Improvement of mechanical characteristics of PLA by applying remelting process

Abstract

In this paper, bone-shaped samples (dogbone) made of thermoplastic polymer PLA were tested according to the ASTM D638 standard. All samples were made on a WANHAO duplicator i3 plus 3D printer. PLA is the most widely used polymer mainly due to its thermoplastic workability and good mechanical properties. The mechanical characteristics of the materials were compared after the realization of the samples on the 3D printer and after the remelting process. All samples were built in horizontal orientation. Remelting process involves stacking / packing samples in a mold and pressing them with sodium chloride (NaCl) powder. Since sodium chloride (NaCl) is a poor conductor of temperature, it takes some time for the experiment to be realized in order to equalize the temperatures throughout the volume of the mold. The mold thus formed was kept at 210°C for 30-45 minutes. The purpose of salt powder molding is to get even curing without deformation on the surfaces of the parts. The samples become rougher after this treatment and it is necessary to remove excess salt from the structure as well as additional surface treatment. The remelting process proved to be very cheap, but also quite unreliable due to the slow and uneven rise in temperature in the mold. The SHIMADZU AGS-X 100 kN tensile testing machine was used to test the tensile strength of the samples. During the experiment, it was found that the samples with remelting process have a much higher tensile strength compared to the untreated samples. Remelting procedure of PLA greatly improves the mechanical properties and gives better performance to complex parts printed on a 3D printer by reducing the anisotropic characteristics of the polymer. Further research would be related to the testing of other thermoplastic materials such as ABS, PET-G etc. It would be interesting to use other materials for molding and to perform a comparative analysis of the obtained results of the new molding methods with the described method of applying salt powder.