The objective of this study was the development of the automated system for crack detection on square steel bars used in the automative industry. The automated system for thermographic crack detection uses brief pulsed eddy curr-ents to heat steel components under inspection. Crack, if present, will disturb the current  flow  and  so generate changes in the  temperature  profile  in  the crack area. These changes  of  temperature  are  visualized using an infrared camera. The image acquired by infrared camera is evaluated through an image processing system. The advan-tages afforede by the system are its inspection times, its excellent flaw detection sensitivity and  its  ability to detect hidden, subsurface, cracks. The system is part of the inspection line  where the  subsurface  and  surface cracks are searched. The system is fully  automated  and 

its ability is to evaluate four meter  blocks  within 20 seconds. This is the unique reason for using this system in real industrial applications

Matz, V

Starman, S

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Section - IIIRADIOGRAPHY & THERMOGRAPHYNDESAI 2011, December 2-3, Jamshedpur, India155 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...Automated System for Crack DetectionUsing Infrared Thermographic TestingS. Štarman and V. MatzSTARMANS electronics s.r.o.V Zahradach 24/836, Prague 8, 180 00, Czech Republic, European UnionABSTRACTThe objective of this study was the development of the automated systemfor crack detection on square steel bars used in the automotive industry. Theautomated system for thermographic crack detection uses brief pulsed eddycurrents to heat steel components under inspection. Cracks, if present, willdisturb the current flow and so generate changes in the temperature profile inthe crack area. These changes of temperature are visualized using an infraredcamera. The image acquired by the infrared camera is evaluated through animage processing system. The advantages afforded by the system are itsinspection times, its excellent flaw detection sensitivity and its ability to detecthidden, subsurface, cracks. The system is a part of the inspection line where thesubsurface and surface cracks are searched. The system is fully automated andits ability is to evaluate four meter blocks within 20 seconds. This is the uniquereason for using this system in real industrial applications.IntroductionInfrared thermography is one of several non-destructive testing techniques which can beused for surface or near subsurface defect or crack detection. Infrared thermography is a technique(1), (2) of producing a live thermal picture of an object based on the infrared radiation receivedfrom it (emitted by any object). In pulse thermography, a thermal pulse is applied to the material tobe inspected. Following the application of this thermal pulse, a measurement of the temporalevolution of the specimen surface temperature is performed with an infrared camera allowingsubsurface defects to be revealed. The temperature of the material changes rapidly after the initialthermal perturbation because the thermal front propagates, by diffusion, under the surface and alsobecause of radiation and convection losses. The presence of a defect reduces the diffusion rate sothat when observing the surface temperature, defects appear as areas of different temperatures withrespect to surrounding sound areas once the thermal front has reached them (3). Consequently,156 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...deeper defects will be observed later and with a reduced contrast. Many methods and systems usingthermographic inspection have already been proposed. In general, the thermographic testing iscommonly used for inspecting solder joints on a surface (4), (5). Methods used for capturing inreal-time thermal images are used and the solution for real-time defect detection is searched (5).The objective of this paper is to present our proposed and designed automated systemprimary used for crack detection using the infrared thermographic testing method. The systemconsists of a circular coil where the metallic material is passed through. By passing the materialthrough the coil, the material is heated and the temperature changes are consequently measuredwith four infrared cameras. Our constructed system uses the mentioned pulse thermography method.The cameras were designed during our research when the best parameters for material surfacescanning were searched. The reason to use four infrared digital cameras is to scan each surface ofbalk steel material separately and, in the following, to have the testing process more precise andfaster. The main advantages of the IR method are that no contacts and wearing surfaces betweenmaterial being inspected and testing equipment and accessories. Thus, service life and reliability oftesting system based on IR principle is much better than using other nondestructive methods (i.e.eddy current). Moreover, IR system is not likely to be affected by irregularities and condition of thesurface under inspection.This paper also addresses the application of the thermographic system used in industry. Thedetection of cracks (defects) in balk steel bars is very important because it can damage the finalproduct and finally cause huge misery. The designed infrared cameras are very sensitive intemperature range and proposed