# Optimization of the 3D Printing Parameters for Tensile Properties of Specimens Produced by Fused Filament Fabrication of 17-4PH Stainless Steel

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Feedstock Filaments

#### 2.2. Material Extrusion AM Trials

#### 2.3. Design of Experiment (DoE)—Central Composite Design

^{k}—where k is a number of adjustable parameters) extended with additional trials in the center of the design (mean values of parameters) and axis for each parameter, in order to be able to estimate parameters with models of second order. Central composite design consists of 2

^{k}trials on the peak values of the observed parameters, 2

^{k}trials in axes of each parameter, and trials at the center of the design (Figure 2).

^{3}); therefore, the α value is 1.68. Therefore, design factors in coded form can be presented as −1.68, −1, 0, 1, and 1.68. Total numbers of trials in that case have to be 14 trials on design peaks and at axis and trials in the design center, where the design has repetitions for estimation of the model error.

#### 2.4. Tensile Testing

^{2}), maximal tensile force (N), and tensile modulus (N/mm

^{2}) were used as characterization parameters for the mechanical tensile properties of specimens. Additionally, the mass of the test specimens was measured in order to relate it to the achieved mechanical properties of the tested specimens. Specimens were tested with a deformation speed of 2 mm/min. The results of tensile testing of 3D-printed specimens are presented in Table 3.

#### 2.5. Scanning Electron Microscopy (SEM)

## 3. Results and Discussion

#### 3.1. Fused Filament Fabrication of Specimens

#### 3.2. Tensile Properties of 3D-Printed Green Parts

#### 3.3. Statistical Analysis of Tensile Testing Results

#### 3.3.1. Statistical Analysis of Tensile Strength

^{2}− 0.275⋅B

^{2}+ 0.025⋅C

^{2}.

^{2}) also has a significant impact on the tensile strength of specimens. However, the effect is much lower compared to the influence of all parameters independently.

#### 3.3.2. Statistical Analysis of Tensile Modulus

^{2}− 4.98⋅B

^{2}− 3.12⋅C

^{2}.

#### 3.4. Statistical Model for Optimization

## 4. Conclusions and Future Work

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Model of central composite design with three factors [55].

**Figure 5.**Top and side views of specimens printed at different conditions of the design of experiment (DoE) after tensile testing: (

**a**) trial 7 (temperature 210 °C); (

**b**) trial 5 (temperature 260 °C); (

**c**) trial 10 (flow rate multiplier 95%); (

**d**) trial 13 (flow rate multiplier 127%); (

**e**) trial 2 (layer thickness. 0.12 mm); (

**f**) trial 6 (layer thickness. 0.28 mm).

**Figure 6.**Morphology of three-dimensional (3D) printed parts investigated by scanning electron microscopy at different magnifications: (

**a**) 39×; (

**b**) 300×; (

**c**) 2300×; (

**d**) 2400×.

**Figure 8.**Top view of specimens from trials with highest values of flow rate multiplier: (

**a**) trial 1; (

**b**) trial 13; (

**c**) trial 16.

**Figure 9.**Two-dimensional (2D) graph of the influence of extrusion temperature on tensile strength (flow rate multiplier 110%, layer thickness 0.20 mm).

**Figure 10.**The 2D graph of the influence of flow rate multiplier on tensile strength (extrusion temperature 235 °C, layer thickness 0.20 mm).

**Figure 11.**The 2D graph of the influence of layer thickness on tensile strength (extrusion temperature 235 °C, flow rate multiplier 110%).

**Figure 12.**The 3D graph of the simultaneous influence of extrusion temperature and flow rate multiplier on tensile strength (layer thickness 0.28 mm).

**Figure 13.**The 3D graph of the simultaneous influence of extrusion temperature and layer thickness on tensile strength (flow rate multiplier 127%).

**Figure 14.**The 3D graph of the simultaneous influence of flow rate multiplier and layer thickness on tensile strength (extrusion temperature 260 °C).

**Figure 15.**The 2D graph of the influence of extrusion temperature on the tensile modulus (flow rate multiplier 110%, layer thickness 0.20 mm).

**Figure 16.**The 2D graph of the influence of flow rate multiplier on the tensile modulus (extrusion temperature 235 °C, layer thickness 0.20 mm).

**Figure 17.**The 2D graph of the influence of layer thickness on the tensile modulus (flow rate multiplier 110%, extrusion temperature 235 °C).

**Figure 18.**Simultaneous effect of flow rate multiplier and layer thickness on the tensile modulus (extrusion temperature 260 °C).

**Figure 22.**Specimen reprinted with optimized fused filament fabrication (FFF) parameters (extrusion temperature 260 °C, flow rate multiplier 130%, layer thickness 0.30 mm).

