Minimize Porosity, Maximize Performance

Few manufacturing processes can ensure the density of a part before it is cast. But with the right engineering expertise and state-of-the-art solidification software, minimizing porosity is not only achievable, but comes standard when you utilize Signicast’s investment casting process.

In this webinar, you’ll discover how designing the proper part with optimized gating can improve part performance during solidification.

We’ll cover:

  • Part geometry
  • Incorporating gating into part design
  • Gating and solidification considerations with different alloys
  • Value engineering and software analysis
  • How minimizing porosity maximizes the performance of your part

 

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Minimizing Porosity, Maximizing Performance Webinar Transcript

 

Taylor Topper, Group Marketing Manager:

Hello, everybody, and welcome to today's metal solutions webinar Minimize Porosity Maximize Performance, presented by Form Technologies. I'm Taylor Topper, Group Marketing Manager at Form Technologies and your hostess for today's webinar. Before we get started, I'd like to go over a few items, so you know how to participate in today's event. There's no dial-in for this webcast, so all of your audio will come through your computer's speakers. If you've joined one of our webinars before, you'll know how to move your widgets on your screen. Every one is resizable, so feel free to organize your console in a way that works best for you. Utilize the resource widget to view additional resources. On there, I have company brochures for you and two of our white papers, one of them, Converting Your Part to Investment Casting, that's one of our newer ones. Feel free to grab that. We also have more white papers and all of our past webinars on our website, Signicast.com, and in our knowledge and resources center. You can submit questions via the Q&A widget.

 

We'll be holding a live Q&A session at the end of the webinar, so I encourage you to submit your questions throughout today's presentation. We will answer them in the order that they come in. So, the sooner you get your question in, the more likely we'll be able to get to it at the end. If you have any technical issues, no sound, or slides aren't moving, please submit a comment via the Q&A widget for that, as well, and as usual, the webcast is being recorded, so if you'd like to rewatch it or if you miss something, you can view the recording from the same link that was emailed to you prior to the webinar starting, or a reminder will also be sent a few hours after. This webinar is presented by Form Technologies. We are a global group of precision component manufacturers, including three major brands.

 

We have Dynacast for die casting, OptiMIM for metal injection molding, and Signicast for investment casting. With our world-class technology and processes, we can serve any industry in any level of ambition with superior precision components and outstanding part to part consistency. Operating 29 design and production facilities in 19 countries worldwide, together, our entire business is focused on delivering the highest levels of quality at scale. Today, we have two engineers from our Signicast team here to help me present. Signicast is the world's most advanced investment casting specialists, helping customers solve their component manufacturing challenges. First, I'd like to introduce Ana Medinger. Ana is a degreed metallurgist. She is one of our process engineers specializing in material development, new part development, process development, and control.

 

She has been with the Signicast team for seven years and is a very valuable asset to our team. Next, I'd like to introduce you to Greg Schmidt. Greg is one of our veteran engineers, being with Signicast for over 20 years. Greg is a degreed mechanical engineer. He started at Signicast as a project engineer and is now a product development engineer. Prior to working at Signicast, he was a hydraulic design engineer, and while both of our presenters today are very humble and wouldn't say they are experts in anything, part design and new product development are definitely their bread and butter. They've worked really hard on this presentation for you all, and as you'll hear, they're experts in a wide variety of topics. Ana and Greg, thank you, kindly, for presenting for us today.

 

Greg Schmidt, Product Development Engineer:  
All right. Thank you. I am Greg.

 

Ana Medinger, Process Engineer:
And I'm Ana.

 

Signicast Investment Casting Capabilities

 

Greg Schmidt:  
So, to get started, we're going to first go over an overview of the investment cast process. We'll then review some of the basics of gating, and then we're going to dive deeper into more specifically solidification and how part geometry will affect porosity, and then we're going to go through a few real-life examples. So, in order to get started, we're going to review a short video that does a great overview of the investment cast process.

 

Male Speaker:
Investment casting solves many of the most critical challenges faced in manufacturing today, but how does it actually work? It all begins with the creation of a wax injection die that allows us to produce precise wax patterns. Pinpoint accuracy is critical as the wax pattern is an exact replica of the finished part. Specially formulated wax is then injected into the die. For this, Signicast employs a unique proprietary system that precisely controls the wax temperature. This allows us to achieve outstanding dimensional conformity at far greater speed and a higher-quality finished component. The wax patterns are assembled onto a sprue to form a complete mold. We then use advanced robotics to coat the assembly with layers of slurry and then rapidly dry the mold using our proprietary drying technology, a process that radically cuts shell build time from a week or longer with other investment casters to just one day.

