Thursday 22 January 2015

Manufacturing gears with the eyes of the designer

By Anna Bonanomi - Organi di Trasmissione
Gear production using 5-axis machine tools shows its full potential in the context of the increasingly small lots required, on the condition that the synergy achieved also includes a software environment and mechanical systems/hardware capable of optimal interpretation of the required specifications.
Manufacturing high quality gears with 5-axis machine tools calls for an essential and winning combination capable of balancing mechanical systems, software and process in order to meet designers' real needs. This is confirmed by Claudio Saurin, engineer and product development manager with Breton, a company based in Castello di Godego (Treviso - Italy) that has spent several years producing tailored machining centers featuring high technical specifications and evolved technology capable of delivering a highly competitive system in a market that is often faced with the need to produce increasingly small lots of parts. The reason lies in the fact that in this type of production (typical of medium/large size gears from 500mm to 3500mm) the tools required are frequently extremely expensive, hard to procure rapidly, etc.
Claudio Saurin continues «The ability for tooling machines capable of meeting the most stringent requirements in terms of accuracy and competitiveness expressed by gear designers and manufacturers calls for a high level of specialization. And it's essential to be able to offer the designer (especially the designer of bevel gear sets in the 400 to 1600mm range, which are perhaps still excessively reliant on tradition, ed.) a technically competent and convincing approach».
A conscious reflection, based on the experience that Claudio Saurin has accumulated during his work as a gear designer and that has been transformed into tangible innovation in the development of new solutions that touch on mechanical aspects and electronics, and that are especially focused on the process software. Just a few years ago an agreement was sealed between Breton and Kiss-Soft, a company with consolidated experience in the creation of specific software for gears and transmissions of all types, that has led to the implementation of programs, supplied on an exclusive basis (by Breton) and that allow the execution of machining processes that are impossible using conventional methods.

«Software – continues Claudio Saurin – that makes it 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 to achieve refinements in the management of surface curvature in order to shift contact points by controlling the distortion of the surface in question rather than the settings on the machine. This involves making highly complex topological modifications».
At this point the transition to bring the surfaces generated by the afore-mentioned Kiss-soft software to the machine is managed by the Gear CAD and Gear CAM applications (developed by Breton using the Rhinoceros CAD engine and the RhinoNC CAM engine), which allow complete management of the process to create surfaces including chamfers, and of the associated machining operations.

Integrated process platform
«The technological synergy we have created – explains Claudio Saurin – allows the designer to develop the best material removal strategies and perform adequate simulations, allowing also the choice of the most suitable tool to create the tooth base until completing the workpiece after hardening. For example, to design a double helical gear the conventional approach is to design the left or right face and then make a specular design CAD, filleting and chamfering wherever necessary. In other words, our modus operandi is to fine tune the geometry as though we were the gear designer».
The greatest effort was therefore, on the one hand, that of creating an adequate design environment, and on the other hand to use machines that are able to optimize efficiency with high performance cutting processes.
«Not only – continues Claudio Saurin – but with the added value of a user-friendly and intuitive CAM system on board the machine. A process guided by a wizard that aids the operator in defining geometries and optimal tool paths. The decision is based on the fact that companies that manufacture exclusively gears and not the associated housings are generally unlikely to possess this kind of software».
In other words, the proposed solution is based on an integrated platform that includes a gear calculation code, a CAD application for generation of surfaces and a CAM application for the machining stage.

5 axes of quality for gears of various types
It is precisely to meet specific gear machining requirements that Breton has developed specific machining cycles to apply to its 5-axis machines, notably the Ultrix series model 1000 RT HD vertical machining center, which is particularly indicated for high speed machining of gears of diameters up to 1000mm.
«This is a high-speed machine featuring a high degree of automation – explains Claudio Saurin – designed and developed for milling, turning and grinding of workpieces of up to 1,200mm in diameter».
Equipped, in this version, with a powerful 75kW spindle with 300Nm of torque at 14,000 rpm and software for the production of helical bevel gears, this machining center can machine steel, aluminum, superalloys and composites. The machine features a monobloc structurewith gantry type travelling beam, with a 5-axis movement achieved by combining 3 linear axes with a rotary-tilting table. 
Gears can also be machined using various Breton machine models in the Maxima and Titan series (with large size gantry solutions and turning diameter). Systems that support an integrated process of turning, milling and hobbing pre- and post-heat treatment of medium and large size gears (up to 2,500mm for single piece parts).

«The know-how and experience acquired  – adds Claudio Saurin in conclusion – allow us to offer the designer a comprehensive set of tools construed in the broadest sense, including both software and process components. This makes it possible to use conventional 5-axis NC machines to design and produce a very large range of mechanical components rapidly and with superb quality results capable of guaranteeing a high level of competitiveness».

In other words, a new way of approaching the culture of gear manufacture. Not merely spur tooth and helical tooth gears, but also double helical cylindrical gears, spur tooth and spiral tooth bevel gear sets in accordance with the most common geometries, and also face gears for drive transmission between right-angle or non-parallel shafts.
To learn more, follow the considerations of Alessandro Verduci on market trends and future prospects:

For info and request about Breton machining centres and gear production using 5-axis machine tools write to mail@breton.it.
We’ll get back to you promptly.
Thanks again to Organi di Trasmissione.
Well, that’s all for today, thanks for your attention.
Bye-bye
Sergio Prior

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