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The refurbishment of aircraft engine turbine blades is important to aircraft owners and operators because of the high original cost of the component. In use, the blade is subject to extensive wear at the top edge. A large amount of hand polishing is required to generate the original shape during refurbishment. Additionally, machining or polishing efforts frequently result in a high reject rate, in some cases requiring the entire blade to be scrapped.
Hermle Machine Company recently developed a new time-saving process when it took on the task of refurbishing a segmented section of a compressor blade used in an aircraft engine. The process involves the addition of metal to the worn edge of the blade by means of a welded bead and subsequent machining on a Hermle 600U five-axis machining center equipped with custom designed software from TTL Expert Systems of Great Britain.
The compressor blades, which formerly required a cycle time of 12 minutes, were machined to specification in a 3-minute cycle. The finished blades required only minimal hand polishing, and the formerly high scrap rate was virtually eliminated. According to Ken Merk, executive vice president of sales and service, "The savings potential here is really tremendous. In the past, airline maintenance shops and subcontractors not only had to contend with long cycle times but extremely high scrap rates. The 600U's composite base construction and five-axis geometry provide the stability and vibration damping characteristics required for this type of work, as well as the flexibility necessary to achieve proper tolerances in such a complex shape."
Additionally, the machining center's Heidenhain control was equipped with a customized software package developed by TTL Expert Systems of Great Britain. Paul Walton of TTL comments, "Our company has an extensive base of experience in the development of programs related to gas turbine component manufacturing and refurbishment. Having created the basic software tools, we input the particular tool path requirements necessary for the customer's individual application to provide a solution that's both timely and cost effective."
The Hermle/TTL solution accommodates turbine blades up to 14 inches in size.