CRITICAL EVALUATION OF ELECTRON BEAM AND LASER BASED POWDER BED ADDITIVE LAYER MANUFACTURING TECHNOLOGIES By Name

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CRITICALEVALUATION OF ELECTRON BEAM AND LASER BASED POWDER BED ADDITIVE LAYERMANUFACTURING TECHNOLOGIES

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Abstract

Manufactureshave been trying to come up with ways to increase the quality oftheir products while at the same time reducing their workload.Additive manufacturing is one such way that they came up with.Additive manufacturing is a high precision manufacturing process thatdeletes the need for use of tools, thus reducing the manufacturingtime. It produces strong metallic parts by stacking up layers ofmaterials together. This technology proved to be quite useful in thefield of mechanical engineering. It sparked particular interest inthe marine, automobile, oil &amp gas and aerospace industries. Inpowder bed fusion technology, lasers, and electron in the fusionprocess to produce reliable metallic parts. This material takes acritical look at this technology in some of its aspects, with anadditional comparison on the electron and laser beam technologies. Itwill base on the characteristics, applications, advantages anddisadvantages.

Additivemanufacturing makes use of the 3D data manufacturing technologythrough the use of a layering process (Gibson,Rosen &amp Stucker 2014).This manufacturing method has reduced the production workload,shortened the production time, reduced energy usage and improved ondesign flexibility. It has been able to find its application indirect part production, rapid prototyping, and rapid tooling. It alsofinds usage in fixing of metallic, ceramic and plastic materials. Theproduction focus is currently shifting to direct part production dueto the new technological changes (Baumers,Dickens, Tuck &amp Hague 2016).

Thisprocess has two main requirements that make its operation viable. Itrequires a source of energy and source of raw material. The source ofenergy applied here is the electron or laser beam. The raw materialsused can be wires or metal powder. Computers are then used to design(through the use of Computer Aided Design) models of the requiredparts and shape them to the specifications stated. Once this is donethe additive manufacturing process takes over, building up the partslayer by layer according to the specifications given by the computer.The AM process and type of raw material used will determine thethickness of the layers. The layering technology gives the materialsproduced a stair-like characteristic. As stated earlier, this paperstakes a look at the electron and laser beam applications in thepowder bed fusion technologies (Prabhakar,Sames, Dehoff &amp Babu 2015).

Energy source (laser or electron beam)

(PBF)Powder Bed Fusion Additive Manufacturing

Inert gas or vacuum environment

Powder

Roller

Part

Build chamber

Powder chamber

Inthe diagram above, the vacuum shields the molten metal. The electronor laser beam is used to scan and melt the material with precisionaccording to the specifications from the computer designed model.When a scan of a layer is complete, the piston in the build chambergoes down while that of the powder chamber goes up in relation to thethickness of the scan. This process goes on repeatedly in layersuntil a completed material is formed. The build chamber can buildseveral parts at once thus maximizing its use and reduces theproduction time. To avoid distortion, prevent overhanging surfacesand dissipate heat, support is added during the pre-processing stage.This support will again be removed when the processing is done afterwhich there will be heat treatment, shot peening, and polishing(Prabhakar, Sames, Dehoff &amp Babu 2015).Laser and electron beam technologies are sources of energy mostlyused by Powder Based Fusion manufacturing as briefly explained below:

LaserBeam Based Systems

Inthe laser beam system, a laser beam is used to melt layers in aclosed chamber for the PBF process(Gu 2015).This process was an achievement done by Carl Deckard in 1986. DTMCorporation was able to commercialize it in 1992. 1995 saw the adventof the EOSINT M250, which was the pioneer commercialized metalsintering machine. SLM (Selective Laser Melting) is an improved formof the SLS (Selective Laser Sintering) process. SLM involves the useof lasers to completely melt or fuse the powder bed particles. Thistechnology was introduced by Schwarze and Fockele in collaborationwith the Fraunhofer Institute. MCP HEK was able to commercialize itin 2004 .

