Test & measurement
Measuring solutions reduce machine tool testing time by up to
6.5 hours
services, worked closely with the country’s largest provider of gas turbine engines who design, manufacture and service high performance gas turbine engines for both fixed and rotary wing aircraft and gas and oil producing sectors. One of Technopark’s customers wanted to
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increase the accuracy and efficiency of its bladed disk milling process. The complex high curvature surfaces of bladed disks used in gas turbine engines make them challenging components to manufacture. To overcome this challenge, Technopark
applied Renishaw’s OSP60 on-machine 3D scanning probe with SPRINT technology and Productivity+ Scanning Suite.
Background
In a precision mechanical assembly comprising compressor, combustor and turbine, bladed disks
ased in Ufa, Russia, Technopark Aviation Technologies, a provider of educational and scientific research and engineering
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
The 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 per cent and 60 per cent 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. 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.” Developing a CNC machining process for
50 January 2021 Instrumentation Monthly
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