Companies invest in welding automation to increase productivity, improve quality and reduce costs. Any unnecessary downtime can quickly interfere with obtaining those goals. But what about small amounts of scheduled downtime for maintenance? In most cases, a well-planned, efficient preventive maintenance (PM) program can yield positive results. Not only does it help ensure reliable throughput, but a properly executed PM program can also lower labor costs, reduce waste and minimize rework. It may even expedite the return on investment (ROI) in the automated welding system.
Caring properly for the whole of an automated welding system is imperative, of course, but so too is maintaining the robotic MIG gun. In fact, the robotic MIG gun and its consumables are frequently overlooked components in the system. They are also relatively easy to maintain, and doing so can positively contribute to the efficiency of the entire welding operation.
PM PROGRAM BASICS: THE WHOS AND WHENS
All companies, regardless of their size or arc count, can benefit from regular maintenance of their robotic MIG guns and consumables. The scope of the PM program, however, will vary according to each company’s application. For example, a company with higher-risk applications — those with large, thick parts; long cycle times and/or expensive rework — generally require more frequent care of the equipment than companies that weld smaller, less expensive parts. They simply stand to lose more (in both downtime and money) should something go wrong in the welding process.
Most of the maintenance on a robotic MIG gun can be completed shift-by-shift with minimal off-line time. Welding engineers, welding supervisors, tool and die employees or members of the maintenance staff are all viable candidates to oversee the process. All personnel involved, however, need to be properly trained to identify potential problems in the weld cell and learn how to prevent them. They should also be aware that “in-process” maintenance does not constitute the whole of a PM program. Some activities may need to take place off-shift due to their complexity and the time needed to complete them.
TAKING ACTION: THE WHYS AND HOWS
There are several key components to a good PM program for robotic MIG guns. Before starting any task, it is important to have the correct tools for the job. For example, be sure to have the proper adjustable or crescent wrench for changing diffusers or retaining heads, as well as the recommended pliers, welpers or tip installation tools for installing contact tips. Keep a sharp pair of side cutters on hand, too, to trim the robotic MIG gun liner. These tools help prevent burrs on the liner that can wear or drag on the welding wire.
After establishing that the proper tools are in place to support the PM program, consider the following practices.
Secure connections on a regular basis
During pauses in production — when the robot finishes welding a part or during routine contact tip changeover, for example — check for clean, secure connections between the MIG gun neck, the diffuser or retaining heads and the contact tip. Also, check that the nozzle is secure and any seals around it are in good condition.
Having tight connections from the neck through the contact tip helps ensure a solid electrical flow throughout the components and minimizes heat build-up that could cause premature failure, poor arc stability, quality issues and/or rework. It also reduces the opportunity for burnbacks, which can lead to unplanned downtime for changeover. Look for changes in consumable colors, too, as those are a good indication that they are loose and require tightening.
Prevent spatter build-up
Spatter build-up can cause excessive heat in the consumables and MIG guns, block shielding gas flow, and increase costs for inventory and downtime to change over nozzles, diffusers and contact tips. Visually inspect consumables on a regular basis for signs of spatter, replacing them as needed. Also, consider adding a nozzle cleaning station (also called a reamer or spatter cleaner) to the weld cell. Like its name implies, a nozzle cleaning station removes spatter (and other debris) that builds up in the nozzle and diffuser. Using this equipment in conjunction with a sprayer that applies an anti-spatter compound can further protect against spatter accumulation.
Mind the liner
Track how long it takes for the liner in the robotic MIG gun to become worn or fouled, and schedule a replacement as needed. Replacing the liner prior to a failure prevents unplanned downtime to remedy wire feeding or quality problems later. Also, always cut the liner according to the manufacturer’s recommendation to prevent kinking and poor wire feeding that can lead to premature contact tip failure and/or arc instability.
Periodically, release the drive rolls and check the force required to pull the welding wire from the feeder through the robotic MIG gun. Excessive drag indicates that there is a build-up of debris in the liner and it needs to be replaced. It is best to perform this task in between shifts, as opposed to during contact tip changeover, as it tends to take more time.
Assess the welding cable and power pin
Check regularly that the welding cable leads are properly secured and assess the condition of the welding cable on the robotic MIG gun. Look for signs of wear and be certain that the cable is not rubbing against any part of the robot’s metal casting, as that friction can cause the cable to loosen or become damaged. A worn spot on the robot (e.g., the absence of paint) or on the tooling is a good indication that the cable is rubbing against it. Rectifying the situation will likely involve repositioning the tooling or a cable management device and may need to occur while the robot is off-line. Still, a quick in-process inspection that identifies the issue can flag it for a later, proactive solution.
PARTING THOUGHTS ON PM PROGRAMS
Preventive maintenance programs don’t have to be complicated — only effective. Most of the robotic MIG gun maintenance discussed here can be completed on a shift-by-shift basis with minimal interference to cycle times and with minimal labor costs. The scope and frequency of a PM program will vary from company to company, of course, but carefully executed maintenance activities can help companies better realize the potential of their automated welding operation. And it can reduce costs by preventing problems, instead of being forced to resolve them.
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