Composite Bonding Pre-Treatment with Laser Radiation of 3 µm Wavelength: Comparison with Conventional Laser Sources

Abstract

To use the full potential of composite parts, e.g., to reduce the structural weight of cars or airplanes, a greater focus is needed on the joining technology. Adhesive bonding is considered favorable, superior joining technology for these parts. Unfortunately, to provide a structural and durable bond, a surface pre-treatment is necessary. Due to its high integration potential in industrial process chains, laser radiation can be a very efficient tool for this purpose. Within the BMBF-funded (German Federal Ministry of Education and Research) project GEWOL, a laser source that emits radiation at 3 µm wavelength (which shows significant advantages in theory) was developed for a sensitive laser-based bonding pre-treatment. Within the presented study, the developed laser source was compared with conventional laser sources emitting radiation at 355 nm, 1064 nm, and 10,600 nm in terms of application for a composite bonding pre-treatment. With the different laser sources, composites were treated, analytically tested, subsequently bonded, and mechanically tested to determine the bonding ability of the treated specimens. The results show a sensitive treatment of the surface with the developed laser source, which resulted in a very effective cleaning, high bonding strengths (over 32 MPa), and a good effectiveness compared with the conventional laser sources.

Effect of Mechanical Pretreatments on Damage Mechanisms and Fracture Toughness in CFRP/Epoxy Joints

“…As contaminants are mainly embedded within the outermost surface layer of the laminates, a light removal of epoxy matrix from the adjoining interfaces has a beneficial effect on adhesion and bond reliability [ 10 , 11 , 12 ]. The most common surface preparation methods for CFRP include the use of peel-plies, corona discharge, flame, plasma, or laser treatments [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Peel-plies are simple to apply and provide (reproducible) surfaces that are often unsuitable for adhesive bonding, unless used in combination with another surface treatment [ 10 ].…”

“…Oxygen plasma can increase carbonyl content and etch the surface, increasing roughness, wettability, and the strength of adhesive joints [ 14 ]. Pulsed lasers at various wavelengths, including ultraviolet [ 15 ], near-infrared [ 16 ], and infrared [ 17 , 18 ], are also very effective and can remove embedded contaminants through photochemical or photothermal interactions, with consequent improvement of wetting and surface energy.…”

Individualized and controlled laser beam pretreatment process for adhesive bonding of fiber-reinforced plastics—Part I: Optical detection of impurities on the component surface

“…There are several publications in the literature on the subject of laser pretreatment of plastics. [3][4][5][6][7][8][9] Important publications are those from Kreling 3 and Kraus et al, 4 but most are based on the investigation of carbon fiber-reinforced plastics (CFRP) with epoxy matrix. Investigations with impurities on joining surfaces were carried out by Palmieri et al 5 and Rauh et al 6 Palmieri focuses on the detection of silicones in the form of release agents on CFRP components under consideration of the ablation product, and greases in the form of fingerprints are not considered.…”

“…There are several publications in the literature on the subject of laser pretreatment of plastics. 3–9 Important publications are those from Kreling 3 and Kraus et al., 4 but most are based on the investigation of carbon fiber-reinforced plastics (CFRP) with epoxy matrix. Investigations with impurities on joining surfaces were carried out by Palmieri et al.…”

Improvement of the adhesive bonding properties of an polyamide 6 injection molded fiber reinforced plastic component by laser beam pre-treatment

“…At a certain fluence range the contact angle was increased. 15 Blass et al 16 compared the experiments on CFRP with laser radiation of 3012 nm wavelength with CFRP specimens pre-treated with common laser sources at 355 nm, 1064 nm, and 10,600 nm wavelength in his publication. It is stated that the common laser radiation has a high risk of causing damage to the material.…”