Additive Manufacturing Overhang Constraint Oriented Design Method Of Self-supporting Structure

With the growing demand for lightweight parts,topology optimization has become an important means of structural lightweight design.However,after topology optimization,the structure is often too complex to be fabricated by traditional manufacturing technology.Although additive manufacturing has great degrees of processing freedom,there are still manufacturing constraints in the actual processing,among which the overhang constraint has the most serious impact.In general,when overhang structure’s angle is less than the critical angle,the overhang structure must be supported by supports below to avoid print collapse.These supports are formed during processing and need to be removed during post-processing,which is a serious waste of raw materials and time.In order to solve the above problem,a self-supporting structure optimization method oriented to additive manufacturing overhang constraint is proposed in this paper.The self-supporting structure is optimized by applying overhang constraints in the topological optimization stage to achieve self-support and greatly reduce the use of support.The main research contents include:(1)Under the framework of the SIMP topology optimization method,based on the density characteristics of the element at the fuzzy boundary of the structure,the overhang constraint method including the overhang angle constraint and the undersize feature constraint was constructed,and the topology optimization formula including the overhang constraint was established.The SIMP based overhang constraint optimization process was formed.An example was used to intuitively illustrate the effect of different overhang constraint conditions on structural optimization,and the validity of the proposed suspension constraint method was verified.(2)Numerical examples of MBB beam and cantilever beam were used to verify the effectiveness of overhang constraint on the optimization of self-supporting structures,Furthermore,the influence of overhang constraint on the structural performance under different printing directions and minimum feature size parameters(m)was analyzed.It was found that the compliance value of the optimized structure is positively correlated with the number of boundaries that violated the overhang constraints in the original structure,and the selection criterion of the printing direction with the least stiffness loss was proposed.It was clear that the compliance value of the structure is positively correlated with the parameter m,and the principle of the optimal stiffness of m was given.(3)Simulation and processing experiments were used to analyze the printing performance of the cantilever beam with the original structure and the optimized structure with overhang constraints,the influence of overhang constraint method in reducing support quantity,saving processing time,reducing residual stress and ensuring printing quality was explored.The results show that the support material and support processing time of the optimized structure are reduced by 86.52% and 96.77% respectively compared with the original structure,and the whole part saved 15.75% of material and 46.67% of processing time.The optimized structure avoided the serious secondary deformation caused by the release of internal stress when the supports were removed,and the optimized structure without supports was printed successfully,which proved that the overhang constraint method can reduce the number of supports while ensuring printing quality.