The Xiris Blog

Triggering Weld Cameras from a MIG Process

Posted by Cameron Serles on Thursday, February 07, 2019 @ 11:00 AM

MIG processes, particularly short circuit MIG, will generate a huge range in brightness during their metal transfer cycle:  when the arc is extinguished as the wire makes contact with the parent material prior to expulsion, the image can be quite dark. However, after an explusion occurs and the arc is re-established, the image may be very bright as the arc intensifies to its maximum.

Using a camera to acquire images of a MIG weld process in free running mode can be problematic when the amount of light present in the image varies considerably. The variation in light is based on when during the metal transfer process the image exposure takes place: when the arc is extinguished, the image will be dark; when there is a full arc, there will be a bright image. However, if the camera acquisition is triggered by an electrical pulse generated by the camera power supply, the result will be a consistent image of the weld process that is repeatable because it is at the same point of the weld cycle.

Image4

(courtesy ESAB Group, Inc.)

A few words about how Short Circuit MIG and certain other kinds of MIG welding function:

  • Wire is fed continuously and makes contact with the workpiece to complete the electrical circuit.
  • At the point of contact, a short circuit occurs, resulting in a huge spike of current moving through the wire between the torch and the workpiece.
  • At point of wire contacting the workpiece, arc gets extinguished.
  • Segment of wire rapidly vaporizes under high current and an arc gets re-established.
  • Current falls as there is no short circuit.
  • Process repeats.

In a constant voltage welding power supply, the current being fed to the torch can rise and fall based on the metal transfer process. When there is a gap between the wire and the workpiece, the conducting current is low, and increases as the wire begins to touch the workpiece and create a short circuit. Then, once the wire tip explodes, the current falls as there is no conducting circuit. The plot of the current levels look something like this:

 Image3

(courtesy ESAB Group, Inc.)

While capturing the welding process to see certain features, it is sometimes interesting to only take images at a certain point in the metal transfer cycle. Rather than using a weld camera in free running mode where image acquisition is based on the clock cycles inside the camera, an efficient alternative is to use an external trigger that is based on the current levels present in the welding power supply.  If a circuit can be designed to generate a trigger signal based on the rising edge of the current level, then the trigger could be used to initiate image acquisition, resulting in video with an increased consistentency in brightness and quality because each frame will be acquired at precisely the same point in the metal transfer process. 

Further enhancement to the performance of the imaging process is possible by tweaking exactly when the images are acquired through adding a delay.  A delay can be added after the trigger signal is generated so that the exact imaging characteristic can be seen.

For example, imagine wanting to see only images of the metal transfer process after the weld arc is extinguished.  To do this, a trigger signal should be generated based on the current pulses coming from the weld power supply.  It may not be possible to receive the trigger at the ideal point in the metal transfer process, so a programmable delay can be added to make sure that the image acquisition occurs at exactly the right point.

With Triggering:

Image2Image1

Successive Snapshots of a MIG Welding Process Triggered from the Rising Edge of Welding Power Supply’s Current Pulse

The above two successive images show a MiG process at roughly the same point of the metal transfer process over different cycles of the metal transfer.  In this case, the imaging was tuned to see exactly what the viewer wanted to see: the melt pool fully visible with the welding arc present.

In Summary

Imaging a MIG welding process can be fairly difficult if using a weld camera in free running mode.  However, if a circuit can be designed to clamp on the rising edge of the current pulse, it can provide an excellent trigger to use to acquire consistent images at similar points in the metal transfer cycle.  The result is much more uniform images with similar brightness levels, allowing for better analysis and increased efficiency of the welding process. 

Better Images. Better Decisions. Better Process Control.

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Topics: quality control, weld camera system, reduced costs, mig welding, MIG process, consistent, HDR, image processing

Robust Weld Cameras for High Frequency Weld Applications

Posted by Catherine Cline on Wednesday, May 03, 2017 @ 09:29 AM

Electromagnetic interference (EMI) that is generated by high frequency weld equipment can often play havoc with other welding equipment, such as cameras, by creating electromagnetic induction in the circuitry of the cameras.  Often the electrical disturbances that occur create a noisy camera image, interrupt image data acquisition or generate continuous lines running through the image. In xtreme cases, it can stop the cameras from functioning altogether.

