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Lost Foam Casting: Process Definition & How It Works

The market for metals has continued to expand in recent times. Products are being innovated by the day, and manufacturers themselves are coming up with new ways to develop metal products and make use of them. 

So, it should come as no surprise that a process as innovative as lost foam casting has become so popular. When you need to cast materials and you find that traditional methods don’t work, this method just might be what you need. 

In this article, we’ll look into the lost foam casting process and what it offers, as well as some important details you might want to keep in mind as you look to implement it. 

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What Is Lost Foam Casting?

Over the years, there have been different names for this process. Some people call it the expanded polystyrene process, while others can even call it “evaporative casting.” Still, most people know it by its conventional name – lost foam casting. 

The process helps when you’ve tried different methods to craft sophisticated and intricate metal materials, but haven’t had much luck with the conventional processes. Here, you get an expanded polystyrene foam mold and cut a pattern – kind of like how you do with traditional injection molding.

From there, the mold is covered with a ceramic refractory material and is buried in loose sand. The covering helps to ensure that it is properly kept separate from the sand around it, and then molten metal is poured into it. As the metal fills the cavity, it completely vaporizes the foam, allowing you to achieve the right shape for the metal. 

The Major Components Of Lost Foam Casting

Every process needs components and parts that help them to operate optimally. If you’re going to engage in them, it’s important to be aware of these components and implement them to ensure that your entire workflow is as seamless as possible. 

If you’re looking for how to cast foam using the lost foam casting process, then here are a few components that you might want to keep in mind generally: 

Get Your Original Pattern Ready 

The first thing you need is a pattern for your lost foam casting process. Most manufacturers make use of expanded polystyrene foam, creating a sophisticated pattern for the part that they’d like to make. Because the material is so easy to carve and work with, you literally won’t have much of an issue here. 

Applying A Refractory Coating

Another important component for casting foam is the refractory coating. Here, you apply the coating to the foam pattern to help it improve its general heat resistance characteristics. 

In most cases, manufacturers combine a binder with fine-grain sand to create this coating. With this, the foam is able to accommodate the molten metal and not wilt when it comes in contact with the latter’s high temperature. And, you’re also able to get a much smoother surface for the part you’re casting. 

A Pattern Cluster For Enhanced Simplicity 

Next, you need to remember to assemble different coated foam patterns to form a tree or a cluster. The use of gating systems ensures that you can connect these patterns together so that metal is able to glow and you can also take out any unnecessary gaseous materials. 

With the pattern cluster, you’re generally able to achieve a much simpler lost foam process. You’ll be able to make several castings with just one pour, and you can trust that the gating system will be able to make metal flow more optima.

Add Some Sand To The Process

Sand is one of the most important parts of the process of making mold foam. But, you don’t just want to get any type of sand – you need loose, unbounded sandy materials, which will help act as the mold material itself. 

As you begin the lost foam process, you’ll need sand to form the cavity for the mold. The material will help keep the pattern straight as you go about the casting process and provide a channel for you to solidify the metal and allow it to take the shape of the pattern. 

Keep Your Sand In A Flask 

You don’t just get sand from anywhere and pour it into the mold – you need a container or a flask to keep it, so it can support your foam pattern cluster. As you would imagine, the flask is usually made of metal – or some other material that can accommodate the temperature and force that is produced as the process of casting foam goes on. 

Compaction Tools 

Different compaction methods can be used to collect the loose sand around the foam pattern cluster and keep it in a single place. The point of this component is to ensure that you can properly handle the molding process and reduce the instances of defects or damages. 

Develop A Solid Pouring System That Works 

As you would expect, different manufacturers have their pouring systems. But, a standard system should come with components like runners, sprues, and gates. Working in tandem, these components will help to ensure that the molten metal is properly guided as it goes into the mold. 

You surely don’t want any turbulence as the filling step takes place, so this is very important. 

Nothing Works Without The Molten Metal 

You could have aluminum, or you could have some other non-ferrous alloy – whatever it is, you need a molten metal material when creating a foam mold

For lost foam aluminum casting, we recommend that you heat your metal to a molten state, and then pour it directly into your mold. From there, it accepts the shape of the vaporized foam pattern as it acts on the base material. 

