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Overview 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.

It is normal, and common, to use the term waterjet to refer to abrasivejets, though in some cases it can be confusing. On this web site, we'll use waterjet when referring to topics that cover both pure waterjets and abrasivejets, and use the terms pure waterjet and abrasivejet when discussing topics that are specific to one or the other.

Article Contents

 


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. Since metals are the most common material cut by machining shops, waterjets tend to cut a lot of metal.

Waterjets also commonly cut stone and glass, because the waterjet can get intricate shapes not possible using traditional machining methods. These materials are popular with artists who like to work with these materials and waterjets because it lets them create almost anything they can envision.

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. Many composite materials cut just fine, though, and there are some techniques to cutting laminated materials.

What do they cost?

Waterjets typically come as complete systems, including the high-pressure water pump, a system to precisely position the waterjet nozzle, a tank to catch the waste water, and an abrasive feed system. Prices run from $50,000 to 300,000, with $150,000 being about average for a mid-range waterjet system.

Prices can run considerably higher than this for custom systems or very large waterjet cutting systems. 

Waterjet systems are not currently something for the home workshop. You'll find them in use in machining shops and industrial workshops. Among other factors, you need industrial levels of electricity to power the pumps (which can pull as much as 50 amps; some pumps require 250 amps to get started).

For the hobbyist interest in waterjets, the more economical approach is to work with a job shop to make the parts. Most job shops can accept computer drawings you create to make exactly the part you want.

List of waterjet job shops by state and country


 

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 (typically called the "orifice" or "jewel") 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.

Diagram of a generic water jet

Typical design of a pure waterjet nozzle

The inlet water for a pure waterjet is pressurized between 20,000 and 60,000 Pounds Per Square Inch (PSI) (1300 to 6200 bar). This is forced through a tiny hole in the jewel, which is typically 0.007" to 0.020" in diameter (0.18 to 0.4 mm). This creates a very high-velocity, very thin beam of water (which is why some people refer to waterjets as "water lasers") traveling as close to the speed of sound (about 600 mph or 960 km/hr).

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 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.

Diagram of typical abrasivejet Abrasive jet in action

(Left): A diagram of an abrasivejet nozzle. (Right): Photograph of the same nozzle, with the guard removed, cutting out some parts.

The cutting action of an abrasivejet is two-fold. The force of the water and abrasive erodes the material, even if the jet is stationary (which is how the material is initially pierced). The cutting action is greatly enhanced if the abrasivejet stream is moved across the material and the ideal speed of movement depends on a variety of factors, including the material, the shape of the part, the water pressure and the type of abrasive. Controlling the speed of the abrasivejet nozzle is crucial to efficient and economical machining.

Waterjet and abrasivejet nozzles Abrasivejet nozzle

(Left) A typical waterjet nozzle to the left of an abrasivejet nozzle.
(Right) An abrasive nozzle installed on a machine. The white tube protruding from the side of the abrasive nozzle brings the abrasive to the nozzle.


This video shows a waterjet cutting a small design from what looks like 1/4" aluminum. The cutting takes place above water which makes it noisier, but easier to see what's happening. This is only the last part of the cutting, but note the intricate shape that the waterjet achieved.

Waterjet nozzle fired into the air

In this video below, a waterjet nozzle is raised a few inches above the work surface, and fired for a few seconds into the air. Keep in mind that there is about 30 horsepower going through that little stream of water.

Abrasivejet nozzle, firing in the air


Cutting 1/2" aluminum at Westec trade show

This video was taken at the Westec trade show some years ago (1997 or so). The video shows cutting from various angles, with narration.

 

Cutting a foam mouse pad

A large mouse-pad, that is designed to wrap around a keyboard, is cut from foam.

"The reason I chose to film foam being cut is because it is fast enough that the video can be worth watching, and you can see a complete part from start to finish," said Carl Olsen. "I also used an abrasive nozzle, which was really unnecessary. I could have used a water-only nozzle which would have made a nicer edge finish, but I did not have one handy. Also, because this was foam, I could have cut it much faster, but I chose a slower speed so that I could have time to react, should it want to float away on me."


