Wilhelm Satzger

Thermographic crack detection by eddy current excitation

Eddy current thermography is a new NDT-technique for the detection of cracks in electroconductive materials. It combines the well established inspection techniques eddy current testing and thermography. The advantage of this method is to use the high performance of eddy current testing without the known problem of the edge effect. Especially for components of complex geometry this is an important factor which may overcome the increased expense for inspection set-up. The principle of this technique and an algorithm to increase the sensitivity for small defects are described. Some inspection examples on aero engines parts are presented which show the potential of eddy current thermography.

Process monitoring of additive manufacturing by using optical tomography

Parts fabricated by means of additive manufacturing are usually of complex shape and owing to the fabrication procedure by using selective laser melting (SLM), potential defects and inaccuracies are often very small in lateral size. Therefore, an adequate quality inspection of such parts is rather challenging, while non-destructive-techniques (NDT) are difficult to realize, but considerable efforts are necessary in order to ensure the quality of SLM-parts especially used for aerospace components. Thus, MTU Aero Engines is currently focusing on the development of an Online Process Control system which monitors and documents the complete welding process during the SLM fabrication procedure. A high-resolution camera system is used to obtain images, from which tomographic data for a 3dim analysis of SLM-parts are processed. From the analysis, structural irregularities and structural disorder resulting from any possible erroneous melting process become visible and may be allocated anywhere within the 3dim stru...

Overview of additive manufacturing activities at MTU aero engines

Additive Manufacturing (AM) is a promising technology to produce parts easily and effectively, just by using metallic powder or wire as starting material and a sophisticated melting process. In contrast to milling or turning technologies complex shaped and hollow parts can be built up in one step. That reduces the production costs and allows the implementation of complete new 3D designs. Therefore AM is also of great interest for aerospace and aero engine industry. MTU Aero Engines has focused its AM activities to the selective laser melting technique (SLM). This technique uses metallic powder and a laser for melting and building up the part layer by layer. It is shown which lead part was selected for AM and how the first production line was established. A special focus is set on the quality assurance of the selective laser melting process. In addition to standard non-destructive inspection techniques a new online monitoring tool was developed and integrated into the SLM machines. The basics of this techn...

Determination of Blade-Alone Frequencies of a Blisk for Mistuning Analysis Based on Optical Measurements

Meanwhile the importance of mistuning especially for blisks is well known. Most of the mistuning studies so far done are based on assumed statistical distributions of the eigenfrequencies. But it is important to know the real eigenfrequency distribution of the blades of blisks as they come out of the manufacturing process or after they are in service for some time and have experienced erosion, wear and FOD. Some of the current analytical procedures for mistuning calculations need the blade-alone frequencies, such as the reduced-order code Turbo-Reduce which is used in the subsequent analysis. One way to determine the eigenfrequency distribution is to ping-test every blade while damping all other blades. This procedure is very tedious and may take several days, depending on the number of blades. Further, it is very difficult to eliminate the influence of the disk and to obtain the pure blade-alone eigenfrequencies. In this paper a method for the analytical determination of the eigenfrequency distribution due to geometric imperfections based on optical measurements is described. Starting from the point-cloud from the optical measurements a procedure to obtain a FEM-Model of all blades of a blisk is presented. As the procedure can partly be run as a batch-job, the time to determine the eigenfrequency distribution is drastically reduced compared to the experimental way. The procedure is applied to a real blisk and the calculated eigenfrequencies are compared with the measured frequencies. Then mistuning calculations are performed based on this eigenfrequency distribution.Copyright

Cooperating twin robots form a new X-ray diffractometer for stress analysis

Abstract X-ray diffraction measurements on large components with complex geometry are needed in industrial applications requiring the non-destructive characterization of the near-surface material condition in terms of residual stresses, work hardening, phase transformation and formation of reaction compounds. Because many regions of interest on these components are not accessible with conventional laboratory or even mobile X-ray diffractometers, a novel center-free diffractometer with two cooperating robots named “Charon XRD” has been developed at MTU Aero Engines. Two six-axis robots are synchronized using a special optical measuring system to achieve the highest positioning accuracies. This paper describes the actual design and operating mode of Charon XRD, its current and potential functionality, and presents calibration and reference measurements, along with results on aero-engine high-technology components like bladed integrated disks.

Evaluation of Ultrasonic Scattering at LCF Cracks Including Optically Measured, Real Roughness Profiles

An approach is presented to theoretically study the effect of surface roughness of real defects on ultrasonic wave scattering. Using an optical measurement system, real roughness profiles are recorded for cracks generated e.g. during LCF testing. These measured profiles are then discretized and used as input for the theoretical model, which has been previously presented by Ogilvy. Having obtained realistic input data to characterize the crack surface roughness, it is possible to evaluate the scattered energy distribution in dependence of frequency, angle of insonification and wave type.

Optimized Image Processing for Eddy Current‐Thermography

Eddy Current‐Thermography is a well known NDT‐technique for the detection of open and hidden cracks in metallic parts. Cracks disturb the induced eddy currents and generate therefore characteristic temperature profiles. These temperature profiles are visualized by a thermographic camera. But, there is a problem arising from the fact that the heat produced by the eddy current coil itself is very inhomogeneous. This inhomogeneous heat transfer masks the temperature of the crack especially when inspecting complex shaped parts. This masking can be removed effectively by using a Fourier transform algorithm focused on a specific region in the temperature — time behavior of the heated surface. The processed final images are of binary form and easy to evaluate automatically. Eddy Current‐Thermography and this image processing were optimized for some aero engine parts. The reliable and automated detection of cracks at these parts show the great potential of this technique.