Thursday, 1 March 2012

Breton MAXIMA - multitasking vertical machining (part 2)

Heads and tools
The machine uses different tools for multitasking operations.
While the head used in turning is relatively simple, a model with Capto C8 taper, the milling one is certainly more complex.
The coupling with the ram is guaranteed  by a Hirth crown assuring the correct and constant positioning of heads and removing the risk that the efforts – especially in turning – are concentrated on the components dedicated to milling. Machines of this type are expected to machine for several years without needing extraordinary overhauls determined, for instance, by excessive stresses on parts not designed to bear them.
Maxima 2500 HD is characterized by the innovative head Tornado HD. This name hides a head with torque motor on the C axis that eliminates backlashes, permitting to achieve precisions in the volume of few hundreds on the five axes and enabling to reach 100 rpm. The flexibility is guaranteed by the fork-shaped configuration with non-coaxial spindle and big roughing power. Besides, the high-frequency electrospindle permits to operate effectively in milling (roughing and finishing) on steel, light alloys and alloys resistant to heat (used in some of the outlet application sectors of this machine, such as aerospace and military).
The change system provides for apposite niches in the structure where replacement heads are housed.
A further option offers the possibility of replacing the spindle cartridge only: in this way a single head can house, for instance, a motor suitable for roughing and a high-speed electrospindle for finishing.
Tornado HD 300/14 is the standard head proposed on Maxima: with a maximum power of 75 kW and a spindle torque of 300 Nm, it is proposed as solution able to meet successfully most requirements expressed by customers. It can reach in fact 14,000 rpm and house tools with HSK-100A taper.
Tools are housed in a wheel-type magazine that, in the change phase, is introduced into the machining field through an apposite panel. A variable number of tools, ranging from 20 to 30, can be housed, depending on their size. As an alternative, a rack with 60, 100 or 150 pockets can be installed, with a shuttle for the tool recovery and an arm that physically carries out the exchange. In both cases, the machining area is perfectly free and completely available for the piece positioning, allowing the movement of the head in the space without constraining it with the presence of tools or tool/head change equipment.

The secret of precision
Maxima has been conceived to satisfy very exacting demands in terms of productivity and precision. We have mentioned the capability of reaching a volumetric precision within 5 hundredths but it was not easy to attain these results.
The stable and stiff structure certainly contributes in essential way but it was necessary to do more: besides the air pressured optical scales, equipping both sides of the machine and the Z axis, and the encoders on rotary axes, the machine is provided with a balancing system for the compensation of the head and ram weight.
In this way, the only forces that affect the structures are the machining ones, widely within design parameters.
The “universal” mission of Maxima guarantees the possibility of machining a big number of materials, such as steel, aluminium, resins, titanium and carbon fibre. For the latter, in particular, they have studied suitable solutions for assuring the constant operation of the machine. First of all the upper part can be closed with bellows that do not limit the possibility of loading pieces with the crane but that, in presence of carbon fibre dust, isolate the machining area and do not allow the removed particles to go out. Moreover, all sliding and supporting surfaces are protected by a standard pressurization system.
Thanks to TM - Tecnologie Meccaniche
(Mr. Andrea Pagani)


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