RESULTS The above process parameters and restrictive DfAM guidelines have been identified as critical through the study and trials of application requests from various industrial sectors. The novel techniques and mechanisms outlined below are focused on loosening the design limitations and delivering increased process control to the manufacturing engineer. Figure 3. Typical panel test to characterize overhanging design guidelines. temperature gradient contribute to the selfsupporting ability of an object during printing. Dependence on the PLT implies then also a time and material dependency. The span of the overhanging surface and other geometry attributes such as wall thickness and convex vs concave curvatures all contribute to this limit. Complex path planning design and wellengineered layer heights can be used to mitigate the slumping effect and expand the practical geometrical limit. Overhanging geometry violating this limit can also be supported from beneath with sacrificial support material, however, this adds to the planned motion path and adversely affect the control of layer times and PLT. The use of support structures also increases print time, post-processing effort, material usage and risk of voids in the finished surface and so are avoided in LFAM and AM processes alike. Figure 4. A fixed 45º nozzle and slice orientation printing a hollow structure with unsupported horizontal surfaces. Printing at Fixed Inclination Utilizing an inclined printing plane addresses many common DfAM challenges. Most importantly, this technique enables relatively long parts to intersected by more convenient slicing planes which avoids long layer times and the resulting excessive cooling for large area parts. This allows for control of the PLT above the low threshold by normalizing the layer times. A 45º or otherwise tilted slicing orientation can often reduce or remove entirely the need for support structures traditionally required to mitigate slump. The overhang angular limits are also shifted by the degree of inclination which allows for a new selectable limit range. This results in traditionally challenging horizontal surfaces behaving as modest and predictable overhanging surfaces with offset print layers. Manually Articulating Nozzle Manually articulating nozzles have been developed to expand on a fixed-angle nozzle and fixedangle inclined slicing plane. These mechanisms allow for the manual choice of operating plane using a single nozzle containing two manually adjustable swivel axes. Design challenges of any articulating nozzle include sufficient and evenly applied heat and unrestricted flow paths to ensure continuous control of the plastic melt and practical maintenance. Manually articulating nozzles have also been implemented to adjust the print orientation between subsequent operations on a single object. This is also known as 'overprinting'. The applicable processing concepts enabled here are analogous to prismatic machining operations (subtractive manufacturing), where the nozzle orientation can be indexed, though not while operating continuously. This class of motion is termed '3+2-axis' implying the 3D motion is paired with a selectable 2-axis orientation remains in a fixed position while in-work. Material deposition is briefly interrupted while a reorientation is performed to solve for the next planned application vector. www. sampe.org NOVEMBER/DECEMBER 2021 | SAMPE JOURNAL | 67http://www.sampe.org