Problem with cutting steel bars

[EngineerNewbie]

Hello all.

I have a problem where I work and want your help.
At forging, when the steel bar is cut, sometimes the bar sticks to the "cutting blade". Then, it takes different shape than the normal one and a defect appears. The process is mechanical, no cutting disc is used.
It's like the bar acts like a dough.
What can we do so this problem doesn't occur?

Thanks in advance!

 

[IRstuff]

If the bar is sticking, then it's possibly too hot, and some form of cooling is needed. Usually, there's a cutting oil that is used to cool the cutting tool and cut.

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[EdStainless]

Temperature and lubrication are the two issues.
The sticking ones are either too hot, or not enough lube, or both.

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Plymouth Tube

 

[racookpe1978]

Like a dough? Is the cast metal still soft enough when cut to actually deform or move under its own weight?

 

[EngineerNewbie]

racookpe1978, it's not cast metal, it's a solid metal, that's heated by induction and then cut.
I thought about lubrification but need to investigate the problem more.
Thanks guys.

 

[Tmoose]

Is this an automated process? Does the machine manufacturer have anything to say in the O&M manual or on the phone?

the way you said it is " heated by induction and then cut" I'm assuming you heat just the section you want to cut, perhaps because it is a thick section.

Does the "defect" resemble the edge on this cold sheared plate?

http://images.discountsteel.com/files/image/oms_product/MEDIUM/Sheared_Edge.jpg

 

[EngineerNewbie]

I can't see very clearly, but I think so.

 

[racookpe1978]

My opinion - and without looking at a video in real time of the sawing operaton and metal temperature of the steel being cut I'm making sort of a guess here - is that the "soft, doughy" steel is getting torn by the saw teeth - not "cut" cleanly by the saw teeth. Then, as the blade pulls the torn metal past the cutting area, it tears and pulls more soft metal from the sides and back of the cut down into the cut and in between the teeth. Eventually, the excess friction between blades and material siezes the blade.

The "goo" squeezes the blade as it seeps back into the cut (think Panama canal's Gailliard Cut: As you remove material more flows back into the groove and gums up the teeth).

 

[tbuelna]

Just to be clear, the steel bar being saw cut is a piece of heated raw material that immediately gets hot forged after cutting? Or is the saw cut performed on the part immediately after hot forging?

Saw cutting a hot steel part may likely result in some welding between the blade and part surfaces. It would be better to saw cut the material while cold so a cutting fluid can be used. If you really need to trim the material while hot, you might consider using some type of shearing or trimming die.

 

[EngineerNewbie]

tbuelna, it's not a cut made by sawing, it's a mechanical process made by a guillotine.
racookpe1978, I think you're very accurate with what you said.

I informed myself a little better about the problem.
When the guillotine makes the first "cut" , it goes blank 3 more times(it's idling) without cutting, and it goes by the bar that's advancing little by little. This is where sometimes the problem occurs.

I hope my English is not that bad and you guys understand the process that I'm explaining.

 

[racookpe1978]

How are you cooling the blade while it is in the 3x idle time?

What are blade approach temperatures, blade removal surface temperatures? That blade is very thin - it will heat up quickly!

 

[weldstan]

Blade wear could be part of your problem. Uneven heating through the cross section of the bar could also contribute as well as the above responses.

 

[EngineerNewbie]

It's not cooled.

 

[btrueblood]

EN,

Your English is fine, but your communication would be enhanced with a sketch.
- Can you sketch the cut end with and without the defect?
- can you sketch what the guillotine and the support provided for the bar during the cut look like?
- does the bar continue to advance during the cut operation?

 

[tbuelna]

EN-

Thanks for the partial clarification. So what I understand so far is that you are locally induction heating a piece of wrought steel bar and then cutting the bar at the heated area using a single blade shearing operation. But for some reason you are not getting a clean separation at the shear plane. I assume you are using a machine designed specifically for hot shearing steel, but have you checked to see if you are using the proper blade and machine settings for the material type, size and shape you have? Also, as others noted, are you sure the material has the correct temperature all through its thickness when it is being sheared?

More specific details about the machine and settings used, material composition and form, process variables such as temperatures, cycle times, etc., and some photos of the defective cuts would be extremely helpful.

Regards,
Terry

 

[EngineerNewbie]

What you said, is correct Terry.

But the process is like 20-30 years old and the temperature I think it's good, maybe needs a little optimization.
Only sometimes this problem occur. Now engineers are investigating the problem.
When I'll have more details, will let you know. I hope tomorrow.

btrueblood, I will make a sketch when I'll get into more details of the problem.

Thank you again.
Be back soon with more details.