Improving of the productivity and the quality of a manufacturing robotized cell for MIG/MAG welding

During the last years, globalization and the necessity to reduce production costs have pushed industry to employ more and more manufacturing robotized cells. This trend has been assimilated by arc welding too. The use of robotic systems allows to increase the performance of productive systems by means of reduction in lead-time, reproducibility of processes and increase in quality. However, process automation needs pre-scheduling of manufacturing cell movements and also a setup of different welding parameters, such as power provided by the welding generator, arc length and robot speed, all of which allows to get a joint without defects. An online scheduling of robotic systems brings certainly a delay in production times, whereas offline scheduling allows to maintain the desired production without any production stop. An interface that allows to easily translate the coordinate points established by a simulation software (such as Robcad) in some complete programs that can be sent to the controller of the manufacturing cell, has been developed. Besides, in order to improve the joint's quality, an analysis of the joint quality has been carried out by macrographic analysis. The employment of image analysis techniques on the obtained macrographs allowed to translate the morphology of each joint in terms of a matrix. After different morphologies have been distinguished in numerical terms and correlated to the joint's quality, these data have been introduced as input to the interface. The output, constituted by the program for the controller of the cell and the best welding parameters, under such conditions, has allowed to increase both the cell's productivity and the quality of the joints. Therefore, during offline scheduling, the initial phase of loop control of the joint morphology allows to evaluate the best welding parameters both in terms of productivity and joint quality. The same interface allows also to plan the best parameters for different welded joints with varying thickness and typology, which makes the system more eflexible and maintains a high level of productivity. The whole system has been implemented on a robotized cell GMAW Gas Metal Arc Welding Comau, that foresees a welding robot with six degrees of freedom and a position system with other six freedom degrees. Different T fillet joints have been realized at using of weathering steel sheets 5 and 6 mm thick.