Whether it be a Top Fuel dragster or your physical body, to keep any system with a level of complexity running at peak performance requires routine maintenance. The same holds true for a robotic arc welding cell. In order to achieve the maximum uptime, life expectancy and return on investment, some maintenance is required that, when done properly and regularly, aids in achieving these results.
Without oversimplifying things, let’s separate the major components of a robotic arc welding system into two categories: the robot and controller and the actual welding process equipment.
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Starting with the robot and controller, what are some of the items that could be found on a typical daily inspection checklist? Before starting up the welding cell for the day or upcoming shift, start with a visual once-over to inspect the overall health of the system.
Look for signs of liquids on the floor or equipment, which could indicate a loose or broken fitting or damaged hoses or hard tubing. Any exposed hoses are going to be subjected to strong UV light from the welding process, which typically breaks down the materials in most flexible hoses over time. The same holds true for the protective coatings of electrical wires. They, too, break down and crack with exposure to UV light over time. Hoses and wires could also be subjected to high heat and weld spatter.
Fortunately, inexpensive solutions, such as fabric covers, are available that can be used to extend the life of flexible hoses and not restrict their movement. These solutions should be considered on hoses routed through and on the robot and also to any end-of-arm tooling or fixed tooling stations.
The buildup of spatter over time can degrade or destroy air and hydraulic clamps. There is also the risk of spatter or slag, if plasma cutting, burning a hole through the tubing in the clamps causing a possible fire hazard. Extra consideration is needed when the hydraulic tooling is under higher pressures. Even the smallest pin hole under pressure can cause a lot of damage to the surrounding area if ignited. Along those lines, there have been great improvements in hydraulic fluid that is more fire resistant than standard fluid and should be considered for such an application.
As you continue safely into the welding cell, visually inspect the hardware on the robot and the surrounding tooling for signs of loose or missing bolts. Visually identify and verify that any applicable safety covers are in place. If the robot has gearboxes that utilize oil instead of grease, they may have a sight glass that can be used for a quick inspection of fluid level and color.
Things to look for are low fluid level, which indicates a leak, and darker color, which indicates high heat or contamination. Most robots and fluids are designed for a maximum temperature of 45 degrees C. At higher temperatures, the grease will degrade faster, changing color.
Next, if possible, listen for air leaks. These, too, could be an indicator of an air line with a burn hole or a fitting that has worked its way loose. And, if possible, listen to the equipment while running in production. If you hear grinding noises or feel awkward vibrations, it could be an indication of a potential mechanical problem.
The final item to include on your daily inspection is the robot master position and corresponding user tool values to validate everything is located properly and accurately before starting production. Tools are available that can perform these functions automatically on a set interval, for example, after every part.
Interval inspection
The next items should be inspected on some interval that is usually dictated by the amount of time the equipment is running or a period of time. These would include, but are not limited to, the following items. Check the grease of robot and positioner gearboxes. Again, look at the level and color of the grease and similarly, if the color is dark it suggests high heat or contamination may be present.
If the robot uses batteries to back up the robot position or programs, replace them on a regular basis, usually yearly.
Inside the robot control cabinet, make sure all the fans and fan ducts are clean of debris. Also, verify the inside of the control cabinet is clean. If it’s not, you may be missing some covers on cable entries or a door seal may be damaged.
If the robot is located close to cutting and grinding operations, you especially want to make sure that airborne contaminants don’t get inside the controller and onto exposed circuit boards. The dust and oil can lead to a short, or worse, a fire.
Lastly, with regard to routine robot maintenance, make it a habit to back up the robotic software on a regular basis. With the complexity of today’s robot systems, it is especially easy to get into trouble quickly with a few bad programming techniques that could potentially shut down production for long periods of time. By restoring a previous working backup, that robot can return to production in a much shorter time frame.
Welding equipment
After inspecting the robot and controller, next focus your efforts on the welding process equipment. The frequency of these checks will also vary, but should be on your list nonetheless.
Starting with the welding leads, be sure to check the cable condition and pay special attention to the connection points. Loose connection points or cable strands that show signs of wear add resistance to the overall system and not only affect welding performance, but also cause the cables to generate more heat.
If you utilize rotary grounds, verify they are properly lubricated with conductive grease.
Also, if the factory environment has machining or grinding processes nearby, make sure the cooling system for the power supply and, possibly, the welding torch is clean and able to exchange heat efficiently. If using a water cooler for the welding process, verify the fluid levels and clarity of water or cooling fluid. If not maintained properly, the water or coolant can grow algae, which will, in turn, diminish the cooling performance of the whole system. This will shorten the life of the components.
In welding applications where a shielding gas is present, it’s good practice to occasionally check all the gas connections and fittings for leaks and validate the pressure and flow are within specified limits. Too much gas flow can be just as detrimental to the welding process as too little.
The final items for the welding equipment checklist are the consumables. These include wire guide rolls, wire delivery systems, torch liners, tips, nozzles and diffusers. The condition of these items will vary based on usage as will the frequency of when they need to be addressed. General recommendations on changing consumables can be obtained from the welding equipment supplier.
Predictive maintenance is the maintenance of the future. Great strides have been made in getting factory automation to communicate with PCs and other factory automation. With the invention of Ethernet communication, a whole new world of data has been made readily accessible. Especially now with the Internet of Things, more data is being collected than ever before.
That abundance of information has made it possible to add more intelligence to automation and collect data to be used with various algorithms and trend analysis. This allows you to monitor and, in some instances, predict when equipment needs attention. This technology is helping to reduce downtime due to unscheduled and unforeseen events.
For instance, you can now tell, based on duty cycle, when the robot’s grease or oil needs to be replaced. You can tell based on previous performance data when a particular piece of equipment is not meeting established requirements. In some cases, this information can also be pulled from welding power supplies independently or through the robot to help provide an overall status on the health of the welding cell.
Adopting a regular routine for inspecting a robotic welding cell helps ensure the end product stays at the quality level you expect and will be conducive to obtaining the longest possible life out of the equipment.
