Robotic heavy welding

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by Eric McKellar

Robotics offer advantages for weld sizes 0.25 in. and larger

Robotics in heavy welding applications are gaining ground because of the advantages they offer: technological advances, decreased capital cost, and increased ease of setup and use. It also makes sense because of the decrease in the skilled manual workforce.

Larger weldment components are more difficult to maintain a geometric shape, so specific sensory devices such as lasers or tactile sensors are often necessary to achieve consistent weld and overall product quality. This article discusses common types of sensing.

One reason robots are popular in the automotive industry is the superior geometric tolerances of the child parts and subsequent tooling to manufacture the end welded product. Robots, being very accurate
and repeatable, feast off these simple point-to-point path driven applications. This leads to increased investment in tooling and fixtures, alleviating the necessity for accessory sensors. So in these applications, particularly in general industry, sensors are commonly used.

Many ideas and technologies for the most part have existed since robotics first arrived on the scene but were expensive and complicated to implement. The price of sensor equipment has decreased greatly in recent years, whereas fixtures, in some aspects (as in material), have gone up in price.

Most people now have a “smart device” on hand at all times. This wouldn’t be the case if these devices were slow and cumbersome to use. The same can be said for robotic welding interfaces. As communications between robots and devices becomes faster and more streamlined, the technology becomes easier to use and more commonplace. Smarter robots now use smarter sensors, which enable them to react and adapt to the inconsistencies and distortions common in heavy welding applications. This essentially is what a highly trained welder does almost unconsciously. Basically, a tacit skill set. This is the advantage of ease of use.

In recent years, there has been a decrease in skilled welders. A highly skilled manual welder is superior to a robotic welder as humans have an uncanny ability to adapt to a given welding condition. Sensors can help the robot welder to adapt just as a human would, but keep in mind, the robot is still just a tool. It requires an experienced, knowledgeable programmer to manage any particular welding application. In the end, one trained welding specialist can manage many robots performing various operations.

Sensory devices on a robotic system include tactile sensing, through-the-arc seam tracking, optical tracking and arc data monitoring. In some cases, all these sensory devices could be required to achieve a high quality product.

Here are some common sensor types.

1.Tactile sensing. Also called “touch sensing,” it can involve location displacement in as many dimensions as needed to give the robot a starting point and allow it to find the part and specified weld start location. Such abilities can be achieved utilizing the weld wire, gas nozzle, probe or laser sensor to provide an offset to what was initially programmed.

2.Through-the-arc seam tracking. Once the weld start is found, the robot can use through-the-arc seam tracking to maintain a proper path if start to end of the weld joint is geometrically uncontrollable or has the potential to move or distort, since arc welding heat is applied. Through-the-arc seam tracking technologies typically involve feedback from the arc variables (current and voltage) and a weaving motion. As the taught robot target position varies, these changes allow the robot to adapt and maintain a centreline in both XY path coordinates.

3. Laser seam tracking. Seam tracking can be done with optical sensors or laser cameras through laser seam tracking systems. These systems involve an oscillating laser beam that recognizes a joint shape and generates a tracking point of reference to follow along where intended. This type of tracking system does not require the weaving motion. After the weld, optical inspection, using the same camera, is a way to visually measure aspects of the weld bead shape and proximity to ensure expected quality and capture defects in real time, allowing for development or efficient repair.

4.High dynamic video. This is another way to “see” the joint, the arc and the weld puddle. Other than the common favourite audible feedback, a trained welder can adapt a robotic device from outside the welding environment by watching a screen to alter welding parameters and position it relative to the joint. This allows an operator to avoid potentially hazardous environments such as a confined space or a harsh chemical area.

During the welding operation, arc data monitoring technologies are available to keep controllable variables at bay. This data is also valuable for historical records.

Sensory technologies are useful in heavy welding applications. Used correctly by skilled welders, they give robots the ability to weld increasingly complicated products. SMT

Eric McKellar is a robotic welding application specialist with ABB Robotics.


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