Faculty of Mechanical Science and Engineering, Institute of Manufacturing Technology, Chair of Joining Technology and Assembly Remanent Magnetization for Non-Destructive Testing of Spot Welds C. Mathiszik, J. Zschetzsche, C. Großmann, U. Füssel 19 th World Conference on Non-Destructive Testing 2016 July 13 17, 2016 Munich, Germany
1. Introduction 2. Theoretical Background of Residual Magnetization and its Application for NDT of Spot Welds 3. Results and Discussion 4. Conclusion and Outlook 2
1 INTRODUCTION 3
1 Introduction Resistance Spot Welding (RSW) F E Iw Iw F E Joule heating: Q 2 I ( t) Rtot ( t) dt ts tw t h tp (1) closing of electrodes (2) (3) begin of squeeze time ts begin of weld time tw (4) end of weld time, begin of hold time (5) end of hold time t h, opening of electrodes (6) end of process F E : electrode force; Iw: welding current 4
1 Introduction Resistance Spot Welding (RSW) F E Iw Iw F E Joule heating: High degree of automation Q 2 I ( t) Rtot ( t) dt High efficiency ts tw t h tp (1) closing of electrodes (2) (3) begin of squeeze time ts begin of weld time tw (4) end of weld time, begin of hold time (5) end of hold time t h, opening of electrodes (6) end of process F E : electrode force; Iw: welding current Very fast 5
1 Introduction Resistance Spot Welding Problem for quality assurance: Concealed position of the nugget nugget State of Art: random collected samples are tested by laboratory-based destructive methods such as: Chisel Test Peel Test [1] [1] [1] 6
1 Introduction Resistance Spot Welding Problem for quality assurance: Concealed position of the nugget Destructive Testing: High Costs & lot of Scrap Metal nugget Economically & Ecologically not Sustainable for Future State of Art: random collected samples are tested by laboratory-based destructive methods such as: Developments Chisel Test Peel Test Methods that allow NDT of the joint are increasingly examined [1] [1] [1] 7
1 Introduction NDT for Resistance Spot Welding For NDT interaction with material is necessary transmission diffraction absorption reflection radiation [2] NDT during welding NDT after welding So far only ultrasonic testing has been prevailed in NDT for RSW after welding Systems with a single transducer Systems with transducers arranged in an array Phased array systems 8
1 Introduction NDT for Resistance Spot Welding For NDT interaction with material is necessary All systems are not suitable for automatization transmission diffraction absorption reflection radiation All systems need a lot of practical knowledge of the testing NDT during welding NDT after welding personnel So far only ultrasonic testing has been prevailed in NDT for RSW after welding Systems with a single transducer New Systems ways for with NDT transducers in RSW arranged are investigated an array at Phased array systems Technische Universität Dresden [2] 9
2 NDT IN RSW WITH ELECTROMAGNETIC FIELDS 10
2 NDT in RSW with Electromagnetic Fields Testing Procedure Step 0: Welding Step 1: Magnetizing Step 2: Measuring, Analyzing y F, I Q I 2 ( t) Rtot ( t) dt Imag t t B r x 11
2 NDT in RSW with Electromagnetic Fields Experimental Setup Step 0: Welding Step 1: Magnetizing Step 2: Measuring, Analyzing Upper Coil Hall Effect Sensor Sample Lower Coil Sample 12
3 RESULTS AND DISCUSSION 13
3 NDT in RSW with Electromagnetic Fields Experimental Results NDT by analyzing the remanence 1.Capturing the characteristic contour automatically 2.Determining the inner area A mag of the green contour A mag 3.Determining the horizontal and vertikal expansion of the contour Overlay of both measurements Torsion test (true to scale) 14
3 NDT in RSW with Electromagnetic Fields Experimental Results NDT by analyzing the remanence 1.Capturing the characteristic contour automatically 2.Determining the inner area A mag of the green contour A mag (true to scale) Torsion test 3.Determining the horizontal and vertikal expansion of the contour Characteristic contour gives information about nugget dimensions Overlay of both measurements 15
3 NDT in RSW with Electromagnetic Fields Results of FEM Simulations Comparison of the magnetic flux density during magnetization and magnetic field lines small nugget, dn = 1 mm big nugget, dn = 8 mm Upper Coil Upper Sheet Metal Nugget Lower Sheet Metal Lower Coil 16
3 NDT in RSW with Electromagnetic Fields Results of FEM Simulations Comparison of the magnetic flux density during magnetization and magnetic field lines small nugget, dn = 1 mm big nugget, dn = 8 mm Nugget has significant Upper Coil influence on the magnetization Upper Sheet Metal Nugget Lower Sheet Metal Lower Coil 17
