High resolution inductive sensor arrays for material and defect characterization of welds

• US 20020105325A1
• Filed: 01/15/2002
• Published: 08/08/2002
• Est. Priority Date: 06/26/2000
• Status: Active Grant

• Current Assignee: Jentek Sensors, Inc.
• Original Assignee: Jentek Sensors, Inc.
• Inventors: Goldfine, Neil J., Grundy, David C., Schlicker, Darrell E., Washabaugh, Andrew P., Zilberstein, Vladimir A., Shay, Ian
• Granted Patent: US 6,727,691 B2
• Time in Patent Office: Days
• US Class Current: 324/242
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/902 by moving the sensors

Abstract

A sensor that characterizes welds in materials. The sensor includes a meandering drive winding with at least three extended portions and at least one sensing element placed between an adjacent pair of extended portions. A time varying electric current is passed through the extended portions to form a magnetic field. The sensor is placed in proximity to the test material and translated over the weld region. An electrical property of the weld region is measured for each sensing element location. The weld quality is determined using a feature of the electrical property measurement and location.

Claims

1. A method for characterizing friction stir welds in materials comprising:

providing a sensor having a meandering drive winding with at least three extended portions and at least one sensing element placed between an adjacent pair of extended portions;

passing a time varying electric current through the extended portions to form a magnetic field;

placing the sensor in proximity to the test material;

translating the sensor over the weld region;

measuring an electrical property of the weld region for each sensing element location; and

using a feature of the electrical property measurement and location information to determine weld quality.

2. The method as claimed in claim 1 further comprising orienting the extended portions in a direction parallel to the weld axis.

3. The method as claimed in claim 1 further comprising orienting the extended portions in a direction perpendicular to the weld axis.

4. The method as claimed in claim 1 further comprising translating the sensor across the weld region, perpendicular to the weld axis.

5. The method as claimed in claim 1 further comprising translating the sensor along the weld region, parallel to the weld axis.

6. The method as claimed in claim 1 further comprising translating the sensor along a path forming a small angle with the axis of the weld region, with the extended portions oriented perpendicular to the translation path.

7. The method as claimed in claim 6 wherein the small angle is 15 degrees.

8. The method as claimed in claim 1 wherein the electrical property is an electrical conductivity.

9. The method as claimed in claim 8 wherein the feature is a DXZ width.

10. The method as claimed in claim 8 wherein at least one sensing element measures the properties of the base material so that the response from the sensing elements is normalized by the response from the base material.

11. The method as claimed in claim 8 wherein the feature is the shape of the conductivity response across the transition region for dissimilar materials.

12. The method as claimed in claim 8 wherein the feature is an electrical conductivity at the center of the weld region.

13. The method as claimed in claim 12 wherein the weld quality is indicated by an LOP thickness.

14. The method as claimed in claim 12 wherein the weld quality is indicated by the presence of planar flaws.

15. The method as claimed in claim 1 wherein the electrical property is a magnetic permeability.

16. The method as claimed in claim 15 wherein the permeability is used to determine weld residual stress.

17. The method as claimed in claim 1 wherein the feature characterizing the weld quality is an image of the weld region created by combining the electrical property values with the position information.

18. The method as claimed in claim 17 wherein the weld quality is indicated by the presence of planar flaws.

19. The method as claimed in claim 1 further comprising the use of multiple excitation frequencies.

20. The method as claimed in claim 19 wherein the excitation frequency ranges from 100 Hz to 10 MHz.

21. The method as claimed in claim 19 further comprising the use of pre-computed databases of the sensor response to determine several material properties simultaneously.

22. The method as claimed in claim 21 wherein the material properties are a LOP conductivity and a LOP defect thickness.

23. The method as claimed in claim 19 further comprising the use of non-linear least-square minimization calculation which minimizes the error between a predicted sensor response and the measurement data to determine several material properties simultaneously.

24. The method as claimed in claim 23 wherein the material properties are a LOP conductivity and a LOP defect thickness.

25. The method as claimed in claim 1 wherein the sensing elements are rows of inductive coils with the rows oriented parallel to the extended portions.

26. The method as claimed in claim 1 wherein the sensing elements are magnetoresistive sensors.

27. The method as claimed in claim 26 wherein the magnetoresistive sensors are in rows oriented parallel to the extended portions.

28. The method as claimed in claim 27 wherein the feature characterizing the weld quality is a high-resolution image of surface and through thickness properties of the weld region created by combining the electrical property values with the position information.

29. The method as claimed in claim 28 wherein the weld quality is indicated by the presence of a crack-like defect.

30. The method as claimed in claim 28 wherein the weld quality is indicated by a LOP defect.

31. The method as claimed in claim 30 wherein the sensor is translated over the top surface of the weld so that the LOP defect is on the opposite side of the weld.

