Quick, mobile, precise. These are the features that make a mobile SWAT squad so resoundingly successful, and they also apply to quality assurance. One example of this is the German machining specialist Rothenpieler, who can maintain a dense testing workload thanks to the flexibility of use of portable measuring arms.
“From arrival to set-up and capturing the first measured points, we are ready for action in 10 minutes maximum. ” This is how Stefan Busenbach, Quality Manager for the Rothenpieler Group, slashed the necessary start-up time for portable 3D measurement. The long arm of quality assurance must reach out to no less than four Rothenpieler facilities in North-Rhine Westphalia – and therefore their ROMER Absolute Arm is continuously on the move. Quick, mobile and precise.
The Rothenpieler Group is Europe‘s leading provider of services for processing and finishing large parts. It uses all the possibilities offered by state-of-the-art CNC machining technology: from special and series-produced mechanical parts for the energy industry, to drive chains for large vehicles or complex components for machinery and plant engineering. With its extensive expertise and experience, many international industrial concerns and SMEs rely on Rothenpieler.
“We drill, mill and turn components weighing anything from 150 kilograms to 150 tonnes. They can be made from conventional grades of steel and cast steel, or heat-resistant and high-alloy steels as well as non-ferrous metals,” explains Quality Manager Stefan Busenbach. “We work vertically on rotationally symmetrical parts up to ten metres in diameter and five and a half metres in height. We can also work horizontally up to two metres and ten metres in length, while on cubic parts we can work up to 15 by 6 metres.” These are not small parts by any means but they are nevertheless always manufactured to the same stringent quality standards.
150 Tonnes Machined to 10 µm Accuracy
“We operate primarily in the micrometre range,” stresses Oliver Groß, one of the most experienced quality inspectors at Rothenpieler. “Even with our really big parts weighing up to 150 tonnes, we need an accuracy of 10 µm.” Precision work on a grand scale then, of which the customer also wants reliable records.
Of course, such records require the shape and position of the part‘s features to be checked, and more and more of Rothenpieler‘s customers were asking for this service. In addition, Rothenpieler also needed to reduce measuring costs and the time taken to complete the final part inspection. But how can such unwieldy components be placed on a conventional measurig machine? How could the coordinate measuring machine be moved from facility to facility? Measurement then, brings with it certain logistical and organisational difficulties.
In view of these difficulties, it quickly became clear to Rothenpieler that the best possible solution was portable measuring arms. However, the size of the components still presented a problem for the reach of such a measuring arm.
The original expectation of positioning the arm in the centre of a part with a diameter of around 4,200 millimetres so as to measure around it, at first remained unfulfilled. All portable arm models from various manufacturers turned out to be either too short – for Rothenpieler totally out of the question – or they did not have necessary accuracy at the required reach. In the end, only one arm stuck out from the competition, in the truest sense of the word.
4.5 Metres Portable Measurement Volume
“Only when we looked at the ROMER Absolute Arm from Hexagon Metrology did we know we actually had something that could do the job,” recalls QA Manager Stefan Busenbach. “With a 4.5 metre measuring volume, volumetric accuracy of 0.082 millimetres and a single point reproducibility of 0.070 millimetres, it has everything we could wish for in terms of performance.”
In fact, with the ROMER Absolute Arm 7545 from Hexagon Metrology, Rothenpieler had hit upon the only portable coordinate measuring machine of its size and accuracy on the market. Equipped with this type of QA “precision weapon”, the Rothenpieler quality assurance mobile SWAT squad would be able to implement the required inspection plan. But first, before the decision could be made, the system would have to survive a severe baptism of fire – in real action.
For the product demonstration, Stefan Busenbach and his team called on the ROMER Absolute Arm with very little notice to perform the final inspection of large pump mechanism housing. Rothenpieler‘s customer had specified the use of a 3D coordinate measuring machine for the inspection – and agreed to the use of a portable measuring arm. “It was an absolutely compelling demonstration with a perfect measurement result,” recalls Quality Inspector Oliver Groß.
“This severe practical test at the end of 2011 won us the order,” recalls Robert Neufeld, who is responsible for portable 3D metrology sales at Hexagon Metrology. Since then he has been delighted to receive an order for a third ROMER measuring arm from Rothenpieler.
Absolute Encoders and Automatic Probe Recognition
After the first arm went into service officially at the beginning of 2012, the quality assurance team came to appreciate more advantages of the portable machine with its six rotational axes.
For example, its remarkably low weight of just 9.2 kilos. “It was no trouble at all to transport in its box between places of use and quite effortless to use by hand – extraordinarily convenient,” comments Stefan Busenbach on the new easiness of daily life in metrology. The result of the carbon-fibre structure of the measuring arm‘s internal and external tubes. Which is also the reason why the ROMER Absolute Arm does not require its own temperature compensation system – unlike so many other machines, especially those made partly out of aluminium.
The absolute encoders fitted as standard are also ideal.
They make referencing and warm-up times things of the past: After switching on, the ROMER Absolute Arm is immediately ready for high-precision measuring. “Very important for our rapidaction mobile squad. We take full advantage of the momentum gained from the ultra-short assembly and set-up times. Ideal commando-tactics: Go in, do the job and get out,” says Oliver Groß when describing this aspect of his work.
Rothenpieler also sees the automatic probe recognition feature of the ROMER Absolute Arm as extremely beneficial. It allows the operator to change at will between various probe types without the need for recalibration, probe changers or special tools. The patented probe mount allow probes to be changed quickly and easily. With its low weight, high speed and simplicity of use, the measuring arm also fulfils Rothenpieler‘s other wish: time savings in the final inspection. For example, the ROMER Absolute Arm reduces the final inspection time on turbine components for Siemens by 72 per cent.
WLAN, Rechargeable Battery and SmartLock
A further advantage the Rothenpieler has come to apreciate is the optional battery operation and wi-fi data transfer. Stefan Busenbach goes on to explain why: “On our machines, the components to be inspected have often risk being sprayed with water in a relatively moist environment. Therefore it is really helpful to be able to keep the PC at a safe distance and yet be able to handle the large quantities of data from the measuring arm. Wi-fi connections perform much better than Bluetooth. We also found the rechargeable battery to be a good solution – good for working through a complete shift or even longer.”
The Rothenpieler quality assurance team has been able to make only infrequent use of one particular feature: the SmartLock function of the Hexagon Metrology system. When the measuring arm is not in use, it can be conveniently and safely locked in its rest position. The SmartLock also allows the arm to be locked in any intermediate position. “A good idea in principle,” jokes Oliver Groß, “But with us the arms have hardly any time to stand still – they are always on the move. In all axes and from A to B.”
Apropos from A to B: The mobile quality assurance SWAT squad at Rothenpieler now has two rapid deployment vehicles of its own. They are painted in typical secret-service black and have a mysterious box on board whose contents ensure law and order prevails in a world where tolerance limits are never allowed to be exceeded.