Thin-walled cavity program design
The titanium alloy lined thin-walled cavity adopts an innovative three-layer structural design: the outer layer is a 0.3mm-thick 316L stainless steel thin-walled tube, the middle layer is a TC4 titanium alloy liner skeleton, and the inner layer is an ultra-high vacuum flange. The liner skeleton has a runway-shaped cross-section and is fixed by 11 evenly spaced ribs and tie rods on the top and bottom sides to form a stable structure. In order to prevent longitudinal movement of the liner skeleton, positioning indentations with a depth of 0.7 mm are distributed at equal intervals on the top and bottom of the thin-walled tube.
Considering the manufacturing cost and cycle time, the liner skeleton is 3D printed by selective laser melting (SLM) technology, and the raw material is TC4 titanium alloy powder with a particle size of 20-63 μm. This technology not only ensures the precise molding of the liner skeleton, but also improves the production efficiency.
In order to evaluate the mechanical properties of the liner skeleton structure, we performed a static structural simulation analysis using ANSYS Workbench software. By simulating the stress and deformation of the liner skeleton with different thicknesses, widths and spacings under 0.1 MPa pressure applied to the outer surface of the stainless steel thin-walled pipe, we reached the following conclusions:
Effect of thickness and width: In the case of a certain spacing, the stress of stainless steel and titanium alloy decreases with the increase of thickness and width. When the thickness reaches 4mm, the effect of continuing to increase the width on the stress becomes insignificant. Therefore, we chose a liner skeleton structure with 4 mm thickness and 11 mm width.
Influence of spacing: In the case of a certain thickness, with the increase of spacing, the stresses of stainless steel and titanium alloys and the deformation of thin-walled cavities are significantly increased. Considering the stress safety margin and deformation, we determined 15mm as the optimal spacing.
Thin plate and filament structure: In order to further reduce the deformation and improve the structural stability, we added thin plate and filament structure on the upper and lower surfaces of the liner skeleton. Simulation results show that the thin plate structure is better than the filament structure in reducing deformation, and the 0.5mm thickness of the thin plate structure achieves an optimal balance between light weight and printing difficulty.
Thermal-structural coupling analysis
Considering that the titanium alloy lined thin-walled cavities need to withstand the in-line high temperature baking at 250°C to obtain the target vacuum level, we conducted thermal-structural coupling simulation analysis. The results show that under the combined effect of 250°C and vacuum extraction, the maximum deformation of the thin-walled cavity on one side is 1.65 mm, which is about 0.29 mm more than that of the room temperature condition; the stainless steel stress is 135 MPa, which is far below the yield strength limit and meets the strength requirement.
Thin-walled cavity deformation test
In order to verify the accuracy of the simulation results, we carried out the deformation test of the thin-walled cavity. Under vacuum, the deformation data of the thin-walled cavity was monitored and recorded in real time using high-precision measuring equipment. The test results show that the actual deformation matches well with the simulation results, which verifies the reliability of the simulation model. Meanwhile, we also simulated the deformation under high-temperature baking conditions to further confirm the stability of the cavity in a high-temperature environment.
