Method for automated testing of a material joint

Abstract

In a method for automated, contactless and non-destructive testing of a material joint ( 4 ), a dynamic threshold value is varied between a minimum threshold value and a maximum threshold value, with regions of a heat flow dynamics through the material joint ( 4 ) being determined which represent values of the heat flow dynamics exceeding the dynamic threshold value. The regions of the heat flow dynamics are examined with respect to an abrupt change in perimeter. An Abrupt change in perimeter occurs if a boundary ( 7 ) between a molten zone ( 5 ) and a non-molten but still adhering zone ( 6 ) of the material joint ( 4 ) is being crossed.

1 . A method for automated, contactless and non-destructive testing of a material joint of at least two mating parts, wherein the material joint being a two-section joint which consists of a molten zone and a non-molten zone surrounding said molten zone; comprising:
 obtaining infrared images by using at least one excitation source to excite a test sample and at least one infrared sensor to detect a developing heat flow in a sequence of thermal images, such that result images are obtained from the sequence of thermal images;   examining the thermal images and the result images to detect the molten zone from a result image, which illustrates a heat flow dynamics (W) through the material joint, in such a way that a minimum threshold value (W min ) is determined which exceeds a heat flow dynamics (W) of an image background (H); a maximum threshold value (W max ) is determined which corresponds to a peak value of the heat flow dynamics (W) through the material joint; a dynamic threshold value (W dyn ) is varied between the minimum threshold value (W min ) and the maximum threshold value (W max ); a sequence of regions (B) of the heat flow dynamics (W) through the material joint ( 4 ) is determined which represent the values of the heat flow dynamics (W) exceeding the dynamic threshold value (W dyn ); the regions (B) of the heat flow dynamics (W) are examined with respect to an abrupt change in perimeter (ΔU); the molten zone ( 5 ) is determined as a region (B i ) from the regions (B), the abrupt change in perimeter (ΔU) indicating that a boundary ( 7 ) between the molten zone ( 5 ) and the non-molten zone ( 6 ) is being crossed; and a position and a size of the molten zone ( 5 ) are evaluated.   
     
     
         2 . A method according to  claim 1 , wherein the minimum threshold value (W min ) is determined from a reference region (R) of the heat flow dynamics (W) of the image background (H). 
     
     
         3 . A method according to  claim 1 , wherein the maximum threshold value (W max ) is determined from a test region (T),
 with the test region (T) being located in the center of a region (S) which represents the values of the heat flow dynamics (W) that exceed the minimum threshold value (W min ); and   with the maximum threshold value (W max ) being an average value of the values of the heat flow dynamics (W) from the test region (T).   
     
     
         4 . A method according to  claim 1 , wherein the maximum threshold value (W max ) is determined from several test regions (T) of the same size, with
 the test regions (T) being located in a region (S) which represents the values of the heat flow dynamics (W) exceeding the minimum threshold value (W min ),   with an average value of the values of the heat flow dynamics (W) being determined for each test region (T) from the test region (T), and   the maximum threshold value (W max ) being a maximum value of the average values.   
     
     
         5 . A method according to  claim 1 , wherein the dynamic threshold value (W dyn ) is varied with an increment size (ΔW dyn ), the increment size (ΔW dyn ) being determined iteratively. 
     
     
         6 . A method according to  claim 1 , wherein the material joint ( 4 ) is a weld point, with the molten zone ( 5 ) being referred to as weld nugget and the non-molten zone ( 6 ) being referred to as weld glue. 
     
     
         7 . A method according to  claim 6 , wherein the weld point is evaluated by means of a material characteristic curve (K), with
 the characteristic curve (K) being determined by means of reference weld points which have different remaining material thicknesses (M) and interconnect at least two mating parts ( 2 ,  3 );   the remaining material thickness (M) being measured for each reference weld point;   a peak value of a heat flow dynamics (W) being measured for each reference weld point; and   the characteristic curve (K) being generated from the peak values of the heat flow dynamics (W) and the associated remaining material thicknesses (M).   
     
     
         8 . A method according to  claim 7 , wherein the maximum threshold value (W max ) is compared with a first limiting value (G 1 ), with the presence of a hole in the weld point being indicated if said maximum threshold value (W max ) exceeds said limiting value (G 1 ). 
     
     
         9 . A method according to  claim 7 , wherein the maximum threshold value (W max ) is compared with a second limiting value (G 2 ), with the presence of a cavity in the weld point being indicated if said maximum threshold value (W max ) is less than the second limiting value (G 2 ). 
     
     
         10 . A method according to  claim 6 , wherein surface damages of the weld point are detected by means of another image, with
 the image being provided with a coordinate system which is identical to that of the result image by means of which the weld nugget was detected; and   the detection and evaluation of surface damages taking place in the detected region (B i ) of the weld nugget.