on the deformation of each CAE model 20 caused by inputting stirring temperatures at the previous stirring positions. For example, when inputting stirring temperatures at the first two stirring positions causes torsional deformation in the main body model 21, the deformation of the main body model 21 is calculated based on the main body model 21 in a torsionally deformed state.

[0060] Steps S72 to S75 are repeated until allocation of stirring temperatures is completed for the entire portion to be joined 24. That is, in step S7, the heat input location is sequentially changed along the portion to be joined 24, and calculations of heat conduction and deformation are sequentially executed until heat input to the entire portion to be joined 24 is completed.

[0061] <Step S76> In step S76, the process adds the joint model 25 to the final stir position. After step S76, the process returns.

[0062] <Step S8> Returning to FIG. 2 , in step S8 after step S7, the deformation of the CAE model 20 is calculated when the entire CAE model 20 is heat-dissipated to a predetermined temperature. In step S8, since the joint model 25 is disposed over the entire joint portion 24, the deformation of the CAE model 20 is calculated assuming that the main body model 21, the first part model 22, and the second part model 23 are integrated. In step S8, the physical property parameters used in step S72 are also taken into consideration. In step S8, the deformation of the CAE model 20 is also calculated assuming that the main body model 21 is fixed at the clamp position set in step S6. The predetermined temperature is what is known as room temperature, for example, 5°C to 35°C.

[0063] After step S8, the evaluation of the friction stir welding by CAE analysis is completed.

[0064] (Comparison of CAE analysis and experimental results according to this embodiment) Next, the results of comparing the amount of deformation of main body model 21 calculated by the above-mentioned CAE analysis with the amount of deformation that occurred in the main body when friction stir welding was actually performed will be described with reference to FIGS. 8 to 10B.

[0065] FIG. 8 shows the measurement points to be compared, with measurement points B1 to B16 being used to calculate the amount of displacement in the up-down direction. Measurement points C1 to C20 are the small diameter holes in the main body mentioned above, and are used to calculate the amount of deformation in the front-to-back and left-to-right directions. The amount of displacement in the up-to-down direction is calculated based on the position of measurement point B10. The amount of deformation in the front-to-back and left-to-right directions is calculated from the change in each coordinate before and after friction stir welding by determining the X coordinate (front-to-back coordinate) and Y coordinate (left-to-right coordinate) of measurement points C1 to C20 using the position of the reference point shown in the front right part as the origin.

[0066] 9 shows the results of comparing the vertical displacement amounts at measurement points B1 to B16. The solid line is the result calculated by the CAE analysis of this embodiment, and the dashed line and dashed dotted line are actual measured values. The displacement amount at position B10 is 0 because it is the reference position.

[0067] 9, it can be seen that the amount of displacement of main body model 21 calculated by the CAE analysis according to this embodiment differs from the actual measurement in magnitude, but the tendency is similar to that of the actual measurement. As can be seen from comparing Measurement 1 and Measurement 2, the magnitude of the amount of displacement also differs between the actual measurements, so it can be said that the difference between the CAE analysis according to this embodiment and the actual measurement is not significant.

[0068] 10A and 10B, the amount of displacement in the front-rear and left-right directions also tends to be similar between the CAE analysis according to this embodiment and the actual measurements. Regarding the amount of displacement in the front-rear and left-right directions, there is also a discrepancy between the actual measurements, so the discrepancy between the CAE analysis according to this embodiment and the actual measurements is not significant.

[0069] Therefore, it can be said that the CAE analysis according to this embodiment is able to adequately reproduce the deformation of the workpieces that occurs during actual friction stir welding. Therefore, by using the CAE analysis according to this embodiment, it is possible to calculate the welding conditions that minimize the amount of deformation of the workpieces, i.e., the diameter of the pin portion 11 of the probe 10, the rotational speed and translational speed of the probe 10, the clamp position of the main body, etc.

[0070] Furthermore, when the inventors of the present application attempted to evaluate the deformation of the welded members as shown in Figure 4 using fluid analysis, the time required for the analysis was approximately 500 hours. On the other hand, when the inventors of the present application evaluated the deformation of the welded members using the CAE analysis according to this embodiment, it took approximately 50 hours. In other words, it was found that the evaluation using the CAE analysis according to this embodiment can be completed in approximately one-tenth the time required to evaluate the deformation of the welded members using fluid analysis.

