How does a waterjet compare with a laser?

General abrasive waterjet discussions.
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Posts: 12
Joined: Thu Sep 14, 2017 3:35 pm

Fri Sep 15, 2017 2:53 pm

A waterjet seems to be a lot like a laser, but I know it is different. How do they compare? Why would one use a laser instead of a waterjet and vice versa? What things that I am used to doing on a laser would be different or weird or whatever on a waterjet?
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Carl O
OMAX Employee
Posts: 30
Joined: Thu Sep 14, 2017 10:43 am
Location: OMAX Corporation

Mon Sep 18, 2017 5:18 pm

Lasers and waterjets are quite similar in some ways, and very different in others. Below are some notable similarities and differences:
  • Both machines share the ability to cut similar shapes. They can both cut pretty much any 2D flat shape with ease.
  • Waterjets are awesome for cutting nearly any material, while lasers are more limited in what materials they can cut. Lasers have issues with materials that burn and can cause fumes. Materials that reflect can reflect the laser and cause issues, and other materials just are not reasonable. Abrasive waterjets, on the other hand, can cut just about anything including copper, aluminum, mirrors, glass, stone, and even layers of different materials, or stacks of thin sheets. The abrasivejet will get the material wet, though, so some ultra water sensitive materials may not be suitable for waterjet cutting, such as cardboard and paper. Wood can generally be cut with either technology.
  • Lasers can cut very fast, but not nearly as thick. High power million dollar lasers might be able to cut metals as thick as 1/2" (12 mm) or so, but even a low power abrasivejet can cut much thicker than that.
  • Lasers can do very fine etching, while abrasivejets like to just blast through. Etching on the ProtoMAX is not recommended, though etching is supported on the higher end GlobalMAX, MAXIEM, and OMAX machines. Even so, such etching is often not as fine or controlled as that of the lasers.
  • Lasers can turn on and off extremely quickly, where with abrasivejets this takes several seconds, and introduces some risk of plugging the nozzle or cracking brittle materials (for this reason, paths with lots of on/off cycles are generally discouraged, though certainly doable with care.)
  • With a laser, the kerf width of the tool is very narrow making it reasonable to "cut down the line" and still have reasonable tolerances, which makes it a little more forgiving for mistakes in the tool path. With the ProtoMAX, the width of the cutting tool is approximately 0.030" (0.68 mm), which means that it is important to cut to the scrap side of the line, so that the part comes out to the correct dimension. For both tools, cutting to the side is important for precision, but with the waterjet it is more so. The ProtoMAX will automatically handle this for you.
  • Fixturing (holding down) the material is more important with the abrasivejet: With the abrasivejet, the jet keeps on cutting for many inches after it has cut through the material, and the water is disturbed in a violent manner (Waves of bubbles coming up, for example). This means that parts that are cut free can tip on the supporting slats and potentially float and get under the nozzle. It is very important therefore to make sure that tool paths do not traverse over areas that had previously been cut, and might crash into the nozzle. For this reason, the ProtoMAX software has features to path around previously cut areas, features to "tab" parts in place, and tools to double check for such collision areas and correct them. It is always good to study the tool path for opportunities to collide with previously cut features before hitting the "begin" button.
  • Lasers heat the material that is being cut, potentially damaging it. This can cause metallurgical changes, make it difficult to create fine details, and also make secondary operations on the piece difficult due to hardening of the edge. For example, powder coating may not adhere to a laser cut part as well as to an abrasivejet cut part, and secondary cutting and polishing operations may be more difficult on the laser cut edge. With the abrasivejet, the cutting process is essentially "cold", and does not affect the properties of the material. This makes it great for the next machining step, and can even make it useful for cutting things like metallurgical samples for tensile tests, etc.
In general they are both pretty capable tools. The waterjet is more flexible in many areas such as what materials it can cut, making it the more versatile tool in general, but the laser also has its place. For this reason, one will often see both lasers and abrasivejets in the same shop.
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