Loading

Module 1: Additive Manufacturing Overview

Notes d'étude
Study Reminders
Support
Text Version

Quality in Additive Manufacturing

Set your study reminders

We will email you at these times to remind you to study.
  • Monday

    -

    7am

    +

    Tuesday

    -

    7am

    +

    Wednesday

    -

    7am

    +

    Thursday

    -

    7am

    +

    Friday

    -

    7am

    +

    Saturday

    -

    7am

    +

    Sunday

    -

    7am

    +

Quality in Additive Manufacturing
Hello everyone. I welcome you to this session in role of quality additive manufacturing. I amAdil Khan working as a quality lead in Wipro 3D.(Refer Slide Time: 00:26)
In this session we will be seeing different certifications, pretty much specific to additivemanufacturing. Then a broad overview on NADCAP. Then quality in additive manufacturing,quality in power management, printing, post processing and qualification of additivemanufacturing parts. So, this will be the content that will be covered in this session.(Refer Slide Time: 00:51)
Since get primarily operating in aerospace and space we have AS9100 certification, which isequivalent to N9100, to shift the parts to aerospace or defence customers we need to haveAS9100. We also shift parts to automobile in various other industries. Many of you may befamiliar from your industrial experience this AS9100 or ISO certifications talks nothing muchabout type of industries you are in.
So, how we basically deal with this? So, several other industry verticals have come up withtheir own certification process. I will take you through some of them and where we standwith respect with them.(Refer Slide Time: 01:42)
We have largest certification, also known as LR is an agent name in oil and gas industry andthere are in this certification is very much specific to additive manufacturing. This is very
much important, in the sense this was the first certificate when we went through our designdevelop pair they went through our design, development, controls. Then additivemanufacturing processes, process build controls.
What type of powders we use? How we handle those powders? So, it is more on additivemanufacturing specific audit was that we had a certification from them. This is the reason,some oil and gas customers from Europe, and Asia show interest in Wipro 3D otherwisepeople will not get orders without these types of certifications.(Refer Slide Time: 02:43)
We had an audit Honeywell have their own certification process. They call it approvedprocessing source list, or APSL. They will go in detail in the audit which is very muchsimilar to LR, but more stringent in more detail. They look more about how we managepowder, powder quality, build quality. These are striking differences from standardprocesses, and they also fall under special process.
As you might be aware of the specific process you have to control inputs in order to ensurethe output. All OEM customers conduct their own special process audits in line withNADCAP audit checklist. The supplier is certified by NADCAP, they get directly approvalinto the approved supplier list. As Wipro 3D is under process of getting NADCAP and thisNADCAP certified for NADCAP, Honeywell have conducted the audit and have provided asa certificate and added as an approve processing sources list.(Refer Slide Time: 03:58)
NADCAP certification is provided by PRI. PRI is a main certifying body for NADCAP andthis is not for profit organization affiliated by society of automotive engineering. Generalaerospace OEMs asked for AS9100 the certification or equivalent for conventionalmachining suppliers in for performance special processes NADCAP certification is mandatedfor series production.(Refer Slide Time: 04:30)
What is a special process? Any process, which changes the inherent physical, chemical, andmetallurgical properties of an item is called as a special process, or any non conventionalmethod, which removes or deposits material on item during or after fabrication, in whichcannot be evaluated by non destructive means is called as a special process.(Refer Slide Time: 04:58)
So, as per point 1 and 2 our additive manufacturing comes under special process. So, theseare the different special process NDT, welding, chemical processing, heat treatment, coatings,even see home inspection comes under special process. So, AC7100 and AC7100/14. Theseare the 2 checklists applicable for NADCAP related to additive manufacturing. If you shouldlook at AS9100, it is very much generic standard, whereas NADCAP is very much specific toa process, say welding.
We have NADCAP separately for EBM, we have NADCAP separately for fusion welding,we have NADCAP separately for laser welding and diffusion welding. So, NADCAP is verymuch specific to a particular process.(Refer Slide Time: 05:51)
When we say quality for additive manufacturing; we get the CAD model from customer.Then we analyze can it be manufactured in AM or not. If yes, what are the modifications wehave to do. You may be knowing that we add material somewhere, we add support. So, wewill be able to be build the part. Then, we also construct parameters like orientation.
Then how precisely the model should be sliced, then what kind of surface finishes expected,what precautions we need to take care and other parameters to be considered. So, that youknow we get a part quality as good as possible. Necessarily all the additive manufacturingparts are always followed by some degree of post processing. In some parts, you have a lot ofpost processing, and in some parts we have very less post processing.
