Sensitivity of PBX 9501 and PBX 9502 to Milling Operations

Explosive driven pulsed power performance benefits from modern polymer-bonded explosives. In practical application, high precision in the dimensional shape is required, and high machining speeds are desired. The limits of machining speed, driven mainly by the thermal response of the energetic material, are investigated. Specifically, the thermal response of PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF by weight) and PBX 9502 (95% TATB, 5% Kel F-800 by weight) under conventional milling methods is examined. The presented work focuses on face milling performed with dry machining on a CNC, remote-controlled milling machine. The primary parameters of interest are the spindle speed, feed rate, step size, and depth of cut, with additional consideration given to endmill diameter, milling technique, and the number of flutes. The temperature of the system is monitored via high-speed IR videography and near the cutting interface with a K-type thermocouple inserted into the endmill’s through-coolant hole. Operational forces and torques are recorded by a 6-axis force sensor mounted beneath the HE samples.An empirical relationship between temperature and the milling parameters is presented. Overall, milling regimes exist outside of DOE-STD-1212-2019 for which milling temperatures remain well below the HE critical temperatures.

I. Introduction

Milling operations generate heat along the cutting interface due to the shearing of material and friction along the back face of the cutting edge. With inert materials, heat can affect tool wear and surface finish. With the introduction of energetic materials to milling operations, extra care must be used due to the possibility of ignition of these materials. The US Department of Energy (DOE) has published machining standards with specific guidelines on safely machining explosives [1] and applies to a wide range of explosive materials. These restrictions result in long machining times for milling processes.