# A Study on the Application of Laser Cleaning on the Weld of the Gas Fuel Supply Pipe for DF Engine
## 4 Conclusions  
This study analyzed the effects of weldment shapes and process parameters on the properties of laser cleaning applied to the weld surface of gas fuel supply pipe for DF engine. Based on the analytic results, it conducted experiments on applying laser cleaning to prototype. The experimental results of this study are as follows.  
(1) As energy density increased, the thermal effects of laser energy on the material also increased. Accordingly, both the spot size irradiated on the material, and the influence of laser energy on the behaviors of molten metal on the metal surface increased. Consequently, oxides on the surface of the specimen were completely eliminated without thermal damage caused by laser heat sources under the condition of energy densities ranging from 5 to 7 J/cm\({}^{2}\). In addition, the result of analyzing roughness indicated that under 5 \(\upmu\)m roughness was formed on the surface of the laser cleaned weldment.  
(2) Laser cleaning could perform at a defocused distance ranging from -5 to +5 mm, owing to the characteristics of the depth of focus. The experimental value of the depth of focus was higher than the theoretically calculated value, 6.9 mm. Nevertheless, it was verified that laser cleaning for eliminating oxides formed on the surface of a weldment can be successfully conducted. As a result, the best cleaning results can be obtained with an energy density of 5 J/cm\({}^{2}\) and a focal position.  
(3) The experimental results verified the applicability of laser cleaning to both butt and fillet weldments, which were shaped in a similar way as those of prototypes. In addition, satisfactory laser cleaning results were obtained despite a change in the angle of a laser head.  
(4) Results showed that the laser cleaning technology could clean the surface of the prototype at a satisfactory level without resulting in a toxic work environment and environmental pollution issues. Since the roughness of about 5 \(\upmu\)m is formed on the weldment surface after laser cleaning, it is expected that a weldment that was laser cleaned  
Figure 12: XRD analysis results of prototype before and after cleaning.  
can exhibit greater adhesive force of paint for anticorrosion of the product than a smooth weldment that was chemically cleaned.  
Conceptualization, J.-D.K. and J.-E.K.; Methodology, J.-D.K. and J.-E.K.; Validation, J.-D.K. and J.-E.K.; Investigation, J.-E.K., J.-M.L., H.-S.C.; Resources, P.-S.K., J.-M.L., H.-S.C.; Writing--Original Draft Preparation, J.-E.K.; Writing--Review and Editing, J.-D.K.; Visualization, J.-E.K.; Supervision, J.-D.K.; Project Administration, J.-D.K.; Funding Acquisition, J.-D.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Acknowledgments: Followings are results of a study on the \"Leaders in INdustry-university Cooperation +\" Project, supported by the Ministry of Education and National Research Foundation of Korea. This work was supported by the Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (P0008763, The Competency Development Program for Industry Specialist). This paper is a revised and expanded version of a paper entitled 'A study on the application of laser cleaning on the weld of the gas supply pipe for DF engine' presented at the International Symposium on Marine Engineering and Technology 2021.  
The authors declare no conflict of interest.  
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