Method and system for real-time monitoring and controlling height of deposit by using image photographing and image processing technology in laser cladding and laser-aided direct metal manufacturing process

Abstract

The object of this invention is to provide a method and system for real-time monitoring and controlling the height of a deposit by using image photographing and image processing technology in a laser cladding and laser-aided direct metal manufacturing process. This invention also provides a method of controlling the intensity of laser power, which is one of the most important process variables, regardless of the operational condition of a laser power unit ( 401 ). The method and system of this invention controls the height of a deposit ( 205 ) by real-time monitoring the position and the height of a melt pool ( 203 ) and controlling the process variables using the image photographing and image processing technology in such a laser cladding and laser-aided direct metal manufacturing process based on a laser surface modification technology, such as laser surface alloying and laser cladding, or a laser-aided direct metal manufacturing technology.

1 - 24 . (canceled) 
   
   
       25 . A system for monitoring and controlling the height of a cladding layer in real time using image photographing and image processing in laser cladding and laser-aided direct metal manufacturing, comprising:
 a laser generator for forming a molten pool on a surface of a specimen by irradiation of a laser beam;   a beam transmitting apparatus for transmitting the laser beam generated by the laser beam generator;   a beam condensing apparatus for condensing the beam transmitted through the beam transmitting apparatus;   a cladding material feeder for feeding a cladding material to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed by the beam condensing apparatus;   a transfer system for keeping a focal distance of the laser beam constant in the process of cladding with the beam condensing apparatus positioned in a z-axis direction, and freely transferring a specimen along a tool path around the laser beam to allow the laser cladding to be performed with the specimen fixed on an x and y-axes table;   a Computer Aided Design/Computer Aided manufacturing (CAD/CAM) apparatus for generating shaping information such as the tool path on the basis of 3D CAD data and transmitting the shaping information;   an image photographing apparatus for obtaining an image of the molten pool in real time;   an image processing apparatus comprising a computer readable medium containing instructions to cause the image processing apparatus to determine a pixel representing height of the molten pool using the image of the molten pool obtained through the photographing to calculate an actual position and height of the molten pool in real time by using an actual physical height of a certain pixel and a variation value of the actual height per pixel corrected by using a standard specimen for which the height of a cladding layer is known; and   a control system comprising a computer readable medium containing instructions to cause the control system to control at least one process parameter affecting the height of the cladding layer in real time to control the height of the cladding layer to reach a target value by increasing a thickness of the cladding layer if the actual height of the molten pool is less than the target height value and by decreasing the thickness of the cladding layer whenever the actual height of the molten pool is greater than the target height value, to form a cladding layer having a shape and a thickness corresponding to 2D sectional information derived from the shaping information from the CAD/CAM apparatus, and thereby to correct overshooting of the actual height at all heights above the target height.   
   
   
       26 . The system according to  claim 25 , wherein the cladding material, which is fed to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed in the beam condensing apparatus, is provided in the form of powder, a wire or ribbon. 
   
   
       27 . The system according to  claim 26 , further comprising a powder-feeding nozzle for simultaneously supplying the cladding material powder supplied from the cladding material feeder to both the laser beam and the molten pool formed on the surface of the specimen if the cladding material is provided in the form of the powder. 
   
   
       28 . The system according to  claim 25 , wherein the laser is one of CO 2 , Nd-YAG, and high-power diode laser. 
   
   
       29 . The system according to  claim 28 , wherein an optical fiber is employed if the laser is Nd-YAG laser. 
   
   
       30 . The system according to  claim 25 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and a Charge-Coupled Device (CCD) camera. 
   
   
       31 . The system according to  claim 25 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and an infrared (IR) camera for rapidly obtaining the image of the molten pool. 
   
   
       32 . The system according to  claim 25 , wherein the image photographing apparatus is positioned on an optical axis of the laser beam to observe the molten pool at an angle of 90−θ°. 
   
   
       33 . The system according to  claim 25 , wherein the image photographing apparatus comprises plural image photographing sub-apparatuses so as to prevent the image of the molten pool from being observed to be different according to a transfer direction of a specimen or laser beam. 
   
