Methods and Systems for Characterizing Laser Machining Properties by Measuring Keyhole Dynamics Using Interferometry

• US 20160039045A1
• Filed: 03/13/2014
• Published: 02/11/2016
• Est. Priority Date: 03/13/2013
• Status: Active Grant

• Current Assignee: IPG Photonics Corporation
• Original Assignee: Queen's University At Kingston
• Inventors: Webster, Paul J.L.
• Granted Patent: US 9,757,817 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B23K 10/02 Plasma welding
• CPC Class Codes: B23K 15/0046 Welding
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/0643 comprising mirrors
• CPC Class Codes: B23K 26/0648 comprising lenses
• CPC Class Codes: B23K 26/082 Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
• CPC Class Codes: B23K 26/14 using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor B23K26/12 takes precedence
• CPC Class Codes: B23K 26/244 Overlap seam welding
• CPC Class Codes: B23K 31/125 Weld quality monitoring
• CPC Class Codes: B23K 9/00 Arc welding or cutting electro-slag welding B23K25/00; welding transformers H01F; welding generators H02K
• CPC Class Codes: B26F 1/26 Perforating by non-mechanical means, e.g. by fluid jet
• CPC Class Codes: B26F 3/004 by means of a fluid jet methods for use of abrasive blasting for cutting B24C1/045; guns for abrasive fluid jets B24C5/02; perforating by non-mechanical means, e.g. by fluid jet B26F1/26
• CPC Class Codes: G01B 11/22 for measuring depth
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01B 5/0037 Measuring of dimensions of welds
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence
• CPC Class Codes: G01N 21/954 Inspecting the inner surface of hollow bodies, e.g. bores
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4817 relating to scanning

Abstract

A method, apparatus, and system are provided to monitor and characterize the dynamics of a phase change region (PCR) created during laser welding, specifically keyhole welding, and other material modification processes, using low-coherence interferometry. By directing a measurement beam to multiple locations within and overlapping with the PCR, the system, apparatus, and method are used to determine, in real time, spatial and temporal characteristics of the weld such as keyhole depth, length, width, shape and whether the keyhole is unstable, closes or collapses. This information is important in determining the quality and material properties of a completed finished weld. It can also be used with feedback to modify the material modification process in real time.

Claims

1. An apparatus comprising:

an imaging optical source that produces imaging light that is applied to a material processing system, wherein the material processing system implements a material modification process and creates a phase change region (PCR) in a material;

at least one element that directs the imaging light at a plurality of imaging beam positions proximate the PCR;

at least one input-output port that outputs a first component of the imaging light to an optical access port of the material processing system and that receives a reflection component of the imaging light;

an optical combiner that combines the reflection component and at least another component of the imaging light to produce an interferometry output, the interferometry output based on a path length taken by the first component and the reflection component compared to a path length taken by the at least another component of the imaging light; and

an interferometry output processor that processes the interferometry output to determine at least one characteristic of the PCR.

2. The apparatus of claim 1, further comprising a material processing beam source that produces a material processing beam that is applied to the material in the material modification process, wherein the material processing beam creates the PCR in the material.

3. The apparatus of any preceding claim, wherein the interferometry output processor processes interferometery outputs over a period of time to determine the at least one characteristic of the PCR.

4. The apparatus of any preceding claim, wherein the at least one characteristic of the PCR comprises at least one of:

keyhole depth;

location of maximum keyhole depth;

average depth;

location;

width;

length;

surface shape;

subsurface shape;

subsurface keyhole length;

subsurface profile;

subsurface keyhole width;

wall slope;

sidewall angle;

collapse;

instability;

dynamics of liquid region of the PCR;

location of interface between liquid and solid region; and

other physical parameters of the PCR.

5. The apparatus of any preceding claim, wherein the plurality of imaging beam positions comprise:

a plurality of imaging beam positions normal to the sample location;

or

a plurality of imaging beam positions having at least two different incident angles that are not normal to the sample location;

or

at least one imaging beam position normal to the sample location and at least one imaging beam position that is at an angle other than normal to the sample location.

6. The apparatus of any preceding claim, further comprising:

a feedback controller that controls at least one processing parameter of the material modification process based on at least one of the determined at least one characteristic.

