Forming of material is simple in theory but much more than just placing a piece of metal between a die and punch and pushing the petal. Our quality driven process to maintain precise repeatability and accuracy is only met with experience and skill of our Press Brakes Operator.
Operators are responsible for the installation of the correct punch and die tooling needed to achieve the necessary bends. The die tooling is installed along the bed of the Press Brake and the punch tooling is installed along the ram. All operators must have the ability to read fabrication blueprints to determine the required bend size, degree of bend, material type, and material thickness assuring the correct tooling is used. It is the responsibility of the operator to know the specifications of all available die and punch tooling to meet product specifications. There are many types of dies available but the most commonly used dies at A-1 Fabricators & Finishers are the V-Die, Offset Die, and the hemming Die. The V-die is the most common type of die. The bottom dies can be made with different-sized die openings to handle a variety of materials and bend angles. The Offset dies are a punch and die set that bends two angles in one stroke to produce a Z shape. The Hemming die is a two-stage die combining an acute angle die with a flattening tool.
The CNC Control system on each brake controls the back gauge and tonnage of each bend. Operators input the material thickness, material tensile strength, determined bend widths, bend lengths, and degree of bend required for each bend. From the entered data the press brake program determines the back gauge position and tonnage requirements of each entered bend. Although the CNC program is accurate the operator must precisely measure each bend dimension and angle to assure that tolerances are held. Each piece of material has uncontrollable variables allowing it to react differently, from piece to piece, during the forming process. Operators must have the skill to make necessary adjustments assuring that dimensional requirements are held.
Air bending is the most common type of bending used in sheet metal shops today and is used by A-1 Fabricators & Finishers. In this process the work piece comes in contact with the outside edges of the die, as well as the punch tip. The punch is then forced past the top of the die into the v-opening without coming into contact with the bottom of the v. The v opening is typically deeper than the angle which is sought in the work piece. This allows for the over bending to compensate for the spring back of the work piece.
Because the punch tip does not penetrate the work piece the inside radius of the bend is controlled almost entirely by the size of the v opening of the bottom die resulting in the larger the v opening the larger the radius. This means that the operator can control the radius of a bend even when working with the same material and thickness just by changing the bottom die. This can be used to compensate for errors in the layout or achieve a wider variety of design options. Below you can see an example of Air Bending, notice there are only three points of contact.
Often in forming there is reference to bend allowance. The bend allowance is factored into the material size when the fabrication engineer is laying parts out manufacturing. The fabrication engineer must factor the bend allowance into the part assuring that material consumed during the forming process is factored properly. Determining proper bend allowance is critical in achieving specified finished dimensions. Definition of bend allowance is the length of the arc of the neutral line between the tangent points of a bend in any material. By adding the length of each flange taken between the center of the radius to the bend allowance gives the Flat Pattern length. This bend allowance formula is used to determine the flat pattern length when a bend is dimensioned from 1) the center of the radius, 2) a tangent point of the radius or 3) the outside tangent point of the radius on an acute angle bend.