Research On Optimization Of Regional Scanning Technology For Large Aircraft Structures

In order to solve the problem that uneven temperature distribution will cause deformation and cracking of the formed parts in the process of laser additive manufacturing,a subfield scanning strategy based on characteristic regions was proposed.The research was carried out from two aspects:scanning starting points position and jump strategy between characteristic regions.Firstly,ANSYS was used to simulate the deposition manufacturing processes of two kinds of characteristic regions including the L-shaped and T-shaped.The influence of the ipsilateral side starting points scanning and the opposite side starting points scanning on the temperature field distribution of the characteristic regions and the thermal cycle of substrates' nodes were analyzed.The best scanning starting points of the two characteristic regions were obtained.After that,the processes of deposition manufacturing the frame structures with three jump strategies including continuous jump,interval jump,and maximum span jump were simulated,and the temperature distribution nephograms of the frame structures under the three jump scanning strategies were obtained.Secondly,the temperature field simulation results were loaded on the stress analysis models to analyze the stress evolution process.Finally,the temperature variations of substrates' nodes during the deposition processes were measured by the thermocouple,and the deformation of substrates after the deposition was measured.The experimental results were fitted with the simulation results.The above research shows that changing the scanning start points will affect the temperature distribution of the L-shaped and T-shaped characteristic regions.when using opposite side starting points to deposit characteristic regions,the influence range of temperature can be reduced and the cumulative heat effect can be reduced,thereby reducing the influence of thermal behavior during the deposition process on the mechanical properties of the substrate.In addition,when using opposite side starting points to deposit characteristic regions,the nodal thermal cycle curve of the substrate rises more slowly,and the peak temperature of the node is also lower.At the moment when the deposition of the frame structure is just finished,comparing the three jump scanning strategies,the maximum temperature is lower than the interval jump and continuous jump.During the deposition process,the stresses of the three jump strategies are all distributed in the characteristic region where the scan starts and junction of characteristic regions.As the height of the deposition layer increases,the phenomenon of stress concentration becomes more obvious.After cooling,the stress distribution range of the deposited layer does not change much,the high-stress area of the substrate gathers to the constrained position,concentrated on both sides of the constrained end.The stress at this position of the maximum span jump is lower than the interval jump and continuous jump.