Issues of dynamics in high-speed milling of aluminum aircraft structures

Structural dynamics often limit metal removal rates in high-speed milling. However, it is very uncommon for the part programmer to have the proper information regarding the cutting capabilities of the machine being programmed. Standardized methods exist for cutting performance evaluation of machining centers; however, no standard exists for evaluating a particular spindle, holder, and tool combination. Presented here is a testing procedure which enables a user to automatically establish the cutting conditions which optimize metal removal rate for chatter-free milling. This test extends the intended use of the standard methods to include the effects of non-square nose geometry tooling, cornering, and extended wall engagements. These tests are conducted with the aid of the CRAC system.; The extensions of the standardized tests to include the non-square nosed geometry and extended tool engagements are a result of difficulty encountered while machining aluminum aircraft parts. The aluminum aircraft components typically consist of deep pockets and thin flexible ribs. The testing procedure solves the problem of selecting the proper cutting conditions to prevent chatter from extended engagements; however, the test does not address the problem of the part flexibility.; Also, presented in this work is a characterization of the process of machining thin flexible ribs. The characterization of the ribs includes time and frequency domain audio spectrum analysis which show that the flexible ribs are forced until the rib engages the upper portion of the flutes. At that time the rib begins to chatter and damage previously machined surfaces.; The last issue of dynamics in high-speed milling presented here suggests one method to adjust the spindle, holder and tool dynamics to obtain increased MRR. The essence of this section is to adjust the placement of the stability lobes by simply changing the tool length.