Milling plastics: producing helmet visors in record time
Every year, according to Germany’s Federal Statistical Office, some 250 million tonnes of plastic are produced worldwide. There are reasons for the fact that polycarbonate accounts for only roughly 1.3% of that total. Nevertheless, although it costs more than other plastics, it retains its shape better and offers higher optical clarity, which is why it is used when a plastic material has to meet certain requirements. A good example of this is the visor of a pilot’s helmet.
Milling polycarbonate is a considerable challenge, as Rob Cliff of LMT Onsrud explains: “On one hand, polycarbonate components have extremely hard surfaces that subject tools to significant stress, which means they wear out quickly. On the other, it’s not easy to ensure that the milled plastic will meet the required surface quality standards. Chips can form so fast and in such large quantities that they adhere to the component and fuse with it again. Eventually, you end up with an unwanted reweld.”
Perfect chip removal
Experts at the Gentex Corporation, based in Simpson, Pennsylvania, are very conscious of this problem. Among other things, the company produces pilot helmet systems with visors made of extremely scratchproof and stable polycarbonate. For this job, the American application engineers are now relying on an LMT Onsrud tool whose blade geometry is ideally suited to milling polycarbonate on a 5-axis machining centre.
The cutting edges of the Onsrud 52-703 solid carbide cutter have a large rake angle and ensure perfect chip removal even at high cutting speeds. “The undesirable rewelding of chips to the workpiece just doesn’t happen with the 52-703,” says Cliff.
Output of 3,000 components per tool
At the same time, Gentex also profits from the tool’s extremely stable and sharp cutting edge. The Onsrud cutter makes it possible to produce 3,000 components at a feed rate of 3.05 metres per minute. In contrast, the previously used tool only achieved an output of 1,300 components at a cutting speed of 2.03 metres per minute. “Ultimately, of course, the visor has to have a perfect surface. That has the highest priority. With our tool, however, we are providing a solution that guarantees greater efficiency in the production of the visor,” concludes Cliff.