Blank Shape Research Articles

Optimization of Initial Blank Shape for Minimizing the Trimming Process in Hot Stamping of T-Shaped Parts

Blank optimization in stamping is a way to reduce the cost of unnecessary material consumption or subsequent trimming operations by acquiring the final target part in a single forming process. There have been many studies on blank optimization in room temperature stamping, but few studies have yet been conducted in hot stamping. In this study, a blank shape optimization was conducted for a T-shaped part simulating a body center pillar. A finite element analysis (FEA) for the hot stamping process was performed using an appropriately assumed initial blank shape, and the blank shape was updated based on the shape error between the outline of the deformed blank obtained from the FEA and that of the target part. The shape error was calculated by applying the modified radius vector method. Hot stamping test was carried out using the optimal shaped blank predicted by the FEA. It was confirmed that the outline of the deformed blank obtained by the actual test was very close to the outline of the target part. From the results of this study, it can be seen that the blank optimum design technique at room temperature stamping can be applied to the case in hot stamping.

The Effect of Flange Length on the Distribution of Longitudinal Strain during the Flexible Roll Forming Process

Flexible roll forming is an advanced sheet metal forming process which allows the production of variable cross-section profiles. In flexible roll forming process, nonuniform transversal distribution of the longitudinal strain can cause the longitudinal bow, which is deviation in height of the web over the length of the profile. To investigate the effect of flange length on the transversal distribution of the longitudinal strain, FEM simulations are conducted with different flange length for three blank shapes; trapezoid, convex and concave. The result shows that the longitudinal strain and longitudinal bow decrease with increasing flange length for a trapezoid and a concave blank. For a convex blank, the longitudinal strain and longitudinal bow increase with increasing flange length. To validate FEM simulation result, numerically obtained longitudinal strain has been compared with experimental results.

Dimensional Characteristics of Tailor Rolled Blanks Having Thickness Variations both in Longitudinal and Width Directions

Tailored blanks with different blank thicknesses are semi-finished parts that can be used to produce stamping parts having a real tailor-made solution. This study investigates a manufacturing process that can produce a tailored rolled blanks(TRB) having variable thickness variations both in longitudinal and width directions. The process was experimentally and numerically investigated using three types of the conventional blank and blanks having circular and square holes. To characterize the process, the deformation behaviors of blanks were intensively analyzed. In order to understand the effect of the blank shape on the manufacturing TRB, the strain behaviors was compared by numerical simulation. The results show that the hollow blanks have good formability in the manufacturing of TRB having variable thickness variations both in longitudinal and width directions compared with the conventional blank.

Hominin raw material procurement in the Oldowan-Acheulean transition at Olduvai Gorge

The lithic assemblages at the Oldowan-Acheulean transition in Bed II of Olduvai Gorge, Tanzania, represent a wide variety of raw materials reflecting both the diversity of volcanic, metamorphic, and sedimentary source materials available in the Olduvai basin and surroundings and the preferences of the tool-makers. A geochemical and petrographic systematic analysis of lava-derived archaeological stone tools, combined with textural and mineralogical characterization of quartzite, chert, and other metamorphic and sedimentary raw materials from two Middle and Upper Bed II sites, has enabled us to produce a comprehensive dataset and characterization of the rocks employed by Olduvai hominins, which is used here to establish a referential framework for future studies on Early Stone Age raw material provenancing. The use of rounded blanks for most lava-derived artifacts demonstrates that hominins were accessing lava in local stream channels. Most quartzite artifacts appear to derive from angular blocks, likely acquired at the source (predominantly Naibor Soit hill), though some do appear to be manufactured from stream-transported quartzite blanks. Raw material composition of the EF-HR assemblage indicates that Acheulean hominins selected high-quality lavas for the production of Large Cutting Tools. On the other hand, the HWK EE lithic assemblage suggests that raw material selectivity was not entirely based on rock texture, and other factors, such as blank shape and availability of natural angles suitable for flaking, played a major role in Oldowan reduction sequences.

Sheet metal anisotropy and optimal non-round blank design in high-speed multi-step forming of AA3104-H19 aluminium alloy can body

A new anisotropic yield function which accurately describes the complex anisotropy of aluminium alloy sheet metal is proposed in this paper. A non-linear least square method is used to determine the coefficients of this yield function based on the experimental results. By employing the back-Euler stress integration algorithm, this anisotropic constitutive model has been successfully implemented in commercial FEM software ABAQUS via user material subroutine UMAT to predict earing profile of AA3104-H19 deep-drawn and redrawn cups. Good agreement was found in the predicted earing profiles and those obtained in experimental deep-drawn and redrawn cups. The FE model was used in an iteration optimisation process to determine the optimal shape of non-round blanks to obtain the ear-free deep-redrawn cups, and non-round tooling was designed accordingly. Results showed the height of the ears is significantly reduced in the cup formed using this non-round blank compared with that of a conventional round blank which is important for smooth running of high-speed multi-step forming of aluminium can body.