 

Advantages of waterjet machining 

"If you need a machine and don't buy it, then you will ultimately find you have paid for it but don't have it" - Henry Ford.

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. You can cut a wide variety of material efficiently and cost-effectively and can create a wide variety of parts.

A two-dimensional shape

Machine any two-dimensional shape with one tool

Cut virtually any material

Because waterjets cut using water and abrasive, they can work with a wide variety of materials. These materials include:

  • Copper, brass, aluminum:
  • Pre-hardened steel
  • Mild steel
  • Exotic materialss such as titanium, Inconel and Hastalloy
  • 304 stainless steel
  • Brittle materials such as glass, ceramic, quartz, stone.
  • Laminated material
  • Flammable materials

One of the few materials that cannot be cut with a waterjet is tempered glass. Because tempered glass is under stress, as soon as you begin to cut it, it will shatter into small fragments—as it is designed to do.

[picture dragon artwork machined with an abrasive waterjet]

Pictured here is a dragon machined from 1" (2.5 cm) thick bulletproof glass, and inlay of marble and granite

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 (although in some custom systems, the material moves past a fixed head). This simplicity means that it's fast and easy to change materials and that no tool changes are required. All materials use the same cutting head, so there is no need to program tool changes or physically qualify multiple tools.

The movement of the machining head is controlled by a computer, which greatly simplifies control of the waterjet. In most cases, "programming" a part means using a CAD program to draw the part. When you "push print," the part is made by the waterjet machine. This approach also means that customers can create their own drawings and bring them to a waterjet machine for creation.

Little fixturing for most parts

There are very low sideway forces with waterjet machining--cutting the material doesn't push it. The downward forces are also small, in the range of a few pounds. Typically, the largest force is from the water in the tank pushing back up against the material.

Fixturing is generally a matter of weighing down the material by placing weights on it. Small parts might require tabs to prevent them from falling into the tank.

The low side forces, means you can machine a part with walls as thin as 0.01" (0.25 mm). This is one of the factors that make fixturing is so easy. Also, low side forces allow for close nesting of parts, and maximum material usage.

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. During piercing 2" (5 cm) thick steel, temperatures may get as high as 120° F (50° C), but otherwise machining is done at room temperature.

The result is that there is no heat affected zone (HAZ) on the material. The absence of a HAZ means you can machine without hardening the material, generating poisonous fumes, recasting, or warping. You can also machine parts that have already been heat treated.

No mechanical stresses

Waterjet machining does not introduce any stresses into the material.

Machine thick material

While most money will probably be made in thicknesses under 1" (2.5 cm) for steel, it is common to machine up to 4" (10 cm). The thicker the material, the longer it will take to cut. A part made from material twice as thick will take more than twice as long. Some companies make low tolerance parts out of metal that is up to 5" to 10" thick (12.5 cm-25 cm), but it takes a long time and tends to be an occasional operation. Typically, most waterjet parts are made from metal that is  2" (5 cm) or thinner.

[picture of 2in ss304 machined with an abrasive waterjet]

Pictured here is a part made from 2" (5 cm) thick 304 stainless steel 

Are very safe

Obviously, you don't put any body parts in front of a waterjet machining head while it is on. 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. Modern systems are designed the same way as many other computerized CAD systems and are quickly learned.

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.

If you are machining lots of lead or other hazardous materials, you will still need to dispose of your waste appropriately, and recycle your water. Keep in mind, however, that very little metal is actually removed in the cutting process. This keeps the environmental impact relatively low, even if you do machine the occasional hazardous material.

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.

The pumps do use a considerable amount of electricity, though, so there is some additional environmental (and cost) impact due to this.

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

The amount of material removed by the waterjet stream is typically about 0.02" (0.5 mm) wide, meaning that very little material is removed. When you are working with expensive material (such as titanium) or hazardous material (such as lead), this can be a significant benefit. It also means that you can get more parts from a given sheet of material.

When machining or roughing out expensive materials such as titanium, your scrap still has value. This is because you get chunks, not chips.


