Automated welding best practices
An automated welding system is a significant investment, and one component that can substantially impact weld quality and productivity in automated welding applications is the layout and performance of the secondary circuit.
The weld cables and circuit in a robotic weld cell are exposed to spatter, corrosion and heat over time, causing them to wear. This can affect the welding parameters in the cell — ultimately impacting weld quality and productivity.
Choosing a welding power source with secondary compensation technology can help operations avoid the issues that stem from wear to the weld cables and circuit — and keep robotic weld cells performing as they should.
How does the secondary circuit wear?
The secondary circuit refers to the welding circuit — the part of the system that carries the welding current from the power source to the weld joint. To reach the weld joint, the current must travel through the weld cable and the work clamp attaching the cable to the tooling or workpiece. If there is any fixturing holding the workpiece in place, the weld circuit travels through this as well. All of these components make up the secondary circuit.
With normal use over time, these components can wear and degrade. For example, weld spatter buildup reduces the contact area, which affects weld current flow. The heat of the welding process can also cause weld cables to break down over time, lessening the connection in the circuit.
These wear factors contribute to increased resistance in the secondary circuit, which significantly impacts weld quality. As resistance increases, it reduces the voltage being delivered to the weld — and voltage is a critical parameter in welding. If resistance increases enough, it can cause the cell to fall outside of its programmed parameters. Any changes that occur in the secondary circuit affect the weld, and the more factors that change, the greater the impact.
Resistance in the secondary circuit is less critical in semi-automated welding applications since the operator is controlling the weld and can easily watch the puddle and make adjustments. It’s a more important factor in robotic MIG welding applications that use advanced arcs, which require the welding power source to constantly monitor what’s happening in the weld and adjust parameters as necessary.
The more resistance that’s built up in the weld circuit, the more difficult it is for the power source to accurately monitor what’s happening during the weld. Without good feedback on what’s happening, the power source can’t make proper adjustments to maintain a good arc.
Following some key best practices — and choosing robotic welding systems with the right technology — can help overcome this issue.
Tip No. 1: Start with proper weld cell design
The design and layout of the secondary circuit within the robotic weld cell is a key factor that impacts performance and weld quality.
As pulsed MIG welding processes have advanced, another welding innovation developed: the voltage sensing lead. This lead monitors weld voltage at the arc outside of the weld cables. Previously, the power source would only monitor the weld voltage output at the welder — before the weld current traveled through the secondary circuit. The voltage sensing lead allows the system to measure the voltage closer to the arc, so the power source can make better adjustments to maintain weld quality.
Proper weld cell layout and design helps ensure the best positioning of the voltage sensing lead. Because of its important role in the cell, the lead should be placed as close to the welding arc as possible without being in the return current path. The lead can often be bolted to the welding fixture. If the lead is placed improperly in the return current path, interaction between the welding circuits will affect voltage drop in the workpiece. Voltage feedback to the power source won’t be correct, resulting in poor arc starts and arc quality.
Cables also must be sized and routed properly to ensure quality performance. Weld cables should be sized for peak amperage rating when pulsed MIG welding, and cables should be kept as short as possible with no extra coils or loops to minimize inductance and resistance.
In addition, minimizing the welding circuit loop helps prevent extreme voltage drops that produce poor welding characteristics.
Tip No. 2: Utilize a secondary compensation circuit
While proper cell layout is important, the secondary circuit will deteriorate with use no matter how well-designed the weld cell is. This is where secondary compensation circuit technology can help.
The secondary compensation circuit, a technology available in advanced MIG welding power sources from Miller, measures the resistance of the entire secondary circuit and the voltage drop that is occurring. Using that information, the system:
- Lets operators see the health of the secondary circuit, a measurement they can use to determine if anything in the cell needs to be changed or fixed.
- Automatically compensates to offset voltage drops in the weld circuit, to ensure the cell isn’t welding outside of specified parameters.
In high-volume manufacturing facilities with dozens or even hundreds of robotic welding arcs, secondary compensation circuit technology can save significant time and money in improper welds and rework.
Tip No. 3: Regular maintenance is critical
Performing regular inspection and maintenance of the welding circuit and its various components plays an important role in the continued optimization of the weld cell. Be sure to have a preventive maintenance program in place to inspect components frequently and repair them as needed.
While this can require building some planned downtime into the welding operation, neglecting or skipping regular inspection and maintenance can cost much more in time and money in the long run.
Consider installing a reamer, a peripheral that can automate part of weld cell maintenance to help maximize performance. A reamer is a nozzle cleaning station that can be integrated into a robotic weld cell and programmed to work during pauses in the welding cycle. Reamers remove the spatter from inside the MIG gun’s front-end consumables that accumulates during welding. Keeping consumables free of spatter helps extend consumable life and reduces downtime for maintenance. Using a reamer also helps prevent loss of shielding gas coverage, an issue that can lead to costly rework.
For the best results, place the reamer close to the robot so it’s easily accessible, and program the system to use it in between cycles, such as during part loading or tool transfer. Investing in a reamer can make the robotic welding process more efficient and productive.
Improve robotic welding performance
Following key best practices for weld cell design, including placement of the voltage sensing lead and layout of the secondary circuit, promotes arc quality and performance in robotic welding applications. In addition, choosing a power source with secondary compensation technology helps welding operations reduce or eliminate costly issues related to wear in the secondary circuit — so they can maintain parameters and keep the weld cell optimized.