This article first appeared on BikeRadar.
In part one of this four-part series, we showed you how Giant takes rolls of raw carbon fiber and turns it into usable unidirectional pre-preg fabric. Now we'll show you how Giant takes that material and turns into a frame – and the process is much more involved than many might expect.
While carbon fiber is more correctly described as 'carbon fiber reinforced polymer', it's the fiber that gives the part its incredible structural properties; the epoxy resin is just there to hold everything together. Every carbon fiber frame is made of a collection of individual pieces – some as small as a SIM card – and all of them have to be placed and oriented precisely in order for the end product to work as intended.
It's not a matter of pulling a lever and spitting out a complete frame as if one were molding plastic toys. According to Giant, just one frame can take up to nine hours to build from start to finish.
Pieces of the puzzle
It's difficult to envision just how many different pieces of carbon fiber are used in a factory of this scale.
According to Giant, a full composite frame such as the flagship TCR Advanced SL comprises more than 500 individual swatches with additional variations for each size. Each frame model then also has its own specific set of pieces and Giant makes dozens of different carbon fiber frame models. Even when two models share the same exterior shape – and thus, use the same mold – their fiber contents are usually different, thus requiring yet another specific collection of pieces.
Do the math and it's a staggering number of little chunks of carbon fiber material to keep straight.
Each of those pieces of carbon fiber starts out the same way, however. Up to six rolls of pre-preg fabric (which are made in-house) are loaded on a big carousel that can be rotated to access the specific type of fabric required for a production run. Sheets are first rough-cut into more manageable pieces, and then the individual swatches are stamped out on hydraulic presses like high-tech cookie dough. Afterward, each 'cookie' is individually marked, collected, and (very carefully) sorted into labeled bins.
All of this is also done in a climate controlled room so as to prevent premature resin curing – a critical requirement given Taiwan's tropical setting.
It's one thing to keep all of those little bits sorted and separated but it's another entirely to make sure they're all placed where they need to go in a mold. Giant's solution for minimizing errors and maximizing the efficiency of the process seems particularly clever.
Every frame subassembly is visually depicted on one or more corrugated plastic boards with individual spots for each piece of carbon fiber. Every spot is clearly labeled in text and images and outlined with rigid borders that correspond to the actual shape of the piece. In other words, if it doesn't fit in the box, it isn't supposed to be there.
Gathering up pieces for a frame, therefore, is sort of like filling out an order form: workers simply match up the description in the tray compartment with the storage bin and if it all goes well, that piece of carbon fiber should fit perfectly.
Once those trays are filled, they're then loaded into covered carts and transported to another climate-controlled room where the pieces are laid up into frame pieces.
While Giant takes great efforts to remove potential errors from the process, actually assembling all those little pieces of carbon fiber is still highly labor intensive. There's a massive amount of tooling involved, too.
Frame sections are built up on a mix of rigid plastic mandrels, internal silicone rubber molds, and steel inserts. The mandrels provide workers with a solid surface on which to lay the carbon pieces and since they closely approximate the desired negative space of the frame, those carbon pieces are more likely to stay where intended after the frame is cooked. Internal silicone rubber molds – which stay in place during the curing process – further help to produce crisp interior dimensions, particularly in areas with complex geometry like bottom bracket shells, head tubes, and seat stay yokes.
Areas with especially tight tolerances like head tube and bottom bracket openings get additional steel inserts so that bearings and bearing cups fit correctly after the frame is fully assembled.
After each assembly is laid up, an inflatable plastic bladder is fed through and then it's all sandwiched inside a massive steel clamshell mold for baking.
As one would expect given an operation of this magnitude, the actual curing process is highly automated. Once the clamshell molds are loaded, robotic conveyors and carriers move each mold into and out of a bank of ovens. This not only guarantees that frames will cook for the prescribed amount of time and at the correct temperature but also helps decrease the risk of injury since workers won't have to directly handle piping-hot steel molds themselves.
Afterward, the molds are cracked open, the cured frame sections are removed, and then begins a series of finishing operations. Excess molding flash is knocked off with files, rough edges are smoothed with a variety of sanding tools, holes are drilled for water bottle bosses, computer sensor mounts, and front derailleur tabs, and seat tubes cut square and slotted.
Once that's all done, the frame sections are sent to yet another room where they're glued together, overwrapped with additional layers of carbon fiber, fixture in alignment jigs, and sent for another round of curing.
After the glue is fully cured, the frames are sent off for yet another round of finish work. Surfaces are buffed with finer-grit sanders, small imperfections are masked with filler compounds (a common practice in large-scale carbon frame manufacturing), and metal pieces such as riveted in place.
It's only after all that (and countless quality control checks) do the frames finally head off to paint, final assembly, and packing.
We'll first take a look at how Giant builds its higher-end aluminum frames in part three of this exclusive series.