[0071] (summary) Therefore, this embodiment includes a model setting step (step S1) for setting a CAE model 20 for each workpiece, a cross-section definition step (step S2) for defining a stir cross-section, which is the cross-sectional shape of the part stirred during friction stir welding, a stir temperature definition step (step S3) for defining a stir temperature generated in the workpiece due to heat generated by stirring, and a deformation calculation step (steps S7, S71-S76) for calculating the deformation amount of each CAE model 20 when heat is input at a defined stir cross-section to the workpiece 24 to be joined by friction stir welding in each CAE model 20. The heat input location is sequentially changed along the workpiece 24, and the deformation calculation step is sequentially executed until heat input to the entire workpiece 24 is complete. As described above, in this embodiment, because the stir cross-section and the stir temperature are defined, it is not necessary to calculate the fluid deformation at the welded part during friction stir welding and the temperature distribution at the deformed location. Furthermore, because the stir cross-section and the stir temperature are constant, the deformation of the CAE model 20 due to heat generated by stirring can be calculated relatively easily. Then, since the deformation of the CAE model 20 is calculated until heat input to the entire welded portion 24 is completed, it is possible to calculate the deformation of each CAE model 20 when friction stir welding is completed. This makes it possible to simply and quickly evaluate the deformation of the welded members during friction stir welding.

[0072] Furthermore, since the part to which heat is input in actual friction stir welding is the part that is stirred, the situation in which heat is input at a defined stirring temperature to a defined stirring cross section can be said to correspond to the situation in actual friction stir welding. Therefore, according to the above-mentioned configuration, the deformation of the CAE model 20 is calculated taking into consideration the situation that corresponds to the actual friction stir welding, so that the deformation of the workpieces can be calculated with high accuracy.

[0073] In particular, this embodiment further includes a stir length definition step (step S4) for defining a stir length, which is the length welded per unit time, and a model addition step (step S74) for adding a joint model 25 connected to each CAE model 20 to a portion of the welded portion 24 for which the deformation calculation step has been completed. The deformation calculation step calculates the deformation of the CAE model 20 when heat is input to a region of the welded portion 24 having the defined stir cross section and the defined stir length. When calculating the deformation of the CAE model 20 due to the (n+1)th heat input (n is a natural number greater than or equal to 1), the deformation of each CAE model 20 is calculated taking into account the joint models 25 added up to the (n)th heat input. This allows the deformation of the CAE model 20 to be calculated taking into account the effects of heat conduction and deformation at the joint where the workpieces are joined. Therefore, it is possible to calculate the deformation of the CAE model 20 corresponding to the actual deformation of the workpieces, thereby improving the evaluation accuracy of friction stir welding.

[0074] In addition, this embodiment further includes a clamping condition setting step (step S6) that defines, for each CAE model 20, a clamping position where each workpiece is clamped in actual friction stir welding, and the deformation calculation step calculates the deformation of the CAE model 20 taking into account the clamping position.

[0075] In addition, in this embodiment, after the deformation calculation step calculates the deformation of the CAE model 20 when the entire to-be-joined portion 24 is joined, a second deformation calculation step (step S8) is further included in which the deformation of the CAE model 20 when heat is dissipated until a predetermined temperature is reached is calculated.

[0076] In particular, when there are a plurality of parts to be welded 24, the second deformation calculation step is executed after the deformation calculation step for all of the plurality of parts to be welded 24 has been completed.

[0077] As a result, the deformation of the CAE model 20 is calculated taking into consideration the conditions corresponding to actual friction stir welding. Therefore, the deformation of the workpieces in actual friction stir welding can be accurately reproduced in the CAE model 20. This further improves the evaluation accuracy of friction stir welding.

[0078] In this embodiment, the cross-section definition step is a step of defining a stir cross section based on the axial length of the pin portion 11 of the probe 10 and at least one of the diameter of the pin portion 11 and the diameter of the shoulder portion 12. By defining the stir cross section in this way, the deformation of the CAE model 20 is calculated taking into account the conditions corresponding to actual friction stir welding, and the deformation of the workpieces in actual friction stir welding can be accurately reproduced in the CAE model 20. Furthermore, because a simple shape is defined as the stir cross section, it is easy to calculate the deformation of the workpieces. This makes it possible to evaluate the deformation of the workpieces more simply and in a shorter time.

[0079] Furthermore, in this embodiment, the stirring temperature definition step is set based on the rotation speed and translation speed of the probe 10. In this way, by defining the stirring temperature taking into consideration the translation speed of the probe 10, the deformation of the CAE model 20 is calculated taking into consideration the situation corresponding to actual friction stir welding, and the deformation of the workpieces in actual friction stir welding can be accurately reproduced in the CAE model 20. This makes it possible to further improve the evaluation accuracy of friction stir welding.

