Manufacturing method for metal products

Abstract

The goal is to enable the manufacture of metal parts with higher precision, even if deformation occurs after machining of the metal material. [Solution] A method for manufacturing a metal product comprises the steps of: predicting the amount of deformation of a metal product that occurs after machining when a metal product is manufactured by machining a metal material; determining the machining conditions based on the amount of deformation so that the required accuracy of the metal product is satisfied; and manufacturing the metal product by machining the metal material under the determined machining conditions.

Description

Technical Field

[0001] Embodiments of the present invention relate to a method for manufacturing metal workpieces.

Background Art

[0002] When machining a metal material such as a profile having a long structure, the shape of the metal workpiece after machining is deformed. The deformation of the shape of the metal workpiece is mainly caused by residual stress generated during the manufacture of the metal material. For this reason, a technique for estimating the amount of deformation of the metal material after machining based on the internal stress of the metal material has been proposed (see, for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In particular, when an aircraft part is a metal workpiece, it often has a long structure and is a metal workpiece having a thin shape that needs to be cut out by cutting from a profile having a large thickness. Therefore, there is a problem that when the residual stress at the time of manufacture of the metal material is released after machining, the metal workpiece is deformed and the required dimensional accuracy may not be satisfied.

[0005] Therefore, an object of the present invention is to enable the production of metal workpieces with higher precision even if deformation occurs after machining of the metal material.

Means for Solving the Problems

[0006] A method for manufacturing a metal product according to an embodiment of the present invention includes the steps of: predicting the amount of deformation of a metal product that occurs after machining when a metal product is manufactured by machining a metal material; determining the machining conditions based on the amount of deformation so as to satisfy the required accuracy of the metal product; and manufacturing the metal product by machining the metal material under the determined machining conditions. [Brief explanation of the drawing]

[0007] [Figure 1] A flowchart showing the process for manufacturing a metal processed product according to an embodiment of the present invention. [Figure 2] A partial perspective view showing an example of a metal product manufactured by the manufacturing method shown in Figure 1, and a metal material used to manufacture the metal product. [Figure 3] This graph shows the relationship between stress and strain measured in a tensile test performed on a heat-treated aluminum alloy at a strain rate of 0.5 mm / m. [Figure 4] This graph shows the relationship between stress and strain measured during a tensile test on heat-treated aluminum alloy at a strain rate of 2 mm / m. [Figure 5] This figure shows an example of residual stress analysis results for an aluminum alloy profile with an I-shaped cross-section. [Figure 6] A diagram illustrating the simplified one-dimensional distribution of residual stress in metallic materials. [Figure 7] Figure 6 illustrates the principle of deformation caused by residual stress when a metal material is machined. [Figure 8] This figure shows an example of determining the relative position of a metal workpiece to a metal material in such a way that the excess material is uniform. [Figure 9] This figure shows an example of offsetting the relative position of a metal workpiece relative to a metal material by predicting the amount of deformation of the metal workpiece. [Figure 10] A diagram showing an example of predicting the amount of deformation of a metal processed product. [Figure 11]This figure shows an example where the deformation of a metal processed product was predicted to be relatively large. [Modes for carrying out the invention]

[0008] A method for manufacturing a metal product according to an embodiment of the present invention will be described with reference to the attached drawings.

[0009] Figure 1 is a flowchart showing the flow of a manufacturing method for a metal product according to an embodiment of the present invention. Figure 2 is a partial perspective view showing an example of a metal product manufactured by the manufacturing method shown in Figure 1 and a metal material for manufacturing the metal product.

[0010] For example, if a long profile 1, as shown by the solid line in Figure 2, is made of metal, a stringer (longitudinal member) 2, shown by the dotted line, can be manufactured as a metal product by machining the profile 1. Aircraft parts with long structures, such as stringers 2, have a thin profile but are often curved or have irregularities. Therefore, it is necessary to cut the stringer 2 from a thick profile 1 by machining.

