Low-Load and High-Precision Forming Technology for Large-Scale Graded Doubly Curved Q890 High-Strength Steel Thick...

Area of Science:

• Materials Science and Engineering
• Manufacturing Processes
• Mechanical Engineering

Background:

• Thick, asymmetric, doubly curved steel shells are critical for deep-sea and nuclear pressure vessels.
• Integral pressing manufacturing faces challenges of excessive clamping force and unpredictable springback.

Purpose of the Study:

• To investigate and overcome the excessive clamping force and springback predictability issues in manufacturing thick high-strength steel shells.
• To develop a new manufacturing paradigm for low-load, high-accuracy forming of these critical components.

Main Methods:

• Characterization of through-thickness plastic gradient and cyclic stress-strain response for Q890 steel.
• Development of a mixed hardening model incorporating gradient plasticity.
• Implementation of a blank positioning strategy to reduce lateral force.
• Proposal and simulation of a normal-direction over-compensation strategy to manage contact evolution and deformation mode.

Main Results:

• A blank positioning strategy reduced lateral force by 65%.
• A striking load surge phenomenon was identified and its causes analyzed (increased contact area, friction, localized upsetting).
• The normal-direction over-compensation strategy achieved a forming force below 1000 t with simulated shape deviation within 0.96 mm.
• Experimental validation confirmed a maximum profile deviation of 1.67 mm, meeting high-accuracy requirements.

Conclusions:

• The normal-direction over-compensation strategy effectively suppresses load surges and ensures high forming accuracy for thick steel shells.
• This work offers a practical pathway for one-shot tryout success in manufacturing critical pressure hulls.
• A new paradigm for low-load, high-accuracy forming of high-strength steel shells is established.