Thick materials can be slow to pierce. For this reason, several piercing methods have been developed as discussed below.
“Wiggle” piercing refers to moving the cutting head back and forth over a short distance while the waterjet is running. This allows for quick clean piercing of thick material in a small amount of space. This also prevents the backwash from the jet from reducing the effectiveness of the pierce, as in a stationary pierce. If you cut thick materials, more than 0.5″ (1.3 cm) thick, this is especially important.
With dynamic piercing, the jet does not wiggle, but rather slowly moves into the material, piercing as it moves. If properly implemented, dynamic piercing can be quite fast—even faster than wiggle piercing. If not properly implemented, it can be significantly slower than wiggle piercing. The proper speed and length of a dynamic pierce is a function of the cutting conditions and is very hard to predict, which is why it is usually slower than wiggle piercing.
A stationary piece is performed without moving the nozzle. The nozzle simply turns on, and waits until the material is pierced. This is the method of piercing if you do not have enough room to perform a dynamic or wiggle pierce, or if the material is valuable and you want to minimize the amount of scrap material. It is much slower that either of the other methods, however, so is reserved only for piercing thin material or tiny holes. In some materials and thickness, it is virtually impossible to pierce using stationary piercing.
Low pressure piercing
For brittle materials, it is often desirable to pierce at a lower pressure than you would normally cut with. This prevents cracking of the material. Low pressure piercing can be combined with any of the above methods.
There are a handful of other methods for piercing for special circumstances, such as spiral piercing, coming in from the edge of the material, and pressure-ramped piercing.