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Waterjet Cutting Glossary

Waterjet Cutting

Abrasive
The cutting medium of a waterjet cutting abrasive jet. Usually garnet or similar "sand like" substance.

Abrasive Flow Rate
The rate at which abrasive flows into the cutting head. Typically, abrasive is added to the nozzle from 0 - 1 lb/minute.

Abrasive jet:
A water jet with the addition of abrasive . Used to cut or machine nearly any hard material such as metal, stone, glass, etc.

Other terms loosely used to mean "abrasive jet":

Attenuator:
An attenuator is a pressure vessel that maintains output pressure for a constant water flow, compensating for uneven pressure generated by some pumps. (Also called accumulator).

AWJ:
Acronym for "Abrasive Water Jet" (or abrasive jet).

Bit Stream
A stream of "bits" used to control machine movements on OMAX controllers. Effectively allowing the machine to set independent feed rates at over 2000 points per inch.

Bridge / Bridging:
When cutting multiple parts that might tip and fall into the tank, it is sometimes useful to "bridge" the parts with a thin piece of metal that connects them together. Then, once the cutting is finished, the parts are removed from the machine, and the bridges are cut off. (This is similar to the way parts are held together in plastic for plastic hobby models).
See also: Tabbing

C-Axis
Sometimes used to refer to a 3rd axis on the machine, such as a rotary lathe axis.

CAD (and CAD / CAM)
C
omputer Aided Design. CAD software is the software that you use to make drawings of parts. CAM is Computer Aided Manufacturing. CAM software is used to make tool paths. Often CAD and CAM software are included in the same software package for convenience.

Catch Tank
A tank of water underneath the cutting head to allow the cutting beam to disperse, and prevent holes in your floor. Often catch tanks are filled with other material to slow the jet down, such as ceramic balls. The catch tank is also used to accumulate spent abrasive, and drop outs from your parts.

CNC
Acronym for "Computer Numerical Control". In basic terms a CNC machine has a computer that is controlling the motion.
See G-Code.

Common Line Cutting:
Common line cutting is used when making multiple parts, so that when one part is cut, a portion of the second part is cut as well. The advantage is that much time is saved, because one cut can make two parts. The disadvantage is that it is sometimes difficult to program (depending on the geometry), and generally produces lower precision cuts than cutting the parts separately.

Crankshaft Pump
A type of pump where the pressure is generated by plungers that are driven by a crankshaft.
See also Triplex Pump or Intensifier pump.
Also often called "direct drive pump".

Cutting index
See Machineability

Cutting Quality

1. Simply the "quality" of cut.
2. A term used on OMAX, and sometimes other controllers to indicate how the machine should cut a given surface of the part. A quality of "1" being a very rough, high speed cut, and a quality of "5" being a very smooth, highly precise operation. "Quality" was coined by OMAX Corporation, and is becoming the standard for describing surface finish for abrasive jet machined parts. Note, however, that different manufacturers of equipment use "Quality" to mean different things. For example what is "Quality of 1" by one manufacturer's definition is not the same as another's "Quality of 1".

Cutting Model
A model of how the abrasive jet or water jet will behave when cutting. Cutting models are used to predict how to slow down and compensate for the effects of cutting with a "floppy tool".

Draft Angle:
The angle caused by Taper.

Dynamic Pierce
A method of piercing a material by allowing the jet to start moving along the part path.
See Pierce for other popular methods of piercing.

DXF File
Drawing Exchange Format. This is a kind of graphical file format, defined by AutoDesk, inc., that is designed to be a common platform to exchange CAD drawing files between various CAD software packages.

DWG File
An Autocad Drawing file. The official specification for this file format is proprietary to AutoDesk corporation, which makes it difficult for third party vendors to be compatible with it.

EDM
Acronym for "Electrical Discharge Machining". A slow, but extremely precise method of machining using electrical sparks to remove material in very small increments.

E-Stop
Emergency Stop. Typically a button that you press to stop the machine in the event of an emergency.

Etch
To mark the material without cutting all the way through. This is typically accomplished by reducing pressure, reducing abrasive flow rate or increasing feed rate.
See also: Scribe

Feed Rate
The speed at which the cutting head moves. See also Cutting Model.

Focusing tube
See Mixing Tube.

Frosting
An effect of stray abrasive particles "frosting" the material you are cutting. It typically occurs right at the edge of where you have cut, or in a circular pattern around where you pierced the material.

Garnet
The most popular abrasive used in abrasive jet machining. It is capable of cutting an extremely wide range of materials, yet is soft enough to give you long life of your mixing tube.

