ABSTRACT
Snap-fit assembly has become more important in the automotive industry and within its subcontractors, as well as, in the consumer goods industry. The reason for this development is particularly related to the increased economic benefits that occur through the accelerated assembly task. However, the ergonomic aspects of snap fit assembly have not been sufficiently studied. Fasteners with sharp-edged head geometry can produce a displeasing perception on the finger pad during the insertion operation. Snap fasteners can also constrain the operators to use a pinchgrasp during the insertion. The high insertion forces during pinch-grasp, particularly due to the small friction coefficient in friction fit coupling, can lead to musculoskeletal disorders and repetitive strain injuries. This study investigates, in two different experiments, the influence of different conditions of grasp-and contact-characteristic of snap fasteners on assembly time. In the first experiment,
the influence of the sharpness of the snap-fit on the insertion time and EMG was studied. The insertion force was set to 20N and 70N. The results showed a significant difference in insertion times of snap fasteners depending on the head geometry (i.e., sharpness). This effect was higher for higher predetermined insertion forces. The significant effect of sharpness on the electromyographic activity of the musculature of the thumb was also proved. According to these results, a second experiment was planned. In the second experiment, the influence of additional grasp and contact characteristics (i.e., sharpness, dimension and slipperiness) on the reach, move, insertion and assembly time was studied. It was found that the slipperiness and dimension had a significant effect on insertion time. Furthermore, the kinematic analysis pointed out that the move-time was significantly affected by only regraspmg.
