Once you have your CNC (Computer Numeric Control) Plasma cutter all set up to manufacture specifications, you may want to start cutting parts right away. However, you must first understand the steps and factors that go into making cuts that produce quality parts. In this article, you will learn the proper components to use per material, the steps in making a cut, and first cut procedures.
The Right Components makes the Right Part.
Many times, plasma cutting is considered a crude cutting technique that leaves heavy dross and a noticeable bevel on the cut edge. However, these negative outcomes are not due to the process but rather due to the improper components used. Most plasma cutter manufactures have cut charts for their model plasma cutters. This chart will show you what nozzle, amp, and speed to cut at. This chart will give you a basic guideline of what components to use per material and material thickness. There are key factors to look out for if your cut quality is not what it should be. When plasma cutting with too many or too little amps you can see high levels of dross and splatter. Even torch height plays a big role in the quality of cut. When there is top splatter, excessive bevel and top edge rounding the torch height is too high and should be lowered. Then if your consumables are running out faster then what they should, and a visible reversed bevel, it may be due to low torch height. Lastly, you will have to be aware of the feed rate. Usually, the feed rate is defined as millimeters per minute or inches per minute. When cutting, your feed rate will drastically affect what the finished part looks like. If your cutting to slow you will see heavy dross and forward-facing arc lines on the face of the cut. When running too fast you will see backward facing arc lines as if the arc is being dragged and excess bevel/corner rounding. Many of these improper cutting characteristics overlap with each other from cause to cause so determining the solution can be hard. By following the plasma cutting manufacture charts of which amps, torch heights and feed rates to follow will help set you on the right path. However, fine-tuning your cuts will require experimentation and constant tweaking.
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Test Cuts for the Best Cuts.
As explained above manufacturers will have basic guidelines to follow to allow for a good head start on making proper cuts. However, by running your own test cuts in your conditions you can fine-tune your machine to produce the best cuts. Some manufacture that supply CAM (Computer Aided Manufacturing) software have a test cut program pre-installed. This typically is a series of straight cuts and circle cuts. Thus, you can run a straight and circle cut at a given feed rate, torch height, and amperage. You can do this over and over and tweak each attribute to see which produces the best cut. Typically for smaller cuts, like slots or bolt holes under 2 inches, a slower feed rate will be needed as compared to a profiling cut which can run faster. The best thing you can do getting started is to run tests on different material and thicknesses and keep a notebook of what works best. This then allows a reliable reference when you making parts that require quality cuts. Another important factor to look out for is material composition. Different raw material suppliers have stock at different purities. Steal and aluminum have different composition makeup and can change from supplier to supplier. There are industry standards that suppliers follow to ensure material is of quality however, you can buy material with a different composition makeup, which can change your cutting conditions. Be sure to know exactly what the purity is of your material and buy what works best for your machine. Sometimes the cheapest material is not the best choice. Be sure to do your research and know before you buy. This can save you a lot of headaches when you are spending hours trying to figure out why your cuts are not turning out like they usually do.
Cutting Features and Factors.
So now that you got all your components set up to run at peak efficiency, its time to make parts. Cutting parts require a bit of foresight because whenever you make a cut you must have a pierce and a lead in. A pierce is where the arc is trying to penetrate the material. This means the arc is increasing in voltage as the arc length increases trying to melt through the workpiece to begin profiling. The thicker the material, the longer the pierce time and higher the voltage as the arc increases. Additionally, as it's piercing the energy is being transferred to the pierce and the walls of the pierce causing the pierce to be bigger than the cutting arc. Thus, you cannot begin on the edge of your part and start cutting. If you did this, you would just scar the surface and not actually cut the part. As well, when you finish your cut you would have a divot where the pierce took place on the edge of your part. To combat this, we use lead-ins. Lead-ins move into the work piece’s edge and then cuts the part. This can be done in various ways. Such as straight, hook, spiral and many more types of lead-ins. When cutting a part, you end up with a male part and a female part. Typically, if we were to cut out a circle plate out of a square sheet. The circle would be the male and the sheet with a circle cut out of it would be the female. Thus, knowing which part you want to keep will determine which side the lead in is on. If you want the male part, the lead in should be on the female side in. However, if you want the female part, you would put the lead in on the male part, which is the inside of the circle. For example, when cutting out bolt holes, you would lead-in from the center of the bolt hole to cut because you don’t want the circle cut out you want the part with the bolt hole.
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Conclusion.
After reading this article it should be understood what needs to be done to produce quality cuts. It also should be known how to correct improper cutting if it were to arise. Lastly, you should understand the procedures needed to obtain the desired cut. What it comes down to is trial and error. By running test cuts and playing around with different features of the plasma cutter can help you to refine your cutting experience to achieve quality cuts. Many plasma cutting operators keep a booklet of their preferred nozzle, amp, and feed rate combinations per material and material thickness. The guidelines given to you by the plasma cutter manufacture is just a guideline. Testing and experimentation will allow you to refine your craft and skills to produce the highest quality cuts.
Nicholas Kinney,
Nicholas is employed at Diamond Manufacturing Company as a mechanical engineer. His responsibilities/experience include the CNC programming of their turrets and fiber laser. Outside of work, he enjoys machining, plasma cutting and working on his invention of an electromechanical anti-jackknifing system for tractor trailers.
1 comment
This had a lot of good information on the different machining processes. I’ve wondered about when
cnc machine would be better to use than laser methods. I can see how it’s more efficient for cuttingstone, ceramics, and thicker metals.