Both technical and economic reasons suggest to join dissimilar metals, benefiting from the specific properties of each material in order to perform flexible design. Adhesive bonding and mechanical joining have been traditionally used although adhesives fail to be effective in high-temperature environments and mechanical joining are not adequate for leak-tight joints. Friction stir welding is a valid alternative, even being difficult to perform for specific joint geometries and thin plates. The attention has therefore been shifted to laser welding. Interest has been shown in welding titanium to aluminum, especially in the aviation industry, in order to benefit from both corrosive resistance and strength properties of the former, and low weight and cost of the latter. Titanium alloy Ti-6Al-4V and aluminum alloy 2024 are considered in this work, being them among the most common ones in aerospace and automotive industries. Laser welding is thought to be particularly useful in reducing the heat affected zones and providing deep penetrative beads. Nevertheless, many challenges arise in welding dissimilar metals and the aim is further complicated considering the specific features of the alloys in exam, being them susceptible to oxidation on the upper surface and porosity formation in the fused zone. As many variables are involved, a systematic approach is used to perform the process and to characterize the beads referring to their shape and mechanical features, since a mixture of phases and structures is formed in the fused zone after recrystallization.
Nickel-base alloys, such as Hastelloy X and René 80, are among the most common ones for aerospace applications, due
to their mechanical strength at high temperatures and oxidation resistance properties, although processing for missile and
space vehicle applications requires extensive fusion and resistance welding for fastening.
Laser welding using a Yb:YAG disk laser in continuous mode emission is investigated in this paper for overlap joining
of Hastelloy X plates on René 80 samples resulting from waste turbine blades. An explorative study is carried out in
order to find an appropriate processing window as well as discussing bead features and common issues.
Special fixtures for clamping have been specifically developed and tested. A 3-factors study with power, welding speed
and focus position as governing parameters has been arranged; 2 levels have been chosen for each factor. Geometric
features, defects and indications are discussed referring to the parameters main effects.
The present work focuses on the use of Selective Laser Melting (SLM) technique for manufacturing of near-net-shape
aircraft component prototypes with Ti-6Al-4V titanium alloy, which has already successfully employed for the
production of turbine blades since it combines mechanical properties with excellent wear resistance.
The main characteristic of SLM is layer manufacturing which allows to obtain complex shaped elements using three
dimensional computer aided design data, with the addition of particular features like channels or cavities which can not
been easily obtained with traditional technologies. The other key aspect in comparison with investment casting is shorter
The feasibility of manufacturing turbine blades with mentioned process using a laser sintered machine EOSINT M 270
(Titanium version) is analysed. The first experimental phase has dealt with the definition of processing parameters which
would guarantee laser sintered part maximum density. Preliminary specimens have been manufactured to define any
material-dependent scaling value to control dimensional shrinkage.
Afterwards a prototype of a turbine blade has been produced using optimal process parameter set. The element
positioning and support definition are discussed as they influence the overall job time and the need of post processing
Further analyses have been carried out to check the whole structure of the prototype using X-rays and Fluorescent
Penetrant Inspection, aiming to point out possible imperfections; no defects have been detected. Furthermore, laser
sintered part dimensional inspection has been successively performed via coordinate measuring machine. Eventually, the
microstructure of the prototype has been examined.
The aim of this work is to investigate the effects of power, welding speed, defocusing on geometric features and on
defects of 1 mm Ti6Al4V laser welded butt joints by a new generation disk laser with 2 kW of maximum power. Them
active gain is a Yb:YAG disk instead of traditional Nd:YAG rods. Disk geometry allows to keep the nominal beam
quality also at high power because there is no thermal lensing effect, typical of rod geometry. A three level Box-Behnken
experimental design with three repetitions is carried out for a total of 45 tests. Linear and quadratic regression equations
are developed to relate the input factors to the output variables in order to predict the geometric features of butt joints.
Lap joints obtained by overlapping two plates are widely diffused in aerospace industry. Nevertheless, because of natural
aging, adhesively bonded and riveted aircraft lap joints may be affected by cracks from rivets, voids or corrosion.
