Keep Your Robots on Track in Demanding Welding Environments
Adding a linear axis to your welding robot will increase its reach and work envelope, but how can you ensure smooth linear motion along tracks in the debris-filled world of welding and metalworking? New track technology can help. The post Keep Your Robots on Track in Demanding Welding Environments appeared first on Fabricating & Metalworking.
There are many reasons to add a linear axis to articulated industrial welding robots. You may want the robot to weld long parts and are looking for a way to bring the robot to the work area, enabling it to perform continuous welding operations and eliminating the downtime associated with repositioning.
You may want your robot to weld extremely large parts and, rather than moving the part around, you would like to smoothly guide the robot to the weld area. Perhaps your metalworking shop needs to maximize floorspace and, rather than deploying multiple robots at each welding station, you’d like to find a way to get your welding robot from one station to another. Or perhaps you simply want to optimize welding performance and throughput and gain a competitive advantage.
The specific reason for adding a 7th axis to your welding robot will vary, but the two primary goals remain the same: to increase your automation’s reach and to expand its work envelope.
For both things to happen, your robot will need to be mounted on a track that smoothly guides it to its destination.
So far so good. However, metal working and fabrication shops can be harsh production environments. Tracks will be exposed to welding spatter, metal dust, base metal fragments dislodged during the preparation or welding processes, and carbonized debris created by paints, primers, or protective coatings burning off during welding operations.
These contaminants can cause the track’s roller bearings to stop rotating, bringing your welding robot’s journey to a sudden halt, with all the hassle and cost unexpected robot downtime creates.
Two Types of Track
There are two primary types of linear axis track technology: profile guides and cam followers. The crucial design difference between the two is the antifriction bearing system used to support and guide the tracks.
As we compare the features and functionality of the two types, keep in mind that the track technology your welding robot runs on will have a massive impact on your maintenance costs, the overall efficiency and adaptability of your system, and how well it handles fab shop contaminants.
Profile guides (sometimes called ‘linear bearings’) usually consist of two rows of small, cylindrical bearings. Each row rides on an opposing and angled surface of a hardened, ground steel guide rail. This provides your robot with both vertical (load) support and lateral guidance. Profile guides have been around for a while and they provide accurate, stable and smooth linear guidance but even with scrapers (devices designed to physically remove debris) the bearings are still prone to contamination.
The newer cam follower (sometimes called ‘track follower’) technology consists of a cylindrical roller bearing mounted at the end of a stud. The cam follower rides on a guide rail and employs a simple block configuration. This modular design enables several cam followers to be arranged on the top and side(s) of a rail to provide support for the robot in all directions. Meanwhile, a wiper/scraper combination on the block scrapes the rail clean of debris, including metal dust and weld spatter.
Crucially, in a cam follower system, the bearings are completely enclosed within the block ensuring that contamination has no way in — a feature that makes cam followers the technology of choice in challenging metalworking environments.
Cam follower’s cylindrical rolling elements tend to be larger than those found in profile guides. Additionally, whereas the bearings of a profile guide directly contact the guide rail, the cam follower has an outer ring that provides a more robust point of contact between bearing and rail.
Finding the Right Angle
The contact angle of the antifriction bearing and the guide rail is also important. For profile guide-based tracks it is essential that any replacement components — either the guide itself or the guide rail — have precisely matched angles.
Cam followers, in contrast, are deployed on simple rectangular guide rails, so this is not an issue. Moreover, the roller and rail can be replaced independently with no performance issues. And, if required, some cam follower systems can incorporate profiled, slightly curved contact surfaces that provide added performance and lifecycle advantages.
Handling the Load
The cam follower’s all-metal construction and larger contact surfaces makes them better suited to supporting larger, heavier robots than profile guides.
Cam followers also allow you to set a preload torque. Higher preload torques ensure greater stiffness and precision, while excessive preload adds stress that increases wear and tear on components. You can easily adjust a cam follower to achieve the optimum balance between precision and the overall lifespan of the system.
Where, Precisely?
Every application brings its own precision requirements for robots and tracks. Cam followers and profile guides offer a range of precision options, with a motion accuracy of +/- 0.5 mm easily achievable.
A Place of Shelter
Both cam followers and profile guides incorporate design elements like shields, seals, scrapers, wipers, and covers to protect internal rolling elements from the contamination caused by the storms of debris and microparticles found in many production environments.
And, when it comes to larger debris such as metal fragments, profile guides and cam followers are equally effective.
But in welding applications where fine-particle contaminants are present, profile guides are much less effective. Metal dust and small particles will find their way into the bearing, consuming lubricant, and accelerating wear on contact surfaces.
With fully enclosed bearings and larger rolling elements, cam followers are more resilient in harsh metalworking environments. Size matters: thanks to their larger internal cylindrical rollers and large outer race, cam followers can simply roll over that debris.
It’s a different story when debris enters a profile guide. The rolling element will typically stop rotating and slide along the guide rail, accelerating rail and bearing wear as it does so. In a worst-case scenario, rolling elements can dislodge from the support block with potentially catastrophic results.
Streamlining Maintenance
Accessing the roller bearings on a profile guide system is not a quick and easy procedure. Typically, the entire carriage, robot, or payload has to be moved away from the track. This is a time-consuming process that often requires a crane and can take an entire production shift to complete. Your robot will be out of action throughout. And, if you’re replacing a profile guide bearing, after pulling the robot and carriage off the track, you will have to re-teach all the robot points and paths.
In comparison, servicing the newer cam follower systems is a cinch. All you need to do is slide out the cartridge containing the bearings on the side of the rail. It typically takes about 10 minutes to remove, replace and adjust the cam follower; the welding robot will quickly return to action and the production manager will thank you for keeping the facilities’ robots on the right track.
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