G-Code
Although not particularly well suited for precision abrasive jet machining, G-Code is the most popular programming language used for programming CNC machinery.

Hard Limit
A hard limit is a stop on the machine that prevents the machine from moving further in a given direction. Typically these are used to prevent the machine from moving beyond its physical limits.
See Soft Limit

Hard Water
"Hard" water is water with a lot of dissolved minerals in it, typically calcium and magnesium. Because water is an excellent solvent, it dissolves small amounts of minerals as it percolates through rocks and soil. As the mineral content increases, so does the "hardness" of the water. Hard water will tend to leave behind mineral deposits, which require frequent cleaning or replacement of pipes, filters, and jewels.

Hazing
See Frosting

Home
1. A spot on the machine that is defined either in software or hardware as a reference point.
2. Where your heart is.

IGES File
A CAD file format for exchanging CAD Drawing data between different CAD software systems.

Intensifier
A type of high pressure pump that uses hydraulics to make very high pressures.

Jewel
The orifice in which water exits to form the cutting stream. Typically jewels are made from sapphire, ruby, or diamond (thus, the name "jewel").

Jet Lag
As the cutting head moves across the material that it is cutting, the spot where the jet exits the material will lag behind the spot where it entered the material. This lag is "jet lag".

Kerf
The width of the cutting beam. Typically the kerf width for an abrasive jet ranges from 0.020" to 0.060", depending on the nozzle. A water jet has a narrower kerf, with 0.005" to 0.014" being typical.
See also tool offset.

Kick back
As the machine accelerates out of a corner that it has just cut, the jet will "kick back".

KSI
Thousands of pounds per square inch. 1 KSI = 1000 Pounds Per Square Inch (PSI)

Lag
See Jet Lag

Machineability
A number used to represent how easy it is for the abrasive jet or water jet to machine a given material. Sometimes referred to as "Cutting Index"

Mesh
The coarseness of abrasive used. For example, 80 mesh abrasive is typical of most abrasive jet applications, but 120 mesh, which is a finer abrasive, might be used for special applications.

Mixing Tube
Sometimes referred to as "nozzle" or Focusing tube. This is a tube, made from extremely hard material, that focuses the abrasive and water into a coherent beam for cutting.

Muff
A sponge or brush around the tip of the nozzle to prevent splash.

Nesting Software:
Nesting software is used to optimally fit many different parts to a single sheet of material.

Newtonian Accelerations
Term used to describe accelerations having to do with the physical limits of the machine, due to Newton's Laws. (As opposed to acceleration limits due to the cutting effects of the jet, and cutting model.).

Nozzle
Usually, when someone says "nozzle" they are either referring to the complete nozzle assembly (mixing tube + Jewel + nozzle body and perhaps some plumbing.) Other times, "nozzle" is used as a synonym for Mixing Tube.

ORD File
OMAX Routed Data File. A file format containing routed tool path information. (I.e. it's a tool path, and not a CAD drawing.). This is the information that the controller needs in order to machine a part. For details on the standard, contact OMAX , or download it from their technical support web site.

Orifice
See Jewel

Offset
See Tool Offset

Pierce
A "Pierce" is the process of drilling through the material to be machined. Abrasive jets make their own start holes by "piercing" the material.

There are various methods for piercing:

Stationary Piercing (very slow on thick materials, but good for small hole drilling or piercing thin materials.)
Dynamic Piercing (usually faster than stationary, but requires a lot of room on thick materials)
Wiggle Piercing (usually the fastest method of piercing where there is not enough room for dynamic)

PWJ (Pure Water Jet)
See Water jet

Quality
See Cutting Quality

Reverse Osmosis
A method for filtering water.

Scribe
This is a word that is sometimes use to distinguish between etching with abrasive, and scribing with water only. Similar processes, except etch uses abrasive and scribe does not.
See also Etch

Silicosis
"Silicosis is a disabling and sometimes fatal lung disease which can afflict workers who are overexposed to fine airborne particles of crystalline silica. Since crystalline silica is the second most common mineral in the earth's crust a basic component of sand, quartz and granite rock more than 1 million workers in many different types of jobs are at-risk of developing silicosis, including highway construction workers, miners, sand-blasters, and foundry workers. When workers breathe in dust containing silica, scar tissue can form in their lungs and reduce their ability to extract oxygen from the air. There is no cure for silicosis -- prevention is the only answer."

- Quote from http://www.cdc.gov/niosh/nmsilcon.html

For the above reason, avoid using abrasives containing silica (like sand). Use at your own risk!

Slat
One of the supports used to support the material you are machining. They are typically disposable.
An alternate to slats, or a complement to them, is to use ceramic balls. It appears to be a good technique, especially for small parts that might otherwise tip or fall in-between slats. A more popular method for accomplishing this is also water jet brick.

