Design for Laser Powder Bed Fusion (LPBF)
Hello everyone, on behalf of advice Wipro 3D IIT Madras NPTEL I welcome all of you tothe course on the role of additive manufacturing in the future of manufacturing business.Today we will be talking about the economic significance of the design guidelines for laserpowder bed fusion process. We will also be discussing about the various opportunities forvalue addition through laser powder bed fusion process.
I am Krishna Kashyap Singh and I am an application engineer at Wipro 3D. I have certainexpertise in the process. I will be taking you to the various design requirements or the variousdesign modifications which will be required in order to make the part amenable to theprocess.(Refer Slide Time: 01:00)
All of us are very well aware that additive manufacturing offers a wide variety of designfreedom because of the nature of the process, since it is a layer by layer phenomena. It is afree form fabrication process and there is no tool required to make the components frompowder. Today laser powder bed fusion process has been the most preferred choice for mostof the industry users across the globe for additive manufacturing of materials all over.
So, this session will focus on laser powder bed fusion and the value addition that can be doneusing laser powder bed fusion process. The value addition can range from masscustomization of a single component to light weighting in serious production or low batchproduction or making components lightweight components and high-performancecomponents for rocket engines or to make satellite components to perform in cryogenicconditions.
But at the same time, we also need to pay attention to the limitations of the process, becausethe limitations of the process will create challenges in manufacturing the component as wellas it will add an extra cost to the production. So, we need to develop certain designconsiderations which will help us in eliminating those challenges and limitations.(Refer Slide Time: 02:26)
Design for excellence DfX. DfX is a very conventional strategy which has been adopted tooptimize a product along with the production system to reduce development time and costand also enhance the performance quality and profitability. Design for manufacturing hastypically meant that designers should tailor their designs to eliminate manufacturingdifficulties and minimize the cost of production.
However, with improvement of rapid prototyping or AM technologies we have been providedwith opportunities to rethink design for manufacturing and take advantages of the uniquecapabilities ordered by additive manufacturing. Hence, in this module they will focus on thedesign guidelines for LPBF which are based on the limitations of the process and also the
opportunities where we can add value to the end application or the component or the productby improving the design using complex geometry and hence achieving an enhancedperformance.
For the rest of the session we will stick to the terminology as designed for LPBF because theprocess that is under study and under discussion is LPBF which is only used for metals.(Refer Slide Time: 03:45)
Designed for excellence encompasses four major verticals. One of them being designed andall four of them are interdependent with each other, none of them can be thought of anisolation and if they are thought in isolation they will not result in the optimized productionof the component. Therefore, it is very much required that we understand the aspect of eachand every of these verticals. So, for this I will get here with an example.
This is an RF antenna of a satellite communication module, basically what is happening inthis RF antenna that there is RF signal which is fed here, there is RF signal which is fed hereand these are mounting points which are used for mounting the component and then thesignal is transmitted using this helical structure. Now in this component the helical structuralprofile accuracy is very important.
And also, since this component will be used in a space communication satellite, we want toknow that what are the working conditions? Therefore, it will help me in deciding thematerial. So, depending on the working conditions the working environment, what are the
static and dynamic loading that is going to work on this component? What is the stiffnessrequired for this component?
What is the factor of safety? What is the margin structural margin that we want thecomponent to have? All these parameters will be decided based on the end application andalso at the same time these parameters have to be converted into reality using amanufacturing process. So, the manufacturing process has to be taken into consideration aswell.
Now suppose your application demands a prismatic geometry from you, then you will choosea suitable manufacturing process for producing prismatic geometries, but if your applicationis requiring a free from geometry from you then you have to go for a process which willallow you to produce flawless free from geometries. Similar way if you have a requirement ofproducing cavities or internal channels.
Then you need to go through a process which will allow you to produce these features withminimum effort. Hence design and manufacturing cannot be looked at isolation. They bothare interrelated to each other. Your design will govern the selection of a manufacturingprocess and your selection of manufacturing process will in turn govern the design of certainfeatures.(Refer Slide Time: 06:29)
Assembly is another important factor which has to be considered in a well-planned mannerduring the design methodology, because as all of us know that design for manufacturing and
assembly is a disciplined methodology which recognizes that 70 to 80% of a product's lifecycle are actually determined in the design phase. So, the cost and time of assembly can beoptimized if proper attention to assembly is being given in the design phase itself.
