Large Aerospace Engine Impeller: CNC Machining Case Study

Project Introduction

In the field of aerospace manufacturing, the machining of large aerospace components not only requires advanced equipment but also demands rich machining experience and strict quality control.

In this case study, we will take an example of an engine impeller project undertaken by WayKen, the part has a diameter of nearly 500mm and is made from forged aluminum alloy. This part must withstand extreme conditions of high temperature, pressure, and high-speed rotation. Therefore, the manufacturing process must ensure precision, strength, and reliability to meet the aerospace standards.

Structural Analysis of the Impeller

This impeller features a structure with a diameter of approximately 430mm, a hub thickness of about 320mm, and a blade height of around 300mm. The surface roughness is Ra 3.2μm, with a concentricity of 0.02mm for the central shaft hole and 0.06mm for the blades relative to the central channel.

In fact, such tolerances might not be challenging for smaller parts, but achieving 0.02mm precision on a large-scale component is not very easy.

Material Selection and Inspection Standards

In this engine impellers, the material used is forged aluminum alloy, compliant with the ASTM B247 standard, and the production process adheres to AS9102 standards. In practical applications, the impeller is subjected to tremendous centrifugal forces and thermal stresses during engine operation. Any material defects could lead to serious consequences.

In addition, for the manufacturer, the large size of the component means that each raw material blank of high value, and any issues during machining could result in losses. Therefore, rigorous material inspection is the first line of defense in ensuring machining quality. It is required that the material be free of internal defects, with strict standards for chemical composition and mechanical properties.

To meet these requirements, WayKen implemented the following incoming quality control (IQC) measures:

• Chemical Composition: The Olympus Vanta Element-S XRF Analyzer was used to verify the chemical composition of the blanks, ensuring compliance with the aluminum 6061 standard.
• Mechanical Properties: Since mechanical properties are influenced by forging and heat treatment processes, tensile tests were conducted on raw material samples to confirm compliance with mechanical requirements.
• Internal Defects: This is the most critical aspect of IQC and a unique requirement in aerospace part manufacturing. We employ ultrasonic testing to inspect the blanks for internal defects, and inspection reports confirmed the absence of any flaws.

Custom Machining Process for Impeller

The impeller machining involves the following processes:

• Rough Machining: Performed on a large-travel CNC lathe to remove the majority of the material.
• Semi-Finishing: Conducted on a GROB 350 five-axis machining center to shape the blades.
• Finishing: Achieves the final dimensions and surface quality requirements.
• EDM: Used to make the locking slots after CNC machining.

Given the large structure of the part, the equipment used must have an oversized travel range. The GROB 350 five-axis machining center, with a travel range of 600*855*750mm and a positioning accuracy of 0.002mm, fully meets the impeller’s tolerance requirements.

Additionally, this CNC machine is equipped with a high-speed electric spindle capable of reaching 24,000 rpm, enabling efficient and precise machining. During the process, we use the specialized fixture to ensure clamping rigidity, and an in-process measurement system is used to monitor machining accuracy in real time.

To control blade deformation, we also employ finite element analysis to optimize machining parameters, and a layered cutting strategy was adopted, effectively minimizing deformation.

Strict Tolerance Control

As mentioned, this impeller’s machining tolerances are strict, with a concentricity of 0.02mm for the central shaft hole and 0.06mm for the blades relative to the central channel. These requirements present challenges for large-scale parts. WayKen addressed this through rational allowance distribution and process optimization, establishing quality control checkpoints at each stage to ensure timely detection and resolution of issues.

During inspections, any deviations were promptly addressed by adjusting process parameters, ensuring quality control throughout the entire process, and avoiding part rejection.

After machining, a coordinate measuring machine (CMM) was used to generate the final inspection report, confirming the stability and reliability of the machining quality.

To Be Continued

The machining of large-scale aerospace components represents the culmination of precision manufacturing technology. From material selection to process design, equipment configuration to quality control, every step of manufacturing the engine impellers requires careful attention to detail.

WayKen boasts a team of experienced engineers and project managers, capable of providing one-stop CNC machining solutions for large-scale, high-precision components, ensuring that we meet our customers’ diverse requirements with excellence.