A common question is, "If the abrasive jet can cut just about anything, then how come the slats don't get cut?" The answer is that they do.
As the jet cuts the parts, it goes right on through, and cuts the support slats. However, the slats are thin in the horizontal direction, and very thick in the vertical direction. What happens then, is that the jet gets part way down the slats, and then skips to the side, and does not cut the slat all the way through. Eventually, the slats wear until they look like a bunch of rusty needles. At this point, they are rotated to a less frequently used area of the table, and / or flipped upside down. Finally, the slats will eventually cut in half, at which point they are replaced.

See also: Water jet Brick

Soft Limit
Software limit. A means of defining an area or boundary of motion for which the machine cannot exceed. Typically these are used to define the cutting envelope in which the head can move without crashing into something. This is done in software, instead of hardware, so that it can be changed when you change your fixturing or setup, and so that the machine can warn you ahead of time before you attempt to do an impossible move.

See hard limit

Splash back
The mess that is made when you don't cut all the way through, or the jet ricochets off of a slat. Very common during piercing, or when nozzles fail. This is the reason you often see sponges or other guards wrapped around nozzles.

Stationary Pierce
A method of piercing the material where the jet turns on, then stays stationary until the material is pierced. This is typically a very slow method of piercing, but is fine for thin materials that pierce quickly no matter what. It also allows you to pierce the material in the minimal amount of space, and is the only option for piercing very small holes. See Pierce for other options.

SUPER-WATER®
SUPER-WATER® is a chemical that is added to the water of an abrasive jet or water jet in order to focus the cutting stream, increase cutting speed, and reduce wear of high pressure components.

Striation marks
The marks left by the jet as it wiggles around. The faster you cut, the more striation marks form.

Tab / Tabbing:
Tabbing is a method for holding parts in place, by leaving a small piece of material that is connected to the original plate from which it is being cut, so that they don't fall into the tank or tip and collide with the nozzle after they are done being cut out.
See also Bridging

Tail
See Jet Lag

Taper
Taper is the difference between the top profile of the cut versis the bottom profile.

The biggest causes of taper are:

Some machines have the capability to remove V and reverse taper by simply tilting the cutting head to compensate, or cutting at a pre-determined speed to minimize the taper.

Tool Offset
Because the cutting beam of an Abrasive jet or a water jet is not infinitely thin, it is necessary to offset the tool slightly from the geometry of the part. For example, a typical kerf width of a nozzle is about 0.030". If you were to trace the exact outline of the part you want to cut, the part would be undersized by 0.015", which is half of the kerf width. Therefore, it is necessary to follow a path that is "offset" by this amount.

So how do you measure the width of the jet?
What you do, is you cut a part of known dimensions, then measure the error. For low precision work, you can just guess that it's 1/2 the width of the mixing tube's inside diameter. For high precision work, it is necessary to measure the error on a previously machined part.

Traverse
Normal machine movement without cutting, for example to move the cutting head into position to cut.

Triplex pump
A type of pump that uses 3 plungers driven by a crankshaft to make pressure. See Crankshaft pump.

Ultra High Pressure (UHP):
A term to describe the extreme pressures that are used in water jet and abrasive jet machining. Typically pressures range from 20,000 PSI to 100,000 PSI. Most pumps are limited to pressures below 60,000 KSI due to metal fatigue limitations in all areas of high pressure plumbing.

Water jet:
A pressurized jet of water exiting a small orifice at extreme velocity. Used to cut soft materials such as foam, rubber, cloth, paper, etc.
Sometimes people use the word "water jet" when they really mean "abrasive jet".
See Abrasive jet

Water Jet Brick
An surface made from corrugated plastic as an alternative to slats. It is very useful when machining tiny parts that would fall between the slats and get lost. It is also useful when cutting scratch-prone materials where splash back from the slats might frost the underside of the material. The primary disadvantage is that water jet brick wears very quickly, and as it wears, it fills the catch tank with gooey plastic powder.
See also: Slats

Weep hole
A small hole drilled into high pressure fittings to allow the water to escape in a safe manner should a leak occur.

Wiggle pierce
A method of piercing where the jet "wiggles" back and forth to "dig" its way down. This is much faster than "stationary" and sometimes faster than "dynamic" piercing because it allows the jet to escape and clear out removed material. See Pierce

WJTA
Water Jet Technology Association. A good source for hard core information on waterjet cutting and abrasive jet related technology. (http://www.wjta.org)

This technical information has been contributed by
3D Machine Inc.

Click on Company Name for a Detailed Profile

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