The outputs include the net heat power qnet , heat source distribution pn , beam location x0 and thus the temperature field. The cooling rate and cooling time of the weld and the HAZ at the given temperature range greatly differ. Schematic diagram illustrating a moving reference frame a and an approximations of the beam by the line heat source with a piecewise-linear function b , an exponential function c or a polynomial function d. Temperature cycles of metal in weld centre points A and B and weld interface points C and D.
Naturally, this large difference in the cooling rate results in large changes of the metal properties in the cross section of the welded joint. For instance, the hardness of the weld metal in the root part reaches HV, which is HV higher than in the upper part, at a hardness of the base metal of HV . Longitudinal section of the solidification boundary is shown in Fig. Bead depth below surface is 8. The beam is modelled by a line heat source Fig. Temperature field around electron beam, quasi-stationary limit state in moving coordinate system x, y, z: a isotherms on topside, b in longitudinal section.
Let us represent the laser beam as the line source with heat density exponentially distributed over the depth hp Fig. Calculated net heat input is W, the bead width is 1. The three-dimensional temperature field is different in all directions Fig. Longitudinal section of weld pool24 a and estimated distribution of heat input along plate thickness b ; dashed line shows calculated weld pool boundary. Cross section of laser beam weldment25 a , estimated distribution of heat input along plate thickness b ; dashed lines show calculated weld interface.
The experimental and calculated weld interfaces have a near-line shape Fig. Let us represent the laser beam as a combination of the line source with heat density q1 app z polynomially distributed over the plate thickness Fig. The temperature field due to line source is described by formula 9 the expression for Im results from the integral N 2. The solution is shown in Figs 14b and 14c. The incident laser beam power remains constant for each weld at W and the welding speed varies between 10 and 50 mm s The interaction of the laser beam with the workpiece is represented by a piecewise-linear continuous line source Fig.
The oscillations are not of physical origin but are inherent in ill-posed problems. The calculated net heat input value is practically independent on the regularisation. Cross section of laser welded stainless steel joint a , estimated heat input distributions at surface b and over plate thickness c ; broken curves show calculated weld interfaces. For the slowest speed of 10 mm s-1, the sides of the weld profile are almost parallel Fig.
As the welding speed is increased, the top and back face width decreases, with heat source non-uniformity increased. However, the weld width decreases along the thickness relatively slower than the heat density q1 app z does. This is caused by considerable vertical heat flows from the upper part of the weld to the lower part. Aluminium alloy weld profiles a and heat input distributions for given speeds b broken curves show weld interfaces. It can be seen from Fig. The efficiency of the heat source and the thermal efficiency of base metal fusing can be evaluated.
Without regularisation the iterative process can diverge.
The authors would like to thank D. Langenfelder for his execution of the experiments presented in Section 4. Uhm for her kind help by preparation of this manuscript. Tikhonov and V. Kozdoba and P. Beck, B. Blackwell and C. Tikhonov, V. Kalner and V. Tikhonov, A. Goncharsky, V. Stepanov and A. Kurpisz and A. Leonov and A.
Tupholme and A. Wood ed. Rappaz, M. Ozgu and K. Mahin ed. Wrobel, G. Comini, C. Brebbia and A. Nowak ed. Karkhin, V. Plochikhine and H. Plochikhine, A. Ilyin and H. Karkhin, A. Ilyin, V. Ploshikhine and H. Rappaz, J. Desbiolles, J. Drezet, Ch. Gandin, A. Jacot and Ph. Cross and J. Campbell ed. Bergmann, S. Mayer, K. Mueller and V.
Cerjak ed. Adams, Moscow, LGTU, Leningrad, Ploshikhin and H. Bashenko and N. Karkhin and A. Lambrakos and J. Vitek, S. David, J. Johnson, H. Smartt and T. DebRoy ed. Dowden, P. Kapadia and R. Davis, P. Kapadia and J. Although somewhat limited in process cost and flexibility in product development, as well as AM product size, powder bed fusion processes involving laser SLM and electron beam EBM melting of powders have proliferated worldwide as a consequence of commercial system availability. Correspondingly, metal and alloy powder sales have also increased in a similar fashion.
But powder costs in contrast to cast or wrought precursor metals and alloys are more than 10 times the unit price. Ti-6Al-4V represents one of the most important powder materials used in both EBM and SLM processing over the past 15 years as a consequence of its importance in medical device and aerospace component fabrication. An important feature of powder bed fusion technologies, Fig. In addition, unlike the much larger technology of powder metallurgy, so-called green compacts do not require flowable, spherical powders which are essential in rolling or raking powder beds in SLM or EBM processes..
The attendant microstructures are also influenced by the beam heating or energy deposition which depends on the beam diameter, raster speed, and current density in the case of EBM. In addition, the necessity to preheat each layer prior to the melt scan, the pre-heat scan rate and beam current, as well as remelt strategies will selectively and often systematically alter the microstructure, and the residual product properties.
The product volume or size will also influence the thermal issues, primarily cooling or rate of cooling, which can also have a significant effect on the microstructure. The sequence of optical micrographs in Fig. Optical micrograph sequences showing microstructure variations for different thermal processing conditions for EBM-fabricated Ti-6Al-4V products.
HRC 37 noted for wrought material denotes annealed product.. In contrast to Fig. This microstructure has been described in detail by Gaytan et al. These features are illustrated in Fig. This alloy, in the form shown in Fig. In this regard, Fig. Optical micrograph showing columnar grains GB and directional carbide Cr 23 C 6 architectures within these grains parallel to the build direction for EBM-fabricated Co-Cr alloy.