The Cooling Step Is Needed Too 

After the entire lost foam aluminum casting process is done, you need to ensure that everything is properly cooled. Let the molten metal cool off and get solid as it stays within the mold, and it will be able to properly conform to the shape of the pattern you’re trying to create. 

You can let it cool naturally, or you can incorporate controlled cooling if you have specific metallurgical properties that you’d like to bring out. 

The Lost Foam Casting Process

So we understand the materials and components that will need to be present to ensure that foam molds can be created. Now, let’s examine how the process of styrofoam mold casting can be done. 

As you would expect, different manufacturers can generally follow their own processes. However, a standard procedure tends to operate like this: 

Start By Building The Product Pattern 

Before you even do anything, you need to create a pattern for the metal part with the use of the EPS foam. The benefit of this is that you can easily carve the foam into intricate parts, so you won’t have much of an issue here. It’s probably why the material has become so popular in recent times.

Take Your Pattern & Coat It

Next, you get a refractory material and use it to coat the foam pattern directly. In most cases, this process is done with fine-grains and – like we said. Simply mix it with a binder, and you’ll be able to create a coat that optimizes heat resistance for your base material. 

The foam will be able to hold its own against the elevated temperatures of the molten metal, and you’ll have a  much easier time processing it. 

Assemble The Patterns For The Foam 

Now, you can create different coated foam patterns and combine them to build a cluster. The use of gating systems is important here, as these systems will create channels where the molten metal will be able to flow – and also add vents for gases to be released seamlessly. 

Introduce Sand To The Mix

With your coated foam ready, place it in a flask. The loose sand will already be in the flask at this point, and if you recall, the job of the sand is to support the entire pattern as the casting process is taking place.  

The loose nature of the sand also ensures that gases will be able to escape easily as the process goes on, so keep that in mind. 

Compact & Set The Sand 

Place the sand materials around the foam pattern cluster so that molding can be done properly. This step also allows you to prevent the formation of any material defects, and it is an important quality assurance process. 

Calmly Pour The Molten Metal

This is one of the most important parts of the entire process. Essentially, you take the molten metal and pour it directly into the mold. 

You can implement lost foam aluminum casting or make use of any other non-ferrous alloy. With its high temperature, the foam pattern immediately disappears, leaving only the cavity behind. 

The Metal Takes Shape

Here, you simply wait. Let the molten metal get solid inside the mold, and it will take on the shape of the pattern by itself. Remember that refractory coating that you added to the foam in the first place? Its job will be to offer a smoother surface finish to the entire cast. 

Let Air Take Its Course

At this point, you’re almost at the finish line. All you have to do is allow the metal to cool down, so it can properly solidify. You can let natural air do its work, or you could implement controlled cooling processes. 

Unveil The Cast Metal 

Break the mold, and you’ll be left with the cast metal part. Separate what you’ve created, remove the gating system, and you’re good to go!

The Finishing Touches

Now that you have your part, you can handle any required finishing operations that are left for you to achieve the final appearance and specs. Inspect your part, conduct any additional quality control processes, and you’re done!

A Few Things To Remember

While the process might seem pretty straightforward, you need to keep an eye out for a few things if you really want this whole process to work as it should:

The Pattern Needs To Be Kept: 

You might be wondering, “Why do they call this process ‘lost foam?’” Well, it’s simply because the original foam pattern ends up getting lost as part of the process. What you’re left with is the shape of the part you’re looking to create itself. 

Be Very Intentional About Your Design 

One of the most important things is for you to carefully watch your pattern design. When done well, you’ll be able to optimize the flow of the metal and ensure that the final cast is structurally sound. 

Don’t Lose Your Guard

Quality control is key when it comes to how to cast foam. All through the process, make sure to keep an eye on all moving parts. 

What Is The Importance Of Lost Foam Casting?

In today’s manufacturing industry, lost foam casting has become one of the most popular processes out there. You might be wondering why that is – well, it’s mostly because you get a host of benefits, such as the following: 

Take Casting To A New Level

Traditional casting methods are just so limited. There are some sophisticated and complex shapes that they just won’t be able to create – and for these, lost foam casting easily works out. 