But it is very rare that we do wire cut, or chipping off the part from this part and do somekind of short blasting and send it to customer. Very few occasions, it has happened like this,but most of the cases to be very elaborate post processing and a lot of NDT involvedfollowed with final inspection and shipping of part to customer. This entire cycle the qualityof part which customer expects us to deliver has some angles.
One is the powder and its management. Second is printing or building. And third is postprocessing post processing on what is documentation final inspection. This comes undertraditional conventional processes. I will be focusing more on build quality and buildmanagement in related issues. That is the crux of this quality control in additivemanufacturing.(Refer Slide Time: 08:00)
In traditional process once you get a build or forging, you always get the MTC, which willgive a heat number and all other details which can be traced back for the part quality that themill supplier issues you. Here, MTC is not there, that is the first thing to see. Only qualifiedholder and what are the precautions we take when we say this build quality is good aboveaverage or beyond the expectation value of the machine provider.
So, we will come to those details. Currently, we will be focusing on raw material, and aboutthe build quality because if you think through the process the raw material, which is powder,and will be laser center and build process, which is something different from traditionalconventional manufacturing process. In conventional manufacturing process you in orderbillet or a rod, and then you have machining process turning in variety of other CNCmachining to finish the final good.
Here you are invading a powder and you have to ensure that the powder is of right qualityand right quantity. Every time part is freshly build. So, to ensure the quality how you assurethat part that is coming from a particular builder will have the UTS value as specified by thesupplier of the machine. So, those are the questions which keep popping up from customerminds.
So, raw material unique is also defined by operator hazard or fire hazard. That is possible.There is a provision that our raw material can get deterioration. So, how do we start the rawmaterial? What do we do to see that the deterioration or ONH pickup will not happen ontothe powder? Then you how RM contamination. See for a billet, or stab it is no way possibleyou may mix up to incoming raw materials and have a cross contamination.
That is not at all possible. But when it comes to fine powder particles which are like 63microns, you are using say common machine, and common accessories, which are notcleaned properly, then you have every chance, you will be mixing and contaminating onepowder with another. If that happens, you are basically creating a powder, which cannot beused for subsequent builds.
In these powders are pretty costly. Just to give you a reference for stainless steel, you willbuy say 200 or 220 rupees a kg. For getting a similar material of excess powder, we have topay almost like 10 to 15 times higher price for the powder per kg. So, powders should not be
wasted at any point of time. If you go through the build process, if we say for example mypart weight is 10 kg.
In order to build the part and meet the height of the particular, we have to use almost like 40sometimes even 50 kgs and 100 kgs of powder. In this case, let us take an example of 50 kgsof powder has been used to produce a particular part. No, after completion of build 10 kg ofpart is removed. In another 10 kgs goes in 2 ways to do to variety of reasons information areoutside the machine, along with the supports.
So, you are left with another 30 kgs. So, this will be split into 10 kgs in the dispenser end andsome 20 kgs on the collector end on the build plate. This is already explosive powder. Youhave to do proper filtration. So, you remove all the particulates, which could have producedduring the time of welding. So, out of 20 kgs, you do IPCM. IPCM basically acts like avacuum cleaner, where it absorbs all the powder from the machine area and it gets collectedinto a bin.
So, after collecting into IPCM, the powder is filtered, this automatically filtered. Then afterfiltration you get like say for example, 18 kgs of powder. Now, this powder is recovered andit can be reused. There is another angle to it. When you are doing all filtration process, youare exposing it to atmosphere where some of the powder can pick up ONH, oxygen, nitrogenor hydrogen.
It may not be all apparent in the very first go, but you think of same order getting used for 10to 15 times, then you have every opportunity of ONH pick up. In the process end it becomespowder, which has a quality issue. In the sense, if there is some pickup of oxygen, then thetype of properties that to get from the build are different and your tensile or fatigue propertiesthey started deteriorating very fast.
If you are reusing the powder without checking the ONH levels. So, you have to use thepowder because it is costly. At the same time, you have to worry about it, that it gets toomuch exposure to atmosphere in basically lose the quality of the powder. And really, youcannot use it for any meaningful build. So, these are the challenges.(Refer Slide Time: 14:04)
I will show you how to counter this, we will still stick to unique raw material. So, what youcan see here is a material safety data sheet. We usually get material safety data sheet alongwith the powder. In this case it is ALSA 10 mg procured for LBW, you know once you getthe material, you need to look into the safety data sheet and always the material provider weshared you our MSDS, along with other test certificates.
