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Module 1: Additive Manufacturing Categories and Process Chain

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Process Chain for Additive Manufacturing of Plastics and Metals

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So, what are the material options that are associated with laser powder bed fusion? To startwith you have got many materials which are significantly in great use in aerospace sector,
like superalloys, including Inconel 625, 718, Haynes alloy, Hastelloy, Waspalloy. These areall the materials that are synonymous with applications in modules like high pressure, lowpressure turbines, combustors, nozzle guide vanes, pulse detonation engines.
So, all these materials which are known for their excellent creep characteristics, hightemperature performance are amenable to powder bed fusion. On the other side you can seethe ready availability of titanium alloy like, Ti-6-2-4-2 and Ti-64, which are not only famousfor the aerospace applications because of high specific strength and low cycle performance.They are also equally famous in case of the medical applications because of its biomedicalcompatibility.
You have got significant array of choices corresponding to steels starting from 17-4, 15-5,31-6L tool steels. and the materials which are more famously used in case of space structureslike aluminium alloys. The whole gamete of the waveguides, the communication modules aremade out of materials like ALSI10mg using the powder bed fusion. In the recent times,because of the maturity of the processes and the no how or no why.
Even the refractory materials have been handled through powder bed fusion, includingtungsten, tantalum and because of the proclivity of the automotive industry in the recenttimes to shift towards e vehicles, the processing of copper and copper alloys has become amatter of immense activity in the world of additive manufacturing. Because you can make theheat exchangers and you can make the parts with the conformal cooling channels, usingcopper.
In given volume the heat exchange of the highest orders are possible through processing ofcopper alloys, through powder bed fusion. It is been also seen that there are efforts to makeprocessing of bimetallic structures, multi-metallic structures possibility, using the process ofpowder bed fusion.(Refer Slide Time: 14:01)
In the initial phases the existing materials, materials which are very friendly to casting orwelding were made compatible, or were operated using powder bed fusion. Today, we arelooking at developing or adapting some of these are non friendly materials to welding andcasting to additive manufacturing. But in course of time, we are also seeing the emergence ofnew materials.
Because of the fact that we are able to design the parts for additive manufacturing, aphenomenon known as DfAM and when you design the parts for additive manufacturing itgoes without saying that you can also design certain alloys for additive manufacturing. So,this is one activity which is attracting the attention of research groups, globally. But for doingthese kinds of tasks, we need to clearly understand the interrelation among process, chemicalcomposition, microstructure, and the properties.
So, the alloy development to start with is targeted towards high performance applications,and I am sure this kind of alloy development will slowly infiltrated different sectors,including non strategic sectors.(Refer Slide Time: 15:36)
If you look at the process of powder bed fusion as I briefly mentioned, initially, you need tofocus on the data preparation. Then spend effort on the machine setup, then build the part inthe post processing phase significant amount of effort could be on the heat treatment andsurface engineering, and eventually the part is taken to testing and certification phase. So,that the end user gets the necessary confidence in substituting conventionally manufacturedpart, or re-engineered part, using additive manufacturing.(Refer Slide Time: 16:17)
One important phenomenon in case of powder bed fusion is about designing the supportstructures, like in other processes, such as stereolithography. These support structures worklike anchors. They provide the references for deposition of the new layers. In case of laserpowder bed fusion, they have got one more important function of taking care of the thermalgradients.
Actually, they drive away the heat from the layer to the substrate. In this way, the thermalgradient management is significantly impacted by the styling, as well as the build density ofthe support structures.(Refer Slide Time: 17:10)
Let us look at some of the possibilities in terms of the support configuration. What you see inthis case is a overhang feature that has been supported by a block support. This is one of thesimplest forms of the support structures in case of powder bed fusion.(Refer Slide Time: 17:28)
But the options of the support design provide even for incorporating perforations. What yousee on the right side is block supports with perforations per building of an aluminum part, and
in the middle of the slide you see block supports with perforation for making one stainlesspart.(Refer Slide Time: 17:53)
The implication of the support structures could also be understood by looking at one morepossibility. In this case the support structure is in the form of the frustum of a cone. Itimproves dissipation and the post processing effort, which is necessitated for removal of thiskind of cone kind of structures is much lesser than that of block supports.(Refer Slide Time: 18:25)
So, how exactly you define the support structures? How do you optimize? Let me pick up theexample of a part called upright. The part which is shown in this case is part of thesuspension system of a formula student Car. It is responsible for carrying the loads from thewheel hub, from the brake caliper. It is also connected to the wishbones.
