Titanium and its alloys are widely used in aerospace, marine engineering, chemical equipment, and medical fields due to their high strength, corrosion resistance, low density, and excellent biocompatibility. However, titanium's processing properties differ significantly from those of traditional metals, requiring specialized processes for forming. This article systematically analyzes the key technical aspects and application scenarios of four core processes: bending, stamping, spinning, and expansion.
Bending: The Art of Balancing Plastic and Elastic Deformation
Bending is the most common forming method in titanium device manufacturing, achieving shape control through a combination of plastic deformation and elastic recovery. Key process points are as follows:
1. Springback Control: Springback occurs in titanium materials due to elastic recovery after bending, and this must be compensated for by adjusting the bend radius or process parameters. For example, a 2° to 5° margin should be allowed in the bend angle to offset springback.
2. Minimum Bend Radius: The minimum bend radius for titanium is typically three times the pipe diameter (cold bending) or two times (hot bending). Titanium tubes with a diameter less than 50mm can be cold-bent, but stress relief annealing (450-550°C for 1 hour) is required after cold bending to eliminate residual stress.
3. Hot Bending Process Optimization:
Temperature Control: The hot bending temperature for pure titanium is 177-350°C, while titanium alloys can be heated to 427°C. At this temperature, the yield strength decreases by 25%-50%, the plasticity significantly improves, and the springback angle is reduced to less than 1°.
Stress-Loading Method: Hot bending can be divided into pull bending (axial tension) and push bending (localized compression). Pull bending is suitable for long tubes, while push bending is suitable for short tubes.
Gas Protection: Hot bending must be performed in an inert gas or vacuum environment to prevent the formation of oxide scale.
Application Example: A deep-sea exploration equipment uses hot bending of titanium tubes, achieving a 180° bend at 250°C with a springback of only 0.5° and a surface oxide layer thickness of less than 0.1mm, significantly improving the equipment's pressure resistance.
Stamping: Precise Control of Temperature and Deformation
Stamping titanium sheets and titanium alloys is more difficult than stamping steel and aluminum, requiring a combination of temperature control and process technology to achieve complex shapes. The process classification and key technical points are as follows:
1. Cold Forming:
Applicable Applications: Workpieces with wall thickness <2mm, deformation <15%, and bend radius >5 times the sheet thickness (e.g., thin-walled shells).
Process Optimization: Final annealing (600-650°C for 2 hours) is required after cold stamping to eliminate residual stress and prevent cracking.
2. Hot Forming:
Low-temperature hot forming (200-350°C): Deformation can reach 40%, suitable for medium-thick sheet metal (e.g., chemical equipment head covers).
High-temperature hot forming (600-800°C): Deformation >50%, suitable for thick sheets (>10mm) or complex structural parts (e.g., aircraft engine nacelles).
Heating Method: Prioritize heating the blank to the target temperature, and preheat the mold to 150-200°C to reduce thermal stress.
3. Hot Straightening After Preforming:
Process Flow: First, cold stamping is used to create the preform, followed by heating to 450-500°C in a dedicated device for straightening to eliminate springback and residual stress.
Advantages: Combining the efficiency of cold stamping with the precision of hot straightening, it is suitable for workpieces requiring high precision (such as medical implants).
Application Case: An aviation company used a high-temperature hot forming process to manufacture titanium alloy wing panels. At 750°C, the process achieved a single deformation of 60%, a surface roughness Ra <0.8μm, and a weight reduction of 40% compared to traditional steel panels.
Spin Forming: Precision Manufacturing with Multi-Process Integration
Spin forming achieves high-precision, low-material-consumption forming through the continuous local deformation of the rotating tool and the blank. Its core advantages and technical highlights are as follows:
1. Improved material utilization: Spinning can save 20%-50% of material, making it particularly suitable for processing precious metal titanium (such as spacecraft fuel tanks).
2. Optimized surface quality: Products achieve surface roughness Ra <0.4μm and dimensional accuracy of ±0.1mm, eliminating the need for subsequent machining.
3. Process Classification:
Conventional spinning: Suitable for thin-walled cylindrical parts (wall thickness <5mm), achieving shape control through multiple deformation passes.
Power spinning: Suitable for thick-walled parts (wall thickness >10mm), achieving up to 50% deformation in a single pass, but requiring controlled work hardening.
Application Case: A satellite propulsion system used spinning to manufacture titanium alloy cylinders, reducing wall thickness from 15mm to 8mm, reducing weight by 47%, and achieving a burst pressure 1.5 times the design value.
Expansion Process: Ensuring Mechanical Connection Reliability
Expansion is a critical process in shell-and-tube heat exchangers, achieving sealing and fastening through plastic deformation of the tube and tube sheet. Key process points are as follows:
1. Tube Expansion Control:
Inner Diameter Expansion: 1%-6% (lower limit for pure titanium, upper limit for titanium alloys).
Tube Wall Thinning: 5%-8%. Finite Element Analysis is required to optimize expansion parameters.
2. Comparison of Expansion Methods:
Mechanical Expansion: Suitable for conventional applications, low cost, but with average sealing performance.
Flexible Expansion: Utilizing hydraulic or rubber expansion joints, this solution improves sealing performance by 30% and is well-suited for high-pressure applications.
Explosive Expansion: Explosive expansion achieves instantaneous expansion through explosive shock and is suitable for thick-walled tubes (wall thickness > 5mm) or for joining dissimilar materials.
3. Quality Inspection: After expansion, pressure testing (1.5 times the design pressure) and penetration testing are required to ensure leaks.
Application Case: A petrochemical company used a flexible expansion process to manufacture titanium tube heat exchangers. The result was five years of continuous leak-free operation at 3.5 MPa and 200°C, representing a threefold increase in service life compared to traditional welded structures.
Conclusion: Process Innovation Drives Expanded Titanium Applications
The core of titanium processing lies in achieving a balance between material properties and forming efficiency through precise control of temperature, deformation, and stress. With the application of automated equipment (such as CNC spinning machines and laser heating devices) and simulation technologies (such as finite element analysis), titanium processing costs have dropped by 30% compared to five years ago, accelerating its application in emerging fields such as new energy vehicles and hydrogen energy storage, and transportation. Going forward, Titanium Home will continue to monitor process innovations and provide technical support for high-end equipment manufacturing.