How safety data sheet is important is? Certain powders are fire hazards. Two of them areTitanium alloy, and Aluminium alloy. Now, these are type D type of fires, which cannot beextinguished by ordinary type of fire extinguishers, we need to have a D type extinguisherintake, which can take out material powder fire or metallic prayers. If you look at LPWALSA 10 mg MSDS, they are very clear that there is a possibility of catching fire.
And what should not be used is water, carbon dioxide, foam, or ABC powder extinguisher.Powder handling in following phases. Generally, if we look at the process in receivinginspection, during the time of issue of raw material, when the sieving operation take placeand filtration happens, and that there is one more area near filters. So, in machinery havefilters where all use it powders in particulates get accumulated.
There is a high chance that these filters can catch fire if they are not handled properly instored and disposed with a care. So, they can be a culprit of catching fire. So, this has to behandled carefully.(Refer Slide Time: 16:08)
This powder is Inconel 718. If you look in its safety data sheet related to health this powder isa little carcinogenic in nature. There are some issues when this powder is directly coming intocontact with eye, or when you inhale it during machine cleaning. The material provider willtell you what to look out for and how to take care of these issues.(Refer Slide Time: 16:37)
So, here if you can see here the metal provider is states should not come into eye contact, if itcomes, what actions to be taken? If it has been inhaled accidentally what actions to be taken?So, this gives you a inputs of what actions to be taken do the time of handling of thesematerial powders. Initially when we started way back in 2013-2014, we used to get powdersfrom our suppliers.
We used to receive them with folded hands, never asked what is the quality that you aredelivering. Whatever is delivered we try to manufacture with it. Over so many years we havelearned what is it we should be looking for and what is the thing we should be asking oursuppliers, mind you, all our suppliers are OEM suppliers. They are all out of India. So,talking to them needs a lot of understanding.
What we want and what we do not want? and make sure that this is communicated. When weare issuing the inquiry itself. We specifically say, what is the chemistry required? otherdetails required, as every right to reject these requirements if they are not moving.(Refer Slide Time: 17:56)
I will show you what we do for a typical powder. Nowadays we are very much specific aboutwhat we want, what standards the supplier should follow and how each test should beperformed on the powder. So, here we define what the different tests to be followed andwhich standard they have to follow. This will ensure that when we perform the same testhere, we will have a correlation between both the results.
If he is following different standards and we are following different standards, then definitelythere would be some correlation issues, which could be triggering during the time ofreceiving inspections. So, we clearly notify them, which standard they have to follow. Thenwe also mentioned, what is the chemical composition expected for this particular material?then what is the flowability expected for this particular material?
What is the apparent density? What is the particle size distribution expected? What is themorphology expected? So, this is the image of how morphology should be and these are theimages of how morphology should not be for any particle. Generally, we expect the particlesto be spherical in shape. If there are any open properties this could result any unfilled or voidduring the time of buildings.
If there are any elongated particles, if one end of the particle gets welded, then the other endof the particle will be left out, which will create undue projections or uneven surface finishes,irregular shapes, or satellite shapes. These sorts of issues will affect the physical andmetallurgical properties of the actual part that is being produced. So, these are undesirableeffects and these are required effects of the particle.(Refer Slide Time: 20:14)
So, when we started flowing down all these requirements we have come across some issuesfrom suppliers, which we will be seeing in the next slide. One mismatch is that we had apowder mismatch. We have received saying that this is a 20 kg powder of we have orderedALSA 10 mg. So, we have received 20 kg powder. When we check the weight, weight wasmatching, there was no issue with the weight.
But when we open the box and see what we identified was one box was fully filled, when youcompared to another box it is almost like 3/4 th filled or half filled. But when we look at theweight both weights are same. So, then we identified that some other material has been mixedup and supplier has shared some other material. We do not know what it is, but some othermaterial instead of ALSA 10 mg.
Then, because there is distribution. We have analyzed the particle size distribution for thecurrent lot in the previous lot that was shared by the same supplier. We noticed that there isso much change in the particle distribution. See, a basically when I say, I need a particle of 50or 53 microns, make every particle need not, may not be 53 micros practically. So, it may layanywhere between 40 to 60 microns.
