GB2625408A - Device and method for determination of laser scanning speed - Google Patents

Device and method for determination of laser scanning speed Download PDF

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Publication number
GB2625408A
GB2625408A GB2312792.1A GB202312792A GB2625408A GB 2625408 A GB2625408 A GB 2625408A GB 202312792 A GB202312792 A GB 202312792A GB 2625408 A GB2625408 A GB 2625408A
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GB
United Kingdom
Prior art keywords
laser beam
laser
holes
photodetector
absorbing material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
GB2312792.1A
Other versions
GB202312792D0 (en
Inventor
Vincent Sankare Simon
Batrinu Dan-Catalin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Oerlikon Am Europe GmbH
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Oerlikon Am Europe GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oerlikon Am Europe GmbH filed Critical Oerlikon Am Europe GmbH
Publication of GB202312792D0 publication Critical patent/GB202312792D0/en
Publication of GB2625408A publication Critical patent/GB2625408A/en
Pending legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P3/00—Measuring linear or angular speed; Measuring differences of linear or angular speeds
    • G01P3/64—Devices characterised by the determination of the time taken to traverse a fixed distance
    • G01P3/68—Devices characterised by the determination of the time taken to traverse a fixed distance using optical means, i.e. using infrared, visible, or ultraviolet light
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/31—Calibration of process steps or apparatus settings, e.g. before or during manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B22F10/366—Scanning parameters, e.g. hatch distance or scanning strategy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y50/00—Data acquisition or data processing for additive manufacturing

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Automation & Control Theory (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)

Abstract

The scan speed of laser beams is determined, particularly in additive manufacturing processes. The laser beam 100 is scanned across a linear reference track across a plate of laser absorbing material 200 with through holes 210 in a regular pattern. The temporal signal from when the laser beam position coincides with the through holes is captured by a photodetector 300 placed behind the plate of laser absorbing material. The temporal signal of the photodetector is captured by a recording device 400, such as an oscilloscope. Alternatively, the frequency of the signal may be determined. The signal of the photodetector is used in combination with the size of the pattern of through holes in the laser absorbing material to calculate the speed of linear motion of the laser beam. The through holes may be a number of slots such as at least 3 but not more than 100.

Description

Device and method for determination of laser scanning speed The invention relates to a cost-efficient device and a method for determination of laser scanning speed, particularly in the context of additive manufacturing.
Background
Additive manufacturing is finding increasing uses for the manufacturing of complex metal prototypes or serial parts, rapidly and without any tooling. In particular, metal additive manufacturing can be accomplished by laser powder bed fusion (LPBF). The technique can be applied to a wide range of material types, including Ni-based alloys, Ti-based alloys and Al-based alloys. In LPBF, a laser beam is used to selectively melt powder with high geometrical precision. One key parameter in LPBF is the laser scanning speed. Gou et. al. notes in the academic publication "Effect of laser scanning speed on the microstructure, phase transformation and mechanical property of NiTi alloys fabricated by LPBF" published in Materials & Design 215 (2022) 110460, that laser scanning speed has profound influence on the microstructure, metallurgical condition, and properties of parts manufactured by LPBF. It is therefore important to accurately control and monitor laser scanning speed in LPBF processes.
In norms and specifications for additive manufacturing processes (for example ASM7003 from 2008), the scan speed is defined as one key process variable in laser powder bed fusion process, and as such the scan speed should be controlled. In this context, scan speed is defined as the speed at which the laser spot moves across the build surface.
Several devices and methods are available to characterize properties of laser beams. For example, US10184828B2 describes an apparatus for determination of geometric parameters of a laser beam, such as beam diameter or focus diameters. However, such devices, employing an array of detectors, are technically complex and expensive for the task of determining only the scan speed. There is as such a need for a device and method for scanning speed determination of high accuracy but low complication.
Objective of the invention The objective of the invention is to provide an economic device and a quick and low-cost method for determining the scan speed of laser beams in additive manufacturing processes. The device and the method can as such be used for process development and quality control.
Summary of the invention
The objective of the invention is accomplished by measuring the scan speed along a reference track of linear motion of the laser beam. The reference track is executed on a device having a combination of a plate of laser absorbing material with through holes in a regular pattern and a photodetector placed behind said plate of laser absorbing material. As the laser beam is in linear motion across said plate of laser absorbing material, a signal will be generated on the photodetector only at moments where the position of the laser beam is coinciding with one of the through holes in the plate of laser absorbing material. The signal of the photodetector is recorded and used in combination with the size of the pattern of through holes in the laser absorbing material to calculate the speed of linear motion of the laser beam.
Description of figures
Figure 1 illustrates a laser beam (100) originating from the laser optical system (110) with direction of linear motion (150) of speed V. Figure 2 illustrates the linear motion of the laser beam, in the case of moveable laser optical system (110): during the time increment from TO to Ti, the position of the laser has moved from position PO to position P1. The linear motion speed V is given by the relation (P1-P0)/(T1-T0).
Figure 3 illustrates the linear motion of the laser beam, in the case of fixed optical system (110): movement of the position of the laser is accomplished by changing angle of the laser beam (100) relative to the central axis (120) of the laser optical system. Linear motion is considered along a plane (130) that is perpendicular to the central axis of the laser optical system (120). During the time increment from TO to Ti] the position of the laser has moved from position PO to position P1, both on said plane (130). The linear motion speed V is given by the relation (P1-P0)/(T1-T0).
Figure 4 illustrate the composition of the device. A plate of laser absorbing material (200) with through holes (210) is combined with a photodetector (300) and a device (400) for measuring the frequency of the signal from the photodetector, such as an oscilloscope.
Figure 5 illustrate the functional principle of signal generation in the device. At a time 12, the laser beam is at a position on the plate of laser absorbing material, outside the through holes, hence no signal is generated on the photodetector (300). At another time 13, through the movement of the laser beam, the position of the laser beam is coinciding with a through hole (210). At the time T3, the laser beam reaches the photodetector (300), a signal is generated which is detected by the oscilloscope.
Figure 6 illustrate the functional principle of signal generation in the device in the case of fixed laser optical system. At a time 12, the laser beam is at a position on the plate of laser absorbing material, outside the through holes, hence no signal is generated on the photodetector (300). At another time T3, through the movement of the laser beam, the position of the laser beam is coinciding with a through hole (210). At the time 13, the laser beam reaches the photodetector (300), a signal is generated which is detected by the oscilloscope.
Figure 7 illustrate a pattern of the photodetector signal recorded through an oscilloscope.
Figure 8 illustrates the plate of laser absorbing material, with the with W of the through holes and distance S between the center of two adjacent through holes.
Figure 9, illustrates the case that the plate of laser absorbing material is not perpendicular to the center axis of the laser optical system In this case, the projection onto the plane (201) that is perpendicular to the center axis of the laser optical system is considered for the dimensions of W and S. Figure 10 illustrates the top view of an example of a plate of laser absorbing material (200) with through holes (210).
Figure 11 illustrate an example of a device combining of a plate of laser absorbing material with through holes together with a photodetector detector.
Detailed description
The problem of determining the scan speed is solved by considering the scan over a reference track of linear motion. Linear motion in the context of the present invention is understood as movement of the position of the laser beam (100) in a direction (150) that is perpendicular to the axis of the laser beam in case of devices where the laser optical system is moveable, see Figure 1. As illustrated in figure 2, after a time increment from TO to Ti, the laser beam has moved from position PO to position P1. The linear motion speed V is given by the relation (P1-P0)/(T1-T0). In devices where the laser optical system is stationary and laser beam movement is accomplished by angular shift displacement of the laser beam, then linear motion is understood as movement in a direction that is perpendicular to the center axle (120) of the laser beam pivot, as illustrated in Figure 3.
Intercepting the direction of the laser beam is plate of laser absorbing material (200) comprising through holes (210) in a regular pattern. As the laser beam is in linear motion, the laser beam passes through the plate of laser absorbing material at only the moment when the position of the laser beam coincide with one of the through holes (210). At other moments, the laser beam is stopped by the laser absorbing material.
The laser absorbing material may comprise copper, silver, or other metals which can withstand the energy brought in by the laser beam.
Placed behind the plate of laser absorbing material in the direction of the propagation of the laser beam, in other words further away from the laser optical system, is a photodetector (300), as illustrated in Figure 4. The temporal signal, i.e. time resolved signal, of the photodetector is captured by a recording device (400), such as an oscilloscope connected to the photodetector. The photodetector must be sensitive to the wavelength of the laser. A photodiode may be used as photodetector, in which case an electric signal is generated which can be readily processed by an oscilloscope or other recording devices.
A signal on the photodetector is generated only at the moments when the position of the laser beam is coinciding with a through hole in the plate of laser absorbing material.
By motion of the laser beam along the pattern of through holes in the plate of laser absorbing material, a signal will be generated at the photodetector at those moments in time when the laser beam is at the position of a through hole, while no signal will be generated at the photodetector at other moments as the laser beam is then being stopped by the plate of laser absorbing material before reaching the photodetector.
The principle for signal generation of the photodetector is illustrated by means of an example in Figure 5, in the case of moveable laser optical system. At the moment in time T2, the laser beam is at a position outside of the through holes in the plate of laser absorbing material. No signal is generated, as the laser beam is stopped by the laser absorbing material. At another moment in time T3, the position of the laser beam has shifted as consequence of the linear motion to a position coinciding with one of the through holes in the laser absorbing material. At this time (T3) the laser beam reaches the photodetector. Hence a signal is generated and measured through the recording device.
A further example illustrating the principle of signal generation is given in Figure 6 in the case of fixed laser optical system. At a time T2, the laser beam is at a position on the plate of laser absorbing material, outside the holes, hence no signal is generated on the photodetector (300). At another time T3, through the movement of the laser beam, the position of the laser beam is coinciding with a through hole (210). At the time T3, the laser beam reaches the photodetector (300). Hence a signal is generated which is detected by the recording device.
The motion speed is calculated by dividing the average distance between the through holes with the signal period as determined from the oscilloscope signal. A signal generation by the photodetector is displayed as a peak in the oscilloscope signal along the vertical axis. The horizontal axis is the time of measurement. The signal period is the time interval between two intensity peaks in the oscilloscope signal. Alternatively, the frequency of the signal may first be determined. The frequency and the signal period are related by a simple mathematical relation where the signal period is the inverse of the signal frequency. A typical oscilloscope signal is illustrated in Figure 7.
The average distance between through holes, denoted with S, is measured in the same direction as the linear motion of the laser beam. The width of the through hole, denoted W, is likewise measured in the same direction as the linear motion of the laser beam.
See illustration in Figure 8. If the plate of laser absorbing material is not perpendicular to the laser beam, then the average distance between the through holes S and the with W has to be measured according to the projection of the plane (201) perpendicular to the center axis of the laser optical system, in the direction of linear motion of the laser beam along said projection (201), as illustrated in Figure 9.
A minimum of two through holes need to be present in the plate of laser absorbing material, in order to measure a signal period. For higher accuracy in the determination of the signal period, preferably 3 or more, but less than 100 through holes should be present in the plate of laser absorbing material. Further preferred are 4-10 through holes, most preferred are 5 through holes.
The average distance between through holes S, should be at least a factor of 3 times the targeted scanning speed divided by the sampling frequency of the signal from the photodetector. The targeted scanning speed is to be understood as a typical value of the scanning speed range to be measured by the device, in particular of the same order of magnitude as the scanning speed range to be measured by the device.
For typical scan speeds in LPBF-processes, the average distance S between the 15 through holes are preferably larger than 0.5 mm but lower than 20 mm. More preferred is an average distance S between the through holes larger or equal to 2 mm, but smaller or equal than 10 mm. Most preferred is a value of S of about 5 mm.
The width of the through holes (W) has to be large enough to be above the refraction limit. In particular the width of the through holes (W) should be at minimum a factor of 10 larger than the laser wavelength, however not larger than 0.5 mm. In other words, according to the relation: x Laser wavelength s W 0 5 mm A regular pattern, in context of the present innovation, is understood in the sense that the average distance S between the through holes and the width of the through holes 25 W are the same, or approximately the same across the whole pattern in the device. In particular, the maximum allowed deviation should be 10% or less.
In a preferred embodiment, to ease the positioning of the measurement device, the through holes in the plate of laser absorbing material consist of slots, which are oriented perpendicular to the direction of linear motion of the laser beam. In a further preferred embodiment, the slots are perpendicular to both the direction of linear motion, and to the axis of the laser beam.
Preferably, for increasing accuracy of the measurement, the width of the slots (VV) is uniform and constant across the extent of the slots in the direction perpendicular to the linear movement.
Example
A device, depicted in Figure 10, was constructed using a circular plate of copper (commercially pure copper) as laser absorbing material. The distance between the slots (S) were 5 mm and the with 0.25 mm. The thickness of the cupper plate was 1 MM. A biased photodiode of type DET10C2 (Thorlabs) was placed behind the cupper plate. The photodiode was enclosed in a housing to avoid stray signals. An oscilloscope, Hantek IDS01070A with sampling rate of 250 MSa/s (i.e. sampling frequency 250*106 s-1) was connected to the photodiode.
The device was positioned inside a Laser Powder Bed additive manufacturing system, positioned with the top surface of the cupper plate 0.5 mm above the focal point of the laser.
A fiber laser with a wavelength of 1070 nm was used to perform linear scans along a path along the cupper plate. The laser power used for the measurement was about 100W.
The time between two consecutive peaks was measured to 0.01 s, corresponding to a frequency of 100 Hz. The scan speed was with then calculated as the distance between the slots divided by the time between two peaks. Hence, the scan speed was determined to 500 mm/s. ( 5 mm / 0.01 s = 500 mm/s)

Claims (12)

  1. Claims The invention claimed is 1. A device for determining the linear motion speed of a laser beam comprising, - a plate of laser beam absorbing material with through holes in a regular pattern, and - a photodetector sensitive to the wavelength of said laser beam, and - a device for recording the temporal signal of said photodetector.
  2. 2. Device according to claim 1, characterized in that the photodetector is placed behind the plate of laser beam absorbing material in the direction of the laser beam.
  3. 3. Device according to any of the preceding claims, characterized in that the photodetector comprises a photodiode.
  4. 4. Device according to claim 3, characterized in that the device comprises not more than one photodiode.
  5. 5. Device according to any of the preceding claims, characterized in that the temporal signal from the photodetector is recorded by an oscilloscope.
  6. 6. Device according to any of the preceding claims, characterized in that the through holes are of constant width (VV), in particular having a width lower than 0.5 mm.
  7. 7. Device according to any of the preceding claims, characterized in that the trough holes are arranged with an average distance (S) in the range of 0.5 mm S s 20 mm
  8. 8. Device according to any of the preceding claims, characterized in that the through holes consist of slots.
  9. 9. Device according to any of the preceding claims, characterized in that the through holes consist of slots, wherein the number of slots are at least 3 but not larger than 100, preferably at least 4 but not larger than 10, most preferred with 5 slots.
  10. Method for determining the linear motion speed of a laser beam characterized in that, - the laser beam is guided in a linear track, across a plate of laser beam absorbing material with through holes in a regular pattern, and -the frequency with which the laser beam passes through said through holes in said plate of laser absorbing material is recorded.
  11. 11. Method according to claim 10, characterized in that the laser beam is part of a device for at least one additive manufacturing process.
  12. 12. Method according to claim 11, characterized in that the additive manufacturing process is laser powder bed fusion.
GB2312792.1A 2022-08-25 2023-08-22 Device and method for determination of laser scanning speed Pending GB2625408A (en)

Applications Claiming Priority (1)

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DE102022003103 2022-08-25

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GB2625408A true GB2625408A (en) 2024-06-19

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04235520A (en) * 1991-01-11 1992-08-24 Canon Inc Optical scanning device
US5570195A (en) * 1992-03-10 1996-10-29 Canon Kabushiki Kaisha Image forming apparatus which detects scanning light through slitted shield plate
US8803073B2 (en) * 2009-04-06 2014-08-12 Eos Gmbh Electro Optical Systems Method and device for calibrating an irradiation device
US20160307731A1 (en) * 2015-01-21 2016-10-20 Arcam Ab Method for verifying characteristics of an electron beam
US20200209107A1 (en) * 2018-03-30 2020-07-02 Edison Welding Institute, Inc. Laser beam profiling system for use in laser powder bed fusion manufacturing

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04235520A (en) * 1991-01-11 1992-08-24 Canon Inc Optical scanning device
US5570195A (en) * 1992-03-10 1996-10-29 Canon Kabushiki Kaisha Image forming apparatus which detects scanning light through slitted shield plate
US8803073B2 (en) * 2009-04-06 2014-08-12 Eos Gmbh Electro Optical Systems Method and device for calibrating an irradiation device
US20160307731A1 (en) * 2015-01-21 2016-10-20 Arcam Ab Method for verifying characteristics of an electron beam
US20200209107A1 (en) * 2018-03-30 2020-07-02 Edison Welding Institute, Inc. Laser beam profiling system for use in laser powder bed fusion manufacturing

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