 

The mold is put into an autoclave. We use steam and pressure to remove the wax from the mold, which is then preheated and ready for molten metal. To ensure it meets specifications, the metal is spectrographically analyzed before being poured into the mold. After the metal is solidified, the shell is then removed with automated high-pressure water jets. The final parts are then separated from the runner. If required, secondary operations such as gate grinding, machining, painting, blasting, and heat treating are performed. Ultimately, because we've automated virtually every part of the investment casting process, Signicast can achieve far higher quality for less total cost, in a fraction of the time of other manufactures. It means that with investment castings from Signicast, you can meet your most critical challenges head on. Signicast, challenge accepted.

 

Optimizing Your Investment Casting Design – Gate Location

 

Greg Schmidt:

Okay, so the first step in designing an IC part is to determine the gate location or gate size. The gate is the geometry that transfers the molten metal into the casting from the sprue. Sort of think of the sprue as the central reservoir of molten metal that will fill out the part cavity on the tree. The gate is ideally located on the thickest section of the casting. This will ensure that an adequate flow of metal will fill out the entire cavity of the part. On this page, we have a few examples of parts with the gate location indicated by the blue arrow. Some of the parts do require multiple gates, such as the bottom two left parts. We're going to discuss this a little bit later into the presentation.

 

Ana Medinger:
So, let's simplify this a little further. Think of the gate as the connection point between the part and the feeding source of the sprue. So, think about when you're putting oil in your car. You use a funnel to transfer the oil from the quart bottle into the oil pan of your car. The gate is the funnel in this example. So, let's talk about gating into the thicker section of our part. Remember, we want to make sure we're keeping that flow of metal from the sprue, that metal reservoir, into the part, but before we dig further into gating, we do need to understand how metal solidifies and then what's happening during the solidification process. So, we need to look at one of the characteristics that what happens to metal when it goes from a liquid to a room-temperature solid?

 

So, when we start off, we have molten metal, which is approximately 3 thousand degrees F. From this initial pouring temperature, the metal will shrink volumetrically as it cools to its freezing temperature of around 2500 degrees Fahrenheit. As the metal freezes from the liquid phase to a solid, there's an additional reduction of volume. This is called solidification shrinkage. Once the metal is then a solid, there's an additional change in volume due to thermal expansion. The illustration that you see on your screen shows the three phases of solidification, number one, the liquid shrinkage, which is the cooling of that liquid metal to the freezing temperature to the solidification shrinkage, which is the phase changes of metal from a liquid to a solid, and then finally the solid shrinkage, the cooling of the solid metal to room temperature

 

Greg Schmidt:  
So, here's an illustration of that concept. Let's say we fill up a 1 inch by 1 inch by 1 inch cube full of liquid metal. The final size will be .96 by .96 by .96 at room temperature. This is due to the change of volume as the cube is solidifying to a room temperature solid. Because of this change in volume, gate and part geometry must be designed so that as it solidifies, the casting is continually fed with liquid metal to replace that lost change in volume. This volumetric change is key to designing part geometry and gating. All right, here's a basic example of a casting and a gate setup. Metal is poured into the sprue. Remember that the sprue is that central reservoir of liquid metal. Metal is fed from the sprue through the gate and into the casting. As the casting is solidifying, liquid metal must pass from the sprue and gate to replace the volume lost as the casting is solidifying.

 

Anticipating Solidification Shrinkage in Investment Cast Parts

 

Ana Medinger:
So, remember from our previous slide, we have that solidification shrinkage, and we know that we have it, and so it's important to keep the gate fed, but what happens when we don't consider gate location and size?

 

Greg Schmidt:
So, if our gate is too small, such as in this example, the gate is going to freeze off before the casting. This then prevents liquid metal from replacing the volume change in the casting as it is shrinking volumetrically. The internals have no choice but to use itself as the reservoir of metal. This creates large pockets inside of the middle of the casting due to the reduction of the volume during solidification because of this, and that is because it is choked off, and that's pretty much it. It's simple as that. That is what solidification shrinkage is.

 

Ana Medinger:
So, now that we understand that gating location is important and that size and geometry is important, there are other things that we need to take into consideration. So, let's assume that we have a gate that's appropriately sized, we have a good feeding path, meaning that the gate's in a good location, we're keeping the molten metal fed from that sprue or that central reservoir of liquid metal. We can still have internal porosity or shrink. Why? To understand this, we first need to go through and explain the concept of what's called directional solidification. Directional solidification is when the thermal gradients are steep enough that feed paths are kept open. So, not only is gating location and size important, part geometry is also a very important factor that needs consideration. So, we're going to use an example of an icicle to describe this.

 

Greg Schmidt:
Yeah. So, casting does not solidify all at once. It cools from the outside in. Sort of think like defrosting a turkey. The legs and outside skin will defrost first, but the center is still ice cold. We ideally want the casting to uniformly cool away from the gate first with the areas near the gate freezing last. So, think of the icicle as the perfect casting. The icicle will solidify at the tip first, and as time goes on, it will directionally solidify back towards the gate with the base of the icicle freezing last. We're going to look at some examples to put this into a little bit more perspective. So, like, right here, let's look at this very basic shape.

