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Function and Applications of Waterjets

Waterjet is an effective cutting tool in two major kinds which is capable of cutting almost any materials.

Function and Applications of Waterjets

Waterjet is a generic term used to describe equipment that uses a high pressure stream of water for cutting or cleaning purposes. Abrasivejet is a subcategory of waterjet in which abrasive is introduced to accelerate the process. Pure waterjet and water-only cutting are phrases for specifically distinguishing waterjets that do not use abrasive. In other words: abrasivejet and pure waterjet are kinds of waterjet  , and waterjet is a kind of machinery.
How do waterjets work?
Take ordinary tap water and pressurize it to 60,000 psi (4,000 bar) and force it through a very small hole. Mix the water with garnet abrasive and you have a very thin stream of water traveling very fast that will rapidly erode most materials. Some waterjets are “pure waterjets” and don’t add the garnet abrasive. These are used to cut softer materials  , such as food , rubber , and foam.  
What can waterjets cut? What can’t they cut?
Waterjets can cut just about any material that can be made into a sheet and placed in front of them. The most popular materials are metals (especially aluminum , because it’s relatively soft and cuts quickly) , because waterjets can cut intricate shapes to a high precision quickly and economically. Waterjets also commonly cut stone and glass , because the waterjet can get intricate shapes not possible using traditional machining methods.
Among the very few materials that waterjets cannot cut are diamonds and tempered glass. Diamonds are too hard to cut (and there may be a few other very hard materials that can’t be cut). Tempered glass will shatter when it is cut with a waterjet (tempered glass is designed to shatter when it’s disturbed and is frequently used in windshields for this very reason). A few advanced ceramics are so hard that it’s not economical to cut them. Some composite materials (layers of different materials sandwiched together) can’t be cut because the water can seep between the layers and “delaminate” the material.

Basic waterjet principles
Waterjets are fast , flexible , reasonably precise , and in the last few years have become friendly and easy to use. They use the technology of high-pressure water being forced through a small hole to concentrate an extreme amount of energy in a small area. The restriction of the tiny orifice creates high pressure and a high-velocity beam , much like putting your finger over the end of a garden hose. Pure waterjets use the beam of water exiting the orifice to cut soft material like diapers , candy bars , and thin soft wood , but are not effective for cutting harder materials.
An abrasivejet starts out the same as a pure waterjet. As the thin stream of water leaves the jewel , however , abrasive is added to the stream and mixed. The high-velocity water exiting the jewel creates a vacuum which pulls abrasive from the abrasive line , which then mixes with the water in the mixing tube. The beam of water accelerates abrasive particles to speeds fast enough to cut through much harder materials.

Advantages of waterjet machining  
There is a reason that waterjet machining has rapidly grown in popularity since the mid-1990’s. Actually there are a number of reasons , listed below , but they mostly come down to “versatility.” A waterjet is a versatile and flexible machining tool.
•    Cut virtually any material
•    Fast setup and programming
With waterjet machining , a flat piece of material is placed on a table and a cutting head moves across the material. This simplicity means that it’s fast and easy to change materials and that no tool changes are required. The movement of the machining head is controlled by a computer , which greatly simplifies control of the waterjet.
•    Almost no heat generated on your part
What little heat is generated by the waterjet is absorbed by the water and carried into the catch tank. The material itself experiences almost no change in temperature during machining.
•    No mechanical stresses
•    Machine thick material
Typically , most waterjet parts are made from metal that is 2″ (5 cm) or thinner.
•    Are very safe
Anything that can cut through 2″ steel will make short work of flesh and bone. Aside from this , however , waterjets are very safe. A leak in a high-pressure water system tends to result in a rapid drop in pressure to safe levels. Water itself is safe and non-explosive and the garnet abrasive is also inert and non-toxic. One of the largest hazards is cuts from the sharp edges of material created by the waterjet.
•    Modern systems are now very easy to learn
Control of the waterjet head is complicated and requires careful calculation to get the proper speed that will give the best result. This means that the system needs to be controlled by a computer , which means that the user-interface for the system can be simplified and made friendlier.
•    Environmentally friendly
As long as you are not machining a material that is hazardous , the spent abrasive and waste material become suitable for land fill. The garnet abrasive is inert and can be disposed of with your other trash. In most areas , excess water is simply drained to the sewer. In some areas , water treatment may be necessary prior to draining to sewer. In a few areas , a “closed loop” system that recycles the water may be required.
•    No start hole required
Start holes are only required for materials that are difficult or impossible to pierce. A few poorly bonded laminates can fall into this category , in which case pre-drilling or other special methods may be used.
•    Narrow kerf removes only a small amount of material
When you are working with expensive material (such as titanium) or hazardous material (such as lead) , this can be a significant benefit.  

Waterjet Applications
Waterjet machines are not specialty machines for niche applications. They are general purpose tools that are useful in any machine shop. Following is a small sampling of specialized applications.
•    General purpose machine shops
•    Artists: Artists use waterjets because they can create intricate designs in materials that have traditionally been difficult to work with , such as stained glass , marble and stone.
•    Architectural: Similar to the art market , there are many machines out there making custom flooring from stone , as well as making architectural details from metal.
•    Aerospace: Companies that makes parts for the aerospace industry machine lots of aluminum , which is easily machined on a waterjet. Exotic metals such as , titanium , and Hastelloy can also be machined by waterjets.
•    Manufacturing: Waterjets are used for making parts of products that are sold , as well as many of the parts used to make the machines on the assembly lines.
•    Model shops / rapid prototyping
•    Schools

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