CNC Plasma Cutting - Part Warpage

[Mike_will8]

Was working with @Janger over the weekend on the CNC Plasma table, cutting his stock (3/8" I believe it was) into strips.

What we noticed was that, even though we were using CNC to cut straight lines, as the cut proceeded the metal was warping due to the heat to the point that the final cut pieces really were not that straight.

@CalgaryPT , @kylemp what do you two reccomend for combatting part warping, presumably from the heat buildup? (Is this a relatively common issue with thicker stock? I haven't come across the issue with thin stuff.)

Possibly related, when we went to move the parts, some of them had bonded to the supports, like the slag had pinned the parts to the supports. Could this be related?

@Janger , could you snag some pics or measurements of those flat bars to help convey the issue?

JW

 

[DavidR8]

I'm guessing the table doesn't have a water table?

 

[phaxtris]

cutting strips always has this problem, a water table will help, faster travel speed (if possible) helps. Constraining the pieces will also help, it will still not yield you with a 100% straight piece, but it will be better than with no restraint.

The longer and thinner the strip the worse it gets.

The problem with a strip is that there often isnt enough material to restrain the expansion and shrinkage on the cut edge. Something that helps is to tack the pieces back together behind the cut, while cutting. Depending on the length of cut, speed, thickness, these tacks often need to be somewhat substantial, there is often enough force from the expansion/contraction to break the tacks.

Unless you can do it completely under water i don't know that it is possible to 100% avoid this problem, when steel is heated it expands...we all know this, but if heated hot enough (melting, or red hot, like in a plasma or torch operation) it will actually contract smaller that the original size when it cools, this is why torch straightening works.

If its worth it to you the metal cutting circular saws work extremely well for this task, much more pricey due to the blade cost

 

[Janger]

Was working with @Janger over the weekend on the CNC Plasma table, cutting his stock (3/8" I believe it was) into strips.

What we noticed was that, even though we were using CNC to cut straight lines, as the cut proceeded the metal was warping due to the heat to the point that the final cut pieces really were not that straight.

Forum members - I have no idea who this "Mike_will8" person is, I was not doing this activity with them or anyone. Caution!

 

[phaxtris]

Forum members - I have no idea who this "Mike_will8" person is, I was not doing this activity with them or anyone. Caution!

wierd

 

[Ironman]

I'm going to say your cut speed is too slow, or you have an undersized machine that can't cut at a decent speed, because too slow will heat the plate excessively, and you will have a major gob of slag on the backside.

 

[DavidR8]

Mike_will8 has been banned.
This is definitely the most sophisticated scammer I've seen.
Not sure of the logic of naming members who could verify legitimacy but at the same time naming members gives almost instant cred.

 

[PeterT]

Forum members - I have no idea who this "Mike_will8" person is, I was not doing this activity with them or anyone. Caution!

Creepy. He seemed so helpful.

 

[CalgaryPT]

Was working with @Janger over the weekend on the CNC Plasma table, cutting his stock (3/8" I believe it was) into strips.

What we noticed was that, even though we were using CNC to cut straight lines, as the cut proceeded the metal was warping due to the heat to the point that the final cut pieces really were not that straight.

@CalgaryPT , @kylemp what do you two reccomend for combatting part warping, presumably from the heat buildup? (Is this a relatively common issue with thicker stock? I haven't come across the issue with thin stuff.)

Possibly related, when we went to move the parts, some of them had bonded to the supports, like the slag had pinned the parts to the supports. Could this be related?

@Janger , could you snag some pics or measurements of those flat bars to help convey the issue?

JW

Testing my memory here...but I believe speed and torch power are the factors. I used the Hypertherm mechanized guidelines in the manual on their site to cut a bunch of sign bases for Janger years ago. They were 3/8" I think. Just a little tweaking WRT speed. I know people like to debate the water cooling theory, but I found it has no or minimal effect on cooling; it's just for dust collection.

Also, check the ground connection. The bonding to supports may be caused by this issue.

 

[Janger]

other factors... Torch height and torch height consistency as material is not perfectly flat. So is the height fixed or do you have a automatic height adjustment?. Type (quality) of torch, torch cutting angle. Air flow CFM, and air pressure. Dry air. Adequate steady and consistent air supply. Voltage and current to the torch - what voltage and current and is the power supply adequate (duty cycle). There is a lot to get right.