Guidelines for 3D printed springs using material extrusion

Purpose Springs are an integral part of mechanisms and can benefit from additive manufacturing's (AM) increased design freedom. Given the limited literature on the subject, the purpose of this paper is to develop guidelines for fabricating helical springs using three-dimensional (3D) printing. Design/methodology/approach Polylactic acid (PLA) is the main material investigated, with ULTEM (TM) 9085 used as a comparison. The experimental procedure is to vary the spring parameters, print the springs and test them in tension or compression using constant velocity. Plots of the force and displacement are used to measure the linear and post-deformation spring constants. Loading of the springs is done both to breakage and cyclically. Cyclic loading is also used to observe the plastic behaviour of the springs. Parameters that are varied include wire and coil diameters, pitch, wire cross-section, in-fill and layer height. Findings A square wire cross-section is used, instead of a circle because it produces more consistent coils. In-fills make no significant difference in the elastic stiffness of the springs but the mono in-fill breaks at a greater extension, so it is recommended. Tension and compression springs are confirmed to behave the same when in the elastic regime. ULTEM (TM) 9085 produces consistently weaker springs compared to PLA. Variation of layer height shows that thinner layers increase the stiffness of the springs. Originality/value This study investigates the behaviour of 3D printed helical springs in tension and compression. Three guidelines are created: square wire cross-section, mono-directional in-fill and thin layers are recommended.