JP2012208884A - Spring back factor analysis method in multi-process press molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spring back factor analysis method in multi-process press molding.SOLUTION: Disclosed is spring back factor analysis method in multi-process press molding characterized to perform processing of alternately performing press molding analysis and spring back analysis in the case of performing press molding analysis and spring back analysis across a plurality of press processes to search a shape A of a press molded article posterior to the release of the final press process, processing of extracting one process of a plurality of press processes of alternately performing the press molding analysis and the spring back analysis, and searching the residual stress distribution of the press molded article prior to the release in the pertinent process, and performing spring back analysis after changing or removing the residual stress distribution, and alternately performing the press molding analysis and the spring back analysis about the next and following processes to search a shape B of the press molded article posterior to the release of the final press process; and processing of specifying the press process affecting the spring back of the press molded article on the basis of the shape A of the press molded article and the shape B of the press molded article.

Description

  The present invention relates to a multi-step press forming analysis method, and more particularly to a method for accurately analyzing in a short time which process of a press-formed product and how the stress of a part affects the springback.

  In recent years, in order to reduce the weight of automobiles, it has been promoted to expand the application of high-strength steel sheets to automobile parts. A high-strength steel sheet has a large elastic recovery after press forming (hereinafter referred to as a springback) as compared with a mild steel sheet, and thus it is difficult to ensure the dimensional accuracy of a part. For this reason, it is necessary to repeatedly adjust the shape of the press mold and adjust the mold several times until the normal dimensional accuracy is achieved.

  Therefore, in order to reduce such press die correction work, a technique for predicting the amount of springback at the die design stage is desired, and an analysis system for the technology has been developed.

These analysis methods consist of the following two stages.
(1) Analysis of deformation, stress and strain of material under restraint by press mold (2) Analysis of springback in a state released from restraint by press mold Here, step (1) is finite Analysis is performed by the element method, and in step (2), the analysis is performed by the springback theoretical formula or the finite element method.

  It is known that such springback is caused by the non-uniform distribution of residual stress remaining in the press-molded product before releasing the press-molded product from the press die. Conventionally, numerical analysis such as the finite element method is used. Prediction using methods has been made. However, it is difficult to predict which region of the residual stress of the press-molded product is dominant in the springback.

  Conventionally, for example, Patent Document 1 discloses a study on the influence of the shape of a press-formed product and molding conditions on the spring back.

  Patent Document 1 calculates how a defined amount relating to springback before and after changing the residual stress distribution changes by changing the residual stress distribution in a certain area of the press-formed product, A method for predicting the impact of a region on springback is disclosed.

JP 2007-229724 A

  However, the springback factor analysis method described in Cited Document 1 only supports the behavior of the spring bag in one molding step, and when the final shape is determined after two or more molding steps, There is a problem that it is not possible to examine whether the influence of the process is large.

  Accordingly, the present invention has been made to solve the above-described problems, and in a press-formed product whose final shape is determined through a multi-step press forming process, which region of the residual stress of the press-formed product is selected. It is an object of the present invention to provide a springback factor analysis method in multi-step press forming that can accurately grasp how things in the process affect the spring bag.

  The gist of the present invention is as follows.

  In the first invention, when performing press molding analysis and spring back analysis over a plurality of press processes, the press molding analysis and the spring back analysis are alternately performed, and the shape of the press molded product after the mold release in the final press process is performed. A process of obtaining A, and extracting one process among a plurality of press processes in which press molding analysis and spring back analysis are alternately performed, and determining the residual stress distribution of the press molded product before release in the process, After changing or removing the residual stress distribution, the spring back analysis is performed, and the press molding analysis and the spring bag analysis are alternately performed for the subsequent processes to obtain the shape B of the press molded product after the mold release in the final pressing process. Press work that affects the springback of the press-formed product based on the processing and the shape A of the press-formed product and the shape B of the press-formed product A springback factor analysis method in a multi-step press forming characterized by identifying.

  In the second invention, when performing press molding analysis and spring back analysis over a plurality of press processes, the shape of the press molded product after mold release in the final press process is performed by alternately performing press molding analysis and spring back analysis. Extract one process from multiple press processes that perform processing to obtain A and press molding analysis and spring back analysis alternately, and determine the residual stress distribution of the press-molded product before mold release in that process. After changing or removing the residual stress of the part, the spring back analysis is performed, and the press molding analysis and the spring bag analysis are alternately performed for the next and subsequent processes to obtain the shape B of the press molded product after the mold release in the final pressing process. Based on the required processing and the shape A of the press-molded product and the shape B of the press-molded product, it has the greatest influence on the springback of the press-molded product. A springback factor analysis method in a multi-step press forming and identifies the constant region.