software with implemented algorithms is simple and very userfriendly. Each detected crack is indicated and evaluated. Based on this evaluation, the statistics ofdamaged and correct blocks are considered.Construction of automated infrared thermography systemThe automated system for infrared thermographic testing was primilary proposed and finallydeveloped in Starmans company Ltd. The main goal of the planned system was to test the squaresteel blocks created by hot rolling. After the rolling the steel blocks were cut and finally shaped intoquadruples. These should be tested in our proposed system to detect cracks or defects.In general, the system consists of the following main parts: high frequency generator, coils,signal processing units, IR detectors (cameras), equipment and software for displaying and evaluationof indications, complete equipment for defect marking, wetting unit, mechanical parts as mechanicalframe for fixing of IR detectors, mechanical frame for HF coils.The high frequency coils are power supplied by the high frequency generator. The coils areused for steel block heating. Blocks were automatically moved onto the belt and wheels, andintroduced to the coil place. Generally, the blocks speed depends on the viewing field of the IRcamera and used computer system. Both used components allow to achieve linear testing speed ofmore than 0.2 m/s. When the steel block was heated, it was automatically scanned by mountedinfrared cameras. To detect cracks and defects on all sides of the tested material, the whole systemcontains four IR cameras. Each camera scans one side of quadruple block. The block drawing ofthe main part of automated thermographic system can be seen in fig.1.Fig. 1: 3D-visualizations of proposed thermographic systemUsing this drawing and consequent visualizations, the system was finally constructed. Ascan be seen in fig. 1, the system contains a huge mechanical frame, with mounted infrared cameras(detectors). During the development and construction, all cameras were considered to beautomatically adjusted. For the appropriate heating of material surface, the coil has to be in thecenter of the material. For this requirement the frame is automatically adjusted, so the automatedcentering system was used. All adjustments are engaged in the software. Before the material isintroduced in to the coil, the surface is wetted by steam machine. The wetting process makes thehomogenous distribution of the heating of the material surface. By passing the steel blocks throughthe coil, the material surface is scanned by infrared cameras and acquired images are sent to PC. Atthe end of the system, the detected cracks are automatically marked with a special marking device.This feature makes it easier for attendants.Fig. 2: Automated thermographic system overview157 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...Principle of material surface heating is based on induction heating. For the safe materialsurface heating, the special high frequency generator for induction heating was designed. Theconstructed system can be seen in Fig. 2.SoftwareCreated hardware mechanical parts were placed as a part of the full inspection system(infrared + ultrasonic for subsurface flaw detection). When the material is wet, passed through thecoils and heated, the IR detectors (cameras) are used for each surface scanning. Measured data issent to industrial PC through USB port and processed and evaluated in software, called DIO5000.The software DIO5000 contains basic control functions with implemented advanced signalprocessing algorithms. The basic display of the scanned material can be seen in the software, asdisplayed in fig. 3. The displayed picture does not show only flat sides of the tested material, butalso the corners where many cracks or defects can be hidden. Based on this presumption, all camerasare located under specific angle to see the right range of material surface. In general, the basicdisplay can be divided into two parts. The first part (bottom in fig. 3) contains basic control buttons.Control buttons enable: to detect connected USB ports, calibration of IR cameras, data saving,different modes of data displaying, choosing of predefined square steel blocks shape (for coiladjustment), buttons for defect marking and database generating. The second part allows measureddata displaying based on choosen display mode (TV mode, MULTI mode).Fig. 3: Basic display of software for data evaluationAs can be seen in fig. 3, data is displayed in TV mode, where each colour corresponds to thedifferent temperatures. Part of this window is the oscilogram where the amplitudes of each row isvisible. This feature is really important, because the defect amplitude is higher than the backgroundamplitudes. This allows indication of the amplitudes in case of defect presence. For this reason, itis very important to have IR camera very sensitive. This IR camera is capable of detecting adiscontinuity with dimension of less than 0.3 mm, i.e. less than 0.3 % of thickness of the thinnestbar mentioned. The defect detection algorithm uses threshold value, which is derived from dynamicrange within amplitudes of measured sample. The defect is indicated in case the defect amplitude is158 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...higher than the derived threshold. As can be seen in fig. 4b, the background amplitude is