Advantages of waterjets compared with lasers

Laser cutting involves using a laser focused on material to melt, burn, or vaporize the material. The laser can be a gas laser (such as CO2) or a solid-state laser. The laser beam can be static, and the material moves in front of the laser, or the laser can itself be moved across the material. When the laser moves across the material, additional optics are required as the distance from the emitting end of the laser changes. Lasers have the advantage over traditional machining methods that the laser never touches the material (avoiding contamination) and the HAZ is relatively small.

Advantages of waterjets

Waterjets have a number of advantages over lasers. In many respects, however, the two tools are complementary and many machine shops own both of them.

  • Can work with more materials
    Waterjets can machine reflective materials that lasers cannot, such as copper and aluminum. Waterjets cut a wide range of material with no changes in setup required. Also, materials which are heat-sensitive can be cut using waterjets.
  • No heat-affected zone (HAZ) with waterjets
    Waterjet cutting does not heat your part. There is no heat-affected zone (HAZ) or thermal distortion, which can occur with lasers. Waterjets do not change the properties of the material.
  • Waterjets are more environmentally friendly
    Abrasivejets typically use garnet as the abrasive material. Garnet is a non-reactive mineral that is biologically inert. The only issue with waterjets is when you are cutting a material that is potentially hazardous (such as lead), since small pieces of the material will be abraded and mix in with the spent garnet.
  • Waterjets are safer
    There are no noxious fumes, such as vaporized metal, and no risk of fires. The distance between the end of the waterjet nozzle and the material is typically very small, although caution is needed when the waterjet nozzle is raised.
  • Uniformity of material not important
    With lasers, the material needs to be relatively uniform. In particular, when cutting over uneven surfaces, the laser can lose its focus and cutting power. A waterjet will retain much of its cutting power over uneven material. Although the material may deflect the cutting stream, it typically has a negligible effect.
  • Lower capital equipment costs
    The cost of a waterjet machine is generally much lower than that of a laser. For the price of a laser, you can purchase several waterjet machining centers.
  • Better tolerances on thicker parts
    Waterjets offer better tolerances on parts thicker than 0.5" (12 mm). For thinner parts, both waterjets and lasers offer comparable tolerances.
  • Waterjets can machine thicker materials
    How thick you can cut is a function of how long you are willing to wait. Waterjets easily handle 2" (5 cm) steel and 3" (7.6 cm). Although some people have used waterjets at thicknesses of up to 10" (25 cm) in steel, it is difficult to maintain precision in materials thicker than  2" (5 cm). Lasers seem to have a maximum practical cutting thickness of 0.5" (12 mm) to 0.75" (19 mm).
  • Simpler maintenance
    Maintenance on a waterjet is simpler than that of a laser.
  • Simpler operation
    Waterjets are computer controlled, so that the operator does not have to be highly skilled and trained. 
  • Better edge finish
    Material cut by waterjets have a fine, sand-blasted surface because of the way the material was abraded, which makes it easier to make a high-quality weld. Material cut by laser tends to have a rougher, scaly edge, which may require additional machining operations to clean up.

Advantages of waterjets compared with EDM

EDM stands for Electrical Discharge Machining and is used to machine electrically conductive materials, such as steel and titanium. An electrical arc rapidly discharges between an electrode and the workpiece material. The series of arcs removes metal by melting it and vaporizing it, essentially eroding the metal using electricity. The particles are flushed away by a continuously circulating non-conducting fluid, such as deionized water or kerosene. EDM can create intricate shapes in hard materials that are difficult to machine using traditional methods.

Advantages of waterjets

Although the above part could be made using EDM, it's much faster to make it using a waterjet

Many EDM shops are also buying waterjets.  Waterjets can be considered to be like super-fast EDM machines with less precision.  This means that many parts of the same catagory that an EDM would do can be done faster and cheaper on an abrasivejet, if the tolerances are not extreme.

New technology allows Abrasive jets to obtain tolerances of up to +/-.003" (0.075mm) or better

Abrasive Jet machining is useful for creating start holes for wire insertion later on. (a mill could do the job, but only after spotting the hole, changing tools to drill a pilot, then changing tools again to drill out the hole).

