STUDY ON THE INFLUENCE OF WELDER’S FATIGUE ON THE QUALITY OF WELD LINES

In this paper a case study is presented, based on certain exercises applied to different welders, to evaluate the influence of welder’s fatigue on the quality of welding. The performed test was aimed at evaluating the technical performance (the welding act) of subjects, as well as the accuracy of weld lines. Five modules of exercises were applied. The exercises of each module were various, they were of medium level, so that they were neither overburdened, nor unsolicited, because both situations could lead to accidents due to fatigue. A weld line was performed after each exercises’ module. The visual quality of welding was appreciated according to the EN ISO 17637:2011 standard.


INTRODUCTION
In carrying out the welding, special importance must be given to the position of performer during the movements, to the effort, because the way in which some movements are executed conditions the load of the whole body and, in particular, of the spine [1]. The main risk factors are: uncomfortable working positions, situations where the muscles contract and the human body is subjected to an increased mechanical effort; repetitive movements or in extended statistical positions, involving the same groups of joints and muscles; prolonged work without rest; vibrations in the hand-arm direction; lack of experience; improper clothing or equipment etc. The materialization of these factors may lead to musculoskeletal disorders, which usually affect the back, neck, shoulder and the upper limbs, but may also affect the lower limbs [2,3].
In Romania, the welding profession is between the first seven professions where the most professional diseases are registered [4]. A predominant osteo-musculo-articular effort is specific to this profession and, consequently, some degree of neuro -psychic and sensory effort intervenes, playing a major role of coordination and control both, on the effector locomotive system and on the cardiovascular and respiratory apparatus as well as on nervous system.
The aim of the case study presented in this paper was to: • test the effort capacity of subjects, so that to get the highest possible performance which, in turn, lead to a higher efficiency and a higher productivity of the welding process; • determine the types of errors and dysfunctions and their consequences on the subjects; • test the subjects' resistance to intense and long-lasting efforts; • test the subjects' possibility of switching from one activity to another; • test the subjects' speed of adaption to new situations; • test the resistance to the action of stressors; • test the subjects' degree of impulsivity or restraint (the psychomotor balance), so that, based on the results, develop a prevention policy that include working conditions, influence factors related to the work environment and work organization.

Selected exercises
The selected exercises are similar in structure to the act of welding, as we tried to challenge the neuro-motor components of each subject (six subjects). Five modules of exercises were applied (Table 1), structured in three phases: • phase 1 -for "body heating", including module 1 of exercises and welding at the end of module (a weld line of 150 mm); • phase 2including modules II and III, welding between the two modules as well as at the end of module III (a weld line of 150 mm); • phase 3including modules IV and V, welding between the two modules as well as at the end of module V (a weld line of 150 mm). Each module consisted in various exercises, with a medium complexity, so that they were neither overburdened, nor unsolicited, because both situations could lead to accidents due to fatigue. Rules and instructions were given clearly and exemplified to each subject, so that to ensure their safety and security, as well as to obtain good quality weld lines.
In establishing the number of modules and the number of exercises for each module, it was taken into account, on the one hand, the principle of balance between the volume and complexity of exercises and, on the other hand, the subject ability to cope with the exercises' execution, as well as the welding process performed after the exercises.
The initial carried out testing was aimed at evaluating both, the technical performance (the welding act) of each subject as well as the accuracy of realized weld lines. The complexity of exercises was increased in modules 4 and 5, the accent being on the neuro-muscular coordination, materialized in: • hand -eye coordination; • hand -hand coordination; • hand -foot coordination; • eye -hand -foot coordination; • eye -foot coordination.

Used equipment and material
The experiments were performed using a SAF MIG 400 BLX, MIG/MAG welding machine, with a SAF FRO DV 44 X wire dosing system and a CITOFLUX R00C electrode [5]. The weld lines were made on a S235 JR steel plate. This steel has a general use in industry, to manufacture elements of metallic constructions such as bridges, road and rail, tanks, pillars, elements of load-bearing structures of machines, chains, welded nets for reinforced concrete etc., welded or joined by other processes.

RESULTS AND DISCUSSION
The performance of the six subjects related to the execution of exercises specific to the five modules as well as to the act of welding performed after each module is presented in the Table 2 -Table 6.

CONCLUSIONS
By analysing the capacity of subjects to perform the five modules of physical exercises and their effect on the quality of welding, the following aspects were remarked: • subject no. 1 (56 years old, 38 years of experience) managed to correctly execute the exercises of the first 3 modules, but he encountered some difficulties in performing exercises from module no. 4, justifying that he cannot perform the exercises with closed eyes; at module no. 5, the phenomenon of fatigue appeared, manifested by lack of concentration and slight imbalances. Regarding the appearance of the weld lines, they have an inclination angle between 1° and 5°. The first weld line was broken at about 130 mm (Figure 1a).