Modern Machine Shop

SEP 2017

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mmsonline.com September 2017 MMS 87 FEATURE I t is part of human nature to cross boundaries and set new records – to run a 100-meter dash faster than ever before, to fly even further into space and enter new realms. Speed can be an addiction. Like mountain climbing, going faster is its own reward, and carbon fiber reinforced plastics (CFRP) play a key role in reaching top speeds for various applications. That's why it's not surprising that CFRP material is used for aircraft, Formula 1 race cars and high-end bicy- cle components. In fact, the entire body of the Bugat ti Chiron hypercar, in addition to other components, is made of CFRP, which lightens the vehicle, enabling it to reach speeds ranging to 261 mph. However, while metal parts can be stamped in seconds, it can take several minutes for a CFRP part to be molded and cured. Plus, the longstand- ing approaches to machining CFRP have led to long machining times and also contribute to higher costs, as does the fiber material itself. One of the common "laws" of CFRP machining is that traditional liquid coolants, particularly those that are petroleum-based, should not be used. This idea is based on fears that these coolants could degrade the material's mechanical proper- ties, which is why nearly all composite machining has traditionally been performed completely dry. This had been the approach taken by Dus- seldorf, Germany-based Capricorn, a specialist supplier in the automotive industry with six pro- duction facilities in four countries across Europe. Capricorn also manufactures components made of fiber composite materials and hybrid materials for the finest car manufacturers in the racing world as well as in the luxury sector, including Bugatti. Until about a year ago, Capricorn only machined its composite components dry or with minimum quantity lubrication (MQL). However, its invest- The use of special coolants significantly improved machining time, tool life and quality for parts such as this CFRP intake pipe machined on a five-axis machine at Capricorn, a Dusseldorf-based specialist supplier in the automotive industry. (Courtesy Capricorn) ment in an FZ33 Zimmermann CNC gantry milling machine laid the path to wet machining. In col- laboration with lubricant manufacturer Rhenus Lub, a specialist in high-performance lubricants and greases located in Mönchengladbach, Ger- many, Capricorn tested and applied coolants in the machining process, achieving improved part quality, decreased machining time and costs, and increased operator safety. ELIMINATING HEALTH HAZARDS The fine dust released during CFRP cutting is a particular cause for concern. High quantities of these fine particles can have a negative effect on the health of shopfloor workers. To avoid endangering employees, employers must install ventilation systems and f ilter systems in the workplace. "This equipment comes at a high cost, but it is mandator y to provide adequate protection against fiber dust," explains Anna Lena Demmerling, part of the R&D team at Rhenus Lub. "It is also essential for machine maintenance: Carbon dust is electrically conductive and may affect electrical parts and increase wear on the spindle. Using coolants binds the dust together, improving health and safet y conditions, and ensuring maximum acceptance of the process among process owners and machine operators. At the same time, the special flushing properties of the coolants keep the machine rooms cleaner." The fact that Capricorn can now machine without dust is a very important point for Tobias Lussi, milling machine operator. "There is no health hazard due to the fine dust particles, as they are all completely bonded by the coolant," he says. "This makes my work much easier. I can now open the machine even directly after a machining operation and no longer need to wait until every- thing has been extracted." DRY MACHINING PITFALLS Because carbon fibers are characterized by high stre ngth, they are dif f icult to cut, and whe n machined dr y, their low-heat-conductive and storage properties force relatively slow cutting s p e e d s i n o rd e r to m a i nt a i n a n a c c e pt a b l e

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