Particle Size | Distribution |
---|---|

D10 (μm) | 4.2 |

D50 (μm) | 12.3 |

D90 (μm) | 28.2 |

Trial Number | Factor 1: Extrusion Temperature (°C) | Factor 2: Flow Rate Multiplier (°C) | Factor 3: Layer Thickness (mm) |
---|---|---|---|

1 | 220 | 120 | 0.25 |

2 | 235 | 110 | 0.12 |

3 | 220 | 101 | 0.15 |

4 | 250 | 101 | 0.15 |

5 | 260 | 110 | 0.20 |

6 | 235 | 110 | 0.28 |

7 | 210 | 110 | 0.20 |

8 | 220 | 120 | 0.15 |

9 | 250 | 101 | 0.25 |

10 | 235 | 95 | 0.20 |

11 | 235 | 110 | 0.20 |

12 | 235 | 110 | 0.20 |

13 | 235 | 127 | 0.20 |

14 | 235 | 110 | 0.20 |

15 | 235 | 110 | 0.20 |

16 | 250 | 120 | 0.25 |

17 | 235 | 110 | 0.20 |

18 | 250 | 120 | 0.15 |

19 | 220 | 101 | 0.25 |

Trial Number | Tensile Strength ± SD (N/mm^{2}) | Maximal Force ± SD (N) | Tensile Modulus ± SD (N/mm^{2}) | Mass (g) |
---|---|---|---|---|

1 | 7.67 ± 0.51 | 109.12 ± 6.77 | 194.70 ± 29.01 | 6.57 |

2 | 5.76 ± 0.15 | 74.32 ± 1.88 | 143.97 ± 9.55 | 5.10 |

3 | 4.40 ± 0.20 | 56.54 ± 2.30 | 114.75 ± 9.78 | 4.80 |

4 | 5.23 ± 0.23 | 62.36 ± 2.90 | 134.16 ± 14.94 | 4.90 |

5 | 6.78 ± 0.37 | 90.63 ± 5.19 | 170.62 ± 29.26 | 5.70 |

6 | 7.90 ± 0.49 | 106.61 ± 7.41 | 201.65 ± 17.02 | 6.30 |

7 | 6.13 ± 0.22 | 82.17 ± 3.95 | 185.30 ± 22.08 | 5.70 |

8 | 6.97 ± 0.26 | 91.14 ± 3.90 | 167.77 ± 25.42 | 5.70 |

9 | 5.89 ± 0.33 | 74.93 ± 4.12 | 166.99 ± 30.59 | 5.70 |

10 | 4.82 ± 0.25 | 62.58 ± 2.98 | 136.08 ± 17.87 | 5.10 |

11 | 7.15 ± 0.31 | 95.37 ± 3.65 | 173.34 ± 14.94 | 5.80 |

12 | 7.03 ± 0.33 | 93.60 ± 5.25 | 180.41 ± 17.55 | 5.80 |

13 | 8.47 ± 0.13 | 124.51 ± 2.31 | 223.92 ± 12.65 | 6.70 |

14 | 6.82 ± 0.23 | 94.14 ± 3.48 | 188.30 ± 17.11 | 5.80 |

15 | 6.44 ± 0.41 | 84.55 ± 5.60 | 183.01 ± 25.80 | 5.67 |

16 | 8.32 ± 0.48 | 116.80 ± 6.95 | 230.50 ± 21.69 | 6.70 |

17 | 6.48 ± 0.18 | 86.79 ± 2.49 | 167.25 ± 10.40 | 5.80 |

18 | 7.73 ± 0.24 | 101.81 ± 2.74 | 187.32 ± 16.04 | 5.80 |

19 | 5.18 ± 0.37 | 65.35 ± 4.75 | 148.62 ± 11.14 | 5.43 |

Trial Number | Factor 1: Extrusion Temperature | Factor 2: Flow Rate Multiplier | Factor 3: Layer Thickness |
---|---|---|---|

The worst trials (combinations of parameters in coded form) | |||

3 | −1 | −1 | −1 |

10 | 0 | −1.68 | 0 |

The best trials (combinations of parameters in coded form) | |||

13 | 0 | 1.68 | 0 |

16 | 1 | 1 | 1 |

Source | Sum of Squares | DoF | Mean Square | F-Value | p-Value | Remark |
---|---|---|---|---|---|---|

