TwinDRIVE helps machine tool achieve exceptional precision

Giuseppe Giana Spa is using Redex Andantex TwinDRIVE rack and pinion drives on a new generation of large machine tools that achieve such high precision that the need for finish grinding can often be eliminated.

With its new GGTronic, Italian OEM Giana decided to position itself in a higher league of machine-tool technology. "It is the only way to survive" explains Giulio Maria Giana, the company manager and technical director. As a milling and turning centre for large components, very high rigidity becomes a crucial design requirement. Positioning has also to be very precise, reaching values as low as +/-0.01mm with a repeatability of +/-0.005mm. To achieve this performance, Giuseppe Giana implemented Redex Andantex's TwinDRIVE rack and pinion system.

Giulio Maria Giana explains: "The GGTronic's outstanding performance enables us to face the pressure of the costs and the evolving needs of our customers. Formerly, our customers were looking first for power and second for high speeds. Nowadays, materials are tougher and tougher, and precision requirements are becoming higher and higher."

The new line of GGTronic turning and milling centres can machine cylinders and complex components up to 4000mm in diameter and 25,000mm in length. These machines are also designed to be used in a completely unmanned environment. High-powered, the machines are particularly suitable for heavy-duty machining in the precision mechanics sector, for the machining of ship masts, wind turbine masts, turbine shafts, oil pipeline valves, crankshafts and rolls, large winch drums, etc.

A need for speed

Machining processes for these parts can last for hours and may need several types of machining. They also have very tight tolerances despite huge weights and dimensions. On the other hand, and to make the machining process as fast as possible, traverse speeds of 20m/min can be reached, as well as accelerations of up to 4ms2. The machine structure, built entirely of cast iron, is even strong enough to hold anti-vibration boring bars suitable for internal boring to a depth of over 5000mm.

Among all the design key requirements taken into account at the beginning of the project (and including the machine's ergonomic features such as ease of clamping, tool visibility during machining and access for measurements after machining), both machining precision and frame rigidity were crucial.

As Giana's idea with the GGTronic was to be one step ahead of the competition, the overall productivity needed to be increased considerably by eliminating most of the usual requirements for regrinding the parts after machining. That target explains the very high demand for precision, and the high level of stiffness which is necessary to reach this level of precision under dynamic conditions.

Rigidity and precision are achieved through a technological concept that is claimed to be unique. The main technical issue in terms of rigidity was the Z axis, which features the longest strokes (up to 25,000mm). To ensure the best performance from the chosen drive technology, Giuseppe Giana decided to implement a TwinDRIVE rack-and-pinion system from Redex Andantex. This turnkey system benefits from innovative features that deliver outstanding performance.

And the final results met the designer's expectations, with positioning precision and repeatability as low as +/-0.01 and +/-0.005mm, respectively, together with an exceptional overall stiffness.

TwinDRIVE rack-and-pinion drive system

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TwinDRIVE rack-and-pinion drive systems consist of two parallel-mounted planetary servo reducers that are coupled electrically. This preloaded system eliminates backlash and contributes to higher precision. Extreme rigidity is provided in all directions by an integrated output pinion shaft that is supported by reinforced output bearings. This innovative Redex Andantex concept provides torsional stiffness characteristics that are said to be among the best on the market, but it also offers exceptional rigidity along the other axes; this often enables the use of up to twice the acceleration rates or weight capacities of alternative drives.

This Redex Andantex design combines strongly reinforced output bearings with pinions integral to the output shaft (chill cast, case hardened and ground, and the same diameter as the shaft). The pitch diameter is optimised to ensure the best ratio between the torque transmitted and rigidity for the rack. The bearing arrangement consists in two tapered roller bearings, preloaded and generously oversized. This arrangement is designed to support the pinion as close as possible to the applied force, with only the thickness of the locknut separating the pinion from the output bearing. This design provides a considerable reduction in radial deflection, which is the cause of 60 per cent of overall deflection but which is often not dealt with satisfactorily by other systems.

In addition, for the longitudinal axis, the X and Y axes also slide on preloaded roller guide shoes. With a B-axis machine, parts can be machined on five sides in a single setup, or by using all five axes to machine any complex profile. If the machine also has a B axis, the workpiece can be machined on five sides after being positioned only once, and the five axes may be interpolated to produce complex profiles.

Technical support

Giulio Maria Giana adds: "This is not the only advantage we get from Redex Andantex. Before, each time we had to respond to a customer-specific request, we had to rebuild the complete mechanical drive system. It was a lot of work to change. Adjusting power and speed meant changing several components including the reducer. Now, we just have to indicate the power and the speed and Redex Andantex prepares the right rack-and-pinion system. Modifying everything, including the speed/load ratio, is very simple.

"With this high-precision and high-rigidity machine, we have served traditional markets such as the USA, Denmark, the Netherlands, etc, but also emerging markets such as China and India. There are no limits on the foreign markets we may serve: we go wherever our technology is needed. The principal sectors we serve are still the same: energy, oil and the aerospace industries, but we will not neglect any other sector that needs machine tools of the type we produce, that is, large-scale lathes, perforators and superfinishing machines. All these machines have a teleservice feature, both for PLCs and NC, guaranteeing the high quality of Giuseppe Giana Spa's technical assistance service.

"Amongst the last orders, we can quote Celsa in Poland for wind propellers manufacturing, or Nordmark Maskinfabrik in Denmark. Parts of more than 80T can be machined."

Once the GGTronic 3000 was installed at Nordmark Maskinfabrik, a quick calibration and adjustment on the Z-axis scale was made. Then a VDI 3441 test was performed on all axes. Results showed a precision close to 0.01mm was achieved very rapidly. Performance on the X axis is close to one micron for the milling, turning and boring processes.

About Giuseppe Giana Spa

Giuseppe Giana Spa is located in Magnago, in the province of Milan, in a 10,000m2 facility. The company's large pool of advanced machine tools is used for contract machining and the production of components new machines. Giuseppe Giana Spa makes grinding machines, boring machines, milling machines and milling and planing machines, including what is believed to be Europe's largest grinder for flat surfaces. Giulio Maria Giana states: "We will be continuing to focus more and more on international markets with highly specialised multitasking lathes."

About Andantex Ltd

Andantex Ltd is the UK subsidiary of Redex-Andantex, the French manufacturer of precision power transmission equipment. Andantex specialises in application engineering, with its qualified sales engineers ready to assist in solving customers engineering problems. In addition, the company provides a complete design and development service and will willingly study and manufacture equipment in accordance with customers' requirements.

Redex Andantex, headquartered in Ferrieres, France, employs 320 people and has three production sites in Europe and North America. More than 75 per cent of sales are generated outside France. Technological progress, a commitment to quality and exceptional technical support are the fundamental values of Redex Andantex.

Andantex Ltd

Rowley Drive
Coventry
CV3 4LS
UNITED KINGDOM

+44 (0)2476 307722

sales@andantex.co.uk

www.andantex.co.uk

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