Basic Fabrication operations consist of common activities performed by steel fabricators. These activities include Bending, Rolling, Shaping, Shearing, Punching and Cutting. Most, if not all of these activities, create a burr which will have to be removed through further processing. These specific processes are covered in detail in the Deburring and Flash Removal section of this site.
This is a process by which metal can be bent by deforming the material and changing its shape. During the bending process, the surface area of the material does not change much. Bending takes place by using press brakes. Larger and smaller presses are used depending on which kind of application is being used. Many different shapes can be produced through the bending process. The two main types are Air Bending and Bottoming or Coining. Air Bending is completed with the punch touching the workpiece, not bottoming in the lower cavity. Bottoming or Coining is the bending process where the punch and the workpiece bottom on the die.
Rolling is common application used in the production of tanks, boilers, and pressure vessels. The metal that needs to be rolled is run through two metal rolls that are adjustable in width and height depending on the thickness of the material.
Shaping metal can be done by forging or casting. Although this shapes the metal, at times there is still more finishing work required. One of the advantages of shaping is that it reduces the material wasted by machining and is usually much faster.
Shearing is the process of cutting metal to size out of a larger stock such as roll or flat stock. Shearing produces a shear edge burr, which can be minimized to less than 10% of the material thickness. During the process, an upper blade and a lower blade are forced past each other with the space between them determined by a required offset. Normally, there is one blade that remains stationary. Commonly, sheared materials are mild steel, stainless steel, bronze, aluminum and brass.
Punching is a process that removes a scrap slug from the metal workpiece each time a punch enters the punching die. As a result of this process, there is a hole left in the metal workpiece. Punched material is most normally done in sheet, roll material and flat stock. The punching process produces multiple size holes in a quick amount of time. The punch diameter is what determines the size of the hole. Commonly punched materials include aluminum, mild and stainless steel, copper and titanium.
Laser Cutting is a type of cutting where machines can accurately produce complex exterior contours. Laser cutting takes direct input in the form of electronic data from a CAD drawing to produce flat form parts that are very complex. The laser beam used is typically 0.2 mm diameter at the cutting surface with a power of 1000 to 2000 watts. The best materials to use lasers on are carbon steel and stainless steels. Copper alloys and aluminum are tough to use lasers on because they reflect the light well and absorb and conduct heat well.
Plasma Cutting is a process that uses a high velocity jet of ionized gas that is delivered from a constricting opening. The most common gases are nitrogen, oxygen and argon. Plasma, conducts electricity from the torch of the plasma cutter to the work piece. The plasma then heats the workpiece, melting the material. The high velocity stream of ionized gas mechanically blows the molten metal away, severing the material. Plasma cutting is generally used for non-ferrous materials.
The Oxy-Fuel Cutting process is also called oxyacetylene welding.
The reason for this is because acetylene is the main choice of fuel. It is the most widely applied industrial thermal cutting process for many reasons. It can cut various thickness from .25 inch to 10 inches, the equipment is low cost and it can be used manually or mechanized. A blowtorch is used until the metal glows. Then a lever on the torch is pressed to blow oxygen into the gas mixture. That is used to blow and melt the metal with the extra heat.
Abrasive Water-Jet Cutting is a ‘cold’ metal cutting technique that combines a high pressure (4,000 bar) ‘beam’ of water with abrasive particles that cuts through material. The abrasive particles are typically garnet. The resultant finish is similar to sandblasting and leaves no burr or heat affected zone (HAZ).
The accuracy of Water-jet cutting is not as good as wire EDM typically ± 0.0015 in. but is up to 10 times faster. Both conductive (metals) and nonconductive (plastics and ceramics) can be cut with water-jet technique. The limitations for water-jet are the maximum thickness of cut. Cutting of thicker work pieces is detrimental to accuracy. Typically water-jet cutting is used for materials 4” and less.
Wire EDM (Electrical Discharge Machining) is a metal cutting process which utilizes spark erosion to remove metal from the work piece. DC electric pulses are passed through a negatively charged wire. As the wire does comes into close proximity with the positively charged work piece a spark is formed which erodes the work piece. The wire and the work piece are always separated by a dielectric fluid. The molten metal and kerf are washed away by the dielectric solution used to promote the spark.
Wire EDM is one of the most accurate metal cutting processes (tolerance ± 0.0001 in.) and can be used to cut metals of any thickness; however, a thickness of 6” is most common. Wire EDM is leaves no burr and very minor HAZ (Heat Affected Zone). As the cutting action does not involve high heat or machining there is very little residual stress at the cut surface. Limitations on wire EDM are speed, up to 10 times slower than water-jet, and the fact that it can only be used to cut electrically conductive materials.