  • Faster
    Abrasive jets are much faster than EDM, which slowly removes the metal.
  • Can work with more materials
    Waterjets can machine non-conductive materials that EDM cannot, such as glass, wood, plastic, and ceramic. There is almost no limit to the type of materials that can be machined with waterjets.
  • Uniformity of material not important
    A waterjet will retain much of its cutting power over uneven material. Although the material may deflect the cutting stream, it typically has a negligible effect. Such material aberrations would cause wire EDM to lose flushing.
  • Waterjets make their own pierce holes
    Some types of EDM, such as wire-cut EDM, a hole needs to be first made in the material, which has to be done in a separate process. Waterjets can pierce the material, requiring no additional fixturing or machining.
  • No heat-affected zone (HAZ) with waterjets
    Waterjet cutting does not heat your part. There is no heat-affected zone (HAZ) or thermal distortion, which can occur with EDM. Waterjets do not change the properties of the material.
  • Waterjets require less setup
    Most of the fixturing with waterjets is weighing down the material so that it does not shift in the water tank. The fixturing needs to withstand forces of pounds and does not need to be elaborate or precise.
  • Make bigger parts
    The size of the part created with a waterjet is limited by the size of the material. In setups where the material passes underneath the waterjet, the finished part size can be huge. Even with an X-Y table setup, part sizes can be quite large.

waterjet EDM fixturing

Wire-cut EDM fixturing in a waterjet machining center.  This makes precision fixturing possible.  It also allows for pre-machining on the waterjet to release stresses in the material, and then use the exact same fixturing on the EDM to do secondary operations and final cutting to extreme tolerance.

Cheese cutter demonstrating the thin-wall machining abilities of an abrasive-jet.

The cheese slicer was made on a waterjet—note the very thin blade


Advantages of waterjets compared with plasma

In plasma cutting, a stream of gas is blown at high speed while an electrical arc is passed through it. This causes some of the gas to become very hot plasma. The gas, at about 27,000° F (15,000° C), then melts the metal or other substance it comes into contact with. The gas is moving fast enough that the molten metal is blown away from the cutting area.

Advantages of waterjets

The clearest advantage that waterjets have compared with plasma cutting is that waterjets operate at much lower temperatures. During piercing, the temperature of the material may rise as high as 120° F (50° C), but cutting typically happens at room temperature. The presence of the catch tank (a large tank full of waste water) helps to moderate the temperature as well. This lower temperature means there is no Heat Affected Zone when material is cut with a waterjet.

Waterjets also can cut materials that don't easily melt (such as granite) or that are destroyed by melting (many laminates). Waterjets are also more precise than plasma cutting.

Plasma cutting is typically faster than waterjet, particularly with very thick metal. Plasma torches can pierce and cut steel up to 12" (30 cm) thick.

Modern waterjets machines are relatively clean and quiet


Advantages of waterjets compared with flame cutting

Flame cutting, or oxy-fuel cutting, is used to cut metals by heating them to a high temperature and then introducing oxygen to melt the metal and perform the cut. Flame cutting only be used with iron and steel.

In flame cutting, the cutting torch combines oxygen with a fuel, such as acetylene, that heats up the metal. Once the metal is cherry red, a trigger on the torch is pressed that blasts oxygen at the metal. The hot metal reacts with the oxygen to form iron oxide (rust), which has a lower metal point than iron or steel. The iron oxide then flows away from the cutting zone. Some iron oxide may remain on the cut as slag, but it is easily removed by tapping or with a grinder.

Advantages of waterjets

While flame cutting can work only with iron or steel, waterjets can machine many different types of materials, both metal and non-metallic. Waterjets also do not appreciably heat up the material they cut--during piercing, temperatures may rise to 120° F (50° C), but during cutting the material is heated only a degree or two.

The edge finish created with a waterjet is smooth, similar to a sandblasted finish, rather than the rough edges left by flame cutting. Waterjets are more precise than flame cutting and have a much smaller kerf as less material is removed (particularly important when cutting expensive material).

Flame cutting can be faster than waterjets, especially when done using a multi-torch cutting machine, and as a result is cheaper than waterjet cutting.

The part on the top was roughed out with a waterjet, with secondary machining creating the part shown on the bottom


Advantages of waterjets compared with milling

Milling is typically done with a milling machine that can perform a series of operations on material, typically cutting, drilling, lathing, and planing. Most modern milling machines are six-axis machines that can perform complex sequences of milling operations rapidly and precisely.

