Criteria for bending

Criteria  for bending

  Regardless of the applicatioand use of available technologies , the production of accurate parts with minimum set -up time must meet and maintain five basic bending criteria.

These are：

1 . Accurate bend angles

2 . Constant bend angle overthe full bend length

3 . Accurate flange length

4 . Parallelism of flange length

5 . Correct position of intemal details

1.Bend angle

  Press brake ram repeatability has always been a key element inproducing an accurate bend angle, however the focus on maintaining critical angular tolerances inbending today is no longer the repeatability of the press brake.

  The focus is on the non-uniformity and varying dimensional tolerances inherent in all materials. Materialvariation will continue to be aconcern in achieving both firstarticle results and consistent parts throughout a production run. If it were possible to control the pressbrake repeatability to ± " 0 " , this still would not solve the problems effected by varying material conditions.

  Furthermore , changes in grain direction generally result in the creation of different bend radii. This will result in varying bend angles if the ram position is not adjusted. See fig 2.

2 . Factors affecting bendangle over the full length

  Deflection : The dificulty in maintaining uniform bend angles along the entire length of the bend line is mainly the result of deflection in the machine frame. If the upper and lower beam do not remain parallel during the bending process , the bend angle will differ along the length of the part.

  Tooling: If the tooling is not recise or is unevenly worn alongI. ts enagth ,the result will be avariation in thte angle produced.

3 . Precise flange dimensions

  To produce the correct flangelength , the backgauge position must be accurately determined according to bend angle , bend radius , bend allowance , die geometry and material type.

4 . Parallel flanges

  Valuable time can be wasted setting up the backgauge to assure the production of parallel bends. In some instances , parts may require the bend lines to be non-paralle , in which case additional complexity will be added , and additional time will be spent setting up the backgauge . Other problems may also hamper the quick and accurate production ofeither condition. These include tool misalignment , tool wear , ora backgauge that is damaged ,inaccurate or out of calibration.

5 . Unfolded length & correct position of interal detail

  Position of internal detail within a part depends primarily on the accurate application of the bend allowance. Bend allowance or K-factor calculations derived from different sources and used to determirie blank development may vary . If the formulas used for calculations vary , blank uniformity will also vary.

  All the criteria previously mentioned will effect the poolton of internal part detail and the development of the precise blank.