three roll bending formulas PDF

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29 9 2014 Thomas Industrial Library Search Full Library PRODUCTS PRODUCT NEWS LIBRARY Agriculture Sheet Metal Forming Published By: Chemicals Processes and Die Design CNC (Sheet Metal BENDING) Industrial Helicopters Press Inc. Historical Acquire this item Industrial Math Inventory by Vukota Boljanov...

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29 9 2014

Thomas Industrial Library

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Agriculture Chemicals CNC Helicopters Historical Industrial Math Inventory Machine Shop Maintenance Manufacturing Materials Processes Sheet Metal Bending Sheet Metal BENDING Sheet Metal BENDING DIES Drawing Sheet Metal_Standards

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Sheet Metal Forming Processes and Die Design (Sheet Metal BENDING)

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Industrial Press Inc.

Acquire this item by Vukota Boljanovic, PhD

This book is a complete modern guide to sheet metal forming processes and die design still the most commonly used methodology for the mass-production. SALE! Use Promotion Code TNET11 on book link to save 25% and shipping. Add To Favorites!

5.4.4 Curling

Two examples of curling are shown in Fig. 5.10 and Fig. 5.11. Curling gives stiffness to the workpiece by increasing the moment of inertia at the ends, and providing smooth rounded edges. In the first example in Fig. 5.10, the edge of the sheet metal is bent into the cavity of a punch.

Fig. 5.10 Curling process.

In the second example in Fig. 5.11, the circular edge of the initial deep-drawn workpiece is curled by a tool that incorporates a cavity punch.

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Fig. 5.11 Circular edge curling.

The curling force is given by the equation:

(5.10) where: M = moment of bending, R i = inside curling radius, and T = material thickness. Example: Define the curling force for the workpiece shown in fig. 5.11. Assume: Diameter D = 400 mm, Material thickness T = 1.2 mm, Inner radius R i = 1.2 mm, The ultimate tensile strength UTS = 176.5 MPa . Solution :

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Known bend and curl forces often are not so important for the process because very often, the maximum force of the press machine is greater than the bending or curling force. However, knowing the magnitude of these forces is necessary for a definition of the blank-holder forces. Because of the phenomenon of material fatigue of the blank springs, these forces need to be 30 to 50 percent greater than the bending or the curling forces.

5.4.5 Three-Roll Forming

For bending differently shaped cylinders (plain round, corrugated round, flattened, elliptical, etc.) or truncated cones of sheet metal, the three-roll forming process is used. Depending upon such variables as the composition of the work metal, machine capability, or part size, the shape may be formed in a single pass or a series of passes. Fig. 5.12 illustrates the basic setup for threeroll forming on pyramid-type machines. The two lower rolls on pyramid-type machines are driven, and the adjustable top roll serves as an idler and is rotated by friction with the workpiece.

Fig. 5.12 Three- roll bending.

In most set-ups, short curved sections of circular work are performed on the ends of the metal workpiece in a press brake or on a hydraulic press. Otherwise, the workpieces would have ends that, instead of being curved, would be straight. In the process described above, the radius of the bend allowance is much greater than the material thickness of the workpiece; under these conditions, the bending is entirely in the elastic-plastic domain.

To achieve permanent deformation in the outer and inner fibers of the material, the following relationship must apply:

(5.11) Otherwise, the workpiece, instead of being curved, will be straight after unloading. The bending force on the upper roll is given by the formula:

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(5.12) where: D = outer diameter of the workpiece, b = length of bend, T = material thickness, YS = yield stress, E = modulus of elasticity, and u = bend angle.

The bend angle can be calculated from the geometric ratio in Fig. 5.12 and is given by the formula:

where: l v = distance between lower rolls, and d = lower rolls diameter.

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