# Function-Based Design Principles for Additive Manufacturing
## 4 Case Study  
To verify the validity of using DPs for the conceptualisation of AM products, a case study was conducted [38]. The case study was a redesign of a gear to be manufactured with AM. As the purpose of the case study was to verify the use of DPs in conceptual design, the only design requirements were that the gear must be made with AM, it must have a lightweight structure, and it must be cooled with a liquid coolant. Other design requirements, such as operating conditions, life span and strength, were ignored in the conceptual design, as they were part of the later design phase.  
Firstly, the function structure of the gear with a function of cooling the gear with liquid was developed (Figure 6). The function structure consisted of 14 functions connected with material flows of liquid and solid, and energy flows of mechanical energy (ME) and thermal energy (TE). Next, DPs that could be used as solutions were found using the FFDP matrix and mapped onto the function structure for each function in the function structure.  
Three different concepts were created by combining multiple combinations of DPs (Figure 7). Due to the design requirements, all three concepts utilised #DP6 (standard geometry) for functions related to interaction with the shaft and the second gear, as this part of that geometry needed to remain as it was in the original design. Hence functions related to guiding mechanical energy and cooling of the gear were solved using various AM DPs.  
Concept A uses a lattice structure (#DP12) to guide ME from shaft to gear teeth. The lattice structure is also used to increase the surface and allow the passthrough of coolant (#DP24). The coolant is scooped using custom blades (#DP7). Concept B utilises  
Figure 5: Function-Flow-Design Principle Matrix.  
topologically optimised geometry (#DP13) for guiding ME. The coolant is pumped through the shaft using openings on the inner surface of the bore (#DP17). The coolant is guided through internal channels (#DP9) to cool the gear. Concept C guides ME using void structures (#DP14). It also incorporates internal channels (#DP9) to cool the gear, as in concept B, but the coolant is scooped using custom blades (#DP7).  
The variety of suggested DPs for a simple product such as a gear clearly shows the benefit of using function-based DPs in a systematic design process, as multiple concepts are created that utilise the unique possibilities of AM. For further evaluation of the DPs and their role in the design process, concept C was chosen using the Pugh matrix and a variety of selection criteria [23] for further development. Due to the need for brevity, the description of the embodiment design and detail design are omitted. Once the final 3D model was created, concept C was manufactured using the FDM (Fused Deposition Modelling) process in polymer and using the DMLS (Direct Metal Laser Sintering) process in stainless steel (Figure 8). The metal gear also included markings, thus embodying additional principle #DP26. The conceptual design and embodiment of gear provide an initial validation of DPs. The fabrication of gear in two different materials and using two different AM processes show the universality and process independence of derived DPs.  
Figure 6: Function structure of a gear with mapped DPs.  
Figure 7: Created concepts of AM gear.