No matter how large or small a company is, the implementation of a robotic welding workcell has the potential to provide transformative productivity gains. These results will
only happen, however, if the robotic welding system is optimized to work as efficiently as possible. This is especially true for workcells acquired to process extremely large, boxy or tubular weldments.
From implementation costs to return on investment (ROI) and everything in between, manufacturers today are looking at the big picture, weighing key factors like flexibility, cycle time, part compatibility and future part considerations before robotic workcell integration. As a result, innovative system designs are being utilized in a growing number of facilities to meet quality standards, reduce operational costs and achieve time-to-market goals.
Many manufacturers looking into robotic automation for the welding of extremely large parts wisely ask the question, “will one large long-reach robot be sufficient, or would several smaller space-efficient arms be more adequate?” The correct answer to this question depends on a series of criteria including concepts such as plant layout, part characteristics and production goals.
While there is not a “one size fits all” approach to robotically welding larger parts, the following examples may provide insight on what could potentially be done on the shop floor to enhance operations.
Multiple robots
For many manufacturers, takt time – the necessary cycle time required to meet customer demand – is a driving factor behind choosing one robotic system over another. To meet lean manufacturing initiatives, it is not uncommon for manufacturers of extremely large parts to implement multiple 6-axis arc welding robots in a single workcell. Today’s contoured robot designs allow easy access to parts, avoiding potential interference with fixtures, and the high-density robot layouts that are often needed are easily achieved.
Extra-heavy payload capacity Ferris wheel positioners are also frequently used in these workcells to facilitate quick loading and unloading of heavy parts with tooling. Similarly, these positioners provide part stability and rotation during welding, optimizing the weld quality and number of welded inches per minute. The heavy castings on either side of the positioner also offer ample space and strength to mount additional robots directly to the positioner, or they can be used to mount an overhead gantry with inverted robots to improve weld accessibility and cycle time.
Customized workcells
At times, the welding of extremely large or uniquely shaped parts requires a highly customized workcell. For Tremcar, a Canadian family-owned manufacturer of stainless steel and aluminum tank trucks and trailers for the North American market, the welding of large, round parts meant the use of an “out of the box” approach.
In this case, a single Yaskawa AR3120 arc welding robot with extended reach was installed on a servo track. This provided a wide work envelope with a small interference zone, allowing the robot to be placed close to parts. Each part was also placed on a headstock/tailstock positioner. Overall, the combination of the 6-axis robot, servo track and headstock/tailstock positioner created an 8-axis system that was controlled from one robot controller, enabling efficient part rotation while keeping all welds in the flat position for optimal weld quality.
While this system delivered the required work envelope to meet production demand, other manufacturers may find that adding a second welding robot to a workcell (sans the use of servo tracks) is more beneficial. For some, adding an extra arc may reduce cycle time as well as provide a more cost-effective solution.
Other manufacturers of extremely large parts may choose to implement a variation of the Tremcar workcell, placing the robot, positioner and servo track with an elevator. This approach is ideal for square or rectangular parts. However, to eliminate the need for the robot to weld in non-ideal positions, a second robot in the same configuration (on the other side of the part) is suggested. Putting a robot on both sides of a larger weldment can greatly improve weld accessibility, eliminating the need for a robot to reach over the part to access the weld.
Welding wisdom
What works well for one manufacturer of extremely large parts may not work for another, making it highly important for company leaders to contact an experienced robot supplier or integrator during the decision-making process. Helpful points of discussion may include:
Adding more robots to an existing workcell. For many manufacturers, modernizing a current production space or workcell by adding a single robot arm (or more) can be highly effective at optimizing floorspace and increasing productivity. For example, if a manufacturer has a single robot workcell (e.g., an ArcWorld 6000) with a cycle time of 10 min., adding a second robot may reduce the cycle time per part in half while not increasing the footprint of the workcell.
Achieving the needed amount of robot uptime. Initially, a manufacturer may think a two-robot system may be ideal for welding larger parts. However, in certain situations, adding an extra robot can create a situation where there is a lot of robot downtime for one robot, making the overall system less efficient and potentially more cost prohibitive. If the weldment is symmetrical, adding a second robot can cut the cycle time in half. However, if a higher percentage of welds are located on one end of the weldment, adding a second robot will not have that big of an impact on the cycle time.
Utilizing the required welding software. The robot must use the appropriate welding software to produce the required welds. Larger weldments typically require weld joint finding and tracking technology. In addition, multilayer software could also be required, depending on the weld size and sequencing requirements.
Determining the proper peripherals. It is important to ensure that the welding power source is sized for the proper amperage and duty cycle. Also, most larger weldments require the use of a water-cooled welding torch for optimal operation and reliability.
The right mix of high-speed robots and advanced technologies can greatly enhance welding operations for larger parts. A trusted robotic welding expert can help determine how many robots are needed as well as guide the selection of system peripherals, driving an operation down a path of success toward rapid ROI.