 

We're going to first look to see how the gating location will affect the internal soundness of the part. There are certainly many areas where we can gate on this part, but we're first going to try the gate on the end of the post. So, if you look on the photo on the right, this shows our tree setup. You can see how we have the parts attached to the sprue. The green bar is the sprue, and remember, think of that as the reservoir of metal. Now that we have our gating location decided and our sprue set up, how are we going to know if this is a good location to gate or not?

 

Ana Medinger:  
So, we use a simulation software to analyze how effective our gating location choice is. This software is a tool that we use to help predict casting porosity. The input variables used in this analysis, such as shell parameters and alloy temperatures, are unique to our process. So, if you look at the video that's playing on the left-hand side of your screen, you're going to see there's a blue color that's moving. This blue color represents the liquid metal feed path from the part back to the sprue. Remember, that's that metal reservoir, and what happens during this feed path, during time, or over time and then during solidification, you can see there's a pretty distinct separation between the part and the sprue. So, if we look at the image on the right-hand side of your screen, you're going to see our geometry or our part with a giant blue blob in the center. What this image is telling us is this is predicted porosity. The blue color is where there is a potential to have porosity inside of the part.

 

Greg Schmidt:
Yeah. So, because of this large area of predicted porosity in the center of this part, we probably need to revisit the gating location. It's indicating that we probably didn't gate into the most suitable location of the part. So, using the same part, let's change the gating location. We're going to choose a location near the heavier section of the part. So, if you look on the left side of the picture, that's the photo of the gating that we just simulated. In the center is our new gating location, and on the right, again, is our tree set up with the parts attached to the sprue. With this, we should be able to provide better feeding using the principles that we've just discussed.

 

Using Effective Simulation Software to Predict and Minimize Porosity

 

Ana Medinger:
So, let's go back to our simulation software. If you look again on the left-hand side of our screen, we've got a revised gating location and we're watching what happens to the feed path over time. You can see that there isn't as large of a separation and doesn't separate as quickly as it previously did before. So, then, if we look at the image on the right-hand side of your screen, you can see that the area of predicted porosity, shown by that blue color, is substantially smaller. So, now, we understand how important gating location is. Let's talk about part design and how that affects part soundness.

 

Greg Schmidt:  
Yeah. So, here's a part that we have, for an example, and we're going to gate and solidify this part from scratch. So, our understanding of this part is that it's a pressure-containing vessel. So, this means that our goal is that this needs to be perfectly sound and no porosity is allowed. By just looking at this part, it initially, to us, looks like a very simple part. We don't see any noticeable, isolated heavy sections, and we don't see a noticeable gate location. So, we're just going to start with our gate in the center of the part just to start off and see how it works. So, we have our gate in the center of the part attached to our sprue setup, and on it, let's just see how this looks.

 

Ana Medinger:

So, again, using that same simulation software, if you look at the video on the right-hand side of your screen, we can see what's happened to the feed path over time. You can see that that blue color is separating itself in the sidewalls and then in the keyhole area in the middle of the part, and we're left with liquid metal that's isolated away from its feeding path. So, now let's review what our software says about predicted porosity. So, the blue colors that you see on your screen represent, again, the areas of predicted porosity, and you can see that we're seeing predicted porosity in these thin sidewalls and then again around the center keyhole. So, as we remember what Greg said earlier, we need this part to be completely sound. So, how do we overcome this?

 

Part Geometry and Part Design

 

Greg Schmidt:
Yeah. So, in this case, we have two things that need addressing. We need to address the isolation that we see in the sidewalls. That is identified by the two vertical lines and that isolation we see in the center keyhole. So, remembering our discussion on directional solidification and the importance of a good feed path, here's where we need to work on part design to achieve a better directional solidification in this part. We're going to add a rib from the gate to feed the center geometry. We're also going to taper the floor just slightly, and our hope with that is that we can feed those sidewalls a little bit longer until they're solid. Ana, let's take a look and see how this worked.

 

Ana Medinger:
So, the first noticeable difference is that as you're watching time progress with the video on the right-hand side of your screen is that we don't have those isolated sections in the sidewalls. This is a pretty good indicator that the tapering of the bottom floor is keeping these walls fed long enough for them to solidify. So, then, let's look at the areas around the keyhole. You can see that the addition of the feed rib, it's keeping the feed path from the sprue, through the gate, and into the part open long enough so that the thicker sections around that center keyhole are being fed long enough for them to completely solidify.

 

So, let's look at revision one, our no-feed rib, as-is geometry, against revision two, where we added a feed rib and tapered the bottom floor. Side by side, there's a pretty clear distinction between what's occurring in revision one and revision two. That minor adjustment to the bottom floor, it made a large impact in the feed path to the sidewalls, and the addition of the material in the form of a feed rib kept that keyhole area fed well. So, now let's look and see what the predicted porosity looks like. Side by side again, there's a very clear difference. One has some blue that indicates predicted porosity, and one's a clean part. So, revision two with the feed rib and the tapered bottom floor was successful. We were able to eliminate the predicted porosity.

