Billet vs. Cast vs. Forged—What’s the Real Difference?

Portal gear lifts are packed with features, materials, and all sorts of other bits and bobs that can leave your head spinning when you’re trying to make sense of them. One of the most in-your-face features is the construction of the portal boxes.

You’ve probably heard a lot of talk about the difference between cast, billet, and forged aluminum housings–everybody seems to have an opinion.

We’re going to take a look at the actual functional differences between these materials, and see why your portal box’s material might not be the most important factor when it comes to the overall strength of a portal kit.

Cast Aluminum

Cast aluminum is a very strong but light metal that’s really great for a wide variety of applications. It’s especially common in the automotive industry where it’s used for engine blocks, transmission housings, differential housings, pistons, cylinders, and more.

It’s right at home on your side-by-side, but how strong is it really? That’s where simply saying “cast is this strong” becomes insufficient. Let’s take a look and see why.

Cast Materials

The exact type of aluminum used is what gives a cast part most of its properties. At SuperATV, we use A380 for our cast aluminum housings. It’s a very common casting metal because it behaves well when melted and cooled in a mold, and it’s strong.

Here are the relevant mechanical properties of A380:

Yield strength is especially important on portals. That’s the amount of force required to deform the material. Deformation of any kind is bad in a tightly engineered box designed to hold perfectly meshed gears. Note how much lower the yield strength is than the tensile strength. Keep this number in mind as we go on. However, these numbers are not the whole story.

The Casting Process and Strength

Simple strength numbers don’t really tell you what’s going on, or what kind of forces an actual cast part can take in real life conditions. You need to know how casting works to understand that.

To make a cast part, you first have to melt down A380 aluminum and pour it into a mold. The mold is then carefully cooled and removed to give you the part you need. This extra melting and cooling process (aluminum is already heated and processed to form ingots, slabs, and bars) disrupts the internal structure, or “grain,” of the metal and gives an opportunity to introduce voids and inclusions—all of which can lower strength.

Thankfully, modern casting can keep those issues to an absolute minimum to keep the final part’s properties very close to the original mechanical properties of the material, but usually not quite as good.

Billet Aluminum

Billet aluminum is generally considered a stronger material than cast. Billet parts are made from a single block of material that is machined down on a CNC mill. The result is a gorgeous part that can be made to match an engineer’s design with perfect precision. And it’s pretty common to see billet aftermarket parts as upgrades to the OEM cast parts on your side-by-side.

Billet Materials

Again, the materials used are more important than the process used to form them. For our billet portal boxes, we use 6061-T6 manifold quality billet aluminum. It’s strong and is typically found on parts with tight tolerance that require high strength like aircraft parts or camera lenses.

6061 aluminum has properties that look like this:

So while the ultimate tensile strength is less on 6061, the yield strength and shear strength are both significantly higher. 6061 is clearly a stronger material, but what does the manufacturing process do?

The Billet Process and Strength

Here’s the great thing about carving out a part from a chunk of billet: it keeps those theoretical strengths all the way to the end. It doesn’t make any significant changes to the grain of the material, so the properties don’t change.

We alluded to the other huge advantage of CNC-machined billet earlier—ultimate precision. We can make exactly what we design, which gives us the freedom to make it even stronger.

Forged Aluminum

One of the big buzzwords on the portal scene right now is forged aluminum. It’s the ultimate way to make a part, right? All other things being equal, forged aluminum is pretty cool, but again, it’s not that simple.

Forging Materials

Materials make all the difference. There are lots of different aluminum alloys that could be used in a forged aluminum part. One of the most common alloys used for forging is 6061, so let’s assume that’s what the forged aluminum portal boxes on the market are using.

Since it’s the same material used in our billet boxes, the mechanical properties will be identical out of the gate.

The Forging Process and Strength

The cool thing about forging is that it alters the internal structure in a good way. When a forge presses the part into shape, the grain of the metal aligns with the shape of the part. So in some ways, it’s stronger than the original numbers. But, just like with all manufacturing processes, the design of the part will determine the parts ultimate strength.

And it does require some compromises to design. Parts have to be designed in a way that they can be forged.

Which brings us to the final point.

Design Matters More

Here’s the whole point: if you’re focusing too much on the properties of the metals and their respective processes, you’re missing the more important details of portal boxes. Namely, its design.

It’s not enough to just make a part out of forged or billet aluminum and say that it’s definitely stronger than cast, it needs the design to back it up. We can’t really speak for the forged housings out there but our billet and cast housings are made with the utmost precision.

They’ve been stress, fatigue, and pressure tested more than any other portal housing. We’ve put them in our breaking machine so we can see how much force it takes to break them, and exactly where they break when they do. We’ve hooked them up to air compressors to see how much pressure it takes to cause a leak or failure (hint, they don’t leak or fail due to pressure). They circulate gear oil efficiently to make sure the internals are well lubricated. And, most importantly, there are hundreds of thousands of individual portal boxes out in the wild today. Whatever one-in-a-million problems our boxes might have, we’ve seen them and addressed them.

Gears Matter More

It’s not just the box itself that matters, the internals make a big difference. The main purpose of the box is to hold all the internal components within tolerance, but if those components can’t maintain tolerance on their own, the strongest box on Earth won’t save them. So pay attention to gear material and finishing—you can’t spell “portal gear lift” without “gear” after all.

The real functional difference between cast and billet aluminum housings is simply that if you break a gear (through neglect or a fluke or whatever), the broken gear is more likely to break a cast housing than a billet housing. Strength starts with the gears, not the housings.

Cast vs. Billet vs. Forged

On paper, forged wins, but in portal boxes, design trumps process. Cast aluminum can beat forged if the design is right. And remember, when considering the differences between two portal gear lifts, look at what matters most: the gears, then the design, then the materials, and then the process.

Forged, cast, or billet—it’s just not as important as you think.