Automated removal of carbon fiber reinforced plastic layers for the repair by adhesive bonding

Abstract

For the industrial repair of carbon fiber reinforced plastics (CFRP), scarfing is used to re-establish the load path. In the industry today, the state of the art removal of CFRP layers for a repair process is done mainly manually, leading to a time-consuming process. Therefore, an automation of this process is desirable. Today, vacuum suction blasting is used to pre-treat CFRP surfaces only for the superficial removal of impurities or the removal of the cover layer before bonding. With the common used blasting agents and nozzle geometries, the even removal of larger areas together with the fiber was not possible. This work shows that the technology of vacuum suction blasting was adapted to be used as an automated scarfing method. A combination of blasting parameters, especially the nozzle geometries together with a blasting agent were found to be able to remove CFRP layers precisely, detecting and correcting errors in-line with a line scanner-measuring unit. The presented method allows treating large-scale surfaces, scarfing the area one single layer at a time, increasing the removal rate in comparison to common blasting. With vacuum suction blasting the grinding dust emissions and process forces are low, post cleaning or further surface activation are not necessary and the removal results can directly be controlled. Challenges still exist with inaccurate removal due to interruptions in the blasting program and the generation of sharp edges for a stepped scarf.

A Model Based Material Removal Simulation for Vacuum Suction Blasting of Composites

“…The industry uses VSB mainly for the roughening of topcoats on CFRP parts before adhesive bonding [22]. The process uses corundum-blasting agents with corn sizes up to 100 µm as well as a working distance of the blasting nozzle of 10-20 mm to not enter and harm the bre layers, low negative pressure of 10 kPa and short blasting cycles of 1-5 s [22,7].…”

“…The usage of silicate blasting agents, a speci c closer blasting nozzle working distance of 7 mm and a higher under pressure of 30 kPa leads to a smooth removal of single CFRP layers while moving the blasting head over the substrates surface [7]. In comparison to conventional methods, removals with VSB show the advanced progress for the scar ng approach especially regarding smooth surfaces, low emissions and low loads regarding heat or process forces [7]. Limitations for the removal with VSB are the inner diameter of the outer nozzle of the blasting head regarding the removal width.…”

“…This is due to a particle ow effect when the blasting nozzle working distance increases. For an e cient scar ng with VSB, the removal has to be layer by layer because of this cavity effect (s. Figure 2b-c) [7]. For larger areas, the tracks need overlap in the area of their edges to generate a seamless removal [7].…”

“…When ignoring these adjustments, the removal rate rapidly increases and the bre area is touched [7]. Scar ng with VSB takes advantage of this potential effect for a larger scale removal of CFRP parts before a bonded repair [7].…”