  According to a third aspect of the present invention, when performing press molding analysis and springback analysis over a plurality of pressing processes, press molding analysis is performed for each process, and only the final process is subjected to press molding analysis and springback analysis. Processing to obtain the shape A of the press-molded product after the mold, and press molding analysis for each process, extracting one process in the press process for performing the press molding analysis and the springback analysis only in the final process, After determining the residual stress distribution of the press-molded product before mold release, changing or removing the residual stress distribution or the residual stress at a specific part, press molding analysis is performed for the next and subsequent processes, and only the final process is pressed. Processing for performing molding analysis and spring bag analysis to obtain the shape B of the press-molded product after mold release, and the shape A of the press-molded product and the above-mentioned Based on the shape B of less moldings, a springback factor analysis method in a multi-step press forming characterized by identifying the pressing step or specific site affect the spring back of the press-molded product.

  Since it is possible to grasp the effect of residual stress on the shape in any one of the multiple pressing processes, it is possible to determine which process should be targeted as a springback countermeasure and which part should be focused on. become able to.

It is a figure explaining a multi-step press molding process. It is an analysis flow figure in a 1st embodiment. It is a shape comparison figure in a 1st embodiment. It is a figure explaining the specific site | part in 2nd Embodiment. It is an analysis flow figure in a 2nd embodiment. It is the figure which compared the shape of the specific site | part in 2nd Embodiment. It is an analysis flow figure in a 3rd embodiment. It is a shape comparison figure in a 3rd embodiment.

  Embodiments of the present invention will be described with reference to the drawings.

  In general, a press-formed product is often formed through a plurality of press processes as shown in FIG. As shown in Patent Document 1, the conventional springback factor analysis is a press forming analysis for one press process. (1) A region A and a region other than a certain region of a press-formed product before release. Calculate the contribution of residual stress in area B to springback, or (2) divide the press-molded product before mold release into area A and area B, and contribute to the springback of residual stress in the divided area A And comparing the contribution of the residual stress of the divided region B to the springback, and repeating the subdivision of the region with the larger contribution to find the region with the highest contribution to the springback. Analysis method is adopted.

  However, when press molding is performed through a plurality of pressing processes, for example, even if the influence of one process is on the + side, it is shaken on the-side in the next process and the influence does not appear in the final process. is there. In such a case, since the above-described analysis method cannot analyze an inherent problem, the analysis method shown in the following embodiment has been invented.

(First embodiment)
As shown in FIG. 2, the springback factor analysis method according to the first embodiment of the present invention includes basic analysis and application analysis. In the basic analysis, a molding analysis is performed for each press process. And mold release analysis (hereinafter referred to as springback analysis) are alternately performed, and a process for obtaining the shape A of the press-molded product after the mold release in the final press process is performed.

  On the other hand, in the applied analysis, one process among a plurality of press processes is extracted, the residual stress distribution of the press-formed product before release in the process is obtained, and after changing or removing the residual stress distribution, the springback is performed. Analysis is performed, and further, press molding analysis and spring bag analysis are alternately performed for the next and subsequent steps, and processing for obtaining the shape B of the press-molded product after release in the final pressing step is performed.

  And, it is an analysis method for comparing and evaluating the obtained shape A of the press-molded product and the shape B of the press-molded product, and evaluating which of the press processes has the most influence on the springback. .

(Second Embodiment)
The springback factor analysis method according to the second embodiment consists of basic analysis and application analysis as in the first embodiment, and analysis is performed according to the processing flow shown in FIG. In addition, the same process as in the first embodiment is performed to obtain the shape A of the press-formed product.

  On the other hand, in applied analysis, after extracting one process among a plurality of press processes, obtaining the residual stress distribution of the press-molded product before releasing in the process, and changing or removing the residual stress at a specific part Then, the spring back analysis is performed, and the press molding analysis and the spring bag analysis are alternately performed for the subsequent steps and thereafter, and the process of obtaining the shape B of the press molded product after the mold release in the final pressing step is performed. In addition, a specific site | part represents the site | part of the components of a press molded product, as shown in FIG.

  Then, based on the shape A of the press-molded product and the shape B of the press-molded product, the specific portion that most affects the springback of the press-molded product is specified.

(Third embodiment)
The springback factor analysis method according to the third embodiment is the same as the first and second embodiments in that it consists of basic analysis and applied analysis, but the flow is shown in FIG. The analysis method of the present invention can also be applied to the case where the springback analysis other than the springback analysis in the final process is omitted for both the basic analysis and the applied analysis. If the springback analysis is omitted, the accuracy of the obtained analysis result is affected. However, it is effective to quickly find out which part of the press-formed product has an influence on the final product shape because the calculation time can be shortened.

  As an embodiment of the springback factor analysis method according to the present invention, the cross-sectional shape shown in FIG. 1 is obtained by press molding in three steps by a mold using a 590 MPa class cold-rolled steel sheet having dimensions of 1.0 mm × 280 mm × 200 mm. The springback factor analysis was conducted for the products of. In the analysis calculation, as the basic analysis, the forming analysis and the springback analysis (mold release analysis) shown in FIG. 2 were alternately performed three times, and then the angle θ after the mold release was measured (FIG. 3B). In the applied analysis, in the first step, the residual stress distribution before mold release was calculated (first step molding analysis), and after removing all the stress, a springback analysis (first step mold release analysis) was performed. Thereafter, molding analysis and springback analysis were performed in the second and third steps, and the angle θ after the release was measured (FIG. 3B).

