Shear tube cutting

[Elb.ab]

Hello,
I would like to have some guidance concerning a little subject that i'm treating.

We're using a machine to cut some aluminum tubes ( through shearing). Recently, due a change in the material ( still aluminum), some small cracks are developed on the surface sheared. I understand that the ductility of the material gives a rough surface, but in addition to this there are some small cracks. I would like to investigate into this by thinking of the different possible parameters responsible for this like strain rate..

Thank you in advance for your help.

 

[EdStainless]

Clearance of the tools will have an impact on how much the tube flexes before shearing.
Also how dull the blade is.
Unless you are facing these off enough to remove all of the cracks you are setting yourself up for some nasty failures later.

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P.E. Metallurgy, Plymouth Tube

 

[rb1957]

I'm guessing you've changed to a harder temper, like from T3 to T6.

Different tempers need different processing. I think it's a hardness problem, not ductility.

I think you need to experiment with your process to find out what works. Or talk to people who do this.

another day in paradise, or is paradise one day closer ?

 

[metengr]

These are probably local tears in the deformed metal because the material is tearing in tension rather than exceeding the shear strength of the base metal.

 

[mfgenggear]

from my memory ~ the gap between the shear tools will depend on the type, thickness and hardness of the material , some times a cold roll mild steel sheet backing helps prevent damage to the part.
trial and error to get the exact gap. there is manufacturing data out there for the starting gap.

 

[Elb.ab]

Thank you all for your answers.
We are now using T6 as a replacement to T9: I don't have the value of hardness of T9, but it seems to be harder than T6. T9 also has both tensile strength and yield stress bigger than T6 ( the range of 2XX to 300 MPa vs 3XX to 4XX). Moreover, the elongation ( ductility) is bigger for the T6 ( 5 vs 10)
It seems that T6 deforms more plastically before fracture(more than T9.


Concerning tearing in tension, i look into ( the length of the bar is small ( about 20 mm)