Modern milling machine

A typical modern milling machine

Advantages of waterjets

Although mills cut faster, in most cases, than waterjets, the setup and fixturing with waterjets is much simpler. Setup with waterjets is typically a matter of just loading the part drawing into the controller software, setting the material and thickness and beginning machining. Similarly, fixturing is mostly a matter of weighing down the material so that it doesn't move on the table during machining. Clean-up on a waterjet is also faster and simpler. As a result, overall, a waterjet can have a greater throughput than a mill on similar parts.

Waterjets can also machine almost any material, including brittle materials, pre-hardened materials, and otherwise difficult materials such as Titanium, Hastalloy, Inconel, SS 304, and hardened tool steel.

titanium sheets cut by waterjet

With a waterjet, there is also no tool changing. The waterjet nozzle is the only tool used, and it is used for all the different types of materials that a waterjet cuts. There is also less wear on tools, especiall in harder and gummier materials, because the cutting action of the waterjet is the stream of water and abrasive. While there is wear on the mixing tube and high-pressure water componenets, this wear tends to be constant with time, and doesn't change with different materials.

Waterjets are frequently used for complimenting or replacing milling operations. They are used for roughing out parts prior to milling, for replacing milling entirely, or for providing secondary machining on parts that just came off the mill. For this reason, many traditional machine shops are adding waterjet capability to provide a competitive edge.

[picture of typical part machined with an abrasive waterjet]

This is a part you might otherwise do on a mill. It took less than 20 minutes to make with an abrasive jet, including setup and cleanup time! Actual machining time is about 6 minutes. Material is 0.5" (13mm) thick hastalloy with a tolerance about ±0.002" (0.05 mm). 


Advantages of waterjets compared with punch presses

A punch press uses a set of punches and dies to form parts out of metal. The metal is formed and cut by the punch press into a part, which may have secondary machining done to it or not. Coins are a common part that are formed using punch presses. The typical commercial punch press exerts about 20 tons of pressure.

Advantages of waterjets

Waterjets have a lower cost-per-piece for short runs than a die press, because of the expense (and time) involved in creating the dies and punches. Creating the drawing for a part on a waterjet machine is all that's needed to begin machining the part, where with a punch press, the drawing is usually only the first step to creating the die.

Lateral forces wtih a waterjet are negligible, which means that holes can be placed very close to the material edge, which is not the case with a punch press. Waterjets can also work with very thick materials, while punch presses are limited in thickness to the amount of pressure they can apply. And, of course, waterjets can work with many different types of materials, including brittle materials and laminates .

Some stamping houses are using waterjets for fast turn-around and rapid prototyping work. Waterjets make a complimentary tool for punch presses because they offer a wider range of capability for similar parts. For high production of thin sheet-metal, the stamp will be more profitable in many cases, but for short runs, difficult material, and thick material, waterjets have their place.

 

Word OMAX machined in the center of a file.  Done on an Abrasivejet

Five minutes is all it took to make this custom file

Waterjets also play a big part as just one part in a larger manufacturing process. For example, waterjets are often used to machine features into an existing part, or to do pre-machining to remove material before precision finishing on other machinery.


 

Where waterjets are used

Waterjet machines are not specialty machines for niche applications. They are general purpose tools that are useful in any machine shop. Following is  is a small sampling of specialized applications.

General purpose machine shops
Waterjets are good all-around machine tools, as it is fast and easy to go from idea to finished part. Waterjets can also work with many different types of materials with minimal fixturing and setup.

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 maching lots of aluminum, which is easily machined on a waterjet. Exotic metals such as Inconel®, titanium, and Hastalloy 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.

Automotive & transportation
Prototyping and production parts for automobiles, and the tooling for making automobiles. Also there are a lot of custom race car parts made on waterjets.

Laser shops
Lasers and waterjets are highly complementary tools. They both pick up where the other leaves off.

EDM shops
Some of the small size and higher precision waterjet machining centers are great complementary tools to EDM because they allow for higher speed machining of similar shapes, and can provide other services for the EDM such as pre-drilling start holes or stress relieving the part prior to skim cutting on the EDM.

