Parent Category: Big Blue Saw Blog
Created: Thursday, 17 December 2015 16:51
Written by Super User
The information below comes from Carl Olsen's website waterjets.org. Whenever a customer comes to me with a very technical question about waterjets or waterjet cutting that I can't answer, I refer them to waterjets.org and Carl. If he doesn't know the answer, he knows who does.
With Carl's permission, I thought I'd post some of the great information he's written concerning the advantages of waterjet cutting.
- Simon Arthur
"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.
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:
Exotic materialss such as titanium, Inconel and Hastalloy
304 stainless steel
Brittle materials such as glass, ceramic, quartz, stone.
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.
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.
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.
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.