[0011] Metal materials can be cut using machine tools such as milling machines and machining centers, or specialized machining equipment. End mills are a typical tool used for cutting.

[0012] Prior to machining the metal material, in step S1, the metal material is heat-treated. At this time, a test specimen made of the same material as the metal material is also heat-treated under the same heat-treatment conditions as the metal material so that the physical properties of the metal material after heat treatment can be measured. The test specimen may be part of the metal material or prepared separately. In addition, multiple test specimens may be prepared to obtain the physical properties of the metal material with high accuracy.

[0013] If the metal material is an aluminum alloy, the heat treatment is a solution treatment at 400 °C followed by water cooling to 20 °C which is room temperature (RM: room temperature). Of course, heat treatments such as quenching and tempering according to the material can be performed for iron-based metals, titanium alloys, etc.

[0014] When heat treatment is performed on the metal material and the test piece, residual stress occurs inside the metal material and the test piece. In other words, the typical process in which residual stress occurs inside the metal material and the test piece is heat treatment.

[0015] Next, in step S2, based on the test piece after heat treatment, the physical property values of the metal material after heat treatment are measured. Incidentally, by heat-treating a plurality of test pieces and taking the average of the plurality of physical property values of the metal material measured respectively based on the plurality of test pieces after heat treatment as the measured value of the physical property value of the metal material, the measurement accuracy of the physical property value of the metal material can be improved. The physical property value of the metal material is obtained as data representing the relationship between the stress and strain of the metal material at each temperature until it returns to room temperature after heat treatment by a tensile test of the test piece.

[0016] Figure 3 is a graph showing the relationship between stress and strain measured by performing a tensile test on the aluminum alloy after heat treatment at a strain rate of 0.5 mm / m, and Figure 4 is a graph showing the relationship between stress and strain measured by performing a tensile test on the aluminum alloy after heat treatment at a strain rate of 2 mm / m.

[0017] In Figures 3 and 4, the vertical axis indicates the stress [MPa] generated in the aluminum alloy, and the horizontal axis indicates the strain [%] generated in the aluminum alloy. As shown in Figures 3 and 4, after heat treatment, a tensile test of the aluminum alloy can be performed at each temperature until it returns to room temperature (R.T: room temperature). That is, the stress-strain curve of the aluminum alloy at each temperature can be obtained using a tensile testing machine.

[0018] In the examples shown in Figures 3 and 4, the strain rates of the tensile testing machine are set to 0.5 mm / m and 2 mm / m. Tensile tests are performed on two specimens at each temperature range of 50°C from 400°C to 150°C, and stress-strain curves are obtained for both specimens at the same temperature. Therefore, the average value of the stress-strain curves obtained using the two specimens can be used as the measured value.

[0019] Next, in step S3, the shape of the metal material is determined according to the metal product to be manufactured. For example, if the metal product to be manufactured is the stringer 2 shown by the dotted line in Figure 2, then the metal material can be determined to be a profile 1 having the shape shown by the solid line in Figure 2. The shape of the metal material can also be changed as described later. If the shape of the metal material is to be changed later, the determination of the shape of the metal material in step S3 becomes the initial shape setting.

[0020] Next, in step S4, the residual stress distribution within the metal material is predicted. The residual stress distribution of the metal material can be predicted by finite element method (FEM) analysis based on the stress-strain curve, which is the data representing the relationship between stress and strain of the metal material obtained as the material property value in step S2. Therefore, the residual stress distribution within the metal material is calculated using electronic circuits such as a computer.

[0021] The accuracy of predicting the residual stress distribution within a metallic material using FEM analysis is thought to improve as the amount of data representing the relationship between stress and strain in the metallic material, which serves as an input parameter to the FEM analysis, increases. Therefore, as shown in the examples in Figures 3 and 4, obtaining stress-strain curves of the metallic material at multiple different strain rates leads to an improvement in the accuracy of predicting the internal residual stress distribution of the metallic material. Of course, tensile tests of the metallic material can also be performed without changing the strain rate to reduce the effort involved in tensile testing.

