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The High Temperature Components Section of aerospace manufacturer Centrax of Newton Abbot, Devon, England, specializes in the machining of turbine nozzle guide vanes and rotor blades for air- and land-based gas turbine engines. The company recently was looking to add to its grinding equipment for machining nickel-based, heat-treated HP turbine blades manufactured for the FJ44 turbofan engine.
The FJ44 is a small, lightweight powerplant that brings the economy of the turbofan to the small business aircraft market previously served by turboprop engines. The compact size and complex profile of the FJ44's HP turbine blades provide a difficult application in terms of workholding and machining.
However, the purchase of the Jones & Shipman (Meriden, Connecticut) Dominator 634 CNC (600- by 300-mm table) to replace a number of large and unreliable reciprocating-type grinders has boosted production and proved invaluable for machining the blades. The company has ramped up productivity even further on specific ‘hot-end' precision grinding tasks with the acquisition of two additional Dominator 634 CNC production surface/creep-feed grinders. This brings the company's total complement of Dominators up to four.
The blade's fir tree root-end is ground in two operations on the Dominator, with each operation carried out in batches of 1,500 to 2,000. The blade is held in a sophisticated fixture, purpose-designed and developed by Centrax for the task.
The fixture supports the aerofoil in six positions, and it takes advantage of machining forces to hold the component in place while grinding is carried out.
A productivity boon is an optional Erowa quick change chuck, which allows the setter to load and unload the fixture quickly, thus removing the ‘dead' time between setups.
Production engineer Patrick Moore says, "We first saw the Dominator at MACH '98 and were very interested in the machine's traveling wheelhead concept and felt that its small footprint would suit our production needs perfectly. Some time later, when visiting a customer, we saw a Dominator grinding powerplant components and were most impressed.
"We reviewed our then-current grinding machine inventory and looked at other suitable new products on the market and deduced that the Dominator offered a significantly reduced footprint, excellent cycle times, strong health and safety features such as totally enclosed guarding, leak-free operation, robust design and online modem support. Naturally then, when funding became available, the Dominator was the obvious choice."
The Dominator concept features a total rethinking of the surface grinding process. Incorporating a reciprocating wheelhead rather than a traditional reciprocating table design, major advances have been achieved in respect to structural rigidity, machine dynamics and a smaller machine envelope.
Mr. Moore was also impressed with the easy-to-use programming system. Windows-based setup pages allow the operator to quickly digitize diamond roll and wheel positions, and, with minimum use of mouse or keyboard inputs, produce a finished program. Graphical images prompt the operator, and spreadsheet-style programming ensures quick and simple input. The option of ISO programming is also available if required.
"The Windows-based programming system allows us to input various parameters at any time during the cycle, therefore it can be as flexible as you like—unlike many other systems," Mr. Moore says. "An operator/setter can be fully conversant with the Dominator in a week or even less."
With the success of the first Dominator, a second machine, an original 634 model, was brought in on lease to cope with a temporary production peak. As with the first Dominator, the 634 impressed with its production capacity, ultra-reliability and a small footprint, so the company bought it. One use of the second Dominator is two-axis radial tip grinding of LP compressor rotor blades. The application is both demanding and time-consuming, requiring the machining of a fine tolerance arc in both the X and Y axes.
"When we used large creep-feed grinders on this application, the surface finish was not always of the required standard, with ‘facet' marks often left along the length of the radial tip. However, since applying the Dominator to this work, productivity and surface finish have been excellent, and we are using it more and more for this type of application," adds Mr. Moore.
Now with the installation and commissioning of two more Dominator model 634s, Centrax is achieving a further boost in production—this time on the GMA 2100 engine line, where both machines are grinding Inconel compressor blade root features.
Another feature of the Dominator purchase is the technical cooperation that has occurred between Centrax and Jones & Shipman International. For instance, on the original Dominator 634, Centrax had a requirement to raise the diamond roll dresser center line by variable amounts and wanted interchangeable diamond roll spindles manufactured that could be stored and re-assembled quickly and easily. "Jones & Shipman designed, developed and manufactured a diamond roll dresser based on a sine bar principal," Mr. Moore says. "The unit also gives us a fully interchangeable diamond roll spindle facility, allowing us to store bespoke diamond roll arrangements that aid setting and storage. The dresser also incorporates a variable height facility."
Summing up, Mr. Moore says, "For high production, reciprocating and creep-feed grinding applications, I wouldn't hesitate in specifying another Dominator. Product, service backup and application support has been absolutely first-class."