Many fabrication projects and fabricated products start with sheet metal. This is cut into shapes that are formed and often welded before being coated. The most widely used industrial sheet metal cutting processes are shearing, punching, abrading, and melting. Here’s an overview of 4 types of CNC machines that do this work.

CNC Punch Presses

This machine works by pushing a small punch down through the sheet. A tight clearance between the punch and surrounding die stops the sheet from deforming while a small piece of metal is pushed out. (Similar in principle to a hole punch for paper.)

In a CNC punch press, the sheet is moved beneath the punch in X and Y directions by fast-acting motors under computer control. Movement is synchronized with punch action, allowing the punch to “nibble” away at the sheet. Larger punch presses will have a carousel of tools of various shapes.

CNC Water Jet Machines

These cut with a high-speed jet of water powered by high pressure. The water jet head is on a gantry that moves left-right over the sheet. Forward-backward motion is supplied by a table and both are under computer control.
Water jet machines are used mostly to cut complex profiles out of plastics and foams. To cut metal an abrasive material, usually, garnet is added to the jet to provide an abrasive action that accelerates metal removal. A major advantage of water jet cutting is that it doesn’t put any heat into the sheet.

CNC Plasma Cutting Machines

These machines cut with an electrical arc similar to that used in welding. The difference here is the high-temperature melts and removes the metal.

CNC Plasma cutters look similar to water jet machines with a gantry-mounted cutting head over a sheet moved by a table. A strength of plasma cutters is their ability to cut thick sheets and plates. Their major disadvantage is poor edge quality which usually needs considerable clean-up before welding.

CNC Laser Cutting Machines

Like plasma and water jet machines, CNC laser machines usually have a gantry-style construction, and, similar to plasma cutters, they cut with heat. The difference is in how the heat is created. Laser machines use a high-power laser focused into a very thin beam. The latest generation of machines produces 10kW or more of power. Higher laser power means faster cutting and the ability to cut thicker sheets.

Most lasers are red or infrared, which is reflected by metals like aluminum and especially copper. Newer blue lasers are however able to cut these materials.

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