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In the precision manufacturing of aerospace and medical fields, the accuracy of titanium material straightening directly affects the performance and reliability of the entire product.

Titanium and titanium alloys, due to their high specific strength, excellent corrosion resistance and good biocompatibility, have become core materials in high-end fields such as aerospace, medical implants and chemical engineering. However, these excellent properties also bring processing challenges - especially in the straightening process.

The high strength and low plastic deformation capacity of titanium materials make them typical difficult-to-straighten materials. Roller straightening technology, as a key process to solve the deformation of titanium materials, directly determines the geometric accuracy and quality performance of the final product.

01 Difficulties and Particularities in Straightening Titanium Materials

Titanium alloys have high specific strength and specific stiffness, are difficult to be bent back, and have a small contact area with straightening rollers, making them difficult-to-straighten materials. This is closely related to the crystal structure and mechanical properties of titanium materials.

The rotary reverse bending straightening theory developed on the basis of the simple reverse bending straightening method, especially the inclined roller straightening machine, has become the mainstream technology for straightening small-sized tubes and bars.

The straightening of titanium materials not only requires consideration of geometric accuracy but also attention to changes in microstructure and properties. Research shows that the ring-shaped defect in pure titanium bars is a low-magnification ring-shaped structure defect produced by the combined effect of the two-roll straightening and heat treatment processes in the finishing process.

02 Mainstream Straightening Techniques and Their Characteristics

Two-roll straightening technology

The two-roll straightening machine uses the method of flattening and reverse bending to achieve a very good straightening effect on titanium alloy pipes. The key component of this straightening machine is the straightening roller, which is composed of complex curved surfaces.

The straightening accuracy depends on whether the design of the straightening roller is correct. Research shows that the adoption of the roll profile design method based on the rolling reverse bending theory can improve the straightening effect and describe the stress-strain relationship of fine bar deformation more accurately.

The main advantage of the two-roll straightening machine is that it has no empty straightening zone and high straightening accuracy. This is particularly important for expensive titanium alloy materials, as it can reduce material waste.

Multi-roll straightening technology

The end rollers of multi-roll straightening machines (such as six-roll and ten-roll straightening machines) adopt a pseudo-hyperbolic roller shape, while the middle straightening roller adopts a deep and shallow concave roller shape. This design solves the "goose head bend" problem that cannot be straightened by the reverse bending of the roller system by adopting an appropriate reverse bending line.

For ultra-fine titanium alloy tubes, the ten-roll straightening machine can significantly improve the straightening accuracy by optimizing the flattening amount and inclination Angle parameters. The advantage of multi-roll straightening lies in its smaller straightening force, which can avoid the ring-shaped defects that may occur in two-roll straightening.

03 Influencing Factors and Optimization Strategies of Straightening Accuracy

Straightening accuracy is the core indicator for measuring the level of straightening technology. There are numerous factors influencing the straightening accuracy of titanium materials, and systematic optimization is required.

The Angle of the straightening roller does not form a strict linear relationship with the diameter of the bar. Considering the influence of the plasticity and hardness of the material on the straightening of the reverse bending line, the Angle of the straightening roller should be appropriately reduced for grades with poor plasticity and high hardness.

The selection of the flattening amount is also of vital importance. Research shows that it is necessary to determine a reasonable range of flattening amounts by analyzing the contact conditions, straightening force, residual stress, straightness and ellipticity at different flattening amounts, providing a reference for the adjustment of the roll gap.

The stress and strain control during the straightening process should not be ignored either. Establishing a three-dimensional elastoplastic finite element model of the two-roll straightening process of titanium alloy tubes is helpful for analyzing the stress and strain of the tubes from being bitten in to being thrown out, and for analyzing the residual stress of the tubes after straightening.

04 Innovate straightening techniques and methods

With the advancement of technology, new straightening methods are constantly emerging.

A straightening method with a front-end rolling device for improving the straightening accuracy of titanium alloy plates. By adding a front-end rolling device to the straightening device, a new straightening system is formed together with a roller straightening machine.

This method, under the condition of increasing the pressure in the hydraulic cylinder, reduces the curvature of the sheet, thereby improving the quality of the sheet and increasing the correction efficiency from 78% to 81.6%.

The hot three-roll longitudinal rolling and hot tension straightening technology is specifically designed for Ti-Zr-Nb shape memory alloys. This combined process can optimize the microstructure and texture of the material, significantly enhancing its mechanical and functional properties.

05 Application Cases and Economic Benefits

Tubes and bars made of rare metals such as titanium, tantalum and niobium are widely used in high-tech fields like aviation, aerospace, military industry, atomic energy and medicine due to their excellent mechanical properties.

The research results of this project have been applied to many metal tube and bar preparation enterprises in places such as Baoji, Shaanxi Province, Ningxia and Shanghai. For enterprises that already have straightening machines, the goal of improving productivity and product quality can be achieved by replacing or repairing the straightening rollers.

This input-output ratio is extremely high: With just this relatively small investment, each straightening machine can increase the economic benefits of the enterprise by over one million yuan every year.

06 Technological Development Trends and Prospects

Titanium and titanium alloy roller straightening technology is developing towards high precision, high efficiency and low damage. The straightening accuracy has been improved from the original 1-2mm/m to below 0.3mm/m.

The digital simulation technology of the straightening process is becoming increasingly mature. By establishing an accurate finite element model, the straightening effect under different process parameters can be predicted, and the roller profile design and process parameters can be optimized.

Intelligent straightening systems have also begun to be applied. By monitoring the straightening force and deformation in real time and adaptively adjusting the process parameters, intelligent control is achieved.

The precision requirements for titanium parts in the high-tech field are still constantly increasing. Medical implants require more precise geometric characteristics, and aerospace components need better fatigue performance.

These demands are driving the straightening technology towards ultra-precision, digitalization and intelligence. Future straightening systems will be able to adapt to changes in material properties and achieve zero-defect manufacturing.

References

High-precision straightening technology for metal tubes and bars with two inclined rollers and multiple inclined rollers.

Research on the Roll Profile of Titanium Alloy Two-Roll Straightening Based on the Rolling Reverse Bending Theory.

Analysis of the Roll profile Curve and Straightening Accuracy of the two-roll Straightening Machine for Titanium Alloy tubes.

The Application of rotational reverse bending Straightening Technology in the Production of Titanium Alloy Precision Forged Bars.

Research on the Roll Profile Curve and Straightening Accuracy of the Two-Roll Straightening Machine for Φ12 to Φ20mm Titanium Alloy Tubes.

Analysis and Improvement of Ring Defects in Pure Titanium Bars

Hot three-roll longitudinal rolling and tensile straightening of superelastic Ti-Zr-Nb alloy for orthopedic implants.

Simulation of the ten-roll straightening process for TA9 pipe materials.

A straightening method with a front-end rolling device for improving the straightening accuracy of titanium alloy plates.