Finite Element Simulation of Flexible Roll Forming with Supplemented Material Data and the Experimental Verification

Flexible roll forming is a promising manufacturing method for the production of variable cross section products. Considering the large plastic strain in this forming process which is much larger than that of uniform deformation phase of uniaxial tensile test, the widely adopted method of simulating the forming processes with non-supplemented material data from uniaxial tensile test will certainly lead to large error. To reduce this error, the material data is supplemented based on three constitutive models. Then a finite element model of a six passes flexible roll forming process is established based on the supplemented material data and the original material data from the uniaxial tensile test. The flexible roll forming experiment of a B pillar reinforcing plate is carried out to verify the proposed method. Final cross section shapes of the experimental and the simulated results are compared. It is shown that the simulation calculated with supplemented material data based on Swift model agrees well with the experimental results, while the simulation based on original material data could not predict the actual deformation accurately. The results indicate that this material supplement method is reliable and indispensible, and the simulation model can well reflect the real metal forming process. Detailed analysis of the distribution and history of plastic strain at different positions are performed. A new material data supplement method is proposed to tackle the problem which is ignored in other roll forming simulations, and thus the forming process simulation accuracy can be greatly improved.

Key technologies of roll forming automobile components with AHSS

Lightweight design is one of the development trends of the automobile industry. An effective way to achieve lightweight auto bodies is to use AHSS （advanced high strength steel ） for the safety components of automobiles. This study has taken doorsill reinforcements made of martensite AHSS as the object ,and performed research on the AHSS roll forming technologies and prototype development of typical asymmetric open components. By means of finite element analysis （FEA） and simulation,studies have been carried out on the springback and edge wave defects during AHSS roll forming ,and an optimized process design has been achieved. The generation mechanisms of vertical bows ,horizontal cambers, twists,pre-punched hole distortion and cut end flare have been analyzed,and solutions to these defects have been given. In addition,tesing of the roll forming process for AHSS has been conducted and typical samples with required dimensional accuracy have been manufactured. This study has provided technical support for the large-scale application of AHSS.

NUMERICAL SIMULATION OF ROLL FORMING FORCHANNEL SECTION WITH OUTER EDGE

The finite strip method in structural analysis has been extended, and elastic-plastic large deformation spline finite strip method based on the Updated-Lagrange method (U. L. method) was established to simulate roll forming process of channel section with outer edge. The deformation characteristics of strip was analyzed, and the three-dimensional displacement field, strain field and stress field of deformed strip were got. The calculation example proves that the peak transverse pressing membrane strain is on the corner part of the deformed strip, and the peak longitudinal stretching strain is on the outer edge part of the deformed strip in front of rolls. In addition, the transverse deformation of the deformed strip is principal, and the longitudinal deformation is small.

Insight into deformation allocation in the multi-pass roll forming of a double-walled brazed tube

Deformation allocation is an important factor that affects 720°curling forming from copper-coated steel strips to double-walled brazed tubes(DWBTs).In this study,four schemes of deformation allocation,considering different weights of the total feed distance,are proposed,and a 3D finite element(FE)model of the multi-pass roll forming process for DWBT is developed and verified to investigate the cross-sectional evolution and deformation features.The results show the following.(i)In the 720°curling forming process from the steel strip into double-walled tubes,the curvature of the formed circular arc initially increases and then remains stable with roll forming,and the inner and outer tubes of the DWBT are formed in the third and fifth forming passes.Size forming can eliminate the gap between the double walls and improve the overall roundness.(ii)For different deformation allocations,the cross-sectional profiles of the roll-formed parts exhibit a discrepancy,and the deformation amount varies with the roll-forming process.The deformation amount in Scheme three is the maximum,and the cross-sectional profile deviates significantly from the ideal shape and fails to form a DWBT,which indicates that the deformation allocation is unsuitable.(iii)The roundness of the outer tube is better than that of the inner tube.Therefore,the roundness of the inner tube is the key to restricting the forming accuracy of the DWBT.Compared with Schemes one and two,Scheme four with a linear allocation of the total feed distance exhibits the best roundness,and the deformation allocation is reasonable;i.e.,when the contact points between the rollers and steel strip are in a straight line,the roundness of the DWBT is in good agreement with the ideal condition.

Numerical Simulation and Sensitivity Analysis of Parameters for Multistand Roll Forming of Channel Section With Outer Edge

Cold roll forming is a high production but complex metal forming process under the conditions of coupled effects with multi-factor. A new booting finite element method （FEM） model using the updated Lagrangian （IAL） method for multistand roll forming process is developed and validated. Compared with most of the literatures related to roll forming simulation, the new model can take the roll rotation into account and is well suited for simulating multistand roll forming. Based on the model, the process of a channel section with outer edge formed with twelve passes is simulated and the sensitivity analysis of parameters is conducted with orthogonal design combined FEM model. It is found that the multistand roll forming process can be efficiently analyzed by the new booting model, and sensitivity analysis shows that the yield strength plays an important role in controlling the quality of the products.

