Laminated Object Manufacturing of Thermoset Composites and Their Mechanical Characterization

Laminated object manufacturing (LOM) is an inexpensive rapid prototyping process in which three-dimensional parts are built sequentially, layer by layer, from a sheet of material, and it is widely used in various industries. LOM can offer considerable advantages compared to other additive manufacturing techniques, such as dimensional accuracy, a variety of material utilization, and design flexibility. It involves cutting, stacking, and bonding layers. Each layer was cut to a cross-section from the sheet of material based on a computer aided design (CAD) file. The cutting technologies have vastly improved with the application of CO2 laser cutters. The cut layers are successively layered and bonded on top of the preceding ones. Recently, LOM has attained wide attention in the manufacturing of composite materials and ceramics. LOM technologies are widely used in the manufacturing of thermoplastic composites. However, the application of LOM in the manufacturing of thermoset composites is limited in literature. The objective of this research article is to develop an LOM based manufacturing process for thermoset composites and to mechanically characterize the manufactured composites. A plain weave symmetrical carbon fiber fabric was cut to the desired shape using a CO2 laser cutter, following a CAD model. Liquid thermoset resin, such as Pro-Set epoxy resin, was infused into the cut fabric using a hand lay-up approach. Successive layers of fabric were then bonded on top to complete the layup. A vacuum bag was applied to the assembled layers to remove any trapped air and excess resin. The manufactured object was thermally post-cured at 80°C for 8 hours to ensure complete curing. In this research, the manufacturing of a wrench and a gear was demonstrated using this technology. Mechanical characterization of the manufactured specimen was conducted. The tensile strength and modulus of the manufactured specimen were measured at 575 ± 26.5 MPa and 46.8 ± 2.8 GPa, respectively. Scanning electron microscopy (SEM) of the failure surface shows evidence of strong bonding between the fiber and the matrix. The interlaminar shear strength of the manufactured composites was measured using the short beam shear (SBS) test, which yielded a strength 48.3 ± 0.5 MPa. Optical microscopy was performed on the failed specimen to confirm interlaminar delamination. The fiber volume fraction of the manufactured composites was measured to be 45.5 ± 1.7% by carbonizing the matrix material. A micro-CT scan was performed on the specimen to measure the overall void content, which was found to be 4.7%. The glass transition temperature of the manufactured composites was measured at 98°C using dynamic mechanical analysis (DMA). Furthermore, differential scanning calorimetry (DSC) testing confirmed a higher degree of cure of the thermoset resin in the manufactured composites. Additionally, thermographic analysis (TGA) provides information about the degradation temperature of the thermoset resin used, which was found to be 325°C. Therefore, these mechanical characterizations reveal that the LOM manufactured composites have mechanical properties comparable to those of conventionally manufactured composites.