Cutting Method Comparison

Plasma vs. Laser vs. Waterjet

 

Waterjet Vs.
 

With the number of CNC cutting methods available to today's fabricator, including laser, plasma and waterjet based systems, making the correct choice between these technologies can sometimes be daunting.  However, when application requirements such as part accuracy, process speeds and material demands are compared against the abilities of these sometimes competing methods, a careful evaluation will often lead to selecting the best cutting method.  Typical criteria used for most process evaluations include the following:

 

Materials To Be Processed

Range Of Material Thickness

Part Accuracy Desired

Production Rate Desired

Target Market For Parts

Operator Skill Requirements

Capital Costs

Operating Costs

    

While a laser cutter can produce part accuracies approaching 0.001” with a very good surface finish, there are limits to the materials it can reliably process in this high tolerance range.  Those limits include types of materials, thickness limitations and material quality.  While a high definition plasma cutter would be unaffected by a coating of scale and rust on 1/2" mild steel plate, a laser cutter would struggle and end up scrapping a lot of parts.  An abrasive waterjet cutter can produce parts from 2” stainless steel to within 0.003” but its cutting speed for 11 gauge stainless steel would be less than one-fifth the rate of a laser cutter.  In another example, a 200 amp high density plasma system can cut 0.5” mild steel at twice the rate of a laser cutter; however, the part accuracy would not be as good as the < 0.003” parts produced by the laser cutter.   As with any machine tool purchase, getting the correct CNC cutting system for the job begins with letting the application drive the purchase.

 

Waterjet Cutting

The waterjet cutting process uses a low volume, very thin stream of ultra high pressure water for cutting high precision parts.  This thin stream of water leaves the cutting head at over twice the speed of sound, and when a small amount of abrasive is added to the stream it is able to cut virtually any material.   Waterjet cutters are able to cut soft materials such as rubber gaskets at very fast rates and with a quick change in cutting heads, thicker materials such as 4" stainless steel can also be cut to to part accuracies < 0.004". 

 

Laser Cutting

The laser cutting process uses a focused beam of high energy infrared laser light to cut material by selectively vaporizing and melting a highly localized area, while an assist gas is used to remove the molten material from the resulting cut.  The laser cutting process is one of the fastest and most accurate methods for cutting a variety of metals and non-metals.  Laser cutters can process 16 gauge stainless steel at speeds up to 400 IPM, while at the same time attaining part accuracies approaching 0.001". 

 

Plasma Cutting

The plasma cutting process uses a controlled electrical arc to create a superheated gas plasma jet.  This electrically conductive, ionized gas plasma is hot enough to easily cut through a variety of metals, with part accuracies better than 0.008" attainable with the high density torch designs.  Plasma cutting systems are most often used when the tight tolerances of a laser cutter (and it's higher capital costs) are not required.

  
  

Process Comparison

  
  

Waterjet Cutting

Advantages

Disadvantages

Cuts everything

Can produce part accuracies better than 0.002"

Doesn't heat part or cause micro fracturing

Able to cut materials over 10" thick

Can produce cut edge squareness < 1 degree

Minimal kerf widths (0.025" to 0.050")

Easily expandable to multi-head cutting

Fast learning curve for operators

Simple maintenance

No fumes generated from process

Can be less than half the purchase price of a similar sized laser system

Slow cutting speeds for most metals as compared to laser or plasma

Can be noisy (unless cut under water)

Area around machine can become coated in abrasive dust generated from cutting process

Process generated abrasive dust can damage unprotected motion components

High cost for cutting media (garnet), can be more than $12 per hour

Disposal of "mud" debris and overflow water from cutting tank can be an EPA issue  (depends on material being cut).

Focusing nozzle in cutting head deteriorates with use, affecting cut quality and accuracy

   
     

Laser Cutting

Advantages

Disadvantages

Cuts a variety of metals and some non metals

Can produce part accuracies better than 0.002"

Can cut thinner metals at over 300 IPM

Can produce cut edge squareness < 1 degree

Narrow kerf widths (0.006" to 0.015")

Can cut hole diameters < 1/2 material thickness

Produces narrower heat affected zone than plasma

Can process thin and thick metals simultaneously

Significantly higher capital cost than plasma or waterjet

Cutting metals reflective to the laser beam (such as aluminum) can be hazardous to the focusing lens

Can cause micro fracturing on some materials, a detriment for some aerospace applications

Variations in material quality for carbon steel plate as well as surface rust can affect cut results

Produces heat affected zone

High cost for cutting assist gas, can be more than $15 per hour

Can be long learning curve for process knowledge

Laser maintenance requires advanced knowledge

Produces fumes from the cutting process

Poor cutting results for most plastics

Safety requirements to protect operator from laser beam

  
  

High Density Plasma Cutting

Advantages

Disadvantages

Cuts a wide variety of metals

Can produce part accuracies better than 0.008"

Can process 16 gauge mild steel at over 200 IPM and 1" thick mild steel at over 45 IPM

Fairly quick learning curve for process

Simple maintenance

Can be less than one third the purchase price of a similar sized laser system

Not as accurate as laser or waterjet

Not ideal for applications with high volume hole cutting or where hole diameters are smaller than the material thickness.

Consumables in cutting head deteriorate with use, affecting cut quality and accuracy

Requires cutting head component change to process different metals and different metal thicknesses

Not as flexible as laser or waterjet in simultaneous processing of thin and thick metals

Edge quality on plasma cut stainless steel not as acceptable in some markets as laser or waterjet processed parts

Can cause micro fracturing on some materials, a detriment for some aerospace applications

Produces fumes from the cutting process

     
    
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