Design optimization of variable blank holder force trajectory and blank shape for S-rail shaped product using a novel springback evaluation

Design optimization of variable blank holder force trajectory and blank shape for S-rail shaped product using a novel springback evaluation

The Effects of Blank Geometry on Gear Rolling for Large Gear Modules: Experiments and Finite Element Simulations

Gear rolling is a forming process to produce gear wheels by plastic deformation. The advantage of the process is to eliminate the chip formation during production and also to improve the product properties since the non-metallic inclusions will be oriented along the cog surface and not perpendicular to it. The method has been developed in the past years for gear production for automobile application with modules up to 3 mm. The successful application of gear rolling in those cases raises the question regarding the feasibility of using cold rolling to manufacture gears with larger modules which can be used for heavy vehicles. In this paper, a gear wheel with normal module of 4 mm has been studied in order to investigate if such large modules can be manufactured by gear rolling. One of the issues in rolling of gears is the design of the blank geometry in order to obtain the right gear geometry after the rolling process. Blank shape modifications are necessary to control and to reduce the undesired shape deviations caused by the large plastic deformations in rolling. The blank modifications also help the process designer to control the forming force and torque. In this paper, the process has been modeled by finite element simulation and the influence of different blanks has been simulated. The validity of the FE model has been checked through several experiments. Both the numerical and experimental results revealed favorable blank modifications to apply for further developments of the gear rolling process.

Characterization of the longitudinal bow during flexible roll forming of steel sheets

Flexible roll forming is an advanced sheet metal forming process that allows for the production of variable cross-section profiles. Longitudinal bow is one of the major shape defects found in roll-formed products. To characterize the degree of longitudinal bow during flexible roll forming, experiments were conducted on three different blank shapes: trapezoid, convex and concave. Symmetric U-sections with variable cross-sections were roll formed using the three sheet materials with different strengths from each blank shape. The effects of process variables on the longitudinal strain and longitudinal bow were analyzed both experimentally and by using finite element simulations based on ABAQUS-Implicit 6.14. The results show that the transversal nonuniformity of the longitudinal strain is one of the fundamental causes of longitudinal bow in roll-formed products. The bow height as a function of blank shape increases in the order of concave, trapezoid, and convex. The bow characteristics on the basis of blank shapes and material parameters provides a better understanding of the non-uniform longitudinal strain and bow height during flexible roll forming with high reliability. Furthermore, to reduce the longitudinal bowing, leveling roll is introduced. The effect of leveling roll on longitudinal bowing was investigated experimentally. The results show that longitudinal bowing was reduced with the use of three blank shapes when leveling roll was applied to a flexible roll forming process.

Forming limit prediction for AA7075 alloys under hot stamping conditions

In this paper, the forming limits of AA7075 demonstrators with different initial blank shape under hot stamping conditions were predicted using the developed model, named the viscoplastic-Hosford-MK model. The developed model enables the representation of non-isothermal conditions, changes in strain rate and loading path for AA7075 material. Additionally, the developed model was calibrated using the fundamental experiments including uniaxial and formability tests. To assess the capability of the proposed model, the forming limit of AA7075 with different initial blank shape designs were predicted, and the optimal initial blank shape was verified by applying it to the practical forming of a demonstrator AA7075 component.

深絞り加工におけるブランク形状と分割可変ブランクホルダー力の同時最適化

深絞り加工におけるブランク形状と分割可変ブランクホルダー力の同時最適化

深絞り加工における耳最小化を目的とした初期ブランク形状と分割可変ブランクホルダー力の同時最適化

深絞り加工における耳最小化を目的とした初期ブランク形状と分割可変ブランクホルダー力の同時最適化

An Industrial Application of the Continuum Damage Mechanics (CDM) Model for Predicting Failure of AA6082 under HFQ® Process

The failure prediction for forming of high strength complex shaped panel made of AA6082 aluminium alloy during the solution heat treatment cold die forming and quenching process (HFQ®), is presented. Experimental trails have been carried out to optimise the blank shape on the success of forming the complex-shaped aerospace panel component (wing stiffener part). Using the traditional set of uniaxial constitutive equations is difficult to predict the forming features in real hot stamping, especially taken the varied stress states during the forming process. A multi-axial viscoplastic constitutive model based on continuum damage mechanics (CDM) has been developed to describe the deformation behaviour of aluminium alloys under hot/warm stamping conditions. By linking such CDM-based constitutive equations into complete finite element solver, PAM-STAMP in this case, via external Subroutine, as a User Defined Material (UDM), the formability for any process conditions, cold or hot and low or high speed, could be predicted. In this paper the CDM model is verified using an experimental forming trail of complex aluminium component. The results show that the CDM model can be used to provide accurate formability and failure predictions.

