The National Research Institute of Mechanical Engineering plans to organize the Institute-level Doctoral Thesis Evaluation Council for PhD Candidate Do Hai Tinh at the end of January 2024. The Institute hereby publishes the information on the doctoral thesis of the PhD candidate as follows:

Full name of PhD candidate: Do Hai Tinh

Scientific supervisors: Assoc. Prof. Dr. Dao Duy Trung and Assoc. Prof. Dr. Le Thu Quy

Field: Mechanical Engineering - Code: 9520103

Training institution: National Research Institute of Mechanical Engineering - Ministry of Industry and Trade

Thesis title: "Research on the influence of some plasma welding technological parameters on the quality of SUS 304 stainless steel sheet weld joints"

Summary of new conclusions of the thesis

1. Scientific significance:

 - Through experiments, proposes a reasonable plasma welding regime for butt welding of 2 mm thick SUS 304 stainless steel sheets, ensuring quality requirements evaluated by a set of strength characteristic criteria;            

 - Develops mathematical models in the form of second-degree polynomials (non-linear) as the required output objective functions, quantifying the influence laws of changes in 3 input parameters on tensile strength (s_ki); yield strength (s_si); relative elongation of the plasma weld joint depending on 3 input technological factors: upper-level plasma pulse current intensity (I_h); lower-level plasma pulse current intensity (I_b); welding speed (v_h);

- Synthesizes experimental results evaluating the mechanical-physical properties of SUS 304 stainless steel plasma weld joint materials on test samples obtained from 27 different welding regimes for 2 mm thick welding sheets, thereby enabling easy prediction of the required weld joint quality level (sufficient for practical user needs) within the survey range of the selected main input technological parameters.

2. Practical significance

 The thesis can be used as a reference document in training for the Mechanical Engineering field in the area of welded structure manufacturing and related fields such as Materials Engineering at undergraduate and postgraduate levels in Vietnam.

3. New contributions of the thesis

- Establishes an experimental research methodology suitable for input technological parameters and technical specifications of the LINCOLN C3-MATIC 32-33 plasma welding equipment system, aiming to provide a solution for surveying, analyzing, and evaluating the quality of typical plasma welding test samples when butt welding 2 mm thick SUS 304 stainless steel, combined with destructive testing of mechanical-physical properties, ensuring sufficient reliability of experimental results;

- Applies the Taguchi experimental design method for exploratory technology-oriented experiments with 4 selected input technological parameters for investigation. From there, focuses on determining 3 input technological parameters to conduct experiments with an orthogonal matrix according to a full factorial design of 3 levels and 3 factors (33), helping to quantify the influence laws of different plasma welding regimes on the required output mechanical objective functions within the reasonably adjusted experimental design domain, ensuring good welding quality;

- Provides intuitive 2D and 3D graphs to easily indicate the influence laws on the quality of SUS 304 stainless steel butt plasma weld joints, ensuring compliance with the technical requirements set for the welded structures of the mechanical products to be manufactured.

Detailed content of the thesis by PhD Candidate Do Hai Tinh can be viewed at here