In most fabrication shops, consumables cost comprises the main part of the production cost. In many shops, consumables are replaced before every shift irrespective of whether they require replacement or not. In fact, some consumables can be used for 50 shifts or even more. The consumable cost can be reduced to a very large extent by following proper inspection methods and preventative maintenance of the parts.
Most of the electrode wear occurs very quickly during the first and last 10% of the electrode life. The wear is slow and predictable during the middle of the electrode life. Usually, the starts are fewer when longer cuts are performed per electrode and the consumables will last longer if you have fewer starts.
You may notice that in plasma torches, the nozzle and electrode don’t wear at the same rate and sometimes, the nozzle lasts much longer than the electrode and vice versa, depending on the torch design, power level and technique of the operator. By changing individual consumable parts, you can solve any problem in cut quality very quickly. However, all problems can be prevented by following a proper inspection and maintenance routine and of course, proper operator technique.
Inspection of the Electrode
The copper body of the electrode must be shiny and clean, even when it has reached the end of its useful life — any greyish heat discolouration can indicate that there is a cooling problem. Since the electrode operates at extremely high temperatures, the tip of the electrode wears. On inspection of the used electrode, if you notice the pit to be off-centered, it can indicate a problem with the gas flow that may be due to a wrong gas flow setting or because of a damaged or incorrect swirl ring. A deep electrode pit may be an indicator that the electrode is close to failure.
Sometimes, operators may discard electrodes as being the cause of poor cut quality; however, the cut quality may be due to other factors such as wrong gas pressure, cutting speed, etc. So, all the other parts and aspects of the plasma torch must be inspected properly before attributing the blame for poor cut quality to the electrode and discarding it.
Inspection of the Nozzle
The nozzle wear and its life are more difficult to determine compared to the electrode. You need to inspect the orifice of the nozzle and also the inside and outside very closely to determine the wear. The orifice bore on the outside should be round without any nicks. The orifice of a new nozzle will have sharp round edges, which will become a bit rounded after use. This affects the cut quality eventually.
The inner bore of the nozzle is also very important and you must ensure that the orifice is perfectly round without any heavy arc marks or nicks. Some black or grey swirl marks and some grey or white residue in the bore is common and will not affect the performance of the plasma torch. You must not try to clean the orifice or scratch the nozzle’s inner bore, as this can affect performance.
Inspect the Entire Plasma System
The advanced plasma cutting system consists of various components such as CNC, CAM software, height control, etc. and all should work together to provide the best cut speed, quality, and consumables life. When you face problems with cut quality, the blame cannot be attributed to the plasma torch or consumables alone and you must check the individual components of the plasma cutting system to isolate the problem instead of blindly changing the consumables.
So, it is recommended that you maintain the plasma cutting system entirely as a whole by following the preventative measures set by the manufacturers. If maintained properly, your plasma cutting system should last you for several decades.
For all your CNC consumables, check out our sister site ESCCO.