Meaning of gauge (gage) :

Unit of thickness of a metal sheet or wire. For sheet metal, a retrogressive scale (higher numbers mean lower thickness) that starts with 10 gauge representing a thickness of 3.416 millimeters or 0.1345 inches. As the gauge number increases, the thickness drops by 10 percent. For example, a 12 gauge sheet is 2.732 millimeters thick, and a 13 gauge sheet is 2.391 millimeters thick. For wire thickness there are two scales, see American wire Gauge for the first one. The second is a metric scale in which a gauge number is equal to 10 times the diameter of the wire in millimeters. For example, a 5 gauge wire is 0.5 millimeter in diameter and a 6 gauge wire is 0.6 millimeter in diameter. (see annex tables for complete information)

Press Brake:

Taking the definition from George Dieter's book:

It's a single action press with a very long and narrow bed. The chief purpose of a press brake it's to form long , straight bends in pieces such as channels and corrugated sheets.

Bending

Springback is commonly encountered in all forming operations but is most common in bending.

- Springback in bending. (figure taken from Dieter's mechanical metallurgy, cap 29, fig 20-9).

Springback is the phenomenon by which sheet rebounds on either side of the bend after the bending tool has been removed. Why? In the center of the sheet—not exactly the geometrical center, but close to it—resides a zone with low stress in which, even under large bend forces, only elastic deformation occurs. This part of the sheet’s cross-section, therefore, wants to return to its original shape after bend force is lifted. The extent to which springback occurs depends on the nature of the sheet material: The stiffer the material, the greater the springback. Soft materials exhibit springback limited to no more than 0.5 deg., and steel to 1 deg., but springback in stainless steel can amount to as much as 3 deg.

Bend angle also is a determining factor. The smaller the relative effect on the elastic area in the neutral zone, the smaller the springback. This is the case with small bend angles and small bend radii (meaning a sharp tool). For example, a steel sheet 0.8 mm thick bent with a bend radius of 1S exhibits springback of 0.5 to 1 deg. The same sheet bent with a bending radius of 77S results in springback of as much as 30 deg., according to Steve Benson in his book, Press Brake Technology: A Guide to Precision Sheet Metal (published by the Society of Manufacturing Engineers). With a leg length of 100 mm, each degree of deviation will mean that the end of the sheet will have a spatial deviation of 1.7 mm. For post-processing, such as robotic welding, a deviation of this size will soon exceed acceptable tolerance limits. In practice, it is relatively easy to correct for springback when bending a sheet, providing that influential parameters are known. For calculating springback for cold-rolled steel, a formula offered by Benson is D = R / (2.1 x S) where R is the radius of the angle in mm and S is the sheet thickness in mm. Using this formula, a steel sheet 0.8 mm thick, and given a bend radius of 20 mm and a bend angle of 90 deg., has a springback value of 11.9 deg. To calculate springback for other materials, Benson uses a correction factor (0.5 for copper, 0.75 for hot-rolled steel and 2.0 for stainless steel).

Keep in mind that under certain air-bending conditions, negative springback can occur, particularly when employing dull tools in combination with a large punch angle as deformations then can occur in the sheet between the punch and die surface. When coining, given high pressing pressure and a sharp top tool, this tool can press into the sheet past the neutral zone. In that case, the plastic phase is achieved everywhere and springback is reduced to virtually zero.

Press Brake Tooling

In press brake we can use tools such as Punches, Dies and holders, in brake forming we can obtain the required conformation by using the right die.

Dies

Press brakes can be used for many different forming jobs with the right die design. Types of dies include

V-dies—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.

Rotary bending dies—a cylindrical shape with an 88-degree V-notch cut along its axis is seated in the "saddle" of the punch. The die is an anvil over which the rocker bends the sheet.

90 degree dies—largely used for bottoming operations. The die opening dimension depends on material thickness.

Acute angle (air-bending) dies—used in air bending, these can actually be used to produce acute, 90 degree, and obtuse angles by varying how deeply the punch enters the die by adjusting the ram.