In case of LPBF, it plays a little bit more important role since there are certain features orcertain limitations of the process which does not allow a LPBF feature or LPBF surface to bewell suitable for an assembly purpose. Hence in any module we need to identify well inadvance during the design phase itself that; what are going to be the assembly points?
What is exactly going to be the assembly mechanism? Whether it is going to be a boltingmechanism? It is going to be a mating mechanism or it is going to be a slight fit, press fit?Based on these assembly requirements we need to provide certain tolerances for thesefeatures and then we need to decide whether those tolerances will be met by as built conditionor in 3D printed condition or if not, then a different post processing strategy has to be devisedfor that particular component.
In this case as you can see, this is a component of an aerospace engine from a very majoraerospace Indian company and this particular component was made through AM, but therewere certain features which were produced in 3D printing with stock and then later on theywere machined. Why?, because there was a requirement of the component to be mating intothe assembly.
In order to that all the mating features have been machined properly or not there was a fixturewhich was used. The fixture had similar mating tolerances as compared to the originalassembly conditions. Therefore, we were able to evaluate each and every point wheremachining is required. We added stock there and later on we machined them together. So,these are 9 different pieces which were individually built.
Then they were pros process machined, after post processing machining they were again puton a fixture and during in assembly condition they were turned together. So, this particularstrategy the series of operation that was decided in the design phases itself. Since we gaveenough considerations to the assembly conditions in the design fed itself, we had to gothrough the minimum possible amount of rework.
Hence rework can be optimized if we are giving enough considerations to assembly in thedesign phase. Now I would like to I have the similar sector what you can see in the slide Ihave a similar sector of the component, you can see this was the component that was melt,something like this was the building orientation and you can see the surface roughness, youcan see the surface finish where we have the as built surface.
Now if you want to use this surface as a mating surface that would not be possible because itis not within the geometric or profile tolerance which is required for the mating surface hencewhat we did we machined these surfaces; you can see the surfaces have been grinded. Nowthis grinding has been done for the purpose of machining. There are another set of holeswhich have been produced with stock.
Now they will be again hold because there is a requirement of 0.1 mm clearance which wethought would be better if we achieved through machining. Since we were already machiningthis particular surface. So, this is how in the design phase itself we have to take care ofmachining because when we are trying to do the machining and match the tolerance requiredas this surface, we want to have the extra material to machine out.
Therefore, machining allowance has to be given in the design phase itself. That is why yousaw the manufacturing technique, the assembly both are very well required when I want tocreate the right cad data to produce in 3D printing.(Refer Slide Time: 11:15)
Another example of assembly consideration in the design phase. This is a turbine assemblyfor an anti-icing aerospace engine, another for an Indian major and in this component a fewcomponents are made through conventional manufacturing, sheet metal fabrication and fewcomponents, the critical components the aerofoil surfaces, the nozzle which has internalcooling channels.
All these things were made through additive manufacturing, but at the same time there was astrategy which was devised in order to reduce the rework when we are going to assemble theadditive manufacturing components and the sheet metal components and the conventionalmanufactured machine components. So, a good strategy will help in reducing the number ofjoints.
If we reduce the number of joints that means we are reducing the number of componentsgoing into the assembly which will help in reducing the assembly time and assembly cost andat the same time if we can give some consideration to assembling 2 or 3 parts which we canjoin together and produce as a consolidated design then that is an icing to the cake.(Refer Slide Time: 12:32)
Now techniques we are going to use and to all the requirements of the manufacturingtechnique and the assembly technique. Now it is time to think about inspecting and validatingyour device design once it has been produced. Now in order to validate a design there aredifferent types of techniques depending on the type of design you want to validate. Forexample, if you want to validate a design where you just have to measure the PCD.