Thesesystems use a fiber laser of between 200 – 1KW in the selectivefusion process of the powder bed layers. Nitrogen gas is used in caseof non – reactive materials while argon is used for reactivematerials in the build chamber. The processing parameters aredictated by the speed, hatch distance of the laser tracks, thicknessof the layers and the power of the laser. This process is able toproduce dense metal alloys such as aluminium alloys, titanium alloys,tool steels, and stainless steels (Kranz,Herzog &amp Emmelmann 2015).The SLM system has its limitations in the build size and build rate.The maximum size of layer it can build is about 250 by 250 by 325mm3.Its build rate is about 4-20cm3/h4. These limitations confine it tothe production of small parts. However, advancements in research andtechnology are trying to improve on the capabilities of this systemin terms of build rate and build size. In 2012, for instance, aGerman corporation came up with a system that makes use of a doublebeam technology that increased the maximum build size to 500 by 350by 300mm3 and the rate to about 35cm3/hr. This system enables fourlasers to make simultaneous scans of the powder layers. In 2013, theGermans produced the EOSINT M400 machine that has increased buildrate due to its 1KW powered laser and a build capacity of 400 by 400by 400 mm3.

ElectronBeam Based Systems

Inthe electron beam system, an electron ray melts the layers in aclosed vacuum chamber for the PBF process. The process wascommercialized in 1997 by a Sweden Corporation, ARCAM. It is similarin character to the laser beam system, its only difference being theuse of the electron beam as the name suggests. Here electrons areproduced at a high speed by a tungsten filament. The electron beamsare then directed by two deflection coils, magnetic fields, and focuscoils. The focus coil is used to produce the required diameter whilethe deflection coil helps direct the beam to the specified point forscanning. When the electron beam collides with the powder bed,thermal energy is generated, thus melting the powder. The scanningprocess is done in two stages which are the preheating and meltingstages. The former stage is a fast scan stage with a strong beam thatpreheats the powder layer. The later melting stage is a slow pacedscan stage where a weak beam melts the powder layer. This process isrepeatedly done in layers until the required material is produced(Manfredi, Calignano, Krishnan, Canali, Ambrosio, Biamino, Ugues,Pavese &amp Fino 2014).This entire process takes place in a vacuum. Helium gas is added tohelp lower the vacuum pressure thus allowing cooling and makes thematerial more stable. Sweden’s (ARCAM) electron beam system usesstrong beams of about 3000W for the melting process. Its processingparameters are dictated by the layer thickness, pre-heatingtemperature focus diameter and strength of the electron beam. Itfinds its use in the manufacture of cobalt chrome, titaniumaluminide, and titanium alloys (Vayre,Vignat &ampVilleneuve 2013).The figure below shows the steps followed in electron beamprocessing:

Build plate heating

Powder spreading

Powder pre-heating scan

Powder melting scan

Build table lowering

Repeat process till part completion

Comparingthe SLM and the EBM based systems

  1. In terms of build rate, the electron beam melting system is higher than that of the selective laser melting system.

  2. The EBM Materials have poor surface and dimensional qualities compared to the SLM – based system.

  3. Both processes are affected by residual stress due to the constant heating and cooling of the powder layers.

  4. The EBM system requires little support during processing (support is also used in the conduction of heat), thus increasing the manufacturing capacity as compared to the SLM.

  5. The parts produced by the SLM system have a higher oxygen content compared to those produced by the EBM systems.

  6. The cost of production of materials by the SLM systems is higher than that of the EBM system. This is due to its low accuracy and high cost of the necessary machines.

Thetable below gives a summary of the comparison:

EBM

SLM

Power source

Uses electron beam – 3000W

Uses fiber lasers – 200 to 1000W

Build rate

80

20-35

Pre-heating mode

Pre-heat scanning

Platform heating

Melt pool size (mm)

0.2 – 1.2

0.1 – 0.5

Maximum build volume (mm)

350 by 380

500 by 350 by 300

Build chamber environment

Vacuum/He bleed

Argon or Nitrogen

Minimum feature size

100

40 – 200

Advantagesand Employment of the Metal Additive Manufacturing Process

TheAM process sparked a lot of interest in the vehicle manufacturing,oil &amp gas, and aviation industries due to the many advantagesthat it offers. A good example is how it has been able to reduce theproduction cost of materials in the aerospace industry (VanDijk 2015).The initial conventional process had a purchase to fly ratio of 20:1.With the implementation of the AM process, the ratio drasticallyreduced to about 1:1. AM can carry out complex manufacturingprocesses while at the same time allowing for design freedom. Thissystem allows aerospace engineers to design and produce strongmaterials that are also light enough to fly around in the air. Thesematerials also have good thermal and energy absorption properties.Such qualities allow for heat dissipation which is a common factor inthe computer, automobile and aerospace industries (Huang,Riddle, Graziano, Warren, Das, Nimbalkar, Cresko, &amp Masanet2016).

