A soda can starts as a flat sheet of aluminum and becomes a finished, filled container in a matter of seconds. The process, called Draw and Wall Ironing (DWI), transforms a metal disc into the thin-walled, pressure-resistant cylinder you crack open without a second thought. Modern production lines run at over 2,000 cans per minute, making beverage cans one of the fastest mass-produced consumer products on the planet.
From Flat Sheet to Cup
Manufacturing begins with a massive coil of aluminum alloy sheet, typically about 0.3 mm thick. The coil is unwound and fed through a lubricator that applies a thin film of oil to both sides. This lubricant prevents tearing during the intense forming steps ahead.
The lubricated sheet enters a cupping press, which uses circular dies to punch out dozens of flat discs and stamp each one into a shallow cup in a single stroke. These cups are roughly three inches in diameter and look nothing like a finished can. They’re short, thick-walled, and flat-bottomed. At this point, the cup holds far more metal than the final can needs, and the next step is where the real shaping happens.
Wall Ironing: Where the Can Gets Thin
Each cup moves into a bodymaker, the machine that does the most dramatic work. A long punch rams the cup through a series of progressively tighter steel rings in a process called wall ironing. There are three ironing stages, and each one stretches the aluminum thinner and taller. Coolant floods the process to prevent the metal from overheating and weakening.
By the end, the sidewall is far thinner than the original sheet, sometimes just 0.1 mm. The bottom of the can, by contrast, stays thicker and is pressed into a concave dome shape during the same stroke. That dome isn’t decorative. It helps the can resist the internal pressure of carbonation, which typically sits between 50 and 60 PSI at room temperature and can climb as high as 90 PSI in hot weather. Without that inward curve, the flat bottom would bulge outward and the can wouldn’t stand up.
After forming, the can’s top edge is ragged and uneven. A trimmer shears it to a precise, uniform height.
Washing, Coating, and Printing
The freshly formed cans are covered in lubricant and metal fines, so they pass through a multi-stage washer that cleans and chemically treats the surface. This treatment helps ink and coatings bond to the aluminum.
Decoration comes next. Most cans are printed using a process similar to offset printing, where a rubber blanket transfers ink from multiple plates onto the spinning can in a single pass. Each color gets its own plate, and registration has to be precise at line speeds of thousands of cans per minute. Some manufacturers use flexographic printing, which relies on flexible relief plates and works well for vibrant, high-volume runs. Inks are typically water-based for environmental and safety reasons, or UV-curable varieties that harden instantly under ultraviolet light for better scratch resistance.
After printing, the exterior gets a clear protective lacquer that prevents the ink from scuffing during shipping. Then the cans move to an oven for curing.
The Interior Liner
If your soda touched bare aluminum, the acid in the drink would corrode the metal within days, ruining both the can and the beverage. To prevent this, every can receives an interior spray coating, a thin polymer film that acts as a barrier between liquid and metal.
For decades, the standard liner was an epoxy resin based on bisphenol A (BPA). It worked exceptionally well, but health concerns over BPA’s potential to leach into food and beverages pushed the industry toward alternatives. Most major manufacturers have transitioned to acrylic or polyester-based liners that contain no BPA. These coatings are sprayed onto the inside of the can and baked at high temperatures to form a continuous, food-safe film just a few microns thick.
Making and Attaching the Lid
The lid is manufactured on a completely separate line from the can body, and it’s actually a more complex piece of engineering. Lids are made from a slightly different, harder aluminum alloy because they need to hold the score line and rivet without failing.
A press stamps flat aluminum sheet into the lid’s shape, complete with a curled edge that will later be crimped onto the can body. Then a scoring tool cuts a shallow groove into the lid in the shape of the opening you’ll eventually push in. This score line is carefully calibrated: deep enough to break cleanly when you pull the tab, but shallow enough to keep the can sealed under pressure during shipping and storage.
The stay-on tab is made separately from another strip of aluminum, then attached to the lid with a small integral rivet formed from the lid metal itself. When you lift the tab, it acts as a lever. The first motion pries the scored metal near the rivet, breaking the seal and releasing pressure. Then the fulcrum shifts, and the tab pushes the scored flap downward into the can to create the drinking opening. The tab never detaches, which solved the litter and choking hazard problems of the older pull-tab design.
Lids aren’t attached to can bodies until after filling. The empty cans ship to a beverage company open-topped, get filled with soda, and then the lid is seamed on using a double-seam process that folds the lid edge and the can body edge together in an airtight lock.
How Thin Walls Handle High Pressure
A finished soda can’s sidewall is thinner than a credit card, yet it holds carbonation pressure that would launch the lid across a room if the seam failed. This works because of geometry. A pressurized cylinder distributes force evenly around its walls, and the dome-shaped bottom redirects pressure inward rather than letting it push outward. At a typical 50 to 60 PSI, the hoop stress in the sidewall reaches about 45% of the aluminum’s yield strength. That leaves a comfortable safety margin, even during warm weather when internal pressure can spike to 90 PSI.
One thing to note: an empty, unpressurized can is surprisingly fragile. You can crush one easily by hand. It’s the internal pressure from carbonation that gives a sealed can its rigid feel. The carbonation and the can are structural partners.
Recycling and the Closed Loop
Aluminum cans are one of the most recyclable consumer products in existence. A recycled can that gets collected and processed can return to a store shelf as a brand-new can in less than two months, making it one of the tightest closed-loop cycles in packaging.
The energy case is even more compelling. Producing aluminum from recycled cans requires 90% less energy than smelting it from raw ore, according to the U.S. Department of Energy. Since the original smelting process is extraordinarily energy-intensive (it involves dissolving ore in molten salts and running massive electrical currents through it), that 90% savings is substantial. A recycled can skips all of that. The aluminum is simply melted down, re-cast into sheet, and fed right back into the same coil-to-can process described above. The metal itself doesn’t degrade through recycling, so a single batch of aluminum can cycle through the system indefinitely.