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How to combine pressure and power in waterjet cutting to maintain the best cutting performance?

Posted by: Fymicohuang 2021-11-16 Comments Off on How to combine pressure and power in waterjet cutting to maintain the best cutting performance?

Since the use of waterjet technology 50 years ago, there has been a debate about how the combination of pressure and power can achieve the best cutting performance. How to get better or faster cutting? Which combination of pressure, horsepower, and nozzle assembly is best for a specific application? Next, the editor of Xianji.com will take everyone to learn together.

First, get started

If you have ever studied buying a waterjet system, then you may be hit by a series of marketing and sales data that show the advantages of each method. Hydraulic booster pumps can provide extremely high pressures at the expense of a very energy-intensive hydraulic system. Others advocate the use of direct drive systems with mechanical crankshaft pumps.

In the past few decades, there have been trade-offs between these technologies. Booster pumps are considered easier and cheaper to maintain, especially at high pressures, while direct drive systems provide higher energy efficiency. Over the years, technology has continued to evolve, and trade-offs have also changed.

In any case, the basic principle of waterjet cutting has not changed. The nozzle/orifice combination helps to pressurize the water because the water is squeezed out of the high-pressure pipe through openings in hundredths of an inch. The water passes through the small diameter orifice to form a continuous water flow, and then through the venturi nozzle, a certain amount of granular abrasive is sucked into the water flow. The mixture of water and abrasive particles passes through a special ceramic mixing tube, and the resulting abrasive/water slurry flows out of the nozzle in the form of a continuous abrasive particle cutting stream and travels at a very high speed.

Abrasives are only cut when they successfully reach the material. The mesh size of the abrasive must fit the orifice to avoid clogging. Eighty-inch garnets are the most common among nozzle sizes, while fifty-inch garnets are rougher and are usually used with larger diameter holes (such as 0.022 or 0.020 inches). Using a narrower nozzle with a 50-inch garnet will increase the possibility of clogging. For smaller nozzles for high precision applications, such as 0.014 or 0.010 inches. The mesh of the nozzle is preferably 120 or higher.

Nozzle size is not the only factor in determining the ideal mesh size for a given application. Just like sandpaper, finer surface finish requires higher, finer mesh size. A 220-inch garnet can provide a smoother and more accurate finish above 80 inches, especially when cutting thin materials.

Understand spray pressure

The pressure is determined by the amount of water that the pump pushes through the nozzle hole. The smaller the orifice, the higher the pressure. Suppose, using a 100-horsepower pump and a wide orifice, you can have a maximum waterjet jet capacity of 30,000 PSI, but no OEM can sell such a product because it has no effect. On the other hand, using a 5-HP pump can reach 60,000 PSI, but the application is severely limited, and the orifice will be very narrow.

Power is proportional to pressure multiplied by volume flow (P = kp×V). For a given pump power, any increase in pressure must be matched with a proportional decrease in volume flow. This means that high-pressure pumps must use nozzles with smaller orifices. For example, a 50-horsepower booster pump with 0.014 inches. The 60 KSI nozzle hole is limited to 0.010 inches.

How to combine pressure and power in waterjet cutting to maintain the best cutting performance?

For pure water jet applications without abrasives, greater pressure may result in faster cutting. In fact, the smaller diameter of the nozzle from the high-pressure system may be more effective in pure water cutting applications such as food or foam rubber. However, in abrasive water jet cutting systems, abrasives are used for cutting instead of water. Instead, the water accelerates the small abrasive particles in the form of a coherent flow, thereby eroding the material being cut.

From 10,000 to 60,000 PSI, the abrasive water jet cutting speed is steadily increasing. Because the higher PSI focuses the particles on a single point, the finish and accuracy are also improved. However, at higher pressures, the direct relationship between PSI and cutting speed begins to break.

According to a paper published in 2018 by Dr. Axel Henning, Pete Miles and Ernst Schubert, the paper is entitled “The Effect of Particle Fragmentation on Abrasive Water Jet Performance”. The paper was published at the International Water Jet Conference. The author studied how the cutting performance is related to Related. They found that under higher pressure, the abrasive particles would break and turn into finer dust before leaving the nozzle, thereby reducing the cutting ability.

Understanding waterjet power

Horsepower determines the amount of water flowing from the sprinkler. For example, the orifice of a 50-HP booster pump running at 60,000 PSI using 0.022 inches will typically output 1 gallon per minute (GPM). A 100HP pump running at 60,000 PSI usually outputs 2 GPM.

The power of the pump is different from the power of the nozzle, and the direct drive and booster systems do have different pump efficiency characteristics. However, if the abrasive flow rate, nozzle/orifice diameter, and nozzle horsepower are all the same, the booster pump and direct drive pump will cut the most common materials and thicknesses at the same speed.

The effect of extra horsepower also depends on the material being cut. Higher horsepower will definitely speed up the processing speed of 3 inches thick aluminum, but when using 0.010 inches to process the gasket, its effect is negligible. . When cutting very thin materials, it is best to run at a lower power to make the frequency change more stable. Another option is to use a pump with a variable frequency drive.

In general, the most effective way to improve the efficiency of water jet cutting is to increase the horsepower pump output, as this will cause more water and abrasives to pass through the nozzles and materials.

Best way

Finding the best combination of horsepower and pressure for a given machine is like telling you the best way to drive a car. The Scion xA drive is completely different from Shelby Cobra. In addition, depending on the engine conditions of these two vehicles, their maintenance, their service life and how they are assembled, the power and performance of the two vehicles may fluctuate drastically. Both vehicles can take you from point A to point B; the problem actually comes down to the comfort of the ride.

That being said, certain combinations of horsepower and pressure tend to work under ideal conditions and with specific orifice/nozzle sizes. To make a car analogy, it’s like the fuel efficiency you posted on a new car. The power/pressure combinations shown in the chart may be considered optimal on paper, but they must never explain what might happen to your machine. Think of them as a good starting point for optimizing waterjet cutting on specific materials. For most standard metals, including aluminum, steel, brass, and titanium, the correct cutting conditions will depend on whether the material is thick or thin.

Acrylic and other plastics are excellent choices for waterjet cutting because they have no heat transfer characteristics, but they do have some chipping or cracking problems during perforation. In this respect, glass behaves similarly. For materials that are fragile or easy to layer, please perform low-pressure perforation first, and then cut.

Foaming requires another method entirely, because the water spray process does not use abrasives. The manufacturer does not need to pay attention to the orifice/nozzle size, but can optimize the foam application by adjusting the jewelry size. A good starting point is 20-50 HP and 60 KSI pressure, with a jewelry size of 0.011 inches.

You cannot optimize waterjet cutting in a vacuum. Even if a perfect balance is achieved between garnet mesh size, pressure, power and orifice/nozzle diameter, the same perfect cycle time and profitability are still out of reach. In any sufficiently complex production environment, productivity problems can be caused by many factors, and pump technology is one of them.

In any case, the grinding waterjet has evolved from a special equipment of the manufacturer to a new type of universal tool in mechanical workshops and manufacturing facilities around the world. Even if the technology changes, the water and garnet remain basically the same. As long as these materials form the basis of all hydrojet cutting, horsepower and pressure will play a major role.

The simplest answer to the horsepower and pressure debate is that there is no debate at all. Both play an important role in optimizing the spraying process, but the relative importance of power and pressure depends entirely on your spray application and the condition of the sprayer itself.

For most shops looking to increase the cutting speed of their existing machines, adding a more powerful pump will provide the greatest advantage. However, the only way to find the best balance between horsepower and pressure is to conduct extensive experiments.

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