The following guest post is by Scott Skrjanc of The Lincoln Electric Company.
Plasma cutting delivers a high velocity jet of ionized gas which pierces metal by conducting electricity from the torch to the work piece. The plasma heats the work piece, melting the material, blowing the molten metal away, and cutting the material.
The Benefits of Plasma Cutting Include:
- Ease of use
- High quality cuts
- Faster travel speeds
Once you have selected the plasma cutting machine that is right for you, here are some tricks-of-the-trade that will help beginners make the best possible cut.
1. Set-up procedures for Plasma Cutting
Before you start, check for the following items:
- A clean compressed air supply, without water or oil. Consumables that wear quickly or black burn marks on the plate may indicate that the air is contaminated
- Correct air pressure – this can be checked by looking at the gauges on the unit
- A nozzle and electrode are correctly in place
- A good connection of the work lead to a clean portion of the work
2. Safety Gear for Plasma Cutting
Some basic safety practices should be observed. You should read your instruction manual thoroughly to understand the machine. Wear long sleeves and gloves while cutting since molten metal is generated during the cutting process.
Eye protection, such as dark goggles or a welding shield, is required to protect your eyes from the cutting arc. Typically a darkness shade of #7 to #9 is acceptable.
3. Piercing the Metal in Plasma Cutting
Many inexperienced users try to pierce the metal by coming straight down, perpendicular (90 degrees) to the work. This results in molten metal being blown back into the torch. A better method is to approach the metal at an angle (60 degrees from horizontal, 30 degrees from vertical) and then rotate the torch to the vertical position. This way, the molten metal is blown away from the torch.
4. Don't Touch the Nozzle to the Work Piece While Plasma Cutting
Do not touch the nozzle to the work when using current levels of 45 amps or more. Doing so will drastically reduce the nozzle life as the cutting will double arc through the nozzle. Double arcing can also occur if the torch is guided by dragging it against a metal template. The result is the same as dragging the nozzle on the work: prematurely worn nozzles.
5. Beginners Should Use a Drag Cup to Facilitate Plasma Cutting
Many systems offer an insulated drag cup, which snaps over the nozzle. This allows the torch to rest on the work piece, allowing it to be dragged along to facilitate a consistent cut.
6. Travel at the right speed
When moving at the right cutting speed, the molten metal spray will blow out the bottom of the plate at a 15 to 20 degree angle. If you are moving too slowly, you will create slow speed dross, which is an accumulation of molten metal on the bottom edge of the cut. When moving too fast, high-speed dross on the top surface is created since you are not allowing time for the arc to completely go through the metal.
Traveling too fast or too slow will create a low-quality cut. Typically, low speed dross can be distinguished from high-speed dross by ease of removal. For example, low speed dross can be removed by hand whereas high-speed dross typically requires grinding.
7. Set the Current to Maximum as you Begin Plasma Cutting
When setting the current, put it on the maximum output of the machine, then turn it down as needed. More power is usually better, except when doing precision cutting or when you need to keep a small kerf.
8. Minimize Pilot Arc Time for Plasma Cutting
Because of the wear it creates on the consumables, try to minimize the amount of time spent in pilot arc mode. To do this, position the plasma torch by the edge of the work before starting the arc so you can get right to cutting.
9. Maintain a Constant Work Distance While Plasma Cutting
Optimally, you should maintain a 3/16" to 1/8" distance from the nozzle to the work. Moving the torch in an up and down fashion will only hinder your efforts.
10. Travel in the Direction that Will Give You the Best Finished Work
If you are making a circular cut and plan to keep the round piece as your finished work, move in a clockwise direction. If you plan to keep the piece from which the circle was cut, move in a counterclockwise direction. As you push the torch away from you, the better cut will appear on the metal that is on the right hand side, since it will tend to have a better, squarer edge.
11. End with a Push Angle on Thick Material
One trick to use on thicker material is to rotate the torch slightly, increasing the torch orientation to a push, rather than drag angle as you cut through the last section of material. This increase in the push angle at the finish will cut through the bottom first and get rid of the bottom corner that is usually left at the end of the thick plate. Never finish a cut by using the torch to hammer away the last corner of the work.
After finding the right machine for your application and learning some of the tricks of the trade, you should be ready to cut. Remember that plasma cutting offers a number of benefits and should provide you with faster, higher quality cuts. Check out this video to learn more plasma cutting basics.