May 3 image 1.png 

The Xiris XVC-1000e Weld Camera

During extensive testing in the field, Xiris XVC weld cameras have proven themselves to be immune to the EMI that is generated by high frequency weld equipment.  EMI immunity has always been a problem identified by the industry when using cameras, so Xiris took this into consideration when designing the XVC camera family.  The camera is an all digital design, rather than the analog design common on most other weld cameras.  The result is that many problems resulting from outside interference are eliminated, allowing for excellent image stability and cable lengths of up to 100 m.  As part of that design, the camera housings have been extremely well shielded and grounded, eliminating any stray electrical noise.

The XVC weld cameras were extensively tested during the design/build process whereby extreme ranges of frequencies and power levels were used, including some of the harshest welding conditions, such as high power GMAW welding tests, with power approaching 1000A.  During those tests, the XVC weld camera cables were stretched parallel to welding power lines, wrapped around welding power lines and laid on/over/in grounded equipment, all without significant degradation of the camera image.

The camera has been tested to the EN 61326-1:2006 standard which includes the following tests:

  • Electrostatic discharge
  • Radiated RF Immunity
  • Electrical Fast Transients
  • Surge Withstand
  • Conducted RF Immunity
  • Magnetic Field Immunity
  • Voltage Dips
  • Short Interruption
  • Harmonic Current Emissions
  • Voltage Fluctuation and Flicker

The Xiris XVC weld camera is now widely used on manufacturing floors running in some of the most challenging welding environments, including alternating polarity GTAW, high powered GMAW and Plasma processes, providing clear images to operators as far as 100 m away from the weld head.

For more information on how Xiris Weld Cameras can eliminate EMI interference and enhance your weld processes visit Xiris.com 

You can visit our

 WELD VIDEO LIBRARY

for dozens of examples of the camera in action. 

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Topics: Xiris, welding, productivity tools, quality control, EMI, image processing

Using a Light Meter for Automatic Weld Monitoring

Posted by Cameron Serles on Tuesday, August 02, 2016 @ 02:30 AM

With the advent of high dynamic range weld cameras such as the Xiris XVC-1000, images of welding processes can be made with enormous ranges of brightness.  As a result, it is now possible to monitor and record good quality video of most welding processes using an HDR camera.  With good quality images of the weld pool, arc and seam, the next logical step is to incorporate image processing into the camera system to extract additional information to help operators better control the welding process.

One of the most basic tools for image processing is a LightMeter.  The LightMeter tool from Xiris provides statistical information about the pixel values in an area of interest.  It can be used as an overall measure of the intensity of a weld process, detect part or feature presence, or be the first step in performing powerful image processing on an area of interest.

Blog_Image_1.png

Figure 1 : LightMeter Window

The LightMeter generates a histogram based on the light intensities of the pixels in an area of interest, calculating a number of statistics, including:

Median – the brightness level that separates all the pixels in the area of interest into two equal halves.

Mean - the average brightness of all the pixels in the area of interest

Mode - the pixel brightness level that appears most often in the area of interest.

Minimum - the value of the darkest pixel in the area of interest.

Dark Tail – the pixel value at which a specific percentage of the total number of pixels in an area of interest are found to be darker.

Bright Tail - the pixel value at which a specific percentage of the total number of pixels in an area of interest are found to be brighter. 

Maximum – the value of the brightest pixel in the area of interest.

Standard Deviation – the amount of variation or dispersion of brightness levels of all the pixels in an area of interest.

Sum – the addition of all the pixel values in the area of interest.

These measurements can be used as building blocks by users and developers to create automatic inspection algorithms to measure welding features and parameters with the goal of performing a level of process or quality assurance.

A sample histogram with some of the key features is displayed below:

Blog_Image_2.png

Figure 2: Sample Histogram

Conclusion:

By incorporating image processing tools such as a LightMeter tool into their weld camera systems, machine builders can measure features of their weld processes in a way that has never before been possible.  It is now possible to find and measures levels of light across an entire image, or in a region of interest in an image.  This can provide information about features of the weld, such as the weld wire, melt pool or weld seam, that could allow for further monitoring or analysis, or form the foundation for seam tracking or weld pool geometry analysis.

