Introduction to Straightening Methods of Titanium Rod, Wire, and Tube

Common Straightening Methods

The primary methods for straightening titanium rods, wires, and tubes include tension straightening, sinusoidal straightening, and pressure straightening.

Tension Straightening

Tension straightening, also known as pullout straightening, involves applying longitudinal tension that exceeds the material's yield limit to correct shape defects. During this process, a tensile stress surpassing the yield limit is applied to the titanium rod, wire, or tube with wavy defects using a tension straightening machine. This stress, when superimposed on the residual stress of the titanium, offsets part of the tensile stress where the extension is large, reducing the actual deformation stress and resulting in smaller plastic extension during straightening. Conversely, where the original extension is small, the superimposed tensile stress increases the actual deformation stress, resulting in greater plastic extension. This process ensures that all parts of the workpiece extend evenly, eliminating wavy defects.

Sinusoidal Straightening

The sinusoidal straightening method is commonly used for rods, wires, and tubes with simple cross-sections. This method involves processing titanium tubes and rods on an inclined roller straightening machine with more than four rollers (typically 5 to 29). The working principle is to continuously and repeatedly bend the workpiece at three points through each roller, gradually reducing the residual curvature variation of the workpiece.

Sinusoidal straightening is often combined with pressure straightening. Workpieces with large curvatures are first straightened using a pressure straightening machine and then subjected to inclined roller straightening. The effectiveness of straightening depends on the machine pressure and the roller inclination angle. The pressure amount is determined by the alloy's yield strength and bending. For high-strength titanium alloys with large curvatures, higher straightening pressure is required. The roller inclination angle is adjusted according to the workpiece diameter; larger diameters necessitate larger angles. If a workpiece remains unqualified after straightening, it undergoes re-straightening or is sent to a tension straightening machine.

Principles of Roller Straightening

Roller Size and Number: Smaller roller diameters and higher roller counts result in better straightening accuracy. A smaller roller pitch value improves workpiece bite and straightening process establishment.

Roller Function: The initial rollers primarily reduce the residual curvature differences along the workpiece's length. The final rollers aim to make the residual curvature uniform.

Reverse Curvature Rate: The straightening quality depends on determining the reverse curvature rate under each roller. Larger reverse curvature rates are used on the first few rollers, while subsequent rates are determined by the maximum residual curvature that can be straightened by the preceding rollers.

Material Hardening Coefficient: Higher hardening coefficients make straightening more challenging. In such cases, a larger reverse bending rate, more straightening rollers, and smaller roller diameters are required.

References

Tension Straightening Process for Titanium Alloys

Sinusoidal and Pressure Straightening Techniques

Principles of Roller Straightening for Titanium Materials

Factors Affecting Straightening Accuracy and Quality