Optimization of blank shape and segmented variable blank holder force trajectories in deep drawing using sequential approximate optimization

Blank holder force (BHF) is one of the important process parameters for successful sheet metal forming. Variable blank holder force (VBHF) that the BHF varies through the forming process is recognized as an advanced forming technology. It has also been reported that segmented VBHF (S-VBHF) is valid to a complex shape forming, but the optimal S-VBHF trajectories are rarely discussed and used. In addition to BHF, blank shape has an influence on the product quality. The blank shape minimizing the earing is still an important issue in sheet metal forming. Simultaneous optimization of both S-VBHF trajectories and blank shape is one of the crucial issues in industries. This paper proposes a method to simultaneously optimize both the segmented VBHF trajectories and the blank shape. Numerical simulation in sheet metal forming is so intensive that a sequential approximate optimization (SAO) using a radial basis function (RBF) network is adopted for the simultaneous design optimization. Based on the numerical result, the experiment using the AC servo press (H2W300, Komatsu Industry Corp.) that can conduct the optimal S-VBHF trajectories is carried out. It has been confirmed from the numerical and experimental result that the proposed approach is valid.

The Refinement Algorithm of Blank Outline Based on One-Step Inverse Analysis

Blank dimensions and outlines can be obtained in one-step inverse analysis. Applying more accurate mesh will achieve more precise outlines while usually lead to the increase of computation time. To ensure operation efficiency, this paper proposes a new blank outline refinement algorithm based on one-step inverse analysis. Firstly, the initial configuration is obtained from the final configuration by one-step inverse analysis. Secondly, all outline nodes is projected to the nearest element in the final configuration. Thirdly, according to the position of projected nodes in the element, the coordinate of outline nodes in the initial configuration is achieved through mapping. Finally the number of outline nodes is increased in rounded corners, the coordinate of added nodes are calculated through interpolation. At last all outlines corresponding to characteristic lines of part surface are acquired. Using A-pillar as an example, outlines are calculated by the refinement algorithm and commercial software. It proves that under the same mesh quality, outlines obtained by refinement algorithm become more accurate and smooth, especially in rounded corner. The results can contribute to judge the rationality of blank shape and improve the final part forming property. This algorithm refines the accuracy of outlines and ensures the efficiency of one-step inverse analysis.

A New Algorithm of the Boundary Restraining Force for One-Step Inverse Analysis

In one-step inverse analysis, the restraining force produced by blank holder and draw bead need to be replaced equivalently by the nodal force to obtain a rational blank shape. But the distribution of the equivalent restraining force should not be uniform. A self-adaptive algorithm of the equivalent restraining force is presented in this paper. By comparing the initial configration contour line of the part obtained from three different methods (self-adaptive algorithm, uniformly distributed algorithm and a commercial software Fastform) with experimental results, the self-adaptive algorithm is proved to be accurate and convenient.

Simultaneous optimization of blank shape and variable blank holder force of front side member manufacturing by deep drawing

This paper presents a method to determine an optimal blank shape minimizing earing for a front side member. In addition, variable blank holder force, meaning that the blank holder force (BHF) varies through punch stroke, is adopted. Blank shape directly affects the material cost, and it is important to determine an optimal blank shape minimizing earing that is trimmed out. BHF also have an influence on the product quality. Large BHF leads to tearing, whereas small BHF results in wrinkling. Variable BHF (VBHF) approach is recognized as one of the advanced manufacturing technologies, but it is difficult to determine the optimal VBHF for successful sheet metal forming. To determine the optimal blank shape and VBHF simultaneously, design optimization is performed. Numerical simulation in sheet metal forming is so intensive that a response surface approach is valid. In particular, a sequential approximate optimization that the response surface is repeatedly constructed and optimized is used to determine the optimal blank shape and VBHF. Front side member provided from NUMISHEET 2011 (BM3) is used for the numerical simulation. It is found from the numerical result that the proposed approach can drastically reduce the earing. In addition, the maximum thinning is much improved, compared with other results reported in NUMISHEET 2011.