3 NDT in RSW with Electromagnetic Fields Experimental Results Examination of the Shape of the Nugget in the Cross Sectional Plane Upper sheet Lower sheet MC4 HX340LAD+Z110 (1,0 mm) HX340LAD+Z110 (1,0 mm) 18
3 NDT in RSW with Electromagnetic Fields Experimental Results Two and three Sheet Metal Combinations with Different Thicknesses MC7: Upper Side (+) DC04+ZE75/75 HDT780C+Z150MB DC04+ZE75/75 22MnB5+AS150 22MnB5+AS150 + X MC7: Lower Side (X) MC2 MC7 Upper sheet DC04+ZE75/75 (0,65 mm) DC04+ZE75/75 (0,65 mm) Middle Sheet - 22MnB5+AS150 (2,0 mm) Lower sheet HDT780C+Z150MB (2,0 mm) 22MnB5+AS150 (1,5 mm) 19
3 NDT in RSW with Electromagnetic Fields Experimental Results A sp = A mag Upper sheet middle sheet Lower sheet MC1 DC04+ZE75/75 (0,65 mm) - HX220YD+Z110MB (0,65 mm) MC2 DC04+ZE75/75 (0,65 mm) - HDT780C+Z150MB (2,0 mm) MC3 22MnB5+AS150 (2,0 mm) - 22MnB5+AS150 (2,0 mm) MC4 HX340LAD+Z110 (1,0 mm) - HX340LAD+Z110 (1,0 mm) MC5 HX340LAD+Z100 (2,0 mm) - HX340LAD+Z100 (2,0 mm) MC6 HX340LAD+Z100 (1,5 mm) HX340LAD+Z100 (1,5 mm) HX340LAD+Z100 (1,5 mm) MC7 DC04+ZE75/75 (0,65 mm) 22MnB5+AS150 (2,0 mm) 22MnB5+AS150 (1,5 mm) 20
3 NDT in RSW with Electromagnetic Fields Experimental Results Assessment of nugget dimensions is for all A sp = A mag investigated material combinations possible, even for three sheet combinations Upper sheet middle sheet Lower sheet MC1 DC04+ZE75/75 (0,65 mm) - HX220YD+Z110MB (0,65 mm) MC2 DC04+ZE75/75 (0,65 mm) - HDT780C+Z150MB (2,0 mm) MC3 22MnB5+AS150 (2,0 mm) - 22MnB5+AS150 (2,0 mm) MC4 HX340LAD+Z110 (1,0 mm) - HX340LAD+Z110 (1,0 mm) MC5 HX340LAD+Z100 (2,0 mm) - HX340LAD+Z100 (2,0 mm) MC6 HX340LAD+Z100 (1,5 mm) HX340LAD+Z100 (1,5 mm) HX340LAD+Z100 (1,5 mm) MC7 DC04+ZE75/75 (0,65 mm) 22MnB5+AS150 (2,0 mm) 22MnB5+AS150 (1,5 mm) 21
Singe Transducer (Pulse-Echo) Array Transducer (Pulse-Echo) In Process US-Testing (through-transmission) Comparison with Test Systems for NDT in RSW: McNemar Test 3 NDT in RSW with Electromagnetic Fields Experimental Results result of Torsion test = result of NDT result of Torsion test result of NDT Decisive Criteria Torsion Test (TT) OK Not OK Number of samples 234 234 234 158 NDT OK A B Not OK C D Ultrasonic testing Analysis of residual flux density (developed in IGF 17539 B) 22
Singe Transducer (Pulse-Echo) Array Transducer (Pulse-Echo) In Process US-Testing (through-transmission) 3 NDT in RSW with Electromagnetic Fields Experimental Results Comparison with Test Systems for NDT in RSW: McNemar Test result of Torsion test = result of NDT result of Torsion test result of NDT Analysis of remanence is more independent of Decisive Criteria testing personnel compared to ultrasonic testing Torsion Test (TT) OK Not OK Number of samples 234 234 234 158 NDT OK A B Not OK C D Ultrasonic testing Analysis of residual flux density (developed in IGF 17539 B) 23
4 CONCLUSION & OUTLOOK 24
4 Conclusion & Outlook Conclusion Results show great potential of this NDT method Assessment can be carried out automatically not only nugget diameter is detected cross-sectional area of the weld nugget can be evaluated Sticking welds and too small nugget diameters can be detected reliably No couplants are necessary A mag 25
4 Conclusion & Outlook Outlook Determining the influence of the electrode indentation on the test result Analyzing material characteristics on the test result Proof of functionality in extreme material combinations with large differences in thickness Design of a compact and suitable test system for mass production A mag 26
References [1] Merkblatt, DVS 2916-1: Prüfen von Widerstandspressschweißverbindungen Zerstörende Prüfung, quasistatisch (Testing of resistance welded joints Destructive testing, quasi static), DVS-Media, 2009. [2] Großmann, Mathiszik, Hipp, Zschetzsche, Füssel: Resistance spot welding quality assurance and new testing methods, International Laser Symposium»FIBER, DISC, DIODE«& International Symposium»TAILORED JOINING«, Dresden, 2014. 27
ACKNOWLEGEMENT THANK YOU FOR YOUR ATTENTION Thanks go to all companies and participants, who contributed their support and knowledge to the project. Das IGF-Vorhaben Nr. 17.539 B der Forschungsvereinigung Schweißen und verwandte Verfahren e.v. des DVS wird über die AiF im Rahmen des Programms zur Förderung der Industriellen Gemeinschaftsforschung (IGF) vom Bundesministerium für Wirtschaft und Energie aufgrund eines Beschlusses des Deutschen Bundestages gefördert. 28