So, the way the particle is distributed we also control it, should look at here there is hugedifference between the particles size which is greater than 53 microns. So, by looking at thisresult we identified that there is in some inconsistency in the powder quality, which is apowder particle size. Then, less quantity received, say for example, in a box if there is 20grams less, you may feel it is not a big issue.
When you are receiving like 20 boxes 20 grams into 20 which will cost of 400 grams ofmaterial. Powders are very costly. So, it is possible to compromise in such type of smallvariations. Then, less quantity receives, like we said earlier, then morphology issues, here ifwe look at this morphology, our ideal preferably should be spherical in shape, you shouldlook at this somewhat elongated, then some are satellite.
Some have uneven surface finish. So, these all particle sizes will result in, they will affect mesurface finish, as well as the desired mechanical end metallurgical properties of the finishingpart, that has been produced by using this powder. So, these are typical issues that we comeacross.(Refer Slide Time: 23:14)
Then we also come across issues like data sheet not received. Like I said earlier, we need togo through the material safety data sheet in order to understand what are the hazards that areimpacted when we are handling these powders. So, sometimes suppliers do not share us thematerial data sheets, sometimes they do not share us the reports. So, we say all this test has tobe done and all these reports along with the shipment.
Sometimes we notice we do not receive all the reports. We receive only some reports will notbe shared by the supplier. So, these are the typical issues that could be arising during the timeof receiving inspection of coders.(Refer Slide Time: 24:59)
Then, every build process is unique. How to ensure uniformity in outcome over a period oftime? So, due to the experience that we had over a period of time; we have identified and
realized; we can build in quality during the design stage itself to avoid pitfalls. There are 2angles to it. One is fast experience, we realized we need to control parameters likeorientation. Can we oriented in a way that it does not sit, perpendicular to the re-coater at anyheight of the entire build?
If it is sitting perpendicular, there is a possibility that it results in liftoff or wrapping, resultingin damage of part, then comes support type. We need to think aspects like can we use softsupports? So, that we can chip off the support easily to reduce the PP activity and want toremove the supports, we need to keep the in-plane cost resulting for machining into removethe supports and additional material added.
Such things to be kept in mind when designing and finalizing the build. Creating additionalsupports or placing the parts freely to fill the build plate also increases the exposure area. Theexposure area is more again this can result in heavy distortion or ware page in undesirableeffects like cracks and delamination. Then second thing that we need to see is build quality.When we say build quality, the first thing that we need to look for is machine health.
When we talk about mission health the first thing, we need to take care of is laser power. So,we need to regularly monitor how is the laser power. We have come across a situation wherethe laser power has dropped during the time of the build. Because the amount of temperatureneeded to melt the particle for that particular material was more than the amount to which thelaser power was dropped, that particular build got rejected.
So, we always have to monitor the laser power. Then comes AMC, annual maintenancecharges or contract. So, what we generally suggest, or do is, it is always preferable to haveAMC or because all these additive manufacturing machines, laser bed machines are specialpurpose machines. So, there is a high possibility that if there is any issue in any of the parts, itcan result the may expected particular machine output from that.
So, we always it is better to have AMC so that they come into calibration maintenance atregular intervals and see that, machine health condition is good. Then third is materialqualification. So, why we generally go for material qualification? In order to ensure that mymachine is not deteriorating because of its usage, like we are using it, 24* 7 for almost 365
days. So, this material qualification will give us confidence that the output delivered from themachine is same as the output that it was delivered, when it was newly procured.
So, what we generally do here is we build coupons, some few coupons in horizontal fewcoupons in vertical, and few coupons in inclined 45-degree angle, in few square coupons formeasurement of density and hardness. So, after getting the tensile and structure, all thereports, we correlate it with the first build results and we see how is our machine life. Is itstill the same or are we observing any abnormalities like difference in some tensile strength?
If we observe some variations, then we will analyze if they have done any changes in internalinputs. If internal inputs, there is no change then we go to the supplier and see why theseresults are varying. Then comes the operator qualification. So, as we said earlier, there is apossibility that cross contamination if the machine is not cleaned properly and also there arefew decisions where operator needs to decide, like, say for example, if build is stoppedwhether the build to be continued.
Or it has to be not a part has to be scrapped. There are 2 decisions which he has to take. Italso includes things like, say for example, loading the recoater and unloading the re-coatersee that there are no edges, damages, or any sharp particulates which are stuck to any edgeswhich could cause line marks or scratch marks on the actual part. Then he also needs toensure that the build plate is flat and there is no variation.
