ANALYTICAL AND LABORATORY EQUIPMENT 35
Using the hexapod at PETRA III
How to position loads to the micrometer accurately. By Birgit Schulze.
S
ince 2010, PETRA III has been the most brilliant storage-ring-based X-ray light source in the world and it provides international scientists with excellent experimentation facilities. In particular, this benefits researchers investigating very small samples or those requiring tightly collimated and very short-wavelength X-rays for their experiments. Te high- energy radiation of up to and above 100,000 electron volts with high light intensity offers versatile capabilities, for example in the broad field of materials research for the inspection of welded seams, or for the
1B. 1A.
examination of fatigue symptoms in workpieces. In some cases, this involves accurately positioning really heavy loads down to the micrometre. At the heart of the P07 beamline, which delivers
the high-energy X-ray radiation required for materials research, is therefore a heavy-duty hexapod. Tanks to its accuracy, it facilitates in-situ measurements of material properties under realistic process conditions.
Hexapods are parallel kinematic positioning systems, available in many versions with travel ranges of up to a few hundred millimetres. With precision below a micrometre, they can position loads weighing from a few kilograms to a few hundred kilograms, or even several tonnes. Teir advantages compared with serial, i.e. stacked systems, are that they have much better path accuracy, repeatability and flatness. In addition, the moved mass is lower, enabling better dynamic performance, which is the same for all motion axes. Depending on the geometry of the hexapod, rotations from a few degrees up to 60° and translations of a few millimetres to several centimetres are possible.
Fig. 1. B. The stress values are measured comparatively at the corresponding location of the metal chip against the process parameters employed and applied in a simulated manner. Image courtesy of the HZG.
Short-wave X-ray radiation Te PETRA III short-wave X-ray radiation penetrates very deeply
Fig. 1. A. Changes to the microstructure of C45E steel were investigated during machining (chip-cutting) operations. A cutting edge was pressed against the workpiece with a 100 kN press mounted on the Hexapod (upper section of Fig. 1A). With X-ray radiation of 61 keV, the workpiece was permeated across a beam area of 20 x 20 microns, and the stress gradient was measured on a corresponding grid matrix. Image courtesy of the HZG.
into the material and thus is also capable of passing through material of greater thickness. Tis enables welded seams to be inspected and fatigue symptoms in workpieces to be measured as an aid to quantifying the anticipated durability and service lives, or to analyse new metal alloys. Here effects can be proven down to the level of domain or crystal structures.
Te opportunities that proceed from this in respect of materials research are leveraged by Helmholtz-Zentrum Geesthacht (HZG) at the High Energy Materials Science Beamline (HEMS), P07, for example when conducting in-situ measurements of the material properties that occur during reshaping processes
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