In Plasma cutting there are two different types of starts, edge starts and pierce starts. They signify how the start of the cut will take place, and will have implications for other elements of the cut such as edge finish and quality. In addition the type of start used can affect your plasma consumable life. As a result it is important to understand the difference between the two types of starts in order to optimize your cutting experience.
A pierce in plasma involves piercing the material with the plasma torch. This means that the plasma is aimed directly at a particular spot on the material and the cut is started there. The piercing ability for most plasma machines is about half the thickness of its severance abilities.
An edge start involves starting the cut from the edge of the material and working inwards to the piece you are cutting. This means that you will have a lead in as well as a lead out of the piece of material you are cutting. Lead ins are the start of the cut, and lead outs are how the toolpath exits the cut job. There are two types of lead ins/outs and they are called arc and line. These can be applied to your toolpath in your CAM software and will represent how the machine will begin and end the plasma cut. If it is following the arc style then it will enter the material in an arched fashion curving around to the start of the cut, whereas if it is following the line style it will approach the cut straight on in a linear form.
Edge starting usually involves a more continuous cut, and is often referred to as severance. Severance is the cut that is created when the molten metal breaks away from the material under the extreme heat of the plasma. Therefore it is often very effective to chain your production cuts in a sequence so that the machine can move on from one straight to the next without having to pierce the material again.
Edge starts are significantly better for your plasma consumable life. This is because when performing the piercing function to start it is often done at an angle that is straight on. This creates the possibility that the metal will backlash at the torch nozzle thus leading to damaged and shorter lasting consumables.