The capability and options for collaborative welding robots have rapidly expanded over the last three years, making these safe and easy-to-use machines highly suitable for adding robotic welding capacity to current production. From supplementing manual welding to addressing high-mix, low-volume demands, welding cobots are helping new and relevant applications come to life. What is it, however, that is making cobots more mainstream in welding environments today?
At its genesis, the only option for a welding cobot was a very basic collaborative arm with a semiautomatic torch attached to it. Today’s offerings provide quite the dichotomy – full functioning collaborative robots with industrial pedigrees, tackling tough tasks and offering a wealth of growing benefits.
Offering pinchless designs with smooth surfaces, cobots can work safely with or in close placement to humans. Built-in safety-rated power and force limiting (PFL) sensors are
the key in most cobot models that allow the monitoring of external force, stopping a robot’s motion as needed to protect workers from potentially harmful contact situations.
The use of PFL sensors reduces and may eliminate the requirements for external barriers, light curtains and other cell safety hardware, saving valuable floorspace and reducing costs. Keep in mind, however, that a welder working with a cobot should still consider all risk mitigation requirements for the welding application being performed.
Another feature making newer cobots reliable and safe for welding applications is their IP67 protection rating to guard against weld spatter or chemicals. No extra protection or “jackets” are required as with older cobots, and the easy-to-clean surface is ideal in harsh environments.
A variety of cobots now have the potential to run at higher speeds compared to traditional cobots. With the use of an area scanner that monitors human presence in the work area or light curtains, cobots can run as fast as weld quality permits, accelerating throughput.
Almost all cobots today have lead-to-teach features that make them easy to use. Software in select cobots as well as some teach pendants can also make programming more intuitive, eliminating the need for conventional Cartesian coordinates (X, Y, Z) that can confuse and frustrate new robot users. Similarly, software is now available that enables robot programmers to set all the weld parameters and their special process features directly from the teach pendant. With some cobot brands, phones and tablets can be used.
Either way, with lead-to-teach or similar control methods, a worker can be trained to program points in very little time, especially if prior knowledge on weld parameters and torch angles exists. The potential to have a cobot up and running in under an hour (as little as 15 min. for a simple part) is there, saving time and money along the way.
Robust welding cobots now offer a trifecta of programming options. Aside from traditional programming from a teach pendant and the lead-to-teach option, I/O jogging may also be available. Made possible from a momentary command device wired to the controller, this joystick-like method is a quick and intuitive way to change things like torch angle and tooling coordinates.
A small number of lighter weight cobots are easily placed on a cart and moved around in a factory setting. This allows them to be placed beside existing weld tables to supplement manual labor or wheeled up to large, heavy workpieces – as some parts are too big to reasonably fit in a workcell without a huge investment. Keep in mind, however, that simple parts, plates, tubes and so on measuring less than 1 m long or wide are ideal. Adding to the portability of welding cobots is the invention of portable fume extraction systems that can also be maneuvered with great ease across shop floors.
With the reduced requirements for safety devices, a cobot with a welder on a cart is generally priced under $100,000 where most industrial robotic workcells exceed that threshold.
Adding capability and reliability to robotic welding processes, a growing number of options are enhancing weld quality and product throughput. With traditional welding cobots – as well as with today’s simple collaborative welding systems – only one type of basic, lower feature semi-automatic welder can be used. However, for not much more investment, a full automation quality welder with higher functionality for a wider range of materials and part thicknesses can be acquired. This includes advanced waveform processes that are designed to work with robots and specific material types, such as aluminum or stainless steel. Also, these processes can be controlled from the cobot’s teach pendant for a simple, single point of control.
Pendant applications like Yaskawa’s Universal Weldcom Interface (UWI) are enabling full utilization of the advanced capabilities on any brand of digital welding power supply (including a basic semi-automatic welder) for arc welding applications. Easy control of any welding process or parameter such as voltage, amperage and wire feed speed can be gained via a common user interface. Weld modes based on process type, wire size, wire type and gas type can also be filtered from hundreds of combinations to a manageable few.
