Friday, 4 December 2015

A suite for 5 axes

Cogwheel for wind turbine
The world engineering market is constantly evolving, and the gears sector follows the same trend. Modern gear manufacturers require machines that are accurate, versatile and user friendly to compete in a market in which production lot sizes are shrinking, and in which production requirements can change abruptly.
Traditional processes (with gear cutting machines) have some significant limitations, concerning product design, prototyping and manufacturing phases. They remain competitive only for high production volumes, but are unsuitable for producing prototypes and small lots (typical of large gears from 500 mm to 3,500 mm in size) as the tools are very expensive, have long procurement lead times and the geometric tooth finishing process is normally very long. It is in this niche that the commercial 5-axis milling machine shows its effectiveness.

Thanks to a partnership with KISSsoft - world leader in developing computation software for the mechanical engineering industry - together with decades of experience in manufacturing numerically controlled machine tools, Breton has developed BretonGear Suite, a vertical software package (BretonGear CAD and BretonGear CAM) developed in synergy with the machine tool for designing and manufacturing gears.

Starting from the very high accuracy of the surfaces generated in KISSsoft, the designer now has a freedom in defining the tooth geometries never seen before with traditional methods. With the BretonGear CAD application (using the CAD Rhinoceros engine) it is possible, in bevel helical teeth for example, to machine the relief groove at the tooth root in the same way as it is created using hobbing cutters with protuberance on cylindrical teeth. Or making topological changes to distort the surface itself, moving the contact area between mating teeth, which is key in reverse engineering.
Double-helical pinion for excavator

Once the gear geometry has been defined, you can pass to the BretonGear CAM environment, available in both the PC and the touch screen version installed on-board the machine, which through an integrated approach can guide the operator in selecting tools and defining cutting strategies. Today, in version 2.1 with an even more intuitive interface and with a tool library that now, for the first time, includes side cutters as well as the more generic cylindrical, toric and spherical end cutters.

This innovation introduces a further degree of versatility to the cutting methods available, resulting in considerable time savings when machining gear wheels with straight or helical teeth. Side cutters can be of two types: shaped (where the tool defines the shape of the tooth), or the more common variety, straight sided, where the machine creates the shape of the tooth by envelopment. All of this can be viewed by the operator through real-time simulations, offering him complete control over the cutting strategies, thereby eliminating the need for the dedicated CAM office required in other specialised sectors such as aerospace.

BretonCAM accompanies the operator throughout the cutting process with dedicated applications even after the gear has been case-hardened. Careful management of the excess metal and a best fit function that determines the piece’s ideal position within the machine with a measuring cycle before and after hardening, limits the distortion that follows heat treatments. In addition, the T.A.O. (Tooth Accuracy Optimizer) algorithm calculates the tooth cutting order to distribute the tool wear and improve the accuracy of the tooth. These technical solutions are the result of research and development in the field alongside experts in the gear sector.

So far we have only talked of 5-axis gear cutting using commercial milling machines, which is competitive compared to the traditional bevel gear cutting methods for more than 5 modules and diameters greater than 300 mm. 
For smaller numbers of modules and diameters, face milling strategies are more effective. The basic difference between the two lies in the fact that, in the face milling method, the profile of the tooth is created by the synergy between the machine’s movements and dedicated shape of the cutter
Breton Ultrix with “face milling”

Traditional CAM software is not able to simulate this delicate interaction between the machine and the cutter. For this reason, Breton has undertaken a collaboration with HyGEARS, developer of a powerful gear design and analysis software.
Through an interface designed together with Breton, HyGEARS replicates the movements of a conventional gear cutting machine. 
The result? A considerable reduction in cutting times. A case study conducted on the same bevel gear cut using both methods found execution times four times shorted (25 mins against 100 mins),  ideal for medium sized lots.

Of course, developments in the world of 5-axis gear cutting are not just limited to software but also hardware. Breton has optimised its range of machines with an emphasis on monoblock models ULTRIX and XCEEDER, now equipped with trunnion tables with a central hole which allows machining pinions up to a maximum length of 850mm and shank diameter of 220mm (until now a limit for this kind of machine), and FLYMILL and MAXIMA gantry models that can machine gears with diameters up to 3500mm.
For INFO and request about Breton machine for gear production, write now to
Well, that’s all for today. 
Sergio Prior

(Software KISSsoft, Rhinoceros and HyGEARS are trade mark ®)


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