Laser surface modification of carbon fiber reinforced composites

The removal of top resin layer is an essential task prior to adhesive bonding of carbon fiber reinforced polymer (CFRP) composites. This paper investigates the technical feasibility of using a low power continuous wave carbon dioxide laser for removing the top resin layer of CFRP without damaging the underlying fiber. The operating window and damaging threshold were experimentally determined. Irradiating the CFRP surface at a power of 14 W, scanning speed of 880 mm/sec, and a beam overlap of 25% provides an optimal thermal condition for removal of top resin layer. A finite element model was used to explain the removal mechanisms

Modelling of the melt pool geometry in the laser deposition of nickel alloys using the anisotropic enhanced thermal conductivity approach

Use of appropriate modes of heat transfer in finite element modelling simulations of laser deposition is important for enhancing the reliability of the predicted results. An important contributory mode is melt pool convection, which is the focus of this work. Using the anisotropic enhanced thermal conductivity approach, this study examines the strategies relating to the choice of appropriate values for the thermal conductivity enhancement factors in the orthogonal axial directions x, y, and z. In order to investigate different combinations of values for these factors in the laser deposition of one track of Inconel 718 powder on an EN-43A mild steel substrate, finite element models were prepared and results from these were compared with the corresponding experimental results. The results of the study suggested that no thermal conductivity enhancement should be enforced in the direction of the depth of the sample. Thermal enhancement factors in the two orthogonal directions are required, but the factor in the direction parallel to the direction of beam scanning should be of greater magnitude. Analysis of the thermal gradients from the model also showed that failure to incorporate any allowance for the melt pool convection effect with appropriate choice of thermal conductivity enhancement factors in the finite element modelling of the laser deposition can result in overprediction of thermal stress, which can lead to undue threats of various forms of distortion during the deposition process

Laser stripping of TiAlN coating to facilitate reuse of cutting tools

The potential of using the laser ablation process to perform controlled stripping of titanium aluminium nitrite (TiAlN) coating from tungsten carbide (WC) substrate is explored in this paper. TiAlN coatings are extensively used in cutting tools to improve machining capability, and to extend the life of the tools. However, if any error is detected on the coated tools, or when the tooling needs to be reused, it is mandatory to remove the existing coating to facilitate reshaping/recoating. The existing coating removal process uses chemical stripping methods, which are not environmentally friendly and not suitable for selective coating removal. In the present work, excimer laser removal of TiAlN from coated WC flat plates has been studied and demonstrated as a viable alternative to existing chemical stripping methods. The ablation thresholds of the TiAlN coating and WC substrate were identified as 1.85 J/cm2 and 2.3 J/cm2 respectively. The paper also presents experimental and theoretical evidence of the process mechanism responsible for laser stripping of TiAlN coating