Engineering topics

Song, Hongtao

Publications and source records attributed to Song, Hongtao.

5 records

DOE OSTI2023

System and method for roll-to-roll film tensioning for reduced separation force during bottom-up stereolithography

The present disclosure relates to a tensioning system for use in a stereolithography manufacturing application. The system may have a build plate for supporting a three dimensional part being formed using a photo responsive resin, a base plate and a release element extending over the base plate. The release element is configured to receive a quantity of photo responsive resin for forming a new material layer of the three dimensional part. A pair of tensioning components are secured to opposite ends of the release element, and apply a controlled tension force to the release element during peeling of the release element to reduce a separation force required to separate the release element from the new material layer after the new material layer is cured.

Duoss, Eric B.↗

DOE OSTI2022

Aging of UV curable PDMS developed for large-scale, high viscosity stereolithography

Polydimethylsiloxane (PDMS) elastomers are silicone rubbers that find widespread application in both academic and industrial settings. This study investigates the use of photosensitive platinum catalysts for UV-activated hydrosilylation of PDMS, which enables the additive manufacturing of PDMS objects through techniques such as stereolithography. Specifically, this study focuses on understanding the aging behavior of Pt-catalyzed, UV-curable PDMS samples, including their mechanical behavior under thermal and UV-accelerated aging conditions. The results show that the Pt-catalyzed, UV-curable PDMS introduced in this research is ‘under-cured’ after being printed and will slowly evolve over time resulting in increased stiffness and decreased elongation, likely due to the formation of additional crosslinks. FTIR spectroscopy indicates that no new chemical bonds or functional groups are generated through the aging process, suggesting that no thermal degradation or polymer chain scissions occur in the polymer matrix. Overall, this PDMS formulation exhibits greater mechanical strength and significantly less reduction in strength with aging, compared with the commonly used, UV-curable thiol-ene PDMS.

36 MATERIALS SCIENCE↗

DOE OSTI2022

System and method for liquid crystal display system incorporating wire grid polarizers for large scale and large volume stereolithography

The present disclosure relates to a liquid crystal display (LCD) system. The system in one example has a light source for generating unpolarized light, and an LCD screen arranged in a path of transmittance of the unpolarized light. First and second wire grid polarizers are arranged adjacent to the LCD screen and each have a plurality of nano-scale wires, with the first and second wire grid polarizers have differing polarizations. A pitch of each of the nano-scale wires is no larger than one-third a wavelength of the unpolarized light from the light source. The wire grid polarizers create, in connection with operation of the LCD screen, a 2D light mask suitable for initiating the polymerization of an optically curable material.

Duoss, Eric B.↗

DOE OSTI2022

Use of wire grid polarizers with liquid crystal display for large-volume stereolithography

Spatial light modulators that use liquid crystal devices (LCDs) to pattern ultraviolet light for vat polymerization suffer from a few limitations: limited range of wavelengths that can be patterned, low damage threshold for incoming light, and low efficiency of light transmission. A monochrome LCD can more efficiently transmit useful wavelengths of light for stereolithography (365–405 nm) than a color LCD, but it still contains two absorptive film polarizers that suffer from the aforementioned limitations. Wire grid polarizers reflect rather than absorb the blocked polarizations of light, resulting in a higher intensity damage threshold. They can also polarize lower wavelength light that is limited only by the wire pitch. In this work, this research investigates the effects of replacing an LCD’s film polarizers with wire grid polarizers to enable polarization and patterning of high intensity UV light, resulting in shorter curing times and the ability to print a wider range of stereolithography feedstocks.

42 ENGINEERING↗

DOE OSTI2020

Development of a variable tensioning system to reduce separation force in large scale stereolithography

Projection micro stereolithography (PµSL) is an additive manufacturing tool that offers multiple advantages, including unparalleled resolution and throughput, but the ability to print high viscosity resin for large-scale parts is limited. One of the key challenges in PµSL is to separate a newly polymerized layer from the vat floor without damaging the part. Since the separation force scales with the printing area, the risk of damaging the part increases significantly with larger-scale systems and must be addressed. In this paper, a novel roll-to-roll, variable tensioning system is proposed to reduce the separation force during printing. A mathematical model is proposed to predict the separation force for different 2D geometries, and a set of experiments is conducted on an experimental prototype to validate the model. Finally, the effects of different separation parameters including peel rate and peel angle are discussed in detail. The results show that the proposed tensioning system reduces the separation force significantly.

36 MATERIALS SCIENCE↗