Springback Nonlinearity of High-strength Titanium Alloy Tube upon Mandrel Bending

Heng Li,He Yang,Fei-Fei Song,Guang-Jun Li 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

Taking the stress-relieved Ti-3Al-2.5V tube as the objective, regarding both angular and radius springback, the nonlinear springback behaviors of the high-strength titanium tube (HSTT) upon the universal bending, viz., mandrel bending (rotary draw bending), are clarified. The experiments are conducted to identify the springback and validate the theoretical models, and the deformation theory of plasticity and the explicit/implicit 3D-FE based models are used to reveal the rules and the physical mechanism of the nonlinearity of elastic recovery. The results show that: 1) At early bending stages, the angular springback increases nonlinearly with larger bending angles, then it increases linearly when the bending angle exceeds a critical one; While the radius growth decreases exponentially with the increasing of the bending angles at early stages, then it remains unchanged when the bending angle exceeds another critical value; The springback behaves more nonlinearly under smaller bending radii; Both the critical values for the two springback phenomena become larger with smaller bending radii; The critical angle for radius springback is larger than the one for angular springback. 2) The relationship between the radius springback and angular one is further identified; The radius springback can be estimated by the angular springback of the bending regions of tube; The variation of bending radii has significant effect on angular and radius springback, while it has little influence on the springback angle by the straight regions; The variation of the material properties affects both the springback phenomena much more significantly than the changing of the processing parameters.

An Experimental and Numerical Investigation on the Twist Springback of Transformation Induced Plasticity 780 Steel Based on Different Hardening Models

Yan-Min Xie,Ren-Yong Huang,Wei Tang,Bei-Bei Pan,Fei Zhang 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.4

Investigation on twist springback is important to improve the accuracy of forming parts. In this paper, a double C rail made of transformation induced plasticity 780 (TRIP 780) steel is designed, and the stamping and twist springback are simulated with ABAQUS based on three different hardening models (including Ziegler, Johnson-Cook and combined hardening models). A new index for calculating the twist springback is proposed, which is based on the angle between two end section lines of the double C rail. The experimental results of twist springback are compared with the calculation results from three different hardening models. The calculation results based on combined hardening model are the closest to the experiment data. In order to compensate twist springback, a curved surface die is designed based on the geometric shape of the double C rail after twist springback. The stamping and twist springback are simulated based on the curved surface die and combined hardening model, and the twist springback is decreased obviously after compensation, which shows that the compensation of twist springback is effective.

Springback Characteristics of Tailor-Welded Strips in U-Draw Bending

Seo, Dae Gyo,Chang, Sung Ho,Heo, Young Moo 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.6

The purpose of this study is to investigate the springback characteristics of tailor-welded strips in U-draw bending. Two different welded strips were adopted to compare the effects of weld-line locations on the springback. One was welded along the centerline of the strip-width and the other was welded along the centerline of the strip-length. To investigate the effect of different thickness combinations on the springback, the tailorwelded strips were joined by a laser welding process. Three sheet thickness combinations were assessed, SCP1 0.8 t * SCP1 1.2 t, SCP1 0.8 t * SCP1 1.6 t and SCP1 0.8 t * TRIP 1.0 t. Three punch profile radii of 3, 6, and 9 mm and three die profile radii of 5, 10, and 15 mm were prepared and three blank holding forces (BHF) of 125 kgf, 250 kgf, and 500 kgf were applied to investigate the effects of punch profile radius (Rp), die profile radius (Rd), and BHF on the springback of tailor-welded strips. With consideration for the thickness of the sheet and the material properties, the extent of the springback on the sidewall of unloaded sheet shapes increases as the thickness and the yield strength of the sheet increase in the U-draw bending process. For longitudinally welded strips, the amount of springback of the TRIP steel sheet in TWB could be reduced through a springback combination of the thinner side and weld-line. For the thinner side (0.8 t) of the centrally welded strips, the deformed shapes after the springback were almost the same regardless of the thickness combination, and the extent of the springback decreased compared with that of non-welded SCP1 0.8 t. Some experimental results are compared with analytical results obtained by using the finite element method.

