Case Studies

Z Notch Grinding on Turbine Compressor Blades

Client: Major Aircraft Engine Overhaul Facility

Background:
An aircraft gas turbine engine has many expensive parts that are frequently rebuilt during an engine overhaul. Some of the most common items are the turbine compressor blades. The blades are forged from difficult to machine high temperature alloys such as Inconel and Hastelloy. The blades have 'Z' shaped edges that match the adjacent blades as they are arranged in a ring to form a compressor fan. When the 'Z' area (or 'Z' notch) wears out, the blades are removed and sent for repair. The typical repair procedure is to build up the worn area with a Stellite weld and then regrind the 'Z' form to the proper shape.

Manufacturing Challenge:
Form grinding the 'Z' notch using conventional abrasive grinders presents a number of challenges. Since Stellite does not grind freely, the grinding wheel needs frequent dressing, sometimes twice per blade. Conventional abrasive grinding is a slow process requiring multiple light cuts to prevent heat buildup. Excess heat from grinding can crack the weld causing the repair to fail. The customer had multiple hand feed surface grinders in use to reshape the 'Z' form after welding. The process was expensive because of excessive wheel dressing and frequent grinding cracks in the weld repairs. Cycle time on each blade was approaching 12 minutes each. Frequent wheel dressing was costing the company over $40,000 in grinding wheel costs alone.

Solution:
The Everite Electrochemical Grinding Equipment surface grinders cut without generating any heat or burrs. The Electrochemical Grinding Equipment process can grind up to 150 blades between wheel dressings and all cuts are done in no more than 2 passes. The process is fast, efficient and reduces the chance of scrap. Since the wheel life is so high the cost of operation is low. The Electrochemical Grinding Equipment process is also used widely for grinding the knife-edge air seals on the shroud end of turbine blades after weld repair. The customer purchased three Everite EG618 grinders and reduced the cycle time to 3 minutes per blade. Wheel cost was cut to under $2,500 per year and rework on cracked blades dropped to almost zero. 

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