Research on Machining Process of Aeroengine Turbine

China Southern Aviation Industry Group Co., Ltd. Liang Songshan

A specific type of turbine component is a critical part of an engine's turbine section, made from GH2132 material. The finished product is ring-shaped, with a large end diameter of 674.8 mm, a small end diameter of 605.5 mm, and a total length of 221.8 mm. The average wall thickness is approximately 2.8 mm, and it consists of three internal sections. Each group has between 23 to 27 grooves, with widths ranging from 18 to 25 mm and depths of about 2 to 6 mm. Due to the large size, the machining and inspection processes are complex, involving over 30 steps. This often leads to clamping deformation, tool vibration, and poor groove processing quality. For many years, these grooves have been processed using traditional milling methods, which are time-consuming, inefficient, and prone to dimensional errors, significantly affecting the final product quality. As production volumes increase, it becomes essential to enhance processing capacity and ensure smoother workflow. Converting the turbine groove process to CNC milling is considered the most effective solution. This paper explores various aspects of the CNC milling process, including process design, feed mode, cutting parameters, equipment selection, and improved measurement techniques.

1. CNC Milling Process Design

Through a comprehensive analysis of existing product quality and the capabilities of CNC milling equipment, a new CNC milling process for turbine grooves was designed, as shown in Figure 1.

2. Technical Solution for CNC Milling

(1) **Equipment Selection Analysis** The main factors affecting the production schedule are the rough machining and milling stages. The capability of the rough machining stage also limits the milling process. To optimize and improve the turbine program, a direct transition to the milling process was implemented. However, certain parts (models 740, 760, and 780) could not be processed by standard CNC machines. Based on dimension data acquisition and process simulation, a non-standard five-axis machining center was selected, equipped with a numerical control indexing turntable and an angle head, based on a vertical machining center. (2) **Feed Method Improvement** During the 530 milling process, the machine produced an elliptical shape of about 0.15 mm, making positioning difficult and affecting the accuracy of the groove milling. Additionally, the flatness of the rib ring and the spacing between ribs were inconsistent, causing issues with G54, G55, and G66 positioning. Continuous tool additions were required during the process. To address this, the 80° external circular cutter was replaced with a straight insert, and a 6 mm wide, R0.8 mm groove cutter was used instead of a R3 mm round groove cutter (see Figure 2).

Figure 2

(3) **Feed Rate Adjustment** The feed rate in the machining program was found to be unreasonable, contributing to part deformation. The solution involved reducing the feed rate from 0.2 mm/r to 0.1 mm/r. (4) **Tooling Design Improvements** Using a spacer clamping method revealed several shortcomings: First, eight supporting blocks under the clamps caused vibration when machining thin-walled S3 grooves, resulting in visible marks. Second, the supporting blocks were prone to loosening and sliding during disassembly, affecting efficiency. Third, the fixture lacked compatibility when machining other parts. To resolve this, a new tooling design was developed: the eight separate blocks were integrated into a single annular block. The middle section was made of aluminum alloy, while the contact surfaces were composed of two wear-resistant steel plates connected via screws. Eight screw pressing plates were added, along with a thick positioning ring, ensuring stability and compatibility with other parts.

Figure 4 Turbine Groove Profile

This improvement significantly reduced vibration and enhanced machining accuracy. It also allowed for easier replacement and better compatibility across different parts. For more detailed information, please download the attachment or refer to *Metal Processing (Cold Processing)*, Issue 15, 2013.

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