One of the most common processes in metal deformation is bending: the modification of the shape of a sheet by a bending action that generates permanent deformation. Several factors must be considered in order to achieve optimum bending of the sheet and one of the main factors is definitely the minimum radius for sheet metal bending.
The strength of the material before it breaks is what is used in the bending process: it’s thanks to this strength of the sheet that is possible to deforme it permanently without causing injury or fragmentation. To obtain a plastic deformation of the sheet it is therefore necessary to carry out a bending stress that exceeds the limit of the material’s elasticity.
Generally, in the bending operations, the material is subjected to a load force that lies between that of the yield strength and that of the breaking load. These values are determined through a tensile test, which is used precisely to understand the behavior of the material and the mechanical properties that affect it.
The are many parameters to take into account to obtain a good sheet bending process: to better control the bending process, it’s necessary to control all the factors that determine the final quality of the bend by correctly evaluating the interaction between stress and deformation inside the bent component.
Among the main factors to consider there is the elastic return of the material after bending, which is attributable to the ratio between bending radius and thickness of the sheet (ri/s), the intrinsic characteristics of the material and the influence of the previous processing to which the sheet has been subjected.
Regarding the ratio of bending radius to the thickness of the sheet, we must keep in mind that the greatest effort during the bending operations is always borne by the fibres of the material that are more external than the angle of bending and, the greater the ratio between bending radius and thickness of the sheet.
It is essential not to fall below in certain values of the bending radius, which are in turn determined by the degree of deformation of the outer fibres of the sheet and the thickness thereof, in order not to risk incurring an excessive thinning of the thickness and, therefore, a greater probability of breakage.
We then arrive at how to precisely determine the minimum bending radius, below which we can’t go during the bending process of the sheet. Depending on the minimum bending radius of the sheet determined of each material, already in the design phase in Prodotti EBI we can state whether a project can be carried out or, if necessary, what changes must be made to obtain a component that is performing, functional and does not risk breaking.
The formula for the minimum bending radius is: ri = c x s.
The minimum bending radius is obtained by multiplying the thickness of the material (s) by the coefficient (c) of the material, which varies according to the specific material and the conditions under which the sheet is bent.
Knowing the mechanical properties of materials is the absolute basis from which to start to check the basic conditions that can ensure a successful bending operation. In this we are true specialists!
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