Sheet Incremental Forming: Advantages of Robotised Cells vs. CNC Machines

In recent years the traditional sheet metal forming processes, suitable for high volume batches, do not correctly meet new market requirements characterised by high flexibility, reduced time-to-market, low cost for small batch production, etc. Moreover, they are not suitable for producing low cost prototypes and pre-series components. Thus new sheet metal forming techniques are very often required and pursued by manufacturing industries and have been intensively undertaken by scientific research groups (Siegert et al., 1997; Amino et al., 2000; Shima, 2001; Kochan, 2001; Shim et al., 2001; Filice et al., 2002; Iseki & Naganawa, 2002; Kim et al., 2003; Yoon et al., 2003; Ceretti et al., 2002, 2004; McLoughlin et al., 2003; Allwood et al., 2005; Lamminen, 2005; Meier et al., 2005). Among the new innovative technologies, the sheet Incremental Forming (IF) can be successfully used for small pre-series batches or prototypes. IF is a process where common and simple tools mounted on CNC machines, instead of complex die sets, are used to deform locally a workpiece. In recent years many studies have been done on IF and many are still in progress with the aim of finding both the most affecting process parameters and the suitable machines and working centres to run experiments and production (Park & Kim, 2002, 2003; Jeswiet et al., 2005a, 2005b; Duflou et al., 2005a, 2005b; Hirt et al., 2005; He et al., 2005a, 2005b; Ambrogio et al., 2005; Bambach et al., 2005). Unlike the standard metal forming process, fast production changes are possible thanks to the very simple IF machine configuration. Even if the time required for making one product is much longer than in the traditional press forming, the IF advantages are gained on tool design and production in prototyping phase. IF could be also successfully applied in completion flexible work cells, for example after hydroforming operations for slots or small parts finishing. Furthermore, instead of using general purpose CNC machines, the modern incremental sheet processes can be directly performed on robotised cells. This will enhance the advantages in flexibility and production time reduction since a robotised cell equipped with the proper tools can produce the part and, on the same fixture, realise the completion operations such as flanging, trimming and so on. To form the sheet into the desired shape an ad hoc tool, mounted on the machine spindle or on a robot gripper, is moved according to the given tool path. Several IF strategies have been developed which mainly differ for equipment and forming procedure. In particular,