In several thermoplastic extrusion based processes the melt flow has to be divided into independent streams that are merged before the flow channel outlet. This promotes the formation of weld lines, usually related to mechanical weak zones and aesthetic imperfections. There is a large amount of scientific publications related to weld lines formed in other processing techniques, e.g. injection molding. However, studies related to extrusion are scarce. This work presents the conception of a new prototype system that allows performing systematic studies aiming a better understanding of the effect of weld lines in extrusion. A case study illustrates the employment of the developed device to study the effect of several process parameters (e.g. spider leg location, processing temperature and flow rate) on the mechanical performance of the extruded profiles.