3 Fundamentals of press design

138 Sheet metal forming and blanking
poses. In certain cases, these parts may be used as pre-production series
(Fig. 4.1.7). A further consideration which justifies the production of
prototype dies is when the timing of their manufacture is close to the
schedule for the beginning of series production. Thus, information on
the formability and tolerances of the parts can be obtained, which contributes
to goal oriented and cost-effective die manufacture.
The following are some of the points which must be taken into account
here:
– the die material
– the complexity of the sheet metal part
– the blank material
– the design of the draw development
– the geometrical parameters such as degree of shrinkage, cambering,
prestressing
– the process-related variable such as lubrication, blank holder forces,
work-flow direction, draw beads
– the size and geometry of the blanks
– special factors and parameters which influence the results of the
stamping operation
The type and design of the prototype dies are influenced by different
factors. The choice of prototype material will be in line with the sheet
metal specification, thickness and the number of parts to be produced.
Today, plastics, aluminium alloys (Fig. 4.1.13), different qualities of cast
metals as well as rolled steel can be used as prototype or soft die
material. A summary of the choice and application criteria is given in
Table 4.1.1.
Methods of process simulation
Computer-aided simulation techniques, e.g. the analysis of the forming
process without any physical dies, will increasingly replace the use
of prototype and soft dies. This development is becoming more practical
through rapidly growing hardware developments which allow the
processing of ever increasing amounts of computerised data in ever
shorter time spans. In addition, the computer software used for process
simulation has become more reliable and more user friendly.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998