Feed rate to reduce dross

[professor]

I recently finished my CNC plasma cutting table and I am having trouble with dross on 16ga sheet metal. I am using a Hypertherm Powermax600 plasma cutter. I was setting the cut speed to 105 ipm at 35 amps and I seemed to be getting a OK quality cut with a little low speed dross. This was not too bad because the dross cleaned up easily. Then on a few cuts later the dross seemed to get very hard and difficult to clean up. I tried changing the feed rates but there was not any difference. Then I tried changing the consumables but this made no difference. I am using the consumables that came with the cutter tip PN 120826. I cannot find any information about that tip on the Hypertherm website so I do not know if the tip is just not good for what I am trying to do.

Any tips, suggestions, will help.

Thanks,
Paul

[jimcolt]

You don't say anything about how you are controlling torch height....fir cutting gauge material torch to work distance is extremely critical to control cut quality and dross. Assuming you can ensure that the torch to work distance is being maintained accurately, the next step is to use the machine cutting parameters listed in the Powermax600 operators manual. Use the part numbers suggested for machine cutting regardless of whether you are using a hand or machine torch, and follow the optimum speed listings, amperage settings, torch height and pierce height for all materials. If you do not have the manual, it can be downloaded (free) from Hypertherm | Plasma Cutters | Plasma Cutting Equipment | Metal Cutting Equipment , click on document downloads at the top of the home page, choose your system. Also on the Hypertherm page are cmplete listings for part numbers and consumable sets for every Hypertherm system ever produced....go to Products, consumables, then choose your system. Here is a link to the consumables available for your Powermax600: https://www.hypertherm.com/library/f...wermax600H.pdf

For best cuts with a 600 on 16 gauge, use the FineCut parts, and follow the cut specs in the manual. The cuts will be virtually dross free (with correct speed and height.

Jim Colt Hypertherm

Originally Posted by professor I recently finished my CNC plasma cutting table and I am having trouble with dross on 16ga sheet metal. I am using a Hypertherm Powermax600 plasma cutter. I was setting the cut speed to 105 ipm at 35 amps and I seemed to be getting a OK quality cut with a little low speed dross. This was not too bad because the dross cleaned up easily. Then on a few cuts later the dross seemed to get very hard and difficult to clean up. I tried changing the feed rates but there was not any difference. Then I tried changing the consumables but this made no difference. I am using the consumables that came with the cutter tip PN 120826. I cannot find any information about that tip on the Hypertherm website so I do not know if the tip is just not good for what I am trying to do. Any tips, suggestions, will help. Thanks, Paul

[professor]

Hi Jim Thanks for the reply.
Currently we are using the hand torch on an adapter to get it to work on our CNC table. We are using the drag tip on the torch so the torch is draging on the surface.
One of the strange problems was that the cut quality changed as we were from one part to another. Some parts had dross that was easily removed and other parts has hard dross. I did reposition the sheet. Is it possible the ground was not as good?
I have downloaded the manual I will give it a look.

Thanks,
Paul

[jimcolt]

More than likely it is not a ground issue. It is a torch height issue. You are piercing and cutting at the same height, and by piercing with the torch contacting the plate you likely are creating a little more nozzle orifice damage with each successive cut.
A full featured height control will sense the plate surface, retratc the torch to the recommended pierce hights (usually 2x the cut height) allow the pierce to complete them index the torch to cut height and maintain that accurately throughout the cut. This eliminates nozzle damaging pierce splatter, and maintains the correct cut height for best angualrity, least dross.

With your setup....here are couple of tips that will minimize dross:

1. Try going faster in 10 ipm increments until the dross goes away. Faster will produce less dross.
2. Spray mig welding anti spatter spray on the bottom side of the plate....this gives the resolidifying molten metal less opportunity to grip the back of the plate.

Height control systems on cnc machines are a little costly, but worth their weight in gold if you are looking for cut quality and consumable life! When I cut 16 gauge with my Powermax45 on my cnc machine (with full featured THC)....there is no dross!

Jim Colt

[professor]

Thanks again Jim,

We do have a system that touches the plate to get the height and moves to .2 inches for the piercing. It seems when we go faster the torch does not cut through the material.
Also, something I thought of when we changed the consumable the sound of the torch changed. When cutting the torch sounds louder (like a rocket sound).

Do you think the machine torch shound be befor the THC? I seems like we need both. do you have any experience with the THC form CandCNC?

I am going out today to get he fine cut consumables.

Thanks,
Paul

[jimcolt]

You said your were drag cutting....so I assumed you did not have a torch height control.

If you have a height control...use the parts listed in the manual for mechanized cutting, especially the shield. Do not use the drag shield, and it does not matter that you are using a hand torch. Set the pierce height at 2x the cut height (from your manual under mechanized cutting specs) and also set the cut height as the manual suggests. Drag cutting is for hand cutting only.....unless you have a machine that is designed for drag cutting such as the older PlasmaCam model 98-z.

Jim

[professor]

I do not have an automating THC I only set up a system that touches the surface of the plate then sets the surface of the plate as Z 0.0 to the tip of the torch. Then the tip drags on the surface of the plate.
I was looking at the suggestions for the torch and there are values given for torch voltage. Where on the Powermax600 can this voltage be measured?

Paul

[jimcolt]

The arc voltage, which can be measured between the electrode and the workpiece, is good as a reference voltage. In other words if you are cutting at a known height off the plate at a fixed speed, the voltage will remain constant. If you raise the torch height the voltage will increase. In plasma torch height control systems this voltage is the feedback to maintain a constant height......but is affected as well by cut speed changes (slower cut speed equals higher arc voltage).

It is most important to maintain a physical height as recommended in the plasma system operators manual. The voltages recommended in the manual will be correct if the cut speed also recommended is maintained, and the consumable parts that are listed on the same page are used.

Jim

Jim

[professor]

Jim,
Where is the best place to get measure the electrode voltage from? I am planning to use a data logging volt meter and record the arc voltage as the cut is being made.

I have been thinking of this THC.
http://www.candcnc.com/LCTHC.html

We are planning to use the plasma cutting system to make decorative items so direction changes and irregular cuts will be standard for us. If speed affects the arc voltage will the type of work we are planning to do be a problem of a THC system?

Thanks,
Paul

[jimcolt]

Torch height control must be interfaced with your cnc control, and the cnc control will freeze the z axis whenever the cutting speed decelerates below a preset speed percentage to minimize diving on slowdown. This technology has been used for over 40 years with cnc plasma cutting machines. If you are looking at the Cand CNC THC systems, Tom Caudle can explain the workings of his equipment better than I can.

I don't have the operators manual for a Powermax600 handy, but the arc voltage can be read from the work cable (sometimes called ground clamp) that attaches to the plate you are cutting to the cathode connection that goes through the torch leads to the torch electrode. It is safest to trace these connections (using a meter) back into the power supply and make your connections there. The electrode is negative, the work lead is positive. Be careful,the voltage can be above 250 VDC open circuit.

Jim Colt