Design and Fabrication of Strong Parts from Poly (Lactic Acid) with a Desktop 3D Printer: A Case with Interrupted Shell

Abstract

The ability to form closed cavities inside the part printed is an important feature of Fused Filament Fabrication technology. A typical part consists of a dense shell bearing the primary load, filled with low-density plastic scaffold (infill). Such a constitution of the part provides in most cases appropriate strength and low weight. However, if the printed part shape includes horizontal (orthogonal to printer’s Z axis) flat surfaces other than its top and bottom surface, then the shell of the part becomes interrupted, which may lead to drastic drop in the ability of the part to withstand loads. In the current study, a representative sample of a part with interrupted shell and testing apparatus is developed. Influence of shell and base thicknesses, as well as influence of the infill density on the part strength, are studied. Different approaches to the sample shape modification were applied and tested. The part shape optimization made with respect to peculiarities of Fused Filament Fabrication technology resulted in increment of the force, required to fracture the part from 483 to 1096 N and in decreased part mass from 36.9 to 30.2 g.

Desktop Fabrication of Strong Poly (Lactic Acid) Parts: FFF Process Parameters Tuning

“…Current study is the continuation of [61], which demonstrated the importance of part shape design with respect to FFF technology peculiarities and its influence on the sample strength.…”

“…The shapes of samples tested were inherited from previous study [61]. An item consisting of two connected coaxial cylinders of large (boss) and small (shaft) diameters was used as basic shape (Shape 1), it's dimensions and constitution (superposition of shell, bases and infill) of the printed part are shown on Figure 2.…”

“…Four different approaches to increase the strength of such a part by modification its shape and constitution resulted in four additional shapes (Shape 2 to 5), which constitution is shown on Figure 3. For CAD models with relatively large volume (Shape 1 and Shape 2) configuration provided maximum strength in the previous study [61] (base thickness 1.2 mm, shell thickness 2.4 mm, infill 60%) were fabricated and tested. For CAD models with lower volume (Shape 3 to 5), the same single configuration that was tested in the previous study [61], was used: shell thickness 1.8 mm, 100% infill and no bases (base thickness 0 mm).…”

“…A turquoise PLA filament of 2.85 mm in diameter was used, produced by REC company (Moscow, Russia). This specific manufacturer of filament was chosen due to locally produced material and the desire to obtain results comparable with previous studies [58][59][60][61].…”

“…Figure 1. Testing part geometry optimization and results of study [61] The Shape 1 part was used as a representative of common issue of FFF parts when the shell mimicking the part geometry interrupts forming a weak spot ( Figure 2). Shapes 2, 3, 4 and 5 represented different attempts to solve the interrupted shell issue.…”