Project Background

YMP received an order from an aerospace customer to machine a batch of stainless steel scroll impeller for an aerospace turbine system. The material is SUS304 stainless steel. SUS304 has good corrosion resistance and mechanical properties, but the hardening tendency during machining and the high requirements for surface quality make this project very challenging. Since the scroll impeller is a core component of an aerospace engine, its machining accuracy and surface finish have a direct impact on the performance of the engine.

Challenges

Material Characteristics: The machinability of SUS304 stainless steel is poor, and it is prone to work hardening. Moreover, the coefficient of thermal expansion of this material is relatively high, and thermal deformation may occur during machining, affecting the dimensional accuracy and surface quality of the final product.

Geometric Complexity: The curved surface and spiral structure of the scroll impeller are complex, and it is difficult to achieve precise machining with traditional machining methods. The five-axis linkage machining path needs to be carefully planned.

High Precision and Surface Finish Requirements: Aerospace-grade parts have extremely high requirements for the shape accuracy and surface finish of the impeller to ensure stable operation and high efficiency under high-temperature and high-speed conditions.

 

Solutions

1. Equipment Selection

YMP uses a five-axis CNC machining center for the precision machining of scroll impeller. The five-axis linkage equipment can achieve continuous machining of complex curved surfaces, avoiding positioning errors caused by multiple clamping and ensuring high-precision machining of complex curved surfaces.

 

2. Optimization of Tools and Cutting Parameters

SUS304 material is prone to hardening during machining, so a coated carbide tool is selected. This tool has good wear resistance and high-temperature performance and can effectively reduce tool wear. By setting a lower feed rate and a medium cutting speed, combined with an efficient cooling system, the work hardening phenomenon is alleviated and the thermal deformation of the workpiece is reduced.

 

3. CAM Programming and Machining Path Planning

Advanced CAM software is used to simulate and optimize the machining path of the three-dimensional model of the scroll impeller in detail. A strategy of combining rough machining and finish machining is adopted. In the rough machining stage, a certain amount of allowance is reserved as much as possible to avoid errors caused by thermal deformation. In the finish machining, surface treatment is carried out with a small step of high precision to ensure the surface quality of the scroll impeller.

 

4. Quality Control and Online Measurement

During the machining process, an online measurement system is used. Through a precision probe, the thickness, curvature, and key dimensions of the impeller are monitored in real time to ensure that adjustments and compensations can be made at any time during the machining process to avoid machining errors. The final impeller product is detected by a three-coordinate measuring machine (CMM) and a dynamic balance machine to ensure that the errors of all key dimensions are controlled within ±3mm and the unbalance amount is within 0.09gmm, and the thinnest impeller thickness is 1.8mm.

 

 

5. Surface Treatment

After machining, the surface of the impeller is finely polished to achieve a surface roughness of Ra 0.2, ensuring that the fluid resistance is minimized when the turbine rotates at high speed and improving the working efficiency of the engine.

Processing Name	Aerospace Scroll Stainless Steel Impeller (SUS304)
Using Equipment	5 Axis CNC
Processing Size	Φ400mmX115mm
Tools Quantity	15 pieces	Machining Total Time	180h55min
Serial Number	Machining Steps	Using Tools	Ap    (mm)	Ae       (mm)	Spindle Speed (rpm)	Feed Speed (mm/min)	Machining Time
1	Rough Machining	R17R0.8	0.35	18	1500	2500	10:20:10
2	Finish Machining	R8R0.5	0.2	5	5000	3000	15:30:00
3	Finish Machining	D8R4	0.12	0.12	6500	3000	20:30:00
4	Finish Machining	D8R4	0.12	0.12	6500	3000	10:15:20
Part Highlights: The incoming material is a turned blank, with the thinnest impeller thickness of 1.8mm (height of 53mm), and stable five-axis machining. The dimensional accuracy consistency of the whole circular impeller is high, and the unbalance amount is within 0.09gmm; The process includes turning the blank - CNC roughing - heat treatment - turning the datum - CNC roughing - deep cryogenic heat treatment - CNC five-axis finishing - turning the bottom surface and inner hole.
Checking Items		Checking Reports
Unbalance Amount (gmm)		<0.09
Detection Instruments		Dynamic Balance Machine

 

Results

High Precision and Consistency: The geometric accuracy of the impeller reaches the design requirements, with the error controlled within ±2 microns, ensuring the balance and stable operation of the turbine system.
Surface Finish: Through polishing treatment, the surface roughness of the scroll impeller reaches Ra 0.2, fully satisfying the strict standards of the aerospace industry.
Production Efficiency: Thanks to the efficient machining of the five-axis CNC equipment and the optimized process flow, the production cycle is shortened by 15%, and the production efficiency is significantly improved.
Customer Feedback: The customer is highly satisfied with the accuracy and surface finish of the scroll impeller. The product performs excellently in the turbine system test, further strengthening the cooperation with YMP.

Summary

This case demonstrates the strength of YMP in machining complex aerospace parts, especially in the high-precision machining of SUS304 stainless steel. Through five-axis CNC technology, reasonable tool selection, optimized machining path, and strict quality control, the high-quality machining of scroll impellers is successfully achieved, satisfying the demanding requirements of aerospace customers.