In this case, the part with the envelops of almost like 180 mm by 90 mm by 50 mm has beenre-engineered to take advantage of powder bed fusion manufacturing, as a substitute forconventional manufacturing with concomitant benefits of weight reduction, withoutcompromising on the functionality.(Refer Slide Time: 19:19)
Now, if you were to orient the part in a completely horizontal condition. Look at the possibleincidences of support in the orientation 1, which is very natural option. In the orientation 3wherein the part is laid vertically, you can see the Z height going up tremendously highercompared to the orientation 1, Z height corresponds to a number of slices in the verticaldirection. The orientation 2, which is that a certain inclination to the build platform liesbetween the orientation 1 and 2 option.(Refer Slide Time: 20:00)
Now when you have got this kind of options, as support configurations, you would like toevaluate these options with reference to the Z height. The risk, which is associated, let us saywith recoating, the possible residual stresses, and more importantly you are building thesupports out of the same material as the actual part. So, you would like to keep an eye onsupport volume.
Last but not the least, the amount of time which is spent on the post processing issignificantly impacted by the kind of supports and the density of supports. So, when youdelineate all these options along all these possible vectors, you understand the compatibilityof one particular orientation, compared to the other orientations.(Refer Slide Time: 20:58)
All these things can also be taken up through simulation. So, we see in the industrial context,more and more user groups, integrating the build simulation as a part of the process chain.What happens when you integrate the simulation as a practice into the powder bed infusionis, you are able to predict, you are also able to preclude the potential build failures. Any failedattempt is going to significantly contribute to the cost of the final component.
So, what do you aim and do is try to look at all the possible part orientations? Look at thesupport generation possibilities, support type possibilities and do all these iterated studiessimulate and find out the specific option through which you are able to predict them properly,and you are also improve the buildability of the part.(Refer Slide Time: 22:03)
So, let us look at the specific case of building the upright. To start with that you import thedata in the form of the STL file, you position the part on the bill platform at a specificlocation, and at a specific orientation to the recoater.(Refer Slide Time: 22:20)
Then, depending upon your access to the data brochures supplied by the powder makers, youwould be in position of the information corresponding to the chemical composition,mechanical properties, thermal properties and flow characteristics. All these things can beused as the inputs for build simulation.(Refer Slide Time: 22:46)
In addition to this, you may have to feed in the values corresponding to the build parameters,could be layer thickness, could be hatch spacing could be laser powder. So, when you havegot control over all these parametric selections.(Refer Slide Time: 23:04)
Then what happens is you will be able to do the simulation of the build process, and be in aposition to identify possible de-laminations, surface deviations, excessive thermal gradients,and once you are able to get hold of all these estimations with a fair degree of conviction,then the realizability of the build gets tremendously enhanced.(Refer Slide Time: 23:35)
As I mentioned the post processing of the part is also an aspect which needs to be treated apriori. When you are talking about post processing it is not just a single operation. You aretalking about removing the unused powder or trapped powder. We are also referring to theheat treatment and relieving of the stresses and removing the part from the build platform.
Finally, you are talking about employment of several processes, machining processes andsurface treatment processes. These are all extremely you can say they are unavoidable whenyou're interested in translating the as-built part for end use application.(Refer Slide Time: 24:18)
So if you are talking about the powder removal. There are some industry grade modules foremploying optimal processes, and with reference to some of the well-known materials, theheating and cooling cycles are specified by the powder suppliers.(Refer Slide Time: 24:43)
The powder recovery using IPCM conveying module is one of the important things whichimproves the process economics. Depending upon the geometrical definition the unfusedpowder and the particles which are entrapped within the part, could be significant. Especiallywhen you are building the parts with internal channels, conformal cooling configurations, and
cavities, it becomes imperative that you make use of automated powder removal involvingvibration and rotation of the built plates and uses of the compressed air and inert gas forremoving the powder, and also for cleaning the part.(Refer Slide Time: 25:30)
As you developed more and more confidence on a particular part or a geometry you maywould like to introduce certain cutouts, certain provisions, in the part for facilitating thepowder removal in the ensuing post processing operations.(Refer Slide Time: 25:51)
So, the design considerations are required with reference to post processing and this designconsiderations may have to be treated right in the early stages of the process chain. So, in thisspecific case perforations are integrated into the block supports for removal or for facilitatingthe removal of the trap part and especial when you are making use of lattice structure and
honey comb like structures. It becomes very important to understand what are the accesspoints and what are the possibilities of removing this powder.(Refer Slide Time: 26:29)
In such a way the parts remain clean after the post processing is completed. Now, I alsobriefly made a mention of the removing of the part from the build platform. So, it mayinvolve the manual cutting with this ubiquitous hack saw blade, or you may would like to usewires are EDM aided by coolant or band saw cutting. So, what are the allowances that youneed to account for while you are doing the build plan?