[0022] Internal residual stress in metal materials after heat treatment arises from the temperature difference between the surface temperature, which decreases first, and the internal temperature of the metal material. Therefore, it is believed that using stress-strain curves at multiple temperatures that the metal material can take after heat treatment as input parameters for FEM analysis will help ensure prediction accuracy.

[0023] The stress-strain curve of a metallic material, which serves as an input parameter for FEM analysis, can be a combination of stress and strain measurements at multiple sampling points. As mentioned above, increasing the number of input parameters for FEM analysis improves the accuracy of predicting the internal residual stress distribution of the metallic material; therefore, the number of input parameters for FEM analysis can be determined according to the required accuracy.

[0024] As a concrete example, 50 points can be extracted from the stress-strain curves of a metal material at various temperatures, and the measured stress and strain values ​​at these 50 points can be used as input data for FEM analysis. In this case, as illustrated in Figures 3 and 4, if the stress-strain curves were obtained at six different temperatures, 300 measured stress and strain values ​​for each strain rate will be used as input data for FEM analysis.

[0025] If it is desirable to further improve the accuracy of predicting the internal residual stress distribution of metallic materials, more stress and strain measurements can be used as input data for FEM analysis. Conversely, reducing the amount of input data for FEM analysis can simplify the analysis process.

[0026] Figure 5 shows an example of residual stress analysis results for an aluminum alloy profile with an I-shaped cross-section.

[0027] As illustrated in Figure 5, a metal material can be simulated using an FEM model divided into numerous elements, and its internal residual stress can be simulated. The internal residual stress of a metal material can be calculated as a stress corresponding to the material properties of each element.

[0028] Furthermore, in order to evaluate the validity of the residual stress analysis results for metallic materials, the residual stress of metallic materials was actually measured using an X-ray residual stress measuring device. As a result, as described above, it was confirmed that the residual stress of metallic materials can be predicted with practical accuracy by using the measured stress and strain values ​​at 50 points extracted from the stress-strain curves of metallic materials at various temperatures as input data for FEM analysis.

[0029] If the accuracy of residual stress analysis is confirmed to be sufficient for metal materials with typical shapes, then residual stress analysis can be proceeded with metal materials with different shapes under the assumption that the accuracy will also be sufficient if the heat treatment conditions are the same. Therefore, although the residual stress distribution differs depending on the shape of the metal material, the confirmation of analysis accuracy by measuring residual stress only needs to be performed for metal materials with typical shapes. For example, if there are 100 different shapes of metal materials, residual stress can be measured for 1 to 3 representative shapes, and the measurement of residual stress can be omitted for the other shapes. Furthermore, needless to say, even if the confirmation of analysis accuracy by measuring residual stress is omitted, it is still possible to predict the residual stress distribution of metal materials using FEM analysis.

[0030] On the other hand, the stress-strain curve of a metallic material, which is used as an input parameter for residual stress analysis of metallic materials, is a material-specific physical property. Therefore, once obtained under the same heat treatment conditions, it can be used regardless of the shape of the metallic material.

[0031] Once the residual stress distribution of the metal material is calculated, in step S5, the relative position of the metal workpiece with respect to the metal material is provisionally determined. That is, the initial position of the metal workpiece is set. The initial position of the metal workpiece can be set by referring to the residual stress distribution of the metal material. Specifically, when a metal workpiece is manufactured by machining the metal material, the initial position of the metal workpiece can be set in such a way that the amount of deformation of the metal workpiece caused by the residual stress of the metal material is reduced as much as possible.

[0032] Figure 6 is a simplified diagram illustrating the residual stress distribution of a metallic material as a one-dimensional distribution, and Figure 7 is a diagram illustrating the principle by which deformation occurs due to residual stress when the metallic material shown in Figure 6 is machined.

