From robust arm designs to intuitive digital interfaces, ever-changing robotic hardware and software continues to enable highly efficient and accurate resistance welding. Widely used for thin sheet metal fabrications, this form of welding (also known as spot welding) remains a top joining method in the automotive industry, providing a cost-effective process that yields solid welds for long-term performance in a variety of structural parts.
One of the first applications for robotic automation, spot welding continues to positively impact automation manufacturing, especially for high robot density assembly lines. To assist these manufacturers and provide the most optimal configuration for completing welds safely, reliably and efficiently, complete automation workcells have included high-performance robots, process equipment, part positioners and integrated safeguarding.
Sometimes pre-engineered into fully integrated, space-saving systems, spot welding workcells are designed to leverage cutting-edge, servo-controlled spot guns and peripherals for improved control, weld quality and reduced cycle time.
Improved hardware
Even for an application as straightforward as spot welding, hardware has come a long way, providing key application benefits. Streamlined, heavy-payload robots can now easily accommodate the average spot gun weighing 80 kg to 200 kg. This is also due to the use of servo-controlled spot guns with DC spot timers that have drastically reduced the mass of spot guns and ancillary equipment compared to AC timers.
Transformer sizes have been reduced by using mid-frequency inverters for DC welding, and higher frequency inverter switching (1,800 Hz to 2,000 Hz) helps to reduce gun size and weight.
Leading spot gun manufacturers, like Obara, CenterLine and ARO, provide the lightest and most versatile welding equipment for nearly any material and part size. More energy efficient and precise than pneumatic guns driven with compressed air, these spot guns also help minimize electrode wear, enable consistent clamping force and eliminate squeeze time.
Axis time
Providing a wide range of motion for obstacle avoidance in tight work environments, 7-axis robots with reduced interference designs can be especially beneficial. These robots, as well as streamlined 6-axis robots, allow for high-density layouts in crowded workspaces, maximizing valuable floorspace for greater productivity. Enhancing application flexibility even further are a variety of servo positioners.
Similarly, the use of a servo spot gun with a DC-powered spot timer can act as an additional axis to the robot, facilitating greater design possibilities with better mobility and subsequent part accessibility. These guns are easy to program from the robot pendant with coordinated motion in a single job and are easily synchronized to provide improved quality at reduced cycle time.
Spot welding robots, such as SP-series robots, add an integrated harness for spot utilities, including water, air, power and servo motor signals. Integrating the “dress” for spot welding reduces the profile of the robot and gives better part access, provides a consistent profile for offline programming and increases cable life, reducing downtime.
Enabling easy programming, newer hollow-arm robots offer much improved cable routing for improved mobility, especially over external cable harnesses. This internal routing of the robot dress package reduces the significant movement a robot would need to orient the spot gun around a part, optimizing uptime and extending cable life.
As the trend for vehicle lightweighting continues, automakers are finding hollow-arm designs especially helpful in accommodating the large cables associated with aluminum spot guns. The larger cables support the spot gun current required to supply the necessary transformer power for robotic aluminum welding.
Control input
Highly beneficial to modern-day robotic welding applications are the robust software platforms and programming options available to optimize production throughput and part quality. Servo spot guns can be integrated with Advanced Robot Motion (A.R.M.) control software to maximize performance by providing easy calibration for X- or C-type spot guns, and integrated weld controllers (or timers) facilitate precise control of weld parameters for extremely reliable welds.
With multiple brands of spot timers available for purchase, manufacturers may want to consider those that offer digital interfaces with feature-rich functionality for optimized programming. This simplifies connections with single-wire Ethernet cables. Options such as Nadex and WTC are easily integrated to allow direct parameter programming from the robot teach pendant. Select timers offer the ability to program and monitor information with up to 255 weld programs supported (for each timer). Likewise, up to four timers can be networked with a multiple robot controller.
Servo motors allow precise motion control by using encoders to monitor the shaft position. These motors can also be controlled to apply a specified torque consistently, making them a good fit for spot guns. The robot control takes advantage of both motor control methods. Key functions often include:
- Tip wear compensation – the encoder can be used to measure tip wear when the gun is closed. Even a marginal shift in travel distance can impact the quality of the weld. However, this function automatically compensates the position of gun tips for greater weld consistency. Worn tips are refinished (or dressed) to remove mushrooming of the tip and ensure weld consistency, or they can be replaced based on the tip wear feedback.
- Workpiece search function – allows the gun to close on the workpiece until it senses contact based on torque feedback. This can be used as a tool to simplify programming, especially where the part or tooling may obstruct line of sight. It can be activated during automatic operation to search for weld locations that may vary due to fluctuation in part batches.
- Workpiece thickness detection – the gun opening is measured during clamping as a check to confirm the material stack-up is within tolerance. This prevents errors from missing parts.
- Gun equalization – the application of force can cause the gun arms to flex and induce forces into the part. The robot uses position control to move the robot arm while applying gun pressure to offset for this flexing motion, which can reduce damaging the part.
- Parameter graphing – an oscilloscope function on the robot pendant allows the gun pressure torque and spot timer sequencing to be monitored for process control and troubleshooting purposes.
Whether the industry is automotive, agriculture, construction or something else, these technologies work together to provide feature-rich operation for application success. From maximizing floorspace layout to improving task capability, spot welding robots provide the reliability, accuracy and efficiency needed to optimize production output. So much so that manufacturers experienced with spot welding robots are modifying their current workspaces with innovative technologies to stay competitive.