보정 공정을 포함한 U-채널 성형 공정에서 스프링백의 강건 설계

김경모,인정제 한국기계기술학회 2018 한국기계기술학회지 Vol.20 No.1

The most time consuming job in the sheet metal forming process is compensating for springback. Factors such as uneven material properties and process conditions generate noise, which in turn create springback. The springback is very sensitive to the process and noise conditions, and the main effects of the design variables cannot be obtained from mean analysis. Therefore, to achieve minimal springback, an effective design countermeasure must be put in place to reduce noise effects. In this study, two robust design methods toachieve minimal springback in U-channel forming, including compensation process, are proposed. The effectiveness of the proposed methods is shown with an example of the sidewall curl springback. The proposed methods consistently outperform our previous work, indicating that the complex method is more preferable to the mean analysis, if there is no evidence of additivity of effects.

박판 성형 공정에서 스프링백의 강건 설계

김경모(Kyung-Mo Kim),인정제(Jeong-Je Yin) 한국기계가공학회 2013 한국기계가공학회지 Vol.12 No.2

Springback is a very typical dimensional discrepancy phenomenon, which occurs usually on the final stamping parts after the tool loading is removed. Variation of springback leads to amplified variations and problems during assembly of the stamped components, in turn, resulting in quality issues. The variations in the properties of the incoming material and process parameters are the main causes of springback variation. In this research, a robust design methodology which combines orthogonal array based experimental design and design space reduction skim to reduce the springback variation for advanced high strength steel parts in sheet metal forming is suggested. The concept of design space reduction is adapted in the experimental design setup to improve the quality of the obtained solution. The effectiveness of the proposed procedures is illustrated through a robust design of springback in metal forming process of a cross member of auto body.

알루미늄 캔 딥드로잉에서 Bottoming을 이용한 스프링백 최소화

박상민(Sang-Min Park),이사랑(Sa-Rang Lee),홍석무(Seokmoo Hong) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.9

다단 딥드로잉의 기술은 제조 비용과 사이클 시간 단축 등의 장점으로 인해서 금속 성형 산업에 널리 적용되고 있다. 다단 딥드로잉으로 만들어진 제품의 형상이 복잡하고 세장비 큰 특징을 가진다. 예를 들어, 휴대전화의 배터리캔은 대표적으로 다단 딥드로잉으로 만들어진 제품이다. 배터리캔의 형상은 높이와 두께의 큰 종횡비를 가지고 있기 때문에 제조하기 무척 어렵다. 또한 최종 조립된 부품은 다단계 딥드로잉 후 스프링백으로 인해 조립 문제가 발생한다. 이러한 배터리 캔의 조립시 발생하는 품질문제를 개선하기 위해서는 드로잉 후 스프링을 줄이기는 것이 매우 중요하다. 스프링백을 감소시키기 위해 산업 현장에서는 over bending, corner setting 및 Ironing 등의 경험적 방법을 적용해 왔으나, 본 연구에서는 유한 요소법을 이용한 보토밍(Bottoming)법을 제안하여 스프링을 줄이는 실용적이고 과학적인 방법을 제안하였다. 보토밍은 드로잉으로 성형된 최종 판재에 펀치로 압축응력을 더욱 부가하여 스프링을 감소시키는 방법이다. 최적의 금형설계를 위해서 다양한 경우의 보토밍 공정 해석 시뮬레이션이 상용 유한요소 해석프로그램 (DYNAFORM)을 이용하여 연구되였다. 보토밍 공정을 적용한 제품의 스프링백 시뮬레이션 결과와 실험 결과와 비교되었고 그 시뮬레이션 결과는 실험과 잘 일치함을 보여 주었다. 결론적으로, 제안된 보토밍 방법은 산업계에서 스프링을 줄이기 위한 실용적인 방법으로 널리 사용될 것으로 예상된다. The technology of multistage deep drawing has been widely applied in the metal forming industry, in order to reduce both the manufacturing cost and time. A battery can used for mobile phone production is a well-known example of multistage deep drawing. It is very difficult to manufacture a battery can, however, because of its large thickness to height aspect ratio. Furthermore, the production of the final parts may result in assembly failure due to springback after multistage deep drawing. In industry, empirical methods such as over bending, corner setting and ironing have been used to reduce springback. In this study, a bottoming approach using the finite element method is proposed as a practical and scientific method of reducing springback. Bottoming induces compression stress in the deformed blank at the final stroke of the punch and, thus, has the effect of reducing springback. Different cases of the bottoming process are studied using the finite element program, DYNAFORM, to determine the optimal die design. The results of the springback simulation after bottoming were found to be in good agreement with the experimental results. In conclusion, the proposed bottoming method is expected to be widely used as a practical method of reducing springback in industry.

