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Choosing the right plasma cutting machine

1.      Specify the thickness of the metal most frequently cut

Most plasma cutting power sources are rated on their cutting ability and amperage. If you most often cut ¼" thick material, you should consider a lower amperage plasma cutter. If you most frequently cut metal that is ½" in thickness, look for a higher amperage unit.

Plasma cutters operating at the limit of their current capacity may make poor quality cuts. Instead, you may get a sever cut which barely makes it through the plate and leaves behind dross or slag. Every unit has an optimal range of thickness - make sure it matches up with what you need. In general, a ¼" machine has approximately 25 amps of output, a 1/2" machine has a 50-60 amp output while a ¾" - 1" machine has 80 amps output.

2. Establish the optimal desired cutting speed
Production plants and job shops often have widely different needs in cutting speed. When buying a plasma cutter, the manufacturer should provide cutting speeds for all thickness of metal measured in IPM (inches per minute). If the metal most frequently cut is ¼", a machine that offers higher amperages will be able to cut through the metal much faster than a low current unit, although both will do the job. For production cutting, a good rule of thumb is to choose a machine which can handle approximately twice your normal cutting thickness. For example, to perform long, fast, quality production cuts on ¼" steel, choose a 1/2" class (60 amp) machine.

Like welding equipment, the duty cycle is important for automated, or continuous cutting. Duty cycle is simply the time you can continuously cut before the machine or torch will overheat and require cooling. Duty cycle is rated as a percentage of a ten-minute period. For example, a 60 percent duty cycle at 50 amps means you can cut with 50 amps output power continuously for six minutes out of a 10-minute period. The higher the duty cycle, the longer you can cut without downtime.

Read more here...http://www.engineering.com/AdvancedManufacturing/ArticleID/9700/How-to-Select-a-Plasma-Cutting-Machine-for-your-Shop.aspx