Waterjets can be attached to a variety of machines. There are hand-held waterblasting wands with rotating tips used to remove paint; stationary jets used for high-speed tissue paper slitting; single axis systems used for cutting baked goods, fiber cement board or other product moving off of a roll; and still others attached to 7-axis pedestal robots used for trimming automotive interiors. But the most common machine used to hold or move a waterjet (or an abrasive waterjet) is the shapecutting machine tool. These are similar to machines that cut with plasma, laser, or router.
With this machine the material is placed (or held) on a work table and the cutting head is moved in an XY plane over top. Sometimes the head has 5 axes of motion for bevel or 3D cutting. I will use the abrasive waterjet shapecutting system in my example from this point forward.
A walk around the machine
The shapecutting system is comprised of:
- The ultrahigh-pressure system; with pump, cutting head, plumbing.
- The control system; with operator interface, motors, feedback system (to ensure we know where the head is at all times), and the software used to program and run the machine (the HMI – human machine interface).
- The machine; with X, Y, Z axes, maybe wrist axes as well, material support catcher.
The ultrahigh-pressure system pressurizes the water and transfers it to a cutting head. Ordinary tap water is filtered and enters the waterjet pump. An intensifier linear pump or a direct drive rotary pump pressurizes water to 40,000 to 94,000 psi (~2700 to 6500 bar). I will be discussing this in more detail in an upcoming post.
The pressurized water is then safely transported to the cutting head via specially designed ultrahigh-pressure plumbing components. These components (shown in the image) send the water from the pump to the cutting head.
The cutting head then focuses the water and shoots it at the target material. The head includes a high speed On/Off valve powered by compressed air. For safety reasons, the On/Off valve should be normally closed (if air pressure is lost the valve will shut off, not open up). When open, the valve allows the pressurized water to pass through a jewel orifice and out of the cutting head. The jewel orifice is a ruby, sapphire or diamond and incorporates a tiny hole – 0.003 to 0.024” in diameter (0.07 to 0.61 mm). Most common size for abrasivejet cutting is approximately 0.013” in diameter (0.33 mm). Abrasive is added after the jewel orifice for abrasive waterjet cutting.
The control system is really part of the machine, but I’ve broken it out here to give it some special attention since it is the portion of the machine we interact with the most. The programmer will create a program in the office or out at the machine and the operator (sometimes also the programmer) will interact with the human machine interface (HMI) to pull up the program, bring the machine to the start location, and start the program to begin the cutting.
When cutting starts, the drive amplifiers send power (as directed by the program) to the motors that move the machine around. There are many variations of electrical systems and control software – far too many to entertain in this general overview. If you’re interested, send me a comment and I can get into detail in a future post.
Lastly, a machine tool needs to physically move around the jet as directed by the control system. The machine provides not only the drive mechanisms to move the head around, but also the material support table and waste holding catcher tank.
Waterjet machines are designed with environmental protection to provide long life to the machine drive hardware (protecting the linear ways, ball screws, rack and pinions, etc.). In the image provided you might notice the accordian bellows protecting the machine.
In other posts I’ll get into details on each of the major components, but for now this is just a high level overview. Let me know what you think in the comments below or send requests for future posts. Thanks for reading.