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A New Level of Flexibility in Gear Grinding

A New Level of Flexibility in Gear Grinding

Figure 1: KNG 350 flex gear centre

KAPP NILES, a globally operating group of companies providing solutions for finishing gears and profiles, has reached a new milestone thanks to the new KNG 350 machine series.

The KX 300 P gear centre was already a true success story. The fact that more than 500 machines have been sold proves how successful the concept has been, with a combination of high flexibility and productivity. This is where the new KNG 350 series story begins. When designing this new machine platform, KAPP NILES took a look back at previous developments. Tried-and-tested solutions were adopted and further optimised, while adding new capabilities.

This has led to a sophisticated modular system which provides a uniform basis for various machine concepts. Thanks to three different configurations for the tool and workpiece drive, KAPP NILES can perfectly cater to the customers’ requirements.

The machine concept

The KNG 350 series is based on a compact, set-up optimised machine concept and is perfect for the job shop environment to large-scale series production of geared components with diameters of up to 400 mm. Thanks to the integrated ring loader, non-productive times are reduced to up to 5 s, and bore parts as well as shaft-type workpieces up to 600 mm length can be auto loaded.

The concept provides full flexibility when it comes to loading the components – from manual loading or simple pallet conveyors up to complex robot solutions.

Figure 2: Flexible robot loading

The functional and ergonomic machine design paired with the user-friendly interface KN grind supports the user during set-up and optimisation of grinding projects. A major aim was also to reduce non-productive times. Thus, the series is characterised by short set-up times, which are achieved e.g. by means of intelligent components (smart tooling). Process monitoring, part tracing and inline quality assurance are available as an integral component for an industry 4.0 capable processing machine.

This gear centre impresses not only with its excellent design (iF Design AWARD), but also with its continuous further development with a view to energy efficiency. The hydraulic functions, which have been reduced to a minimum, are provided by a controlled pump unit, and pneumatic functions have largely been replaced by electric drives. Moreover, when considering the entire lifecycle of the machine, the switch from a machine base made of cast iron to one made of polymer concrete reduces the overall CO2 equivalent of the machine. These are aspects which are increasingly important to OEMs.

The assessment from our long-standing partner Scania in Södertälije/Sweden provide an example. Anders Urefors, responsible maintenance technician, has followed the technical evolution since the KX 300 P. He recently was in Coburg to see the KNG 350 during the technical machine acceptance and was excited with the results. Things that previously had to be implemented upon individual customer requests, e.g. the height-adjustable operator panel, have now become standard. In addition, you are now much closer to the workpiece and tool axis when opening the operator door. Together with the quick-change systems for complete workpiece-dependent tooling, a new benchmark has been set for the machine set-up. It is immediately noticeable that ergonomics and usability were heavily emphasised in the requirements specifications during the development of the machine.

“Lessons learned”, says the usually rather reserved Swede with a relaxed smile on his face.

In terms of feedback, this is as good as it gets – and everyone involved in the project knows that if Anders is happy, SCANIA is happy too!

Figure 3: Optimum Operability

KNG 350 expert

The starting point for the new series was the expert machine, with an exclusive focus on the generating grinding of gears. The concept of a grinding spindle without counter bearing has already been proven in the DYNAMIC machines. The automatic HSK interface allows for a semi-automatic tool change, which is implemented consistently in both the expert machine and the other variants of this machine series.

The machine features high-performance technology options, for example bias-free grinding of gears or in order to meet greater surface requirements by using combined grinding worms. Thanks to selectable dressing methods, all requirements can be met in a cost-efficient way, from single item production (topological dressing) up to mass production (multi-ribbed dressing). An integrated measuring device is available for all machines of this family. The probe allows for a complete gear measurement within the machine and is also used to cyclically measure definable gear characteristics.

KNG 350 flex HS

E-mobility presents new challenges when it comes to the production of gears. High power density in a compact space in passenger cars, and miniaturisation for complex bicycle drives often lead to challenging workpiece geometries for manufacturing.

In the past, the hard fine machining of gears with interfering geometries was primarily implemented by means of discontinuous profile grinding or gear honing. The reason for this was simple: the typical grinding worms with a diameter of 300 mm are too large for components with interfering contours.

However, compared to continuous generating grinding, both profile grinding and gear honing have disadvantages in terms of productivity, economic efficiency and consistent quality. In order to achieve high cutting speeds with smaller tool diameters, smaller grinding worms require state increased RPM. Previous machine concepts were not designed to meet the substantial dynamic requirements regarding tool and workpiece drives.

The KNG 350 flex HS is characterised by superior grinding quality and productivity, even if such small tools are used. Thanks to a high-speed grinding spindle (HS) with a speed of 25,000 rpm, even gears with interfering contours can be ground using tools with a diameter of at least 55 mm (generating grinding) or 20 mm (profile grinding).

KNG 350 flex

A bit bigger?

When machine tool manufacturers ask this question, it’s not about getting bigger portion sizes for lunch.

Especially when it comes to electrically driven commercial vehicles, there is currently a trend towards gears with greater diameters. While typical gear wheels for trucks used to have diameters of no more than approx. 300 mm, current components can reach diameters of up to 350 mm, or even 400 mm in individual cases. The KNG 350 flex machine is also equipped to handle such cases thanks to the optional diameter extension.

The performance-optimised grinding spindle with counter bearings allows cutting speeds of up to 100 m/s and is designed for the use of large grinding worms with widths of up to 200 mm. This allows an efficient realisation, especially when machining of components with large modules and using 2-sector worms for fine grinding or polishing applications.

Using a standard tool, values of an average roughness depth Rz = 2.5 – 3 micrometres can be reliably achieved with continuous generating grinding. For higher requirements, KAPP NILES offers tool sets that have two different zones: one featuring standard grit and another designed for fine or polishing grinding, depending on the surface requirements. This makes it possible to achieve roughness values of Rz <1 micrometre. The significantly increased contact ratio of the tooth flanks boosts the maximum load capacity of the gear. Another advantage of this process is that it can be integrated into automated process chains with “one-piece-flow”, which was not possible with the vibratory finishing that was often used in the past. As a unique selling point, Kapp Niles also offers polishing as a single technology, for example in order to only polish gears after shot peening.

Figure 4: Various tool axes of the KNG 350 series

Two further aspects highlight the flexibility of this machine.

Due to the use of auxiliary spindles very small grinding wheels with the minimum root circle of the gear to be grind can be applied. The integrated reduction stage enables a cutting speed of up to 50 m/s even with a grinding wheel diameter of 30 mm. Both involute internal gears and special profiles can be machined with the internal grinding device. Thanks to the new quick-change interface, auxiliary spindles and internal grinding arms can be directly and quickly set up on the tool spindle.

External and internal gears of small and large workpieces can be machined both by generating grinding and profile grinding, depending on the application, with dressable corundum or non-dressable CBN tools.

This machine type truly deserves the name “flex” and leaves nothing to be desired in terms of gear grinding.


Ralf Dremel, Technical Product Manager at Kapp Niles