Cast Once And For All 

The styrofoam mold casting process results in what experts refer to as near-net-shape casts. Essentially, the results you get from this process are almost perfect – you won’t need to conduct any additional machining, and you’ll be able to save a great deal of money as a result.

Spend Less On Tools

Compared with traditional casting methods, lost foam casting doesn’t necessarily require any solid molds or patterns. As such, you won’t need to pay for permanent toolins, and your overall cost profile ends up significantly reduced. 

You’re Free To Build Whatever You Want 

Nothing describes freedom like being able to build what you want. And with lost foam casting, you’re able to do just that. Enjoy higher levels of flexibility in your casting, and create parts that are as sophisticated as you want them to be. 

The Surface Finish Is Much Better

Thanks to the presence of a refractory coat on your foam, you’re able to create a considerably smoother surface finish on the cast part. Once again, this means that you don’t need any more finishing operations. 

Cut Lead Times & Get The Job Done 

The implementation of lost foam casting means that you won’t have to deal with lengthy lead times. Compared with traditional casting methods, you’re able to get the job done quickly with foam for lost foam casting and move on to the next thing. 

Here, you have a single-pour process that allows you to make different castings at one go. By cutting time spent, you get higher levels of efficiency and won’t need to go through so many production processes.

No Cores As Part Of The Process

One of the biggest drawbacks of traditional casting processes is the fact that they rely on cores to create most of the internal features. With lost foam casting, you don’t need these – the foam material defines its internal features, so you get higher levels of efficiency. 

The Environment Benefits Too 

It’s pretty rare to see an industrial process that doesn’t affect the environment. But, somehow, lost foam casting manages to do this. Compared to many traditional casting processes, you’ll find that this one doesn’t produce much waste or use so much energy. The result is that you get to protect the ecosystem as you also achieve efficiency in creating your desired parts. 

You Can Add Automation As You Want 

By its nature, the process of getting foam for mold-making allows you to add elements of automation. This improves the quality of the product you end up with and can go a long way to cut down on your overall cost profile too.

Possible Process Challenges To Note

With all the advantages we’ve pointed out here, it’s understandable if you feel like lost foam casting is a completely foolproof process. But, things don’t necessarily work that way. There are a lot of things to keep in mind when it comes to this process, and many of them can affect the final outcome or seamlessness of your workflow: 

Watch The Foam Patterns

When done right, lost foam casting ends up with a product that is solid and reliable. But, for that to happen, you also need to keep an eye on the foam patterns as they have a tendency to get damaged while you handle or transport them. As long as you can ensure that they’re good, you shouldn’t have any issues. 

Coating Needs To Be Uniform

Another important stipulation has to do with the thickness of the coating. You need to make sure that it is spread evenly across the foam, because any inconsistencies can lead to differences in the surface finish and the dimensions of the finished product. 

Ensure A Strong Connection 

It is beyond critical to make sure that the foam pattern and the refractory coating are properly joined. If the adhesion isn’t strong enough, the coating will fail when you pour in the molten metal. 

Don’t Keep Any Gases In The Loop 

If you want the finished product to be of high quality, then you need to make sure that vapor and gases are allowed to escape properly. This allows you to prevent issues like voids and gas pockets, which will only affect the quality of your casting even more. 

How Does The Metal Move? 

You need to make sure that the molten metal properly and wholly fills the mold cavity without penetrating too much inside the coating. If the filling is incomplete – or if the level of penetration is too deep – you can end up with a faulty finished product. 

Control The Metal’s Temperature

As you pour the molten metal, make sure that you keep tabs on its temperature. The last thing you want is for the pattern to vaporize too early or too late. 

Ensure Proper Sand Compaction 

Doing this sees to it that the mold is structurally sound. If compaction isn’t adequate, you could find that the mold will collapse, or that the casting will develop structural defects. 