7. The apparatus of any preceding claim further comprising:

a record generator that generates a record of the material modification process based on at least one of the determined at least one characteristic at a plurality of times.

8. The apparatus of any preceding claim, further configured to evaluate quality of a weld produced by the material modification process optionally based on the record.

9. The apparatus of any preceding claim, further comprising:

an acoustic energy source and/or an optical energy source configured to excite waves in a liquid region of the PCR to provide information regarding PCR dynamics.

10. The apparatus of any preceding claim, wherein:

at least one of the plurality of imaging beam positions is outside the PCR.

11. The apparatus of any preceding claim, wherein:

light is applied to at least two of the plurality of imaging beam positions simultaneously.

12. The apparatus of any preceding claim, wherein:

light is applied to at least two of the plurality of imaging beam positions sequentially.

13. The apparatus of any preceding claim wherein:

the plurality of imaging beam positions are achieved by changing the position and/or angle of at least one imaging beam relative to the material processing beam during the material modification process.

14. The apparatus of any preceding claim, wherein:

the number of positions where imaging light is applied to the sample is changed during the material modification process.

15. The apparatus of any preceding claim, wherein:

at least one of the plurality of imaging beam positions does not have an incident position that is on a line formed by the material processing beam.

16. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to determine a width or diameter of the keyhole when viewed from the same direction as the material processing beam is applied.

17. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that is smaller than a diameter of the material processing beam.

18. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that is similar to a diameter of the material processing beam.

19. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that is larger than a diameter of the material processing beam.

20. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that encompasses the PCR.

21. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of the imaging beam positions is focused to a diameter that is larger than the PCR.

22. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 1 kHz or more.

23. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 10 kHz or more.

24. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 100 kHz or more.

25. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to determine a maximum depth achieved by a keyhole in the PCR over a period of time.

26. The apparatus of claim 25 wherein:

the determination of maximum depth is used to control at least one parameter of the material modification process to reduce a number of instances where material modification fails to penetrate beyond a specified depth and/or into a specified material.

27. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to determine a shape and size of a keyhole in the PCR over time.

28. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to determine if a keyhole collapses or fails to maintain a specified depth.

29. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to calculate a speed for the material modification process.

30. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to calculate an output power level for the material modification beam.

31. The apparatus of any preceding claim, wherein:

measurements for at least one of the plurality of imaging beam positions are processed, output, and fed back to a material modification beam process control system to provide closed loop operation.

32. The apparatus of any preceding claim, further comprising:

a common objective lens;

wherein the material processing beam and the imaging light applied to at least one of the imaging beam positions are focused by the common objective lens.

33. The apparatus of any one of claims 1 to 31, further comprising:

a first objective lens and a second objective lens;

wherein the material processing beam is focused by the first objective lens and the imaging light applied to at least one of the plurality of imaging beam positions is focused by the second objective lens.

34. The apparatus of claim, 33 further comprising a mirror for combining the material processing beam and the imaging light applied to at least one of the plurality of imaging beam positions after being respectively focused by the first and second objective lenses.

35. The apparatus of any preceding claim, further comprising:

a movable mirror for combining the imaging light with the material processing beam, the movable mirror allowing control over an angle of the imaging light for at least one imaging beam position.

36. The apparatus of any preceding claim, further comprising:

a movable mirror for allowing control over an angle of the imaging light; and

a dichroic mirror for reflecting the material processing beam towards the sample while allowing the imaging light to pass through the dichroic mirror to and from the sample for at least one imaging beam position.

37. The apparatus of any preceding claim, further comprising:

a sacrificial covering glass to protect other optics in the apparatus from emissions from the material modification process.

38. The apparatus of any preceding claim, further comprising:

one or more pressurized orifices that produce a cross jet of gas to protect optics of the apparatus from emissions from the material modification process by blowing the emissions away.

39. The apparatus of any preceding claim, further comprising:

at least one nozzle that applies a cover gas to produce or prevent specific chemical effects on the sample.

40. The apparatus of any preceding claim, further comprising:

an auxiliary measurement system that uses electronic, mechanical, optical and/or capacitive techniques for determining a distance from a laser head that outputs the material processing beam to the sample.