It depends on the material. It depends on the exposure area and it also to some extent dependson the dimensions of the build platform. As you can see here in this case, we have analyzedthe allowances which are required for the part separation for Titanium and Aluminum somesteels with reference to different exposure areas, and with reference to different build plateconsiderations.(Refer Slide Time: 27:26)
When it comes to post processing the ferrous alloys may require a specific treatmentconsisting of annealing, tempering, hardening, normalizing, and case hardening and in case ofnon ferrous alloys, you may employ annealing and solution treatment, through proper heattreatment, you can achieve significant improvements in tensile properties, yield properties, tosome extent in the elastic modulus and hardness.
So, you could develop these kinds of functional insights into the materials, and depending onthat the users of the powder bed fusion can specify the solution treatment and aging treatmentcorresponding to a specific material on a specific system.(Refer Slide Time: 28:20)
Now when it comes to surface treatment there are several possibilities, including highlyaffordable shot peening and tumbling and polishing or when you have to deal with high
quality surface finishes that you encounter in case of an aerofoil of a compressor blade. Youcan even employ abrasive flow machining electrochemical polishing and slightly expensivemicro machining processes for converting relatively coarse surfaces into acceptable surfacequality situation.(Refer Slide Time: 29:00)
So, you can see here in this case, a turbine blade made out of IN625, what you see in thebottom is the duotail zone, which are responsible for connecting this blade to the turbinedisk?(Refer Slide Time: 29:20)
So, in this case, the whole planning with reference to fixturing was done right in the initialstage of the process development. So, that the thin cross sections corresponding to the bladeprofile are held properly without causing any damage to the aerofoil portion, while you are
doing the machining of the duotail portion. So, the thin platform as well as the thin aerofoilsections were very carefully handled, while ensuring that the duotail that has got impressionscreated due to the surface removal is finished using substantial post processing effort.(Refer Slide Time: 30:03)
In this case you see an aero engine nozzle guide vain assembly with a diameter of almost like540 mm, where in the post processing related planning it as significant as the part building,because in this case each sector, consisting of 3 nozzle guide vanes, was made as a singlepart, 9 of these sectors were assembled together. They were subjected to machining, and aVMC, and the post processing stays.
The importance of this particular operation is the airfoils that control the flow of hot gases onthis are sacrosanct with reference to the operation efficiency of the nozzle gate vanes, at thesame time these modules operate at very high pressures and temperatures, and it goes withoutsaying that the residual stress management while doing the part building is extremely crucialto the integrity of the part.(Refer Slide Time: 31:21)
It is important to note and appreciate that not all the features are compatible to powder bedfusion. In this case of pedicle screw an implant for animal applications, made out of Ti64, thepart you can see as built heat-treated part on the left side. As you can see, the pedicle screwportion which has been mentioned, which has been realized through post processing on theright side.
So, in this case, the extent of additive manufacturing was decided in such a way that you areable to take advantage of conventional manufacturing, while ensuring the compatibility of thepedicle screw to the intended application.(Refer Slide Time: 32:13)
One more very popular application of powder bed fusion is with reference to the developmentof the injection tools with the conformal cooling channels. In one of the case studies
published by a tool manufacturing company based out of Hyderabad in 2016. You can see theinjection tooling, corresponding to realization of the spray caps, has been reconfigured usingthe conformal cooling design approach, and powder bed fusion.
