If you were to walk into a high-end aerospace machine shop, the first thing you would notice is not the gleaming airplane parts, but the garbage.
Next to every massive, multi-million dollar CNC (Computer Numerical Control) machine, there are bins filled with twisted, sharp, shimmering metal shavings. This is “swarf.” To the casual observer, it looks like trash. To a manufacturing accountant, it looks like burning money.
This waste is the visible symptom of an accounting metric that haunts the aviation industry: the Buy-to-Fly ratio.
In simple terms, the Buy-to-Fly ratio compares the weight of the raw material purchased to the weight of the finished part that actually flies on the aircraft. For decades, this ratio has been alarmingly high. To build a 1-kilogram titanium bracket, a manufacturer might have to buy a 10-kilogram block of metal. The ratio is 10:1. For complex, monolithic structural components in military jets, that ratio can skyrocket to 20:1 or even 30:1.
This means that for every pound of high-grade metal that makes it into the air, nine to twenty-nine pounds are machined away, turned into scrap, and swept off the floor. In an era where sustainability and cost-efficiency are paramount, the Buy-to-Fly crisis is becoming an untenable business model.
The Sculptor’s Dilemma
The root of this problem lies in “Subtractive Manufacturing.” For the last century, the only way to make a strong, precise metal part was to start with a billet—a solid block of metal—and cut away everything that didn’t look like an airplane part.
It is the industrial equivalent of Michelangelo carving David from a block of marble. The result is beautiful, but the process is inherently wasteful.
This method is particularly painful when working with titanium. Titanium is the darling of the aerospace world because it is incredibly strong, lightweight, and heat-resistant. However, it is also notoriously difficult to refine. Extracting titanium from ore and processing it into a “sponge” and then into an ingot requires immense amounts of energy. It is expensive to buy and expensive to ship.
When an engineer designs a complex wing rib that is mostly empty space (to save weight), the manufacturer still has to buy a solid block that encompasses the entire volume of that part. They then spend days or weeks using high-speed cutters to turn 90% of that expensive block into chips.
The “Swarf” Trap
One might assume that the scrap metal is simply recycled, mitigating the loss. While true for aluminum (which is easily melted down), recycling titanium swarf is fraught with difficulty.
Titanium is highly reactive. During the machining process, the chips are often contaminated with coolants, cutting oils, and tool fragments. To be reused in aerospace-grade applications, this scrap must be cleaned and processed to an incredibly high standard of purity. Often, the cost of cleaning the swarf exceeds its value, meaning it is “downcycled” into golf clubs or paint pigment rather than being turned back into airplane wings.
The financial loss is double-ended: the manufacturer pays for the raw material up front, pays for the electricity and tooling to cut it away, and then recoups only pennies on the dollar for the waste.
The Additive Solution: Near-Net-Shape
The solution to the Buy-to-Fly crisis is to stop acting like sculptors and start acting like builders. While carbon fiber manufacturing has successfully revolutionized the production of lightweight fuselages and wings, the metal components of the aircraft have lagged behind in efficiency. This is where Additive Manufacturing (AM) steps in to close the gap.
Additive manufacturing flips the ratio on its head. Instead of starting with a block, the process starts with a bed of metal powder (titanium, Inconel, or aluminum). A laser or electron beam fuses the powder layer by layer, building the part from the ground up.
The critical difference is that the laser only melts the material that is needed for the part. The surrounding powder remains loose and unaffected. Once the build is complete, that loose powder can be sifted, reclaimed, and used for the next build.
This brings the Buy-to-Fly ratio down from 10:1 to nearly 1:1.
The “Weight Spiral” Reversal
The benefits extend beyond just material savings. In the subtractive world, engineers are often discouraged from designing truly optimized shapes because they are too expensive to machine. A hollow, lattice-filled bracket might save 20% of the weight, but if it takes 50 hours to machine the complex internal geometry, it isn’t worth it.
With additive manufacturing, complexity is free. The printer does not care if it is printing a solid block or a complex honeycomb; the time and cost are roughly the same. This allows engineers to design parts that are topologically optimized—placing material only exactly where the stress loads require it.
This creates a virtuous cycle.
- Lower Buy-to-Fly: We buy less raw material.
- Lighter Parts: The parts we build are 30-50% lighter than their machined counterparts.
- Fuel Savings: A lighter aircraft burns less fuel over its 30-year lifespan, reducing operating costs and carbon emissions.
The Supply Chain Shift
The implications of solving the Buy-to-Fly crisis ripple all the way back to the mine. If the aerospace industry adopts additive manufacturing at scale, the demand for raw titanium ore may stabilize, even as aircraft production rates increase.
We are moving from a supply chain defined by volume (moving massive billets of metal around the world) to one defined by value (moving high-quality powder and digital files).
The transition is not without its hurdles—powder management requires strict safety protocols, and certifying printed parts for flight is a rigorous process. However, the economic argument is settled. In a world of finite resources and thin margins, the days of carving airplanes out of blocks are numbered. The future of flight belongs to those who can build with precision, leaving the waste—and the swarf—in the past.
