Browsing by Subject "temperature history"

Now showing 1 - 4 of 4

Feedforward Control for Polymer Laser Sintering Process Using Part Geometry
(University of Texas at Austin, 2015) Abdelrarhman, Mostafa; Starr, Thomas L.
For the polymer laser sintering process, achieving optimum mechanical properties requires that every volume element of a part experience a temperature history sufficient to reach full density. This history must include a peak temperature high enough to fully melt, but not degrade, the polymer and a cool-down period that ensures elimination of porosity, interlayer bonding and relaxation of stress. Real-time thermal monitoring of the laser sintering process has shown that this temperature history depends on the geometries of both the current and prior layers. In this paper we demonstrate a feed-forward control system that improves uniformity of the temperature history for parts with variable cross-sections. The control algorithm for this system will utilize information from layerwise geometry models for parts in a multi-part build. The cross-sectional area for every layer will be used at run-time for feed forward control the laser scan parameters. The results confirmed maintaining constant peak temperature throughout the part. This control system ensures optimized sintering for parts with complex geometries.
Numerical Simulation of the Temperature History for Plastic Parts in Fused Filament Fabrication (FFF) Process
(University of Texas at Austin, 2019) Zeng, D.; Rebandt, Matthew; Lacaria, Giuseppe; Lee, Ellen; Su, Xuming
Fused Filament Fabrication (FFF) is one of the major Additive Manufacturing (AM) processes for polymer materials. In FFF process, repetitive heating and cooling cycles occur when the filament is dispositioned onto a build platform to fabricate a three-dimensional part. The uneven temperature gradients and non-uniform cooling in the part may cause significant amount of warpage. The current practice of making an AM part to match the design intent is largely relied on time consuming trial-and-errors. Numerical simulation is an effective way to predict warpage. Accurate prediction of the thermal history during the FFF process is key for the success of warpage simulation. In this paper, an integrated approach is developed in LS-DYNA to model the FFF process and predict the temperature profile. Different from the traditional approaches, the tool path and FEM mesh are decoupled in this study to enable the flexibility of FEA mesh generation and improve computational efficiency. An innovated micro thermocouple is used to measure the temperature history inside the parts. The evolution of the thermal history is predicted and compared to the measurement data to demonstrate the accuracy and efficiency of the developed simulation model.
Predicting Strength of Thermoplastic Polymer Parts Produced Using Additive Manufacturing
(University of Texas at Austin, 2016) Bartolai, Joseph; Simpson, Timothy W.; Xie, Renxuan
The weakest point in polymer parts produced by Fused Filament Fabrication (FFF) is the interface between adjacent layers and deposition toolpaths, or “roads”. We introduce a novel approach that uses the temperature history of these interfaces, polymer rheological data, and polymer welding theory to predict the mechanical strength of parts subjected to uniaxial tension. Interface temperature history data is collected in-situ using infrared imaging. Rheological data of the polycarbonate (PC) used to fabricate the parts in this study was determined experimentally. The prediction of strength of the interfaces was performed using polymer weld theory from the literature adapted to the PC feedstock used in this study. Understanding how the strength of the road and layer interfaces develop mechanical strength will lead to stronger FFF parts through intelligent toolpath optimization and temperature control.
Temperature History within Laser Sintered Part Cakes and Its Influence on Process Quality
(University of Texas at Austin, 2015) Josupeit, Stefan; Schmid, Hans-Joachim
The temperature distribution and history within laser sintered part cakes is an important aspect regarding the process quality and reproducibility of the polymer laser sintering process. Especially the temperature history during the build and cooling phase is decisive for powder ageing effects and the development of part quality characteristics. In this work, a measurement system for three-dimensional in-process temperature measurements is set up and the influence of different parameters on the inner part cake temperature distribution and history is analyzed. Important factors are not only geometrical build job parameters like the part packing density and build height, but also process parameters like the layer thickness and bulk powder density. Individual in-process temperature profiles at different positions within a part cake are finally correlated with powder ageing effects. The results of this work help to understand the temperature history dependency of powder and part properties and can therefore be used to develop optimized process controls.