In this case is the surface finish within the cavity becomes paramount in ensuring the heattransfer characteristics.(Refer Slide Time: 33:08)
So, the post processing of different types and different possibilities, need to be consideredwhile ensuring the application of the part in the intended context. You can see in this case, atitanium 64 part processed through various options, including abrasive blasting, vibratoryfinishing, short peening, super finishing and electro polishing and chemical polishing in acompetitive study carried out by Fraunhofer.
Depending upon the intended application, depending upon the intended surface quality thepost processing, could be chosen and integrated into the entire process of powder bed fusion.(Refer Slide Time: 33:59)
As I mentioned, in this case of upright, which is the part of the formula student Car. The,original configuration has been re-imagined in such a way that you are able to cut down theweight without compromising the structural requirements or commitments, or requirementsto meet the performance characteristics of the suspension system. So, in this case some of thefeatures were re-engineered to suit the design for additive manufacturing approach.
Needless to mention, once you start reimagining the designs, you need to go through theengineering simulation to understand how exactly the part is going to deform or function,under the expected operating loading conditions and once you gain confidence on thesuitability of modified part to meet the functional requirements, then you look at theconfiguration, corresponding to suitability for powder bed fusion.
Once this aspect is ensured, then you build the part, do the necessary post processing and
quickly inducted into the test bed, understand the performance possibilities with this re-engineered part and after necessary testing and qualification, you induct the part into the final
system of relevance.(Refer Slide Time: 35:43)
So, to be able to do this kind of additive engineering approach the departments which areconnected with additive manufacturing need to develop different sets of proficiencies. On oneside, you are talking about running the system, which is the build technology, on other sideyou're talking about reengineering the parts, reimagining the designs and ensuring that theyperform with reference to envisioned operating loading conditions.
So, these specific instances demand enough insight, and proficiency in the simulationpractices. There are occasions you are developing the material specific to the application. So,material related research becomes an integral piece and the post processing, as I haveillustrated is an extremely important consideration, with reference to controlling the costs ofproduction in additive manufacturing and also for ensuring the thermo mechanicalcharacteristics on par with the expectation.
So, all the post processing related considerations, need to be accounted for, right in thebeginning of the process development and last but not the least, having realized the part, it isimperative that you need to prove out the part for its performance with reference to envisagedloading conditions.
So, testing of the part validation of the performance and certification of the part are alsoextremely important when you are talking about strategy applications with additivemanufactured parts.(Refer Slide Time: 37:35)
So, if you look at the parameters that need to be controlled and that can also have significantimpact on the part quality. They could be mission related or they could be metal part related.For example, the powder can have certain flowability characteristics. The particles may havecertain PSD values, that is particle size distribution values, the morphology of the samematerial coming from one source, compared to the other sources could be different.
So, all these things need to be taken care and within the production, you may be usingspecific support style, some specific type of recoater. You might be developing the processwindow corresponding to the material, and the orientation of the part. The extent of packingcould be dependent on the space. So, all these things need to be accounted for and veryimportantly, even the input data need not have to come always in the classic CAD modelform.
You may simply have an access to a physical part which needs to be replicated or you mayalso be required to look at the existing design and redesign in such a way that you can takeadvantage of the additive manufacturing. So, even the input data becomes very important.The final considerations are with reference to the post processing and quality inspection.(Refer Slide Time: 39:23)
So, to account for some of these variables standardization roadmaps for additivemanufacturing are getting developed. This roadmap defines the topic areas forstandardization in basic groups like design, processes and materials, qualification andcertification, non destructive evaluation, and finally connected with maintenance and report.(Refer Slide Time: 39:49)
It is very relevant to talk about these standards corresponding to these processes. There arestandards, released by ISO ASTM just with reference to the general principles of additivemanufacturing and the terminology, which is associated with this technology. If you aredoing the dimensioning and tolerancing of the AM parts there are certain standards, releasedby ASTM that can be compliant with.
With the maturity coming in the standards are also getting delivered specific to the process.For example, if you are talking about laser powder bed fusion based processing of polymersand metallic materials, they award the relevant standards and sometimes the standards couldbe specific to the material. For example, if you are talking about processing of nickel alloysyou have a standard released by AMS wide AMS 7001.
