Metal forming, also known as hot forming, metal pressing, or cold forming, is the method of shaping metal objects and parts through physical deformation; the physical workpiece is formed without removing or adding material, and the overall volume of the object remains unchanged. In non-metal forms such as wood, fabric, leather, plastics, or ceramic, the process does not alter the shape of the object directly, but works around it. In metal forming, the metal object must be formed with some sort of pressure or heat in a particular manner to form the internal stresses and strains that are part of forming alloys, metals, and other materials.
The process is accomplished by turning the metal to create the desired shapes. A two-stage metal forming process is used, with each stage using a different process like cutting, stamping, or rolling. These processes are sometimes combined, but the most common combination is a die-cutting operation and a spinning or press die. When using a press die, the metal forming process is more precise because the metal is formed directly on the sheet metal casting. Also, when using a die-cutter, the process can be faster since the operator doesn’t have to manually turn the metal while the cutting is occurring.
A basic example of sheet metal forming is plastically fitting two pieces of wood together. If you look at the two ends of a wooden board, what do you see? There are long thin strips of wood between them, but if you were to use a hot glue gun to glue them together, they would quickly snap apart. The same thing happens with practically fitted sheets. The plastically fitted sheets are not hot pressed, but rather the sheet metal is heated and bent so that the two sheets fit tightly together.
The basic metal bending operation begins with a mandrel, which has an opening at the top to accept the sheet metal that will be bent. The mandrel is bent into an angle so that the edges of the sheet metal are slightly overlapped. A tool called the clamps is then used to hold the sheet in the desired angle. As the clamps are pulled down, the edges of the board to bend slightly. In this process, the angle of the bend is changed, which alters the shape of the metal.
Another metal bending operation is to change the angle of the board to one that is perpendicular to the mandrel. When the bent board is pushed into the mandrel at a different angle, the sheet metal will bend back into the original position, creating a positive tilt. The board can now be placed in a new, flat position. This operation is also known as a cut in operation, or runoff. The reason why the angle is changed is so that the sheet will be able to withstand the pressure at the end of the bend angle.
A third metal bending technique is used to form a flat length of metal from a mandrel, called a miter, or blade, that extends out at a specific angle to the flat length. This type of operation is known as a blade lift, or springback. A springback mold line is used to help form a flat length of metal by allowing the blade to exert a downward force that is counteracted by a downward force that is exerted on the metal from the mandrel. The metal will automatically bend back toward the mandrel at the end of the springback, creating the desired thickness.