Then you can go with a probing CMM where you can measure the center points of all theholes and you can conclude the PCD. Then now imagine you have to scan; you have toinspect something like this. This spiral surface, now it will be very difficult to scan this spiralsurface using a CMM probe or using conventional methods like screw gauges, pin gaugesand all these things.
Therefore, the best way is to use a 3D scanner. So, what you see in the image right now is afaro arm which is integrated with a probing unit as well as a red-light laser unit. Now whatthis laser in it does that? For free form surfaces it replicates the surface and creates cloudpoint data on the screen of the connected computer and for regular surfaces, for geometricsurfaces we can take point measurements using the probe unit. So, this type of unit or in somecases.
For example, there are certain features which are not at all accessible. In this example wherewe are talking about this component, now why this component was made in AM? That is thequestion. So, I would like to answer that for you. Can you see the thin features here?. So,these are the internal features which we got after taking a cross section of this component.
Now this feature is something which I need to validate which has got a critical functionbecause it is allowing the passage of air flow for cooling the turbine blades. So, what wouldbe the methodology by which I can check this? We tried we thought of doing a CMM, wethought of doing x-ray inspection or CT scan in order to get the profile of this inner cavity butthis profile was not well captured by a CT scan that was the input given by the quality person.
So, what was the methodology device there we built a component a trial component only todo the destructive testing. We bisected the component and then now we could easily see whatis the continuity of the hollow profile. Whether it has been blocked by powder? Whether ithas been sintered or not? Whether we are able to maintain the minimum gap in the profile orin the cavity channels that we want to maintain? So, this is that section you can see.
So, these are different type of techniques that needs to be employed. Because you want tocheck your design what you have made? A design again I would like to repeat the same thing,a design that cannot be validated is not a good design.(Refer Slide Time: 16:01)
So, the extent of value addition depends on the level of adoption of AM, the four-tier modelshown here demonstrates the value which is being added at each level of the tier. So, rightnow we will focus on the prototyping and tooling level and we will see that which kind ofcomponents are the right candidate for prototyping and tooling application and why do oneneed to go for additive manufacturing when it comes to prototyping and tooling?
First let us talk about the prototype. So, what you see here, this is a cylinder head, this is acylinder head of a two-wheeler automotive, by these fins, you can feel or you can be you arevery familiar of this fin, they are put for cooling of your engine. So, most of you would haveseen such a component in any two-wheeler engine. Now this component is being made at aprototyping level.
So, what does it tell me about the quantity of the production? That it is a low volumecomponent and these components if we go for AM they can be made directly from CADeither in near net shape configuration or in net shape configuration. When I say near netshape configuration that means you are adding some allowance and then machining. So, thebasic point here is why does one would want to go for additive manufacturing for prototypingis; it is a free-form application.
It is free from fabrication, it is a tool less production, you do not need to invest any certainamount in tooling, hence you are not bounded by the minimum number for production. So,my design iteration basically my prototyping is enabling me to make my design iteration
more cost effective and it is also at the same time giving me an advantage to reduce the totaltime involved in the prove out duration.
So, that was the word prototyping. Now, tooling is a way to take advantage of indirectadvantage of any AM process. Your end application component will not be made throughAM, but the tools that you are going to use for manufacturing your end applicationcomponents, those tools will be made through AM. Now what is the advantage of makingthose tools through AM.
The basic advantage of making these tools through AM is that they are providing me a certainamount of design freedom to make my conformal cooling channels. So, this tool that you seehere it is a tool made for injection molding process. Now in injection molding process thecomponent that is being made is usually of plastic. In this particular plastic component, whichis being made if the cycle period of the component is 10 seconds.
Then 7.5 seconds nearly 75% of the total cycle time is dictated by the cooling cycle, thatmeans if you are able to cool your components faster you are able to do produce morenumber of components in the same amount of time. So, this is one economic benefit of usingAM and how AM is facilitating this benefit is? If we are able to make very complex coolingchannels as you can see here.
Then we have the freedom to design our cooling channels in such a way that they areconforming, they are completely conforming to the contour of the part that we are going tomake using these tools and when they are conforming then they are able to control thetemperature during the cooling time in a more efficient manner. Hence, they contribute incooling down the part faster.