   
       34 . The system according to  claim 25 , wherein the system is applied to restoration, remodeling and repairing of a metallic product or mold. 
   
   
       35 . The system according to  claim 25 , wherein the pixel representing the height of the molten pool is the mass center of the image of the molten pool. 
   
   
       36 . The system according to  claim 25 , wherein the pixel representing the height of the molten pool is determined by one of methods in which pixels corresponding to the longest row representing the image of the molten pool are selected as the height of the molten pool, or the center of an actual molten pool is obtained on the basis of a circular or an ellipse shape of the molten pool and pixels corresponding to the center are determined in the images. 
   
   
       37 . A system for monitoring and controlling a height of a cladding layer in real time using image photographing and image processing in laser cladding and laser-aided direct metal manufacturing, comprising:
 a laser generator for forming a molten pool on a surface of a specimen by irradiation of a laser beam;   a beam transmitting apparatus for transmitting the laser beam generated by the laser beam generator;   a beam condensing apparatus for condensing the beam transmitted through the beam transmitting apparatus;   a cladding material feeder for feeding cladding materials to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed by the beam condensing apparatus;   a transfer system for freely transferring a laser beam around a specimen fixed on an x and y-axes table to allow the laser cladding to be performed;   a Computer Aided Design/Computer Aided manufacturing (CAD/CAM) apparatus for generating shaping information such as a tool path on the basis of 3D CAD data and transmitting the shaping information;   an image photographing apparatus for obtaining an image of the molten pool in real time;   an image processing apparatus comprising a computer readable medium containing instructions to cause the image processing apparatus to determine a pixel representing height of the molten pool using the image of the molten pool obtained through the photographing to calculate an actual position and height of the molten pool in real time by using an actual physical height of a certain pixel and a variation value of the actual height per pixel corrected by using a standard specimen for which the height of a cladding layer is known; and   a control system comprising a computer readable medium containing instructions to cause the control system to control at least one process parameter affecting the height of the cladding layer in real time to control the height of the cladding layer to reach a target value by increasing a thickness of the cladding layer if the actual height of the molten pool is less than the target height value and by decreasing the thickness of the cladding layer whenever the actual height of the molten pool is greater than the target height value, to form a cladding layer having a shape and a thickness corresponding to 2D sectional information derived from the shaping information from the CAD/CAM apparatus, and thereby to correct overshooting of the actual height at all heights above the target height.   
   
   
       38 . The system according to  claim 37 , wherein the cladding material, which is fed to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed in the beam condensing apparatus, is provided in the form of powder, a wire or ribbon. 
   
   
       39 . The system according to  claim 38 , further comprising a powder-feeding nozzle for simultaneously supplying the cladding material powder supplied from the cladding material feeder to both the laser beam and the molten pool formed on the surface of the specimen if the cladding material is provided in the form of the powder. 
   
   
       40 . The system according to  claim 37 , wherein the laser is one of CO 2 , Nd-YAG, and high-power diode laser. 
   
   
       41 . The system according to  claim 40 , wherein an optical fiber is employed if the laser is Nd-YAG laser. 
   
   
       42 . The system according to  claim 37 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and a Charge-Coupled Device (CCD) camera. 
   
   
       43 . The system according to  claim 37 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and an infrared (IR) camera for rapidly obtaining the image of the molten pool. 
   
   
       44 . The system according to  claim 37 , wherein the image photographing apparatus is positioned on an optical axis of the laser beam to observe the molten pool at an angle of 90−θ°. 
   
   
       45 . The system according to  claim 37 , wherein the image photographing apparatus comprises plural image photographing sub-apparatuses so as to prevent the image of the molten pool from being observed to be different according to a transfer direction of a specimen or laser beam. 
   
   
       46 . The system according to  claim 37 , wherein the system is applied to restoration, remodeling and repairing of a metallic product or mold. 
   
   
       47 . The system according to  claim 37 , wherein the pixel representing the height of the molten pool is the mass center of the image of the molten pool. 
   
