Many objects that we call 3D printed, from crayons and chess pieces to turbines and dental aligners, and were actually created using 3D printed molds, rather than being fully printed themselves. A trio of researchers from the Singapore University of Technology and Design recently published a paper, titled “Design and Robotic Fabrication of 3D Printed Moulds for Composites,” about their work in fabricating molds using a robotic additive manufacturing process, as well as “introducing the integration of AM and AFP process.”
The abstract reads, “3D printing technologies have a direct impact on manufacturing the composite structures and in particularly fabrication of molds. Molds produced through additive manufacturing methods would greatly improve product features. The material selection and process conditions involved for producing mold tooling, mainly towards Automated fiber placement (AFP) work cells. In this study, the main objective is to improve the design and fabrication of composite parts through complex molds as well as to assess and improve the production workflow through the development of an effective design environment for the existing fiber placement operation. A robotic arm will be used to hold the print surface and to follow a pre-programmed print path with a stationary extruder to fabricate the mold tooling. This paper will present a review on the selection process for mold materials and the initial experimental work carried out to investigate required properties of 3D printed molds.”
The team explained that molds are made out of composites in the form of blocks, and manufactured using lamination, casting, or 3D printing in the required shape of the object they’ll later be used to mold. For the purposes of the study, the researchers worked specifically with mold fabrication for prepreg composite structures and the use of automated fiber placement (AFP) for the “prepreg layup.”
“AFP process achieves high production rate, better quality, efficient and low cost of manufacturing of large scale composite structures,” the researchers explained. “When integrating AFP process with the robots, leads to highly automated process, further reduction in material wastage, good processing quality and repeatability.”
There are many advantages to fabricating molds with 3D printing, including the ability to achieve and easily share complex designs, less material waste, lower costs, automated manufacturing, and increased production speed. Here, the team focused on a robotic extrusion method of 3D printing.
“Integrating the additive manufacturing design freedom method and the multi-axis control or industrial robotics are further step towards development in the 3D printing revolution,” the researchers wrote. “The complex design fabrication can be achieved, fiber alignment can be manipulated and controlled degree also reliable when adding multi-axis motion platforms. The X-Y gantry system has limitations on complex structure lay-up, transfer molding, filament winding and automation. The robot-based 3D printed mold has unique features like potential on fabricating light weight structures, freedom on degrees of geometric complexity, part consolidation and design optimization.”
As shown in the image to the left, this researchers was structured into four components: composite part design – which covers structural analysis and fiber distribution – tool path planning, work cell setup, and application and prototyping.
“Due to the complexity of the fabrication process, including two robotic arms with specialized end-effectors, the toolpath planning requires careful coordination, motion and collision simulation,” the researchers explained. “The research developed with the required systems to optimize and streamline the toolpath planning process. In this way, the fiber placement process becomes a part, or option, in a more ambitious production line that includes additive manufacturing and subtractive manufacturing processes.”
Robot-based 3D composites were used in order to increase both the flexibility and potential of manufacturing, and the “AM robust work cell system” helped to produce geometric-specific molds that support AFP. The resulting mold is representative of “the negative form of the target geometry.”
“The additive manufacturing robot fabricates the mold structure and the AFP robot places the prepreg tapes on the surface of the substrate. Eventually, the work flow would be continuous process like the AM robot arm will move on to AFP robot for tape placement after the substrate have been build using extruder on the work platform,” the team explained. “The build platform is designed and fitted at the end of the robot arm and the extruder placed above the platform in the aluminum frame. In general, the extruder moves in X and Y direction and the build platform moves along Z direction in the FDM system, here the concept focused to fix the extruder and the robot arm fixed with build platform will move in all direction with respect to the part design.”
Once the researchers produced the mold, the robotic arm moved to the AFP side for the prepreg placement process.
“The initial experiments have shown that AM modelled mold can indeed stabilize the prepreg sheets while fabrication,” the researchers concluded. “From the above description and discussion, the conclusions and future works are: Robotic additive manufacturing has a unique advantage in complex geometry printing and large-scale manufacturing. It can be simulated in an industrial robot simulation and offline programming software platform. The future work is to model complex geometry modelling mold to fabricate the composite structures. In addition to develop the system that uses the process simulation as a tool in AM part design and optimization with respect to the mechanical, thermal and electrical property requirements.”
Co-authors of the paper are Rajkumar Velu, Nahaad Vaheed, and Felix Raspall.
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