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Design News, January 2013

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Fluid Power/Motion Control Influence of position measurement on accuracy in 5-axis machining – part 2 Five-axis machining provides considerable potential for increasing productivity. By Dr. Jens Kummetz, Dr. JOHAnnes HeIDenHAIn GmBH Editor's Note: This is the second in a two-part series from Heidenhain. Read part one online at http://bit.ly/VQ2Pyf. P roductivity and accuracy are important attributes in the competition for machine tools. Five-axis machining provides considerable potential for increasing productivity. In many cases it permits higher metal removal rates than 3-axis machining. Production times can be significantly shortened thanks to a reduction of time required for resetting, for example, or through multi-operation machining in one setup. In any case, with increasingly complex workpiece geometry, 5-axis machining is becoming an indispensable part of the machining process. Source: HeidenHain FIve-AxIs sImultAneOus mAcHInInG wItH telstAr sOccer BAll • Three-axis milling of the pentagons with vertical paths and inclined cutter; • Three-axis milling of the hexagons with horizontal paths and inclined cutter; • Five-axis milling of the seams. • A perfect optical appearance of the Telstar workpiece is possible only if the "seams" between the pentagons and hexagons are milled with consistently superb precision despite a machining time of over two hours. mAcHInInG sequence OF tHe telstAr wOrKpIece At the intersections, exactly three seams meet that are milled with various cutter inclinations. An intersection can therefore be machined precisely only if the cutter's tool center point (TCP) is positioned with three differing inclinations at exactly the The soccer ball for the FIFA World Championships of 1970 and 1974 were named after the Telstar, the first non-military communication satellite, which was launched into space by NASA and AT&T in 1963. The Telstar ball bears over 20 white hexagonally milling the pentagons: 3-axes, inclined cutter and 12 black pentagonal pieces that were sewn together. This ball serves as the model for climb milling a workpiece that can be milled on machining time: 22 minutes a 5-axis machine tool. The resulting 6 m/min workpiece is being used as a test Feed rate: piece to prove machining accuracy cutter: Ø = 16 mm with 5-axis milling. 1.5 mm The Telstar workpiece was manu- line spacing: factured in three machining steps Inclination angle: 40° on the basis of pre-turned blanks: [ w w w. d e s ig n n e w s . c o m ] same point. However, the three inclination angles of the cutter require large compensation movements in the linear axes. For each seam, a much different position of the linear and rotary axes results at the TCP position of an intersection. During milling, positioning errors in one or more feed axes inevitably prevent the TCP positions from coinciding when milling the three seams at their intersection. High accuracy in the positioning of all feed drives is indispensable for precise machining of the seams, including the intersections. For a simple visual evaluation of the Telstar workpiece's accuracy, a 0.15mm deep seam is manufactured throughout with a 25mm diameter cutter. This results in a very flat seam cross-section, so that even the smallest error in the seam's depth causes clear fluctuations of the seam width. milling the hexagons: 3-axes, inclined cutter milling the seams: Five axes simultaneously climb milling machining time: 2 h 17 min feed rate: cutter: 6 m/min Ø = 16 mm line spacing: inclination angle: machining time: 11 minutes feed rate: cutter: 0.4 m/min Ø = 25 mm 0.2 mm 40° inclination angle: 55° J an uary 2013 f luid p o we r / mo t io n co nt r o l / a s up p le me nt to de s ign n ews F7

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