Automatic Cap Nut Welder: A Nut Welding Guide

Posted on Jan 27, 2021

An automatic cap nut welding machine needs to be capable of welding different types of materials, especially one of the most common welding materials – steel. Steel has low thermal conductivity and high electrical resistance, making it one of the most excellent candidates for projection welding and spot welding.

What Is an Automatic Cap Nut Welder?

An automatic cap nut welder is essentially a type of projecting welding machine that was developed via the resistance welding (RW) process, which uses the design or shape of the part to make individual point contacts through concentrated current during welding. As the name suggests, a cap nut welding unit excels at producing cap nuts, the surface of which features multiple, small, and formed projections – this includes elongated ridges or rings, round dimples, or extended corners of cap nuts. When the parts to be welded come together, the current flow is concentrated by the projections and generates heat in the relative locations. Then the hot projections collapse as the weld nugget forms.

Automated Systems Explained

Adding to the above, an automatic cap nut welding machine incorporates automation and robotic technology so that welding can now be done in even smaller physical spaces and easily integrates parts of the assembly process. Compared with conventional welding machines, an automated cap nut welding unit can provide more consistent results and achieve repeatable welding output with optimum quality in less time. And with the growing popularity of automation systems, this type of welding machine continues to be the perfect candidate for applications in which tiny parts of an assembly can easily be joined. Click here to see the good-quality automatic welding machines for your shop.

:: Read More: Automated Resistance Welder: An Evolution

What Do We Know about Cap Nuts?

A cap nut is commonly known as an acorn nut, a type of nut that features a dome head. Because of its shape, it is also referred to as crown hex nut, blind nut, cap nut, domed nut, or dome nut. What distinguishes a cap nut from others is that it is closed on the top, while other nuts are open on both the top and bottom. Cap nuts cannot be twisted or installed to the length of the bolt because of its unique, dome-shaped head.

When cap nuts are used in conjunction with a threaded fastener, the domed end encloses the external male thread by which the nearby objects are protected from contacting the thread. As a bonus, the dome end also provides a more finished appearance. 

Cap nuts can be made of steel, stainless steel (low carbon content), brass, or nylon. They may even be chrome plated for a mirror finish. Therefore, an automatic cap nut welding machine needs to be capable of welding different types of materials, especially one of the most common welding materials – steel. Steel has low thermal conductivity and high electrical resistance, making it one of the most excellent candidates for projection welding and spot welding.

There are usually two types of cap nuts that you can weld with a cap nut welding machine, one is a low (or standard) cap nut, and the other is a high cap nut. You’ll typically have an easier time with high cap nuts because of their wider surface and higher body. You might also have the opportunity to work with a self-locking cap nut that has a distorted thread in the hex area to produce tight friction fit to avoid vibration loss.

Common Challenges with Nut Projection Welding

As previously mentioned, the welding of nuts and studs usually undergoes the projection welding process. While this is an improved version of resistance welding, it still faces certain challenges despite the generally simple procedure, especially given that a few standard guidelines aren’t strictly followed during the fabrication. For instance, weld spatter in the threads or hole misalignment may occur if you are not careful. Cold welds and thread distortion are also likely to occur and come undetected. All these issues can easily lead to a loss in production time and scrapped parts, which will end up incurring more manufacturing costs that cannot be recovered until the problems are resolved. Fortunately, all of these problems can easily be avoided if the fabricators follow simple guidelines and recommendations, and ensure profitability amid the projection-weld nuts and studs.

Ensuring Consistent Result in Nut Welding

The quality of your cap nut welding machine and how well you set up the unit determine how successful your projection welding for nuts is going to be. This includes ensuring good equipment alignment to ascertain the delivery of an identical amount of force. The delivery system of the projection nut welding machine must be able to move fast enough as the projections collapse, maintaining full force. This is generally referred to as quick follow-up. A larger scale, poorly set up welding unit may cause problems to the cylinder or servo motor. Moreover, you want to keep variation in the projections to the minimum to get consistent results for nut welding. If the feeder misplaces a cap nut, misalignment can occur as we said earlier.

Another way you can ensure consistency in nut welding is to undertake force follow-up. This is a method by which projections begin to heat during welding and collapse, allowing the weld head to maintain full force and pressure on each projection as it collapses. This leads to stronger welds. And if the weld head ticks, weld strength will be affected, and in extreme cases, no spatter expulsion, weld, and flash may result. 

Last but not least, to ensure consistent results, a well-mapped-out weld schedule will help. A proper weld schedule will serve as a good reminder of what your weld force should be, which helps bring projections to the desired temperature and forming the weld with proper fast follow-up procedure.

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