## 2 Materials and Methods  
The FDM process involves the following steps. A CAD model is generated and then converted into STL files for stereolithography. Three-dimensional surfaces are represented in this file as an assembly of planar triangles. The greater the number of triangles, the better the accuracy. Once the STL file has been converted, the slicing process involves steps including describing the 3D part, dividing the parts into slices, and determining the support material and path as well as the angle of the tool. Various parameters are set in the STL file to specify how the machines will operate in the various layers. The FDM samples are created using a Creality Ender 3 machine with a bed size of 220 \(\times\) 220 \(\times\) 250 mm\({}^{3}\). CATIA software is used to design the parts. It is then converted into an STL file, which is sliced into machine-readable g-code files using the Cura engine of the Repetier software. The dimensions of the tensile specimen are 63.5 \(\times\) 9.53 \(\times\) 3.2 mm\({}^{3}\), which are as per the ASTM D638 requirements. The impact specimen dimensions are 63 \(\times\) 12.7 \(\times\) 3.2 mm\({}^{3}\), follow the ASTM D256 requirements. The dimensions of the flexural specimen are 125 \(\times\) 12.7 \(\times\) 3.2 mm\({}^{3}\), which are as per the ASTM D790 requirements. The dimensions are shown in Figure 1. The material used to create the specimen is polylactic acid (PLA), which is commonly used for FDM-processed parts. The tensile strength of the specimens is determined using the uniaxial tensile tests. The three main aspects of DOE are factors, levels, and response. The term level indicates the number of different values a variable can assume according to its discretization. Design matrices are used, which have tables that have all of the combinations of levels between the different factors. The DOE factors considered in these experiments are as follows:  
1. Infill Percentage--The infill percentage measures the amount of material inside the fabricated part. It represents the density of the part. The infill percentage is set according to the part's requirement. The values for the infill percentage are chosen as 10, 33, 55, 78, and 100%. 2. Layer Thickness--In FDM, the thickness of a single layer deposited by the nozzle is the layer thickness. The type of nozzle used decides the paper thickness. The nozzle diameter used in this case is 0.4 mm. The values for the layer height are chosen as 0.08 mm, 0.16 mm, 0.24 mm, 0.32 mm, and 0.4 mm. 3. Print Speed--The speed of the nozzle with which the material will be deposited is denoted as the print speed. A very high printing speed will cause the wear and tear of physical parts and lead to improper distribution of materials. Moreover, a low printing speed is not suitable as it will increase the time required to print one specimen. Hence, the values for print speed are set as 20, 35, 50, 65, and 80 mm/s. 4. Extrusion Temperature--The extrusion temperature is the temperature at which the material is extruded from the nozzle. The extruder contains a heater that heats the material up to a semi-liquid state. As the temperature increases, the viscosity of the material increases. As a result, it is necessary to set the extruder temperature within the limits where semi-liquid materials can be kept. The capacity of the heating system decides the temperatures at which materials are extruded. Temperatures are set at 190, 200, 210, 220, and 230 \({}^{\circ}\)C.  
Table 2 depicts the experimental runs and observed values of responses. Tensile test specimens were prepared as per ASTM D638 standard, flexural test specimens were prepared as per ASTM D790 standard, and impact test specimens were prepared as per ASTM D256. Tensile and flexural test was conducted on UTM of VEEKAY TESTLAB and the impact test was conducted on an impact testing machine of ADVANCE EQUIPMENTS having a least count of 0.0001 J. Figure 2a-c shows the setup of the tensile, flexural, and impact test. Figure 2d-f shows the actual test piece after the performance of tests.