The principles of abrasive water jet machining

The Principles Of Abrasive Water Jet Machining Overview Before getting into the principles of abrasive water jet machining, it is important have a brief overview of abrasive water jet cutters. Abrasive water jet cutters are machines capable of slicing metals among other hard materials using a water jet at high pressure and velocity. It is important to note that the machines utilise water mixed with an abrasive substance hence the name abrasive water jet machine.

Abrasive water jet machining is similar to water erosion. The only difference is; the process is accelerated as well as concentrated by order of magnitude. Abrasive water jet machining is used mainly in the manufacture or fabrication of machinery parts among other metal parts/devices. The process also has applications in a variety of industries from aerospace to mining. In these industries, abrasive water jet machining is used in operations such as cutting, reaming, carving and shaping.

How does abrasive water jet machining work?

Having understood what abrasive water jets are and their applications, lets now focus on the principles of abrasive water jet machining. To do this, we have to understand exactly how abrasive water jets work. Let's start by describing the structure of abrasive water jet machines. A typical abrasive water jet machine is made up of 6 main parts namely; a water tank, a nozzle, sand reservoir, a computer, a piston pump and a motor. The motor is usually connected to the piston pump which pumps water from the tank through a tube. The water is then mixed with an abrasive (usually sand) in the mixing chamber. The mixture comes out through a nozzle at high pressure aimed sharply on the sheet of metal or material to be machined.

Dominant physics To understand the principles of abrasive water jet machining in detail, it is important to look at the dominant physics. This requires a discussion on how power flows through the machine. The machine’s motor is responsible for changing electrical power into mechanical power when the machine is powered. The motor moves the piston pump which converts mechanical power into another form of power known as fluid power.

The whole process has 7 variables i.e. 3 electrical power variables, 2 mechanical power variables and 2 fluid power variables. The electrical power variables describe the AC current that is supplied to the machine motor, the net motor resistance and the AC voltage across the motor. The mechanical power variables describe the angular speed and the torque produced by the motor shaft. The fluid power variables describe the volume flow rate (of the water mixture) and the pump pressure difference.

In regards to pressure, the water mixture flows out of the pump at approximately 40,000psi. The mixture is forced out of the nozzle at approximately 2,500ft/sec.

Typical abrasive water jet machine nozzles measure 0.030 inches (diameter). The distance between the nozzle and the material being cut is usually 0.06 inches. These

dimensions can however vary depending on the application, preferences e.t.c. Cutting is usually achieved via a grinding process. A fluid garnet mixture is used in place of a grinding wheel.