Optimizing the laser-welded butt joints of medium carbon steel using RSM
Introduction
Laser welding with high power density, high degree of automation and high production rate is extremely advantageous in automotive application [1]. But the point is how to express the weld bead parameters in terms of process input factors to determine the optimum welding conditions. Considering that welding is usually done with the aim of producing a good joint at low cost. However it is impossible to achieve low-cost welding and good junction without optimization. Trial and error methods were previously used to determine the optimal process conditions for the required weld joint quality [2], [3]. Optimization of the weld bead volume ‘minimize’ in SAW was studied [4]. Also, optimization of the impact strength of spiral-welded pipes in SAW at different serving temperatures was investigated [5]. Despite the different optimization techniques used in the previous studies, the goals were reached and optimal welding conditions were identified to achieve the desirable weld quality with minimum cost [4], [5]. For a strong weld, bead penetration should be maximized and the heat input, bead width of fusion zone as well as bead width of HAZ should be minimized.
Minimizing the heat input would result in reducing the welding cost through reduced energy consumption and increased welding productivity through high welding speed. By utilizing the above advantages, the weld bead profile could be optimized. The objective of this study is to optimize the autogenous laser-welded joints subjected to maximize penetration and minimize both the fusion zone width and HAZ width. In order to achieve these objectives, mathematical models were developed to relate the important weld bead parameters and the laser welding input variables [6].
The mathematical models developed and optimized for the weld bead profile are very useful to identify the correct and optimal combination of the laser welding input variables, in order to obtain superior weld quality at relatively low cost.
Section snippets
Experimental
Medium carbon steel with chemical composition in weight percent of 0.46% C, 0.2% Si, 0.7% Mn and Fe, balance was used as work piece material. The size of each plate was 180 mm long × 80 mm width with thickness of 5 mm. Trial samples of butt joints were performed by varying one of the process variables to determine the working range of each variable. Absent of visible welding defects and at least half-depth penetration were the criteria of choosing the working ranges. The experiment was carried out
Optimization
The optimization module in design-expert searches for a combination of factor levels that simultaneously satisfy the requirements placed (i.e. optimization criteria) on each of the responses and process factors (i.e. multiple response optimization). Numerical and graphical optimization methods were used in this work by choosing the desired goals for each factor and response. The optimization process involved combining the goals into an overall desirability function. The numerical optimization
Results and discussion
Table 4 shows the welding conditions, which lead to full-depth penetration at relatively low welding cost. It is evident that to achieve full-depth penetration, the optimal working range for the laser power has to be between 1.38 and 1.42 kW and the welding speed has to be between 30.48 and 35.55 cm/min using a focused position spanning from −0.43 to 0 mm. However, the full-depth penetration achievement has a negative effect on both the bead width of WZ and HAZ, due to the high laser power and
Conclusions
The following points were concluded from this investigation among the factors limits considered:
- 1.
Design-expert software can be used for optimizing the weld bead parameters and finding the corresponding optimum process factors.
- 2.
Full-depth penetration has a strong effect on the other bead parameters investigated.
- 3.
Strong, efficient and low-cost weld joints could be achieved using the optimum welding conditions.
Acknowledgements
The authors gratefully thank the Libyan Government for providing the financial support through the cultural affairs office in London. The authors also thank the technical support from the workshop in the School of Mechanical and Manufacturing Engineering, Dublin City University.
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