This could happen if there are some, no dust particles or powder particles. Below the buildplate, which can result in uneven flatness. Generally, we accept up to 40 microns asacceptance criteria for flatness, or if it goes beyond then he has to know either remove theplate clean it once again and load it or send it for ringling. So, there are a few aspects whereoperator has to take decision and proceed further accordingly.
Then, machine cleanliness like we discussed earlier. This is very costly mistakes that canhappen during the time of powder handling and machine cleaning. So, if even a small particleleft out we create unnecessary issues, which will affect the physical and mechanicalproperties of the parts because of this cross contamination. Then operating parameters andtheir impact. This is an advanced topic. So, during the time of advanced session we will becovering this operating parameters and melt pool monitor.
(Refer Slide Time: 31:11)
Then build observations. So, when build is running operator has to see how the powderspread is? What I mean by powder spread? For example, if the flatness of the build plate is 40microns. Then what happens is that top most surface of the build plate will have lessexposure of powder spread due to a recoater rubbing, than the build, which has a shorter. Sayfor example, I am just making it very exaggerated to just say what I am trying to say.
So, recoater moves in this way, because it is rubbing here, more amount of powder will beaccumulated here, and less amount of powder will be accumulated in this area. So, when weincrease the powder spread what happens is automatically more powder will be accumulatedhere, then our, the required amount of powder for the first layer would be compensated withthe help of powder spread.
Then comes the recoater rubbing. When it comes to recoater rubbing there is alwayspossibility that even after taking full precautions. The recoater could be rubbing and creatingvibrations, sounds, or landmarks. So, operators should be attentive. In case if he absorbs anyvibration or sound like recoater is getting rub. Then he needs to reduce the speed of therecoater moment or he depending upon the observation he needs to respond and take actions.
So, once again the qualification of operator becomes very crucial here. Then particulates.There is a possibility that particles could be stuck onto the recoater edges or anywhere ontothe machine areas and get mixed up with other particles. So, operator has to ensure that he is
ensuring that no particles are left out on the machine after completion of the build. So, whatwe generally suggest here is, he applies, isoprobe to the tissue paper.
And he claims, he should not be able to see any black marks or any powder marks on thetissue paper, he will be doing this until it is confirmed that no more particles are found on tothe machine bed or its powder exposed surfaces. Then comes the proof of build quality. Proofof build quality is something most of our customers are concerned about. It is like, I do notknow your builds looks okay alright but how do you ensure quality?
Many times, they say, how the test coupons? How multiple test coupons? have them indifferent directions, different orientations, some may be horizontal, some may be vertical,some may be inclined at 40-degree angle. Some square coupons for testing density andhardness, to check if there is proper fill and was proper all the requirements have met, as percustomer expectation.
They want to be sure, in many of the customers ask why you build the part, build thecoupons, along with the part. So, that I am sure that same type of properties that are attainedon the coupons will be present on my part as well. They do not want separate build for testcoupons. They ask okay. Some customers are okay with establishing parameters on thecoupon.
And then, using the same force and parameters to run the part for producing the actualfinished part. Many customers also asked for dummy parts. Dummy parts in the sense, thesame platform build with some dummy parts, which is similar to the part, but may not be acomplete part, then we do a microstructure study and tensile coupon study, made from thedummy parts and show the results.
So, some customers go to that extent as well. So, these are like proof of the build quality.There cannot be any questions beyond that, either we pass or will fail. In most of the cases ifthings are done properly there is no reason for failing. Then comes, post processing, byconventional method. So, in post processing what we generally do is, we always do stressrelieving in order to remove the residual stresses that could have generated during the time ofactual part build.
Then few customers asked for solution treatment, few customers ask for precipitationtreatment, few customers, depending upon the stock or you know dimensions criticality. Wemay choose to go for machining. Then some customers asked for surface treatments likesolution, surface treatment like anodizing, primer, Nickel coating or any other type of surfacetreatments.
Some customers ask for short blasting. So, it depends upon customer parts function, thenmeasurement. In measurement what we generally do is we scan the full part with Faro 3Dscan, and we compare this with model.(Refer Slide Time: 37:47)
So, this part also consists of non destructive testings both radiography and fluorescentpenetrant inspection. This is our airworthiness part. So, it is very much exhaustive. You can