Backlash-free combined unit for high-quality machining
With the MC series, NILES-SIMMONS offers CNC machining centers for turning and milling that combine maximum precision with a high degree of flexibility and adaptability. These machine tools are in great demand in the aerospace industry, for which they were originally developed, but demand also comes from other sectors. The Redex combined system consists of two planetary gearboxes with integrated pinion, preloaded and backlash-free, which helps ensure exceptional machining with workpiece accuracy of up to +/- 2 µm.
This is CNC turning and milling at the highest level: with With the NILES-SIMMONS N40 MC machining center, users can produce rotationally symmetrical components up to nine meters in length, with a swing diameter of up to 1,100 mm, and weighing up to four tons in a single setup and, if necessary, as a 100% automated machining process. The machining center allows for the integration of various machining operations, such as turning, milling, grinding, and measuring, all performed with high precision. The 60° tilt-bed technology of the welded steel frame, filled with concrete, contributes significantly to machining accuracy.
Target applications: High-precision complete machining for the aerospace industry
This machining center is primarily used in the aerospace industry, which also uses the smaller and larger models of the MC series: from the N20 MC to the N60 MC series. Some of the components produced by these machines are subject to high stress over time, such as aircraft landing gear. This type of application is virtually integrated into the machines from the design stage.
Carsten Hirche, project manager for the N40/N50/N60 series at NILES-SIMMONS, explains: «The goal was to develop a new generation of lathes in collaboration with a leading international supplier of jet engines. However, the series is also used in the oil and gas pipeline industries, and for general heavy-duty machining; in other words, wherever complex workpieces with extreme requirements in terms of precision and stability need to be produced."
Modular options, flexible machining
The characteristic profile of these machines, in this case the N40 MC model, can be summarized as follows: it can be designed as a single or multiple-slide machine, offers maximum precision, and is also very easy to operate and extremely flexible. The modular system allows for the addition of variable machining units, and with different tool systems, tool magazine sizes, and a wide range of options, users can tackle even the most challenging machining tasks. They can also adapt the dimensions of the N40 MC machine to their needs, as the machining center is available in various nominal lengths.
The challenge: designing powerful, high-precision mechanical axis control
One of the many challenges the design team faced during development was selecting an axis guidance system that could meet the highest positioning and machining accuracy requirements. The choice was between direct drives or geared drives. For the bed carriage, the NILES-SIMMONS designers opted for a rack-and-pinion drive from Redex. This allows for rapid machining processes for large components. Key specifications: the maximum travel speed is 30 m/min with an acceleration of 3 m/s² and a moving mass of up to 4,500 kg. Depending on the model, the machine can achieve a feed force of up to 30,000 N.
A rack-and-pinion system with electrical preload was chosen.
Although the aforementioned specifications are already impressive, they still say nothing about precision. Carsten Hirche continues: "The precision requirements that are met are very high. The machine must guarantee maximum precision and zero backlash even under high forces and accelerations." Here's another fact: we achieve repeatability accuracies in the µm range, with overall part accuracy of up to +/- 2 µm.
Why was the Redex DRP2 series chosen for this application? «The factors that influenced the decision were power transmission, vibration behavior, precision, and optimized integration, in terms of space, into the machine architecture.»
DRP: High-precision, backlash-free combined system
The DRP combined system consists of two high-quality planetary gearheads housed in a torsion-resistant spheroidal cast iron monoblock. The two integrated pinions on the output side engage the rack and, via the master-slave operation of the motors, create the desired preload to enable highly precise, backlash-free movement.
This design is well-suited in theory and practice and allows designers to achieve greater travel distances and precision than ball screws, which also have limitations in terms of achievable machining accuracy on the workpiece due to high travel speeds and increased temperatures on the machine frame.
The NILES-SIMMONS team is completely satisfied not only with the product used, but also with the collaboration during the design phase. Carsten Hirche sums up: "Redex provided us with excellent support, and we always received competent answers to our questions." And the result speaks for itself: the N40 MC machining center is used worldwide in extremely demanding applications, not just in the aviation industry.
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