Complete machining of parts for vehicle transmissions

Armoured vehicles need huge levels of drive torque to get going. In order to deliver the necessary propulsive force, manufacturers rely on transmissions from Augsburg-based Renk GmbH, the specialist in fully automatic transmissions for heavy tracked military vehicles. In turn, Renk relies on solutions from WFL.  

Unlike cars, a tracked armoured vehicle can be driven, steered and even braked all through its transmission. Essentially, it’s the central mobility unit of these vehicles. Not only that – these 70-tonne monsters need to be extremely manoeuvrable at speeds of up 72km/h on both roads and open terrain.

Renk is a global market leader in transmissions for tracked military vehicles weighing over 40 tonnes and supplies more than 40 armies around the world. Every transmission is designed for a specific type of vehicle and is specially adapted to suit the respective level of equipment and powertrain. It won’t be surprising therefore that there’s a wide range of complex parts involved that need to be manufactured to stringent quality requirements. 

The components needed for the transmission are divided into three categories: housing parts, small cubic parts (force-carrying, valve blocks, brakes and fluid mechanics-related) and rotating parts with gear teeth for speed transmission. The latter are the typical parts installed in the powertrain of the transmission – and components perfectly suited to complete machining on machines from WFL Millturn.

"If it's round and features gear cutting, it goes on a WFL machine," explains Martin Wimmer, Renk’s head of production. "Typically these parts are produced in small batch sizes of one to 300 units, with the average batch size around 50 pieces. But for prototype transmissions, batch sizes of one to five units are also not unusual.

“Due to the flexibility of the WFL machines, a separate prototype production line with different manufacturing processes isn’t required – even the smallest of batch sizes can be produced economically using the existing machinery. The need for cost-intensive special clamping devices is also negated as workpieces are clamped on the Millturns by either standard jaws or a few special jaws with a three-jaw chuck.”

A critical factor in determining the productivity of a machine is its programming, which is carried out exclusively using the Siemens NX CAD-CAM programming system. On the WFL machines, post-processors have been standardised across all machines with the advantage that production can initially be planned independently of the machine. The entire production process is simulated in CAD/CAM before machining takes place.  

Gear teeth are an exception during the simulation and are cut on the Millturns up to Module 4. It is predominantly special WFL cycles that are used for gear hobbing, as these can be applied quickly and easily by entering the gear cutting parameters.

The first WFL Millturn was delivered in 2010 and Renk has been working intensively with complete machining ever since. "We wanted to have a machine concept that followed an identical structure for all parts of all sizes,” Mr Wimmer affirms. “WFL had the perfect offering for us with the M35 to the M50. In addition to turning, drilling and milling on a single machine, it was important to us that the gear cutting – especially of Module 3 in Quality 8 – could be performed with a hobbing cutter clamped at one end.

“While many manufacturers promised this, it was only WFL who actually delivered. A positive aspect is the very stable indexing of the B-axis with the large Hirth coupling in particular. The WFL-typical setup of the turning-boring-milling unit, where the milling spindle is designed as a high-torque gear spindle, ensures exceptionally high machining performance in all speed ranges. The benefits of the stable machine frame are not only measured in terms of productivity, but also the ability to hit the tightest geometrical tolerances and optimum surface finish quality.

"We no longer want  to have to use different machines or external suppliers for occasional special tasks," Mr Wimmer asserts. "Not only does this bring about a significant reduction in lead-times, but the number of operations can also be cut dramatically. Individual operation sequences have been halved thanks to complete machining.

“Combination machining has also allowed us to make runtime savings with capacity freed up through more efficient use of our machine resources. Renk now has nine WFL Millturns of three different sizes and two different turning lengths operating on its vehicle transmission production lines."

To boost efficiency and the level of utilisation even further, the M35 delivered in 2017 was kitted out with an automation solution from Frai Robotic Solutions, which has led to the more efficient production of workpieces such as planetary gears. An M40 has also since been automated.

In the UK, the sole distributor for WFL machines is Kyal Machine Tools.

Kyal Machine Tools
www.kyalmachinetools.co.uk

WFL
www.wfl.at