41. The apparatus of any preceding claim, further configured to measure and/or compensate for gas pressure in one or more path segments of one or more imaging beam paths.

42. The apparatus of any preceding claim, further configured to compensate for optical path length changes resulting from scanning the imaging light and/or the material processing beam.

43. The apparatus of any preceding claim, further configured to determine a period and/or phase of oscillation of a melt pool in the PCR, and to use the determined period to determine at least one of melt viscosity, material type, material state and geometry.

44. The apparatus of any preceding claim, further configured to determine at least one of porosity and keyhole instability by detecting rapid momentary enhancements in material modification process penetration depth.

45. The apparatus of any preceding claim, further configured to use the interferometry output to sense an occurrence of a gas phase explosion or similar transient and to generate an output indicative that a gas phase explosion or similar transient may have compromised the quality of a weld.

46. The apparatus of any preceding claim, further configured to use the interferometry output to sense keyhole instability from small transients prior to an occurrence of a large transient and to generate a warning of risk of a future large transient or gas phase explosion.

47. The apparatus of any preceding claim, further configured to synchronously or asynchronously drive, inhibit, stabilize, or otherwise control an oscillation in or near the phase change region.

48. The apparatus of any preceding claim, further comprising:

a mechanically actuated objective lens that is controlled to keep focus of the material processing beam a certain distance from the sample location.

49. The apparatus of claim 48, wherein the another path length is a reference path length which is changed in correlation with actuation of the mechanically actuated objective lens.

50. The apparatus of claim 49, comprising:

a reference mirror actuator that synchronizes a position of a reference mirror with that of the mechanically actuated objective lens to change the reference path length in correlation with actuation of the mechanically actuated objective lens.

51. The apparatus of claim 50, wherein:

a surface attached to an actuator of the mechanically actuated objective lens is used as the reference mirror such that the reference path length changes in correlation with actuation of the mechanically actuated objective lens.

52. The apparatus of any preceding claim, further comprising:

a section in another optical path in which a reference imaging light component is coupled out of an optical fiber into air, and then back into optical fiber, the section having an air component with an adjustable length.

53. The apparatus of any preceding claim, further comprising:

a capacitive height sensing mechanism;

a mechanical actuator for adjusting focal position of the material processing beam based on a height determined using the capacitive height sensing mechanism; and

a reference path length that is adjusted based on the focal position.

54. The apparatus of any preceding claim, further configured to digitally compensate for DC signal changes arising from reference path length adjustment.

55. The apparatus of any preceding claim, comprising an acousto-optic or electro-optic deflector that is used to control a direction of at least one imaging beam.

56. The apparatus of any preceding claim, further configured to use the interferometry output to detect surface composition.

57. The apparatus of any preceding claim, further configured to determine a location of an interface by at least one of intensity peak pixel, centroid fitting and fringe phase.

58. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 10 Hz or more.

59. The apparatus of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 100 Hz or more.

60. The apparatus of any preceding claim, further comprising:

a birefringent optic used to multiplex the imaging light and spatially separate it onto different parts of the sample.

63. The method of any preceding claim, further comprising:

processing interferometery outputs over a period of time to determine the at least one characteristic of the PCR.

64. The method of any preceding claim, wherein the at least one characteristic of the PCR comprises at least one of:

keyhole depth;

location of maximum keyhole depth;

average depth;

location;

width;

length;

surface shape;

subsurface shape;

subsurface keyhole length;

subsurface profile;

subsurface keyhole width;

wall slope;

sidewall angle;

collapse;

instability;

dynamics of liquid region of the PCR;

location of interface between liquid and solid region; and

other physical parameters of the PCR.

65. The method of any preceding claim, wherein the plurality of imaging beam positions comprise:

a plurality of imaging beam positions normal to the sample location;

or

a plurality of imaging beam positions having at least two different incident angles that are not normal to the sample location;

or

at least one imaging beam position normal to the sample location and at least one imaging beam position that is at an angle other than normal to the sample location.

66. The method of any preceding claim, further comprising:

controlling at least one processing parameter of the material modification process based on at least one of the determined at least one characteristic.

