Novel method of multi-axis EDM machining of thin-walled Al-Mn parabolic reflector for aerospace applications

Abstract

The production of high-precision parts and assemblies for aerospace applications requires not only mechanical but also physical and chemical methods of machining the workpieces to achieve required tight tolerances. Aerospace parts are often produced out of hard materials such as titanium or nickel alloys as well as soft materials such as aluminium alloys. In this paper, the improvement of the manufacturing process of thin-walled reflector for the narrow directional onboard antenna is investigated by applying multi-axis electroerosion machining. Due to advances in the technology of assembling waveguides, channels and flanges, it became necessary to change the material of the parabolic antenna reflector, which has excellent solderability, however, is poorly suited to stamping. Since stamping is no longer able to ensure precision in manufacturing, the edge of the reflector is machined using electrical discharge machining (EDM) which performance has low dependence on the material hardness. The mirror material is an aluminium-mangenese alloy of high corrosion resistance, high plasticity (relative elongation at break is 18%), high resistance to puncture loads and low weight. Cutting forces arising during the turning process can cause bending of the antenna mirror surface. The imperfection of the mirror creates uncorrelated areas which are parasitic radiating surfaces. These parasitic radiating surfaces reduce the efficiency of the antenna. A novel machining strategy using a wire EDM machine with an additional inbuilt two axes rotary table is used to replace mechanical cutting, as this machining no longer meets the high requirements for surface quality paired with geometrical tolerances. Measured Ra values of the machined edge machined by wire EDM are lower than 1.6 µm and the geometrical accuracy of the produced part is significantly improved, the standard deviations from the roundness of produced reflector surface are below 30 µm.