For more information on how Xiris Weld Cameras and the LightMeter image processing tool can enhance the quaity and economy of your welding processes, visit Xiris.com

Topics: Xiris, welding, High Dynamic Range, weld camera, image processing, area of interest

How to Get the Best View of an Open Arc Weld

Posted by Cameron Serles on Thursday, July 17, 2014 @ 06:00 PM

Attaining a good image of a weld and the surrounding background has been a struggle ever since video cameras for welding became available.  The problem has always been the range of brightness that occurs during welding: the ratio between the maximum and minimum light intensity is usually too great for a standard camera to measure properly.  Standard cameras on the market today can typically measure about 1,000 levels of brightness between the maximum and minimum light levels in an image.  However, in a typical open arc welding environment, there is a brightness range that can exceed 10,000,000 levels of brightness between the brightest portion of the welding arc, and the darker areas surrounding the weld.  Using a standard camera to image such a weld will create an image similar to the image below on the left, where the camera sensor will image the scene up to a point and then saturate when it gets too bright. This causes the bright areas of the image to appear as a white blur.

 

To solve this problem, Xiris Automation has developed the XVC-O View Camera that uses advanced electronics with logarithmic sensitivity to be able to see more than 10,000,000 levels of brightness in an image.  As a result, more image detail is visible than ever seen before. The detail of the weld arc, the shielding gas, weld pool, torch tip, and weld seam can all clearly be seen.  The image below on the right is an image taken from the XVC-O camera of an open arc welding process. The weld arc is no longer saturated and is clearly visible as is the detail of the background, providing better quality information for the weld operator.

 

GOOOOOOD resized 600       Standard Camera Image of a Weld                      Xiris XVC-O Camera Image of a Weld

With the ability to see more detail of the weld arc and the surrounding environment, welding technicians are able to use the XVC-O to better control their welding processes through better quality assurance and process feedback. 

To see examples of the video quality possible with the XVC-O across a variety of welding processes and materials, please see our Weld Video Library here.

 

Topics: welding automation, weld environment, weld inspection, Machine Vision, image contrast, Laser welding, image processing, weld camera, Education, Welding Process, weld video, Xiris

Monitoring Tube and Pipe Production to Find SCARFING Defects

Posted by Cornelius Sawatzky on Tuesday, June 17, 2014 @ 12:53 PM

Recent advancements in machine vision technology have made a new type of inspection able to see defects related to the forming and welding area of a tube or pipe.  The result is improved quality assurance and process control on the production line.  The new type of inspection device is a laser-based triangulation system that measures the outside contour of a tube or pipe in the vicinity of its weld. 

Typically NDT systems are placed at the end of a production as a final check.  However, the laser inspection system can be placed directly after the weld box.  This system can let operators know what is changing in their welding process, allowing them to perform corrective action before significant scrap occurs. This capacity is especially helpful for one of the most common defects found across all types of Tube manufacturing: Tube Scarf defects.

 

The Scarfing Width

In certain situations on ERW/HF tube and pipe production lines, there is not enough space to perform the Non Destructive Inspection (NDI) measurements right after the weld box because the scarf tool (used to remove excessive bead from the tube) is placed directly after the weld box.  In such situations, the measurement process must be made after the scarfing tool, measuring the flat area of the tube where the scarf has occurred. On some production lines, this measurement is essential to identify the shape and profile of the tube, and to understand how it is travelling through its forming process.

Known as the scarf width, this measurement is defined as the length of the “flat” portion of the tube that appears after the weld bead has been removed by scarfing.  Scarf width measurement changes quickly during production, so it is best averaged over a number of inspections in order to make the measurement stable.

 June 17.14 Blog Scarfing resized 600

The Scarf Width, where “w” = the width of the defect.

How the WI2000p System Measures the Scarf Width

Xiris Automation Inc. has developed a non-destructive inspection system called the WI2000p Weld Inspection System. The WI2000p includes a laser line and a camera whose optical axis is offset to the axis of the laser line by an “offset angle”.  The WI2000p creates a visible cross-section of the tube by projecting the laser line on to the tube and capturing an image of the line using the camera.  The resulting image shows a profile of the tube surface as if it were cut in cross section.  If a tube is ideally round, the laser image will represent a section of an ellipse and any anomaly such as a freeze line defect can be mathematically detected. 

