I am using hypertherm 45 with 45 amp consumable (machine torch) and arc voltage is 120 and 42 to 47 ipm. The material is 304 SS and when we cut it at the recommended specs as per the hypertherm manual it does not cut good. There is lots of low speed dross, some tapering in different areas etc. Also where the torch stops and ends (both at the holes and outside edges) it is not smooth. How do we start and stop properly to get a smooth final cut at this point? We have tried lead out, slowing down the speed at the end, pausing at the end for a overburn with no luck.
See images.
We have have read Jim Colts presentation on cutting holes at http://www.metalwebnews.com/howto/plasm ... tation.pdf and was useful and it works good with carbon steel. We have cut this exact piece with carbon steel (using the parameters recommended) and it cuts perfect.
What parameters do you suggest we start with?
Thanks
Dan
1/4 stainless steel cutting problem
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DanUBCUSTOM
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1/4 stainless steel cutting problem
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jimcolt
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Re: 1/4 stainless steel cutting problem
Dan,
I wrote a lengthy response to this earlier this morning....however before I submitted it the site crashed and I lst everything I wrote! I'll try again...
First, let me explain the differences between plasma cutting stainless steels and carbon steels. Carbon steel oxidizes easily, stainless, especially 300 series, does not. The best way to cut carbon steel is with a high temperature plasma arc that is created with oxygen as the plasma gas. Using oxygen adds an exothermic reaction to the cutting process (similar to oxy fuel and oxy laser) that increases cut speeds, allows for lower power levels, increases edge squareness, and improves metalurgy (softer edge). Oxygen plasma systems are much more difficult to control in terms of consumable life and cut quality.....so oxygen plasma systems tend to have far more complex power supply, gas flow control, and torch designs, increasing the price, and generally pushing them into the industrial plasma market.
Air plasma systems take advantage of the exothermic reaction on a smaller scale....as air has roughly a 20% oxygen content. Because the majority of the content of air is nitrogen, it is relatively easy to control, and generally air plasma torches are limited to 100 amps and less for best performance in terms of low capital equipment cost and acceptable cut quality/consumable life.
So, for cutting steel with an air plasma.....you get the high temperature, high enrgy density plasma jet, combined with an exothermic reaction that can produce a resonably square cut edge with decent speed at relatively low power levels. When you cut stainless steel with an air plasma....since SS is not easily oxidized, you only have the high temperature arc doing the cutting...effectively melting the material and using the velocity of the arc to blow it out the bottom of the kerf.
Consequently, cuts on stainless steel with an air plasma are not comparable in edge squareness or accuracy to a similar cut on carbon steel. Many of the higher end industrial plasma systems with accurate gas flow control systems use special gas mixes (argon/hydrogen, hydrogen/nitrogen) as a plasma gas and nitrogen as a shield gas to provide a cleaner cut edge....but even with the best high definition class plasma systems there is more taper in the cut edge than on carbon steel. Lasers use a technique commonly called "high pressure nitrogen" cutting to produce nicer, squarer edges on stainless.....unfortunately the high flowrates involve with this type of process do not work (with todays technology) with plasma.
It does sound like you can make some improvements in your situation.....I have a Powermax45 on a cnc machine in my home shop, and I have been succesful with cutting up to 3/8" stainless steel for a few applications. I will post a picture of a stainless cutting job I did last year...interestingly it was cutting 5 1/4" 304 SS signs for 5 Hypertherm plants located in the Lebanon, Hanover NH area!....I'll post that on another message.
The fact that you have noticed variation in cut angularity around you part indicates one of two things.....either the torch is not perpendicular to the plate, or the consumables are damaged, especially the nozzle or shield. The single most common thing I run into with plasma cutting is cut edge angularity /variation. Almost always it is caused by nozzle damage that can occur on the first pierce. You did not provide details about your cutting machine....so I'll have to assume that you have very smooth motion, and I am assuming that you have a full featured THC (torch height control) that has the ability to find the surface of the plate, retract to the recomended pierce height, hold at this height through the recomended pierce delay time, then index rapidly down to the physical cut height, then maintain that physical height throughout the cut....to within plus or minus .010".
Here's what I would suggest:
Put new consumables in your torch, make sure they match the part numbers in the Powermax45 mechanized cut chart suggestions for stainless steel cutting.
Settings
Set cut speed to 40 IPM
Amperage 45 Amps
Pierce height: .200" (critical)
Pierce delay: .6 seconds (critical)
Physical cut height: .08"
Arc voltage: 121 volts
You may have to do a couple of test cuts as there are some slightly different THC calibrations, as well as variations in alloying on the SS plates. Start with the exact settings above and observe:
1. Torch finds the surface and retracts to .200". Measure this if you can. There are many different methods of finding initial height....accuracy is a must. As I said earlier, one pierce too close to the plate will blow back material that will cause a nick in the nozzle orifice, and cause varying cut angularity.
