In one contour operation
Even an experienced machining specialist would imagine that it is not possible to fully machine the ball head and ball neck of a trailer coupling on one machining centre in just one clamping system, at least not immediately using conventional methods. To perform this operation, Manfred Herzog, Managing Director of HFT in Saxony, uses a KOMET® KomTronic® U-axis system, and is pleased with what it can achieve technically.
The ball head trailer coupling was developed in 1932, with a ball diameter of 50 millimetres. Today, it is used throughout the world and is regarded as a widely trusted feature which can simply be taken for granted. Nobody seems to give it a second thought, apart from those who always want to discover more convenient solutions, ranging from a removable variant to an automatically pivotable version.
In principle, not much has changed since then, as far as the ball head and ball neck are concerned. The people who are racking their brains about it, however, are the machining specialists, like those from HFT Hydraulik- und Fahrzeugtechnik GmbH in the spa town of Wiesenbad in Saxony. However, their thinking is not so much about changing the shape as about improving the manufacturing process. The company is based in the automotive triangle made up by the cities of Zwickau, Chemnitz and Leipzig, and specialises in turning, milling and grinding. Modern production and testing technology is used to produce components for hydraulic system and automotive components, ranging from individual parts to mass production. Trailer couplings are also manufactured in large-scale production, in a wide variety of designs.
“Until now, this was done using conventional individual operations, i.e. machining procedures. In the process, three different clamping systems were required as well as an extremely complicated arrangement for providing imbalance compensation during turning,” Mr Herzog explains. Today, there are two special tools and a U-axis system that can also be automatically exchanged, with which the ball and the neck of trailer couplings, once clamped, are machined to completion in the machining centre. The special tools are both also made by KOMET® and take the form of a milling cutter and bell tool which are used for contour preparation and measurement reduction for the subsequent complete machining process using the KomTronic® U-axis system.
KomTronic® u-axis systems are freely programmable and enable contour machining and lathing on parts which are not rotationally symmetrical. They essentially consist of a compact facing head and single slide which is driven by a servo motor and threaded spindle. The power supplied to the electronics and the drive is transmitted contact-free and inductively to the U-axis system. Similarly, the data is exchanged inductively with the U-axis system. A so-called stator is mounted on the spindle side. It is segment-shaped, which permits the tools to be replaced automatically.
The ring-shaped inductive transmission unit (rotor) on the U-axis side ensures reliable data and energy exchange in every angular position, even when coolant is being used. In this way, the mechatronic U-axis systems are automatically replaceable NC-axes, thanks to the freely programmable cutting edge that can be dynamically adjusted during machining. For flexible contour machining and grooving operations, the U-axis is interposed with the Z-axis. Programming is carried out in the usual NC programming language and is integrated into the machine control system. All the functions of normal ISO programming are available.
Through the combined use of customised snap-on tools and optimally selected indexable inserts, it is possible to machine contours in bores as well as external contours, as on the trailer couplings. In this case, a pincer-like snap-on part with two indexable inserts from the KOMET® standard range is used to machine the ball head and ball neck in two steps, in a forward and backward direction. Thanks to the new U-axis, Mr Herzog confirms a reduction in the machining time of 50% and reminds us of the saving made through the absence of the imbalance compensation mechanism which is required for turning, because the tool is now in the machining centre itself.
“In addition, because the clamping situation remains the same, we achieve a more uniform level of accuracy, which is required for the subsequent machining procedures, Mr Herzog adds, pleased with the flexible machining possibilities provided by the 'interpolating rotational axis' in the machining centre and already looking at ways to use these for other workpieces.
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