Sri Sai Durga Engineering (SSDE), a company specialising in supplying the power-generation industry in India, is using a Nikon Metrology Altera coordinate measuring machine to increase the energy efficiency of its production of supercritical turbine blades by around 40 per cent. The company, based in Patancheru, Hyderabad, has a particular focus on reducing lead times for components with challenging specifications.
Components for supercritical systems tend to need tighter tolerances, different dimensions and more complex shapes than those for conventional (sub-critical) power generation, whose turbines operate at a much lower pressure. This has made metrology more challenging for the company, and to maintain required levels of quality assurance it has needed new measuring equipment that combines speed, accuracy and automation.
To optimise steam flow within the turbine, supercritical turbine blades need to be much stronger and have a more complex design than those for subcritical turbines. They are made from a variety of custom alloys, as well as a composite known as X20, which is often used for high-temperature steam piping.
Self-critical turbine blades have a fixed section geometry, which can be measured using manual methods such as calipers. However, supercritical blades have a twisted aerofoil with varying geometry from root end to the shroud end; these are difficult to measure using manual methods, and particularly challenging within the short timescales to which SSDE works.
According to managing partner Naveen Reddy, a new automated system was necessary. “Customer satisfaction is always a priority in my business and limitations of the previous method would mean uncertainty and product quality, leading to customer dissatisfaction.” Reddy consulted several CMM suppliers looking for a machine capable of fast, accurate inspection. The choice of the ceramic bridge 8.7.6 Altera with SP 25 continuous scanning probe and Digigraph blade analysis package – part of the Nikon Metrology Camio software suite – has given the company accuracy and repeatability that has been a major bonus in inspecting components with complex shapes and contours.
Use of the Altera system has reduced inspection cycle times by at least 30 per cent since moving from manufacturing subcritical to critical components. According to Reddy, the Camio software’s automatic best-fit feature has been particularly useful, as it helps the quality-assurance team be certain that inspector components conform to specification.