## 3 Results and Discussion
### Analysis Using Desirability Approach  
Using a computerized uniaxial tensile testing machine in accordance with ASTM D638 standards, the mechanical behavior of the parts was investigated. When the specimen breaks under the load, as in tensile testing, the breaking load is noted on the digital screen. From Figure 3, it can be understood that the tensile strength increases with the increase in infill percentage. A greater infill percentage implies a higher density of the part. This will increase the strength required for pulling and breaking the specimen. Hence, the tensile strength will increase. In the extrusion process, the nozzle temperature causes the material to melt into a semi-liquid phase. The material tends to shift slightly towards a liquid state when the extrusion temperature is increased, resulting in reduced viscosity. The less viscous material is now in an oval shape and not circular. The contact area between layers is enlarged as the brittleness of the material is increased with an increase in temperature. Moreover, one can expect that the material becomes more brittle with a larger temperature increase. Thus, larger contact areas tend to increase strength, but the increase is very minimal. As the infill filament has had less time to cool down between each passage, the adhesion between the filaments in a faster-printed object is better. Thus, the filament's maximum strength may be slightly improved. Owing to the unevenness of the material  
Figure 4: Effect of process parameters on the flexural strength. deposit, the overall strength of the fabricated part can be reduced at high speeds. Therefore, the strength increases through adhesion are cancelled out and the tensile strength remains almost constant as the printing speed changes. If the layer height is increased, the tensile strength of the part will decrease. As a result of fewer layers, the printed part has less adhesion and accuracy, which significantly decreases its tensile strength. Flexural strength indicates the amount of bending it can withstand. Flexural strength increases with the increase in infill percentage, layer height, and extrusion temperature, while it decreases slightly with the increase in print speed. Owing to a lower infill percentage, there is less density in the fabricated part. Owing to more hollow space inside the part, there are no proper supports from the inside, hence the part is weaker. For this reason, the part is easily broken upon bending. An increase in infill percentage strengthens the part, thus increasing the flexural strength. However, we have seen that a change in the combination of different parameters actually increases the properties more than just changing one parameter at a time. The above graphs show us that maximum flexural strength can be obtained with a lower value of extrusion temperature, while simultaneously setting a higher value of the infill percentage. Figure 5: Effect of process parameters on the impact strength. Impact strength is the toughness of the part, which in turn indicates its ability to absorb energy during plastic deformation. Figure 5 shows that the impact strength of the FDM-printed parts is affected by every parameter. Impact strength increases with an increase in infill percentage, layer height, and print speed, while it decreases considerably with an increase in extrusion temperature. Based on our study, there was a significant relationship between the apparent density and the impact absorption capacity, both of which were measured for the components in terms of dissipation of energy. However, the result of layer height was less significant. As discussed earlier, the rise in extrusion temperature reduces the viscosity, which in turn decreases the layer thickness slightly. The dimensional accuracy of the part is affected. There is a decrease in the thickness of the fabricated part and less impact energy is required to cause the failure of the part. Thus, as the extrusion temperature increases, the impact strength decreases.