[0033] After heat treatment, the metal material 3, such as the profiled material, contains residual stress. Specifically, in the metal material 3, compressive residual stress occurs near the surface where the temperature decreases relatively quickly after heat treatment, and tensile residual stress occurs near the center where the temperature decreases relatively slowly after heat treatment. Therefore, as shown in Figure 6, when the metal material 3 is placed on the jig 4, compressive residual stress occurs on the surface and back surface of the metal material 3, and tensile residual stress occurs near the center of the interior, as shown in the graph with the horizontal axis representing the relative value of residual stress. As a result, the compressive residual stress on the surface and back surface of the metal material 3 balances out.

[0034] In contrast, as shown in Figure 7, when the portion of the metal material 3 indicated by the dotted line is machined to produce the metal product 5, the balance of residual stresses is disrupted, generating a bending moment M, as shown in the graph with the relative value of residual stress on the horizontal axis. As a result, both ends of the metal product 5 deform upwards.

[0035] Therefore, the relative position of the metal workpiece 5 with respect to the metal material 3 can be initially set based on the residual stress distribution of the metal material 3, so as to reduce the amount of deformation of the metal workpiece 5. Specifically, the position of the metal workpiece 5 in which the internal residual stress of the metal workpiece 5 after machining is balanced as much as possible and the amount of deformation is small can be predicted and set as the initial position of the metal workpiece 5.

[0036] The initial position of the metal product 5 is not limited to one position; multiple positions can be set. In other words, based on the analysis results of the residual stress distribution of the metal material 3, multiple candidate positions for the metal product 5 can be determined as initial positions.

[0037] Figure 8 shows an example where the relative position of the metal workpiece to the metal material is determined so that the excess material is uniform, and Figure 9 shows an example where the relative position of the metal workpiece to the metal material is offset by predicting the amount of deformation of the metal workpiece.

[0038] When determining the relative position of a stringer 2, an example of a metal processed product, to a profile 1, an example of a metal material, the relative position of the stringer 2 can be determined so that the machining allowance, i.e., the excess material, is uniform, as shown in Figure 8. However, depending on the residual stress distribution of the profile 1, the deformation of the stringer 2 may become large.

[0039] Therefore, as illustrated in Figure 9, a candidate position can be determined based on the residual stress distribution of the profile 1 in which the deformation of the stringer 2 is reduced. Figure 9 shows an example in which the relative position of the stringer 2 is offset in the direction of the arrow.

[0040] Once the initial position of the metalworked part 5 is set, in step S6, the amount of deformation of the metalworked part after machining is confirmed by FEM analysis. That is, based on the residual stress distribution of the metal material calculated in step S4 and the initial position of the metalworked part set in step S5, the amount of deformation of the metalworked part that will occur after machining when the metalworked part is manufactured by machining the metal material is predicted by FEM analysis.

[0041] Therefore, the amount of deformation of a metal product after machining is calculated using electronic circuits such as computers, similar to the residual stress distribution of the metal material. Specifically, the amount of deformation of the metal product after machining can be determined by simulating the machining of the metal material and performing calculations to release the internal residual stress of the metal material and generate strain.

[0042] Furthermore, simulations of machining metal materials revealed that the residual stress distribution of the metal material is dominant in determining the deformation of the metal workpiece, and that cutting conditions such as the type of tool used, the starting position of the cutting process, and the tool path do not significantly affect the deformation of the metal workpiece. Actual cutting tests also yielded results consistent with the simulations. Therefore, it is considered sufficient to input the relative position of the metal workpiece to the metal material as an input parameter for FEM analysis.

[0043] Figure 10 shows an example of predicting the deformation amount of a metal processed product, and Figure 11 shows an example where the deformation amount of a metal processed product was relatively large as a result of the prediction.

[0044] As shown in Figures 10 and 11, the amount of deformation of a metal workpiece after machining can be visually determined by simulation. Figures 10 and 11 show the amount of deformation in the stringer portion, which has a Z-shaped cross-section, and Figure 11 shows an example where the deformation of the stringer is relatively large.

