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.

Short Circuiting Arc Metal Transfer

(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:

 Current vs Time

(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:

MIG Welding Process Triggered from Rising Edge of Power Supply's Current PulseMIG Welding Process

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, image processing, HDR, mig welding, reduced costs, weld camera system, consistent, MIG process

Weld Safety: Before and After

Posted by Margaret Montgomery on Friday, May 18, 2018 @ 01:37 PM

According to the Bureau of Labor Statistics, welders and cutters "have one of the highest rates of injuries of all occupations." [1] 

safety before+ after larger

Before installing a weld camera, welders are often perched at unsafe heights, giving them a poor view of their welding activities. 

Welders Work in Precarious Positions

Many welding activities are done at unsafe heights, while the welder attempts to monitor and control the welding process. The moving machinery around them forces them to work in small, constrained working areas- which is often dangerous and uncomfortable for the operator. In these conditions- behind a helmet and perched above the welding process- welders miss important details in the welding arc, which can lead to mistakes and inaccuracies that are costly and timely to fix. Not only are these conditions a safety risk, but they make it harder for welders to ensure that they execute a high quality weld.

Weld Cameras Give Welders an Eye Into Detail

Xiris Automation weld cameras enable workers to perform a weld without leaving the ground. Our solutions give welders a consistent image quality regardless of the angle of the weld. They can view multiple images of the weld from leading, trailing or side views of the weld process. 

 

Don't pay for accidents, prevent them using machine vision technology. 

 

If you are interested in learning more about our company and products, please contact us here.

 

[1]“Welders, Cutters, Solderers, and Brazers.” U.S. Bureau of Labor Statistics, U.S. Bureau of Labor Statistics, 13 Apr. 2018, www.bls.gov/ooh/production/welders-cutters-solderers-and-brazers.htm#tab-3.

Topics: weld camera, weld safety, arc welding, mig welding, weld camera system

Weld.com Partners with Xiris Automation

Posted by Cameron Serles on Tuesday, March 29, 2016 @ 10:42 AM

Weld.com_Partners_with_Xiris.png

 

Weld.com is a one of the welding industry’s fastest growing online resources.  Their new weekly series entitled MIG Mondays aims to educate welders on all aspects of MIG welding.  Weld.com approached Xiris Automation when they wanted to replace their existing weld camera with one of much higher quality and they were amazed by the clarity and precision of the XVC-1000.  In order to understand exactly what is happening during the welding process, professional welders are embracing High Dynamic Range camera technology to see their processes in great detail.

Visit Weld.com to see the latest episode of MIG Mondays, as Paul and Justin discuss the applications, benefits and more of the XVC-1000 series HDR cameras.

http://weld.com/

https://www.youtube.com/watch?v=o9qpqKdvH6o

Topics: weld camera, Laser welding, Education, High Dynamic Range, mig welding

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