Model | 23.56 | 9 | 2.62 | 21.49 | <0.0001 | Significant |

A—Extrusion temperature | 1.20 | 1 | 1.20 | 9.84 | 0.0120 | Significant |

B—Flow rate multiplier | 18.56 | 1 | 18.56 | 152.31 | <0.0001 | Significant |

C—Layer thickness | 2.86 | 1 | 2.86 | 23.51 | 0.0009 | Significant |

AB | 0.0015 | 1 | 0.0015 | 0.0119 | 0.9154 | |

AC | 0.0064 | 1 | 0.0064 | 0.0524 | 0.8241 | |

BC | 0.0058 | 1 | 0.0058 | 0.0477 | 0.8320 | |

A² | 0.1682 | 1 | 0.1682 | 1.38 | 0.2701 | |

B² | 0.6866 | 1 | 0.6866 | 5.63 | 0.0417 | Significant |

C² | 0.0072 | 1 | 0.0072 | 0.0592 | 0.8132 | |

Residual | 1.10 | 9 | 0.1219 | |||

Lack of fit | 0.6840 | 5 | 0.1368 | 1.33 | 0.4038 | Not significant |

Pure Error | 0.4127 | 4 | 0.1032 | |||

Corrected Total | 24.66 | 18 |

Source | Sum of Squares | DoF | Mean Square | F-Value | p-Value | Remark |
---|---|---|---|---|---|---|

Model | 14,316.59 | 9 | 1590.73 | 10.11 | 0.0010 | Significant |

A—Extrusion temperature | 355.08 | 1 | 355.08 | 2.26 | 0.1674 | |

B—Flow rate multiplier | 9204.05 | 1 | 9204.05 | 58.47 | <0.0001 | Significant |

C—Layer thickness | 4001.95 | 1 | 4001.95 | 25.42 | 0.0007 | Significant |

AB | 51.60 | 1 | 51.60 | 0.3278 | 0.5810 | |

AC | 28.91 | 1 | 28.91 | 0.1837 | 0.6783 | |

BC | 1.33 | 1 | 1.33 | 0.0085 | 0.9288 | |

A² | 11.75 | 1 | 11.75 | 0.0747 | 0.7908 | |

B² | 225.21 | 1 | 225.21 | 1.43 | 0.2622 | |

C² | 115.74 | 1 | 115.74 | 0.7352 | 0.4134 | |

Residual | 1416.72 | 9 | 157.41 | |||

Lack of fit | 1143.52 | 5 | 228.70 | 3.35 | 0.1325 | Not significant |

Pure Error | 273.20 | 4 | 68.30 | |||

Corrected Total | 15,733.31 | 18 |

Parameter/Property | Goal | Lower Limit | Upper Limit | Importance |
---|---|---|---|---|

A: Extrusion temperature | Is in range | 200 °C | 260 °C | 3 |

B: Flow rate multiplier | Is in range | 90% | 130% | 3 |

C: Layer thickness | Is in range | 0.1 mm | 0.3 mm | 3 |

Tensile strength | Maximize | 8 N/mm^{2} | 12 N/mm^{2} | 5 |

Maximum tensile force | Maximize | 100 N | 160 N | 5 |

Tensile modulus | Maximize | 200 N/mm^{2} | 270 N/mm^{2} | 5 |

Parameter/Property | Goal | Unit |
---|---|---|

A: Extrusion temperature | 260 | °C |

B: Flow rate multiplier | 130 | % |

C: Layer thickness | 0.3 | mm |

Tensile strength | 9.36 | N/mm^{2} |

Maximum tensile force | 144.31 | N |

Tensile modulus | 264.24 | N/mm^{2} |

Property | Value ± sd | Unit | Variance from Estimated |
---|---|---|---|

Tensile strength | 9.95 ± 0.27 | N/mm^{2} | +6.3 |

Maximum tensile force | 132.27 ± 2.86 | N | −8.3 |

Tensile modulus | 275.14 ± 6.22 | N/mm^{2} | +4.1 |

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Godec, D.; Cano, S.; Holzer, C.; Gonzalez-Gutierrez, J.
Optimization of the 3D Printing Parameters for Tensile Properties of Specimens Produced by Fused Filament Fabrication of 17-4PH Stainless Steel. *Materials* **2020**, *13*, 774.
https://doi.org/10.3390/ma13030774

**AMA Style**

Godec D, Cano S, Holzer C, Gonzalez-Gutierrez J.
Optimization of the 3D Printing Parameters for Tensile Properties of Specimens Produced by Fused Filament Fabrication of 17-4PH Stainless Steel. *Materials*. 2020; 13(3):774.
https://doi.org/10.3390/ma13030774

**Chicago/Turabian Style**

Godec, Damir, Santiago Cano, Clemens Holzer, and Joamin Gonzalez-Gutierrez.
2020. "Optimization of the 3D Printing Parameters for Tensile Properties of Specimens Produced by Fused Filament Fabrication of 17-4PH Stainless Steel" *Materials* 13, no. 3: 774.
https://doi.org/10.3390/ma13030774