and Your Overall Investment in Automation
Given that the single-most enticing reason for companies to invest in welding automation is to improve productivity, it may seem counterintuitive to stop or slow production — for any reason. But what if minor downtime could save your company vast amounts of time, trouble and money in the long term? Or give you a greater competitive edge by improving your overall efficiency? Simply put, that is the basis of a preventative maintenance or PM program.
Unfortunately, far too often companies fall victim to the ‘if it isn’t broken, don’t fix it’ mentality when it comes to caring for automated equipment, including the robotic MIG gun and consumables. Doing so, however, can have dire consequences. Not only is there a risk of losing productivity and lowering throughput if the entire system isn’t functioning properly, but even the slightest malfunction can result in higher labor, lower weld quality, greater rework and wasted materials. But most importantly, downtime associated with troubleshooting and completing repairs can significantly lower the return on investment sought by transitioning to welding automation in the first place.
And while caring properly for the whole of an automated welding system is imperative, maintaining the robotic MIG gun itself is just as important. In fact, the robotic MIG gun (including the consumables) is often one of the most overlooked components of the system — and also one of the easiest to maintain. Fortunately with some simple steps, you can make robotic MIG gun maintenance an important part of your overall preventive maintenance program and ensure the most consistent performance of your entire automated welding system along the way.
The Who, Why and Whens of PM
Preventative maintenance programs, particularly those for robotic MIG guns, are not just beneficial for large companies with multiple automated welding cells. All companies, regardless of their size or arc count should regularly care for this equipment. Like the key tenets of the 5S methodology (Sort, Straighten, Shine, Standardize and Sustain), taking proactive steps to ensure the productivity of your automated welding operation, starting with the guns (no matter how many you have) can positively affect your company’s workflow, throughput and bottom line.
The scope of a preventative maintenance program varies according to each particular application. Specifically, the higher the risk of problems in your process — logistically and fiscally — the more frequently you should take steps to prevent them. Take for example a heavy equipment manufacturer that welds thick plate and has an average welding cycle time of 4 hours per part. This company stands to have greater downtime and more expensive rework to remedy a problem than a company that welds smaller, less expensive parts in a four-minute weld cycle. Therefore, this higher risk process needs more frequent care of its equipment, including its robotic MIG gun, as part of an overall preventative maintenance program.
Welding engineers, welding supervisors, tool and die employees or members of the maintenance staff are all viable candidates to oversee a preventative maintenance program. There is, however, one single key to these employees executing a program successfully: training. All personnel involved need to be trained to be aware of the potential problems that could arise in the weld cell and how to prevent them.
Getting Down to the Specifics
To make your robotic MIG gun a central part of a preventative maintenance program takes significantly less time than you might imagine. In fact, most of the maintenance can be completed shift-by-shift with minimal off-line time. Note, however, that such ‘in-process’ preventative maintenance does not constitute the entirety of a PM program. There may be procedures that need to take place off-shift due to their complexity and the time necessary to complete them.
The first thing to know about maintaining your robotic MIG gun is to always use the proper tools for the job. When changing diffusers (or retaining heads), use a proper adjustable or crescent wrench. Contact tips should also be installed with a proper pair of pliers or welpers, or a specific tip installation tool. Always use a sharp pair of side cutters when trimming your robotic MIG gun liner, as any other type of tool will likely create a large burr that can wear or drag on the welding wire.
Secondly, during your in-process robotic MIG gun maintenance, always check that the connections on the gun, consumables and cable are secure, in good working order, and that these components are all as clean as possible. This task can be completed relatively quickly when the welding operator overseeing the weld cell changes out a finished part and/or during a routine contact tip changeover.
Specifically, check that the diffuser is tightly connected to the neck (or neck) and that, in turn, the contact tip fits snugly in the diffuser. Similarly, be certain the nozzle and any seals around it (depending on the style you use) are secure. Having tight connections from the neck through the contact tip ensures that you have a solid electrical flow throughout the components and that there is minimal heat build-up that could cause a premature failure. Minimizing heat build-up also lessens the chances of troublesome occurrences like burn-back, which could result in unplanned downtime to change over the contact tip and diffuser, as well as poor arc stability, which could cause quality issues and rework. Note, any change in the color of the consumables (particularly if the copper changes to a dark orange or purple) is a good indication that they are loose and require tightening.
