Sheet metal bending is a manufacturing process used to bend flat pieces of metal into V, U, or channel shapes at lower cost and time with less hassle than solid material machining processes.
When designing bent parts in CAD, bend deductions usually don’t become an issue: simply tell the software what k-factor and material bend radius are appropriate.
Bending Angle
Sheet metal bending involves deforming a flat blank of sheet metal into an angular shape by applying force against it. In order to reach plastic deformation and create lasting bends, this force must exceed the material’s yield strength.
Bending sheet metal often results in elastic recovery; this phenomenon, commonly referred to as spring back, can be detrimental during the forming process and lead to major issues with shaping it into its desired bending angle. To combat spring back’s effects and achieve optimal results with your forming project, over-bend your part slightly before reaching desired bending angle.
Bending parts closely can also present challenges. When trying to create bends on one side of a component, too close bending angles may interfere with tooling and prevent proper placement of bends; in such a situation, “joggling” tooling setup is available as a solution.
Another key consideration is the k factor and bend allowance, used to account for material stretch that occurs during bending, to create an accurate flat pattern reflecting your intended angle of bend. Each bending method, material type and thickness has their own k factor which should be taken into account.
Bend Radius
Sheet metal bending is an intricate process involving several variables. The final radius will depend on factors like material, thickness and angle of bending; bend deduction is another key consideration which compensates for any “stretching” in the metal when designing parts for sheet bending.
Bending a sheet metal component requires stretching material on its outer edge while compressing its inner portion in the fillet area, creating opposing forces which must be balanced out by an internal neutral axis located within its full thickness. Depending on which bending process is chosen, this neutral axis will differ, however typically can be found by measuring distance from bend axis to closest point of contact within radius.
Once a bending force is removed, the neutral axis should return to its original geometry unless other forces deform the part beyond its intended shape. The amount of springback depends on material type and thickness as well as bend angle/inner radius as well as method used (air vs bottom bending). K-factor and bend allowance are also key considerations.
Curl Radius
Sheet metal bending offers engineers great design flexibility; however, it is important to recognize its limitations before trying to craft complex designs with this fabrication method. For instance, tool size dictates a physical limit on how close bends can be made together – any bends that come too close would interfere with tooling and make the desired shape impossible to form. Furthermore, springback – caused by stretching material during bending process – must also be considered when planning complex projects using sheet metal bending – most projects typically will overbend by an amount to account for this stretch effect.
The type of bending process utilized will also have an effect on the final curve of the bent part. Air bending is an efficient technique for many angles; however, its inside bend radius will be limited by V-die opening size. Joggle bending produces tight radiuses with minimal offset from unbent face to resultant flange (one material thickness max).
Most engineering materials can be bent with sufficient force, although certain will crack or break under this strain. To avoid this happening again, certain metals may require pre-bend by hot forming or annealing for added resistance to bending forces.
Relief Cuts
Bend reliefs help distribute stresses evenly around a bend, minimizing distortion and cracking. They are particularly essential when working with complex shapes or thick materials such as steel. Furthermore, bend reliefs protect edges near bends from becoming distortible during bending processes.
Designing sheet metal parts requires taking into account both the bending process and heat’s effects on material. Laser and plasma cutting can create Heat Affected Zones which impede proper bending resulting in issues like inconsistent bending around holes or edges or even cracking during manufacture.
Selecting the appropriate material and thickness is also key when it comes to bent part manufacturing. Thicker materials require larger bend radii to prevent cracking, while thinner ones tend to deform more easily – finding a balance between attractive design features and material integrity can be challenging!
Engineers often forget to include corner reliefs in their designs, leaving gaps that can cause material tears during bending and lead to wasted materials and time spent repairing the part. Modern CAD programs provide tools for calculating bend allowances and bend radius based on material properties to help engineers push the limits of what can be accomplished with sheet metal.
