Abstract: In a roll forming research projects, the use of finite element software MARC DP800 for advanced high strength steel roll forming process simulation, production practice through the application of validated simulation model is correct. Established a rounded roll model, DP800 and Q235 for the model analysis shows that: With the increase of the angle formed, compared with Q235, DP800 rebound increment and roll deformation energy increment are increasing. Simulation and biswas formula will be calculated compared rebound and found that the formula can not be directly applied to rebound BISWAS DP steel roll Bending calculation formula should be used in the bending angle increases with the yield stress. Roll forming machine

Keywords: advanced high strength steel roll forming FEA springback deformation formula can BISWAS

1 Introduction

Advanced high strength steel (AHSS: Advanced High Strength Steel) has excellent material properties [1,2]. International Iron and Steel Institute's report on the AHSS applications from concept to all aspects of performance and made a detailed presentation [3]. As the ultra-light steel body in Europe to meet the advanced vehicle concept (ULSAB-AVC: The Ultralight steel Auto Body-Advanced Vehicle Concepts) security, energy, economy, advanced concepts, AHSS in the automobile industry has been increasingly widely used [4] .

In the automobile part of the processing process, roll forming (Rollforming) method with high productivity, was forming in some parts of other process has irreplaceable advantages. Of AHSS in the roll forming process, as the application of advanced high strength steel is an important topic.

Introduction 2 AHSS and dual-phase steel

AHSS concept is based on high-strength steel (HSS: high strength steel) put forward, and the mechanical properties of steel, mainly in its plasticity and strength, AHSS research is also based on the two directions towards the development of HSS. Direction is essentially the same strength, improve the efficiency of the plastic properties; while the other direction is essentially the same and increase the plastic strength. Plastic to improve the steel has dual phase steel (DP: double phase), transformation induced plasticity steel (TRIP); strength steels have improved composite steel (CP), martensitic steel (Mart) [3]. Roll former

In this paper, using advanced high strength steel for the DP. DP by the ferrite (Ferrite) islands form the matrix and to the distribution of hard second phase - martensite (Martensite) composition. Strength of the material with martensite content is usually increased. Figure 1 Schematic DP microstructure [3], Figure 2 for this research DP800 phase diagram.

Figure 1 DP diagram of Figure 2 DP800 metallurgical phase diagram (1000X)

The mechanical properties of DP can be explained from the phase diagram of soft ferrite phase is usually continuous, giving good ductility dual phase steels. When the deformation is focused in low-intensity phase - ferrite, the hard phase martensite dual-phase steel to give a unique high strain hardening rate. High strain hardening rate and good ductility makes the tensile strength of dual phase steel than ordinary steel products (such as high strength low alloy steel HSLA: High-strength, low-alloy). Figure 3 shows the same yield strength of HSLA and DP quasi-static stress-strain curve compared [3]. Compared with the HSLA, DP showed high initial strain hardening rate, high tensile limit, low yield ratio. Especially be noted that, DP mechanics curve shows no yield point of its extension.

DP Figure 4 that the structure for ULSAB-AVC proportion of cases [4], the study further shows the importance of DP roll bending process.

       cold roll forming machine

Figure 3 HSLA and DP compared stress-strain curves for ULSAB-AVC Figure 4, the steel (by weight division)

Simulation of 3 items

3.1 Project Description

The project comes from the car to enhance beam production line of roll forming R & D projects. Figure 5 is a cross section diagram of the products of the project.

Figure 5 products section diagram

Table 1 shows the Institute for the project, with the DP material parameters [5].

Table 1 Material parameters of the project research DP

Material
 Yield Strength (MPa)

 
 Tensile strength (MPa)
 Uniform elongation

 
 
DP800
 600
 850
 16%
 

3.2 Project Simulation Model

According to finite element theory assumptions [6,7]: The ideal mill, idealized state of the installation and commissioning; assumptions roll does not account for the rigid body roll and the friction between sheet; assuming isotropic plate; interception of a length of the segment sheet metal forming process to replace the entire coil to simulate the material. According to the above assumptions, according to the mechanical equivalent relations campaign, using 1 / 4 turn slip roll of sheet metal for forming.

Unit selection: This project sheet thickness of 1.5mm, compared to sheet width 142mm and the simulation of sheet metal the length of 400mm, small size, simplified shell theory according to Shell. By Marc's unit analysis of the characteristics of roll bending process, select the 75 shell elements [8]. 75 shell elements for the bilinear, four-node shell elements, each node has six degrees of freedom, consider the transverse shear effect.

Material model: According to the plasticity parameter power function fitting.

Work conditions: According to the contacts between the roller and sheet metal features, each time to set up a working condition.

Analysis option: use with a strain modified NR method and completely stress correction method [9].

Boundary conditions: longitudinal end fixed, the initial establishment of the tail clamp in the deformation constraint.

3.3 Project simulation results and the final product

The completion of the project design were conducted two, two simulation analysis. Roll the first design through analysis, we found there in the ninth pass relatively large edge wave, shown in Figure 6. Analysis underestimated the resilience of the AHSS, as amended, roll design, re-simulation, the result is better shown in Figure 7.

The second design will be used for actual production, the product is ideal as shown in Figure 8.