Modern Machine Shop

SEP 2017

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88 MMS September 2017 FEATURE equilibrium between heat generation and heat disposal. "Additionally, CFRP layups can easily delaminate on the exit side of a drilled hole, even though the speed and feed rate during process- ing are very low in comparison to the possible feed rate during wet machining," Ms. Demmerling says. "The tools are also under remarkable stress. The abrasive fibers contained in the composite can cause drilling, milling and grinding tools to wear extremely quickly, resulting in frequent tool changes. In the case of drilling, the hole quality determines when the tool needs to be changed or indexed. To counteract this heavy wear, high- quality tools made from polycrystalline diamond or tools with diamond-like coatings are generally used. The resulting tool costs can have a sig- nificant impact on the competitiveness of the pioneering material." An improvement in part quality and hole qual- ity, in particular (as in the case of airframe manu- facturing, where CFRP-titanium stackups are becoming popular), increased tool life and reduced secondary operations will generate a large gain in productivity through shorter lead times. Capricorn says the introduction of wet machin- ing processes has paid off. "Compared to dr y machining, we were able to increase tool life by up to six times," Mr. Lussi says. "This creates real savings potential. The processing time has also been reduced. Before using the coolant, we had to conduct several roughing and finishing operations in order to achieve optimal process- ing. Due to wet machining, we managed to reduce these operations to one roughing and one finish- ing operation." So why is dry machining of composites still common practice, if machining time, quality and tool life can be drastically improved through the use of cutting fluids? According to Ms. Demmer- ling, the main reason is the lack of appropriate research and testing to ensure that a wet machin- ing process does not degrade the material's mechanical properties. COOLANTS DESIGNED FOR FIBER-REINFORCED PLASTICS To realize the benefits of wet cutting, Rhenus Lub decided to develop coolants specifically for the sustainable machining of fiber-reinforced plastics. "We have been testing the machining of CFRP with coolants for some time and joined forces with strong partners from the outset of the research Quality improvements when using coolants for hole-making operations in CFRP are obvious: No delamination (as shown in the top image) means better quality and the elimination of costly post- processing operations. (Courtesy Capricorn)

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