Charlotte, North Carolina
June 20, 1999
June 20, 1999
June 23, 1999
4.288.1 - 4.288.9
High Velocity Coolant Delivery System
Sung Kim and Kevin Logeais
Piedmont Technical College/Jarvis Cutting Tools Inc.
This paper is for the design and implementation of a high pressure coolant delivery system that will aid in making a step drill grinding process more efficient. Work related and pertinent to a grinding process is used to produce the pilot section of a step drill.
Step drills are used to create highly accurate holes in aircraft skins and stringers. These holes are for the fasteners that hold the aircraft skin to the stringers or ribbing. The step and double margin configuration allows for the drilling of close tolerance holes with hand drilling equipment. The step section acts as a center-drill and stabilizes the tool for the entry of the larger drill body into the hole. The transition angle from the pilot diameter to the main body diameter acts as a secondary cutting lip. The main body has a double margin configuration, which yields contact at four opposite points in the hole. The four contact points improve hole eccentricity as well as minimize hole size variation.
The step grinding process uses a seven-inch diameter resin bonded CBN (Cubic Boron Nitride) grinding wheel. The wheel speed on this machine is seven thousand revolutions per minute. This rotational speed at the wheel periphery translates into thirteen thousand surface feet per minute. This velocity generates an envelope of air around the wheel that deflects flood oil coolant away from the point of work. This oil coolant has great lubricity characteristics, but is poor for dissipating heat. An aggressive feed rate generates enough heat to breakdown the CBN wheel bond, glazing over the wheel, thereby reducing the effectiveness of the wheel. The area of the wheel greatly affected this bond breakdown is the point of transition between the two wheel faces that create the pilot diameter and the transition angle.
The most critical section of the part, with respect to wheel wear is the customer-specified radius at the juncture of the pilot with the transition angle. The lack of coolant at the point of work is only one parameter that can effect this grinding equation. Other parameters that can be adjusted are the wheel diameter, wheel speed, wheel composition, and workpiece-wheel speed ratio. Improvements in these other parameters will generate even more heat at the point of work, making the coolant delivery system even more critical.
To design and implement a high-pressure coolant delivery system is more efficient to aid in making a step drill grinding process. To produce the pilot section of a step drill is work related and pertinent to a grinding process. In aircraft skins and stringers, step drills are used to create highly accurate holes that are for the fasteners or rivets that hold the aircraft skin to the stringers or ribbing, see Figure 1.
Kim, S., & Logeais, K. (1999, June), High Velocity Coolant Delivery Paper presented at 1999 Annual Conference, Charlotte, North Carolina. https://peer.asee.org/7709
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