Session: 02-01-04: 7th Annual Conference-Wide Symposium on Additive Manufacturing: Polymers II

Paper Number: 94341

94341 - Toolpath Planning With Thermal Stress Awareness for Material Extrusion Additive Manufacturing 

Additive manufacturing has emerged as a next-generation technology for advanced fabrication. Fused Filament Fabrication (FFF) is the most widespread form of material extrusion additive manufacturing for makers and education and has growing applications in large scale construction. FFF works by extruding lines of material to fabricate the desired design layer-by-layer. Despite its advantages, FFF is limited by structural weaknesses introduced by the fabrication process at the interlayer boundaries. As each layer cools, internal thermal stress is introduced by the shrinking of the material, leading to weak spots and in-fabrication deformation, which can cause manufacturing failures.

This paper presents an approach to reduce the probability of failure for a given object under known loading conditions through improved toolpath planning during fabrication. By considering and accounting for the time to print between layers, and therefore the amount of cooling, the internal thermal stress induced by the fabrication process can be reduced. We consider the intended final stress distribution in the part and use this information to find regions of the object most likely to fail. Our approach then reorders the fabrication sequence to vary the time to print between layers such that the thermal stress induced in fabrication is reduced in regions most likely to fail at the expense of increasing thermally induced stress in less critical areas.

In our simulation experiments, we compared the default print order for commercial FFF machines to our reordered plan. This comparison is used to compute the improvement in our cost function over a range of cooling rates. We found that changing the print order made little difference when the cooling rate was very fast, as print speed is too slow to affect the temperature differential regardless of print order. Similarly, when the cooling rate was very slow, the difference in temperature was not significant between print orders, and thus the print order had little effect. A temperature decay rate in between leads to the greatest improvement in changing the print order. Performing this experiment on multiple models, the critical factor was identified as being the ratio of layer size to cooling rate, with larger layers requiring slower cooling rates to fall in the greatest improvement range. We ran this test for ABS and Aluminium and found greater improvements in aluminium through the proposed planning approach. The combination of Aluminium’s elastic modulus and thermal expansion coefficient creates a larger potential for thermally induced stress. Our approach offers the potential to improve the performance of 3D printed components under known loading conditions by considering the temperature of the print in the planning of the toolpath.

Presenting Author: Lee Clemon University of Technology Sydney

Presenting Author Biography: Dr. Lee Clemon, P.E. is a research scientist in advanced manufacturing and high consequence design and licensed professional engineer. He focuses on the interplay of materials, design, and manufacturing for a more reliable and environmentally conscious industrial world. His current research interests are in process improvement and material property manipulation in advanced manufacturing processes, with an emphasis on additive and hybrid additive-subtractive manufacturing through particulate, wire, layer, and ensemble fabrication methods.<br/><br/>He is a management member of the Centre for Advanced Manufacturing, program co-lead of the ARC Training Centre for Collaborative Robotics in Advanced Manufacturing, and member of the RF and Communications Laboratory. Lee also serves the mechanical engineering profession as an active volunteer for ASME providing professional development and training. <br/><br/>Lee M Clemon holds a Ph.D. and a M.S. in Mechanical Engineering from the University of California at Berkeley, and a B.S. in Mechanical Engineering from the University of Kansas. He was previously a staff member at Sandia National Laboratories as a design and Research and Development engineer on hazardous substance processing systems and manufacturing process development. Lee became a Lecturer at the University of Technology Sydney, in the School of Mechanical and Mechatronic Engineering.

Authors:

Jayant Khatkar University of Technology Sydney
Lee Clemon University of Technology Sydney
Ramgopal Mettu Tulane University