FORMING BASICS FOR SHEET METAL DESIGN

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FORMING BASICS


       i)                   Press Brake Forming:-

            The fundamental advantage of press brake as a forming tool is its flexibility. Standard vee-dies are used for cost savings on small lots and prototypes. These rules increases manufacturability of designs:-
      a)      Dimension the part in a single direction wherever possible
      b)      Use consistent bend radius for all bends per part
      c)      Generally, dimensioning should be done from a feature to an edge
        Tolerances in the title block of a drawing may be restrictive for certain dimensions and angles, while appropriate for others due to above guidelines.

       ii)              Critical Dimensions:-

             Outside dimensions should be used unless the inside dimension is critical.

       iii)            Embosses & Offsets:-

           Emboss and offset dimensions should be to the same side of material unless overall height is critical. Placing higher tolerances and critical dimensions increase the cost of the part.


       iv)              Bend Radius:-
                                     Inside bend radius = Material thickness
           If radius is less than recommended, it causes material flow problems in soft material and fracturing in hard material.


       v)                Bend Relief:-

           When a bend is made close to an edge, the material may tear unless bend relief is given or the bend should be made with sufficient distance.

       vi)              Forming Near Holes:-

           Bend should never be too close to hole, if so then the hole becomes deformed. It should maintain minimum distance.

                 Minimum distance, D = 2T + R    (hole dia < 1”)
                 Minimum distance, D = 2.5T + R (slot or hole dia > 1”)
                                                                                    Where, T = Thickness of Material
                                                                                                 R = Bend Radius

       vii)           Form Height to Thickness Ratio:-

          Minimum form height for sheet metal is determined by the same formula, D=2.5T + R. If the height is less than this, then it requires secondary operations, which are costlier.
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       viii)         Edge Distortion:-

                      The overhang caused by the distortion in the edges due to bending is termed as edge distortion. It increases with increase in material thickness. Relief cuts are provided on the bend line to avoid this overhang.

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