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Overview Of Sheet Metal Bending Operations, Calculations, Terminolgy

The sheet metal industry may be one of the most encountered metal industries that produce different kinds of parts for different kinds of applications. You may see various kinds of metal products or parts around you that are produced with sheet metal manufacturing techniques. For example, the outer shell of refrigerators and other household appliances is produced with sheet metal bending and cutting operations. 

Metal cooking pans, pots, and metal food containers are probably produced with sheet metal cutting and drawing operations. 

Also, lots of structural parts in the automotive industry are produced with sheet metal processes. These structural parts are carrying the other parts in automobiles, trucks, etc. 

Fundamentals of Modern Manufacturing: Materials, Processes and Systems, Seventh Edition

If you are interested in the guidebook that is used for this article, click on the given link or the ‘Shop Now’ button to check it from Amazon!

What Is Sheet Metal Bending?

Sheet metal bending operations are another manufacturing operation around other sheet metal part production techniques. With the sheet metal cutting operations, sheet metal bending operations are the two main categories that all the sheet metal techniques. 

In sheet metal bending operations, flat sheet metal workpieces are shaped with deformation without any cutting or separation. 

In sheet metal bending operations, the outer surface of the metal is stretched and the inner surface of the workpiece is compressed. There is no change in thickness. Plastic deformation takes place after the application of bending force or load. 

Two Types Of Sheet Metal Bending Processes

Sheet metal bending processes are applied with dies and punches. Dies are tooling that gives the required bending shapes to sheet workpieces and punches are the tools that give primary forces or loads to shape the metals. 

There are generally two types of straight bending operations for sheet metal workpieces; V-bending and edge bending. 

V-Bending Of Sheet Metal Parts

V-Bending.

In V-bending operations, the die is designed with a groove on which a metal workpiece is placed. And the punch also has the same positive shape as this v-shaped die. When the punch makes the required motion on-die, the sheet metal workpiece takes the shape of the die. Various kinds of angles are used from very narrow to very wide. 

Edge Bending Of Sheet Metal Parts

Image Source:http://mold-technology4all.blogspot.com/2011/08/bending.html

In edge bending operations, the sheet metal workpiece is squeezed between a pressure pad and the die. The section of the workpiece which is desired to be bent hung from the edge of the die. A punch makes a reciprocating motion to bend the sheet metal workpieces. 

The bending angles are changing between 0 to 90 degrees. The angles above 90 degrees can be very burdensome and costly. 

Comparison Of These Two Types

In terms of the cost and manufacturing speed, edge bending is much more applicable for very high production rates. But the cost of the tooling of edge bending is more expensive than the v-bending technique. 

Engineering Analysis And Calculations Of Sheet Metal Bending Operations

If a sheet metal bending operation must be designed for a specific workpiece, three parameters must be calculated to obtain a healthy production; Springback, Bend Allowance, and Bending Force.

Calculation Of Springback

In plastic deformation processes, especially for metals, there is a phenomenon called springback. If a ductile metal is plastically deformed under pressure or force, when the pressure or force is released, a portion of the plastic deformation is also relieved according to the last shape under the load. 

In sheet metal bending operations, this effect must be calculated accurately to obtain the required shape in tight tolerances.

Springback is referred to as the increase of the included angle of the workpiece after the application of an included angle of the forming tool. It can be calculated with this formula; 

a’ is the included angle of the workpiece and a'<sub>t<sub> is the included angle of the tooling.

You can use this quick calculator to make your springback calculation for your sheet metal bending operation. The use of the calculator is very simple. Just enter the required values inside the brackets then click on the ‘Calculate!’ button. If you want to make another calculation, click on the ‘Reset’ button then re-enter the new values. 

Sheet Metal Springback Calculator












How To Compensate The Springback?

The compensation of spring back is very simple actually. Overbending is a method to compensate for the springback of sheet metal workpieces in where the angle of the tooling is smaller than the actual angle. The other method is called bottoming in which sheet metal parts are squeezed at the end of the production step.

Calculation Of Bend Allowance

The bend allowance factor is important for the situation in where the bending radius is small relative to the workpiece thickness. The neutral axis of the workpiece will shrink because of the stretch of the bending section of the sheet metal. Because of this stretch, this length change is called bend allowance and it must be calculated to meet the required dimensional expectations from sheet metal parts. 

Bend allowance can be calculated with this formula again; 

In this formula, ‘α’ is the bending angle of the workpiece, ‘R’ is the bending radius and ‘t’ is the thickness of the workpiece. 

If the 2t>R, ‘K’ must have a 0.33 value. If the 2t<R, ‘K’ must have a 0.50 value. These are the standardizations of the value of the ‘K’. 

Use the calculator below to calculate the bend allowance quickly. 

Sheet Metal Bend Allowance Calculator
















Calculation Of The Bending Force

Bending force is maybe the most important sheet metal bending process parameter to be calculated wisely. Because the calculation of bending force is related to the power consumption of the whole machşnery in each step of bending operation. Power means money that will be spent on this process. 

The calculation of the required force is very simple. You need to use the formula below to calculate the force required for the sheet metal bending operations. 

K<sub>f</sub> is a constant that must be selected according to the type of bending. In general, K<sub>f</sub> value is selected 1.33 for V-bending operations and 0.33 for edge bending operations. ‘TS’ is the tensile strength of the metal. ‘w’ is the width of the sheet metal part and the ‘t’ is the thickness of the part. ‘d’ is the die opening dimension which is; 

the mouth opening length of the v-bending dies and the distance between the die and punch for edge bending. 

Illustration of the ‘d’ distance(Image Source: Image Source: Mikell P. Groover; Fundamentals Of Modern Manufacturing, 4th edition, pg 453)

You can use the calculator below to calculate the required bending force for the sheet metal bending operations. 

Sheet Metal Bending Force Calculator


















NOTE: Please take care of the units when you are doing your calculations to obtain correct results. A good engineer must use consistent sets of units for calculations.

Conclusion

Mechanicalland does not accept any responsibility for calculations made by users in calculators. A good engineer must check calculations again and again.

You can find out much more calculators like this in Mechanicalland! Take a look at the other engineering calculators available in Mechanicalland!

Do not forget to leave your comments and questions below about sheet metal bending operations. 

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