Gr.5 Titanium Alloy Impeller

Gr.5 titanium alloy, corresponding to the domestic grade TC4, has a nominal composition of Ti-6Al-4V. It is a two-phase titanium alloy with a molybdenum equivalent of 2.9 and an aluminum equivalent of 7.0. It possesses a series of advantages including high strength, high toughness, good plasticity, as well as high-temperature resistance and corrosion resistance. Titanium alloy impellers are critical components of aero-engines, and their service life is directly related to the engine's service life, with their operational performance directly affecting the performance of the entire machine. However, Gr.5 titanium alloy integral impellers have long been recognized as complex and difficult-to-machine parts. On one hand, this is due to the poor machinability inherent in the physical and chemical properties of titanium alloys; on the other hand, it is because integral impellers feature large surface twists and narrow flow channels. Therefore, the machining process of titanium alloy impellers places very high demands on the machining conditions, including machine tools, cutting tools, fixtures, and processes. Precisely and efficiently completing high-performance, complex-surface part machining is a key technology for improving the overall manufacturing level of Chinese aerospace components and the operational performance of products. Currently, five-axis CNC machining centers are an advanced processing technology characterized by high precision and efficiency, and are the main equipment for machining complex impeller parts.
 

1. Dimensional Tolerance
Figure 1 shows a Gr.5 titanium alloy impeller being processed on a five-axis CNC machining center, with the workpiece's room-temperature tensile and microstructure indices meeting the AMS4928 standard. Figure 2 shows the finished Gr.5 titanium alloy impeller, with a large-end outer diameter of 900mm, small-end outer diameter of 200mm, inner diameter of 150mm, and a height of 400mm. The impeller's inner cavity is splined to facilitate connection and transmission with the shaft. The roundness of the impeller is required to be within 0.05mm, the surface form tolerance of the blades and hub is required to be within 0.2mm, and other tolerances meet the ISO2768 standard requirements.

Figure 1 Five-axis CNC machining of titanium alloy impeller                                        Figure 2 Finished titanium alloy impeller

2. Surface Roughness
After machining, the Gr.5 titanium alloy impeller's surface should be smooth and flat, without cracks, burrs, or sand holes. Surface roughness should be tested using a roughness tester, and the outer surface roughness requirement is Ra < 1.6μm.

Integral impellers have large twists and narrow flow channels, making them typical complex-shaped components. The combined effects of titanium alloy's inherent mechanical, physical, and chemical properties determine its difficult-to-machine characteristics. The Gr.5 titanium alloy integral impeller combines the difficult machinability of titanium alloy with the complex structural characteristics of an integral impeller, forming a highly complex part. Impeller blades are thin-walled components with large overhangs, resulting in poor rigidity, making them prone to deformation and machining vibrations during processing, which seriously affects the surface quality of the blades. To prevent vibration and reduce noise, integral impellers have very high dynamic balance requirements. Impellers are mainly used in aerospace engines, ships, and propulsion systems for underwater unmanned equipment and other critical areas.

The Gr.5 titanium alloy impeller needs to be thoroughly cleaned with an ultrasonic cleaning machine, and dimensional tolerances are measured using a coordinate measuring machine, with inspection data provided. The appearance color must be uniform and consistent, with a smooth and flat surface, and defects such as cracks, burrs, and sand holes are not allowed. Custom wooden boxes are used for packaging and transportation to prevent damage during transit.
 

The company has been specializing in the forging of titanium, titanium alloys, aluminum alloys, and other non-ferrous metal materials, as well as precision component deep processing, for 20 years. It is a high-tech enterprise and a specialized, refined, and innovative small and medium-sized enterprise, equipped with 260 sets of production equipment, including HELLIER, DMG five-axis milling-turning composite machining centers, CNC gantry milling centers, and coordinate measuring machines. The company has the full industrial chain deep processing capability from titanium and titanium alloy raw materials to impeller components.

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