 

Greg Schmidt:
Yeah. So, this was a very successful iteration of part design. We worked with our customer to tweak the overall design of the casting. We tapered the bottom of the floor, and then we were also able to add some feeding material in an area that did not affect the fit, form, or function of the part.

 

Ana Medinger:
Okay, so up until this point, we've covered the importance of gating location, gate size, and now we've also talked about part geometry, but what happens in areas when we can't modify part geometry, because we can't always do that?

 

Controlling Part Solidification

 

Greg Schmidt:  
Yeah. So, there are other things that we have at our disposal that can affect how a part solidifies, and we can take that and use that to our advantage, such as this part. This part has two thin walls that are connecting two plates on each side. With gating on one side of the part, there's significant shrink predicted on the opposite side. So, if you look on the right-hand side, the yellow areas are showing where we will have porosity in this design, which was not ideal for the customer.

 

Ana Medinger:

So, one solution would be to increase the width of the thin wall to add more feeding, but this is going to add more ___ 0:18:54 machining, and this isn't the ideal course of action. So, our solution was to take advantage of the radiant heat to keep adjacent geometry hot. We designed a gate with two arms that go up alongside the thin walls. This keeps the thin walls hot for just the right amount of time to feed the end plate as it solidifies. Thus, we have a solid part without the need to change part geometry. Now, if you look at the predicted porosity on the right-hand side of your screen, you see a little bit of that yellow color, but if you look closely, the predicted porosity is not in the part. It's in those feed ribs that we…or those ribs that we added to the gate and not the sidewalls of the part.

 

Greg Schmidt:
Yeah. So, by using a creative tool in our toolbox, we're able to do something with minimal impact to our customer. So, by working together with our customers and understanding the part function, we can optimize part geometry as well as gating to meet the requirements of the application. This ensures that we have a low-cost and robust casting.

 

Ana Medinger:
So, let's look at another example. So, this part was another part that needed to be completely sound. So, if you look, the part has three gates, as indicated by the red arrows. A section view shows how the geometry is designed around the gating locations, and the walls are tapered to promote directional solidification. The gates are in the thicker section of the wall, and then again, we have that wall tapering. So, Greg, we've got a couple more examples to share.

 

Greg Schmidt:
Yeah. So, here's some other examples of geometries that we developed with our customers. The part on the right has a teardrop geometry from the gate. This is promoting that directional solidification back to the gate, and circular parts, this is a common feature that we design into castings, but in many cases, it is not possible to design out 100 percent of the shrinking porosity. Sometimes, the part geometry just does not allow it, but that is perfectly okay as long as it is strategically designed, such as in low-stress areas.

 

Ana Medinger:

So, let's talk about that in practice. So, if you'll look at the part on the left-hand side of your screen, this was designed so that the higher-stress areas were porosity-free and a non-critical area of the part wasn't changed because it didn't matter whether or not the section had porosity or not. So, if you look at that part, the high-stress area was between the two slotted holes, which are on that lower right-hand side of the part, and then we did a simulation on this part, and we had predicted porosity in two areas. One was between those two slotted holes, and the other was in the boss, which is at the upper end of that photo. So, between the two holes, again, remember that was a high-stress area, and so this needed addressing. We overcame this by adding a dimple between the two slotted holes, modifying how this area of the casting feeds and solidifies. The boss was in a low-stress area, so the predicted porosity was not a concern. So, we didn't need to modify the geometry. We left the geometry as-is.

 

Greg Schmidt:
Yeah. So, by involving us early in the development cycle, we can ensure that your casting will meet your expectations and not delay your time to market. We have several options that we can use to develop parts through prototyping. We can use 3D-printed patterns or manual wax pattern tooling. We can use all of these to quickly produce an investment cast part that you can use to utilize prior to the expenditure of production tooling just to confirm your design, part soundness. You can do some field testing and much more. A robust casting design does not happen by accident.

 

Alloy Porosity and Gate Removal

 

Ana Medinger:
So, in addition to design considerations, the alloy and how the gate is removed are also considered during this design process. The alloy chosen has a great effect on the solidification of a casting. So, if you guys look at the chart on the right-hand side of the screen, where we've got…we're looking at three alloys here. 17-4, there's a lot of different elements that go into making that alloy, versus, say, 10-35 or 86-20, where there aren't as many alloying elements. So, each of these elements has a different solidifying temperature.

 

So, because of this, some alloys, such as 17-4, stainless steel, will have a larger temperature range in which it's going through its phase change from a liquid to a solid. In the middle of this range, the metal is in this sort of mushy or jelly-like state, and it inhibits feeding. Thought, 17-4 is less forgiving of an alloy than, say, a low-carbon steel. A sound part in a low-alloy steel may not be sound when poured in 17-4. So, we use our processing parameters, our experience, and expertise to help ensure we can meet our customers' requirements when we are involved early in the development cycle. So, now that we've considered the alloy, let's look at gate removal and how we consider that during our process.