Theconventional manufacturing process can involve a lot of additionalinput such as rolling, welding, casting, and drilling which take alot of time and manpower, thereby increasing the production time andcost. The AM system, on the other hand, is a tool less process thateliminates the need for such kinds of input. It drastically reducesthe production process in terms of time and cost. The assemblyrequirement of materials is also reduced through integration method.A good example of this is where the Oak Ridge National Lab was ableto integrate a robot base accumulator and hydraulic reservoir to forma light, but, strong underwater robotic system structure. AM enablescustomization of parts for quality production.

and Conclusion

Anumber of achievements have been realized through the implementationof the PBM AM technology, however, a lot of work still needs to bedone to improve on efficiency, process control, accuracy andproduction speed. For improved consistency and reliability, closedloop control systems should be utilized, and the in-process qualitymonitored. Monitoring the in-processing quality can help increase themanufacturing speed while at the same time reducing the raw materialinput. A reduction in assembly requirements and increased build ratecan help lower the production cost and increase its application ofthe AM process.

References

Baumers,M., Dickens, P., Tuck, C. and Hague, R., 2016. The cost of additivemanufacturing: machine productivity, economies of scale andtechnology-push.&nbspTechnologicalforecasting and social change,&nbsp102,pp.193-201.

Gibson,I., Rosen, D. and Stucker, B., 2014.&nbspAdditivemanufacturing technologies: 3D printing, rapid prototyping, anddirect digital manufacturing.Springer.

Gu,D., 2015.&nbspLaseradditive manufacturing of high-performance materials.Springer.

Huang,R., Riddle, M., Graziano, D., Warren, J., Das, S., Nimbalkar, S.,Cresko, J. and Masanet, E., 2016. Energy and emissions savingpotential of additive manufacturing: the case of lightweight aircraftcomponents.&nbspJournalof Cleaner Production,&nbsp135,pp.1559-1570.

Kranz,J., Herzog, D. and Emmelmann, C., 2015. Design guidelines for laseradditive manufacturing of lightweight structures in TiAl6V4.&nbspJournalof Laser Applications,&nbsp27(S1),p.S14001.

Manfredi,D., Calignano, F., Krishnan, M., Canali, R., Ambrosio, E.P., Biamino,S., Ugues, D., Pavese, M. and Fino, P., 2014. Additive manufacturingof al alloys and aluminium matrix composites (AMCs).&nbspLightMetal Alloys Applications,&nbsp11,pp.3-34.

Morgan,J.A. and Prentiss, J.M., 2014.&nbspAnanalysis of item identification for additive manufacturing (3-Dprinting) within the Naval supply chain&nbsp(Doctoraldissertation, Monterey, California: Naval Postgraduate School).

Prabhakar,P., Sames, W.J., Dehoff, R. and Babu, S.S., 2015. Computationalmodeling of residual stress formation during the electron beammelting process for Inconel 718.&nbspAdditiveManufacturing,&nbsp7,pp.83-91.

VanDijk, Y., 2015.&nbspAdditiveManufacturing: Will it be a potential game changer for the aerospacemanufacturing industry? A qualitative study of technologyadoption&nbsp(Doctoraldissertation, Master Thesis, Eindhoven University of Technology).

Vayre,B., Vignat, F. and Villeneuve, F., 2013. Identification on somedesign key parameters for additive manufacturing: application onelectron beam melting.&nbspProcediaCIRP,&nbsp7,pp.264-269.

Abbreviations

EBM– Electron Beam Manufacturing

SLM– Selective Laser Manufacturing

AM– Additive Manufacturing

PBF– Powder Bed Fusion