Deformation mechanism analysis of roll forming for Q&P980 steel based on finite element simulation

Roll forming is a sheet metal forming process,which can form the profiles gradually to improve the formability of Q&P980 steel.The plastic deformation mechanism of roll forming was expounded by analysing the stress and strain distribution at the comer of a hat-type profile when the Q&P980 steel sheet passed through a series of continuous stands.And the plastic deformation mainly accumulated when the sheet metal was not in contact with the rolls.A simple mathematical model was derived by considering the longitudinal bending strain and the geometrical relationships of forming parameters,to analyse the longitudinal strain development in the deformation process.In addition,the roll forming experiments on hat-type profile parts of Q&P980 steel were carried out,and the theoretical analysis and simulation results are consistent with the experimental results.

Mechanism investigation and strategies for reducing residual stress at open ends of the roll-formed part

Increasing geometrical accuracy at open ends of the roll-formed part is difficult due to the release of residual stress after end cutting.In this work,a typical rail with a high requirement of geometry accuracy was selected to realize the behaviors of residual stress release.First,residual stress distribution after roll forming is discussed in detail by finite element analysis with ABAQUS.In addition,two different approaches are proposed to check their capabilities in reducing the residual stress level.The results indicate that both additional rolling passes and multiple bending processes are beneficial to reducing uniform residual stress.

Modeling of the Shape Forming of Composite Roll

A shape modeling of spray formed composite roll, which is utilized to predict the shape and dimension of roll during spray forming process, is developed in this paper. The influences of the principal spray forming parameters, such as the spatial distribution of melt mass flux, spray distance, rotating and translating speeds of substrate bar etc. , on the geometry and dimension of spray formed product were investigated.

Millipede forming-a new metal forming approach

Millipede Forming is a novel metal forming method that has been proposed and developed recently.It can be applied to overcome fundamental limitations in conventional roll forming,and,in addition,used for incremental forging and integrated into a strip casting or extrusion process for downstream thickness reduction. In this new method,there are two main principles:①the use of an optimal transitional surface or space linking of the incoming material to the outgoing product,and②implementation of a method to feed the material through the forming device so that it conforms with this ideal space and the required deformation is imposed on it by the tooling. The system described here is called "Millipede forming" because deformation is accomplished in a large number of small steps.A prototype has been built to demonstrate the working principle applied to the replacement of a roll forming process;it can be used to produce simple profiles within a forming length an order of magnitude shorter than the conventional process. In this paper,the working principle of "Millipede forming" is introduced and some fundamental research on forming a channel section and a circular tube is discussed.Following the success of the small scale prototype, research on a full scale pilot machine has been proceeding.It is expected that this process can be developed and extended as a useful alternative to conventional roll forming,incremental forging and within a strip casting or other novel strip material(e.g.nanostructured metals) system.

Simulation Analysis and Optimization of Rolling Process of Steel Rim

In order to solve the problems of rolling forming accuracy and fillet thinning of alloy steel rim, a three-dimensional model of three pass rolling process was established, and the influence of different process parameters on forming quality was analyzed by using the finite element software, and the optimal process parameter combination was obtained. On this basis, the simulation results of wheel rim stress and strain for each pass rolling are analyzed, and the particle tracking technology is introduced to analyze the variation rule of stress in each incremental step. Finally, the simulation and experimental results show that the simulation thickness is basically consistent with the actual thickness, which improves the accuracy of rim rolling forming, and further verifies the correctness of rolling process simulation.

Forming-Induced Residual Stress and Material Properties of Roll-Formed High-Strength Steels

Martensitic steels are widely used in the automotive lightweight application but less understood in aspects of post-forming material properties.The steels show good ductility in roll forming but occasionally experience delayed(hydrogen)fracture issues,which are believed to be due to the formation of localized residual stress and a reduced product of strength and elongation.To characterize the effect of roll forming process on the formation of residual stress and material properties variation of martensitic steel components,this paper investigates the forming-induced longitudinal residual stress and material property variation in a roll-formed high-strength MS1180 automotive rocker panel.The finite element analysis results for residual stress are validated by neutron diffraction measurements.The numerical model is used to analyze the full evolution of residual stress during the roll forming process and the effect on material properties with major focus on the product of strength and elongation.It is found that the flower design,in particular the overbending stages,play a significant role in the formation of residual stress and the change in material properties.The product of strength and elongation is significantly reduced across the profile,in particular in the corners.The achieved understanding will assist researchers comprehend the material properties of roll-formed component and therefore assist future studies aimed at preventing the occurrence of hydrogen fracture.