   
       48 . The system according to  claim 37 , wherein the pixel representing the height of the molten pool is determined by one of methods in which pixels corresponding to the longest row representing the image of the molten pool are selected as the height of the molten pool, or the center of an actual molten pool is obtained on the basis of a circular or an ellipse shape of the molten pool and pixels corresponding to the center are determined in the images. 
   
   
       49 . A system for monitoring and controlling the height of a cladding layer in real time using image photographing and image processing in laser cladding and laser-aided direct metal manufacturing, comprising:
 a laser generator for forming a molten pool on a surface of a specimen by irradiation of a laser beam;   a beam transmitting apparatus for transmitting the laser beam generated by the laser beam generator;   a beam condensing apparatus for condensing the beam transmitted through the beam transmitting apparatus;   a cladding material feeder for feeding cladding materials to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed by the beam condensing apparatus;   a transfer system for keeping a focal distance of the laser beam constant in the process of cladding with the beam condensing apparatus positioned in a z-axis direction, and freely transferring both a specimen and the laser beam along a tool path around the laser beam to allow the laser cladding to be performed with the specimen fixed on an x and y-axes table;   a Computer Aided Design/Computer Aided manufacturing (CAD/CAM) apparatus for generating shaping information such as the tool path on the basis of 3D CAD data and transmitting the shaping information;   an image photographing apparatus for obtaining an image of the molten pool in real time;   an image processing apparatus comprising a computer readable medium containing instructions to cause the image processing apparatus to determine a pixel representing height of the molten pool using the image of the molten pool obtained through the photographing to calculate an actual position and height of the molten pool in real time by using an actual physical height of a certain pixel and a variation value of the actual height per pixel corrected by using a standard specimen for which the height of a cladding layer is known; and   a control system comprising a computer readable medium containing instructions to cause the control system to control at least one process parameter affecting the height of the cladding layer in real time to control the height of the cladding layer to reach a target value by increasing a thickness of the cladding layer if the actual height of the molten pool is less than the target height value and by decreasing the thickness of the cladding layer whenever the actual height of the molten pool is greater than the target height value, to form a cladding layer having a shape and a thickness corresponding to 2D sectional information derived from the shaping information from the CAD/CAM apparatus, and thereby to correct overshooting of the actual height at all heights above the target height.   
   
   
       50 . The system according to  claim 49 , wherein the cladding material, which is fed to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed in the beam condensing apparatus, is provided in the form of powder, a wire or ribbon. 
   
   
       51 . The system according to  claim 50 , further comprising a powder-feeding nozzle for simultaneously supplying the cladding material powder supplied from the cladding material feeder to both the laser beam and the molten pool formed on the surface of the specimen if the cladding material is provided in the form of the powder. 
   
   
       52 . The system according to  claim 49 , wherein the laser is one of CO 2 , Nd-YAG, and high-power diode laser. 
   
   
       53 . The system according to  claim 52 , wherein an optical fiber is employed if the laser is Nd-YAG laser. 
   
   
       54 . The system according to  claim 49 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and a Charge-Coupled Device (CCD) camera. 
   
   
       55 . The system according to  claim 49 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and an infrared (IR) camera for rapidly obtaining the image of the molten pool. 
   
   
       56 . The system according to  claim 49 , wherein the image photographing apparatus is positioned on an optical axis of the laser beam to observe the molten pool at an angle of 90−θ°. 
   
   
       57 . The system according to  claim 49 , wherein the image photographing apparatus comprises plural image photographing sub-apparatuses so as to prevent the image of the molten pool from being observed to be different according to a transfer direction of a specimen or laser beam. 
   
   
       58 . The system according to  claim 49 , wherein the system is applied to restoration, remodeling and repairing of a metallic product or mold. 
   
   
       59 . The system according to  claim 49 , wherein the pixel representing the height of the molten pool is the mass center of the image of the molten pool. 
   