32. The method as claimed in claim 28 wherein the weld quality is indicated by the presence of an internal flaw.

33. The method as claimed in claim 26 wherein the sensing elements have a secondary coil surrounding the magnetoresistive sensors.

34. The method as claimed in claim 33 wherein the secondary coils are used in a feedback configuration.

36. The method as claimed in claim 35 wherein the electrical property is an electrical conductivity.

37. The method as claimed in claim 36 wherein the feature is a DXZ width determined from a property image.

39. The method as claimed in claim 38 wherein the feature characterizing the weld quality is an image of surface and through thickness properties of the weld region created by combining the electrical property values with the position information.

40. The method as claimed in claim 39 wherein the weld quality is indicated by the presence of a crack-like defect.

41. The method as claimed in claim 39 wherein the weld quality is indicated by a LOP defect.

42. The method as claimed in claim 41 further comprising that the sensor is translated over the top surface of the weld so that the LOP defect is on the opposite side of the weld.

43. The method as claimed in claim 39 wherein the weld quality is indicated by the presence of an internal flaw.

44. The method as claimed in claim 38 wherein the magnetoresistive sensor is surrounded by a secondary coil.

45. The method as claimed in claim 44 wherein the secondary coil is used in a feedback configuration.

46. The method as claimed in claim 38 further comprising an array of magnetoresistive sensors for producing an image of the material properties.

48. The method as claimed in claim 47 wherein the joining process involves tracking the seam between the joint materials.

49. The method as claimed in claim 48 wherein the orientation of the extended portions is varied with respect to the seam axis.

50. The method as claimed in claim 47 wherein the electrical property is an electrical conductivity.

51. The method as claimed in claim 47 wherein the joining process is a friction stir welding process.

52. The method as claimed in claim 51 further comprising mounting at least one sensor in the anvil.

53. The method as claimed in claim 51 further comprising positioning a sensor ahead of the anvil and a sensor behind the anvil.

54. The method as claimed in claim 51 further comprising positioning a sensor ahead of the welding tool and a sensor behind the welding tool.

55. The method as claimed in claim 47 wherein the joining process uses a tool and the position of the sensor relative to the position of the tool is kept constant.

56. The method as claimed in claim 55 further comprising positioning a sensor over the front surface of the test material.

57. The method as claimed in claim 56 further comprising positioning another sensor near the back surface of the test material.

58. The method as claimed in claim 55 further comprising positioning a sensor ahead of the welding tool and a sensor behind the welding tool.

59. The method as claimed in claim 55 further comprising positioning a sensor over the front surface of the test material and a sensor near the back surface of the test material.

60. The method as claimed in claim 47 wherein the at least one sensor is not in contact with the test material.

61. The method as claimed in claim 47 further comprising the use of multiple excitation frequencies.

62. The method as claimed in claim 61 wherein the excitation frequency ranges from 100 Hz to 10 MHz.

63. The method as claimed in claim 47 wherein the sensing elements are inductive coils.

64. The method as claimed in claim 63 wherein the inductive coils form rows that are oriented parallel to the extended portions.

65. The method as claimed in claim 47 wherein the sensing elements are magnetoresistive sensors.

66. The method as claimed in claim 65 wherein the magnetoresistive sensors are giant magnetoresistive sensors.

67. The method as claimed in claim 47 wherein the sensing elements form an array for creating property images.

68. The method as claimed in claim 67 wherein the excitation frequency ranges is high to image surface breaking flaws.

69. The method as claimed in claim 68 wherein the excitation frequency ranges from 100 kHz to 10 MHz.

70. The method as claimed in claim 67 wherein the electrical property is magnetic permeability.

71. The method as claimed in claim 70 wherein the image provides a stress mapping of the heat affected zone and weld region.

35. A method for characterizing weld quality comprising:

placing an eddy current sensor in proximity to the test material;

translating the sensor across the weld region;

measuring an electrical property at each sensor location across the weld region; and

using a feature of the electrical property measurement and location information to determine weld quality.

38. A method for characterizing friction stir welds in materials comprising:

providing a sensor having several concentric circular drive windings with varying numbers of turns in each winding and a magnetoresistive sensor placed at the center of the drive windings;

passing a time varying electric current through the drive windings to form a shaped magnetic field distribution;

placing the sensor in proximity to the test material;

translating the sensor over the weld region;

measuring an electrical property of the weld region for each sensor location; and

using a feature of the electrical property measurement and location information to determine weld quality.

47. A method for joining process quality control comprising:

providing at least one sensor having a meandering drive winding with at least three extended portions and at least one sensing element placed between an adjacent pair of extended portions;

passing a time varying electric current through the extended portions to form a magnetic field;

placing the sensor in proximity to the test material;

measuring an electrical property of the test material with the sensor and test material in relative motion, and using a feature of the electrical property measurement in the control of the joining process.