Are billet casings really better than cast casings?

Billet vs casted sequential gearbox

There are a lot of myths and half-truths around the comparison of billet and casted parts. In the following lines we will therefore compare the advantages and disadvantages of both methods and their suitability for the gearbox parts in question.

Billet sequential gearbox

What is billet aluminum?

Billet aluminum is a type of metal created by taking a single block of material, machining it into a 3D designed shape by a CNC milling machines. The result is a very good-looking part that is also very strong.

It is therefore very suitable to use this method on extremely stressed gearbox components such as shafts, wheels, shift forks, shift mechanism components and other smaller parts. On the other hand, this process required a lot of machining time and there is a large percentage of material waste. This means that the production of large parts such as casings is much more time-consuming and expensive than casting. Billet is therefore more suitable for prototype or small (one-off) production.

Casted sequential gearbox

What is casted aluminum?

Cast aluminum is a type of metal created by melting it down and pouring it into a mold. The material used is a high-quality alloy commonly used in the aerospace industry. The casting passes through a heat treatment to remove internal tensions, followed by hardening. But, due to the alloy melting, the cast part has less strength as the billet part (at least 380MPa tensile strength compared to approx. 580 MPa tensile strength) and also has a higher surface roughness. However, this method is faster, less expensive, more suitable for larger (mass) production and can have a more complex and optimal design than the billet version due to the casting technology.

Design – an important game-changer.

A typical argument for the choice of billet casing is the insufficient strength of the cast casing compared to the billet version due to the material. However, you can't simply make a billet aluminum casing and say it is stronger than a cast casing. We must not focus too much on the material, very important is also design of the casing, such as internal parts of the gearbox.

The main job of the casings is to keep the shafts and gears with an appropriate clearance to each other. Thanks to good design verified by strength analyses of the packaging (FEM), the cast packaging is reinforced in the shaft bearing area. According to casting method, the casing design can also be
light-weighted to the maximum in less important areas where machine tools (in billet method) would not reach. Like the billet, the cast casings are made from high-strength cast aluminum. The overall strength is therefore comparable.

Strength starts with the gears, not the housings.

The other thing is that even the strongest casings is useless if the components inside the gearbox are weak. Ask yourself: Has a gearbox case been broken due to its insufficient of strength, or was it due to an internal component failure (e.g. broken tooth, shaft, dog ring) or an external factor (e.g. crash accident)? That's why we make calculations of tooth geometry, shaft and dog ring strengths by SOLIDWORKS and KISSOFT software at top priority. This is an area, where billet technology plays an indispensable role.

So, what kind of housing does X SHIFT prefer?

There's a relatively simple answer to that: Casted. On paper, the billet wins, but a casted case can beat the billet if the design is right. So, if you're comparing two gearboxes - one billet and one cast - you should look at the following hierarchy: Strength of gears, proper case design, used material and manufacturing process.

Cast packaging is a high standard not only at our company but also at other top gearbox manufacturers. Our gearboxes work perfectly even in the most powerful drag specials over the world and can withstand over 1000 Nm of engine torque.

Overall, casted casings are quite sufficient for use in the racing industry and there is really no benefit to using a "billet" casing other than it’s look great and shiny.

X Shift Gearboxes Team