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PRESS BRAKE CAPACITIES SPRINGBACK a True 90° Air Bend, the Tooling Must Formed Flanges and Causing Distortion

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PRESS BRAKE CAPACITIES SPRINGBACK a True 90° Air Bend, the Tooling Must Formed Flanges and Causing Distortion www.e-ci.com 1 CONTENTS 2 Safety 2 Bending on a CI Press Brake 8 Press Brake Bending Capacity 9 Mild Steel Air Bend Capacity Chart 13 Bending Factors Chart 17 Punching on a Press Brake SAFETY Good safety practices and proper training of each press brake operator is mandatory. Comprehensive operator, maintenance and safety manuals provide instruction on proper procedures and safety methods and BENDING ON A CINCINNATI should be with the press brake at all times. Warning signs and a checklist PRESS BRAKE of operator safety guidelines should be placed at strategic locations on PRESS BRAKE RATING For thicker than 1/2” mild steel, it may the press brake. be necessary to increase the vee die All CINCINNATI press brakes are opening up to ten times the material Users are responsible for proper rated for maximum bending pressure, thickness to minimize cracking of the installation and continued use of or tonnage. Tonnage can then be material. To determine the vee opening point-of-operation safeguarding converted into bending capacities for a simple 90° bend, multiply the and other machine guards. This through an understanding of basic metal thickness by eight. The answer helps assure operator safety factors affecting the formability of is then rounded to the next higher 1/8” and compliance with OSHA metal. Bending factors, or “rules of figure. For example: 14ga. (.075”) x 8 requirements. thumb,” for press brake forming are = .600”. This is rounded to a 5/8” vee based on using mild steel (60,000 Each new CINCINNATI press opening. psi maximum tensile strength). An brake displays a tag showing that explanation of these factors will help The inside radius of a bend in mild it meets ANSI B11.3 construction you understand the performance of steel is about 5/32” (.156”) x the requirements. A copy of the your press brake and the mild steel air vee die opening regardless of the standard, which covers the proper bend capacity charts presented in this gauge of metal being formed. This care and use of press brakes, is booklet. figure was determined by measuring included to help users with their formed samples bent over various die safety programs. Refer to the Safety openings. To illustrate: If a 1/8” (.125”) Manuals, Press Brake Safeguarding VEE DIE OPENING AND sheet and a 1/4” (.250”) plate are Bulletin PI-50686, ANSI B11.3 Safety INSIDE RADIUS formed over a 2” vee die, each will have Standards or consult Cincinnati The recommended vee die opening the same inside radius of approximately Incorporated for further information. for mild steel up to 1/2” (.500”) thick 5/16” (.312”). is eight times the metal thickness. 2 PRESS BRAKE CAPACITIES SPRINGBACK a true 90° air bend, the tooling must formed flanges and causing distortion. be cut to allow sufficient springback to Potentially smaller inside radii may Metal formed by an upper and lower attain a 90° bend. In most cases, the also be achieved using the coining die as shown in Figure 1 only has three angle cut on the dies will be between process. There are three different points of contact. If metal is pushed 30° to 85°. For air bending, the nose types of forming which are classified into a lower die sufficiently to form radius of the upper die should be as “bottom” bending: bottoming with a specific angle, when the force is equal to or slightly less than one metal spring back, true bottoming and released, the angle will open up due thickness using simple fractions. coining. to springback. Normal springback for mild steel is 2° to 4°. If the material is hard, has a higher tensile strength, or BOTTOMING WITH Note: If parts are to be formed with a larger than normal inside radius, the SPRINGBACK (FIGURE 2) air bend dies on a press brake with springback will be greater. computer control to determine ram Bottoming with springback is not reversal positions, the dies must be considered “true” bottoming. When AIR BENDING (FIGURE 1) cut to an angle that will allow for all metal is pushed into recommended possible material springback. tooling, it will form an inside radius Air bending metal into a straight line that is equivalent to the 5/32 x vee die angle is the most common form of opening rule. Pressure is then built up press brake work. A top, or upper die, BOTTOM BENDING at the bottom of the stoke causing the pushes the metal into a lower vee die. Bottom bending material with dies formed metal to “kink” in the inside The metal only touches the point of cut to approximately the finished radius area. This causes the legs of contact of the upper die nose and the angle (e.g. 88°,89° or 90°) will increase the formed metal to overbend enough two edges of the lower vee die (Figure the forming tonnage. The reason for to touch the corners of the upper die 1). The material does not contact