Global manufacturing is increasingly placing a premium on product quality and durability and, to support this, leading-edge manufacturers are investing heavily in advanced automation platforms offering two fundamental advantages – the ability to manufacture in volume coupled with extremely detailed control of every key process, including use of latest generation digital platforms capturing detailed production data. 

The widespread implementation of high-speed, automated MFDC (medium frequency direct current) resistance welding is one example of this.

Robotic resistance welders can cost-effectively and rapidly weld numerous parts hourly. To track weld quality, post-weld destructive and ultrasonic testing of selected components are widely conducted. However, in-process inspection and real-time adaptive control of resistance welding can revolutionise quality, flexibility and productivity.

This process utilises cutting-edge controls to precisely adjust functional characteristics, ensuring every weld is performed within the tightest tolerances – reducing or potentially replacing ultrasonic inspection technology.

Typical, manual ultrasonic inspection methods involve manual, standalone single part inspection. While non-destructive, this is time-consuming and can introduce repeated inconsistencies, based on opinion of the individual tester on what represents a good weld. Adaptive control integrates each inspection task, and real-time weld control, to vastly improve process reliability while optimising throughput.

Under adaptive control, actual current, voltage and resistance values are compared with previously established reference values for a good weld. Modern adaptive systems work together with the weld controller’s constant current control system to adjust current and weld time in real time, keeping actual values as close as possible to the reference curve. 

They also measure current and voltage across the weld, ideally as close to the electrodes as possible. Mathematical algorithms calculate resistance curves and energy balance. Data such as PSF (Process Stability Factor), UIP (Weld Quality Factor) and weld expulsion are stored and used for monitoring and trend analysis. The current is then adjusted to compensate for minute differences as welding proceeds. In special circumstances, sheet combinations with different thicknesses and coatings can be welded by a single program.

Enhanced flexibility

This kind of control also enhances welding flexibility, helping manufacturers be more responsive to fast-changing market needs. The latest automated platforms can store and operate multiple welding programs, as well as changing programs rapidly to meet sudden changes in demand.

Adaptive resistance welding control automatically compensates to maintain production and quality. As gun tips undergo wear, for example, adaptive welding can compensate for the changes, ensuring welds remain reliable.

It also provides an information framework to assure weld reliability. A warning or error message can be communicated when a process limit is exceeded, halting the process while the cause of the disturbance is checked. The system also allows for the documentation of process data enabling greater traceability. 

A further benefit surrounds safety. Many automated resistance welding operations, with multiple robots carrying out hundreds of welds a minute, if not optimised correctly, can generate a significant amount of expulsion because the process lacks real-time control. This can create a constant cascade of hot, dangerous sparks, necessitating enclosures and other protective devices. 

As the adaptive system allows the weld engineer to now ‘see’ what is happening during the welding process, it is far easier to identify ‘hot’ welds and adjust weld current. Once optimised correctly, the adaptive weld control modulates current flow to the welding gun so that expulsion levels can be drastically reduced. 

This also reduces the dirt and contamination associated with constant expulsions, creating a cleaner environment, with less need for maintenance and also eliminating contaminants that can interfere with sensitive electronic connections, sensors and other equipment. 

Furthermore, some studies have shown it is possible to reduce overall energy consumption by using adaptive control, since only the energy needed to complete the weld is delivered to the weld gun.

For the reasons outlined, there is a real momentum towards conversion to resistance spot welding adaptive systems which can correct many of the disturbances occurring during the course of the welding process.