Welding Tech: Air to water – is it time?

For many fabricators, the choice between an air-cooled and water-cooled robotic gas metal arc welding (GMAW) gun is easy. Their heavy-duty applications simply demand a water-cooled model because of the high amperage and duty cycle requirements of the job — an air-cooled gun would overheat and fail prematurely under such conditions.

In the right application, a water-cooled robotic GMAW gun often can prove beneficial by minimizing downtime, increasing productivity, and reducing consumable costs. These guns typically have higher duty cycles than air-cooled models and operate at higher amperages, which means they can run for longer periods of time.

Still, deciding whether an operation would benefit from converting from an air-cooled to a water-cooled GMAW gun involves a careful analysis of several factors. In addition to considering the amperage requirements and duty cycle, a fabricator should consider the upfront costs, potential return on investment (ROI), and the specific application.

For example, some fabricators may choose a water-cooled robotic GMAW gun because of the length of their welds — they need a long arc-on time to produce long welds, which generates more heat in the gun. Similarly, critical start and stop points along a longer weld joint typically require a gun that can handle extended weld times.

The weld joint design and type or thickness of the material also can help determine whether to switch to a water-cooled GMAW gun. For instance, heavy plate sections that have been preheated can generate substantial radiant heat that affects how well a gun cools, and this heat can adversely affect the life of the front-end consumables. In this scenario, a water-cooled gun would be better suited for the job.

When deciding whether a water-cooled robotic GMAW gun is the best choice for an application, it’s important for fabricators to keep in mind some maintenance and replacement costs. While a water-cooled gun costs more upfront, there is the possibility to conduct maintenance on each individual component within the cable assembly, such as water lines and gas hoses. However, an air-cooled cable combines all its components into one common part, and if any single component fails, the entire cable needs to be replaced, resulting in higher replacement costs. It is necessary to weigh those factors against each other.

Understanding the Technology

Welding guns — whether air- or water-cooled — must stay cool to protect the power cable, gun body, neck and consumables from heat damage during welding. That heat takes three forms: radiant heat from the arc; resistive heat from the electrical components in the welding circuit; and reflective heat from the welded part, particularly aluminum or preheated parts.

Whereas an air-cooled GMAW gun relies on the ambient air, shielding gas and arc-off time to dissipate heat, a traditional water-cooled gun circulates a coolant from a radiator unit through cooling hoses inside the power cable and into the gun body and neck. The coolant then returns to the radiator, where the radiator’s baffling system releases the heat absorbed by the coolant. Some guns cool only the front of the gun, where heat is generated, and still use an air-cooled cable.

Air-cooled GMAW guns also have much thicker copper cables and inner neck tubes, whereas water-cooled robotic GMAW guns have much less copper in the power cables and thinner wall sections in the necks because the coolant carries away the resistive heat before it builds. Water-cooled GMAW guns, however, do have multiple inner lines that run through the neck to the front-end consumables, making this portion of the gun heavier than an air-cooled neck.

When to Make the Switch

Three key indicators signify a welding operation could benefit from converting to a water-cooled GMAW gun:

1. Excessive consumable usage
2. Excessive gun temperature (overheating)
3. Excessive cycle time (high duty cycle)

All these factors are interconnected, because if the weld is too hot, excessive consumable usage and gun temperature will automatically result.

In general, water-cooled robotic GMAW guns are most beneficial for high-amperage applications in the 350- to 600-amp range.

Closely related to amperage is duty cycle, which refers to the amount of time during a 10-minute cycle that the gun can operate at its rated capacity without overheating. Water-cooled robotic GMAW guns have varying duty cycle capacities depending on the manufacturer and model. It is important to make the appropriate comparison during the selection process, as some guns may be rated at either 60 per cent or 100 per cent duty cycle, which results in different amperage ratings.

The Conversion Process

Fabricators who plan to change from an air-cooled to a water-cooled robotic GMAW gun should follow these three steps to help ensure a smooth conversion.

1. Match the existing tool centre point (TCP) and approach angle. Be sure that all the weld joints are accessible and that the tooling will work with the new system. The gun may require a special neck or special mounting arm to achieve the desired TCP. Often, converting to a water-cooled gun requires a new mounting arm and insulating disk to maintain or achieve a specific TCP while changing the dimensions of the neck itself to create better access.

2. Ensure overall clearance. A 3-D simulator can help determine whether all parts of the new system will clear all tooling or any other obstructions. In addition to having front-end clearance and access, it’s important that the gun body and cable bundle fit properly to avoid getting caught on tooling or other equipment.

3. Get a water cooler. It is necessary to invest in a radiator for a water-cooled gun. Ensure that the water cooler has been installed and maintained per the manufacturer’s specifications.

Maintenance and Usage Tips

Because all the lines and hoses in a water-cooled robotic GMAW gun are separate, it is possible to conduct maintenance on individual components if they become damaged. However, because the lines are internal to the gun, it is difficult to perform preventive maintenance on them. There are options, though, to care for a water-cooled gun.

As with an air-cooled gun, it’s important to inspect a water-cooled gun to ensure that all consumables and connections are tight and working properly. Inspect the water lines frequently to make sure they are tight and have no leaks, and replace the O-rings when necessary (e.g. when cracks or wear appears). Ensure a flow switch is installed in the return line from the gun and the radiator to indicate any leaks within the system — this component will save time and money in the event of a failure.

Using a reamer or nozzle cleaning station significantly simplifies the preventive maintenance of water-cooled robotic GMAW guns. A reamer eliminates the need to manually clean out the front-end consumables and can, with the addition of an automated sprayer, add anti-spatter compound to help further extend consumable life. This feature adds to the overall cost of the equipment, but it helps increase uptime for production since less manual intervention is needed.

It is important to always use the correct coolant; do not fall prey to the notion that it is cheaper to use tap water in a water-cooled gun. Tap water can cause algae growth or mineral buildup and eventually lead to costly clogging. Instead, use deionized water or the specially treated coolant solution recommended by the manufacturer. These coolants contain special additives to lubricate internal pumps and O-rings, as well as to prevent algae growth.

Lower Operating Costs

Although converting to a water-cooled robotic GMAW gun is often more of a necessity than a choice (because the application demands it), this type of gun has its value. Applying a water-cooled gun to the appropriate application can result in more efficient system performance and lower overall operating costs.

Consider the various costs, specific application needs, and joint accessibility to determine whether a water-cooled robotic GMAW gun is the best option for the specific robotic application, and don’t hesitate to consult a trusted welding distributor, welding equipment manufacturer, or robotic welding system integrator with questions.

Ryan Lizotte is a field technical support specialist at Tregaskiss, 855-644-9353, www.tregaskiss.com, and Ralf Burmeister is key account manager – automation at DINSE GmbH, 517-416-5294, http://dinse-us.com.