 

Greg Schmidt:
Yeah, so tying this all the way back to the beginning of the presentation, gate removal is an often-overlooked aspect of part design. After the part is separated from the sprue, the gate witness can be removed with an abrasive belt machine or left as-is. The top two pieces were ground with an abrasive belt, flush to the part's surface, whereas the bottom two parts are left as broke. If you take a look at the part on the left, you can see that we recessed that gate witness into the part a little bit. So, after it was removed from the sprue, there was no extra machining or grinding that was necessary. So, if this had to fit into a cavity, we were not needing to do any secondary removal operation of that gate, and thus not needing a separate operation shortens your lead time and lowers your overall cost.

 

So, we know that was quite a bit of technical information, but pretty much in summarizing, not every casting can be an icicle. Although we would love that, and our engineers would love that, that's just not possible. So, really, the things to take away are that the part geometry is the main factor in how much porosity a casting may have. In the design of a part, you really need to think about the gating location and keeping those isolated sections to a minimum, and by involving your investment casting house early in the design process, you can take advantage of many of the benefits an investment cast part can give, the near-net shape, the tremendous alloy selection, premium tolerances, and just optimizing for the lowest-cost part, but coming to us after your design is locked down can require additional gating, secondary operations, such as machining, and all of this can lead to higher cost and a much longer processing lead time.

 

Ana Medinger:
All right. So, this completes our webinar. We're going to turn it over to Taylor for questions and wrap-up.

 

Frequently Asked Questions

 

Taylor Topper:  
Thanks, guys, so much. That was really, really good. Those videos for the solidification process, a nice addition. We have a few questions in. So, for our listeners, the length of our webinar is determined now by our live Q&A, so while we have Greg and Ana here, please feel free to put any questions you have into the Q&A widget. I also do want to remind you and urge you to visit our website, Signicast.com. We have all of our past webinars on our website, Prototyping for Production, Converting to Investment Casting, and also Design Freedom With Soluble Cores, just a few of our past webinars. We also have our metal selector tool, so choosing all of your materials, and a variety of white papers and blog posts, tons of knowledge on there to do more research when we don't have a webinar, but starting with our first question, guys, if the metal contracts when solid, isn't the end part smaller, too?

 

Greg Schmidt:
Well, yes, actually it is. So, when we're designing our tooling and our wax patterns, or even a printed wax pattern, we are making that pattern larger than what the final casting is, kind of similar to, it's like injection molding, where that die cavity is larger. Typically, we're probably about two percent larger, but that's just sort of a rule of thumb because we do have other things that constrict the solidification. So, yeah, the tool part, the pattern is larger.

 

Taylor Topper:  
Next question, and Ana, toward the end, you answered some of this, but maybe it would be useful to reiterate, this is on material selection, how does it affect gate design, solidification, and porosity, and are there materials that are more forgiving than others?

 

Ana Medinger:

Certainly. So, we generally have certain alloys that we all love. You know we have icicles and alloys that we love. So, for some of the alloys, like 86-20, you know, low-carbon steels, they are going to be more forgiving because there are less components that are making them up. So, it's a little bit easier. For gate location and gate size, we do take into account, and again, we use our expertise to help us out when we're using alloys that are trickier, such as 17-4, and Greg, is there anything else you want to…?

 

Greg Schmidt:
Yeah. I think just knowing the alloy ahead of time, we can certainly use that into our simulation software and get that prediction of porosity before we actually start tooling.

 

Ana Medinger:
Right.

 

Greg Schmidt:
So, we certainly can work with our customer to optimize the alloy, if that's needed, but it's just something to be aware of as we're working on a part.

 

Ana Medinger:
Right. Yeah.

 

Taylor Topper:
I think that's a good segue into our next question. Someone is wondering what simulation software does Signicast use?

 

Ana Medinger:
We use a simulation software package called SolidCast.

 

Taylor Topper:
Next question, what about tolerance comparing to die casting?

 

Greg Schmidt:
Sure. I think we have pretty good tolerances. I don't think we're, you know, we'd probably be comparable to die casting. If there's certain areas where it's very critical, we can hold plus or minus probably 5 thousandths of an inch up to almost 2 inches in some locations. It's just very geometry specific, so certainly working with us early on in identifying those tight tolerances, you know, we can make a better determination if they're adequate to the application, but there's a lot of things that we can do during the development of the part, you know, such as doing a tool rework to basically ensure that our Cpk is then centered on the tolerance band, you know, just to try to optimize whatever the critical feature is of the part.

 

Taylor Topper:
Thanks. Next question, are there any rules to designing the parting line on the part, or is it usually done based on the toolmaker's recommendation?