Springback Reduction by Using Tool Rollers

Chetan P. Nikhare 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.1

Springback is defined as a geometric defect, which occurs due to elastic recovery in the part after it has been unloaded. This challenge is most common in lightweight alloys as well as in advanced high strength steels. The materials, which exhibit lower elastic modulus or higher tensile strength, would be more prone to springback. In this paper, a novel patented technique is introduced to eliminate the springback by using rollers in the forming tool. It was found that due to the rotation of rollers in the tool during forming, reduces the stress in the part and, thus reduces the springback.

가변금형 성형에서 탄성회복 제어 연구

하석문(S.M. Ha),박종우(J. W. Park),김태원(T. W. Kim) 한국소성·가공학회 2008 소성가공 : 한국소성가공학회지 Vol.17 No.6

Springback is one of the most difficult phenomena to analyze and control in sheet forming. Most of traditional springback control methods rely on experiences of skilled workers in industrial fields. This study focuses on prediction and generation of optimum reconfigurable die surfaces to control shape errors originated by springback. For this purpose, a deformation transfer function(DTF) was combined with finite element analysis of the springback in the 2D sheet forming model of elastic-perfectly plastic materials under the condition without blank holder. The results showed shape errors within 1% of the objective shape, which were comparable with analytically predicted errors. In addition to this theoretical analysis, DTF method was also applied to 2D and 3D sheet forming experiments. The experimental results showed ±0.5 mm and ±1.0 mm shape error distribution respectively, demonstrating that reconfigurable die surfaces were predicted well by the DTF method. Irrespective of material properties and sheet thickness, the DTF method was applicable not only to FEM simulation but also to 2D and 3D elasto-reconfigurable die forming. Consequently, this study shows that springback can be controlled effectively in the elasto-RDF system by using the DTF method.

U-채널 성형 시 스프링백 보정 공정의 강건 설계

인정제 한국기계기술학회 2016 한국기계기술학회지 Vol.18 No.1

The most time consuming operation during the tryout of new parts is the compensation of geometric deviations induced by springback. The variation of springback due to the noise factors such as material properties and forming conditions increase the difficulties of the compensation operation. If the forming process includes a drawing operation followed by a restriking operation, a robust design for springback compensation is needed for both operations. In this study, a new 2-stage procedure for robust springback compensation using Taguchi's orthogonal array experiments combined with the Pick-the-Winner rule and the design space reduction method is proposed. The effectiveness of the proposed method is shown with an example of the sidewall curl springback compensation in U-channel forming.

Yoshida-Uemori 모델을 이용한 Al 판재의 스프링백 예측

서오석(O. S. Seo),이은국(E. G. Lee),홍석무(S. M. Hong),최선철(S. C. Choi),유수열(S. Y. Ryu),이명규(M. G. Lee),김헌영(Heon Young Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5

Springback is caused by the recovery of elasticity of a flat-rolled metal, which occurs when the forming force is released from a flat-rolled metal. Springback takes place in a large degree when a high strength steel plate or AI alloy sheet is processed. It has been known that hardening model is the most efficient for the prediction of springback. Recently, various researches have been carried out. In particular, Yoshida-Uemori model has been proved to be the most suitable for forecasting the springback of a high strength steel plate. In this paper, Uniaxial tension tests and cyclic loading tests(T-C-T, C-T-C) were conducted on the 1050 Al alloy sheet, 3003, and 5052 series. And based on the test results, coefficients required for Yoshida-Uemori model have been figured out. In addition, the test results were put into commercial finite element program PAM-STAMP to predict the springback of Al Alloy sheet and the outcome has been proved to be quite accurate.