If you read my recent blog on heat balance, you know that there are five different techniques that can be used to balance weld heat that don’t involve making changes to materials or part design. And at the end of the blog I mentioned that if you’re still having difficulty after trying all five of the techniques, you may want to consider adding projections to one of the parts.
So what are projections?
Sometimes referred to as “energy directors”, projections are “dimples” or “bumps” that are pressed or machined into the material at the location where the weld is to be made. Typically, the projections are pressed into the thicker piece:
Benefits of projection welding:
As already mentioned, adding projections can promote heat balance. It does this in three ways:
- Reduces thermal mass of thicker piece (less material to melt)
- Increases current density (more focused current)
- Increases part interface resistance (generates more heat)
Another benefit to adding projections is longer electrode life. Since the projection is doing the job of focusing the current, you can use a larger electrode face, and larger electrodes will last longer than smaller electrodes.
Projections also ensure that the current path is consistent for every weld. And a consistent current path is essential for consistent welding!
Welding with projections:
In most cases, the goal is to achieve a total collapse of the projection during welding. A partial collapse is acceptable in some cases, but anything less than 50% collapse is probably not going to result in a robust weld.
Projection shapes and sizes:
Round projections are commonly used when welding two flat sheets together. A rail projection (or line projection) is preferred when welding a wire or component lead to a terminal. Ring projections are often used on the lids of component packages to ensure a hermetic seal.
Images, left to right show: round projection, rail projection, ring projection
The top of the projection can be rounded, flat, or pointed. The height, width, and exact shape of the projection will be different for different material combinations and part sizes. When designing your projections, keep in mind that a projection that is too big won’t collapse, and a projection that is too small won’t be useful, as it will melt too quickly.
If you decide you want to add projections to your parts to improve welding, but you are not sure of the exact design you want to use, feel free to contact our Resistance Welding Applications Lab for help. We have several welding engineers with many years of experience who would be happy to lend a hand and offer advice on your specific application.
For more information, read our Fundamentals of Resistance Welding.