Problem cutting 3mm stainless

[sjclaser]

Hi all,
I am cutting 3mm stainless with a 2.2kw bystronic bysprint but having problems. When cutting holes approx 10mm dia, the head comes down pierces fine, and then cuts around - but, when it is approx half way round the head keeps moving but jumps up slightly and then down again to 1mm clearence. Its like there is a lump on the sheet it is jumping over.. but there isn't and the pierce isnt leaving any lumps on the surface!! Any ideas would be much appreciated!

Because it jumps up, the focal point goes out and you get a horrible bubble on the bottom edge of the hole.

There is a video of it at

https://www.facebook.com/photo.php?v=10152271648174783&l=4168832280394757367

which shows it best on the first hole. It does it on most holes but not all.

Many thanks for any help given!!
Best regards,
SJClaser

 

[MacGyverS2000]

What does the G-code look like?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[berkshire]

Check your Z axis on the toolpath.
B.E.

You are judged not by what you know, but by what you can do.

 

[berkshire]

Also,
check to see if an M code got slipped into the middle of a cut.
B.E.

You are judged not by what you know, but by what you can do.

 

[sjclaser]

Hi all,
Thanks for your replies. Right I have finally done some more tests and I am sure it is not the code. I nested 1 of the parts (disc 3.5mm I/d 12mm o/d) on a small blank. I then cut this program many times on the same sheet and same parameters etc. One will cut fine, then on another the head will rise up slightly on the outer circle in one place, and some times it would rise up twice while cutting the outer circle. When rises up it affects the focal position and the cut is bad or doesn't cut through at all! Where the head is at the right height the cut is perfect!

Can it be to do with the sensitivity of height sensing? cut control or something? I also slowed the cutting speed right down from about 3000mm per min to about 1000mm/min, and the same problem exists. I did this to prove it is not because it is going to quick to cut through and then looses the cut.

Any help would be really be appreciated - its driving me mad!! Thanks Sjclaser.

 

[krugtech]

make sure you use bystronic ceramics in the head. aftermarket ceramics are too porous. make sure there's no internal leaks either, high pressure N2 can blow on the electronics and destabilize them from the resulting temperature swing.

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[sjclaser]

Hi,

Thanks Krugtech for the reply. The ceramics are from bystronic. When you say internal leaks, you mean leaks in the head? cutting larger circles (e.g. 25mm dia) are absolutly fine... so if it was an internal leak would it not affect all circle sizes?

When ever i have cutting problems, i ring bystronic and the first thing they say is nearly always 'clean the ceramics in the head'!! I don't understand how the head works and why they need such clean ceramics - surly all ceramics do is stop heat getting up to the lens? Ceramics do not conduct electricity so they surly can't have much to do with height sensing do they??

Any help is always very much appreciated. Thank you very much.

 

[krugtech]

is th ehead tight on the z-axis? there should beno gap between the head and mount. The cermaics are not for heat, the entire nozzle body is insulated from the head and radio waves detect the material. Only high quality ceramic can insulate radio waves properly.


Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[sjclaser]

Thanks Krugtech, i never knew it was radio waves! Im sure the head is tight on the Z axis. I just cant figure it out. I have noticed when the head comes down it seems to go right down to the sheet (but not dent it or move it) then quickly go back up to the pierce height (say 2mm), pierces, then drops down to cutting height (1mm). It does this very quickly, and on every peirce. I am sure it never used to do this, and im sure the 7.5" head doesn't do it!!

If the pierce height is set to 1mm (same as cutting height) then it doesnt seem to do this. Cant work out why it goes down to the sheet first then up to the pierce height!

thank you for all help given.
Best regards.

 

[krugtech]

watch the z-axis dimension on the computer screen while cutting. what you are looking for is if the number on the screen reflects the behavior of your z-axis. If you can see the nozzle height is correct, then the head jumps and the nozzle height is about the same but suddenly the number on the screen is of say 1 or 2 mm and you know it did not change that amount, there's slop in the drive. Slop between the encoder and axis itself, either bearings are sot or the coupler is busted.

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[GrouperGenius]

I'm not familiar with Bystronic, but in our Amada laser cut conditions there is a value for thickness of material. Maybe something got changed there??

 

[SGAFFNEY]

In your original post you wrote

but, when it is approx half way round the head keeps moving but jumps up slightly and then down again to 1mm clearence. Its like there is a lump on the sheet it is jumping over.. but there isn't and the pierce isnt leaving any lumps on the surface!!

Are you sure? I know that the pierce is done quickly but in nitrogen cutting (and piercing) you are just melting the material and not vaporizing it. Until the pierce is complete and there is a hole in the sheet the melted material has no place to go but back up and can sometimes create the situation you have described. I am used to working with LVD lasers and when you look at the pierce point you usually see little fingers of stainless spreading out from the pierce hole. These can cause the cutting head to jump with the Precitec capacitive sensing system that LVD used.

On the LVD lasers that I am familiar with the post processor would change the code for small holes in stainless to help with this. For small (less than 24 mm dia) holes we would issue a G code to lock the height of the cutting head (z-axis) after piercing and after the nozzle height was set for cutting to prevent the head from jumping. It was assumed that the plate would be level enough in that small of an area that not following the plate would not cause the nozzle to hit the plate. Again, this was only done for small holes. Krugtech could tell you if anything similar is used for the Bystronic or if he has seen this in the past.

Good Luck!

 

[HenryRollins]

have you gotten any "plausibility errors" recently?? Does this problem happen with only one cutting head??
-HR

 

[tstc]

Have you 'really' checked the code?
Make sure the element (outer or inner circle in this case) only contains one contour.
If using Bysoft, use the 'Display Options' to show 'End of Contours' in the 'Geometry' section.
Machines hate 'unclean' code, and this is quite common when importing from a DXF or similar.
Bystronics, when faced with this, jump around, skip parts, quit cutting halfway through etc.
Pain in the @$$ trying to convince the customer, 'machine is fine', its 'your programming!!' (spoken from experience )