STUDY OF THE USE OF THERMAL DRILLING IN MECHANICAL JOINING OF MG SHEET AND GFRP/CFRP COMPOSITES WITH THERMOSOFTENING MATRIX

The paper discusses the joining of magnesium based metallic sheet and composites with thermosoftening polypropylene matrix reinforced with bi-directional continuous glass and carbon fibers by thermal drilling technology. The bushing formation has been investigated by separately drilling AZ91 Mg alloy sheet at two rotational speeds and feed rates to find out the parameters at which a bushing with optimum length and thickness, suitable for joining with the composite, is formed. Under these conditions, the joining of the metal sheet and composite was then carried out by simple thermal drilling. During simple drilling, delamination of the composite occurred in the vicinity of the hole, which was resolved by flanging the bushing with a penetration of the tool from the opposite side. When AZ91 was joined to carbon fibers reinfirced composite, there was a lack of bushing formation due to the higher resistance of the carbon fibers, which are present in the composite in greater numbers compared to the glass fibers. This problem was solved by sequential drilling, which means that a flowdrill tool was used to create a hole in the composite itself, then overlaid with Mg sheet and again drilled, forming the bushing and flanging the bushing from the opposite side. The sequential drilling resulted in joints with a load capacity of 0.8 - 1.4 kN, which exhibit the characteristics of a hybrid - mechanical and adhesive joint.