So, what we do instead of making conventional straight holes and plugging them later wedesign conformal cooling channels and then realize them through additive manufacturing andwe end up in saving a lot of time in rejection of parts as well as we end up in reducing thetotal cycle time of one part produced which can also be expressed in another way that we areincreasing our production capacity.
If in a day I was able to produce 2000 parts with the help of conformal cooling channels in aday I will be able to produce 2500 or maybe 300 parts. So, the numbers are just indicative butthat was about tooling.(Refer Slide Time: 20:40)
The second level of adoption of AM is called as part substitution. So, what does basically partsubstitution means? That you are substituting the manufacturing method of the componentwithout substituting, without making any design changes. Now this can depend whether onyour end application whether you have the freedom to change the design or not? But youhave the freedom to change the manufacturing process.
So, let us talk about the idle candidates, who would be the ideal candidates for part product,part substitution? So now batch production components, batch production components whichhave very complex manufacturing process where we are it is taking too much time or thereare certain defects due to that manufacturing process which we are not able to eliminate evenafter controlling the process.
So, that means that manufacturing process, the existing manufacturing process is posingcertain problems to me and that needs to be changed. So, that is one scenario where we canlook at additive manufacturing as an option but then again, I would suggest that this is forsmall batch production, low volume production. Otherwise, the economics of it would not bejustified.
Then the second scenario is spare parts for inventory management. Now I have the perfectcandidate here for that. What you see here is an impeller, it is a impeller for a very efficientand suction pump oil and gas industry and this particular impeller it usually takes around 6 to7 months to make such an impeller and the reason being that it has got a number of cavities.
It has got a number of cavities and in order to make this component through casting which isthe conventional manufacturing process it takes around 2 to 3 months to only manufacturemy tool, then a validation, check is being done, trials are run on those tools and designiterations are done for the tools also, even for the tools there is rework required. So, all thesetimes I am losing out if I am depending on a manufacturing method which involvesproduction of tools.
Because the complete reliability is on the tools, hence for such components additivemanufacturing gives me the perfect solution by providing me a tool less fabrication. Also forexample this particular component which takes around 6 months and it is from oil and gasindustry. Now if this component is damaged, then their oil and gas line will be shut down fortill the time there is no replacement done.
So, we actually are running short on time depending on the application. So, the application isalso governing, is the application is actually demanding me that I try to choose amanufacturing method which has to be the most effective method in terms of time involved.So, what are the benefits? that we are trying to reap through part substitution.
One of the benefits is that we are trying to facilitate lower minimum buys. The other one iswe are manufacturing a near net shape part which might save a lot of time for few of thedesigns where my 90% of the com material is being machined out. Hence, I am also able toachieve a higher flight to buy ratio when compared to any other manufacturing process in air.Also, my material can be saved if I am dealing with expensive material say Titanium.
Then I have the motivation of directly adopting to the manufacturing process of AM, even if Ido not aim for any design change if I take the same design which is being made inconventional manufacturing in Titanium and if I take the same design and produce in additivemanufacturing it can be cost effective because Titanium processing through conventionalmachining has challenges in its own.
So, see like this is one of the material workability issues. So, these are the various factorswhich govern the selection of a component for part substitution and at the same time they aregiving all these value additions to the primary process which can be getting rid of a supplychain issue or trying to go for a distributed supply chain. Suppose if your supply chaindemands from you that you have to provide 100 components in USA, 100 components inEurope and 100 components in India.
So, you would not want to manufacture all these components at a single place and thendistribute it to 3 different locations to the world, because that will add a very high cost to thelogistics. Sometimes the logistics cost can be higher than the actual manufacturing cost of thecomponent. So, for such manufacturing logistic chain issues, supply chain issues additivemanufacturing provides me the solution by putting up 3 different AM centres very close tothe actual use of the end component.(Refer Slide Time: 26:17)
Now let us talk about part consolidation, once we have adopted components for AM ormodules at AM only for the purpose of part substitution. Then the next year is partconsolidation. In part consolidation what we are trying to do our basic objective is to create amonolith design which earlier was not possible because of various manufacturing constraintswhich were posed by the conventional manufacturing techniques.
