Why are chips hot?

[FOMOGO]

Because they dress so sexy? Mike

Quote: Why are chips hot?

 

[pontiac428]

Sure, friction, transfer of energy, but the entropy of breaking metallic bonds releases a ton of energy as heat. If it was anything else, you wouldn't have to pour overwhelming energy into metal at the foundry in order to reform those bonds.

 

[strantor]

Nearly all of the energy provided by the motor ends up in the chips.

Several others have said the same and with supporting details but I think this is simplest statement of the piece of the puzzle I was missing. It's so obvious that I am embarrassed it had to be pointed out to me. But I'd rather learn late than stay ignorant.

I suppose it follows that if drilling a certain hole will require a certain amount of energy and generate a certain amount of heat, then using a sharper tool that dumps that energy into those chips faster, results in hotter chips. Or in other words:

it's simply doing so much work in a short amount of time hence still generates a lot of heat

And the other missing piece:

Sure, friction, transfer of energy, but the entropy of breaking metallic bonds releases a ton of energy as heat.

Molecular bond? Particle bond? Whatever the bond that holds a sheet of steel together into a sheet of steel instead of a pile of ferromagnetic dust, is much stronger than the bond that holds a sheet of paper together into a sheet of paper instead of a pile of pulp. So it takes a lot more energy to break that bond.

Thanks for this expanded version of the first concept:

General heat transfer when turning is that about 70-75% of the heat generated is transferred to the chip, 10% to the cutter and the remainder to the material being cut.

This will help me on the lathe. I've noticed sometimes chips are less hot and the workpiece gets too hot. It seems now that it means I was doing something wrong. Wrong cutter geometry I assume.

 

[MrCrankyface]

I would probably use the term molecular bond but I am far from an expert on the subject. I imagine a very basic type of paper would just be a great amount of cellulose molecules in chains. Again guessing but maybe in a semi-crystalline manner.
Some polymers behave like that so it makes intuitive sense(to me) that paper would but I'm sure it can vary wildly depending on additives.

Metals, if we look at pure iron for example, has metallic bonds. The atoms themself are wildly attracted to eachother(Similar to electromagnets) and start sharing electrons.
This is one of the strongest bonds there is as far as I can remember at the moment.
The strength of the bond can of course vary wildly depending on the metal itself, the melting temperature is usually a good indicator of how strong the bonds are. I believe 'metallic bonding' will get you a lot of informative hits to dive deeper into.
I believe their electronegativity was also related to their bond strength and thus melting temperature.

pontiac428: entropy of breaking metal bonds releasing heat confuses me. Would this not mean that melting a metal would make it even hotter than "inserted" heat energy?
Also pouring energy into the metal would sure break the bonds, not reform them? Forgive my phrasing if it's rude, it's not my intention.

 

[pontiac428]

A crystal structure is a low energy state but has order and takes energy input to create. When a crystal is broken, the energy of that order is released as heat. It moves towards a state of disorder. To bring order back to disorder, you put energy in. Remove most of the energy from matter, and the result is a neutron star. Remove the matter from energy, and you have cosmic background radiation. Break a bond and you remove energy from the system, releasing heat.

Friction and other forces are all transformed from the spindle's power. The heat of cutting is that plus energy released from the cut.

 

[strantor]

A crystal structure is a low energy state but has order and takes energy input to create. When a crystal is broken, the energy of that order is released as heat. It moves towards a state of disorder. To bring order back to disorder, you put energy in. Remove most of the energy from matter, and the result is a neutron star. Remove the matter from energy, and you have cosmic background radiation. Break a bond and you remove energy from the system, releasing heat.

Friction and other forces are all transformed from the spindle's power. The heat of cutting is that plus energy released from the cut.

See I knew this discussion would go into the ether at some point; into the infinite realm of things that are over my head. When I see the word "entropy" I choose to pretend I didn't. I've got mental battle scars from trying to wrap my head around that. Neutron stars? I don't even want to know what you're talking about . I'll settle for "Nearly all of the energy provided by the motor ends up in the chips."

 

[pontiac428]

"Nearly all of the energy provided by the motor ends up in the chips."

Yes, what energy isn't converted to noise is released as heat. Plus the bond energy released.

Regardless of how it works, I adjust my surface speed, DOC, and feed rate by reading the chips on both mill and lathe. Finish is important, but the chips tell all.

If it sounds like reading tea leaves, here's a diagram to help:

 

[strantor]

It’s called plastic deformation and is a state the metal goes through as part of the cutting process.

Imagine pushing clay with your hand and how it would pile up in front of it before curling up and flowing away in some direction.

ETA: Found a good video n this.

Thanks, that video was just about on my level. It was very interesting to see the formation of chips at that scale and speed. Good and bad surface finishes make a lot more sense now. And after seeing everything that chip has just been subjected to when it flies free, the heat makes more sense too.

Why are all the best practical demonstration videos from that time period? It seems we have lost some skill in educating over the years.

 

[pontiac428]

It seems we have lost some skill in educating over the years.

Ain't that the truth? Whatever happened to the Henry Ford Trade School? Oh, nevermind- they made the machinery smart and the people who run it cheap, then they sent the work overseas. Emphasis on marginal gains in profit have killed education. Corporate duty to provide returns to shareholders have cut developmental programs, in favor of bare base OJT. We've lost a lot of our nation's strength to it.

 

[strantor]

Yes, what energy isn't converted to noise is released as heat. Plus the bond energy released.

I think I understand what you're saying; if I've got it right (or close enough), just nod, because I am already at the limit of my comprehension. I think you're saying that the total energy released in cutting is greater than the energy consumed by the motor, because of some abstract woowoo juju akin to nuclear fission that occurs when the metalic bonds are severed, so the chips may be hotter than can be accounted for by the oversimplification "Nearly all of the energy provided by the motor ends up in the chips?"