Approach for CFRP/Ti Large Size Hole-Making Application by Replaceable Head Type Drills 2011-01-2746
Due to the recent increase of fuel price, the Aerospace Industry has extended its focus on reducing airplane structure weight by using more Carbon Fiber Reinforced Polymer/Plastics (CFRP). The majority of airframe parts is made and structured with CFRP, Titanium (Ti), corrosion-resistant steel (CRES) and Aluminum (Al).
Hole-making is a common problematic issue for machining these materials. Because there are hundreds of thousands of holes, there is frequent machining and fastening of parts; however, machining CFRP along with other material (Clad material) which has different physical characteristics has proven to be a challenge. Since hole-making must occur at different positions (horizontal, vertical, and a variety of angles), a high mobility machine capable of Positive Feed Drilling (PFD) is commonly used. Large diameter drills are used for connecting the airframe part. This creates the problem of the main cutting resistance against PFD spindle being larger than spindle horsepower, and often results in spindle seizure. To resolve the issue, a pre-hole process is frequently used before drilling the final diameter for reducing the main cutting resistance; however, the pre-hole process creates chipping on the finishing diameter drill. The chipping usually occurs at the pre-hole diameter on the final diameter drill due to the excess resistance on the cutting edge.
This process can drastically shorten the drill tool life and increase the tool change / setup cycle time. Cost performance is one of the most important issues for managing tools. Therefore, a replaceable head type is one of the solutions for this application due to the easy indexability. This paper investigates machining CFRP / Ti (Clad material) and determining the design of the cutting edge geometry with or without pre-hole application.