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Exploring Profile Stretch Forming Processes

With lightweighting becoming one of the important development directions in high-end equipment manufacturing technologies such as automotive, aerospace, and high-speed trains, profile products have gained increasing application due to their advantages of lightweight and high strength. In multiple application fields, as the design level improves, the auxiliary design methods become more advanced, and the functional and aesthetic demands of related products increase, the structures of most profile products are trending towards complex streamlined designs. Traditional two-dimensional bending processes are no longer able to meet the forming requirements, making precise three-dimensional bending plastic forming methods a hot topic in the field of metal material processing.
Due to the complexity and difficulty in controlling the shape of profile three-dimensional bending forming, based on the current status of profile bending forming, numerous scholars and researchers have studied the laws of springback deformation of formed components and optimized bending process parameters, aiming to provide references and new methods for profile bending processes.
In this series of articles, we summarize the research status of profile bending processes and discuss the urgent technological breakthroughs needed for profile three-dimensional bending forming, providing valuable references for research in the field of profile three-dimensional bending.

Three-dimensional stretch forming

Three-dimensional stretch forming is one of the most widely used processes in the bending and forming of aluminum profiles. It relies on the three-dimensional movement of the clamp and the bending die to bend the profile into a predetermined shape. Compared with bending forming, the profile deforms while bending , each point on the section is under the action of axial tensile stress, which avoids the wrinkling phenomenon caused by tangential stress, and can reduce the springback, thereby improving the quality and precision of the profile stretch bending.

Stretch Forming Process of Aluminum Alloy Automobile Roof Rack【Stretch Forming Machine

The stretch forming process is generally divided into three steps: pre-stretching, stretching and supplementary stretching. Pre-stretching is to pre-stretch the profile to a plastic state through the clamps at both ends of the profile; the stretching stage refers to controlling the three-dimensional movement of the clamps. Make the profile fit the mold gradually until the profile is in full contact with the mold; Supplementary stretching means to continue to apply additional supplementary tension to the profile after the mold is closed, and its main purpose is to reduce springback.

Three Different Stretch Forming Processes

With the continuous development of stretch forming technology, based on the basic principle of stretch forming, a variety of different stretch forming processes such as stretch arm stretch forming and rotary table stretch forming have been derived.

Tensile Stretch Forming

The mold is fixed, and the rotating arms on both sides drive the clamps to translate and rotate under the drive of multiple hydraulic cylinders or motors, so as to produce a stretching effect on the profile, so that the profile is gradually attached to the stretch forming mold. Since the two sides can be controlled The side arm moves independently in a large range, so this stretch-arm stretch forming method is suitable for three-dimensional stretch formingof large geometric dimensions, complex shapes, and asymmetrical profiles [5]. When using stretch-arm stretch bending, the clamp can also be fixed , Control the movement of the stretch formingdie to make the profile and the mold close to each other. This method is difficult to achieve complex shapes of profiles, and is mainly used in two-dimensional stretch bending.

Rotary Table Stretch Forming

This process method was first used in aircraft manufacturing. This stretch forming method is to drive the stretch forming mold to rotate through the rotation of the turntable, so that the profile is gradually clamped with the mold under the action of axial tension. This process method is suitable for small-sized profiles The processing of products has the characteristics of high forming efficiency and high precision[5]. They are respectively installed on two different turntables. With the movement of the double turntables, the clamps and molds move relatively at the same time to complete the bending and forming of the profile. In this way, since the clamps and molds both follow the turntables, the processing time is shorter. Shorter, and the accuracy is further improved, it is mainly used in mass production of auto parts.

Flexible Stretch Forming

Generally, it can be divided into two types. One is the stretch forming with flexible loading, which can be regarded as the deformation improvement of the stretch arm stretch forming machine. Workbench, through the movement of the workbench to adjust the processing range of profile products, has a certain degree of flexibility; the other is multi-point flexible mold stretch bending, and its forming mold is composed of multiple discrete parts, making the mold flexible and adjustable, which can be Transform into any shape, and then meet the various requirements of the processed parts.


Achieving Perfection: The Quality Finish Advantages of Stretch Forming
Achieving Perfection: The Quality Finish Advantages of Stretch Forming

Profile stretch forming is a versatile technique used in the bending and forming of aluminum profiles. With the ability to shape complex three-dimensional profiles, reduce springback, and enhance precision, it finds application in various industries. The different stretch forming processes, including tensile stretch forming, rotary table stretch forming, and flexible stretch forming, offer unique advantages and are suitable for different profile bending requirements. By leveraging the capabilities of profile stretch forming, manufacturers can achieve precise a

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.

Stretch Forming Process of Aluminum Alloy Automobile Roof Rack【Stretch Forming Machine】

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

Stretch Forming Automobile Bumper Beams 【Profile Stretch Bending & Forming Press Equipment For Sale】

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.