distance between neuron i and j (Chapter 11)SmaxSpreading ratioSmeasAmount of signal (Chapter 11)SØSource term corresponding to ØS (ϕ)Shape factorSSScan speedStrain rate deformation tensorΔ SExpansion of surface areatTime and/or laser interaction timet*Dimensionless timetc = tμViscous timetCDACorresponding penetration timetfSolidification timetIInertial‐capillary timetVViscous‐capillary timeTTemperatureTαReference temperatureTaveAverage temperatureTinFilament temperatureTgGlass transition temperatureToutOutlet temperatureTemperature of the liquefier wallTdDrying timeTeEquilibrium temperatureTlLiquidus temperatureTAmbient temperatureTmMaterials melting pointTpMaximum temperatureΔTUndercooling temperatureΔTtotTotal undercooling temperatureΔTCUndercooling temperature: solute diffusionΔTTUndercooling temperature: thermal diffusionΔTKUndercooling temperature: attachment kineticsΔTRUndercooling temperature: solid–liquid boundary curvatureTEMplGaussian–Laguerre transverse electromagnetic modesUBeam velocityUTravel velocity vectorUGlobal displacement vector (Chapter 10)UpParticle velocity vectorUsRate of solidificationvScanning speedvcCollision velocityυjJet velocityvpVelocity of the particlevprintVelocity of the print headVVolume of melt poolVDesign volume (Chapter 10)VaAcceleration voltageVSVolume of nucleusVEDThe energy enters the substrate from the surface in LPBFwTrack or melt pool widthwNeuron weight (Chapter 11)wiWeight factorWLaser pulse widthWeWeber numberXs + cWeight percent of element X in the total surface of the clad regionXcWeight percent of element X in the powder alloyXsWeight percent of element X in the substrateyDendrite arm spacing (Chapter 8)zDistance from the surfacezWaist location with respect to an arbitrary coordinate along the propagation axisZPrintability of a liquidZhHeat penetration depth
Greek Symbols
αThermal diffusivityαtCoefficient of thermal expansionβAbsorption factorβAbsorption factorβpPowder particles’ absorbed coefficientβwSubstrate laser power absorptivityγSurface tensionγNet electron beam energy (Chapter 5)γESpecific surface energyγSLSolid–liquid interfacial free energyγSVSolid–vapor interfacial energyγLVLiquid–vapor interfacial energyShear rateΓTorque of electrical motors in FDMΓSurface function (Chapter 10)δSolid/liquid interface thicknessδDirac delta function (Chapter 6)εTotal strainεcCooling rateεtEmissivityεMMechanical strainsεTThermal strainsεpEquivalent plastic stressεVacuum permittivityεmMechanical strainεthThermal strain∑Covariance matrixηDynamic viscosityηPowder catchment efficiency (wherever it refers to throughout chapters)ηNumerical damping coefficient for OCM (Chapter 10)ηLearning rate (Chapter 11)ηeAbsorption efficiency for electron beamηdDynamic viscosityηpPowder catchment efficiencyθRepresenting different angles based on figuresθWetting angle (Chapter 2)θFar‐field divergence angle (Chapter 3)θDimensionless temperature in numerical models (Chapter 7)θjetAngle between powder jet and substrateθdDynamic wetting angleθeqSteady‐state angleΘDimensionless temp in analytical modelsλWavelengthλLagrange multiplier (Chapter 10)λnRoots of zero‐order Bessel function of its first kindμViscosityμMembership function (Chapter 11)υFrequency (Chapter 3)υKinematic viscosityρDensityρbDensity of binderρpbPowder bed densityρcDensity of melted powder alloyρsDensity of substrate materialρsPacking density of the pores (Chapter 6)σStefan–Boltzmann constantσCovariance (Chapter 11)σcCharge densityσijElastic stressτThermal time constantτcDimensionless capillary timeϕDifferent label for angles as indicated in the associated figures ϕPowder bed porosityϕShape factorΦInterpolation function (Chapter 10)ϕ(x, y)Level‐set equationϕtapTapped porosityϕ(t)Rate of heat liberation in a continuous point sourceØAngle of incidenceΨStrain energyωSpinning speedωRelaxation factor (Chapter 11)ωiStrength of anisotropyωrAngular velocity of the actuating motorΩSubstrate surfaces or melt pool boundary and material domain
1 Additive Manufacturing Process Classification, Applications, Trends, Opportunities, and Challenges
Learning Objectives
At the end of this chapter, you will be able to:
Understand the standard definition of additive manufacturing (AM) and seven standard classes of AM processes
Gain basic knowledge on AM market size
Gain basic knowledge of opportunities, threats, and trends in the AM industry
Gain insight into applications of metal AM
1.1 Additive Manufacturing: A Long‐Term Game Changer
Additive manufacturing (AM), also known as 3D printing, is a layer‐by‐layer fabrication technology “poised to be one of the most valued forms of manufacturing in history” [1]. AM is becoming a major research target for industrialized countries as they seek to regain leadership in manufacturing through innovation. The global economy is on the verge of the next industrial revolution, known as “Industry 4.0”, i.e. the fourth industrial revolution. Sector after sector is pulling away from traditional/conventional methods of production in order to engage in and utilize AM. This fresh manufacturing method has garnered a great deal of public curiosity and international publicity. Every week brings news of novel and astounding AM innovations. This technology, which builds up objects by layers, has piqued the industrialized world's curiosity and imagination. This public interest was triggered around 2013–2014, as shown in Figure 1.1, in which the Google Trend suggests that a public interest in “3D Printing” has been increased more than 50‐fold from 2012 to 2016. The trend stays very much the same from 2017 to 2020, but it is the highest in Google Trend compared with counterpart advanced manufacturing technologies. This figure also sheds some light on the geographical distribution of the public interest. North America, Europe, and Australia are among the regions with the highest number of news and interests related to “3D printing” technologies.
distance between neuron i and j (Chapter 11)SmaxSpreading ratioSmeasAmount of signal (Chapter 11)SØSource term corresponding to ØS (ϕ)Shape factorSSScan speed