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Projection welding belongs to the group of resistance welding techniques. With this process, the shape of the workpiece is used to make discrete contacts at particular points to concentrate current on during the welding process. In most applications, multiple small protrusions are formed on one surface of the part to be welded. These protrusions can be round dimples, elongated ridges, round or extended angles of weld nuts. Two circular lines placed together at an angle of 90 degrees form a point contact.
This will also be projection welding. When mating parts are put together, these protrusions will concentrate current and generate heat at these locations. When the bumps get hot, they collapse as the solder nugget forms. After cooling, the result is a few weld nuggets joining the parts together. Of course, in the case of cross-wire welding, there is only one weld at each intersection, but it is usually welded many at the same time with the fence. In this article, we will introduce you to the project welding technique and all its complexities.
Like spot welding, the projection welding process also relies on the heat generated by the current to connect the metal sheets. Projection welding electrodes can carry more current than spot welding electrodes, so thicker materials can be welded. Two flat electrodes cover the surface of the fastener during the projection welding process. The bump itself absorbs and radiates heat, which can produce a strong weld with excellent aesthetics. Uniform contact and pressure between the protrusion of the fastener and the base metal helps to avoid excessive electrode pressure. The projection welding process is very suitable for joining metal parts with relief. It is frequently used in electrical, automotive, and construction applications, partly because of the weld strength it produces.
The annular protrusion at the bottom of the hydraulic joint may form a tight hydraulic seal. Cross-wire welds may be steel bars in fences or roadways. Welding nuts fasten the bolts to various parts of the car. The process is the same as spot welding, but in this case, electrodes are not used to concentrate heat. When there are multiple bumps, multiple welding can be performed at the same time. This is a very effective process and does not rely on electrodes like spot welding. Other factors must be controlled, such as alignment, consistency of protrusion, follow-up by the welder, and protection of the nut welding thread. Projection welding and welding process design and development are suitable for various applications. Compared with other resistance welding methods, projection welding can also achieve excellent heat balance, especially suitable for scenarios requiring thick pieces of metal to be joined together.
Projection welding produced by the resistance welding process uses the form or shape of the component to make discrete single-point contacts to focus the current during the welding process. For most applications, one of the workpiece surfaces has a variety of small but shaped protrusions — circular holes, elongated ridges or circles, or extended angles of welding nuts. When the mating parts are gathered together, the protrusions will concentrate current and generate heat at these locations. Then, as the solder nugget is formed, the thermal bump will collapse.
If projection welding is not set up and planned correctly, it may cause the weld seam to splash or spray. Let's take a look at some of the most important attributes to remember when performing project welding operations:
• Alignment
The welding pressure must force the protrusions to contact the same pressure at the same time, otherwise, one or more protrusions will withstand most of the current and overheating. One or more overheated bumps will expel material. When the final projection touches, it will be performed under current, which means that an arc will be generated and cause a discharge.
• Projection size or shape
When using multiple bumps for welding, make sure that the size and shape of the bumps are the same. Projections of different sizes that are in contact at the same time will heat up at different rates, resulting in overheating and ejection. In some cases, the protrusions may not come into contact for the first time, causing arcing (as described above) and causing flashing, jetting, or splashing.
Excessive projection can cause problems. What happens when the punching tool wears out and the protruding shape and size exceed the specifications? Or if the punch breaks and some parts lack projection? Projection sizes that exceed specifications can cause unpredictable processes. The welding schedule to provide the current for the projections of a given size and number is still ongoing, but the projections may now be smaller or larger than the original design. Larger projections will not heat up so fast, and they will not collapse when appropriate. The nugget may not have time to grow or form at all. Moreover, projections that are smaller than designed or that are lost can create the opposite problem-they may overheat, discharge, or collapse prematurely. Or, the weld nugget may be small or missing.
• Force follow-up
When the protrusions begin to heat and collapse during the welding process, the welding head must maintain force and full pressure on each protrusion as it collapses. This will ensure a good and firm weld. If the welding head sticks, it will affect the welding strength. In extreme cases, it will not cause welding, flashing, spraying, or splashing.
• Weld schedule
A proper welding schedule will help to ensure that the recommended welding force is used to bring the protrusions to temperature, and to forge the weld with appropriate quick follow-up
Traditionally, projection welding uses AC controls and power supply, as well as pressure welders or fixed welding arms. All settings have good synchronization and can be configured for low-inertia fast-tracking systems. Rocker machines cannot be used effectively for projection welding because they exert stress on the arc and are unable to maintain good alignment. For all cases, a simple follow-up cylinder or servo system is needed to ensure the best results.
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