[0045] If the deformation of the metal part is not reduced as expected or falls outside the acceptable range after FEM analysis, the relative position of the metal part with respect to the metal material can be changed. Therefore, in step S7, it is determined whether or not it is necessary to change the position of the metal part.

[0046] If the position of the metal part needs to be changed, the position of the metal part is changed in step S8. In this case as well, multiple positions can be reset as the next candidate positions. Then, the FEM analysis simulation in step S6 is executed again using the reset positions of the metal part as input data. Therefore, by repeatedly setting the position of the metal part and calculating the amount of deformation of the metal part, the position of the metal part can be optimized to reduce the amount of deformation of the metal part.

[0047] If the resetting of the position of the metal workpiece is also performed automatically by computer, the computer can perform optimization calculations to determine the position of the metal workpiece that minimizes the amount of deformation of the metal workpiece. In this case, the initial position of the metal workpiece set in step S5 may be set to one location and may be set independently of the residual stress distribution of the metal material.

[0048] Conversely, when an operator determines multiple possible positions for a metal workpiece by referring to the residual stress distribution of the metal material, it is possible to easily determine the position of the metal workpiece while avoiding large-scale calculations. As a practical example, the position of the metal workpiece that minimizes deformation among the multiple candidates determined by the operator can be selected as the actual position for machining the metal workpiece.

[0049] If the deformation of the metal part is not sufficiently reduced regardless of the position of the metal part, or if the position of the metal part is determined according to the deformation of the metal part, resulting in excessive excess metal material, the shape of the metal material can be changed. Therefore, in step S9, it is possible to determine whether or not it is necessary to change the shape of the metal material based on the deformation of the metal part.

[0050] In step S10, the shape of the metal material is changed when the shape of the metal material is modified. For example, if the deformation of a part of the metal workpiece is excessive, the shape of the metal material can be reset to a new shape with increased excess material so that the residual stress distribution in the part of the metal material with excessive deformation becomes a desirable residual stress distribution to reduce the amount of deformation, or so that the degree of freedom of the position of the metal workpiece is improved. Conversely, if excess material is created as a result of determining the position of the metal workpiece, the shape of the new metal material can be reset so that the excess material is reduced.

[0051] Then, the FEM analysis simulation in step S4 is executed again using the reset shape of the metal material as input data, and the residual stress distribution of the metal material corresponding to the material properties of the metal material is calculated. Therefore, by repeatedly setting the shape of the metal material and calculating the amount of deformation of the metal workpiece, it is possible to optimize the shape of the metal material so that a residual stress distribution is generated in the metal material that can reduce the amount of deformation of the metal workpiece, and the relative position of the metal workpiece with respect to the metal material can be determined to be an appropriate position that can reduce the amount of deformation of the metal workpiece. In addition, it becomes possible to reduce the excess material of the metal material.

[0052] If the shape of the metal material is also automatically reset by computer, it becomes possible to perform optimization calculations using a computer to determine the shape of the metal material that minimizes not only the deformation of the metal processed product but also the excess material of the metal material. Of course, it is also possible for an operator to reset the shape of the metal material.

[0053] After the determinations in steps S7 and S9, in step S11, it is possible to determine the shape of the metal material and the position of the metal workpiece, which can at least reduce the amount of deformation of the metal workpiece. In other words, based on the amount of deformation of the metal workpiece obtained by FEM analysis, the shape of the metal material and the relative position between the metal material and the metal workpiece, which is one of the machining conditions, can be determined so that the dimensional accuracy requirements of the metal workpiece are satisfied by reducing the amount of deformation of the metal workpiece.