 

Greg Schmidt:
Again, we have a lot of different options as we're designing tooling. So, if there are specific areas that cannot have a parting line, oftentimes we can get around that by maybe adding a slide or changing the orientation of the pattern into the pattern tool. That is definitely something that we always work with our customers is anticipated parting line and the ejector pen locations, but yeah, any of that can be modified. It's not up to the toolmaker. It's always up to the application of the part.

 

Taylor Topper:
Do all of these concepts to eliminate porosity apply to both casting types, die casting, and investment casting?

 

Greg Schmidt:
Yeah. I would certainly say probably more so in like sand casting and investment castings because those are usually more gravity-fed processes, whereas in die casting, they're more high-pressure fed, but certainly, if you have heavy isolated sections away from the gate or where you're injecting the die cast material into, those are more prone to porosity than areas that are closer to the gate. So, yeah, certainly try to minimize those isolated sections and keep all thicknesses uniform.

 

Taylor Topper:  
Next question, does it matter where the part is on the tree? At that point, does porosity change?

 

Ana Medinger:
So, we take this into account when we're doing the analysis and design phase of bringing in a part. We do simulate for different locations on the tree, and we design and make sure that our process is robust enough, and our process is consistent so that once we have that design, we sort of eliminate that risk.

 

Taylor Topper:
Great. Next question, how does material density in investment casting compare to die casting or sand casting?

 

Greg Schmidt:
Yeah. I think this is sort of a little bit different. With the density, we pretty much have near 100 percent density in those solid sections. So, it's not like a die casting, where my little knowledge of die casting is sort of the material is almost like atomized into the tool as it's being injected. We don't have that with investment cast or sand casting. So, if we have a sound part, you can be assured that it's 99 percent plus solid and will basically meet the requirements that you would see for rod steels in like a table for yield and…

 

Ana Medinger:
Tensile.

 

Greg Schmidt:
Tensile strength.

 

Ana Medinger:  
Mechanical, material properties.

 

Greg Schmidt:

Yeah, material properties, yeah.

                                                             

Ana Medinger:  
Basically, yeah,

 

Greg Schmidt:
Yeah.

 

Taylor Topper:  
On the bracket that had a dimple added between two slotted holes, how does this feature remove porosity?

 

Ana Medinger:  
So, it's really, it's all about changing how that section of the part cools and is fed. So, those slotted holes are going to, we have to basically feed around those slotted holes, and so by changing the section's thickness, we're able to reduce the cross-section and promote, once again, that directional solidification around those holes.

 

Greg Schmidt:
Yeah. So, with that dimple, if we're able to make it deep enough, we can almost make that freeze first, and then we let the rest of the material freeze around it, so then we do have that directional solidification where we don't have that isolated hot pocket of liquid metal still in there during…when the rest of the casting is solid.

 

Taylor Topper:
Next question here, we build structural automotive parts from A-360, A-380, and A-383. Which is less or more prone to porosity and why?

 

Greg Schmidt:
Yeah, I think those are mostly die cast materials. A great investment cast alternative is A-356. That's actually a very forgiving alloy through our process. It solidifies very well and even with isolated sections, it can be solid, so probably the most equivalent investment cast material to those would be A-356.

 

Taylor Topper:  
Thanks, Greg. This next question is a little bit long. There's a few questions in it, I think, but is there a standard that sets an acceptable porosity percentage or pore size? If I wanted to spec and control porosity on my drawings, what would be the best choice, weight or another suggestion?

 

Ana Medinger:  
Sure. So, there are industry standards, and then there's also the AMS2175, which is a MIL spec, basically, and it has different classes that specify porosity size, the number or the quantity of porosity you can have within a specified area. That's a great spec to use. It also goes into sampling size. It's a great spec to us as a reference when you need to sort of create a standard for how much porosity you want to allow.

 

Greg Schmidt:
Right, because, naturally, in casting, there is some porosity. It's just trying to design how much is in there and its location.

 

Ana Medinger:
Right.

 

Greg Schmidt:
So, within that 2175, I believe there's also specs for how close the porosity can be near the surface.

 

Ana Medinger:
Surface, yeah.

 

Greg Schmidt:
More of the more stringent standards.

 

Ana Medinger:
Correct.

 

Greg Schmidt:  
But there's also very basic standards that just have a size limit that you can see, and we also verify that through an x-ray. So, every time we develop a part through our processing, every part is then…or on those first lots that we produce, we do an x-ray sampling of a tree, and then we evaluate that and share that with our customers to ensure that, you know, we're making a robust part for their application.

 

Taylor Topper:
Do you do solidification modeling on every new part design? With that, how long does it take to run several iterations for complex parts?

 

Ana Medinger:  
So, we do solidification analysis on every new part, and the length of times really, it kind of falls into a couple different classes. If we're involved early with our customer, it allows us to kind of tweak as we go, so we're both meeting our customers' needs and we're making sure we're making a good casting. If it's a very complex geometry, I mean, it could take, you know, a couple days, maybe.