Friction stir welding has been proposed as a valid alternative, although large heat affected zones are produced both in the
top and the bottom plate due to the pin diameter. Interest has therefore been shown in studying laser lap welding as the
laser beam has been proved to be competitive since it allows to concentrate the thermal input and increases productivity
Some challenges arise as a consequence of aluminum low absorptance and high thermal conductivity; furthermore,
issues are due to metallurgical challenges such as both micro and macro porosity formation and softening in the fused
Welding of AA 2024 thin sheets in a lap joint configuration is discussed in this paper: tests are carried out using a
recently developed Trumpf TruDisk 2002 Yb:YAG disk-laser with high beam quality which allows to produce beads
with low plates distortion and better penetration. The influence of the processing parameters is discussed considering the
fused zone extent and the bead shape. The porosity content as well as the morphological features of the beads have been
Higher productivity, lower distortion and better penetration are the main advantages which laser welding provides in
comparison with conventional processes. A Trumpf TruDisk 2002 Yb:YAG disk-laser is used in this work, as it
increases productivity and quality.
Materials which involve many technological issues in welding, resulting in shallow penetration and defects, are
aluminum alloys. In particular, AA 2024 behaviour is investigated in the paper, being this alloy extensively used in
automotive and aerospace industries.
Defocusing has been considered, as it affects key-holes conditions. Bead-on-plate and butt autogenous welding tests in
continuous wave emission on 1.25 mm thick sheets have been examined from morphological and microstructural point
of view. Geometric and mechanical features of the welding bead have been evaluated via a 3-levels experimental plan
with power, welding speed and defocusing as governing factors. Softening in the fused zone through Vickers
microhardness test and magnesium loss through energy dispersive spectrometer analysis have been discussed. Optimal
welding conditions have been suggested.
This paper reports the findings of a research Design of Experiment (DOE) based to assess the impact of changes in a set of technological parameters on the morphological characteristics - in particular the microhardness of the welded section - of laser welded stainless steel (AISI 304 and AISI 430) lap joints. The Authors also highlight future research directions.
The employment of laser systems for completely automated welding processes needs an analysis of physical mechanisms by means of mathematical models to correlate the characteristic quality indexes of welding to working parameters. In this paper we describe the application of neural networks method in order to correlate, for different kinds of stainless steel, the melting area and the welding efficiency to working parameters, leaving out of account the knowledge of the chemical and thermo-physical properties of working materials. The results are quite satisfactory even if a direct search of the optimal process conditions is not possible.
Surface morphology of oxygen assisted laser cutting of low carbon steel sheets exhibits characteristic drag lines regularly spaced and more or less pronounced depending on process parameters and depth of observation. Examination of roughness profiles does not correspond directly to the periodicity of the drag lines, especially with cutting speed near to oxidation reaction front speed (about 2 m min-1). In these conditions the two phenomena (laser cutting proper as opposed to oxygen cutting) overlap and the two types of accidents, superimposed over the cutting surface with different periodicity and amplitude, become confused. In this case the roughness profile can be considered as a sum of two populations with different mean and standard deviation, therefore, the height density probability distribution is bimodal and it can be represented as a mixture of two univariate distributions. In this paper a new algorithm is illustrated in order to establish the two parameters of each unimodal distribution, which is well modeled by a Beta-distribution, and the degree of mixing, useful for the evaluation of the relative influence of the two phenomena previously described.
The employment of laser systems for completely automated welding processes needs an analysis of physical mechanisms by means of mathematical models to correlate the characteristic quality indexes of welding to working parameters. In this paper we describe the application of neural networks methods in order to correlate, for different kinds of steel, the form factor and the penetration depth to working parameters and chemical and thermal properties of working materials. The results are quite satisfactory even a direct search of the optimal process conditions is not possible.
Quality control criteria, traditionally adopted for manufactured parts by laser cutting, have related generally to cut characteristics as kerf width, inner side slope of it, heat affected zone extent, dross appearance; all these methodologies require sample examination, appropriately prepared. That can provide useful results on process control only after quite a long time that a possible misworking is happened.
This paper propose to adopt the appearance of cutting surface microgeometry as process control method; this morphology has been detected by means of a new rugosimeter which uses a laser beam as stylus, therefore the profile can be measured without contact between stylus and workpiece, while the related measures can be elaborated soon after the carrying out of cut.
In this stage of study the methodologies of acquisition and elaboration of experimental roughness profiles, the specification of more significant parameters and the correlation between these last and the main variables of laser cutting process are reported.
The employment of laser system for very automatized welding processes needs an analysis of physic mechanisms by means of mathematical models that correlate the characteristic quality index of welding to working parameters.
In this work we used the Group Method of Data Handling (GMDH) mathematical model in order to correlate, for different kinds of steel, the penetration depth to working parameters, chemical composition and thermal properties of the material. Results showed the very important influence of material composition which, in some cases, can be related to that of the main parameters as beam power and welding speed.