67. The method of any preceding claim, further comprising:

generating a record of the material modification process based on at least one of the determined at least one characteristic at a plurality of times; and

optionally evaluating quality of the material modification process optionally based on the record.

68. The method of any preceding claim, further comprising:

exciting waves in a liquid region of the PCR using an acoustic energy source and/or an optical energy source to provide information regarding PCR dynamics.

69. The method of any preceding claim, wherein:

at least one of the plurality of imaging beam positions is outside the PCR.

70. The method of any preceding claim, wherein:

light is applied to at least two of the plurality of imaging beam positions simultaneously.

71. The method of any preceding claim, wherein:

light is applied to at least two of the plurality of imaging beam positions sequentially.

72. The method of any preceding claim, wherein:

the plurality of imaging beam positions are achieved by changing the position and/or angle of at least one imaging beam relative to the material processing beam during the material modification process.

73. The method of any preceding claim, wherein:

the number of positions where imaging light is applied to the sample is changed during the material modification process.

74. The method of any preceding claim, wherein:

at least one of the plurality of imaging beam positions does not have an incident position that is on a line formed by the material processing beam.

75. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to determine a width or diameter of the keyhole when viewed from the same direction as the material processing beam is applied.

76. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that is smaller than a diameter of the material processing beam.

77. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that is similar to a diameter of the material processing beam.

78. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that is larger than a diameter of the material processing beam.

79. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is focused to a diameter that encompasses the PCR.

80. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of the imaging beam positions is focused to a diameter that is larger than the PCR.

81. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 1 kHz or more.

82. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 10 kHz or more.

83. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 100 kHz or more.

84. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to determine a maximum depth achieved by a keyhole in the PCR over a period of time.

85. The method of claim 84, further comprising:

using the determination of maximum depth to control at least one parameter of the material modification process to reduce a number of instances where material modification fails to penetrate beyond a specified depth and/or into a specified material.

86. The method of any preceding claim, further comprising:

using imaging light applied to at least one of the plurality of imaging beam positions to determine a shape and size of a keyhole in the PCR over time.

87. The method of any preceding claim, further comprising:

using imaging light applied to at least one of the plurality of imaging beam positions to determine if a keyhole collapses or fails to maintain a specified depth.

88. The method of any preceding claim, further comprising:

using imaging light applied to at least one of the plurality of imaging beam positions to calculate a speed for the material modification process.

89. The method of any preceding claim, further comprising:

using imaging light applied to at least one of the plurality of imaging beam positions to calculate an output power level for the material processing beam.

90. The method of any preceding claim, further comprising:

processing measurements for at least one of the plurality of imaging beam positions and feeding back an output to a material modification beam process control system to provide closed loop operation.

91. The method of any preceding claim, further comprising:

focusing the material processing beam and the imaging light applied to at least one of the imaging beam positions by a common objective lens.

92. The method of any one of claims 61 to 9,1 further comprising:

focusing the material processing beam by a first objective lens and focusing the imaging light applied to at least one of the plurality of imaging beam positions by a second objective lens.

93. The method of claim 92, further comprising:

combining the material processing beam and the imaging light applied to at least one of the plurality of imaging beam positions after being respectively focused by the first and second objective lenses.

94. The method of any preceding claim, further comprising:

combining the imaging light with the material processing beam with a movable mirror, the movable mirror allowing control over an angle of the imaging light for at least one imaging beam position.

95. The method of any preceding claim, further comprising:

controlling an angle of the imaging light with a movable mirror; and

reflecting the material processing beam towards the sample with a dichroic mirror while allowing the imaging light to pass through the dichroic mirror to and from the sample for at least one imaging beam position.

96. The method of any preceding claim, further comprising:

providing a sacrificial covering glass to protect other optics in the apparatus from emissions from the material modification process.

97. The method of any preceding claim, further comprising:

producing a cross jet of gas to protect optics of the apparatus from emissions from the material modification process by blowing the emissions away.

98. The method of any preceding claim, further comprising:

applying a cover gas to produce or prevent specific chemical effects on the sample.

99. The method of any preceding claim, further comprising:

using electronic, mechanical, optical and/or capacitive techniques for determining a distance from a laser head that outputs the material processing beam to the sample.

