The melting of an ABS resin was simulated using a three-dimensional finite element simulation of the two-phase flow in the compression section of a single-screw extruder. Screw freezing experiments were also conducted to compare the numerical predictions with the corresponding experimental data. Numerical simulations as well as experiments exhibited the Maddock melting mechanism and numerical predictions were in good agreement with the corresponding experimental data. The sensitivity of the melting profile to various material properties and processing conditions was numerically analyzed. With a constant flow rate enforced at the entrance of the screw channel, the screw and barrel temperature were found to have a minor effect on the melting profile. However, these parameters were found to have a significant effect on the predicted pressure profile along the screw channel. When the zero-traction boundary condition was imposed at the entrance of the screw channel, a change in the screw or barrel temperature affected the flow rate in the screw channel, which resulted in a significant change in the solid fraction at the same cross-section.

Purpose This paper aims to analyze experimentally and numerically the effect of the nozzle temperature and feed rates on the dimensions of the fused deposition modeling (FDM) polymer parts. Design/methodology/approach In total, 30 strips per sample were printed with the same width as the nozzle diameter. The strips were printed with one vertical movement of the nozzle head. The width of the strips was measured with a caliper at five locations. A linear regression model was created based on the experimental data to understand the correlation between the strip width deviation and the parameters of interest. Numerical simulations were performed to predict the swell of the polymer exiting the nozzle using finite element method combined with level set method. The experimental results were then used to validate the models. Findings The average accuracy of polylactic acid (PLA) samples was better than that of acrylonitrile butadiene styrene (ABS) samples. The average strip width had a tendency to increase with increasing temperature for PLA samples, whereas ABS samples showed mixed behavior. The strip width decreased with increasing feed rate for most cases. The measurement positions had a major effect on strip width when compared to nozzle temperature and feed rate. The numerical model predictions were in good agreement with the experimental data. A few discrepancies were observed at high feed rates and nozzle temperatures. Originality/value This study will contribute to gaps in knowledge regarding the effect of processing conditions on dimensional accuracy of FDM-printed parts. The developed numerical model can be efficiently used to predict the dimensional accuracy of FDM-printed parts.

The mechanical and tribological behaviors of the parts manufactured with 3D printing methods differ with variations in the manufacturing parameters. This paper aims to investigate the effect of the layer thickness and layer orientation parameters on the hardness, friction coefficient and wear properties of PLA samples printed by Fused Deposition Modelling (FDM) method. Samples were printed with three different layer thicknesses in two different build orientations. The hardness of the samples was tested by D-type shore hardness durometer and a pin-on-disc setup was used to measure the friction coefficient and wear rate of the samples. The analysis of the experimental results showed the distinctive effect of the layer orientation and layer thickness which further discussed in the paper.

In robotics, origami-based design methodology can be used to create small scale parallel mechanisms with easier assembly processes. Delta mechanisms are one of the famous parallel mechanism used mostly in pick and place operations due to their capability to reach high speeds and accelerations. In this work, we present a novel Delta mechanism fabricated with fully 2D layer by layer methods. In our design we have eliminated manual 3D processes in order to provide parallel movement of the links. We have designed a new flat parallelogram providing pure translations in X-Y-Z directions respecting to the conventional kinematic models for Delta mechanism. The assembly process is reduced to an only cut – laminate – repeat steps which are very basic operations in 2D. The kinematic performance of the mechanism has been analyzed using a 6 DoF position sensor placed on the end-effector. The mechanism has a 20x20x20 mm3 cubic stable workspace with a 17.5 mm radius circular footprint when it is completely flat. The tests were done for circular trajectories having 10 mm radius circles with different heights and circles with different radiuses in a specific height. Despite having no feedback control from the end effector, the mechanism was able to follow the trajectory with 1.5 mm RMS precision. We have also changed the materials of the flexible layers in passive links and presented the trajectory results of the end-effector showing how it effects the kinematic performance of the mechanism.

Frictional forces (for temperatures less than the melting or devitrification temperature) and viscous forces (for higher temperatures) have important roles on solids conveying and melting processes in plasticating single-screw extruders. These forces are related to the shear stresses at polymer-metal interfaces. For temperatures at which the frictional forces are the main factor for the shear stresses, it is experimentally difficult to obtain the shear stresses at the polymer-metal interface. The interpretation of the data has further complications due to the frictional energy dissipation at the polymer-metal interface. An instrument called the Screw Simulator was used for further understanding of shear stresses at the polymer-metal interface and comparison of melting fluxes of different resins. This article presents the shear stress and melting flux measurements for low density polyethylene (LDPE), linear LDPE (LLDPE), acrylonitrile butadiene styrene (ABS), and high-impact polystyrene (HIPS) resins as a function of sliding velocity and interface temperature at a fixed pressure of 0.7 MPa. The relationship between the experimental data and the extrusion process is also discussed.