[0080] (Other embodiments) The technology disclosed herein is not limited to the above-described embodiments, and can be substituted within the scope of the claims.

[0081] For example, in the above-described embodiment, the stirring cross section is defined as a triangle, but the stirring cross section is not limited to this and may be defined as a trapezoid whose upper base is longer than its lower base.

[0082] Furthermore, in the above-described embodiment, the stirring cross section is defined taking into consideration the diameter L1 and height H of the pin portion 11 and the diameter L2 of the shoulder portion 12. However, the stirring cross section may be defined only from the diameter L1 and height H of the pin portion 11 without taking into consideration the diameter L2 of the shoulder portion 12.

[0083] Furthermore, in the above-described embodiment, after calculating the deformation of the CAE model 20 when it is cooled to room temperature, it is also possible to further calculate the deformation when the constraint conditions on the CAE model 20 are released, that is, the deformation of the CAE model 20 when the clamp on the CAE model 20 is released. This makes it possible to more accurately estimate the deformation of the workpieces that are actually joined by friction stir welding.

[0084] The above-described embodiments are merely examples and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and variations that fall within the scope of the claims equivalents are within the scope of the present disclosure. [Industrial Applicability]

[0085] The technology disclosed herein is useful for evaluating, by CAE analysis, the amount of deformation of each workpiece when two workpieces are joined by friction stir welding using a rotating probe. [Explanation of symbols]

[0086] 10 probes 11 Pin section 12 Shoulder section 20 CAE models 24 Part to be joined 25 Joint Model

Claims

1. A method for evaluating friction stir welding in which deformation of two workpieces when the workpieces are joined by friction stir welding using a rotating probe is evaluated by CAE analysis, a model setting step of setting a CAE model of each of the workpieces; a cross-section definition step of defining a stir cross section, which is a cross-sectional shape of a part to be stirred in friction stir welding; a stirring temperature definition step of defining a stirring temperature generated in the workpieces by heat generated by the stirring; a deformation calculation step of calculating deformation of each CAE model when heat is input at the defined stir temperature to the defined stir cross section of the welded portion to be welded by friction stir welding in each CAE model, A method for evaluating friction stir welding, characterized in that the heat input location is changed sequentially along the welded part, and the deformation calculation step is performed sequentially until heat input to the entire welded part is completed.

2. The method for evaluating friction stir welding according to claim 1, an agitation length definition step for defining an agitation length, which is a length to be joined per unit time; a model adding step of adding a joint model to each of the CAE models constituting the to-be-welded part at a location of the to-be-welded part where the deformation calculation step has been completed, The deformation calculation step is a step of calculating the deformation of the CAE model when heat is input to a region of the welded part having the defined stir cross section and the defined stir length, and when calculating the deformation of the CAE model due to the (n+1)th heat input (n is a natural number greater than or equal to 1), the deformation of each CAE model is calculated taking into account the welded part models added up to the nth heat input.

3. The method for evaluating friction stir welding according to claim 1 or 2, a clamping condition setting step of defining, for each CAE model, a clamping position at which each of the workpieces is clamped in order to fix the relative positions of the workpieces in actual friction stir welding; The method for evaluating friction stir welding, wherein the deformation calculation step is a step of calculating the deformation of the CAE model taking the clamp position into consideration.

4. The method for evaluating friction stir welding according to any one of claims 1 to 3, A method for evaluating friction stir welding, characterized in that it further includes a second deformation calculation step of calculating the deformation of the CAE model when the entire welded portion is welded in the deformation calculation step, and then calculating the deformation of the CAE model when heat is dissipated to a predetermined temperature.

5. The method for evaluating friction stir welding according to claim 4, A method for evaluating friction stir welding, characterized in that the second deformation calculation step is a step that is executed after the deformation calculation step is completed for all of the multiple welded parts when there are multiple welded parts.

6. The method for evaluating friction stir welding according to any one of claims 1 to 5, the probe is axially shaped and has a pin portion that contacts the workpieces, and a shoulder portion that is located on the opposite side of the pin portion from the workpieces in the axial direction and has a larger diameter than the pin portion; a step of defining the stir cross section based on the axial length of the pin portion and at least one of the diameter of the pin portion and the diameter of the shoulder portion;

7. The method for evaluating friction stir welding according to any one of claims 1 to 6, The method for evaluating friction stir welding, wherein the stirring temperature definition step is set based on the rotation speed and the parallel traveling speed of the probe.

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