Papers by Keyword: Laser Melting

Abstract: The article presents the results of studies of the surfaces of parts processed by the contactless method of laser polishing. The results of technological surface treatment using a laser technological complex based on an ytterbium fibre laser with a power of 5 kW are presented. The results of studies of the surface roughness of the samples after laser treatment, including the non-uniform character due to the redistribution of the liquid metal melt over the surface, are shown. Requirements for metrological support of additive technology have been developed using the example of the process of laser remelting in order to improve quality and further automation.

Abstract: In the process of metal parts fabricated by Laser Melting Deposition (LMD), a high temperature gradient will generate due to the instantaneous high laser energy input, which will cause residual stress in the formed part of metal parts, the residual stress will result in defects like warping deformation or even cracking. In this paper, a finite element method based on inherent strain method is proposed to predict the deformation of metal parts fabricated by LMD. Firstly, combing with the birth and death element technology, a local model is established to simulate the layer-by-layer deposition in the LMD forming process, and the values of inherent strain is obtained. Secondly, the obtained inherent strain values is applied to large-sized part layer by layer, and the final deformation of large-sized part is calculated. Based on the proposed method, the efficiency of deformation prediction of large-sized metal parts fabricated by LMD could be effectively improved.

Abstract: Based on the Paris model of fatigue crack growth theory, the fatigue crack growth behaviour of Center Crack Tension (CCT) specimens of laser melting deposited 12CrNi2 alloy steel is studied by extended finite element method (XFEM). The crack growth rules and fatigue life are analyzed by experiment and finite element simulation. The experimental results are in good agreement with the finite element results, which verifies the accuracy of XFEM method to simulate the fatigue crack growth behaviour of laser melting deposited 12CrNi2 alloy steel components. Based on this, the effects of initial crack direction and load amplitude on fatigue crack growth behaviour are discussed. The results indicate that even if the initial crack direction is different, the crack will finally propagate in a direction perpendicular to the load. With the increase of the load amplitude, the fatigue life of the specimen with initial crack decreases exponentially.

Abstract: Production of the honeycomb or thin walled structures by the selective laser melting of powder is of a great scientific and practical interest. It’s because that such approach allows producing structures practically of any configuration and thickness, unobtainable or very hard to produce by traditional methods. Using the additive technology, the principal difference from the traditional is that the honeycomb structures can be produced practically of any shape, and the method itself is 100% waste-free, because there is no need in supporting structures. The results of the structure investigation of the honeycomb structures with the wall thickness of 80-170 μm and 44 mm height are presented along with the correlation dependencies between samples mass, wall thickness, activation and compression loads.

Abstract: Ni60AA and DZ-WC-12Co cemented carbide layer was prepared on 45 steel by high-speed flame spraying, then remelted by 5KW continuous wave CO2 laser. The micro-structure was analyzed by Olympus GX51 .micro hardness and the micro hardness was measured by HXY-1000TAY micro hardness meter. The wear resistant of coating was tested by MM-W1B vertical universal testing machine. The results showed that laser melting significantly eliminate the carbide layer unmelted carbide particles, holes and cracks and other defects, the micro-structure is finer and more uniform. After laser re-melted, the average micro hardness of hard alloy layer is up to 647HV, which is five times of the matrix. Under the experimental conditions, the friction coefficient of hard alloy layer drops from 0.1373 to 0.0948 by 31%.The wear-resistance of cemented carbide layer is improved by laser melting.

Abstract: Laser surface melting was carried out on the surface of Ti-6Al-4V alloy with Ti-BN-C mixed powders. In this paper, an influence of the mole ratio of BN/ C on microstructure, chemical composition, element distribution and hardness were separately analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA) and Vickers hardness test (HV). The results showed that the melting layer mainly consisted of TiC_xN_1-x (x=0, 0.3, 0.7), TiB and Ti. The hardness was increased with improving the mole ratio of BN/C ratio.

Abstract: Shape memory alloys (SMAs) are a class of material that undergoes a reversible shape change after a plastic deformation. The recovery of the original shape is possible due to a structural transformation upon heating to a critical temperature. The shape memory effect is related to a martensitic-austenitic transformation from a phase with a low symmetry (martensite) to a high-temperature phase (parent phase) [1]. Cu-based shape memory alloys have the advantage of large thermal and electrical conductivities and the system Cu-Al-Ni alloys are quite attractive due to better stabilisation against aging phenomena [2].

Abstract: Additive Manufacturing (AM), also designated as 3D Printing (3DP), is one of the mostvisionary and friendly approaches for flexible manufacturing with conservation of energy andmaterial resources. It is a factory in a box that can generate multiple objects. It requires littlemanpower to bring virtual innovations into the real world. AM for metals can be mechanisticallyassociated with welding. The technique employs a variety of energy sources (laser, electron beam,electric Arc, …), feed stocks (powder, wire and ribbon) and motion kinematics & control(articulated robot and 3-5 axes CNC machine ). From the materials perspectives, akin to fusionwelding in many respects, AM involves a multitude of complex and interacting physical phenomenasuch as heat transfer, fluid flow, discrete and continuum mechanics, sintering, melting,solidification, solid state transformations, grain growth, diffusion, textures etc. The desired processperformance can be achieved by controlling the parameters of energy, feed stock and motion. Theeffect of successive thermal cycles along with the epitaxial relations between substratum anddeposits constitute some of the challenging tasks for developing optimized parts. This paper reviewsthe state of the art and presents some challenges facing metal product development for serviceapplications.

Abstract: Additive Manufacturing (AM), also designated as 3D Printing (3DP), is one of the most visionary and friendly approaches for flexible manufacturing with conservation of energy and material resources. It is a factory in a box that can generate multiple objects. It requires little manpower to bring virtual innovations into the real world. AM for metals can be mechanistically associated with welding. The technique employs a variety of energy sources (laser, electron beam, electric Arc, ...), feed stocks (powder, wire and ribbon) and motion kinematics & control (articulated robot and 3-5 axes CNC machine ). From the materials perspectives, akin to fusion welding in many respects, AM involves a multitude of complex and interacting physical phenomena such as heat transfer, fluid flow, discrete and continuum mechanics, sintering, melting, solidification, solid state transformations, grain growth, diffusion, textures etc. The desired process performance can be achieved by controlling the parameters of energy, feed stock and motion. The effect of successive thermal cycles along with the epitaxial relations between substratum and deposits constitute some of the challenging tasks for developing optimized parts. This paper reviews the state of the art and presents some challenges facing metal product development for service applications.

Abstract: There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress.