CN109269453B - Method for determining number of single detection layers in high-frequency ultrasonic online detection in PBF additive manufacturing - Google Patents
Method for determining number of single detection layers in high-frequency ultrasonic online detection in PBF additive manufacturing Download PDFInfo
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- CN109269453B CN109269453B CN201811140303.8A CN201811140303A CN109269453B CN 109269453 B CN109269453 B CN 109269453B CN 201811140303 A CN201811140303 A CN 201811140303A CN 109269453 B CN109269453 B CN 109269453B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
- G01B17/02—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations for measuring thickness
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
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- G01N29/11—Analysing solids by measuring attenuation of acoustic waves
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Abstract
The invention discloses a method for determining the number of layers in single detection by PBF additive manufacturing high-frequency ultrasonic online detection, which comprises the following steps of S1, preparing a sample S2, and testing the attenuation coefficient of the sample; s3, determining the thickness of the simulation test block; s4, preparing a simulation test block; s5, testing transverse hole echo; s6, linear fitting of data A and D; s7, calculating the detection rate; and S8, obtaining the corresponding defect depth according to the value requirement of the detectable rate. The invention accurately calculates the attenuation coefficient according to the sample, and then accurately calculates the maximum detection layer number by using the simulation test block with the transverse hole on the premise of meeting the detection rate requirement, thereby maximizing the printing efficiency.
Description
Technical Field
The invention belongs to the field of printing detection, and particularly relates to a method for determining the number of layers in single detection by PBF additive manufacturing high-frequency ultrasonic online detection.
Background
The PBF additive manufacturing technology has the characteristics of high dimensional precision, good surface roughness, high efficiency and the like, and is a representative technology for metal additive manufacturing of complex thin-wall structures and special-shaped cavity structures. Then, as the printing process has many process points, and the long-term stability of process parameters and environmental atmosphere is difficult to be ensured, various defects such as air holes, cracks, interlayer fusion failure and the like are often generated in the printing process.
Image detection techniques represented by infrared thermography and CCD have been applied to monitoring of metal additive manufacturing processes, but these techniques can only detect surface defects, and defects buried under layers are difficult to find. The non-contact high-frequency detection technology represented by laser ultrasound can detect the internal defects of the material through ultrasonic waves, and is an effective means applied to online detection of PBF additive manufacturing. In order to improve the detection efficiency and ensure the timeliness of defect detection, the conventional method adopts a way of performing edge detection while polishing, such as the technical scheme disclosed in patent application with publication number CN107102061A, but it does not provide how to specifically implement edge detection while polishing, and details of each step are not related at all, so how to determine a method for determining the number of layers to be detected once in the way of performing edge detection is an urgent problem at present.
Disclosure of Invention
The invention aims to provide a method for determining the number of layers for single detection in high-frequency ultrasonic online detection in PBF additive manufacturing, which can effectively measure and calculate the number of layers for single detection so as to achieve the maximum detection and printing efficiency on the premise of ensuring high detection rate.
In order to solve the technical problems, the invention adopts the following technical scheme: a PBF additive manufacturing high-frequency ultrasonic online detection single detection layer number determining method comprises the following steps,
s1, preparing a sample: printing out samples of the same material according to the same printing process parameters when the online detection is carried out;
s2, testing the attenuation coefficient of the sample: logarithmically representing the reduction of the amplitude of the two bottom echo waves and the ratio of the thickness of the sample;
s3, determining the thickness of the simulation test block: calculating the corresponding thickness as the thickness of the simulation test block when the attenuation reaches mdB by using the attenuation coefficient;
s4, preparing a simulation test block:
(1) drawing a three-dimensional graph of the simulation test block, arranging transverse through holes with the diameter d0 at different depth positions, wherein the thickness of a single layer printed in printing parameters is d0, and the central interval height of the transverse holes is also d 0;
(2) printing a simulation test block by using the same printing process parameters as the test sample;
(3) polishing two sides of the simulation test block to expose the transverse hole, and extruding and polishing powder in the transverse hole to be flat by utilizing machining;
s5, transverse hole echo testing: testing the transverse holes with different depths by using the same detection parameters when testing the attenuation coefficient of the sample to obtain the maximum echo amplitude of each transverse hole to form a one-dimensional array A (a1, a2.. an); the depth values of the transverse holes form a one-dimensional array D (D1, D2.. dn), and n is a positive integer;
s6, data linear fitting A and D, namely carrying out logarithmic linear fitting on the depth value array D and the amplitude value array A to obtain the intercept β 0, the slope β 1 and the standard deviation sigma of a fitting straight lineδ，
ln(A)＝β0+β1ln(D)+σδ；
S7, detection rate calculation: and calculating a relation curve between the defect depth and the defect detection probability by using a cumulative normal distribution model. POD is the defect detection rate, d is the defect depth variable, adTo detect the threshold, the amplitude height of the background noise is taken as the detection threshold,
and S8, obtaining corresponding defect depth according to the value requirement of the detectable rate, wherein the defect depth is the limit depth of detection, and the limit depth is divided by the layer depth of single printing to obtain the number of detection layers.
Optimally, the value range of the attenuation is as follows: 0< m < 20.
Optimally, the sample is a cuboid.
Preferably, the interval width of two adjacent transverse holes is the same.
Preferably, the detection parameters include frequency and energy.
The invention has the beneficial effects that: the invention accurately calculates the attenuation coefficient according to the sample, and then accurately calculates the maximum detection layer number by using the simulation test block with the transverse hole on the premise of meeting the detection rate requirement, thereby maximizing the printing efficiency.
Drawings
FIG. 1 is a schematic view of a simulation test block and a cross-hole;
FIG. 2 is a graph showing a relationship between a defect depth and a defect detection probability of a stainless steel material having a limit detection depth of 0.4 mm;
FIG. 3 is a graph showing the relationship between the defect depth and the defect detection probability of a fine-grained stainless steel having a limit detection depth of 0.55 mm.
Detailed Description
The invention is described in detail below with reference to the embodiments shown in the drawings, and the method for determining the number of layers in single detection by high-frequency ultrasonic online detection in additive manufacturing of PBF comprises the following steps:
example one
S1, preparing a sample for testing the attenuation coefficient of a material:
printing a square sample of the same material according to the same printing process parameters during the online detection, wherein the thickness of the sample is 5mm (or other thicknesses of 10mm and 15 mm);
s2, testing the acoustic attenuation coefficient of the material by using ultrasonic waves:
the attenuation coefficient testing method is a conventional method and utilizes the reduction of the amplitude of the two bottom echo waves and the logarithmic expression of the ratio of the thickness of the sample;
s3, simulating the thickness design of the test block:
and calculating the thickness corresponding to the thickness of the simulation test block when the attenuation reaches 20dB by using the attenuation coefficient.
S4, preparing a simulation test block:
(1) drawing a three-dimensional graph of the simulation test block, wherein as shown in the figure, the cuboid test block is provided with transverse through holes with the diameter d0 at different depth positions (the thickness of a single printing layer in printing parameters is d 0); the central spacing height of the cross holes is also d 0;
(2) printing a simulation test block by using the same printing process parameters;
(3) and (4) polishing two sides of the simulation test block to expose the transverse hole, and extruding and polishing the powder in the transverse hole to be smooth by utilizing machining.
S5, transverse hole echo testing:
testing the transverse holes with different depths by using the detection parameters (frequency and energy …) which are the same as the ultrasonic online detection, and obtaining the maximum echo amplitude of each transverse hole to form a one-dimensional array A (a1, a2.. an); the cross-hole depth values form a one-dimensional array D (D1, D2.. dn);
s6, linear fitting of data A and D:
carrying out logarithmic linear fitting on the depth value array D and the amplitude value array A to obtain an intercept β 0, a slope β 1 and a standard deviation of a fitting straight line;
s7, calculating the detection rate
And calculating a relation curve between the defect depth and the defect detection probability by using a cumulative normal distribution model. POD is the defect detection rate, d is the defect depth variable, adTaking the amplitude height of the background noise as a detection threshold value for the detection threshold value;
and S8, determining the defect depth corresponding to the detection rate of 90 percent as the limit depth of detection.
As shown in fig. 2, 0.4mm is the limit depth of inspection for a stainless material for a certain printing process.
Example two
S1, preparing a sample for testing the attenuation coefficient of a material:
printing a square sample of the same material according to the same printing process parameters during the online detection, wherein the thickness of the sample is 5mm (or other thicknesses of 10mm and 15 mm);
s2, testing the acoustic attenuation coefficient of the material by using ultrasonic waves:
the attenuation coefficient testing method is a conventional method and utilizes the reduction of the amplitude of the two bottom echo waves and the logarithmic expression of the ratio of the thickness of the sample;
s3, simulating the thickness design of the test block:
and calculating the thickness corresponding to the thickness of the simulation test block when the attenuation reaches 20dB by using the attenuation coefficient.
S4, preparing a simulation test block:
(1) drawing a three-dimensional graph of the simulation test block, wherein as shown in the figure, the cuboid test block is provided with transverse through holes with the diameter d0 at different depth positions (the thickness of a single printing layer in printing parameters is d 0); the central spacing height of the cross holes is also d 0;
(2) printing a simulation test block by using the same printing process parameters;
(3) and (4) polishing two sides of the simulation test block to expose the transverse hole, and extruding and polishing the powder in the transverse hole to be smooth by utilizing machining.
S5, transverse hole echo testing:
testing the transverse holes with different depths by using the detection parameters (frequency and energy …) which are the same as the ultrasonic online detection, and obtaining the maximum echo amplitude of each transverse hole to form a one-dimensional array A (a1, a2.. an); the cross-hole depth values form a one-dimensional array D (D1, D2.. dn);
s6, linear fitting of data A and D:
carrying out logarithmic linear fitting on the depth value array D and the amplitude value array A to obtain an intercept β 0, a slope β 1 and a standard deviation of a fitting straight line;
s7, calculating the detection rate
Calculating defect depth and defect by using cumulative normal distribution modelAnd detecting a relation curve between the probabilities. POD is the defect detection rate, d is the defect depth variable, adTaking the amplitude height of the background noise as a detection threshold value for the detection threshold value;
and S8, determining the defect depth corresponding to the detection rate of 90 percent as the limit depth of detection.
As shown in fig. 3, 0.55mm is the limiting depth for fine grain stainless steel for certain printing processes.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (5)
1. A PBF additive manufacturing high-frequency ultrasonic online detection single detection layer number determining method is characterized by comprising the following steps,
s1, preparing a sample: printing out samples of the same material according to the same printing process parameters when the online detection is carried out;
s2, testing the attenuation coefficient of the sample: logarithmically representing the reduction of the amplitude of the two bottom echo waves and the ratio of the thickness of the sample;
s3, determining the thickness of the simulation test block: calculating the thickness corresponding to the thickness of the simulation test block when the attenuation reaches m dB by using the attenuation coefficient;
s4, preparing a simulation test block:
(1) drawing a three-dimensional graph of the simulation test block, arranging transverse through holes with the diameter d0 at different depth positions, wherein the thickness of a single layer printed in printing parameters is d0, and the central interval height of the transverse holes is also d 0;
(2) printing a simulation test block by using the same printing process parameters as the test sample;
(3) polishing two sides of the simulation test block to expose the transverse hole, and extruding and polishing powder in the transverse hole to be flat by utilizing machining;
s5, transverse hole echo testing: testing the transverse holes with different depths by using the same detection parameters when testing the attenuation coefficient of the sample to obtain the maximum echo amplitude of each transverse hole to form a one-dimensional array A (a1, a2.. an); the depth values of the transverse holes form a one-dimensional array D (D1, D2.. dn), and n is a positive integer;
s6, data linear fitting A and D, namely carrying out logarithmic linear fitting on the depth value array D and the amplitude value array A to obtain the intercept β 0, the slope β 1 and the standard deviation sigma of a fitting straight lineδ，
ln(A)＝β0+β1ln(D)+σδ；
S7, detection rate calculation: calculating a relation curve between the defect depth and the defect detection probability by using an accumulative normal distribution model, wherein POD is the defect detection rate, d is the defect depth variable, adTo detect the threshold, the amplitude height of the background noise is taken as the detection threshold,
and S8, obtaining corresponding defect depth according to the value requirement of the detectable rate, wherein the defect depth is the limit depth of detection, and the limit depth is divided by the layer depth of single printing to obtain the number of detection layers.
2. The PBF additive manufacturing high-frequency ultrasonic online detection single detection layer number determining method according to claim 1, characterized in that: the value range of the attenuation is as follows: 0< m < 20.
3. The PBF additive manufacturing high-frequency ultrasonic online detection single detection layer number determining method according to claim 1, characterized in that: the sample is a cuboid.
4. The PBF additive manufacturing high-frequency ultrasonic online detection single detection layer number determining method according to claim 1, characterized in that: the interval width of two adjacent transverse holes is the same.
5. The PBF additive manufacturing high-frequency ultrasonic online detection single detection layer number determining method according to claim 1, characterized in that: the detection parameters include frequency and energy.
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