die punch design 1

[kkg123]

we do extruded hole operation. the extuded hole cracks up after brazing. i heard about thumb rule to give radius on die punch. will any body share information

help please

kkg123

 

[Artisi]

?

 

[ctopher]

Need more info...maybe a picture?

Chris
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[ajack1]

Kkg123 where are the cracks at the open end or the joined end?

If it is the open end try machining or forming a chamfer on the underside of the pierced hole, when you pierce a hole the bottom end is full of very small cracks in the breakaway, the part that is die size, these will only get worse when you stretch them in the extrusion.

If it is the other end consider putting or larger radius on the die and also polishing the die and forming punch and even coating them. A full radius is not the best way to form the extrusion either most punch manufactures do specials for this look at Lane, AWPrecision, Porter or the like websites for information.

 

[kkg123]

we are getting cracks at the bottom of the extruded hole.
i heard that the die punch radius is dependent on thickness of sheet.

 

[kkg123]

I AM ATTACHING THE PHOTO

 

[kkg123]

ATTACHEMENT LINK

 

[btrueblood]

kkg123,

It would appear that you are brazing a copper rod or tube into a stainless or nickel-alloy vessel wall? Perhaps using a silver (Ag) containing braze alloy, such as a BAg-8 or similar. Most of all - it looks like the crack has braze alloy in it, from your photo. This is a symptom of liquid metal embrittlement - residual stress in the parent metal, combined with the dissolving power of molten silver to nickel alloys, cause rapid crack growth (similar to SCC). Try annealing the parent metal, or using a braze alloy without silver content, or reducing the silver content. Others (metallurgists) here should be able to offer more help to solve the LME problem.

 

[Darken99]

Is the cracking occurring while it is cooling? Possible your brazing alloy is contracting at a rate which causes excess stress on top of the residual stress from punching. Regulating the cooling of your metals may prevent this.

 

[kkg123]

3 mm HRSP sheet has exctruded hole in which coppeer tube is brazed with 25 % silver brazing rod.cracking occurring while brazing.
can some one throw light on liquid metal embrittlement.how to avoid it

 

[btrueblood]

What is HRSP?

 

[kkg123]

HRSP long form is hot rolled steel plate

 

[chicopee]

I can not tell how deep is the extrusion of the 3mm sheet at the hole location but its seems that high stresses are ocurring during the extrusion. You may want to anneal during a two or three step extruding operation before brazing.