This project belongs to the field of plastic processing.
Roll-forming high-strength cold-formed sections and straight welded pipes is an important means to ensure automobile safety and achieve automobile lightweight. They are high value-added products that my country's steel industry focuses on development, and annual demand continues to grow at 20%. However, due to the decline in formability and significant rebound of high-strength steel, the forming quality problems of high-strength steel rolled products are very prominent. The level of high-strength steel roll forming process technology and equipment of my country's enterprises is backward. The variety and quantity of cold-formed sections made of high-strength and low-alloy steel are very few. Ultra-high-strength cold-formed sections are even blank. Basically, they can only rely on imports to make up for it. The pricing and positioning rights of high-strength cold-formed sections have seriously restricted the application of high-strength cold-formed sections in automobiles. How to accurately evaluate, predict and control the shape accuracy and formability of high-strength steel rolled products is an urgent problem.
Starting from the deformation and failure mechanism of high-strength steel under complex loading paths, this project establishes a forming limit prediction model of high-strength steel sheet that introduces bending effects, expands the sheet forming limit theory based on in-plane deformation mode, and improves the evaluation accuracy of high-strength steel roll forming performance; Establish a full-process simulation model of high-strength steel roll forming based on implicit algorithm to reveal the influence laws of residual stress in high-strength cold-formed steel, and propose a shape-control process design method for high-strength cold-formed steel; Develop new forming and processing equipment to realize efficient and precise forming of high-strength cold-formed steel and straight seam welded pipe components.

1. Theoretical forming limit model and failure mechanism of high-strength steel under bending effect: High-strength steel has poor forming performance, especially when forming with small radius, and is prone to cracking. However, classic forming limit models cannot accurately describe the effect of out-of-plane bending deformation on limit forming ability. This project introduces out-of-plane bending deformation to establish a forming limit prediction M-K model under tension-bending deformation conditions, and proposes a bending effect forming limit (BFLD) based on top-layer strain to accurately calculate the small radius bending limit strain of high-strength steel, revealing the mechanism by which bending effects lead to premature failure of high-strength steel.
2. Full-process simulation and process design method for rolling forming high-strength cold-formed steel: Aiming at the deformation characteristics of high-strength cold-formed steel with long rolling process, multiple passes, and repeated loading and unloading, a multi-pass forming-closure-welding full-process simulation analysis model of closed cold-formed steel is established based on implicit algorithm, revealing the residual stress distribution and influence laws of high-strength cold-formed steel, and the prediction accuracy of residual stress distribution and springback of high-strength cold-formed steel reaches more than 85%. Aiming at the problems of large springback and poor size accuracy of high-strength cold-formed steel, a "square into square" roll forming process of "fixed radius + multi-pass shaping" is proposed, and a process control method for shape accuracy indicators such as bending angle, straightness and flatness of high-strength cold-formed steel and residual stress performance indicators is established.
3. Development of forming equipment for high-strength cold-formed steel and straight welded pipe components: Develop universal roll bending shaping dies and six-continuous punching pre-punching equipment to achieve coverage and interchange of full-specification products of high-strength cold-formed steel and ensure the forming accuracy of liquid leakage holes and pass shape. Taking into account the heterogeneity effect and closed loading mode of the weld seam in high-strength straight welded pipes, a new device for testing the forming limit of full-strain spatial pipes was developed and authorized by invention patents.
   Based on the above core technologies for shape control of high-strength steel roll forming, the product quality of high-strength square rectangular pipes for passenger cars and cold-formed square pipes for tower cranes produced by Shanghai Baosteel Steel Co., Ltd. has reached the international advanced level, and high-strength martensitic steel square rectangular pipe has been successfully developed. High-quality products such as (HC700/980MS) and bainite high-strength steel square rectangular tubes (QStE700TM) have improved the technical level of manufacturing and using high-strength cold-formed steel sections in my country, and promoted the successful application of high-strength steel rolling products in Yutong Bus, Huanghai Group, Zhongtong Group, Gestamp Automotive Components and other companies, with an added output value of 201.57 million yuan and a profit of 60.472 million yuan in the past three years. Published 40 papers (38 papers included in SCI/EI), and he cited them 101 times. Apply for 13 invention patents and authorize 8.