Gooseneck (return-flanging) dies—The punch is designed to allow for clearance of already formed flanges

Offset dies—a combination punch and die set that bends two angles in one stroke to produce a Z shape.

Hemming dies—two-stage dies combining an acute angle die with a flattening tool.

Seaming dies—There are a number of ways to build dies to produce seams in sheets and tubes.

Radius dies—A radiused bend can be produced by a rounded punch. The bottom die may be a V-die or may include a spring pad or rubber pad to form the bottom of the die.

Beading dies—A bead or a "stopped rib" may be a feature that stiffens the resulting part. The punch has a rounded head with flat shoulders on each side of the bead. The bottom die is the inverse of the punch.

Curling dies—The die forms a curled or coiled edge on the sheet.

Tube- and pipe-forming dies—a first operation bends the edges of the sheet to make the piece roll up. Then a die similar to a curling die causes the tube to be formed. Larger tubes are formed over a mandrel.

Four-way die blocks—A single die block may have a V machined into each of four sides for ease of changeover of small jobs.

Channel-forming dies—A punch can be pressed into a die to form two angles at the bottom of the sheet, forming an angular channel.

U-bend dies—Similar to channel forming, but with a rounded bottom. Springback may be a problem and a means may need to be provided for countering it.

Box-forming dies—While a box may be formed by simple angle bends on each side, the different side lengths of a rectangular box must be accommodated by building the punch in sections. The punch also needs to be high enough to accommodate the height of the resulting box's sides.

Corrugating dies—Such dies have a wavy surface and may involve spring-loaded punch elements.

Multiple-bend dies—A die set may be built in the shape of the desired profile and form several bends on a single stroke of the press.

Rocker-type dies—A rocker insert in the punch may allow for some side-to-side motion, in addition to the up-and-down motion of the press.

Punches

Another used toll are the punches which work in a similar way, making pressure on a sheet until we get the desired conformation, the punches also have a particular form which helps to conform the material into a required form.

Illustration of 90° dies and punches, one of the most common tools.

In the previous figure 90° dies and punches were shown, but there's plenty variations of this punches and dies we can find commonly 26°, 30°, 45°, 60° and 88° punches an dies, as well as radius punches and dies.

radius dies to different kind of final products

Schematic illustration of radius punches

The following figure illustrates the process and knowing the key factors on it we can understand the mechanics of the work.

scheme for the process in both hydraulic and mechanical press.

Sheet metal processes

Sheet metal processes involve plane stress loadings and lower forces than bulk forming

Almost all sheet metal forming is considered to be secondary processing

The main categories of sheet metal forming are :

Shearing Bending Drawing

Shearing

Shearing is a sheet metal cutting operation along a straight line between two cut-ting edges by means of a power shear.

Blanking and punchingBlanking and punching are similar sheet metal cutting operations that involve cutting the sheet metal along a closed outline. If the part that is cut out is the desired product, the operation is called blanking and the product is called blank. If the remaining stock is the desired part, the operation is called punching

Bending

Bending is defined as the straining of the sheet metal around a straight edge

Drawing

Drawing is a sheet-metal operation to make hollow-shaped parts from a sheet blank

References

1. George E Dieter, Mechanical Metallurgy, SI metric edition

2. www.srmuniv.ac.in/downloads/sheet.ppt

3. Amada, Handbook, Press Brake Tooling

4. http://www.metalformingmagazine.com/magazine/article.asp?aid=4928

5.  Fournier, Ron; Fournier, Sue (1989), Sheet metal handbook, HPBooks, p. 37, ISBN 978-0-89586-757-5

6. http://www3.nd.edu/~manufact/MPEM_pdf_files/Ch07.pdf

7. http://www.businessdictionary.com/definition/gauge.html

This Document was made as a research/study - back up material.

Compiled by: Camargo Fiorillo Carlos Jeyson Cod: 702121055Presented to: Ing Mec. Dipl. M.Sc. Julián Salas Siado.