Additionally, check that the power pin and welding cable lead are properly secured and that the cable is not rubbing against any part of the robot’s metal casting, as this can eventually cause it to loosen or wear out the cable. A worn spot on your robot (e.g. the absence of paint) or on your tooling is a good indication that the cable is rubbing against it. Remedying such a problem needs to occur while the robot is off-line, since it could require repositioning the tooling or adding some form of cable management device; however, a quick in-process inspection that identifies the issue can flag it for a later, proactive solution.
Visually inspecting your contact tip, nozzle and diffuser for spatter build-up is also a crucial part of a preventative robotic MIG gun maintenance program. Check, too, that your grounding blocks are clean and free of spatter in order to make good contact.
Like loose connections between components, spatter build-up can cause excessive heat to be generated from the contact tip to the MIG gun neck, fouling the internal and external threads—even to the point of causing the torch itself to overheat and fail. Spatter can also block shielding gas flow, causing problems like porosity or other defects that require costly rework. It can also add to your overall costs for the consumables themselves, as spatter build-up will require you to changeover nozzles and contact tips more frequently than necessary.
To prevent such problems, inspect your consumables regularly for spatter accumulation. Even better, consider using an automated consumables cleaning device, often called a nozzle cleaning station, reamer, or spatter cleaner to minimize spatter build-up. As with any part of your automated welding system, adding equipment like a spatter cleaner also adds costs to the initial capital investment; however, as with any part of a preventative maintenance program, it can save you money over the long term.
Like its name implies, a spatter cleaner device removes spatter (and other debris) that builds up in the nozzle and diffuser as part of the normal welding process. Using this product in conjunction with a sprayer that applies an anti-spatter compound provides further protection against spatter accumulation and reduces downtime needed for fixing weld defects.
Next in the preventative maintenance of your robotic MIG gun, determine how long it takes for the gun liner to become worn or fouled using your particular process, and
schedule a liner replacement as required. Replacing it prior to a failure prevents unplanned downtime to remedy wire feeding or quality problems later.
As a side note, remember to cut the liner to the correct length, per the manufacturer’s recommendation. A liner that is either too long or too short can lead to poor wire feeding and poor weld quality. Improper liner lengths can also lead to premature contact tip failure.
Periodically, check the force required to pull the welding wire from the feeder through the robotic MIG gun to ensure that there isn’t too much drag, which indicates that there is a build up of debris the liner. To complete this task properly, the drive rolls of the feeder should be released first. Also, it is best to perform this task in between shifts, as opposed to during contact tip changeover, as it will take a bit more time.
During this time, you should also check the force needed to pull the welding wire from the coil through the wire conduit to the feeder. While the conduit and feeder are obviously not part of your robotic MIG gun, caring for them directly affects the performance of the gun itself. For example, debris in the wire conduit, if undetected through regular inspections, can be pulled through the length of the robotic gun, causing liner and consumable problems — especially wire stoppages that lead to burn-back.
Similarly, too many twists or bends in the welding wire that feeds through the gun, can also affect the longevity of your gun liner, as well as arc stability and weld quality. It is a good preventative measure to check that the wire conduit is clean, that drive roll pressure is properly set and that you inspect and replace worn drive rolls and wire guides.
Parting Thoughts on PM
Maintaining your robotic MIG gun is just part and parcel of an overall PM program, but it is significant nonetheless. Most of the robotic MIG gun maintenance, as discussed here, can be completed on a shift-by-shift basis with minimal interference with your cycle times and with minimal labor — especially when you consider the time and cost of resolving problems instead of preventing them in the first place. Remember, preventative maintenance programs don’t have to be complicated, only effective. So take some time to consider the preventative maintenance needs specific to your automated welding operation in order to establish the scope and frequency of your own program.