BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

84 Marius Ionuţ Rîpanu et al.
The objective of this paper is to elaborate a comparative study upon the
nesting for the classical presses and nesting for the numerical commanded
centres in order to emphasize the advantages and the disadvantages of both
operations and, not the last, based on the effectuated researches, to obtain high
quality and high precision parts at the smallest cost possible.
2. Particularities of the Nesting Operation
The cold plastic forming researches and especially the nesting for numerical
controlled pressing centres researches made by J a c k s o n and M i t t a l [2] are
based on blanking-punching using a very well planned algorithm, method that
leads to the automatical generation of the CNC program. R a g g e n b a s s and R
e i s s n e r [2] have researched the connection between pressing and laser, with
applicability on the processing centres with CNC. In Twente University was
studied and developed the processing of the metal sheets domain through
planning and managing the factors that influence the machinability of metal
sheets using NC [2], [3]. Some of the most important CAD/CAM programs that
are used to perform this technological process are: RADAN, WICAM, Nesting
Software, EditCNC, CNCezPRO TM , and some of the pressing centre with NC
are TRUMPF, AMADA ARIES, Finn-Power, Mazak, Bystronic, etc.
The nesting of the blanks for classical presses takes into account certain
coefficients that depend on the nature of the material, the placing of the part
and the nesting style of it (with waste, without waste, with little waste).
During the nesting of the parts for the NC pressing centres it must be taken
into consideration the type of the material of the metal sheet. The software used
for modelling, simulating and generation of the numerical control scheme will
consider all the factors and parameters that may influence the process
productivity.
3. Comparative Study
For this study was chosen a pinchbeck part made of CuZn15, SR EN
1653:2003, having the configuration from Fig. 1 and the thickness of 1 mm.
The processing of this part was followed both for the classical presses and the
CNC pressing centres. For the classical nesting, three variants of placing were
considered, as in Figure 2. For those variants were calculated the coefficients
with values of 53.77%, 54.16 % and 30.75%.
In case of using the NC cutting centres, CAD/CAM software were used in
order to realise and integrate the designing, modelling, simulating, planning and
development functions of the CNC program for processing the metal sheet,
choosing the optimum cutting variant with minimum waste.