Attaching components to one another requires in-depth understanding of the qualities of the metals in each component.
Everyone knows about welding. Fewer know about sinter bonding and sinter brazing, useful processes that are specific to powder metallurgy. Compared with traditional brazing, sinter brazing uses different materials.
We’ve already covered sinter bonding, which allows you to achieve a sintered bond between parts with no additional materials necessary. But in other situations, the way each part will react to the heat makes sinter bonding impossible. The answer in these cases is not to resort to welding, but to use sinter brazing.
Sinter Brazing – What You Need to Know
You may already be familiar with the sintering process in powder metallurgy. If you aren’t, a quick explanation will make it easier to understand how sinter brazing works.
Powder Metallurgy Sintering
What is sintering in powder metallurgy terms? It’s the process of putting a compacted part through a furnace to fuse the tiny particles. The furnace will heat up enough to improve the component’s hardness but not enough to melt the part. When you are finished, you have a sintered metal part.
Sintering is a vital step in powder metallurgy, and it plays an important role in numerous applications.
Combining Two Parts
One of the coolest things about sintering is that you can fuse two parts together along the way. You just need to use the right process based on your materials.
In powder metallurgy, you can use either sinter brazing or sinter bonding. Sinter bonding is one such process -- why not just always use that? Each metal handles heat in its own way -- as long as your components shrink or grow appropriately, the metals will push against one another and bond, and you save the cost of a third, filler material.
While sinter bonding is the most economical way to bring together two parts, it’s not feasible in all applications.
Here’s one example: Say you want to bond a stainless steel component to an iron part. Stainless shrinks dramatically post-sintering, but it also grows tremendously when it’s in the furnace. As it heats it will grow away from the other part, making sinter bonding impossible.
You need something to bridge that gap -- that’s where sinter brazing comes in.
“Why can’t you just weld them?” you might ask. Yes, welding is an option. But, powder metal parts can contain contaminants -- sometimes due to the material’s porosity and sometimes due to other factors. This can make welding these parts more difficult, and requires much more technical expertise. Plus there is the additional cost penalty of welding that can be eliminated by sinter brazing.
How Does Sinter Brazing Work?
We mentioned that in brazing, you introduce a third, filler material. This filler melts into the pores of the two parts to create what basically becomes a third component.
The filler material must be in place before the parts go into the furnace. As the parts go through the furnace, they’ll sinter and the filler material will connect them for life.
Applications for Sinter Brazing
You may not have the luxury of being able to use two materials that will bond without a middleman. Perhaps your application requires a metal that's not conducive to welding or sinter bonding.
So, the main reason you use sinter brazing is to assemble multiple parts with differing materials. It comes in especially handy when you want to create a more complex shape. It’s also got another hidden use: when you’re trying to limit material properties to a specific location on an assembly.
To explain: If you only want one section of an assembly to be magnetic, you can use sinter brazing to separate the magnetic portion from the nonmagnetic portion. Making the whole part magnetic would defeat the purpose; sinter brazing serves as a neat workaround.
Bond. Sinter Bond.
Sinter brazing serves much the same purpose as sinter bonding. Sinter bonding requires fewer steps because there is no filler material to apply, but sometimes your material needs will eliminate that as an option. If so, look toward sinter brazing before you resort to welding.
For additional examples of when to use sinter bonding and when to use sinter brazing, check out this article.
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