Information For the Manufacturing Engineer

As a manufacturing engineer one must be familiar with all the available manufacturing processes. In this article we will be discussing water jet cutting and how it can be used to improve your manufacturing process. Waterjet cutting at its simplest form is a jet of water at a very high pressure that abrasively removes material. This water usually has an abrasive material such as Garnett added to aid in the abrasive material removal qualities.

It works by pressurizing water up to 60,000 psi, and forcing it through a tiny opening Waterjets are capable of cutting a variety of materials with CNC accuracy. Typical part tolerances range from between 0.005 and 0.010 of an inch. When small amounts of abrasive particles, such as garnet, are mixed into the jet stream, the resulting "abrasive waterjet" can cut virtually any hard material such as metal, composites, stone and glass.

Waterjet Cutting vs. Lasers
Laser cutting is a very productive process and certainly has its place. However, Waterjets do have several advantages over lasers:

There are no thickness limitations. A typical 1500 watt CO2 laser is limited to about .625" thick steel plate. There are no problems cutting with reflective materials such as Brass, Copper and Aluminum. There is no heat output, so there is no heat-affected zone (HAZ). Waterjets can cut materials, which are heat sensitive such as plastics, rubber or composites.

Waterjet vs. Plasma
Plasma removes material around 5800 deg f. leaving a large heat-affected zone. The surface finish of plasma generally is very course with a lot of slag. This slag requires secondary operations to remove where water jet cutting does not. Abrasive Waterjets have no thickness limitation, and can be much more closely nested.

What tolerances can we expect from waterjet cutting?
The accuracy you will get Typically +/- .010" but depending on part size and part thickness.

How thick can it cut?
Typical waterjet's can cut up to 8.00" in thickness depending on material type and hardness.

What materials cannot be cut?
Almost any material can be cut by water jet. There are some exceptions that can prove to be difficult; these materials tend to be laminated in construction. Test cuts have resulted in delaminating.

How thick is the Kerf?
The Kerf is about 10% of the diameter of the cutting orifice. If a .040" diameter tip is used Kerf is around .043" in diameter.

What is the minimum radius/ diameter that can be cut?
The radius limitations are dependent on the diameter of the orifice being used and are equal to the Kerf diameter. Using a .040" diameter tip the minimum radii and hole diameter will be around .043".

What taper can I expect?
The taper you get is a function of the cut speed. However, the worst taper you will get will be equal to the maximum Kerf width at the top (example: 0.043") and 0.000". At the bottom. As you slow down the taper will be reduced until you get parallel sides.

What fixturing is required?
Since the force exerted on the work piece is very small (under 5 lbs. for average cuts), the need for very large, stiff fixtures is eliminated.

For more information on waterjet cutting services and how they can benefit your manufacturing production visit http://www.e-bti.com.

Brent Cohagan
President
Cohagan Engineering, Inc.
http://www.CohaganEngineering.com

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