Experimental Study On Machining Technical Characteristics Of Deep Cavity Inner Surface Functional Structure

Frequency Selective Surface is a periodic structure composed of one or more layers of patches or aperture arranged on the Surface of substrate medium,which has spatial filtering characteristics and is widely used in the field of aircraft stealth.At present,the production of FSS mainly focuses on the outer Surface of radome.However,FSS distributed on the surface of radome is easily damaged by air resistance during high-speed flight.Therefore,it is urgent to propose a processing technology that can manufacture electromagnetic functional structure of deep cavity inner surface with high efficiency,high quality and low cost.This paper proposes to fabricate electromagnetic functional structure on deep cavity inner surface by laser machining technology.Firstly,the electromagnetic characteristics of FSS on deep cavity inner surface are analyzed by HFSS simulation.Then set up the main body of laser processing equipment and design and select the relevant experimental devices;Then,a laser machining method for the functional structure of the deep cavity inner surface with weak degrees of freedom was proposed,and the processing technology was designed to carry out machining experiments on the deep cavity comparison model,aluminum plate and silver coated plate to analyze the machining technology characteristics of the inner surface.Finally,the whole inner surface of deep cavity is machined and the machining error is analyzed.(1)The electromagnetic transmission characteristics of the cross element are simulated by HFSS software to analyze the influence of the change of the characteristic size of the element within a certain range on the transmission characteristics,and then the RCS characteristics of the wedge deep cavity and hemispherical surface FSS are simulated and analyzed.The results show that the length of the cross arm has the greatest influence on the electromagnetic transmission characteristics,and the accuracy of the characteristic size of the element is obtained.At the same time,the RCS characteristics of FSS on the inner surface of the wedge deep cavity are obvious because of the hemispherical surface FSS,which can effectively reduce the radar cross-sectional area.(2)According to the processing principle and requirements,the gantry multi-axis laser processing equipment is built,the laser processing system components and corresponding auxiliary devices are designed and selected,the positioning fixture suitable for all kinds of workpiece is designed,and the hand-held microscope was selected for observation.The results show that the equipment has high repeatable positioning accuracy of each axis,good zoom capability,and can effectively expand the processing range,and can meet the positioning and processing of large deep cavity workpiece.(3)A weak degree of freedom laser machining method using 3d laser machining system and servo guide is proposed.The machining inner surface is modeled and partitioned.The 3d laser machining system is used to etch the divided area directly,and the machining of the deep cavity inner surface is completed with the complete regional connection and focal length adjustment of servo guide rail.The feasibility of the scheme is verified and the effect of light spot deformation on machining quality is analyzed by comparing the physical model of the wedge cavity and the machining experiment of aluminum sheet at different tilting angles.In the processing experiment of silver coated small plate,root mean square difference of sample points and removal rate are used to characterize the processing quality,and the best etching parameters of silver coating are obtained by laser parameterization experiment.Using the modified pattern and the best etch parameters to complete the whole machining of the ceramic wedge deep cavity inner surface,to achieve the required machining accuracy;All kinds of errors are analyzed,including positioning error,displacement mechanism error and laser machining system error.The results show that the proposed laser processing technology can efficiently and accurately process FSS on different surface materials of deep cavity inner surface,and has good electromagnetic characteristics.