Currently, we are not talking about standards which are being relevant only to the aerospaceand defense applications, we are talking about offshore standards.(Refer Slide Time: 41:10)
The standards released by DNBGL talks about how do you make the part out of additivemanufacturing process of powder bed fusion and how do you ensure that they can be used inthe context of oil and gas industry, through proper testing? So, the standards of this kind aregoing to play a significant role in ensuring the industrialization and widespread use ofadditive manufactured parts.(Refer Slide Time: 41:40)
Let me go to the other process of vat polymerization synonymous with the processing ofphotosensitive polymers. In this case, you have got a UV laser beam, working onphotosensitive or photocurable resins, the resin has got photoinitiators and premixedproportions of hardener, as the laser beam is scanning on the surface of the photopolymer.There is instantaneous solidification and very similar to powder bed fusion after a specificlayer is cured.
The build platform moves down by an extent, equivalent to the layer thickness. Typically, itcould be 50 to 100 microns. You have got a pair of galvanometric scanning mirrors that areresponsible for a movement of the laser beam in the x axis and y axis, and you have got aperforated the build platform, through which the polymer material flows for making thecurrent layer, and similar to the quarter, in case of a powder bed fusion.
You have got a sweeper, or a Z fire controller in stereolithography system. The process hasgot 5 or 6 discernible phases, starting from input data to correcting the STL files to planningthe build to part building to the post curing and finally, part finishing before you take thestereolithography part.(Refer Slide Time: 43:31)
and start using for intended application in the context of industrial users. So, what happens incase of stereolithography is part building is captured in the slide. You can see here, a crosssection, corresponding to a steering wheel of a car. So, the liquid material, photosensitivematerial is residing on the perforated build platform and on exposure to the UV layer or laserit is instantaneously solidified.
The tracing of the layer with reference to the infields and with reference to the externalperiphery follows a distinct pattern.(Refer Slide Time: 44:24)
So, this slide shows the snapshots, taken from industry grade stereolithography systems. Thetypical build sizes can range anywhere between 100 mm by 100 mm by 100 mm to about halfa meter by half a meter by half a meter for making large sized parts.
(Refer Slide Time: 44:43)
In this slide you can see the support structures for overhand features of the part which isgetting built on in a stereolithography system. Incidentally, this part happens to be thehousing of a combustor or combustor casing and what you are looking at is sectoral modulesof the combustor housing; and you can see the distinct support structures for ensuring nonsagging of the overhanging geometrical features.(Refer Slide Time: 45:27)
The materials in case of industry grade stereolithography systems could consist of epoxybased, acrylate-based resins or you have got specific materials for high temperatureapplications with the necessary moisture assistance for scenario connected with the castings,you have got biocompatible materials, specific to the flow visualization studies. There arematerial options which are extremely translucent.
One of the important applications of stereolithography is with reference to jewelry patternsand anatomical modeling, in case of health sector. So, these applications demand highaccuracy very high levels of surface fidelity and detailing.(Refer Slide Time: 46:29)
These are all imminently enabled, because of proper selection of materials. Typically, thewall thickness, depending upon the overall part size could be between 1 to 3 mm. Most of thepreprocessing software prompts for hollowing of thick parts, because of the fact that it allowsdraining of the excessive resin. It also reduces the shrinkages which are connected with theface transformation.
It is also possible to impose the features to a depth of 0.5 mm and post processing typically isdone using processes like sandblasting, shot peening, tumbling. You can also doimpregnation and spray painting to improve the overall aesthetics of the stereolithographyparts.(Refer Slide Time: 47:19)
The applications of stereolithography part are wide ranging, starting from stress analysis toflow visualization to structural parts where in the mechanical loadings are not significant towind tunnel applications to design communication models as you can see in the next slide.(Refer Slide Time: 47:40)
This is the gearbox housing of an aircraft. The original part is made through investmentcasting out of aerospace Aluminum alloy or Magnesium alloy. The part which hasdimensions of about 700 mm by 500 by about 450 mm could take close to 18 months forrealization. In this specific case the part was made out of acrylate resin-based photopolymerusing stereolithography within a week of the CAD model or design being frozen.
So, this greatest utility associated with this specific application is for about 17 to 18 months.This full-scale model of gearbox housing was used as a design communication model.
The user groups connected with upstream activities and downstream activities were able toconnect seamlessly because of the availability of the part and many times, the principles of