In a precision mechanical assembly comprising compressor, combustor and turbine, bladed disks play an important role in minimising drag and optimising airflow in the engine and the amount of thrust it produces.

Introduced in the mid-1980s, a bladed disk is a single component comprising a rotor disk and multiple curved blades. By removing the need to attach separate blades to a bare rotor, bladed disks have helped transform turbine design, substantially reducing component counts, increasing reliability and maximising engine efficiency.

Bladed disks are machined from very hard high-value metal, typically titanium or nickel-based alloys. Milling is by far the most important machining process during their manufacture, and due to the bladed disk's high curvature surfaces, multi-axis CNC machine tools and advanced software are required.

Bladed disk milling usually involves rough slot-milling and semi-finishing to create a near net component, followed by fine milling to arrive at the finished high-precision blade and rotor surfaces.

Challenges:
he high complexity of the bladed disks and the stringent manufacturing precision they demanded meant the fine milling process for a wide range of different bladed disks was a labour-intensive and increasingly costly process.

Despite using a touch-trigger probe for on-machine disk measurement, each workpiece needed to be removed from the CNC machine after milling for offline measurement and inspection, and then remounted for any further machining. This process needed to be repeated several times and was subject to human error.

The company deduced that the off-machine inspection and milling process was accounting for anywhere between 30% and 60% of the total labour cost involved in bladed disk production. In addition, statistical analysis of the dimensional deviation in blades (after leading and trailing edge machining) identified the presence of errors.

Multiple blades require a fast measurement system

Deviations in blade cross section were observed as: residual allowance fluctuation ±0.064 mm, offset from nominal profile 0.082 mm. Deviations in the longitudinal section were similar: residual allowance fluctuation ±0.082 mm, offset from nominal profile 0.111 mm.

The main reasons for deviations arising during edge machining were concluded to be: kinematic errors of the machine during five-axis operation; elastic deformation of the blade during the cutting process due to its low rigidity; and elastic deformation of the tooling during metal cutting.

“The large number of operator interventions necessary for this process simply increased the risk of irreparable rejects due to human error. There was an obvious need to develop a fundamentally new solution for faster, high-precision bladed disk milling.”

Solution:

Contact scanning of blade freeform surfaces

 

Visit : https://www.renishaw.com/en/3d-scanning-boosts-accuracy-and-efficiency-of-bladed-disk-milling-process--45503 for more info.

• Follow @CNCTimes