   
       60 . The system according to  claim 49 , wherein the pixel representing the height of the molten pool is determined by one of methods in which pixels corresponding to the longest row representing the image of the molten pool are selected as the height of the molten pool, or the center of an actual molten pool is obtained on the basis of a circular or an ellipse shape of the molten pool and pixels corresponding to the center are determined in the images. 
   
   
       61 . A system for monitoring and controlling the height of a cladding layer in real time using image photographing and image processing in laser cladding and laser-aided direct metal manufacturing, comprising:
 a laser generator for forming a molten pool on a surface of a specimen by irradiation of a laser beam;   a beam transmitting apparatus for transmitting the laser beam generated by the laser beam generator;   a beam condensing apparatus for condensing the beam transmitted through the beam transmitting apparatus;   a cladding material feeder for feeding a cladding material to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed by the beam condensing apparatus;   a transfer system using a three or more-axis transfer system or robot to increase a degree of freedom for performing laser cladding;   a Computer Aided Design/Computer Aided manufacturing (CAD/CAM) apparatus for generating shaping information such as the tool path on the basis of 3D CAD data and transmitting the shaping information;   an image photographing apparatus for obtaining an image of the molten pool in real time;   an image processing apparatus comprising a computer readable medium containing instructions to cause the image processing apparatus to determine a pixel representing height of the molten pool using the image of the molten pool obtained through the photographing to calculate an actual position and height of the molten pool in real time by using an actual physical height of a certain pixel and a variation value of the actual height per pixel corrected by using a standard specimen for which the height of a cladding layer is known; and   a control system comprising a computer readable medium containing instructions to cause the control system to control at least one process parameter affecting the height of the cladding layer in real time to control the height of the cladding layer to reach a target value by increasing a thickness of the cladding layer if the actual height of the molten pool is less than the target height value and by decreasing the thickness of the cladding layer whenever the actual height of the molten pool is greater than the target height value, to form a cladding layer having a shape and a thickness corresponding to 2D sectional information derived from the shaping information from the CAD/CAM apparatus, and thereby to correct overshooting of the actual height at all heights above the target height.   
   
   
       62 . The system according to  claim 61 , wherein the cladding material, which is fed to the molten pool formed on the surface of the specimen by the irradiation of the laser beam condensed in the beam condensing apparatus, is provided in the form of powder, a wire or ribbon. 
   
   
       63 . The system according to  claim 62 , further comprising a powder-feeding nozzle for simultaneously supplying the cladding material powder supplied from the cladding material feeder to both the laser beam and the molten pool formed on the surface of the specimen if the cladding material is provided in the form of the powder. 
   
   
       64 . The system according to  claim 61 , wherein the laser is one of CO 2 , Nd-YAG, and high-power diode laser. 
   
   
       65 . The system according to  claim 64 , wherein an optical fiber is employed if the laser is Nd-YAG laser. 
   
   
       66 . The system according to  claim 61 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and a Charge-Coupled Device (CCD) camera. 
   
   
       67 . The system according to  claim 61 , wherein the image photographing apparatus includes a Neutral Density (ND) filter, a filter mounting fixture, a lens, and an infrared (IR) camera for rapidly obtaining the image of the molten pool. 
   
   
       68 . The system according to  claim 61 , wherein the image photographing apparatus is positioned on an optical axis of the laser beam to observe the molten pool at an angle of 90−θ°. 
   
   
       69 . The system according to  claim 61 , wherein the image photographing apparatus comprises plural image photographing sub-apparatuses so as to prevent the image of the molten pool from being observed to be different according to a transfer direction of a specimen or laser beam. 
   
   
       70 . The system according to  claim 61 , wherein the system is applied to restoration, remodeling and repairing of a metallic product or mold. 
   
   
       71 . The system according to  claim 61 , wherein the pixel representing the height of the molten pool is the mass center of the image of the molten pool. 
   
   
       72 . The system according to  claim 61 , wherein the pixel representing the height of the molten pool is determined by one of methods in which pixels corresponding to the longest row representing the image of the molten pool are selected as the height of the molten pool, or the center of an actual molten pool is obtained on the basis of a circular or an ellipse shape of the molten pool and pixels corresponding to the center are determined in the images.