With UWI, terminology matches a user’s preferred power source and standard ARCON commands are used, eliminating the need for complicated macro jobs. The option to save up to 16 unique processes from the power source library to the interface library for easy access is available as is the ability to access up to 1,000 custom arc files with specific processes and parameters for use in motion programming.
Furthermore, up to six weld parameters in a weld sequence such as pre-flow, start, main, crater and finish condition can easily be set. Standard functions such as arc-retry, arc monitor data enable, re-start and weld line shift can be conveniently utilized, as well. Newer dual pulse functionality also allows cobot users to alternate between two MIG welding processes and parameters for aesthetically pleasing TIG-like cosmetics.
The right path
Crucial to some parts where a weld joint could slightly vary from part to part, a thru-arc seam tracker that utilizes a current sensor in the welding power supply is now available for many welding cobots. Intuitive options like ComArc LV (low voltage) are compatible with any brand of welder and help compensate for workpieces or workholding fixture inaccuracies, providing the utmost in weld quality and productivity.
Using these types of simple and reliable methods goes far to measure the arc characteristics of a weave pattern, determining variations between the cobot’s taught path and desired path. T- and V-groove butt joints in mild steel with up to 500 amperes of welding current can typically be tracked.
ComArc LV can be enhanced and used in conjunction with several optional software functions, including pause weaving and multi-layer welding. For example, with multi-layer
welding, once the root pass is established, the robot will adjust the torch angle and make preprogrammed offsets for multiple weld passes.
Seam tracking can also be combined with a high-speed laser-based seam finder for arc welding cobots. Options like the AccuFast non-contact point laser offer impressive sensor capabilities for increased performance, providing more reliable and repeatable feedback to the robot controller regarding part position. Readings on a variety of materials and angles of measurement (that were not formerly possible) are achievable, as well. This method requires a torch-mounted sensor, is fairly easy to teach and can detect lap joints down to 1/16 in. thick. It is not recommended for square butt joints or highly reflective surfaces.
Well-suited for collaborative welding – as touch-sensing is ideal for finding the orientation of parts with simple joints and geometries – this popular option is appealing to job shops or situations where part tolerances or tooling allow for some variance from part to part. Sometimes referred to as “wire touching,” touch sense packages use low-voltage circuit during a low-speed search to detect the weld joint.
No hardware is mounted on the cobot; however, a wire cutter and wire brake for steady and accurate sensing are needed. This method is not suggested for lap welds with less than 3/16-in. material thickness or with square butt joints.
Other options that have recently come to the forefront for welding cobots are cable management devices that protect the torch cable. Either an on-arm device or a cable balancer for overhead cable management is suggested. The latter helps to expand the cobot work area. Moreover, the possibilities of further advanced laser sensors, servo torches and weld systems are endless as long as the application calls for it in a collaborative system.
Seen as a stepping stone to traditional welding for high-volume, low-mix production runs, the use of welding cobots makes the adoption of standard welding automation with industrial robots a little smoother. Mastering the use of a particular welding cobot brand will most likely make it easier to “graduate” into using standard robots by the same manufacturer as there is a common welding “ecosystem” (i.e., pendant layout) that is well understood.
While all robot OEMs are not poised to help manufacturers in this way, select brands, including Yaskawa, facilitate this transition into full automation for faster cycle times and return on investment.
Manufacturers looking for a robot option with a longer life span (15 years or more) should consider industrial cobots for welding applications. The growth in diverse support services like 24/7 technical support, regionally located field service technicians, 24/7 emergency parts availability, IACET-accredited training, modernization options, and preventative and predictive maintenance programs are all helping to extend the life of collaborative and industrial robots alike.
Fabricators wanting to gain flexibility and optimize operations would be wise to consider safe and easy-to-use cobots for their welding workspaces. The significant improvements made to many cobots and their peripheral technologies over the last few years can effectively address many high-mix, low-volume welding concerns as well as other tasks such as palletizing and machine tending.
As always, a clear understanding of any application will help determine the ideal robot type, and a thorough risk assessment with adherence to ISO standards will guide the proper selection of peripheral tools for optimal and safe use.