What is destined for fine riding and precise lines, first comes out of a brute of a machine at the beginning of its life. This 24 t machine injects 680°C hot liquid magnesium in 0.2 seconds and produces 35 lowers each hour. The standard way to make a fork lower is a magnesium die casting process. However, and like in real life, it takes a lot to get the best out of it. In this chapter we show you the process from an magnesium block to the lower of the F 535 ONE.
1. THE LIQUID MAGNESIUM ALLOY
starts out as bars of solid magnesium that are fed into the melting oven by an automatic feeder and heated at 680°C, temperature at which the alloy becomes fully liquid. For ideal production efficiency the liquid magnesium is stored in a highly insulated melting oven. From there, it is brought into the machine that injects it into the mold. The mold is closed by hydraulic cylinders exerting a force of 350 tonnes to keep it closed and tight. The actual injection then only takes 0.2 (!) seconds. After that the pressure is kept up for a few seconds to allow the material to fill all the voids and to start cooling. Next, the mold opens and the part is removed by a robot. The mold is then sprayed with a lubrication fluid and cooled before it closes again to begin a new cycle.
2. THE MOLD
is made from steel using a mix of 3D machining and eroding. It is composed of a top and bottom part, the core that creates the hollow section inside the lowers, and two side inserts which create the hollow sections of each dropout. The liquid magnesium is injected into the mold through four entry ports and exits it into multiple overflow cavities. It’s important to make sure no air gets trapped inside the part and to always assure the mold is completely filled to result in a faultless part.
3. INJECTION & COOLING
The liquid alloy is injected into the mold, immediately water cooled and removed from the mold for further cooling. Since a magnesium die casting machine can’t simply be switched off in the evening like you can turn off your computer when you leave the office, production runs 24/7. Until here it’s an almost fully automated & robotized process.
4. ROUGH FINISHING/DEBURRING
This is where it gets quite labor intensive. All the excess material which has flowed through the mold and filled the so-called «risers» designed to take it up, has to be removed. It is broken off by hand and cut with bandsaws. At this stage any eventual «flash», material that has exited between the two mold halves, has to be removed too.
5. SANDING, POLISHING & PRECISION MACHINING
The cold and deburred lower is sanded and polished for a uniform and smooth surface. For the final fork assembly and for its smooth function in the bike, all the contact areas of the lower are CNC machined in a few different steps, ensuring perfect alignment of all critical areas: the wheel-, the brake-, the bushing-, the fender- and the brake hose clamp-interfaces.
Yes, cleaning is crucial for high end performance. The lower is automatically washed with different solvents and water in order to make sure it is 100% clean and degreased, ready for powder coating.
7. POWDER COATING
First, a grey base layer/primer is applied to the raw part. The parts are electrically charged to make sure the color powder sticks to their surface. Machines cover the easily accessible parts of the lower while humans take over the hard-to-get to areas. A fast paced, work environment demanding high accuracy from both man and machine, since the whole process is not easy to stop when mistakes happen. That’s because directly after the powder is applied, the lowers run through an oven heated to 200° C, where the powder is melted to form the actual coating. After that, the whole feat is repeated when the final color is applied.