Analysis and Suppression of End Flare in AHSS Roll‑Formed Seat Rail

Roll forming has been widely used to manufacture long channels with complex cross-sections.End flare,one of the typical shape errors,seriously affects the forming accuracy of roll-formed parts,especially using advanced high-strength steel.In this paper,the mechanism of end flare during the roll forming process of a high-strength automobile seat rail is analyzed.The roll forming process of an actual seat rail is designed.The finite element models of the roll forming process and cut-off springback are established to predict the deformation process and occurrence of end flare.Simulation results indicate that the uneven distribution of longitudinal and shear residual stress along the length of the part is the main reason for the end flare.Based on the simulation,two strategies are proposed to mitigate the end flare.Employing multiple bending processes in the transverse direction effectively balances the longitudinal and shear residual stress.Additionally,the longitudinal bending process can make the longitudinal residual stress in the roll-formed parts more homogenised.Finally,verification experiments are carried out,and the forming accuracy of the seat rail is significantly improved.

Numerical Study of the Forming Process of High Frequency Welded Pipe

The roll forming process is applied to the manufacturing of high frequency welded (HFW) pipes,section steels,etc. In this paper,the roll forming process of the HFW pipe is simulated with the finite element method (FEM). A user-defined material routine of the commercial finite element code ABAQUS/Explicit is developed,and the mixed hardening constitution model is realized through the user-defined material routine. Based on the mixed hardening constitutive equation,the numerical simulation of roll forming process of HFW pipe is performed. The evolutions of equivalent stress and strain are analyzed,and the calculated results are also compared between different hardening models. The results show that the different material hardening models have some important effects on the variation of equivalent stress and strain of strip steel during the simulation of the roll forming process.

Numerical Simulation and Experimental Study on Interlock Deformation for Roll Formed U-Section Steel Piling

The interlock of a roll formed U-section sheet steel piling under loading was analyzed by means of numeri- cal simulation, and meanwhile the tensile failure experiment was conducted. The results indicated that under the same load, the interlock corners of roll formed steel piling are not only the regions with the lowest safety factor, but also the regions with the highest stress; there are two slippages in the tensile instability process of interlock, Each slippage can be regarded as a failure, and different types of failure mode should be used to evaluate the performance of steel pilings according to different applications. Due to the work hardening effect during the roll forming process, the hardness of the interlock material increases by 16% compared with that of the original sheet steel. It was also found that the instability strength obtained in tensile failure test is only 15.6 % of the tensile strength of the original sheet steel.

Innovative manufacturing technology enabling light weighting with steel in commercial vehicles

Improved manufacturing technology is often needed when working with high strength steel. In this re- spect manufacturing technology has to adapt to the altered （and typically reduced） formability and weldability of modern high strength steel. However, this is a rather passive approach from a manufacturing point of view. An indeed much more powerful approach is to generate synergies between innovative manufacturing technology, design and material enabling additional weight savings and efficiency gains. Laser-based material processing, in particular laser welding, offers a wide range of opportunities in this sense. Furthermore, hot stamping and roll forming open up new possibilities for advanced manufacturing of commercial vehicle components. Applications and examples of these technologies will be given in terms of producing innovative semi-products as well as final components.

Manufacturing of Long Products Made of Innovative Lightweight Materials

The processing of innovative lightweight materials to sheet metal components and assemblies with globally or locally defined properties is the object of this work. It takes a load-dependent design of components and assemblies, for example, based on the composition of different construction materials or a targeted setting of component areas with specified characteristics to fully exploit the lightweight potential when substituting conventionally used materials. Different process chains for the manufacturing of roll-formed long products made of magnesium alloys and high-strength steels with locally defined properties will be presented in this paper. Depending on the kind of material to be formed and the desired product characteristics, different temperature managements are needed for capable processes. Due to limited formability at room temperature, magnesium alloys require a heating of the forming zones above 200–225 °C throughout the bending process in order to activate additional gliding planes and to avoid any failures in the radii. The realization of local hardening effects requires at least one process-integrated heat treatment when roll forming manganese–boron steels. For both processes, it is imperative to realize a heating and cooling down or quenching appropriate for the manufacturing of long products with the required quality. Additionally, proper line speeds that allow a continuously operated economical production have to be considered. Research results including design, FEA, realization and experimentation of the mentioned process chains and strategies will be described in detail.