The public discussion of the master’s student Ruba Khalil Yousif, from the Department of Mechanical Engineering – College of Engineering / University of Baghdad, was held for her thesis entitled:
“Multi-Objective Optimization (MOO) Based on TOPSIS-Quality Loss Function Approach of Laser Spot Welding Process”
The discussion took place in Dr. Ihsan Yahya Hussein Hall on Wednesday, September 10, 2025.
Examination Committee:
- Prof. Dr. Qasim Muhammad Doos – Chairman
- Prof. Dr. Fadhel Abbas Abdullah – Member
- Lect. Dr. Ban Bakir Jawad – Member
- Asst. Prof. Dr. Bassim Shaheen Bachy – Supervisor
This thesis studied the laser spot welding (LSW) process as an advanced manufacturing technique with wide industrial applications, focusing on improving the weld quality of transparent and black polymethyl methacrylate (PMMA) materials.
The researcher adopted a multi-objective optimization (MOO) methodology using the TOPSIS approach and quality loss function to analyze the effects of laser power, welding speed, beam diameter, and spot size on several responses, including:
- Mechanical joint strength
- Weld modulus of elasticity
- Defect percentages in the weld zone
- Width of the heat-affected zone (HAZ)
- Welding accuracy
The experiments were conducted using a fiber laser with a wavelength of 1064 nm, power of 50 W, maximum frequency of 200 kHz, and speed of 10,000 mm/s, based on an L9 orthogonal array design of experiments.
Results and Conclusions:
- The minimum exhaust defect percentage recorded was 17%, and the maximum was 60%.
- Increasing laser power and beam diameter at low speed led to higher defect percentages.
- Smaller spot size reduced burn marks but increased exhaust defects.
- Laser power and beam diameter contributed 43% and 41%, respectively, to exhaust defects.
- The multi-objective optimization results showed that the best weld quality was achieved at the following parameter values:
- Laser power: 10 W
- Speed: 10 mm/s
- Beam diameter: 0.002 mm
- Spot size: 4 mm
Recommendations:
- Adopt smaller geometric spot designs (4 mm) to achieve higher weld quality.
- Consider the influence of laser parameters on defect percentages during industrial operations.
- Apply the proposed methodology to improve welding processes of other polymeric materials.
After the scientific discussion by the members of the examination committee, the researcher Ruba Khalil Yousif was granted the degree of Master of Science in Mechanical Engineering with a grade of Excellent.