Model shops / rapid prototyping
Fast turn-around of single piece production in nearly any material makes waterjets great for these kinds of applications.

Schools
Many of the larger size universities that offer engineering classes also have waterjets. They are great tools for the classroom environment because they are easy to learn, program, and operate, and because they can make one-off kind of parts quickly. They also provide a great service to other departments within the university that may need job-shop services.

Looking for somebody to make your part? Check our listings of waterjet job shops.


 

What it costs to make waterjet parts

There are a variety of ways to calculate the cost of making parts with a waterjet. This is true of most businesses, and the calculation of "Cost of Goods" is the subject of many books and business classes. This page looks at some approaches to calculating the cost of goods for parts made with a waterjet, which will then help you determine how much to charge for a part.

A lot of people price the work on their machines on dollars per hour basis. This may make sense for some kinds of machines, but not for a waterjet. A job shop with a multi-head machine running two pumps or a high power pump might have a much higher cost of operation than a shop with a small machine with a low power pump. If these two shops compete against each other purely on dollars per hour, then the shop with the smaller cheaper machine will make a lot more money. This is because the parts will take longer to make, and they will be cheaper to make, so the customer pays more yet the part costs less to make. The shop with the faster machine must therefore charge more per hour to take advantage of their faster machine.

waterjet with multiple cutting heads

A waterjet machine with four heads (Photo courtesy Pegasus Northwest, Inc.)

Another strategy is to price the work based on a dollars per square inch basis. This has the drawback that a part with a lot of geometry to it (curves and corners and pierces) will take a much longer time than a straight line cut, because the waterjet must slow down to avoid blow-out at the corners and turns. Likewise, material thickness and many other factors come into play, and cutting speed is not a linear function relating to thickness. So, while $/square inch may make sense for some machines, it does not for waterjets.

The best approach is to figure out how much it will cost you to make the part. Then estimate how much it would cost to make the part by competitive methods (either other kinds of machines, or your competitor with an waterjet). See if there are other savings such as being able to squeeze more parts from expensive material. Then, price from there. Your customer does not need to know if you are charging them $100per hour. They are not paying you for your time, they are paying your for the part.

Another option that can work, if you prefer a simpler, more objective formula, is to simply cost your work based on your true cost to make the part. Many machines have software built in to make this easy. Simply take the cost to make the part, and multiply by a factor, and there you have it.

The cost to make your part should include the following factors:

  • How much time will it take to program the path into a tool path? (And if the customer provides the toolpath in a compatible file format, any price break you might choose to give them.)
  • How much risk is there that you might break something (such as when cutting glass) and need to scrap it and start over?
  • Does the customer provide the material, or do you need to purchase the material?
  • How many times must you pierce the material? Each pierce is extra wear and tear on machine, and the associated risk of a nozzle plug or material cracking during piercing.
  • How much do your consumables cost you?
    • Electricity
    • Water
    • Abrasive
    • Spares and wear parts
  • Is there any special setup or risk to consider?
  • How much time will it take to actually do the cutting?
  • How much time will it take you to load and unload the parts and material, and clean up the machine afterwards?
  • Is the customer ordering a large quantity?
  • Is this taking your machine away from doing another possibly more profitable job?

Typical price ranges

Prices range up to $2000.00 per hour for some parts, but $100 to $135 per hour is more typical, and it can be as low as $80/hour. You should look at the part to machine, and think of what it would cost on a mill, or other competing equipment. Then price the part slightly under that, and make a good profit. However, pricing and pricing strategies are highly dependant on local market conditions.

Bidding

If you are looking to have a part made, you should contact several job shops in your area. Each job shop has their own strengths and weaknesses. Some are better at long production runs of the same part over and over, while others are better at short runs, cheap prototyping, or high precision.

They may charge you quite a bit more money per hour for waterjet machine time, than they would for time on other machines. However, you will probably also get more parts per hour for an overall savings. If you don't like the dollars per hour that they charge, then consider getting your own machine so that you can start your own business.

Note that often you get what you pay for. The lowest bid is not necessarily the best part, on time, and with good service.



 

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