[0054] Furthermore, once the shape of the metal material and the position of the metal workpiece corresponding to various metal workpiece shapes have been determined, the FEM analysis may be replaced with calculations using artificial intelligence (AI) with neural networks such as DNN (Deep Neural Network). That is, by training the AI ​​with training data that uses the physical properties of the metal material and the shape of the metal workpiece as input data and the relative position of the metal material and metal workpiece as output data, it becomes possible to determine the shape of the metal material and the position of the metal workpiece that can reduce the deformation of the metal workpiece using a neural network without performing FEM analysis for each shape of the metal material and metal workpiece. In that case, the prediction of internal residual stress of the metal material can be omitted.

[0055] Alternatively, the internal residual stress distribution of the metal material can be calculated using FEM analysis, and the relative position of the metal product relative to the metal material can be determined using AI based on the internal residual stress distribution of the metal material. In this case, the input data of the neural network would be the shape and internal residual stress distribution of the metal material, and the output data of the neural network would be the relative position of the metal product relative to the metal material.

[0056] Once the machining conditions, including the relative position of the metal part with respect to the metal material, are determined, in step S12, machining of the metal material is performed under the determined machining conditions. That is, the metal material is cut using a machine tool such as a milling machine, machining center, or stringer. This produces the metal part.

[0057] The manufactured metal parts are cut from the metal material at positions determined to minimize deformation caused by the release of residual stress during the cutting process, resulting in metal parts with minimal deformation. In other words, metal parts with good dimensional accuracy can be manufactured.

[0058] The above-described method for manufacturing metal products involves predicting the internal residual stress distribution of the metal material and the amount of deformation of the metal product after machining, based on the previously acquired physical properties of the metal material, using FEM analysis, etc., and determining the machining conditions, including the relative position of the metal product, so as to reduce the amount of deformation of the metal product.

[0059] (effect) Therefore, according to this method for manufacturing metal products, it is possible to produce metal products having a desirable shape with reduced deformation. In addition, it is possible to shape the metal material in a way that is suitable for reducing the deformation of the metal product. Specifically, the shape of the metal material can be determined so as to create a residual stress distribution that can reduce the deformation of the metal product, and the relative position of the metal product with respect to the metal material can be determined to be an appropriate position that can reduce the deformation of the metal product.

[0060] (Other embodiments) Although specific embodiments have been described above, these embodiments are merely examples and do not limit the scope of the invention. The novel methods and apparatus described herein can be embodied in various other forms. Furthermore, various omissions, substitutions, and modifications can be made in the forms of methods and apparatus described herein, without departing from the spirit of the invention. The attached claims and equivalents include such various forms and modifications as being encompassed within the scope and spirit of the invention. [Explanation of Symbols]

[0061] 1. Shaped material 2 Stringer 3 Metal materials 4. Jig 5 Metal products M Bending moment

Claims

1. A step of predicting the amount of deformation of a metal product that occurs after machining when a metal product is manufactured by machining a metal material, The steps include determining the machining conditions based on the amount of deformation so that the required precision of the metal product is satisfied, A step of manufacturing the metal product by machining the metal material under the determined machining conditions, A method for manufacturing metal products having the following characteristics.

2. A method for manufacturing a metal product according to claim 1, wherein the relative position between the metal material and the metal product is determined as a condition for machining, such that the amount of deformation of the metal product is reduced.

3. A method for manufacturing a metal product according to claim 1, wherein the shape of the metal material is determined based on the amount of deformation.

4. A method for manufacturing a metal product according to any one of claims 1 to 3, comprising predicting the residual stress distribution inside the metal material by finite element analysis based on the physical properties of the metal material, and predicting the amount of deformation of the metal product based on the predicted residual stress distribution.

5. The steps include: performing heat treatment on the metal material and a test piece made of the same material as the metal material prior to machining the metal material; The steps include obtaining data representing the relationship between stress and strain of the metal material at each temperature during the heat treatment by performing a tensile test on the test piece after the heat treatment, It has, The method for manufacturing a metal processed product according to claim 4, wherein the physical properties of the metal material are data representing the relationship between stress and strain of the metal material.

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