4 Piercing Methods In Abrasive Waterjet Machining
Abrasive waterjets make it easy to quickly cut precise parts from almost any material. How the machine pierces the material affects the overall production time and resource usage. Several piercing methods have been developed to deliver optimized cutting for various material types, thicknesses and part geometries.
#1 Stationary Piercing
This is the simplest and earliest piercing method used by abrasive waterjets. The jetstream is turned on directly above the material and stays stationary until the material is pierced. The advantage to stationary piercing is that the piercing hole is very small. It’s typically the best piercing method when there’s not enough room for a dynamic or wiggle pierce, if the material being cut is very expensive and you want to use the minimum possible space to pierce, or if the material is very thin and pierces very quickly. Stationary piercing is slower than dynamic or wiggle piercing, especially in thick materials.
#2 Wiggle Piercing (sometimes called “dwell piercing”)
During “wiggle” piercing, the jetstream moves back and forth over the material across a very short distance until it pierces through. Wiggle piercing was a big improvement over stationary piercing and until recently was the preferred piercing method used by abrasive waterjets. Wiggle piercing can be efficient when making holes in thick materials or where there is not enough available space on the material to create the ideal lead-in length for a dynamic pierce.
#3 Dynamic Piercing
Today, the fastest piercing method for most abrasivejet cutting jobs is dynamic piercing. During dynamic piercing, the jetstream starts off the material and gradually moves into the material, piercing as it moves. Model testing has shown that there is an optimal pierce length for the fastest pierce time. And for any given pierce length, there is an optimum traverse speed at which to pierce. To find this ideal piercing length and traverse speed requires some complex calculating. In the best abrasive waterjet systems, advanced software uses a cutting model to predict the optimal pierce distance and speed for piercing any given material. It then automatically grows or shrinks the lead-in without interfering with other features in the part. Properly implemented dynamic piercing is usually faster and easier to use than wiggle piercing. Without advanced software however, dynamic piercing is slow compared to wiggle piercing because it is difficult to predict the ideal pierce lengths and traverse speeds.
#4 Low-pressure Piercing
Low-pressure piercing helps prevent material from cracking and is a good method for brittle materials like glass, stone and some ceramics. It’s also a good piercing method to use with laminated materials to prevent delaminating during the pierce. Low-pressure piercing can be combined with any of the above methods. For optimal cutting times, the pump should be capable of switching from low to high pressure (and vice versa) and the controller software should be able to automatically switch the pump pressure at the appropriate time. This way, the pump can operate at low pressure for piercing then quickly ramp up to high pressure for the fastest cutting speed without interruption.