Laser-aided Directed Metal Deposition of Ni-based superalloy powder

Abstract The subject of repairing Ni-based parts with state-of-the-art technologies is increasingly addressed both for research and industrial purposes, aiming to cost saving mainly in aerospace and automotive. In this frame, laser-aided Directed Metal Deposition (DMD) with injection of powder is investigated in this paper since minimal distortion of the work-piece, reduced heat-affected zones and better surface quality are benefited in comparison with conventional techniques. Actual application to overhaul Ni-based components is aimed, therefore homologous powder is fed by means of a 3-way feeding nozzle over the substrate; a disc laser is used as heat source. The chemical composition of both the substrate and the powder is preliminarily investigated via areal and punctual EDS inspections. A 2-factor, 2-level experimental plan is drawn to discuss the main effects of the processing variables laser power and processing speed. Namely, the resulting trends are given and compared with similar findings in the literature. Interestingly, dilution as a measure of metal affection is found to be lower than 25%, hence the operating window is deemed to be suitable for both repairing and fabrication of parts. Eventually, repairing by means of side overlapping and multi-level deposition traces on artificial square-shaped grooves is performed: indeed, similar slots are made before DMD to preliminarily remove any local imperfection upon improper casting of the part in the actual industrial process. Although a number of micropores are found, the process is deemed to comply with usual referred standards; in particular, a proper processing window has been found to prevent the occurrence of hot cracking which usually affects the compliance to stress

Directed Energy Deposition of stainless steel wire with laser beam: evaluation of geometry and affection depth

Abstract This paper is aimed at investigating the process of Directed Energy Deposition of steel wire to the purpose of maintenance and repair: this technology is receiving increasing interest in the frame of Additive Manufacturing and has been investigated for different metals and different substrates. An experimental plan has been designed here to investigate the dependence of the geometry on the governing factors in single-track deposition and quantify the depth of the affection in the substrate in terms of geometrical dilution and variation of the micro-hardness

Optimization of laser beam welding of steel parts made by additive manufacturing

AbstractTo pursue all the benefits of additive manufacturing of metals, recent studies have been aimed at assessing a proper welding technology to obtain large products by means of joining smaller parts. Indeed, at present, two or more parts must be manufactured individually and then assembled to produce the final component, when the size is incompatible with the building chamber or severe deformations arise during building. In this paper, laser beam welding is explored to join stainless steel components made by the process of laser powder bed fusion, in order to benefit from all the known advantages of this joining technique, aiming at producing a welding bead with homogeneous mechanical features with respect to the unwelded counterpart: a factorial plan is built, and the response surfaces are presented; then, the consolidated method of the desirability function is used to find the optimum condition of welding with reference to the current international standards, taking into account the geometry, the welding imperfections, and the extent of the heat-affected zone. The suggested optimum is eventually assessed via tensile testing and compared to the unwelded sample

Definition and Analysis of Uncertainty Contributors in the Dimensional Measurement of Bronze Sintered Samples

The paper concerns the definition and estimation of uncertainty elements. This topic is matched with Direct Metal Selective Laser Sintering used for manufacturing the samples. The UNI ENV ISO 14253-2: 2003 standard deals with uncertainty sources in dimensional measurement. This paper treats just those ones regarding measurement procedure, measurement equipment and workpiece. The aim of this paper is estimating combined standard uncertainty. Measurement repeatability, workpiece fixing and number of points for the definition of geometric elements arise from measurement procedure. Measurement equipment uncertainty is connected with Maximum Permissible Error. As far as workpiece uncertainty components, surface roughness, form error and temperature are checked

Dimensional Analysis in Selective Laser Melting

This paper aims to use dimensional analysis technique for evaluating the properties of laser sintered components manufactured with Selective Laser Melting (SLM) process from metallic powders. The complexity of SLM does not allow to define an exhaustive mathematical model which involves all governing parameters and, therefore, the dimensional analysis might be a powerful tool for the expression of output parameters as function of dimensionless numbers appropriately defined from the input parameters set. As an example of the developed procedure, the paper explains the construction of a response function for the expression of relative density

Additive manufacturing of biomorphic scaffolds for bone tissue engineering

AbstractBone tissue engineering has evolved owing to new opportunities of deep customisation offered by additive manufacturing technologies. Gyroid structures, which have been widely used for energy absorption or chemical catalysis, are now being employed as biomorphic structures as well to provide customer-oriented scaffolds for missing or injured bones. Unfortunately, limited data in terms of manufacturability and mechanical properties are available in the literature to support a wide application scope, because the bone to match is strongly dependent on the individual. Therefore, the study aimed at addressing this lack of knowledge, assessing the manufacturability of metal gyroids and further developing the correlation of the structural response with the designed geometry, so to allow the designer to provide the proper biomorphic structure on a case-by-case basis. Biocompatible steel was used to manufacture samples via laser powder-bed fusion; their elastic moduli and yield strengths were evaluated as a function of the orientation of the elementary cells, the symmetry and the wall thickness based on compression testing. Grounds have been given to support potential applications for tibias and vertebras

Laser powder-bed fusion of Inconel 718 to manufacture turbine blades

In the frame of additive manufacturing of metals, laser powder-bed fusion is investigated in this paper as an advanced industrial prototyping tool to manufacture Inconel 718 turbine blades at a predesign stage before flow production. Expediting of the evaluation of any upgrade to the part is aimed. To this purpose, possible anisotropy of manufacturing is preliminarily investigated via tensile testing at room and elevated temperature as a function of the sloping angle with the building plate; the normalized strength is given and compared with similar studies in the literature. Positioning and proper supporting in manufacturing are discussed; the parts are further investigated to assess their compliance with the intended nominal geometry

Porosity evolution in aluminum alloy 2024 bop and butt defocused welding by Yb-YAG disk laser

In many industrial applications, in order to obtain good results in laser welding processes, it may not be sufficient to use a focused beam on the upper surface, so a defocused beam is required instead. This study aims to investigate which advantages a defocused beam may offer in welding aluminum alloy 2024 using Yb:YAG disk laser. A characterization of laser beam geometry is preliminary necessary, in order to correlate bead features and effective specific energy provided. Porosity content decrease and enhanced penetration depth have been obtained with defocused beam; welding behavior has been related to magnesium loss via EDS analysis. Considering the shape of the cross sections of the bead in butt welding, the relation between key-hole instability and porosity formation has also been discussed. For the alloy in exam, the welding range to perform structurally sound and defect-free welds is found to be tight

Laser cutting of different polymeric plastics (PE, PP and PC) by a CO2 laser beam

Thiswork investigates the application of theCO2 laser cutting process to three thermoplastic polymers, polyethylene (PE), polypropylene (PP), polycarbonate (PC) in different thicknesses ranging from 2 to 10 mm. The process parameters examined were: laser power, range of cutting speed, type of focusing lens, pressure and flow of the covering gas, thickness of the samples. Furthermore, the values of kerf widths on top (Lsup) and bottom (Linf ) thicknesses, the melted transverse area, the melted volume per unit time and surface roughness values (Ra) on cut edges were also measured

On the welding of different materials by diode laser

In technical literature, there are few papers about the use of diode lasers in material processing and particularly in metal welding. In this paper, different materials, according to specific and particular industrial needs and requests, have been tested with a welding process by a diode laser, emitting a 808 nm laser radiation. Beads on plate have been studied. The goal was to evaluate the maximum weldable thickness and define the best process parameters for each material. The experimental evaluation has been carried out considering the following parameters: power level, welding speed (WS), shielding gas, gas nozzle and orientation of the focused elliptical spot as to the welding direction