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Exploring Profile Stretch Forming (2): Research Status of Profile Stretch Forming Processes

In the process of profile stretch forming, the quality of forming is not only related to material mechanical properties, profile geometric dimensions, temperature, and the friction coefficient between the profile and the mold but also closely related to the stretch forming process parameters. Improper process parameters can easily cause problems such as profile rupture, wrinkles, cross-sectional deformation, and springback, thereby affecting processing quality and precision.

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Research Results of Process Analysis Methods

The process research methods adopted by scholars both domestically and internationally mainly include theoretical analysis, experimental analysis, and numerical simulation.

The theoretical analysis method is based on material mechanics theory, analyzing the stretch forming deformation process, constructing a springback model, and studying the relationship between process parameters and springback.

Research result 1-3

In the available literature, there are references that point out and study the issue of material springback for L-shaped profile sections in a two-dimensional rotary stretch forming process. The analysis includes the distribution of cross-sectional stress, derivation of the unloading springback angle formula, and the development of a springback prediction model. Furthermore, researchers have investigated the influence of pre-strain and post-strain on springback behavior.

Researchers have also established an improved theoretical prediction model considering the neutral layer shift, aiming to enhance the prediction accuracy of springback for Z-shaped profile sections. This proposed model takes into account material properties, geometric characteristics, and forming radii, and it has been utilized to predict the springback displacement of Z-shaped profile sections with varying thicknesses made of 7075 O and 7475 O aluminum alloys.

Through theoretical analysis, researchers have constructed a mechanical model for the stretch forming forming process under displacement control and a springback prediction model for profile stretch forming. They have also provided a compensation algorithm for mold springback. Based on a bilinear material model, they have developed a two-dimensional stretch forming mechanical model for rectangular profile sections, calculating the neutral layer strain and cross-sectional stretch forming moment, and analyzing the relationship between tension and stretch forming radius.

Research result 4-7

Furthermore, researchers have analyzed the distribution of stress and strain in profile sections during small curvature and large curvature stretch forming using a bilinear isotropic hardening model. They have derived the analytical expression for the elastic recovery of the profile after stretch forming unloading.

Researchers have conducted an analysis of the displacement-controlled two-arm stretch forming process and studied the influence of stretch forming process parameters on cross-sectional deformation. They have identified the relationship between process parameters and the degree of stretch forming deformation.

These research efforts have provided valuable insights into the understanding and prediction of springback behavior in profile stretch forming processes. They contribute to the development of effective techniques for controlling and optimizing the stretch forming process.

While publicly available literature has provided some guidance and reference for research on stretch forming processes, theoretical analysis cannot consider the differences in profiles themselves and the non-uniformity of material properties, leading to certain deviations between the analysis results and actual situations. Moreover, such methods involve extensive calculations, making it difficult for general engineering professionals to apply them as references.

Experimental Analysis Research on Profile stretch forming

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Typically, single-factor or multi-factor experiments are conducted to obtain the most direct experimental results, which are then further analyzed to investigate the influence of profile geometry parameters and stretch forming process parameters on springback, cross-sectional deformation, wrinkling, etc.

Research results 1-4

  • Researchers have used multiple high-strength steel plates for in-plane stretch forming tests, measuring the maximum forming strain at the outer edge of the curved strip, and comparing the experimental results with those of conventional hole expansion tests.
  • Some researchers have conducted stretch forming tests using YLM CNC stretch forming machines to study stretch forming characteristics such as wall thickness variations and cross-sectional deformations.
  • The Chinese researchers have developed a new flexible stretch forming machine for small-radius stretch forming of non-circular pipes and verified the numerical simulation results through experiments, demonstrating good compatibility between the experimental and simulated results.
  • Researchers have studied the springback of rectangular section profiles through experimental investigations, establishing the relationship between the radius after profile recovery and stretch forming force.
stretch forming machine
stretch forming machine

Research results 4-8

  • Researchers have examined the influence of mold structural parameters on cross-sectional distortion during the stretch forming process of L-shaped aluminum profiles, proposing specific methods to suppress cross-sectional distortion.
  • Researchers have analyzed the effect of stretching on the forming quality and precision of end beams in rail vehicles, improving product quality by adjusting the stretching amount.
  • Researchers have employed experimental methods to discuss key process parameters in aluminum profile stretch forming and used stochastic simulation methods to determine the optimal process parameters for aluminum profile stretch forming. They found that the sensitive factors affecting the curvature radius of aluminum profile stretch forming are, in order, supplementary stretch forming amount, preload amount, and friction conditions.
  • Researchers have conducted studies on the thinning rate of multi-point flexible formed components using a self-developed flexible three-dimensional stretch forming device for aluminum profiles. They obtained certain rules during the profile stretch forming process, which are intuitive and effective for specific stretch forming objects and can be used to guide production. However, if there is a need to extend the generality of experimental conclusions, a large number of experiments are required for effective analysis of profile stretch forming processes.