As shown in FIGS. 3 (a) and 3 (b), the product shape is set to θ ₀ = 180 ° before the third step release, and the angle θ after the third step release is obtained. Then, the angle change after mold release (θ−θ ₀ ) was evaluated. The result is shown in FIG. 3, and it can be seen that when the residual stress in the first step is removed, the angle change (θ−θ ₀ ) after release is very small. This means that the residual stress in the first step has a great influence on the spring back of the product.

In Example 2, press forming analysis was performed using the same cold-rolled steel sheet and product shape as in Example 1. In Example 2, stress calculation was performed paying attention to the product parts (A: concave R part, B: convex R part, C: plane part) shown in FIG. The calculation flow is shown in FIG. Since the basic analysis calculation is the same as in Example 1, details are omitted in this section, but after the third step, the angle change (θ−θ ₀ ) of the product after mold release was obtained.

In applied analysis, when the residual stress distribution is calculated by forming analysis in the first step, the residual stress is removed for part A, and the springback analysis (release analysis) is performed, the residual stress is removed for part B. When the springback analysis (release analysis) is performed, the residual stress is removed from the part C, and the stress calculation is performed up to the third step for each of the cases where the springback analysis (release analysis) is performed. After the mold, the angle change (θ−θ ₀ ) was determined for each case.

The analysis results are shown in FIG. It can be seen that the angle change (θ−θ ₀ ) of the concave R portion A is the smallest among the portions A, B, and C. This can be understood that the stress generated in the part A: the concave R part in the first step molding process greatly contributes to the angle change (θ−θ ₀ ).

Example 3 is a flowchart showing a calculation process when a springback analysis (release analysis) other than the final process is omitted. In the case of this section, the stress calculation shown in Example 1 and Example 2 can be applied, the calculation efficiency is prioritized over the calculation accuracy, and the tendency of angle change (θ−θ ₀ ) after mold release is obtained in a short time. This is a convenient analysis method when you want to.

Comparison between the basic analysis shown in Fig. 7 and the case where the stress after the first process molding analysis is removed and the subsequent second and subsequent molding analysis and the final process springback analysis (mold release analysis) are performed The results are shown in FIG. When the residual stress in the first step is removed, it can be seen that the change in angle (θ−θ ₀ ) after release is very small. This means that the residual stress in the first step has a great influence on the spring back of the product.

A Concave R part B Convex R part C Plane part

Claims (3)

  In performing press molding analysis and springback analysis over a plurality of press processes, processing for obtaining the shape A of the press molded product after demolding in the final press process by alternately performing press molding analysis and springback analysis; Extract one process among multiple press processes that perform press molding analysis and spring back analysis alternately, and obtain the residual stress distribution of the press molded product before mold release in the process, and change the residual stress distribution or After the removal, the spring back analysis is performed, and the press molding analysis and the spring bag analysis are alternately performed on and after the next process to obtain the shape B of the press molded product after demolding in the final press process, and the press molding Based on the shape A of the product and the shape B of the press-formed product, the press process that affects the springback of the press-formed product is specified. Springback factor analysis method in a multi-step press forming characterized by.   In performing press molding analysis and springback analysis over a plurality of press processes, processing for obtaining the shape A of the press molded product after demolding in the final press process by alternately performing press molding analysis and springback analysis; Extract one process from multiple press processes that perform press molding analysis and springback analysis alternately, and determine the residual stress distribution of the press-molded product before mold release in that process, and change the residual stress at a specific part. Alternatively, after removing, the spring back analysis is performed, and the press molding analysis and the spring bag analysis are alternately performed for the subsequent processes and thereafter, and the shape B of the press molded product after the mold release in the final pressing process is obtained, and the press Based on the shape A of the molded product and the shape B of the press molded product, the specific part that most affects the springback of the press molded product is specified. Springback factor analysis method in a multi-step press forming characterized by Rukoto.   In performing press molding analysis and springback analysis over multiple pressing processes, press molding analysis is performed for each process, press molding analysis and springback analysis are performed only for the final process, and then the press molded product after mold release The process for obtaining the shape A and press molding analysis for each process, extracting one process in the press process for performing the press molding analysis and the springback analysis only in the final process, and press molding before releasing in the process After determining the residual stress distribution of the product and changing or removing the residual stress distribution or the residual stress at a specific part, press molding analysis is performed for the next process and after, and press molding analysis and spring bag analysis for the final process only. To obtain the shape B of the press-molded product after mold release, and the shape A of the press-molded product and the press-molded product Based on the Jo B, springback factor analysis method in a multi-step press forming characterized by identifying the pressing step or specific site affect the spring back of the press-molded product.

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