Despite these enhancements, the basic
Figure 2: Bäumer’s cutting head unit is a steel framework that hovers above the foam block which requires fast and accurate height adjustment to guide the knife’s precise, high-speed movement on the Z (vertical) axis
±0.5mm, which must be consistent across a stroke of up to 1530mm (60in). A numerical control system changes the cutting position constantly in an oscillating movement at feeds of up to 40m/min @ 1000 rpm, which is the maximum spindle rotation speed.” The Bäumer design achieves high speed via
a geared servo motor that translates the force to the vertical axis of the cutting system via a ball screw carrying a flanged nut. The cutting structure bolts to the flange and rides up and down with the thread as a geared motor rotates the screw. Movement at such high speeds produces friction, which jeopardises precision, efficiency and reliability – all of which are vital in foam cutting automation. Ball screws minimise that friction by distributing the load over the wide surface maintained by the rolling contact. “Two ball screws, one on each side of the
overhead mechanism, are responsible for quickly and accurately positioning the cutting knife on the vertical axis. The lower table moves the load on the horizontal axis. The circulating knife rotates continuously, following the shape defined by the numerical control system and forming the required two-dimensional contour in the foam,” explained Groos.
Bäumer engineers were familiar with Thomson metric ball screws from previous machine designs, and internal testing confirmed that these components’ fluctuation range was lower than competitors
Figure 3: Thomson
high lead ball screws precisely move the cutting head unit along vertical axes at high speed with minimal friction
and could deliver the precision necessary for the OFS-HE3 cutting machine (Figure 3). “To rate the effectiveness of location misplacements on cutting quality, our engineering team ran the Thomson ball screws against competitor products in a combined axis configuration, comparing the repeatability of positioning and noise levels. We are very satisfied with Thomson’s product quality,” said Groos. “During operation, even at max speed, the Thomson ball screws run smoothly and quietly. They always fit perfectly, are very precise and provide a long service life. The Thomson ball screws contribute to our best-in-class tolerances and high repeatability,” said Groos. In addition to Thomson’s product enhancing the performance of the overall cutting unit, Bäumer chose them for the reliability of the ball screw hardware itself. Groos added: “The ball screws are one of the main components of our machine. Consistent high-quality cutting is critical, especially
in this tight market. If we ever have to
replace them, we want to be certain that the
replacement fits exactly in the machine, not only in the
consistency of the dimensions but also in terms of overall quality. And we rely on Thomson for that.”
In addition to using the ball screw in the OFS-HE3 horizontal cutting machine, the company is also implementing the same basic configuration in their OFS-Twincut horizontal contour cutting machine, which uses both circulating and oscillating knives. “We make machines for almost all aspects of
foam-cutting and when I look around the plant at the ones that use ball screws, they come mostly from Thomson,” concluded Groos.
technical data remains unchanged, while targeted optimisation measures improve process reliability and ensure longer service life and reproducible precision. Lubrication: The guide carriages now have additional lubrication points, which distribute the lubricant better and more evenly within the recirculating ball unit. The systems are still delivered pre-lubricated. When lubricating from above, an adapter ensures targeted distribution in the carriage. New sealing concept: Double lip seals on the front and double lip seals on the sides are used as standard, providing effective protection against particles and contamination. Additional variants are available as options: non-abrasive seals, additional abrasive seals, and metal wipers.
Higher accuracy: The previous standard
accuracy N is no longer available. Instead, class H becomes the new standard. The tolerances for height and width have been reduced by around 50% compared to the previous N version. Accuracy class P will only be available on request in future. Class Z2 is no longer available for preload; Z0, Z1, and Z3 remain available. Specifically, this means higher repeat accuracy – particularly relevant in robotics and automation – and better parallelism, i.e., multiple guides run more smoothly in parallel. In addition, the number of ground carriage
surfaces has been increased from two to three. Cover caps made of plastic or, optionally, brass are available for the rails. Proven features remain unchanged:
• Four rows of balls in an X arrangement with a 45˚ contact angle for load acceptance in all main directions
• Variants A, B, AL, BL, BS as well as versions with and without flange
• Existing coatings still available • Metal cover tape can be used • Individual rail lengths up to 3,900mm • Interchangeability within a precision and preload class.
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