The sheet format to be punched is one of the factors that can influence the quality of the piece machined in a punching machine. If the sheet format introduced in the punching machine is the same size as the part, the following effects could be encountered:
· Problems with the sheet metal length: the part’s size is not exact, due to the accuracy problems most of the manual shears have. Consequently, the theoretical value of the length is, for instance, 1 mm less that the real one. The resulting effect is that a 1 mm strip is left uncut. In order to avoid this, the cutting program must be set so that the punch overlaps the metal by 1 mm.
· Squaring errors: A squaring error on the format to be punched may mean faulty measurements taken on the format relating to the outline of the metal. To ensure perfect squaring on different cuts in the sheet metal, the outer cuts should be made on the punching machine.
· Shaping in an “arrow”: This effect can cause the sheet metal to move when repositioning because it is being pushed by the clamps. This effect can be partially avoided. When the clamps are opened during repositioning, the machine is made to go back a value (2mm), and once the repositioning has been made, the forward movement is less than the backward (1mm), with the program compensating the difference between the backward and forward movements. This allows compensation for errors up to 1 mm.