3D scanning can greatly improve the accuracy and efficiency of the blisk milling process

Technopark Aviation Technology, located in Ufa, Russia, is a provider of education, scientific research and engineering services. It works closely with Russia’s largest gas turbine engine provider, which designs and manufactures high-performance gas turbine engines for the fixed-wing and rotary-wing aircraft industry, as well as natural gas and oil production.

A customer of Technopark wanted to improve the accuracy and efficiency of the blisk milling process. The blisk of a gas turbine engine has a complex high-curvature surface, so the manufacturing process is very challenging.

In order to overcome this problem, Technopark adopted the Renishaw OSP60 in-flight 3D scanning probe equipped with SPRINT™ technology and
Productivity+™ scanning software package.

Background

In the precision mechanical components composed of compressor, combustor and turbine, blisks play an important role in reducing resistance and optimizing the air flow in the engine and the thrust generated by it.

The blisk was introduced in the mid-1980s as a single component consisting of a rotor disc and multiple curved blades. Since the blisk does not need to connect each blade to the exposed wheel, the turbine design is effectively improved, the number of parts is greatly reduced, and the reliability and engine efficiency are improved.

The blisks are made of very hard, high-value metals (usually titanium or nickel-based alloys). So far, milling is the most important processing technology in the blisk manufacturing process, and because the blisk has a high-curvature surface, it requires the use of multi-axis Cnc Machine tools and advanced software for processing.

The blisk milling usually firstly uses rough milling and semi-finish milling to make a near-final shaped workpiece, and then finish milling to make the final high-precision blade and rotor surface.

Challenge

The blisks have high complexity and strict manufacturing precision requirements, which means that the finishing milling process of various blisks is a labor-intensive and cost-increasing process.

Although the touch-trigger probe can be used to measure the blisk in the machine, after milling, each workpiece needs to be removed from the Cnc Machine tool for offline measurement and inspection, and then reinstalled on the machine tool for subsequent processing. This process needs to be repeated many times and is susceptible to human error.

According to the company’s inference, the out-of-machine inspection and milling process accounts for about 30% to 60% of the total labor cost of blisk production. In addition, the statistical analysis results of the blade size deviation (after the machining of the leading and trailing edges) proved the existence of errors.

The results show that the deviation of the blade cross section is: the residual margin fluctuates ±0.064 mm, and the actual profile deviation is 0.082 mm. The deviation of the longitudinal section is similar to that of the cross section: the residual margin fluctuates by ±0.082 mm, and the actual profile deviation is 0.111 mm.

The main reasons for the deviation in the edge machining process can be attributed to: the five-axis movement error of the machine tool during the machining process; the blade elastically deforms due to its low rigidity during the cutting process; and the tool elastically deforms during the metal cutting process. ”

“This process requires a lot of manual intervention, but due to the inevitable human error, it will lead to an increase in the scrap rate. We urgently need to develop a new solution to improve the speed and accuracy of blisk milling.”

The cnc machining process developed for blisk milling includes the following requirements:

• • Use parameterized control program for semi-finish milling
• • In-machine workpiece detection
• • Modify the parameterized control program according to the test results
• • Use the modified parameterized control program to finish milling the workpiece

Solution

Technopark is designated to be responsible for the development and deployment of the required process control technology. Semen Starovoytov, associate doctor of Technopark and head of the innovation department, said: “We have been cooperating with Renishaw for many years. We have equipped Renishaw touch probes on various machine tools to achieve perfect measurement accuracy.”

“For this project, it is obvious that we need to develop software based on scanning probes, so we decided to seek cooperation from Renishaw. Renishaw’s SPRINT 3D scanning measurement technology for machine tools met all our technical requirements.”

Result

After the introduction of Productivity+ software and OSP60 probe, the machining accuracy, speed and labor cost of the blisk manufacturing process have undergone significant changes.

Through the high-speed 3D scanning and measurement of the blisk on the machine tool, the production time is greatly saved, thereby significantly improving the production efficiency of the Cnc Machine tool.

In terms of the milling accuracy of the blisks, the cross-section and longitudinal section deviations of the blisks after machining have been significantly improved: from the original 0.082 mm and 0.111 mm to the current 1 µm and 28 µm.

In terms of machine tool staffing, Starovoytov said: “The execution of the process control mode can automatically adjust the CNC control program based on the 3D blade scan data provided by the OSP60 probe. This means that engineers no longer need to monitor the machine tool operation all the time.”

He concluded: “Combining SPRINT 3D scanning technology with Productivity+ CNC software, even the slight deviation of the blisk shape can be recognized in real time, but the trigger system cannot detect these deviations.”

“The return from this investment has far exceeded our expectations. The precision milling of the blisk has been increased by more than three times, and the related labor costs have been reduced by half.”

SPRINT™ technology

OSP60’s built-in 3D scanning probe is equipped with Renishaw’s unique SPRINT technology.

The stylus tip (stylus ball) can be accurately measured and moved along the surface of the blisk. The stylus can accurately record high-resolution stylus deflection data and obtain sub-micron movement data of the ultra-sensitive stylus tip on the X, Y, and Z axes.

The OSP60 probe uses a high-speed, noise-resistant optical transmission connection, which can transmit 1000 XYZ probe center data points to the OMM-S receiver per second. Then, use advanced algorithms to process probe deflection data and machine tool position encoder data to generate accurate blisk surface data, and finally use these data to accurately calculate feature positions, sizes and shapes.

Productivity+™ technology

Using Productivity+ CNC plug-in software can achieve scanning speeds of up to 15,000 mm/min, and the in-machine measurement speed can sometimes even be 5 times faster than traditional trigger systems. Scanning the blisk on the machine tool eliminates the need to remove the workpiece during processing.

The software can display high-precision measurement results in real time on the screen, and use these data to automatically adjust machine settings for the subsequent finishing milling process. The measurement report can also be exported to a file for analysis or used to perform quality assurance.

Using the existing external graphics programming tools, the leaf disc inspection program can be quickly and easily generated based on the geometric characteristics of the solid model.
The Productivity+ interactive front-end platform has a simple and easy-to-understand graphic screen to edit and simulate the probe detection program, and users do not need to directly deal with complex NC codes.