sometimessimilar to defect amplitude. In this case, it is very important to consider only the amplitudes withinrange of the raw signal. The amplitudes of backround have to be suppressed and are not considered.This implemented feature makes the defect detection process more efficient. Another issue arisesat the edges of the squared steel bars. In case of defect presence at the adge, the amplitudes are alsohigher, but lower than the background. For this reason, we change the position of IR cameras forscanning the surface under the specific angle. In this configuration, the surface of squared steelbars is efficiently scanned.ApplicationBased on the proposal and theoretical analysis, the automated thermographic system usinginfrared detectors were designed and installed in industrial applications. This system as a part ofthe automated non-destructive line was used for the sufrace detection on square steel bars. Squaresteel bars can be used for the axle or shaft construction in automotive industry hence the system hasto be accurate and reliable in terms of defect detection. The system was successfully installed andthe first test was accomplished on the calibration gauge containing small and large defects. Besidesthe small changes and parameter settings (hardware and software) on the system, the system reliablymarked all defects on the calibration gauge (see fig. 4a).Fig. 4a: Surface defect detection Fig.4b. Surface amplitude visualization 159 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...After these initial tests, real testing of squared steel bars was performed. For the succesful defectdetection it was necesary to set appropriate threshold. The threshold is based on a dynamic rangeof amplitudes within a certain range (see fig. 4b).  Based on this threshold, the defects weredetected, saved and finally statistical analysis was performed. The statistical analysis can be seenin Table 1.Table I: Statistical analysis of defect detection  Defect thresholdDefect                     z toho Defect No> threshold Total o -0.05 o > 0.05 in edge defectMarked defects      64 159 - - 24 67ELKEM systemMarked defects     75 244 18 7 39 68DIO5000 systemEqually marked     44 104 - - 13 10defectsUnmarked       5 2 - - 0 0defectsBased on the analysis in Table I., the comparison between already existing thermographicELKEM system and our proposed Starmans DIO5000 system, it can be seen that defect detectionability is better with Starmans DIO5000 system. In present, the proposed system is succesfullyinstalled and squared steel bars containing defects are repeatedly melted. The main screen of thefinal software is displayed in Fig. 5. Using our implemented signal processing algorithms, it iseasily possible to detect all cracks of defects on steel bars. The results of testing process areimmediately indicated on the main screen. As can be seen in Fig. 5., each side of the steel bar iscontrolled individually.Fig. 5: Main screen of the software part of proposed thermographic system160 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...ConclusionThis paper presents our proposed and developed fully automated robust system for crackdetection on steel blocks used for axle construction in the automotive industry. The proposed systemconsists of a circular coil where the steel blocks are passed through and heated; self designedinfrared cameras and software with implemented evaluation algorithms. The system is fullyautomated and in case there is a different material size, it can be easily transposed by coil changing.Developed infrared cameras involve implemented signal processing algorithms. By theoretical andexperimental measurements, the methods for efficient noise suppression and crack detection wereproposed and finally implemented to the system. The presence of surface and subsurface flaws isautomatically indicated and finally evaluated on display monitor. In future the system can be extendedby adding of algorithms used for automated crack recognition. Our presented system can be alsomodified to test circled or oval blocks.AcknowledgementThis work has been partially supported by research project 2A-2TP1/147, "Research ofsemiconductor nanotubes used for photoelectric components realization" sponsored by Ministry ofIndustry and Trade of the Czech Republic.References1. X.P.V.Maldague. in 'Nondestructive evaluation of materials by infrared thermography',Springer Verlag, 1993, London,.2. Maldague, P.V.Xavier, "Theory and Practice of Infrared Technology for NondestructiveTesting," May 2001.3. M. Giovanni,. Carlomagno, Carosena Meola, NDT & E International,  35, (2002),p-559.4. P.C.M. Hartless, D.C. Whalley, Automated thermographic inspection of surface mountsolder joints. Automotive Electronics, 1991., Eighth International Conference on Volume, Issue , 28-31 Oct 1991 Page(s):178 - 181.5. X. Maldague, J. Cote, D. Poussart, V. Valvilov "Thermal Tomography for NDT ofindustrial materials" Canadian Society of Nondestructive Testing Journal pp. 22-32,May-Jun. 1992.161 NDESAI 2011, December 2-3, Jamshedpur, IndiaŠtarman et.al., Real implementation of ultrasonic phased array technology...

Automated System for Crack Detection using Infrared Thermographic Testing

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Automated System for Crack Detection using Infrared Thermographic Testing

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