Cut Quality

[miketodesca]

Hi,
I am new to this forum, but have been trying to get my plasma cutter to work properly for the better part of 2+ years.
I have run quite a bit of work on the machine, but with less than desirable results.The saving grace is that we have to finish machine pretty much everything we have run.

The machine is a4' X 8' precision plasma gantry,candcnc control, hypertherm65 plasma cutter.

I have checked arc gap, earth grounded the machine,light bulb tested,removed the setscrews on the motor gears,loctite & reinstalled all of the setscrews, installed a motor guard filter and a small air tank to maintain pressure,tried grounding the table as well as the material,and I still get poor quality cuts.

The last parts we ran were in 1/4" Steel. used factory settings 1 part looked good and was consistent. The second part was cut using the same plate, same settings, and looked awful.consumable life is minimal.

I believe that the machine and components we have should be capable of doing a much better job than what is being done now. I need this machine to run properly and as accurately as possible. Any help would be greatly appreciated! Thanks.

[Largemouthlou]

Post some pictures of your results may help diagnose problem..

[tnbndr]

Are you using a machine torch or hand torch?
Hypertherm consumables or Chinese knockoffs?
A lot of things affect cut quality.

[jimcolt]

Some pictures of parts that you have cut would be good. Consistency with plasma cutting is the result of using the same settings (pierce height, pierce delay time, cut height, arc voltage (the correct voltage to maintain the recommended physical height), cut speed, amperage, etc. If all of these parameters are maintained cut to cut, and day to day, then you will get the same cut quality on a day to day basis. The plasma system itself has a bit of a learning curve as well.....and requires clean dry air at the right flow and inlet pressure. It needs periodic consumable parts inspection (especially the shield, the nozzle and the electrode) in order to cut with the consistency that it is capable of. Bottom line, there are a lot of parameters that need to be set correctly and consistently with any plasma cutter in order to achieve repeatable performance.

The fact that you say one part cuts acceptably, then the next does not....clearly indicates to me that something is changing from part to part. It could be the height is not consistent, it could be that slugs of moisture are getting to the torch altering its performance, it could be that the first part was piercing too closely and damage occurred to the shield or nozzle that affected cut quality on the second cut.

Provide some pictures of your cuts (good one and bad ones, show edges around the perimeter), pictures of the consumables.....specifically closeups of the nozzle orifice and shield orifice that were used for unacceptable cuts, from these we can help steer you in the right direction.

Further, let us know material types and thickness, power levels you are using, and last but not least....what equipment (motors, drives, THC), etc on your machine. I'm sure we can help.

Jim Colt Hypertherm

Hi,
I am new to this forum, but have been trying to get my plasma cutter to work properly for the better part of 2+ years.
I have run quite a bit of work on the machine, but with less than desirable results.The saving grace is that we have to finish machine pretty much everything we have run.

The machine is a4' X 8' precision plasma gantry,candcnc control, hypertherm65 plasma cutter.

I have checked arc gap, earth grounded the machine,light bulb tested,removed the setscrews on the motor gears,loctite & reinstalled all of the setscrews, installed a motor guard filter and a small air tank to maintain pressure,tried grounding the table as well as the material,and I still get poor quality cuts.

The last parts we ran were in 1/4" Steel. used factory settings 1 part looked good and was consistent. The second part was cut using the same plate, same settings, and looked awful.consumable life is minimal.

I believe that the machine and components we have should be capable of doing a much better job than what is being done now. I need this machine to run properly and as accurately as possible. Any help would be greatly appreciated! Thanks.

[OTHill]

Your equipment sounds the same as mine and definately is capable of very precise good looking cuts.I am amazed time and again at the quality and consistency of cuts.Follow the above instructions and good luck.
PS I am using a hand torch and don,t think a machine torch would do any better.

[Zippo]

Reference Cut Quality

When talking about set-up your cut quality it is a combination of Speed, Height, and Amperage. Each one of these values will have an effect on the quality of cut in every type of material. When talking about quality, I would define that as Bevel (angle of the face of the cut) and Dross (slag building on top and bottom of the material). Kerf, or Cut width is a factor as well, but because most machines have the ability to offset for this width, it doesn't tend to matter nearly as much as the Bevel or Dross. If you run a Line Speed test at a particular set height and amperage. Most plasma cuts on .125" material and thicker , usually recommend running at or above 40 amps. Thermal Dynamics and Hypertherm cutters recommend a cutting height of approximately .125" to .1875" for these amperages. This is set value number one for your line speed test. The Amperage is a matter of installing the correct tip into the torch head, and setting the amperage value on the face of the plasma cutter to match this tip, +/- 5%. With the second part of this equation is then set. At these values run your line speed test. As the pictures illustrate , basically run from too fast to too slow, 130 to 10 inches per minute (ipm) at 10 ipm intervals. With this coupon of material cut out, You can easily look at the Bevel, Dross, and even measure kerf width from it at our best cut speed. Say none of the cuts look good, You can make an adjustment to the height or amperage and run the same test again. This is an easy way to determine appropriate values for your Speed, Height, and Amperage.

SPEED: If your speed is too fast, you will usually experience a wider cut at the top of the material, to a skinnier cut at the bottom with a small bead of dross that is difficult to remove. If the speed is too slow you will have a wide kerf, with good bevel but large dross accumulation. While the bevel may be good, and the dross easy to remove, cutting too slow will result in longer cuts for paths, quickly degrading consumable life, and excessive warpage of the material. A correct speed results in a uniform dross accumulation of manageable proportions and good bevel defined as 3-8 degrees of bevel by the plasma cutter manufactures.

HEIGHT: If you height is too far away from the material, you will have a wide bevel at the top of the material, and the torch may have trouble extending the arc that far resulting in missed cuts, and bad consumable life. If the height is too low, you will have a wide bevel at the bottom of the cut, and may have trouble piercing the material or keeping the torch going if it comes into contact with the material during a cut. On both Thermal Dynamics and Hypertherm plasma cutters, if the tip comes into direct contact with the material at an amperage higher then 40, it will automatically reduce it's amperage output to 40 amps. For example, cutting at 80 amps it would reduce your cut capacity be half, and you will more then likely lose your pierce at this point. With correct height, you should have appropriate bevel, and it won't be stressing the torch by being to far away or possible damage the cut or consumables by touching it.

AMPERAGE: This one is a little trickier, and when running a line speed test comes in handy. You can cut .125" plate with 100 amps, and you could probably run it at a rapid speed that would make the cut look decent. Just because you can, doesn't mean you should. You can make the same cut at a reasonable speed with much less heat distortion running 40 amps. It is always recommend running the lowest amperage possible that the line speed test determines gives you the best cut. This will reduce duty cycling and air consumption.

Little Note:
Cut direction matters, when dealing with Plasma, the right hand side of the torch moving away from you will give you less degrees of bevel, and less dross. This is due to the circulation of plasma coming out of the tip. This means Clockwise external (male) cuts, and Counter-Clockwise internal (female) cuts.

Quality of air also matters. Having moisture in the air lines not only decreases consumable life, but it can also have an effect on your cut quality. The results may be negligible (Very small or insignificant), but I have heard of reports of less dross on the cuts from people who have changed their air system to run a dedicated air dryer for their Plasma cutter.
Volume of air has its consequences as well. You should have at least 75psi to 85 psi. The longer the torch lead the higher this should be.