What's involved in abrasive waterjet maintenance?

The abrasive moving through the nozzle is the culprit behind the component's wear and tear. The abrasive slowly wears away at the inner diameters of the abrasive nozzle; the orifice grows by approximately 0.001 inch per hour of cutting.This wear pattern is not always even, so one side of the nozzle may wear faster than the other.

Symptoms that alert a fabricator that it's time to change the nozzle are inside cuts that become larger and outside cuts that become smaller than intended. Also, operators may see poor cut quality in one or more directions.

Repair time takes 5 minutes to 10 minutes to switch out the nozzles.

Diagram of Waterjet cutting machine

The best way to avoid poor-quality cuts related to worn nozzles is to:

· Track hours on the nozzle and begin to monitor cut quality and tolerance as hours mount.

· Adjust kerf compensation as required to remain within tolerance limits.

Older nozzles don't necessarily have to be tossed in the garbage. Save them for less critical work.



Clogging of the abrasive nozzle also can cause problems. Clogs can occur from too much abrasive or an abrasive mesh size that is too large for a particular orifice diameter, large contaminants in the abrasive, or the nozzle tip contacting the workpiece during piercing or cutting.

A clog is easy to detect. The waterjet stops. Water may back up in the abrasive feed tube all the way back to the minihopper until the machine is stopped.This entire feed line and the minihopper must then be emptied and dried out entirely.

Because of the speed at which the abrasive is moving, generally the nozzle is clogged to the point where it cannot be used anymore.Sometimes people have success at clearing clogged nozzles by turning them upside down and turning on the water at lower power. The time necessary to repair or replace components related to clogging can be anywhere from 5 minutes to 30 minutes.



The best way to avoid clogging is to:
· Use the proper mesh size and quantity of abrasive for the abrasive nozzle being used.

· Ensure that the abrasive bunker has a screening device to filter out most contaminants from the abrasive.

· Use a clean knife to cut open abrasive bags to avoid getting paper from the bag into the abrasive.

· Use height sensing to maintain constant height during piercing and cutting.

· Ensure that proximity switches are inline with the abrasive feed tube to sense when water or abrasive backs up in the feed tube.

Occasionally an abrasive nozzle breaks. The tungsten carbide material the nozzles are made from is very hard, but very brittle as well. Breaking usually occurs when the nozzle drags on the material surface, collides with a tipped-up part, collides with the edge of the sheet material, or simply is dropped during regular maintenance. Obviously, breaking can have a huge impact on operating cost, especially if it happens early in the nozzle's life while it is still good.

The best way to avoid breaking a nozzle is to:
· Rely on height sensing and collision protection to extend nozzle life.

· Invest in software that has collision avoidance, which allows the operator to change the lead-in position, depending on where the cutting head is going next.

It takes about 5 minutes to 10 minutes to replace the broken nozzle.