2. Ensure that after the torch retracts to pierce height and the torch fires....that it stays at that .200" height until after the pierce delay times out..this allows the molten material to avoid the nozzle orifice, and finished piercing the plate. If the torch moves before the pierce is complete...increse the pierce delay time.
3. As soon as the pierce delay times out and the sparks are going through the bottom of the plate....watch that the torch indexes down quickly to the physical cut height of .08", this move should be complete before any x-y movement of the torch occurs. It is important that this move is completed while the torch is at the beginning of the lead in....because at the same time the torch moves down, the gas flows have changed slightly from pierce to cut flows, and it takes a few miliseconds for them to stabilize. If possible, or necessary, increase you lead in length.
4. Ensure the torch is at .08" when it starts moving to the cut path......soon after it is on the cut path the arc voltage feedback control loop of the THC takes control of torch height. If you see the torch either rise, or get closer to the plate soon after x-y movement....then you should adjust te arc voltage so that .08" cut height is maintained. The arc voltages listed in the Hypertherm manual are correct on a perfectly calibrated system at the cut speed listed with new elctrode and nozzle in the torch, however it is common to have to make adjustments....and the physical torch to work distance is more important than your voltage reading. If the torch is too close, increase the voltage until it is correct, iff too far away, decrease the voltage......when you change the voltage during steady state cutting you should see the torch height change.
Once you are sure that all of the above is operating as described....you can go back and adjust cut speed. I usually start at exactly book recommended (not maximum) speeds, and if I need a little better edge squareness I will try 10% slower, or if I am trying to minimize dross formation, I will go faster about 5% faster on each test until I see aresult that I like. Once the speed is dialed in....you may have to go back and readjust the arc voltage to get the height correct...as speed changes affect height. Faster speed requires a lower voltage, slower speed a higher voltage. Using this technique you should be able to get a reasonably good cut on 1/4" stainless with your system. It will not be 100% dross free, but the dross will file or grind off easily. With more power (perhaps 80 amps) you can expect dross free cutting on 1/4" SS.
One other thing....make sure your air is clean and dry. Moisture is a very common problem this time of year in compressed air systems.
Let me know if this helps. I will post a picture of some stainless that I have done using the above specs / procedure.
Jim Colt
I wrote a lengthy response to this earlier this morning....however before I submitted it the site crashed and I lst everything I wrote! I'll try again...
First, let me explain the differences between plasma cutting stainless steels and carbon steels. Carbon steel oxidizes easily, stainless, especially 300 series, does not. The best way to cut carbon steel is with a high temperature plasma arc that is created with oxygen as the plasma gas. Using oxygen adds an exothermic reaction to the cutting process (similar to oxy fuel and oxy laser) that increases cut speeds, allows for lower power levels, increases edge squareness, and improves metalurgy (softer edge). Oxygen plasma systems are much more difficult to control in terms of consumable life and cut quality.....so oxygen plasma systems tend to have far more complex power supply, gas flow control, and torch designs, increasing the price, and generally pushing them into the industrial plasma market.
Air plasma systems take advantage of the exothermic reaction on a smaller scale....as air has roughly a 20% oxygen content. Because the majority of the content of air is nitrogen, it is relatively easy to control, and generally air plasma torches are limited to 100 amps and less for best performance in terms of low capital equipment cost and acceptable cut quality/consumable life.
So, for cutting steel with an air plasma.....you get the high temperature, high enrgy density plasma jet, combined with an exothermic reaction that can produce a resonably square cut edge with decent speed at relatively low power levels. When you cut stainless steel with an air plasma....since SS is not easily oxidized, you only have the high temperature arc doing the cutting...effectively melting the material and using the velocity of the arc to blow it out the bottom of the kerf.
Consequently, cuts on stainless steel with an air plasma are not comparable in edge squareness or accuracy to a similar cut on carbon steel. Many of the higher end industrial plasma systems with accurate gas flow control systems use special gas mixes (argon/hydrogen, hydrogen/nitrogen) as a plasma gas and nitrogen as a shield gas to provide a cleaner cut edge....but even with the best high definition class plasma systems there is more taper in the cut edge than on carbon steel. Lasers use a technique commonly called "high pressure nitrogen" cutting to produce nicer, squarer edges on stainless.....unfortunately the high flowrates involve with this type of process do not work (with todays technology) with plasma.
