| 1. |
- Svenman, Edvard, 1969-
(författare)
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An inductive gap measurement method for square butt joints
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A recent method in aero engine production is to fabricate components from smaller pieces, rather than machining them from large castings. This has made laser beam welding popular, offering high precision with low heat input and distortion, but also high productivity. At the same time, the demand for automation of production has increased, to ensure high quality and consistent results. In turn, the need for sensors to monitor and control the laser welding process is increasing. In laser beam welding without filler material, the gap between the parts to be joined must be narrow. Optical sensors are often used to measure the gap, but with precise machining, it may become so narrow that it is difficult to detect, with the risk of welding in the wrong position. This thesis proposes the use of an inductive sensor with coils on either side of the gap. Inducing currents into the metal, such a sensor can detect even gaps that are not visible. The new feature of the proposal is based on using the complex response of each coil separately to measure the distance and height on both sides of the gap, rather than an imbalance from the absolute voltage of each coil related to gap position. This extra information allows measurement of gap width and alignment as well as position in a working range of about 1 mm around the gap, and decreases the influence from variation in gap alignment to the position measurement. The sensor needs to be calibrated with a certain gap width and height alignment. In real use, these will vary, causing the sensor to be less accurate. Using initial estimates of the gap parameters from the basic sensor, a model ofthe response can be used to estimate the measurement error of each coil, whichin turn can be used for compensation to improve the measurement of the gap properties. The properties of the new method have been examined experimentally, using aprecise traverse mechanism to record single coil responses in a working range around a variable dimension gap, and then using these responses to simulate atwo coil probe. In most cases errors in the measurement of weld gap position and dimensions are within 0.1 mm. Different coil orientations were studied using numerical simulation, and validated in experiments using a two coil probe. The influence of scratches, chamfers and variation in plate thickness was investigated at different frequencies.
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| 2. |
- Svenman, Edvard, 1969-, et al.
(författare)
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Experimental validation of an inductive probe for narrow gap measurement based on numerical modelling
- 2019
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Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 146, s. 396-402
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Tidskriftsartikel (refereegranskat)abstract
- Experimental validation of numeric results for an inductive probe shows that narrow gaps between two plates can be measured with accuracy suitable for laser beam welding. A two-coil inductive probe for measurement of the gap was built based on finite element modelling results. The individual coils were calibrated using a complex response method, and results from the physical coils closely match the numerical results regarding distance to gap and lift-off above the plate. The measurement of a realistic gap shows results that can be used in industrial applications for position, plate height and height alignment.
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| 3. |
- Svenman, Edvard, 1969-, et al.
(författare)
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Weld gap position detection based on eddy current methods with mismatch compensation
- 2015
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Ingår i: Proceedings of JOM 18 International conference on joining materials, Helsingör, Danmark, april 26-29, 2015. - : JOM-institute. ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- The paper proposes a method for finding the accurate position of narrow gaps, intended for seam tracking applications. Laser beam welding of butt joints, with narrow gap and weld width, demand very accurate positioning to avoid serious and difficult to detect lack of fusion defects. Existing optical and mechanical gap trackers have problems with narrow gaps and surface finish. Eddy current probes can detect narrow gaps, but the accuracy is affected by mismatch in height above the surface on either side of the gap. In this paper a non-contact eddy-current method, suitable for robotic seam tracking, is proposed. The method is based on the resistive and inductive response of two absolute eddy current coils on either side of the gap to calculate a position compensated for height variations. Additionally, the method may be used to estimate the values of height and gap width, which is useful for weld parameter optimization. To investigate the response to variations in height, the method is tested on non-magnetic metals by scanning one commercially available eddy current probe across an adjustable gap and calculating the expected response for a two-probe configuration. Results for gap position are promising, while mismatch and gap width results need further investigation.
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| 4. |
- Andersson, Angelica, et al.
(författare)
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Digital speckle-pattern interferometry: fringe retrieval for large in-plane deformations with digital speckle photography
- 1999
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 38:25, s. 5408-5412
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Tidskriftsartikel (refereegranskat)abstract
- The compensation of large in-plane motions in digital speckle-pattern interferometry (DSPI) with the use of digital speckle photography (DSP) is demonstrated. Ordinary recordings of DSPI are recombined and analyzed with DSP. The DSP result is used to compensate for the bulk speckle motion prior to calculation of the phase map. This results in a high fringe contrast even for deformations of several speckle diameters. In addition, for the case of an in-plane deformation, it is shown that the absolute phase change in each pixel may be unwrapped by use of the DSP result as an initial guess. The principles of this method and experiments showing the in-plane rotation of a plate and the encounter of two rounded plates are presented
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| 5. |
- Batungwanayo, Guillaume, et al.
