Waterjet has been the favorite cutting process for a wide range of industries over alternatives like laser cutting.
However, certain professionals are still new to the technology and in the early stages of adoption for their industry. One common question that comes up frequently from these professionals is ‘what is the correct water jet cutting pressure?’
To help everyone in the manufacturing world, this article will discuss all the details regarding waterjet cutting pressure. You will also learn the factors that influence the pressure pump you require and the difference between a hyper pressure pump and a normal pressure pump.
What is the Average Pressure of a Water Jet Cutter?
To have an understanding of the average waterjet cutting pressure, it is important to understand the range within which it varies. There is no single value for water pressure because of the huge variations that can occur based on a number of factors.
Water pressure for this cutting process starts at 30,000 psi (210 MPa) going up to 90,000 psi (620 MPa).
Effect of Pressure on Cutting Thickness
Since abrasive waterjet cutting machines utilize high pressure water for piercing the materials, many people (including professionals) wrongly believe that using higher pressures will lead to higher thicknesses. However, that is an incorrect assumption.
A 30,000 psi machine can cut the same thickness of a given material as a 90,000 psi machine can. However, higher pressures provide a significantly faster cutting, increasing productivity exponentially. Additionally, the increasing water pressure also increases the accuracy of the process.
Factors That Influence Water Jet Cutter Pressure
Here are the factors that decide the water pressure of a waterjet cutter:
When buying a pressure pump, most people focus on the water stream pressure. However, the horsepower of the pump is also an important factor one should consider. The horsepower determines the pressure required at a given flow rate. This is derived from the formulae:
Horsepower = Pressure x Flow Rate
Therefore, for a given pump horsepower, an increase in pressure will mean a decrease in the flow rate. To make up for the decreased flow, the waterjet will need a smaller nozzle orifice.
As mentioned earlier, an increase in water pressure will increase the cutting speed. Therefore, the first inference would be that increasing productivity is easy by using higher pressures. That is indeed true, but only up to a pressure of 50,000 psi to 60,000 psi.
Beyond that, when we venture into the hyperpressure range. The waterjet cutting speed here also increases with pressure, but so does the equipment wear and tear. This leads to frequent breakdowns of the waterjet system resulting in downtimes. These downtimes can lower the productivity of the operation.
In abrasive waterjet cutting, the choice of abrasive can also dictate the effective water pressure. Finer mesh abrasives allow the possibility to use narrower nozzle orifices without clogging them. This increases the water pressure output at the nozzle.
80 mesh abrasive is usually suitable for most requirements. In the case of high precision cutting, 120 mesh abrasive is the recommended choice. A 120 mesh abrasive material also provides a better quality cut when cutting thin materials.
Using appropriate hardness for the abrasive leads to creating high efficiency without increasing pressure. For instance, super hard materials like aluminum oxide as an abrasive means an increased cutting speed for harder materials. However, these also lead to faster wear of the mixing tube and other components.
Therefore, super hard abrasives are not used for soft materials like aluminum and gold. Softer materials can work with usual abrasives such as garnet.
The cutting process in waterjet occurs due to the high water velocity. Many people use water velocity and pressure interchangeably, but that shouldn’t be the case. The velocity of the water jets varies depending on the pressure and the nozzle orifice. At any given pressure, the water velocity can be increased by decreasing the orifice size. However, the orifice size is limited by the size of the garnet abrasive.
Therefore, the easier way to extract high speed water is by increasing the water pressure. It is important to note that an increased water velocity will only increase the cutting speed and not the thickness of the materials. Additionally, water jet speeds also govern the speed of the garnet since it travels in the stream.
Multiple Cutting Head
Professionals often use multiple cutting heads for increasing productivity without increasing pressure in the hyperpressure range. However, while production speed increases, it also requires a high horsepower pump to provide adequate pressurizing on the individual cutting head.
Additionally, parts of the individual cutting heads such as the waterjet nozzle will deteriorate at their own rate. This can lead to inaccurate cutting since the wear and tear of different cutting heads will be at different levels.
Type of Pumps
There are two common types of pumps available for waterjet cutting: intensifier pump and direct drive pump. Intensifier pump works on a hydraulic mechanism while direct drive pumps utilize a crankshaft mechanism.
These two pump technologies vary in terms of many factors, such as the maximum pressure they can provide. The direct drive pumps can go up to a pressure of 60,000 psi, while the intensifier systems can provide up to 100,000 psi. It is vital to note that the higher maximum pressures of intensifiers come with disadvantages such as high failure rates, coolant requirements, and a high noise level.
Hyperpressure vs. Normal Pressure
In waterjet cutting, normal pressure refers to a water pressure of up to 60,000 psi. Of course, this value is not ‘normal’ compared to the water pressure in non-cutting applications. However, it is termed so due to its comparison with the Hyperpressure pump which goes from 60,000 psi to 90,000 psi and even more.
Using hyperpressure pumps means a faster cutting process, so it might seem like the obvious thing to use all the time. However, hyperpressure pumps have a higher wear and tear of the components due to the extreme force of the water. These components include not only the internal components of the pump but also the delivery system components like the tube and nozzles.
Hyperpressure pumps will undoubtedly have a significantly more efficient cutting lead to high production rate in abrasive waterjet cutting. However, the costs saved by higher efficiency can be nullified by the higher costs of consumables due to lesser life, higher maintenance costs, and higher failures in orifice, valve, fitting, joints, and tubing.
Choosing the right pressure is one of the major questions for users of waterjet cutting technology. To make matters difficult, the ideal pressure for this process is not a one size fits all solution. It varies based on the requirement of the situation, so machine shops need to adjust the pressure based on their experience with the machine for their applications.
For best results, it is important to use a good quality machine that can provide the full benefits of a high-pressure pump without the high failure rates and replacement costs. Techni Waterjet cutting equipment is a winner in this regard, renowned for its good build quality and rugged design to suit the requirement of any job.
Frequently Asked Questions
Here are the answers to some common questions that people ask regarding waterjet cutting:
What is the optimal waterjet cutting pressure?
The optimal waterjet cutting pressure varies based on the situation requirement. In general, pressures between the 50,000 psi to 60,000 psi range provide the best results for most applications of waterjet technology.