But now since the advancement on AM as all of us know that AM allows a higher degree ofcomplexity to be achieved in our design. Hence, now we can overcome those constraints and
we can actually integrate 1, 2, 3 or more than 3-4 components into a single assembly andproduce as a single design. Now what it will help me? It will help me in avoiding all themechanical joints, it will help me in avoiding leakages in case the component is for fluidflow.
It will help me in reducing the total number of part counts. It will also help me since my partcount is reduced it will also help me in managing my inventory in a better way or it willreduce the supply chain problems associated to the spare parts. Hence, making a consolidateddesign or a part consolidation is one of the factors which largely adds to the economicbenefits of the organization or the enterprise.(Refer Slide Time: 27:55)
The next level; Once we are done with part consolidation the next level is to design thecomponent for AM. Now by going through each tier step by step, now the user has a clearunderstanding of value being added at each and every level. They also have an understandinghow the design or how the additive manufacturing process is going to affect their endapplication.
Whether it be in terms of surface roughness, whether it be in terms of quality of thecomponent which can be measured either in tensile strength or if it is a component thedynamic loading then we can also talk about strength such as fatigue strength, impactstrength and other factors such as the geometrical dimensional accuracy of the process whatis the accuracy that we are getting in the process.
and what is the accuracy that is required in the end application? By going through all these 3tiers, all these fundamentals are clear to us. So, now we have sufficient knowledge of ourprocess which will help us in designing the component or I would say rather redesigning thecomponent for additive manufacturing where what we can do? we can bring in benefits suchas customization, we can topology optimize the components.
So, when I say topology optimization this is a typical component that you would see. This isa topology optimized component, when I say topology optimized component then thetopology is optimized based on the load parts and the stress that the component is goingthrough. So, the funda is simple wherever the component is experiencing more stress or moreload passing through there will be more material in those reasons.
Wherever there are minimum stresses and there are no load parts at all the software or theuser will remove material from those points. So, just to make it clear this is a component, thisis a conventional component which was designed for conventional manufacturing and this isthe similar component for similar end use, but this one is a simulation driven design usingtopology optimization in all tier inspired print 3D platform.
And this one has been designed in solid works by IIT Bombay and VIT students. So, what isthe value that you are adding when you are talking about 4 these different steps?(Refer Slide Time: 30:31)
The value that is being added they have 3 different kind of impacts. These impacts can berealized at a component level, at a module level or at a process level, at an enterprise level.
So, let us try to understand what are these 3 different kinds of process or benefits, that we aregetting by deploying AM in our manufacturing process. So, the first one is the direct benefitwhich is a process benefit.
You can reduce your process time because there is no tooling involved, you are not wastingtime in removing material from a block. You are only utilizing your time in melting thematerial which is required to build the component. If you adopt your components for additivemanufacturing then you also get an opportunity to optimize your surface quality, as all of usknow that surface quality is a very big limitation or a challenge in additive manufacturing.
Especially when we are talking about powder bed fusion processes, because of the powderparticles nature of the powder particles being the feedstock there is a surface bad surfacequality which is inherent, usually this lies in the range of 4 RA to 20 RA-30 RA. This wide itcan vary. So, it is very important that you design your component in such a way or when youare consolidating your components, your comparts together then you are keeping the printingorientation in mind.
Because the printing orientation will have a direct impact on the surface quality and hence,we can achieve benefits from the process by reducing the surface roughness by designing forAM process. Then we are talking about dimensional accuracy. So, the accuracy which isrequired for the end application sometimes can be achieved through AM directly if thecritical dimensions where these accuracies have to be met or given enough attention duringthe time of orientation.
Then of course high reliability, if we are designing our components or we are having ourcomponents orientation of printing the machine, the blade, the base plate everything thewhole environment is known to us and then we start designing our components, thenobviously we will be getting a higher reliability in our manufacturing AM process. There willbe less build failures and then there will be a minimum cost and optimized cost associated tothe manufacturing process.
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