The WI2000p bases all of its measurements on the differences between the actual laser profile line seen by the camera, and the ideal mathematical profile based on the tube parameters.  By knowing the position of the actual laser profile, the ideal profile, and the size of the pixels in the image, the WI2000p can detect weld bead profile defects that often escape detection by other quality tools such as Eddy Current testing, or Ultrasonic Testing techniques

 

Conclusion

Overall, laser-based 3D imaging systems, such as the WI2000p from Xiris, offer an excellent measurement option for tube mill owners/operators who want additional, real-time monitoring of weld features. They can be used in a proactive manner, warning operators what is changing in their welding process so that they can perform corrective action before significant scrap occurs And by measuring the outside contour of a weld, laser-based 3D imaging systems can operate on any type of material, regardless of its reflectance or magnetic properties, using a single head to perform the measurement.

Topics: weld inspection, High Dynamic Range, Laser welding, Tube and Pipe welding, image processing, quality control, laser-based monitoring, weld camera, Pipe Cladding, welding defect, scarfing

Monitoring Tube and Pipe Production to Find FREEZE LINE Defects

Posted by Cornelius Sawatzky on Tuesday, June 03, 2014 @ 03:09 PM

Recent advancements in machine vision technology have made a new type of inspection able to see defects related to the forming and welding area of a tube or pipe.  The result is improved quality assurance and process control on the production line.  The new type of inspection device is a laser-based triangulation system that measures the outside contour of a tube or pipe in the vicinity of its weld. 

Typically NDT systems are placed at the end of a production as a final check.  However, the laser inspection system can be placed directly after the weld box.  This system can let operators know what is changing in their welding process, allowing them to perform corrective action before significant scrap occurs. This capacity is especially helpful for one of the most common defects found across ERW Tube manufacturing:  Freeze Line defects in the weld bead. 

 

The Freeze Line Defect

Particularly in Electric Resistance Welding (ERW) or High Frequency (HF) welding processes, incomplete heating of the faces of the parent material can sometimes occur, resulting in a potentially cold-welded joint, which manifests itself as a line or seam extending from the top surface of a weld down into the welded area, in the shape of a sharp valley. Such a defect could indicate major metallurgical or structural problems in a weld, such as cold welding or improper forming.  It can very often be a point of a major failure of a weld in high-stress applications because the freeze line acts as a crack initiator into the welded material.  The Freeze Line becomes a concern to weld operators when it goes below the surface of the parent material of the tube because once the weld bead has been removed through grinding or scarfing, there is a risk that a void of non-welded material could be left behind.

The freeze line is measured from the lowest point of any contour in the weld bead to the surface of the parent material as defined by the ideal circle scribed by the walls of material beyond the weld zone.  If the freeze line goes below a pre-defined height, then it is considered a defect.

June 3.14 Blog Freeze Line resized 600

The Freeze Line Defect, where “h” = the height of the defect.

 

How the WI2000p System Measures the Freeze Line Defect

Xiris Automation Inc. has developed a non-destructive inspection system called the WI2000p Weld Inspection System. The WI2000p  includes  a laser line and a camera whose optical axis is offset to the axis of the laser line by an “offset angle”.  The WI2000p creates a visible cross-section of the tube by projecting the laser line on to the tube and capturing an image of the line using the camera. The resulting image shows a  profile of the tube surface as if it were cut in cross section.  If a tube is ideally round, the laser image will represent a section of an ellipse and any anomaly such as a freeze line defect can be mathematically detected. 

The WI2000p bases all of its measurements on the differences between the actual laser profile line seen by the camera, and the ideal mathematical profile based on the tube parameters.  By knowing the position of the actual laser profile, the ideal profile, and the size of the pixels in the image, the WI2000p can detect weld bead profile defects that often escape detection by other quality tools such as Eddy Current testing, or Ultrasonic Testing techniques

 

Conclusion

Overall, laser-based 3D imaging systems, such as the WI2000p from Xiris, offer an excellent measurement option for tube mill owners/operators who want additional, real-time monitoring of weld features. They can be used in a proactive manner, warning operators what is changing in their welding process so that they can perform corrective action before significant scrap occurs And by measuring the outside contour of a weld, laser-based 3D imaging systems can operate on any type of material, regardless of its reflectance or magnetic properties, using a single head to perform the measurement.

Topics: weld inspection, High Dynamic Range, Laser welding, Tube and Pipe welding, image processing, quality control, laser-based monitoring, weld camera, Pipe Cladding, welding defect, freeze line

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