The image plane is parallel to the vertical specimen product plane.. Examples of complex, open cellular structure models which have been fabricated in various metals and alloys by SLM and EBM. As we noted previously, the fabrication of complex or porous geometries as illustrated in Fig. Consequently, there are severe limits on the complexity and size of 3D printed parts, and the requirements for flowable powder feed increases the manufacturing costs in contrast to equivalent weights of more conventional feed stock, including wire forms.
In addition, scale-up or enlargement of build volumes is not trivial since there are limitations on the ability to direct the beam to extended product dimensions in particular an electron beam in EBM processing , and there are problems in maintaining level powder beds because roller or rake flexure can become serious over large areas or powder spans..
In this context, Zenon et al. Indeed, to put metal 3D printing; especially high-temperature materials represented by Figs. Applied to metal droplet generation and 3D product printing, the initial breaklength to form a droplet distance from orifice exit surface to droplet formation in Fig.
Schematic view of drop-on-demand ink jet generator. Droplet deposition on a substrate is shown in the context of contact or contact angle.. Generally, droplets or a droplet stream generated as shown in Fig. Some drops or fraction can rebound depending upon the size, velocity, and angle the droplet or droplet stream makes with the line of emission and formation from the orifice and the substrate plane. Average splat diameter is denoted D s.
In the two upper splat patterns, a portion of the drop rebounds.. The final shape of each solidified droplet on the substrate surface is a complex issue affected by heat transfer and fluid dynamics occurring at the droplet collision point with the solid substrate.. Efforts to develop metal droplet generators began in the context of additive manufacturing or 3D printing of metal products with the work of Orme and Muntz  published 3 decades ago; followed by a patent issued in . This work, focused on droplet generation and fabrication using aluminum alloys, was followed by extensive research spanning nearly 15 years [28—30].
As illustrated schematically in Fig. Many ink droplet printers also have scanning electrodes. In addition, Orme et al. This requirement is similar in effect to the substrate and pre-heat scan temperatures required for optimal melting in powder bed fusion systems Fig. Furthermore, Orme et al. In addition, Fig. In fabricating products as illustrated in Fig. Metal droplet generator schematic based on the concept of Orme et al. Aluminum product examples fabricated using a metal droplet generator shown in Fig. The largest square tube at left is 11 cm in length. T and B indicate component top and bottom or base respectively in the building process.
Adapted from Orme et al. After Murr and Li in Ref. Aside from the work of Orme and colleagues for aluminum alloy AM products in Fig. More recently, Harkness and Goldsmid  described a patent assigned to Boeing U. This points out that not only is precision controlled molten droplet stream production imperative for advanced AM applications, but the computer control of such printer heads, the clustering of such heads to allow multimaterial deposition, or the enhanced quantity of material deposition is important for large structure and large component fabrication.
In addition, the positioning of efficient droplet emitters and their movement and subsequent droplet stream direction will require novel gantry designs and other diverse deposition schemes, including robot arm or other robotic integration into gantry systems to allow large structure and subsystem or component manufacture.. In this design concept Fig.
The feed wire can be preheated prior to entering the melt regime and droplets can be heated well above the melting temperature. The metal feed wire is connected to a target potential or grounded, and a charging electrode Fig. Metal droplet generator design using wire feed system. Adapted from provisional patent application number by Johnson et al.
Because, in principal, the deposition scan range of a droplet generator as in Fig. As noted previously, clustered droplet generator emitter heads can be mounted on flexible gantry arrays, robot arms, etc. It should be emphasized that large-scale AM, 3D printing systems envisioned in Fig. In addition, the nozzle spacing to the printing surface would be considerably reduced from the exaggerated view provided in Fig.
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In addition, large, integrated deposition systems implicit in Fig. It can be recognized that necessary CAD and related, integrated computer control for emitter head operation and metal droplet stream direction, as well as their orientation for optimal deposition will require a very large and sophisticated computer control platform as a major process component.. Exaggerated cartoon view showing large-scale AM of aircraft structure and components using wire fed, metal droplet generator clusters in vacuum enclosure.
The metal or alloy wires are fed from spools upper left. Modular analytical components which can be strategically placed during the build process are denoted, S , for diagnostic source electron, X-ray beam, etc. S can also represent electron or laser beam sources for thermal manipulation during layer building.
The multiaxial, clustered droplet-emitter heads can be mounted on movable gantry arrays or movable robots or robot arms.. This includes 3D metal droplet printing of complex structures, such as those illustrated in models in Fig. Using multi-wire metal and alloy cluster 3D droplet printers shown conceptually in Fig. Wire feed systems implicit in Figs. Our analysis is that parts built by this technique have cost of production significantly lower than obtained by subtractive processes..
It is apparent that in addition to prospects for large-scale AM using wire feed technologies implicit in Figs. Such smaller-scale application would also benefit from lower precursor material costs and improved net shaping, as well as the elimination of material removal and recovery processes which currently limit powder bed fusion processes. Droplet printing implicit in Fig.
The authors declare no conflicts of interest.. Lawrence E. The holder of 5 patents, Dr. Wayne L. ATIG is a group of experienced technical leaders that initiate technical projects with significant impact potential on manufacturing systems. He has authored 65 patents, several papers and a book chapter..
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Article information. Show more Show less. Issues concerning process optimization, including product structure and properties affected by oxidation are discussed and some comparisons of related additive manufactured microstructures are presented. Droplet deposition. Unbound powder is recovered. HRC 37 noted for wrought material denotes annealed product. The image plane is parallel to the vertical specimen product plane. Droplet deposition on a substrate is shown in the context of contact or contact angle. From Murr .. In the two upper splat patterns, a portion of the drop rebounds.
The multiaxial, clustered droplet-emitter heads can be mounted on movable gantry arrays or movable robots or robot arms. Zhai, D. Lados, J.
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Chronology and current processes for freeform fabrication.
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