Finepart | Waterjet Cutter | Waterjet kerf angle – About kerf & taper in waterjet cutting

Waterjet kerf angle – About kerf & taper in waterjet cutting

What is the waterjet kerf angle? – In this article we cover what you need to know about kerf and taper, what affects the kerf, and how to adjust the waterjet cutter to compensate for the kerf angle.

What is the waterjet kerf angle?

The cutting process of the abrasive waterjet forms a slit through the material as the jet moves along a programmed path. This slit is called the jet kerf. As with any cutting method, the cutting stream will leave a characteristic fingerprint.

Illustration of waterjet kerf angle

What is kerf width in a waterjet?

The kerf width primarily depends on the diameter of the jet but it is also affected by the time the material is exposed to the jet.

The center part of the kerf will be subjected to more particle impacts compared to near the sides of the kerf. This will result in quicker material removal at the centre and less removal at the sides. Consequently, the width of the cut will be wider at the top than at the bottom.

If the feed rate (cutting speed) is reduced and there is more jet stream exposure time, more material towards the bottom will be removed. As the jet will exhibit a diverging shape, the kerf will also become wider at the bottom with reduced feed rates.

waterjet kerf angle and kerf width illustration
v

What is kerf taper angle? 

The kerf taper angle is the angle of the kerf side compared to the perpendicular edge. With a kerf that has a different width at the top, compared to the kerf at the bottom, the taper angle is defined as one half of the included angle of the two sides. By tilting the waterjet angle, equal to the kerf angle, the part will get a perpendicular edge.

Waterjet tilted to compensate for kerf angle

What tolerance can an abrasive waterjet hold? 

The abrasive waterjet is a dynamic tool having its shape determined by the interaction between the energetic jet and the material being exposed to the cutting action. Besides a taper the jet typically also exhibits some lag, and in case of high feed rates also a pendulum action. This jet shape deviation will cause a discrepancy between the top of the kerf and the bottom of the kerf, which limits the tolerances due to form errors related to the jet dynamics.

jet tool

For a well aligned and coherent jet the programmed to avoid dynamic form errors a tolerance of ca +/- 10 µm can be achieved.