(författare)
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Weld Joint Tracking System in an Automatic Inspection Cell by Using Emissivity Variation
- 2014
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Ingår i: Proceedings of the 6th International Swedish Production Symposium 2014. - 9789198097412 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Thermography has proven to be a suitable nondestructive testing method for automatic crack inspection of welds. However automatic weld inspection raises challenges. E.g. the position of the weld might not be exactly as the predefined weld seam, and a weld joint tracking system is needed. To reduce the number of equipment used, a solution is presented in this papers. The infrared camera in the thermography system is a carrier of information of the weld path. This is used for the weld joint tracking system. It is shown that the weld joint tracker is fast enough for an on-line automatic inspection.
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| 6. |
- Bergström, Per, 1981-, et al.
(författare)
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Automatic in-line inspection of shape based on photogrammetry
- 2016
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Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- We are describing a fully automatic in-line shape inspection system for controlling the shape of moving objects on a conveyor belt. The shapes of the objects are measured using a full-field optical shape measurement method based on photogrammetry. The photogrammetry system consists of four cameras, a flash, and a triggering device. When an object to be measured arrives at a given position relative to the system, the flash and cameras are synchronously triggered to capture images of the moving object.From the captured images a point-cloud representing the measured shape is created. The point-cloud is then aligned to a CAD-model, which defines the nominal shape of the measured object, using a best-fit method and a feature-based alignment method. Deviations between the point-cloud and the CAD-model are computed giving the output of the inspection process. The computational time to create a point-cloud from the captured images is about 30 seconds and the computational time for the comparison with the CAD-model is about ten milliseconds. We report on recent progress with the shape inspection system.
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| 7. |
- Broberg, Patrik, 1983-, et al.
(författare)
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Analysis algorithm for surface crack detection by thermography with UV light excitation
- 2016
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Ingår i: Quantitative InfraRed Thermography 2016. - Gdańsk, Poland : Publishing Gdańsk University of Technology. ; , s. 160-165
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Konferensbidrag (refereegranskat)abstract
- Surface crack defects can be detected by IR thermograpgy due to the high absorption of energy within the crack cavity. It is often difficult to detect the defect in the raw data, since the signal easily drowns in the background. It is therefore important to have good analysis algorithms that can reduce the background and enhance the defect. Here an analysis algorithm is presented which significantly increases the signal to noise ratio of the defects and reduces the image sequence from the camera to one image.
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| 8. |
- Broberg, Patrik, 1983-, et al.
(författare)
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Comparison of NDT-methods for automatic inspection of weld defects
- 2015
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Ingår i: International journal of materials & product technology. - 0268-1900 .- 1741-5209. ; 50:1, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to investigate different NDT-methods for weld inspection in an objective manner. Test objects are produced with known variation of flaws: internal pores, surface and internal cracks, toe radius and weld depth. The NDT-methods compared are: phased array ultrasound, radiography, eddy current, thermography and shearography. The results show that radiography is the better method for volumetric defects in thin plates while ultrasound is better for flat defects and thicker, non-flat plates. Thermography was shown to have a good ability of detecting surface defects. A combination of ultrasound and thermography results in a detection of all the non-geometrical defects investigated in this study.
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| 9. |
- Broberg, Patrik, et al.
(författare)
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Comparison of NDT-methods for automatic inspection of weld defects
- 2015
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Ingår i: International journal of materials & product technology. - : InderScience Publishers. - 0268-1900 .- 1741-5209. ; 50:1, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to investigate different NDT–methods for weld inspection in an objective manner. Test objects are produced with known variation of flaws: internal pores, surface and internal cracks, toe radius and weld depth. The NDT–methods compared are: phased array ultrasound, radiography, eddy current, thermography and shearography. The results show that radiography is the better method for volumetric defects in thin plates while ultrasound is better for flat defects and thicker, non–flat plates. The thermography was shown to have good surface defect detection abilities. A combination of ultrasound and thermography results in a detection of all the non–geometrical defects is investigated in this study.
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| 10. |
- Broberg, Patrik, 1983-, et al.
(författare)
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Detection of Surface Cracks in Welds using Active Thermography
- 2012
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Ingår i: Proceedings18th World Conference on Non-Destructive Testing. - : South African Institute for Non-Destructive Testing (SAINT). - 9780620528726 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Surface cracks in welds can be detected using several non-destructive testing methods; among the more popular ones are eddy current, penetrant and magnetic particle testing. For an automatic inspection cell, the traditional techniques have limitations. Here we have investigated the possibility of using active thermography for detecting surface cracks in welds. This technique features advantages such as non-contact and high speed. The weld is illuminated using an infrared light source. Due to higher energy absorption in a surface crack, the defect will be identified as a hot spot when imaged by an infrared camera. Artificial weld defects (notches) are investigated by use of active thermography. Results from an inspection of real longitudinal cold cracks in a weld are also presented. The results show that active thermography looks promising for detection of even small cracks and notches, as long as they are open to the surface.
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