The special alloys used for hot gas path turbine components require unique machining processes not found in conventional machining facilities. Continual investment has been made in state of the art CNC Grinding machines costing up to £1M. These highly complex machines require up to 10 axis of programming in order to generate to complex forms required.
Two grinding techniques are used. Continual Dress Creep Feed (CDCF) grinding uses alumina oxide wheels which are formed using diamond encrusted rollers to shape the wheels. The wheels are continually dressed during the machining process to ensure the component specifications are achieved. Steel wheel coated with Cubic Boron Nitride (CBN) are also used. This type of wheel is particularly suited to producing smaller aerospace components.
Latest generation CNC 5 axis milling machines are used where component geometry prevents machining by grinding. High machine rigidity and high torque at low speeds are a special requirement of vane milling machines, a requirement again determined by the casting alloys used.
Two basic processes are required in the machining of rotor blades
EDM die sinking
Conventional machining techniques can not produce narrow, enclosed features such as sealing slots used to prevent the hot gases in a turbine leaking between components. Here an Electrical Discharge Machining (EDM) process is used where a male form ‘electrode’ of the shape required is produced in copper or graphite. Electrical current is then passed between the electrode and the component and electrical sparks used to erode the required female form. Over 15 CNC EDM machines are used on the production of industrial gas turbine components.
EDM Hole drilling
The same generic process is also utilised to machine cooling holes. Here specialist machines use conductive fluids pumped through hollow electrodes and pulsed electrical signals to achieve quicker machining cycle times.
NGV is at the forefront of drilling of cooling holes using high energy YAG Laser beams. Development of this technology has enabled the component designers to include ever more complex cooling holes patterns including small diameter holes, fan shapes to diffuse the cooling air and drilling of parts through protective metallic and ceramic coatings. This has significantly improved the performance, efficiency and emissions of the turbine and would not be possible without the Laser technology used at NGV.
Aluminide coatings used to protect the parts are applied using a combination of gas vapour and pack powder techniques. Vacuum furnaces heat the parts and coating mixtures to around 1100 degrees C and under these conditions an alumina coating is diffused into the base material. A variety of other corrosion protection, wear protection and thermal barrier coatings are applied to parts using an European coating supply base.
Finished components require a variety of sub components such a cooling air inserts, Boroscope inspection bushes, etc. to be permanently assembled. NGV has capability for all assembly processes including TIG Welding. Electron Beam Welding and high temperature brazing.
Parts manufactured are supplied in a condition fully certified for build into the turbine engine. This requires that all inspection and testing is completed by NGV where we maintain fully accredited inspection process to include CMM dimensional, X-Ray, Airflow, Waterflow and Flourescent Penetrant Inspection (FPI) for checking of material cracking.
NGV facility has over 40 years experience in machining Nozzle Guide Vanes for aerospace and industrial gas turbines. Based in south Leicester the facility developed its capability supplying Rolls Royce with some of the early military and civil jet engine components.
NGV has always been at the forefront of manufacturing technology and pioneered laser drilling and single piece grinding techniques. All NGV’s used to be machined in engine ring sets but NGV installed the first single part grinding machine. This technique is now used to produce 90% of all NGV’s machined worldwide.
Based in a state of the art Facility NGV continues to invest in and develop the latest machining technologies. 2008 again saw NGV leading the industry when the first of it’s kind large scale single piece grinding machine, fitted with full wheel change capability, was installed.
In addition to manufacturing technology NGV uses ‘lean manufacturing’ techniques including product cells, single piece flow and six sigma to achieve true world class performance.
Sustained capital investment, continuous process improvements and a proven record in terms of quality, cost and delivery to our customers means that today NGV enjoys rapid growth. A technical capability ranging from the smallest aerospace parts to the largest industrial means that NGV is placed to take advantage of all opportunities and maintain continued growth.