The Risk Of Pattern Collapse

Apart from temperature, weight is another thing you need to be careful of when it comes to the metal pouring process. Make sure that the foam pattern can properly withstand the metal’s weight so that the pattern doesn’t collapse and you don’t end up with a defective cast. 

Problems With Mold Breakout

When the mold solidifies and you need to take it out, you might find that breaking it apart can be a bit of a hassle. If there are any residual sand particles, then you might need a little bit more effort to take them out. 

There’s A Lot To Keep Tabs On

The general process of lost foam casting tends to be very finicky. There are so many moving parts, and you need to keep an eye on all of them to make sure that quality is as optimal as possible.

What Makes Lost Foam Casting Stand Out?

Casting is done in different forms – and as you can imagine, lost foam casting is just one of the many options available. But, how does it hold up against the other forms that we have? 

Lost Foam Casting vs. Sand Casting

Much has been said about sand casting and its relation to lost foam casting. Both operations involve the use of loose sand, and there are some who actually believe that the sand casting process can be used interchangeably with lost foam casting. 

But, as you’d imagine, both processes have their differences, and understanding them will helo you make a decision on which to work with. Here is a quick breakdown of what those differences look like:

Parameter Lost Foam CastingTraditional Sand Casting 
What Are You Working With Expanded polystyrene (or, EPS, as it’s called)Mostly wood – although you can work with some plastics and metals 
The Speed Of Making PatternsIt’s quite fast It takes time, and you need to be very skilled here
How Are Patterns Removed? Vaporization takes care of this You can remove patterns and use them again in other castings 
How Much For The Equipment Generally low, since you’re not dealing with permanent moldsCosts can be pretty high since molds need to be made and maintained 
Do They Work For Intricate Shapes?Yes, this process has no issues with complex formsFor complexity, this process is quite limited 
How Does The Surface Finish Look? You get a smooth, refined finish overallFinishes can be rough around the edges, so you might need additional processing work
Comparing Material EfficienciesPretty high, since you’re not working with a permanent patternMaterials can waste since you tend to use them for more permanent patterns 
How Quickly Can You Get Done? Lead times are short, and the process has been cut down in terms of complexityYou get longer lead times – especially if you’re working with a complex pattern. 
Their Impacts On The Environment This process is pretty eco-friendly. You don’t have much material waste, and energy use is optimized The presence of material waste means that this process will most likely leave a mark on nature.

 

Lost Foam Casting vs. Investment Casting

Next, we have investment casting. Another of the traditional casting processes, this one is generally loved because it also allows manufacturers to work with some pretty complex shapes. But, how does it compare with the process of casting foam?  

 

Parameter Lost Foam CastingInvestment Casting 
What Are You Working With Expanded polystyrene (or, EPS, as it’s called)Wax, or some other material that can be used in disposable pattern creation 
The Speed Of Making PatternsIt’s quite fast Not so fast, and there’s a considerable skill requirement
Do They Work With Complex Shapes? Yes. You won’t have any issues with intricate geometries Also very suitable with complex shapes – a big benefit for the process
How Efficient Are The Materials? Very efficient. Waste is minimized, so you don’t have to worry about thisRelatively efficient, although you need to be very vigilant to avoid wastage
Do They Work For Intricate Shapes?Yes, this process has no issues with complex formsFor complexity, this process is quite limited 
Do They Need Additional Machining?In most cases, noGenerally, no. But, when compared to lost foam casting, this process doesn’t do so well when acting as a standalone option
How Much Material Can You Make?Lost foam casting works well in high-scale production settingsAlso solid for high-volume production, so you don’t have to do so much work to get multiple products  
The Risk Of Wear On Tools You don’t have to deal with permanent molds, so this risk is minimalTooling wear is a bit of a risk – especially if you want to run multiple casting cycles
Can You Automate Your Process?The process is already highly automated, but there’s always room for moreThere are some aspects of the process that can be automated, but much of it remains highly manual

 

Conclusion

Lost foam casting has become a standard manufacturing process. While there are several components that need to be watched, there is no doubt to the fact that the process offers a myriad of advantages. 

With KDM Fabrication, you have a partner that can help you ensure that everything with this process is done right. Reach out to us today, and let’s help you out. 

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