CNC turn-mill machining Backlash-Free Slide Drive for High-End Machining

Related Vendors

Redex S.A.

Fastems Systems GmbH

item Industrietechnik GmbH

The N40 MC machining centre from NILES-SIMMONS produces rotationally symmetrical components up to nine metres in length (approx. 30 ft) and weighing up to four tonnes with accuracies of ± 2 µm. This is made possible, among other things, by an electrically preloaded rack-and-pinion drive from Redex.

With the MC series, NILES-SIMMONS offers CNC turn-mill machining centres that, firstly, enable maximum precision and, secondly, provide a very high degree of flexibility and adaptability. Accordingly, these machines are in demand in the aerospace industry, among others—but not exclusively—for which they were originally developed. The slide drive from Redex, a backlash-free rack-and-pinion drive with two preloaded planetary gear units arranged against each other, contributes to precise and efficient machining with overall part accuracies down to +/- 2 µm.

This is CNC turn-mill machining at the highest level: With the N40 MC machining centre from NILES-SIMMONS, users can produce rotationally symmetrical components up to nine metres in length, with a swing diameter of up to 1,100 mm (approx. 40 inches) and a weight of up to four tonnes—in a single setup and, if required, within a closed manufacturing process according to the concept of “closed door machining.” Various—and consistently highly precise—operations such as turning, milling, grinding and measuring are integrated. The 60° slant bed technology of the steel-welded frame with concrete filling makes a significant contribution to machining accuracy.

Application: High-precision complete machining for aerospace

It is primarily companies from the aerospace industry that use this machining centre, as well as the smaller and larger models of the MC series, from N20 MC to N60 MC. Components manufactured on these machines include highly stressed parts such as aircraft landing gear components.

This application purpose is essentially “designed into” the machines from the outset. According to Dipl.-Ing. Carsten Hirche, project manager for the N40/N50/N60 series at NILES-SIMMONS: “The goal was to develop a ‘new generation lathe’ in cooperation with an internationally leading supplier of jet engines.” However, the series is also used in the oil and gas industry as well as in general heavy-duty machining—wherever complex workpieces with the highest demands on precision and stability must be manufactured.

Variable equipment, flexible machining

The distinctive feature profile of these machines, in this case the N40 MC, can be summarised as follows: it can be configured as a single- or multi-slide machine, offers maximum precision and is at the same time very user-friendly and exceptionally flexible. Thanks to the modular system, variable machining units can be added, and with different tool systems, tool magazine sizes and a wide range of options, even the most demanding machining tasks can be handled. The user can also adapt the size of the N40 MC to their requirements, as the machining centre is available in several nominal lengths.

Task: Designing a high-performance and highly precise slide drive

Among the numerous tasks faced by the design team during development was the selection of drive concepts capable of meeting the highest requirements in positioning and machining accuracy. Users can choose between an electronic spindle direct drive and various gearbox versions.

For the bed slide, the designers at NILES-SIMMONS opted for a rack-and-pinion drive from Redex. It enables fast machining processes for large components. In figures: the maximum traverse speed is 30 m/min (approx. 100 ft/min) with an acceleration of 3 m/s² (approx. 10 ft/s²) and a moved mass of up to 4,500 kg. Depending on the configuration, the machine can achieve a feed force of up to 30,000 N.

Decision in favour of an electrically preloaded rack-and-pinion drive

And these already impressive values say nothing about precision. Carsten Hirche: “The requirements, which are met, are very high. The machine must ensure maximum precision and zero backlash even under high forces and accelerations.” Again, a figure: repeatability in the micrometre range is achieved, and overall part accuracy can be up to +/- 2 µm.

Why was the decision made in favour of the DRP2 series from Redex under these conditions? “Decisive factors were power transmission, vibration behaviour, accuracy, and the space-optimised integration into the machine concept.”

DRP: Highly precise, backlash-free linear drive

The DRP drives consist of two high-quality planetary gear units combined in a torsionally rigid monoblock. Two integrated output pinions engage with the rack and, through the electrical preloading of the motors, generate the desired preload of the rack-and-pinion drive to enable highly precise and backlash-free movement.

This concept is convincing both in theory and in practice and enables designers to achieve longer travel distances and higher accuracies compared to ball screw drives, which also have limitations regarding high traverse speeds and temperature development on the machine frame, affecting the achievable machining accuracy on the workpiece.

Not only with the “hardware” of the drive, but also with the collaboration during the project phase, those responsible at NILES-SIMMONS are completely satisfied. Carsten Hirche: “Redex supported us well; we always received competent answers to our questions.” And the result speaks for itself: the N40 MC is used worldwide in highly demanding applications, not only in the aerospace industry.