100. The method of any preceding claim, further comprising:

measuring and/or compensating for gas pressure in one or more path segments of one or more imaging beam paths.

101. The method of any preceding claim, further comprising:

compensating for optical path length changes resulting from scanning the imaging light and/or the material processing beam.

102. The method of any preceding claim, further comprising:

determining a period and/or phase of oscillation of a melt pool in the PCR, and using the determined period to determine at least one of melt viscosity, material type, material state and geometry.

103. The method of any preceding claim, further comprising:

determining at least one of porosity and keyhole instability by detecting rapid momentary enhancements in material modification process penetration depth.

104. The method of any preceding claim, further comprising:

using the interferometry output to sense an occurrence of a gas explosion or similar transient and generating an output indicative that a gas phase explosion or similar transient may have compromised the quality of a weld.

105. The method of any preceding claim, further comprising:

using the interferometry output to sense keyhole instability from small transients prior to an occurrence of a large transient and generating a warning of risk of a future large transient or gas phase explosion.

106. The method of any preceding claim, further comprising:

synchronously or asynchronously driving, inhibiting, stabilizing, or otherwise controlling an oscillation in or near the phase change region.

107. The method of any preceding claim, further comprising:

controlling a mechanically actuated objective lens to keep focus of the material processing beam a certain distance from the sample location.

108. The method of claim 107, wherein the another path length is a reference path length, the method further comprising:

changing the reference path length in correlation with actuation of the mechanically actuated objective lens.

109. The method of claim 108, further comprising:

synchronizing a position of a reference mirror with that of the mechanically actuated objective lens to change the reference path length in correlation with actuation of the mechanically actuated objective lens.

110. The method of claim 109, further comprising:

using a surface attached to an actuator of the mechanically actuated objective lens as the reference mirror such that the reference path length changes in correlation with actuation of the mechanically actuated objective lens.

111. The method of any preceding claim, further comprising:

providing a section in another optical path in which a reference imaging light component is coupled out of an optical fiber into air, and then back into optical fiber, the section having an air component with an adjustable length.

112. The method of any preceding claim, further comprising:

sensing height with a capacitive height sensing mechanism;

adjusting focal position of the material processing beam based on the height determined using the capacitive height sensing mechanism; and

adjusting a reference path length based on the focal position.

113. The method of any preceding claim, further comprising:

digitally compensating for DC signal changes arising from reference path length adjustment.

114. The method of any preceding claim, further comprising:

controlling a direction of at least one imaging beam with an acousto-optic or electro-optic deflector.

115. The method of any preceding claim, further comprising:

using the interferometry output to detect surface composition.

116. The method of any preceding claim, further comprising

determining a location of an interface by at least one of intensity peak pixel, centroid fitting and fringe phase.

117. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 10 Hz or more.

118. The method of any preceding claim, wherein:

imaging light applied to at least one of the plurality of imaging beam positions is used to take successive readings at a frequency of approximately 100 Hz or more.

119. The method of any preceding claim, further comprising:

using a birefringent optic to multiplex the imaging light and spatially separate it onto different parts of the sample.

120. The method of any preceding claim, further comprising:

using the determination of maximum depth to control at least one parameter of the material modification process to ensure material modification does not go too deep and/or into a specified material.

121. The apparatus of any one of claims 1 to 60, wherein the determination of maximum depth is used to control at least one parameter of the material modification process to ensure material modification does not go too deep and/or into a specified material.

61. A method comprising:

applying an imaging light to a material processing system, wherein the material processing system implements a material modification process and creates a phase change region (PCR) in a material;

using at least one element to direct the imaging light at a plurality of imaging beam positions proximate the PCR;

outputting a first component of the imaging light to an optical access port of the material processing system and receiving a reflection component of the imaging light;

combining the reflection component and at least another component of the imaging light to produce an interferometry output, the interferometry output based on a path length taken by the first component and the reflection component compared to a path length taken by the at least another component of the imaging light; and

processing the interferometry output to determine at least one characteristic of the PCR.

62. The method of claim 61, further comprising applying a material processing beam to the material in the material modification process, wherein the material processing beam creates the PCR in the material.