Dimensioning Sheet Metal Bends

Bends in sheet metal are manufactured using sheet metal brakes.

Dimensioning sheet metal bends.

Uncontrolled dimensions contain two different categories of tolerances. You only have to insert interior angle flange lengths k factor inside radius and material thickness. When designing parts for laser cutting one should not make holes smaller than the thickness of the material. A 1 degree tolerance on all bend angles.

Bends specified as angles may be toleranced at plus or minus one half degree at a location adjacent to the bends. Bend relief is provided at the end of bending edge in sheet metal design to avoid any crack tearing in the corner. All of those tolerances are added together. Sheet metal parts with a minimum of 0 9mm to 20mm in thickness can be manufactured.

This is a common occurrence when manufacturers receive a sheet metal layout dimensioned in the flat pattern. 5 edge distortion an exaggerated example of edge deformation is pictured in figure a below. Remember if you do outside dimensions the fabricator has to deduct the material thicknesses and bend allowances whereas with inside dimensioning he she merely has to add the bend allowances however if you give an acute bend a dimension to a theoretical intersection of the two outside faces this is easier to inspect by laying two rules on the outside faces this is better than trying to measure the center point of a radius on the inside of the part. As one who daily works with sheet metal design and fabrication use outside flange lengths for several reasons.

Extrude hole size position guidelines creating an extruded hole using a punching process requires extreme pressure force. 1 all manufacturing tolerances used up to that point such as laser cutting tolerances welding tolerances and more 2 all bend tolerances for the entire part added together we call this an uncontrolled dimensions because there are additional tolerances to consider. Geometry of tooling imposes a minimum bend dimension. In low carbon steel sheet metal the minimum radius of a bend should be one half the material thickness or 0 80 mm 0 03 inch whichever is larger.

No worries of forgetting a material thickness along the way 3. Avoid large sheet metal parts with small bent flanges. The diagram shows one such mechanism. Form height to thickness ratio to determine the minimum form height for sheet metal use the following formula.

Cells on the right will output the desired values. Relief height is generally kept greater than two times of sheet thickness plus bend radius. Refer to the chart for values for folder as well as various press brake tooling combinations. Use the minimum bend dimension values in the charts below for your minimum closeness of cutout to a bend.

When you figure flat pattern length you simple add up all the outside flanges and subtract the bend deductions. With this free online tool we quickly get the sheet metal bend deduction and therefore the sheet metal blank initial flat length from the finished part measurements.