Today’s waterjets can cut much faster than CNC mills and wire EDM machines, and with high precision. But it is not only the cutting speeds and tight tolerances that make them so attractive. By Dr John H Olsen, vice president of operations at Omax Corporation.
Over the last few decades, abrasive waterjet cutting has been an increasingly popular method for cutting metal and a wide variety of other materials. Abrasive waterjets that have good software do not require any special programming skills to set up cutting jobs or to operate the machine.
Fixturing flat sheets of work material is quick, and sheets of material can be stacked to cut multiple parts with one pass. As waterjets do not cut with heat, there is no heat-affected zone which can reduce material waste and reduce the need for secondary operations. All these factors can significantly increase a shop’s overall throughput.
Articulating Cutting Heads
Articulating waterjet cutting heads were developed to create bevelled and angled cuts in flat material. With software advancements, cutting heads were further developed to precisely compensate for taper and jet lag, two attributes inherent in waterjet cutting.
Waterjet Taper & Jet Lag
A typical waterjet cut has a v-shaped taper where the top of the cut is slightly wider than the bottom because the jet stream loses some of its cutting energy as it cuts deeper into the material. Slowing down the cutting speed can reduce the taper.
If slowed too much, it can produce a reverse taper where the kerf width is wider at the bottom of the cut than at the top. This is the result of the jet stream removing more material at the bottom of the cut than at the top.
While slowing the cutting speed reduces the taper on part edges, it does not eliminate it. And most job shops do not want to slow down their cutting speeds.
The other issue advanced waterjet manufacturers sought to overcome was jet lag. The high pressure jet stream from a waterjet nozzle is the machine’s cutting tool.
This jet stream “lags” or trails a little. The faster the jet stream cuts, the more it lags. This jet lag can reduce accuracy when cutting around corners. Advanced waterjet manufacturers then started searching for solutions.
The Tilt Solution
Waterjet manufacturers found that tilting the cutting head at just the right angle will compensate for both taper and jet lag. Parts with taper-free edges can be cut on an abrasive waterjet without slowing cutting speeds using an articulating cutting head.
With the introduction of the articulating cutting head, waterjets developed into fully controllable, multi-axis cutting machines.
Software Advancements Into 3D Cutting
While the 5-axis cutting heads brought exciting new capabilities to waterjet machining, manually programming the cutting heads to create bevels, chamfers and intricate shapes was a time-consuming task. It required the operator to import a 2D file, do complex calculations of multiple angles, manually assign those angles along each line segment, and finally generate a 3D toolpath for cutting.
It simply was not practical for most manufacturers to spend the programming and testing hours necessary to cut complex geometries on the waterjet.
Recent advancements in software technology have made it possible for waterjet manufacturers to create sophisticated cutting models that do all the complex calculations for the user.
With this waterjet-specific software, a waterjet operator can directly import a solid 3D model from almost any 3D modelling program, such as Rhino3D, AutoCAD, SolidWorks and Fusion 360.
The software automatically calculates the appropriate cutting head angle along each section of the toolpath based on the material type, thickness, and edge quality selected by the operator, and a 3D toolpath ready for waterjet cutting is generated, all within the same software program.
Today, complex shapes such as blades with multiple thicknesses and angles on a single edge are easy to program on an abrasive waterjet with the right software.
Pipe And Tube Cutting
Adding a programmable rotary axis allows cutting of cylindrical surfaces and turns an abrasive waterjet into a 6-axis cutting machine. With a rotary axis, the waterjet can cut flat plate as well as pipes, tubes and bars.
When cutting tubes and pipes, material such as ceramic is often inserted into the tube or pipe so that the waterjet stream is deflected and does not mar or cut through the opposite wall. With some advanced programming, the waterjet can cut shapes that are “wrapped” around a cylinder.
The capability to process 3D parts such as tubes and pipes has created new possibilities for shops working with metal and many other types of materials.
Preparing For The Future
Abrasive waterjet continues to be one of the fastest growing machine tool processes in the world due to its versatility, accuracy, and ease of operation.
As turnaround times and tolerances for jobs continue to tighten, shops that adopt the latest technologies such as abrasive waterjets with 3D cutting capabilities will have the best chances at thriving in the industry.
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