any “true” bottoming and coining is to (Figure 2). The force buildup will be other part of the tooling during the “set” the material in order to overcome about 1 1/2 to 2 1/2 times the tonnage forming cycle. springback and obtain better angular required for air bending. When the Most “air bend” tools are manufactured accuracy (see Figures 3 and 4). forming pressure is released, the part so that the upper and lower dies Bottoming is often selected when may spring back to the desired angle. have the same angle. This is done to forming boxes or panels. Minimizing The angular consistency of this method minimize set-up time. In order to obtain the overbending keeps the final is dependent on uniform material bends from hitting the previously thickness. Normally, angular tolerances are similar to air bending. 90° UPPER DIE NOSE RADIUS 90° FIGURE 2 - OVERBENDING DURING FORMING OPERATION VEE DIE OPENING LOWER (OR VEE) DIE FIGURE 1 - AIR BENDING www.e-ci.com 3 TRUE BOTTOMING (FIGURE 3) metal, in order to obtain a sharper than one metal thickness inside radius, the When the upper die is made with a term “coining” is applied. radius of one metal thickness (to the closest simple fraction), sufficient RAM tonnage must be built up at the bottom CRACKING of the stroke to “set” the metal and When forming plate, “cracking” can eliminate spring back. The required be erratic. Small flanges can often be tonnage will range from three to five formed whereas making the same bend times the normal air bend tonnage. in the center of the sheet will cause THROAT failure. Differences will also be found DIES ALIGN when bending across the grain versus WITH BED & RAM bending with the grain. Cracking is CENTERLINE 90° ONE METAL often minimized by increasing the nose THICKNESS radius of the upper die. RADIUS FILLER BLOCK 90° DIE SPACE (FIGURE 5) BED Always total the height of the press brake dies and the height of the filler block (die holder) to make sure the FIGURE 3 - BOTTOMING tooling will fit into the available die space. For complete information on “die FIGURE 6 - DIE ALIGNMENT height selection,” contact Cincinnati COINING (FIGURE 4) Incorporated. When the upper die is made with less BEND ALLOWANCE than one metal thickness radius, the DIE ALIGNMENT (FIGURE 6) In order to determine the proper blank nose of the die will embed into the size prior to forming a part on a press metal causing an apparent overbend In order to obtain good accuracy in brake, a bend allowance for each bend condition. In order to push the upper press brake forming, the tooling must must be determined. This information die into the metal far enough to obtain be aligned so that the nose of the upper has been made available through the desired inside radius and bend die is as central to the lower vee die many engineering textbooks, but the angle, the required tonnage will be at as possible. With most press brakes, information provided is not consistent. least five times the air bend tonnage. many bends could be made with an If questions arise concerning a If the desired inside radius is one-half alignment accuracy of ±1/64” around blank development for your part, the metal thickness or less, the forming the centerline of the vee opening. CINCINNATI has available a bend load could approach ten times the Press brakes featuring computerized allowance chart which may be helpful. tonnage shown on the air bend chart. controls that allow the operator to Contact CINCINNATI at www.e-ci.com When the top die embeds, or displaces input a specific bend angle depend to obtain more information. on mathematical models to obtain good consistency. If the dies are not INSIDE RADIUS 90° closely aligned to the tooling centerline, To obtain any brochures on LESS THAN inaccuracies can occur. As a result, it METAL CINCINNATI press brake models, die THICKNESS is important to evaluate the available sets and accessories, please contact tooling with respect to the type of press CINCINNATI at: (513) 367-7100, 90° brake being used in order to obtain the [email protected], www.e-ci.com best possible forming angles. Vee dies with a 5/8” vee opening or less may require a ±.005” alignment to obtain FIGURE 4 - COINING good consistency. 4 PRESS BRAKE CAPACITIES ECCENTRIC CYLINDER PISTON ADJUSTMENT SCREW HYDRAULIC PRESS BRAKES MECHANICAL PRESS BRAKES RAM RAM STROKE STROKE RAM ADJUSTMENT THROAT THROAT OPEN HEIGHT DIE SPACE MINIMUM CLOSED DIE SPACE HEIGHT FILLER FILLER BLOCK BLOCK BED BED DOVETAIL SLOT DOVETAIL SLOT CROSS HOLD DOWN SLOT CROSS HOLD DOWN SLOT FIGURE 5 - DIE SPACE L FRONT-TO-BACK OFF CENTER LOADING BED & RAM CENTERLINE L - LOAD .5L (forming or punching) .4L .3L L D- Distance between .2L machine centerline and load centerline .1L D LOAD 50% 55% 62% 71% 83% 100% CENTERLINE % Available Tonnage for Bending FIGURE 7 - OFF CENTER LOADING www.e-ci.com 5 NO LOAD 20° BEND 40° BEND 90° BEND FIGURE 8 - TONNAGE BUILD-UP ACTUAL TENSILE OR YIELD FORMING HIGH TENSILE but will increase the forming tonnage STRENGTHS STEELS and could necessitate some shimming of the dies.
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