A model for chatter stability enhancement through lattice support structures

The machining of near net shapes (NNS) produced by laser powder bed fusion (L-PBF) presents challenges regarding the stiffness of components. Notably, complex geometries featuring thin-walled, slender and hollow regions are of particular interest to additive manufacturing technologies, yet to meet the dimensional and surface quality requirements of functional parts, machining is often deemed necessary. Compliant regions of a workpiece are prone to chatter, and workholding becomes difficult with complex surfaces. Previous works have explored the pure stiffening of flexible workpieces with solid elements such as buttresses and lateral stiffeners. Meanwhile, advances have been made in mesostructural design for a range of metamaterial functions due to the maturation of L-PBF. Building upon these two concepts, the present contribution investigates what damping and stiffening effects a lattice support structure would have on the chatter stability of a flexible workpiece produced by L-PBF. A dynamic model of a cantilever beam supported by a spring and a viscous damper is proposed to predict the vibrational behaviour of a workpiece supported by a lattice support structure. A preliminary modal test is carried out to acquire damping behaviour to inform the model, and provide a deeper understanding of the relationships between lattice parameters and damping. This study is part of an ongoing discussion into the post-processing of NNS parts produced by L-PBF. It presents the concept of additive design for machining, and prompts investigation into how a mesostructural support could be designed to enhance machining operations. As the proposed structure is an addition to the functional part, it should be sacrificial, and to be sacrificial it should be removed effectively and efficiently. The present contribution seeks to provoke a discussion around these emerging concepts.