 

Greg Schmidt:
A couple days, yeah.

 

Ana Medinger:  
A couple days to go through a couple of different iterations. Yeah.

 

Greg Schmidt:
Yeah. A lot of it just depends on how detailed we want to be in that solidification modeling.

 

Ana Medinger:
Right.

 

Greg Schmidt:
We can do a very quick one that can just take under an hour just to get an overview if we're on the right track, and then, as we get detailed, then we increase the mesh size to get more detailed solidification.

 

Ana Medinger:
Correct. Yeah.

 

Taylor Topper:
If we do more solidification modeling, will it eliminate our need for prototyping?

 

Greg Schmidt:  
It can, certainly, and we do that with a lot of customers, as well, as we're going through the design cycle. You know we'll be taking their designs, running our solidification modeling, giving that feedback to where we're going to have that predicted porosity, and then, yeah, so prototyping isn't necessary. It's just something if we got designs that are on the edge.

 

Taylor Topper:

Are there specific elements within aluminum alloys A-360, A-383, of those we have to choose, which…I'm sorry, from which we should be aware that have more of a casual effect on porosity?

 

Greg Schmidt:
Can you repeat that again, Taylor?

 

Taylor Topper:
Yeah. Let me…let's see. So, I think are there specific elements within the aluminum alloys that have more of a casual effect on porosity?

 

Greg Schmidt:
Yeah. So, we got some aluminum alloys, such as A-356, that, again, I mentioned earlier that solidify very well. It's actually very forgiving. We can have isolated sections and it still solidifies fairly solid. Another alloy that we have for aluminum that's a little bit stronger is like, I believe it's A-201, and that is much less forgiving in this solidification realm, so we really have to design those icicles when we want to choose that alloy, but it does have some strength advantages. So, certainly, especially in aluminum, that would be…

 

Taylor Topper:
Yeah. Sorry. We have quite a few questions here about aluminum alloys, and I think some of them probably would be better answered by one of our die casting engineers with Dynacast, so I may have them follow up with you folks offline, but I do think it's important to mention, you know, in my experience, working with you guys that while a specific material might be a good fit for die casting, there are similar alloys that Signicast can pour that has as good or even better properties. Is that true, and you know could you touch on that?

 

Greg Schmidt:  
Yeah. Yeah. So, the differences between some of the die cast aluminums and what we can traditionally cast are a little bit different, but we have had some success with some of the die-cast aluminums, such as 380. We can and have been successful pouring that. It's a little trickier to ensure a sound part, but again, the most common casting alloy is A356.

 

Ana Medinger:
Yeah, Greg, I actually had a conversation with Pat Morrison recently about prototyping with A-380, and he was saying that Signicast has been pouring a lot of prototypes with A-380, so that's a really good thing to add there.

 

Greg Schmidt:
Yeah, I would also like to mention that we can certainly prototype die cast designs quite easily. It's not like in the die cast world, where you have a tremendous expenditure in the die cast tooling, whereas here, you know, we could do printed patterns on a very limited run and then pour a comparable die cast aluminum and use that for prototyping. It doesn't matter if we're going to be used as the production source or not, but you know we're just offering services to help our customers through rapid development, and I think this is one that a lot of our audience could probably take advantage of.

 

Taylor Topper:

Yeah. So, adding onto that, we have a question here, what types of volumes per year is typical for investment casting?

 

Greg Schmidt:
Oh wow. They can really be anything. We do some where it's just dozens a year up to millions of parts. Anything pretty much goes, especially on small parts. It's more of how many molds, how many trees can we process through our facility. So, the smaller the part, you know, we can get into the millions, but even on large parts, where the part is essentially its own gate and sprue, dozens are completely adequate. So, there's really no rule of thumb for that.

 

Taylor Topper:  
Going back to aluminum here, could A-356 be heat treated?

 

Greg Schmidt:

Yeah. There's some standard tempering temperatures. I believe the one that's most common is a T6 tempering temperature for the aluminum. Some of the aluminum's naturally age hardened. We can accelerate that through a heat treatment process. So, yes, there is multiple ways to heat treat aluminum alloys.

 

Taylor Topper:
Is it common to see porosity at the gate location after gate removal, and can the remaining gate be polished off or grinded off smoothly.

 

Greg Schmidt:
Yeah. So, oftentimes, you can see shrinkage porosity through the gate, and essentially what's happening is that reservoir of metal, as it's solidifying, remember, it's changing in volumetric, it'll actually pipe through the sprue and through the gate into the part if it's not designed properly. So, you know, then also after gate removal, we can remove it, and then, if needed, we could do a weld repair to fill that area in if it's still on the casting, but we sure do try to design this out, and we do that through our initial sampling and through our solidification software just to ensure that we're not going to have that problem, but it certainly is possible.

