Analysis of Continuous Rolling Deformation Process and Optimization Design of Pass System for Titanium bar

Titanium alloys, known for their low density, high strength, excellent heat resistance, corrosion resistance, biocompatibility, non-magnetic properties, non-toxicity, and good thermal stability, are widely used in aerospace, marine vessels, biomedical applications, metallurgy, construction, and consumer goods . As the demand for titanium alloy products increases and their applications expand, the quality requirements for these products have also heightened, necessitating further optimization of their production processes. For titanium alloy wire rods, traditional methods involve reciprocating rolling using a cross-rolling mill. To enhance the mechanical properties and processability of titanium rods, it is essential to adopt hot continuous rolling technology for producing small-sized titanium alloy rods. This study addresses issues such as ears, twisting, and poor roundness encountered during the continuous rolling production of titanium alloy rods on a specific production line in China, using theoretical analysis and ANSYS finite element software to simulate the rolling process and optimize the pass system to resolve these issues.

The titanium alloy rod continuous rolling production unit at a certain plant consists of an 8-stand three-roll Y-type mill, processing TC4 titanium alloy from a 25mm diameter billet to a 15mm diameter finished product through 8 passes. The original pass design was flat-triangle-round-flat-triangle-round-flat-triangle-round-round-round pass. However, the finished titanium alloy rods often exhibited defects such as ears running through the entire length, significant twisting, and poor roundness, ultimately leading to non-compliant product dimensional accuracy. To address these issues, an idea was proposed: can the flat-triangle pass be improved to reduce the circumferential flow unevenness of the metal, thereby mitigating twisting and reducing the flow amplitude of the metal in the round pass?

Key Points of the Study

1. Simulation of Deformation Process: Using an improved "flat-triangle-round" pass system and ANSYS/LS-DYNA nonlinear finite element software, the deformation process of titanium alloy rods in the continuous rolling unit was vividly simulated.

2. Improvement of Flat-Triangle Pass: The improved flat-triangle pass involves adding a trapezoidal block at the bottom of the traditional flat roll. During rolling, the trapezoidal block presses into the rolled piece, positioning it so that the pressed-in part appears at the roller gap in the next round pass, reducing the flow amplitude of the metal towards the roller gap and thus decreasing the formation of ears.

3. Reduction of Twisting: The trapezoidal block also serves to position the rolled piece, significantly reducing the circumferential flow unevenness caused by uneven metal density, elastic recovery, and rolling mill vibrations in the traditional flat-triangle pass. This greatly decreases the probability of twisting issues commonly observed in the traditional "flat-triangle-round" pass system.

4. Enhanced Axial Extension: The presence of the trapezoidal block limits the circumferential flow of the metal, forcing axial extension. This improves the extension coefficient of each pass and increases the reduction per pass, addressing issues arising from excessive reduction while fully utilizing existing equipment and enhancing the processing capability of the billets.

5. Improved Roundness and Dimensional Accuracy: The final simulation results clearly show that the improved "flat-triangle-round" pass system significantly improves the roundness of the titanium alloy rods, thereby enhancing the dimensional accuracy of the products.

In conclusion, the improved pass system effectively addresses the issues of ears, twisting, and poor roundness in the continuous rolling process of titanium rods, leading to higher product quality and dimensional accuracy. This optimization is crucial for meeting the increasing demands and quality requirements in the production of titanium alloy products.

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