Broken Punch Tool Causes

[rglanz77]

Hello,

One of the punches we use at the shop recently broke, and I been trying to find out why. It has an angular fracture, instead of a trasverse fracture, so I've been having a hard time understanding what cause it to break.

attached are some pictures.. any ideas?



thanks!
RGL

 

[awemawson]

some how slightly out of alignment with the die ?

 

[rtbcomp]

Are there any marks on the die where it may have caught?

 

[Shox Dr]

Are you using the correct die/punch clearance for the thickness to metal you are punching

 

[morph]

I'd guess there was a very hard bit in the steel you were punching, I had the same sort of thing today. Mag broach wouldn't go through the last couple of mil so I had to plasma the rest of the hole out. I've broken punches with the same sort of steel.....

End of the day **** happens and it was only a £15($25) part- well they are in the uk!

 

[Hitch]

End of the day **** happens and it was only a £15($25) part- well they are in the uk!

Quite.

Did it break on the punching, or the return stroke?

Theres a few causes for them to break usually...

Thickness of material too large, generally, dont punch more than the diameter of the punch, dont try putting a 10 through 15mm material...but, as you get bigger, you can get away with it, eg 18 through 20 goes okay usually,22 through 25 is okay....but reduces the punch life. Offset the cost of a new punch against labour, and its a no brainer.

Misalignment with the die, occasionally, if the punch is worn, it can start to bend slightly under pressure, messing up the alignment with the die, and putting a sideways load on it.

If it broke on the return stroke, chances are you havn't been lubricating it....worse, and even more important if you are punching a freshly profiled plate thats still warm.

Stripper, is the stripper level, and a fairly close fit to the punch? If not, the plate can pull up slightly unevenly, sometimes grabbing the end of the punch and litterally pulling it apart.

Clearance/Condition, Both in reasonable condition? Clearance, generally, these types will have a +1mm clearance for most applicatons.

 

[Normsthename]

Clearance, generally, these types will have a +1mm clearance for most applicatons.

Magic formula for Die clearance is usually 20% of Material Thickness so :-

1.5mm = 0.3mm Clearance
3mm = 0.6mm Clearance
6mm = 1.2mm Clearance

Etc etc

Reason for breakage could just be old age, punches do have a service life of so many hits.

Andy