5 axis waterjet cutting

• Fabricating

Click image to enlargeby Dr. John Olsen

Cutting 2D and 3D parts on the same machine 

While five axis operations such as bevel cutting and other weld-prep-type work have been possible on abrasive waterjet machines for some time, the capability to also process 3D parts such as tubes and pipes on the same machine is relatively new.    

This being said, fabricating shops that once focused primarily on flat 2D work now have the opportunity to diversify into taking on 3D work with a five axis abrasive waterjet machine. And those shops specializing in tube and pipe fabrication can now process their 3D cylindrical-shaped parts on one five axis machine. Plus, that same machine will allow fabricators to also process–in-house–any flat 2D parts, such as gussets or supports, that may have been previously farmed out to other shops.

Because abrasive waterjets cut practically any material, fabricating shops with five axis  machine capability can broaden their markets based on the materials they are able
to process. An added benefit is being able to do so with the same piece of equipment used for cutting their metal parts.

In some instances, shops can easily and cost-effectively upgrade their existing bridge-type 2D abrasive waterjet machines by simply adding software, articulating heads and rotary units to obtain full five and six axis 3D cutting capabilities.

Articulating heads are the key to five axis waterjet cutting. In addition to a machine’s X, Y and Z axes, articulating heads provide
two tilt angles–one perpendicular to the X axis and the other perpendicular to the Y axis. These heads can also be used to compensate for the natural taper that occurs with a waterjet stream.

Articulating heads work within the safety limitations of abrasive waterjet cutting. While there are five axes of motion, the range of the two tilt axes is controlled to a specific limited distance so that the abrasive waterjet stream is always shooting in a generally downward direction toward a machine’s water tank. 

Currently, the most common use of 2D machines with added articulating heads are for weld prep bevel work or miter cuts for parts that intersect at an angle. They are also being used to cut countersinks on large size holes.

When a bolt-on rotary axis unit is paired with an articulating head, the combination gives fabricating shops the ability to perform five axis  operations on tubes, pipes and other cylindrical-shaped parts. Such operations include imparting fish-mouth shapes and other end cuts necessary to join tubes or pipes to one another.

Articulating heads and rotary units provide the machine motion for five axis waterjet cutting, but improvements in machine programming were what really progressed the capability. 

Early on, parts could be programmed manually, but the task was very involved and extremely time-consuming. The development of advanced software functions has helped overcome these five axis programming issues and continues to play a key role in spurring the increased use of five axis abrasive waterjet cutting.

Many fabricating shops assume five axis abrasive waterjet cutting is complex. But the ease of retrofitting existing 2D machines with articulating heads, rotary units and innovative software functions has made 3D cutting easy and attainable. While technology advancements have simplified five axis cutting, there are certain workpiece factors that must be considered when using abrasive waterjet cutting.

Workpiece shapes, for example, can geometrically limit the use of five axis cutting capabilities. 

Shops must be cognizant of exactly where an abrasive waterjet stream will be pointing, especially when cutting angled features such as countersinks on holes. If the angle of the countersink is too steep or the corresponding hole’s diameter is not big enough, the waterjet will cut into the opposite sidewall of the hole. Visualize countersinking a 0.500 in. (12.7 mm) diameter hole in a 3 in. (76.2 mm) thick part as compared with countersinking a 3 in. (76.2 mm) diameter hole in a 0.500 in. (12.7 mm) thick part.

Most fabricating shops are working with part material thicknesses of 2 in. (50.8 mm) or less. In most instances, five axis waterjet cutting is used for creating bevels and angles that are 0.250, 0.375 or 0.500 in. (6.35, 9.5, or 12.7 mm) wide. Making such cuts on an abrasive waterjet eliminates having to generate them in secondary operations on other pieces of equipment.

As far as tube and pipe cutting is concerned, the main restriction to five axis abrasive waterjet cutting is inside diameter (I.D.) size. The smaller the I.D. of a tube or pipe, the greater the risk is of the abrasive waterjet stream cutting into an opposite part sidewall while processing an end or side.  To prevent such an occurrence, pieces of ceramic can be inserted into the tube or pipe that would deflect the waterjet stream and prevent it from cutting the opposite part surface. The use of a deflector would only apply if the part I.D. were big enough. A 0.062 in. (1.6 mm) part I.D., for instance, would not provide enough room for a deflector.

However, introductions of larger abrasive waterjet table sizes are enabling shops to process longer tubes and pipes. Since there is minimal force/torque involved in the rotation of parts, the only other requirement for long lengths would be a steadyrest for supporting the part. 

As manufacturing materials and part designs continue to change, fabricating shops must consider what technologies will increase their manufacturing versatility. Fabricating shops wanting to remain relevant in the next 20 years will be those who continue to adapt the latest technologies, such as five axis abrasive waterjet machines. SMT

Dr. John Olsen is co-founder of OMAX Corp., Kent WA.

Omax Corp.