 

Taylor Topper:
Two more questions here on gating, you remove the gate in that first example, did that change the cost?

 

Ana Medinger:

Which first example? Oh.

 

Greg Schmidt:
Yeah. Yeah. So, a lot of this depends on, so, the major cost-driver in investment casting is really the parts that we can get on the tree, and we try to optimize the number of parts that we get on that tree through our development and then ensuring that they solidify well. So, gate location certainly can have an effect on part cost. So, if it's not ideal in a location, then we could get fewer parts on that tree, which raises cost, but we always try to work with our customers on all the options of the gating location, how well it's going to solidify, and how that relates back to the cost.

 

Taylor Topper:  
Do you verify the soundness of the component after simulating the gate?

 

Ana Medinger:  
Yes. So, we do, as part of our development, after we do simulations, we do NDT or x-ray every single new part that we work with our customers on to verify the simulation results and verify the soundness of it meets our customers' expectations. So, we have thousands of parts where we both made sure that we're meeting our customers' requirements and then verified our simulation software with what we're seeing during the simulation process.

 

Taylor Topper:
Let's go with this question next. We have more experience with die casting than investment casting. How much design assistance could you or are you willing to give us?

 

Greg Schmidt:
Oh, well, I…

 

Taylor Topper:  
I guess if you wanted to convert to investment casting.

 

Greg Schmidt:
Sure, or it could be during if we're going to prototype a die cast design. Yeah. We'll certainly take a look at the part and make sure that it's certainly within our wheelhouse that the size of the part, the wall thicknesses, and just the general shape of the part, but more often than not, I think we can certainly take a look at it, take a look at the part, give ideas on what we would have to do to make an investment casting, but then to also understand what your end result is of the part. We really need to understand what the application is.

 

Taylor Topper:  
Does porosity ever appear on the surface of the casting, or is it generally contained to the interior part?

 

Ana Medinger:
Sometimes, it can appear on the surface, and again, this is all…depends on whether or not we can allow that. It depends on what our customers' requirements are. So, in some applications, some customers are not concerned with that, but in others, you know, there might be certain requirements that, you know, say they're painting it, they don't want it to look bad, or something like that, we will design that out as part of the design process. So, you know, part of that part geometry process and the simulating of the gates, we're looking for areas that could potentially be a problem for surface shrink.

 

Greg Schmidt:
Sure. Sometimes like inside corners, we like to have a large radius in there because just as that example that we had on radiant heat, inside corners also reflect heat, and sometimes we can have an isolated hot corner that then solidifies last, and we could have shrink on that inside corner. So, we also work with our customers on making sure that the part is designed so we can eliminate those type of defects.

 

Taylor Topper:
Perfect. There are a few questions left, but I'm actually going to follow up online. One of them is just, well, here's a good one you can actually answer, probably generic for everyone, if we send you a STEP file for a part, how long does it take to get a quote back?

 

Greg Schmidt:
Typically, it's taking us a week to get a quote back. Again, that's sort of standard. It also depends on, you know, the part geometry, if there's anything that we have questions about, specifications that we have to hold, or premium tolerances, external operations that may be, you know, like plating or painting can affect the lead time, but typically we can get it within a week.

 

Ana Medinger:
Within a week, yeah.

 

Taylor Topper:  
And what is the typical lead time for you to produce a part about the size of your hand?

 

Greg Schmidt:
Sure. So, I think, if we were given a part, and we have it approved with the customer, and we're ready to launch, if we're going into basically a production-type launch phase, we'd probably be looking at about six weeks to get metal parts. If we're looking at prototyping, typically we could have that done in, you know, 3 to 4 weeks, depending on that part and if it's just a one-off part that we can 3D print.

 

Taylor Topper:
Okay. I think I'm going to have that be the conclusion of our live Q&A. A couple of these, I think are very specific to die casting, which I think would be beneficial to have one of our die cast engineers hop in and answer those. Just to remind everybody about our website, Signicast.com, you can actually request a quote on there. You can ask an engineer anytime. We are typically very speedy at answering any sort of website inquiry, or if you want to email back a reply to the webinar invite that you got, that will come to us, as well, and we'll make sure that your questions get into the right hands.

 

You will, in a couple hours, receive another email reminder, or I guess an email follow-up, with the recording to this webinar. Again, we have everything on demand on the website. Thank you, everybody, for participating today. We have a webinar once a month, whether it be for Signicast, Dynacast, or OptiMIM, so be on the lookout for any of our other webinars. You can also opt in on any three websites. To make sure that you are receiving those webinar invites, follow us on any of our social media, as well. Ana, Greg, thank you. This is a really, really wonderful presentation.

 

 

Greg Schmidt:  
You are welcome.

 

Ana Medinger:  
You're very welcome.

 

Taylor Topper:
Thanks, all, have a good day.

 

Greg Schmidt:  
All right.

 

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Last updated 07.29.2020