How to get the most out of your consumables for optimal cuts
Plasma cutting is the process of ionizing a vortex of pressurized gas to melt electrically conducive materials. A plasma torch focuses this vortex of gas on the material until it cuts it. A CNC moves the plasma torch along a programmed path to cut the material using torch height control and a gantry for x, y, z movements. Although CNC plasmas can produce high-quality cuts at a relatively low cost, their cut quality diminishes over time. To prevent cut quality from suffering, you need to understand how it happens and methods you can use to combat it.
How the power supply allows you to improve cut quality
The power supply is the lifeblood of the plasma cutting system. It determines the types of plasma gases that can be used and how these gases are mixed. If your power supply is capable, you can prolong the life of your consumables by ramping up the voltage and gas before each cut. By doing so, your consumables will remain virtually undamaged which will maintain good cut quality for a longer period of time.
The parts of the torch and how they typically fail
Consumables by definition eventually need to be replaced; however, you can improve the lifespan of your consumables by diagnosing how they fail and taking measures to prevent these issues. The torch consists of four different parts: the electrode, the nozzle, the gas distributor, and the shield. Each of these parts plays a necessary role in the plasma cutting process so it is important to understand their shortcomings.
Gas Distributor and Electrode:
The gas distributor is the part that creates the vortex of ionized gas and keeps it concentrated on the electrode tip. An emitting element is inserted into the electrode tip that produces the plasma arc used for cutting. When this emitting element is worn down to its casing, the plasma arc begins to emit off this casing and subsequently causes the electrode to fail. The electrode can also fail due to improper gas flow from the gas distributor.
The nozzle’s design is crucial to obtaining optimal cut quality. It is designed so that the orifice is slightly larger than the vortex of ionized gas. This allows the nozzle to direct the flow of gas without being damaged itself. If the orifice is not large enough, the nozzle will be damaged and negatively impact cut quality. Internal nozzle damage is generally caused by a blown electrode, gas flow problems or incorrect voltage levels. External nozzle damage on the other hand, is caused mainly by excess metal splatter that occurs when the torch cuts too close to the metal. This can be prevented by increasing the torch’s cutting height.
The nozzle shield aims to protect the nozzle from being damaged during the cutting process; however, if the nozzle’s orifice is damaged it will impact gas flow and could cause cut quality to suffer.
How the torch height control allows for accurate piercing
The torch height control (THC) is used to maintain the cutting height of the torch. Before every cut, the THC uses a height-sensing mechanism to detect the plate so that it can pierce from 0.25″ to 0.5″ above the plate. The torch then briefly lowers before rising again to the arc voltage-controlled cutting height. The torch remains at this height for the remainder of the process. Newer THC’s compensate for electrode wear by maintaining the same cutting height throughout their life. Older THCs do not have this feature so you need to manually compensate for electrode wear by increasing the current in 2-volt increments. A pierce height too high or too low will cause bevels to form on the part being cut.
These are just some of the ways in which you can improve cut quality, and more importantly preserve a high standard for your product. Ultimately, wear and tear of your consumable parts is unavoidable, but by understanding how these parts are damaged, you can extend their useful life and improve the precision of your plasma cuts.