Effect of loading pattern on longitudinal bowing in flexible roll forming

The flexible roll forming process can be used to fabricate products with a variable cross-section profile in the longitudinal direction. Transversal nonuniformity of the longitudinal strain is one of the fundamental characteristics of blank deformation in flexible roll forming. Longitudinal bowing is a shape defect caused by transversal nonuniformity of the longitudinal strain. In this study, loading patterns in flexible roll forming are investigated in order to reduce the longitudinal bowing in a roll-formed blank. To analyze the effects of loading patterns on longitudinal bowing, two different forming schedules are implemented. In schedule 1, loading patterns with different bending angle increments are designed under fixed initial and final bending angles. In schedule 2, loading patterns with different initial bending angles under the fixed final bending angle are designed. Our results show that the bowing heights are significantly affected by the loading patterns. The bowing susceptibilities vary with blank shape such as trapezoid, convex, and concave shapes. In addition to the peak longitudinal strain at the respective roll stands, the cumulative longitudinal strain from the initial to final stands is shown to be a reliable index in predicting the tendency of longitudinal bowing.

타원형 다단 딥 드로잉 제품의 성형성 향상을 위한 초기 소재 형상 최적 설계

다단계 딥 드로잉(multi-stage deep drawing)은 산업현장에서 대형의 금속 제품 뿐만 아니라 소형의 제품에 까지 많은 제품으로 확대되고 있는 제조 공정 중 하나이다. 예를 들어, 스마트 폰에 사용되는 USB-C형 소켓은 매우 작고, 정밀하며 세장비가 큰 부품이며, 이 제품은 타원형 다단계 딥드로잉 방법으로 제조된다. 다단계 딥 드로잉에 최종 제품의 두께 분포를 보장하기 위해서 다단계 딥드로잉 전체 공정에서 제품의 두께 분포가 균일하게 유지되어야 한다. 따라서 첫 번째 드로잉 작업 후에 타원형 제품의 장변과 단변쪽 측벽의 높이 차를 최소화하는 것은 최종 제품의 균일한 두께를 보장하는 가장 중요한 공정 설계 인자이다. 본 연구에서는 첫 번째 드로잉 공정 후 소재가 균일한 높이를 지속적으로 유지될 수 있도록 하기 위해서 유한요소해석을 기반으로 초기의 타원형 소재 형상 결정에 대한 최적 설계를 수행하였다. 최적 설계된 초기 블랭크 형상으로 성형된 제품의 경우 전체 균일한 두께 분포를 가질 뿐만 아니라 드로잉 후 제품의 장변과 단변의 높이 단차가 최소화 되었다. 최종적으로 최적 설계로 예측된 초기 소재 형상은 실제 실험 결과와 비교하여 검증되었고, 매우 양호한 결과의 일치를 보여주었다. Multi-stage deep drawing is a widely used industrial manufacturing process, and its applications are gradually expanding to both small products and large metallic products. The USB C-type socket used in smart phones, for example, is manufactured using oval multi-stage deep drawing. The socket is very small and slender and it requires precise manufacturing. The thickness distribution of the final product is guaranteed only if it is uniform throughout the overall process. Therefore, minimizing the height difference between long and short sidewalls after the first operation is important for this goal. An initial blank optimization was performed for an oval-type drawing process based on finite element simulations. The goal was to determine an initial blank geometry that can maintain uniform height and thickness after the first draw operation. The initial blank shape of the sheet metal was optimized, and the results show that it satisfied the conditions of minimal thickness reduction and even thickness distribution. The geometry from the optimized simulation was compared with experimental results, which showed good agreement.

Deep Drawability and Bendability in Hot Stamping of Ultra-High Strength Steel Parts

The deep drawability and bendability in hot stamping of ultra-high strength steel parts were examined. Although the cold drawability is greatly influenced by the blank shape, the limiting drawing depths for the square and circular blanks were equal for hot stamping because of small flow stress. In hot hat-shaped bending using draw-and form-type tools, the effect of the blankholder force generated with the draw-type tools on the springback was small, and the seizure for the form-type tools was smaller than that of the draw-type tools. Since both edges in contact with the electrodes are not heated for resistance heating, cracks were caused at the edges for resistance heating in the transversal directions in hot stamping of an S-rail with form-type tools, and thus it is required to control deformation of the non-heating zones.

Genetic Algorithm optimization of initial blank shape in deep drawing of a stepped work piece

This study considers the effect of forging direction on the initial shape of sheet to create a stepped work piece. The purpose of this study is to consider rolling direction in 0°, decreasing the waste while producing workpieces and so decreasing total cost of process. To this end, the assumed workpiece was made of a low carbon and anisotropic st14 steel sheet. To find the most appropriate direction and the shortest modification steps for final shape, the expansion level of the sheet was first imaged in the rolling direction and then the piece was shaped by the geometry. This approach was based on the coupling between the simulation and Genetic Algorithm. A Genetic Algorithm based approach is developed to optimize dimensions through integrating a finite element code running to compute the objective functions for each generation. Those points with a few materials modified through Genetic Algorithm yielded better results.