It does sound like you can make some improvements in your situation.....I have a Powermax45 on a cnc machine in my home shop, and I have been succesful with cutting up to 3/8" stainless steel for a few applications. I will post a picture of a stainless cutting job I did last year...interestingly it was cutting 5 1/4" 304 SS signs for 5 Hypertherm plants located in the Lebanon, Hanover NH area!....I'll post that on another message.
The fact that you have noticed variation in cut angularity around you part indicates one of two things.....either the torch is not perpendicular to the plate, or the consumables are damaged, especially the nozzle or shield. The single most common thing I run into with plasma cutting is cut edge angularity /variation. Almost always it is caused by nozzle damage that can occur on the first pierce. You did not provide details about your cutting machine....so I'll have to assume that you have very smooth motion, and I am assuming that you have a full featured THC (torch height control) that has the ability to find the surface of the plate, retract to the recomended pierce height, hold at this height through the recomended pierce delay time, then index rapidly down to the physical cut height, then maintain that physical height throughout the cut....to within plus or minus .010".
Here's what I would suggest:
Put new consumables in your torch, make sure they match the part numbers in the Powermax45 mechanized cut chart suggestions for stainless steel cutting.
Settings
Set cut speed to 40 IPM
Amperage 45 Amps
Pierce height: .200" (critical)
Pierce delay: .6 seconds (critical)
Physical cut height: .08"
Arc voltage: 121 volts
You may have to do a couple of test cuts as there are some slightly different THC calibrations, as well as variations in alloying on the SS plates. Start with the exact settings above and observe:
1. Torch finds the surface and retracts to .200". Measure this if you can. There are many different methods of finding initial height....accuracy is a must. As I said earlier, one pierce too close to the plate will blow back material that will cause a nick in the nozzle orifice, and cause varying cut angularity.
2. Ensure that after the torch retracts to pierce height and the torch fires....that it stays at that .200" height until after the pierce delay times out..this allows the molten material to avoid the nozzle orifice, and finished piercing the plate. If the torch moves before the pierce is complete...increse the pierce delay time.
3. As soon as the pierce delay times out and the sparks are going through the bottom of the plate....watch that the torch indexes down quickly to the physical cut height of .08", this move should be complete before any x-y movement of the torch occurs. It is important that this move is completed while the torch is at the beginning of the lead in....because at the same time the torch moves down, the gas flows have changed slightly from pierce to cut flows, and it takes a few miliseconds for them to stabilize. If possible, or necessary, increase you lead in length.
4. Ensure the torch is at .08" when it starts moving to the cut path......soon after it is on the cut path the arc voltage feedback control loop of the THC takes control of torch height. If you see the torch either rise, or get closer to the plate soon after x-y movement....then you should adjust te arc voltage so that .08" cut height is maintained. The arc voltages listed in the Hypertherm manual are correct on a perfectly calibrated system at the cut speed listed with new elctrode and nozzle in the torch, however it is common to have to make adjustments....and the physical torch to work distance is more important than your voltage reading. If the torch is too close, increase the voltage until it is correct, iff too far away, decrease the voltage......when you change the voltage during steady state cutting you should see the torch height change.
Once you are sure that all of the above is operating as described....you can go back and adjust cut speed. I usually start at exactly book recommended (not maximum) speeds, and if I need a little better edge squareness I will try 10% slower, or if I am trying to minimize dross formation, I will go faster about 5% faster on each test until I see aresult that I like. Once the speed is dialed in....you may have to go back and readjust the arc voltage to get the height correct...as speed changes affect height. Faster speed requires a lower voltage, slower speed a higher voltage. Using this technique you should be able to get a reasonably good cut on 1/4" stainless with your system. It will not be 100% dross free, but the dross will file or grind off easily. With more power (perhaps 80 amps) you can expect dross free cutting on 1/4" SS.
One other thing....make sure your air is clean and dry. Moisture is a very common problem this time of year in compressed air systems.
Let me know if this helps. I will post a picture of some stainless that I have done using the above specs / procedure.
Jim Colt
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jimcolt
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- Posts: 3087
- Joined: Mon Jul 20, 2009 11:18 pm
- Location: North Carolina
Re: 1/4 stainless steel cutting problem
Here is one of the 5 large 1/4" 304 SS signs that I cut with a Powermax45 using the specifications in the previous post. The cut quality had some brownish oxidation, and some very light dros that came off easily with a chainsaw file.....about 5 minutes of secondary work on each sign. All 5 signs were cut with on set of consumables......consumables looked essentially new when done.
Jim colt
Jim colt
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