Type of Proposal
24-3-2015 2:50 PM
24-3-2015 2:50 PM
Faculty of Engineering
R. Jill Urbanic
Importance of the Project
For the feasible implementation of everyday use of 3D printing models, it is important to conduct research regarding the light weighting of models to efficiently reduce variables such as time, cost, and material while keeping the structural integrity of the designed sample. Experimental research needs to be conducted to understand the impact of variables such as build parameters, interior support structures, and orientation. With growing popularity of additive manufacturing processes, time and material costs remain relatively high in comparison to other existing processes, research quantifying strength versus build costs will provide users additional optimization choices.
Existing State of Knowledge
Additive manufacturing is still a fairly new branch of design technology. Process standards are yet to be established internationally and work is continuously being done to improve the printing quality of these machines. There are existing light weighting methods for 3D printing, for example the control of bead sparsity and bead width in samples before printing, however this project explores a new method of light weighting samples through ‘spongefication’ and attempts to quantify its strength characteristics and performance on an optimization stand point.
This project aims to create a user-friendly programmable light weighting method for various internal structures, and to explore the associated mechanical properties for ABS and polycarbonate materials.
The development of this light weighting option required the creation lattices which control the placement of spherical voids within a part model. Different modelling software are analyzed for use in order to quickly generate adaptable internal voids. To be able to create models and simultaneously view parameter modifications, the 64-bit version of Rhinoceros® is used with the Grasshopper graphical programming add-on to create and visualize readily adaptable models. Inspired from atomic crystal structures are three base sponge model designs which take primitive, body center, and face center hole distributions. Various elements are controlled in the Grasshopper coding used to generate these models. User inputs such as the amount of holes in the X, Y, and Z 3-D space geometry, the shell width of the model, as well as the models dimensions are dynamically controlled in Grasshopper files through various algebraic functions and designed limitations. Certain limitations being that holes cannot overlap (unless that is desired in the user's design) and that voids are added only in the volume specified within the shell of the part model. The coding also allows for the input of different types of voids and is not necessarily limited to spherical holes. To limit the amount of experiments needed, compressive and tensile testing samples are created with consistent shell widths and object dimensions, while varying internal structure arrangements (the radius of the voids: r=2mm, r=4mm; the hole distribution: primitive, face center cubic, body center cubic). Models are converted into *.STL format for fabrication on the Fortus 400 FDM (Fused Deposition Modelling) machine, using the Insight process planning software. To experimentally determine the corresponding strength characteristics, three copies of every model are suggested for fabrication and then should be submitted to tensile and compressive testing using the MTS** Criterion Model 43, along with the MTS** Test Suite Elite software. An average of the results is taken and the data must be critically analyzed with consideration to strength, material used, and build time to determine the most optimal option.
**’MTS’ is the name of the company that manufactured this machine.
The compressive testing of the printed samples show varying strength characteristics amongst the designed models. During experimental testing, the solid sample exhibited the highest load resistance, as predicted. However, the primitive and body center cubic models succumbed to comparable compressive loadings while using less material. Unexpected failure occurred during the compression testing of the face center cubic models, which is believed to be caused by the discontinuities in the tool path of the deposited material during printing. For the face center models, the build material used is approximately 11.5% less than the theoretical volume due to unwanted voids created during the printing process. This observation suggests that the path taken during the printing process has a significant influence on the observed mechanical properties.
Tensile testing must still be conducted to complete this research. Tensile models have been designed and printed for testing. Furthermore, different internal structure configurations must be explored to establish a better understanding optimization in regards to light weighting solutions. Alternative light weighting models will be explored in continuation of this research, one in particular which involves overlapping but non-intercepting internal support struts which are fused together during the material extrusion process and enveloped in a shell.
Selected experimental results will be presented corresponding to testing, build time, material usage, and model design configurations.
Conceptualization of Adaptable Light Weighting Methodology for Material Extrusion Processes