At this time the parameters of supporting to FEM simulation by DEFORM programming are shown in Table 1。

Through Fig。 6a——d, it was predicted that the U-bending crack is not created by the parameter of sheet metal of SPCC as shown in Table 1 and the other database。

Also, we considered that the result of FEM simulation for U-bending in this production part never occurred the crack phenomena。 Therefore, it could be well done to the strip process lay out design as showing in Fig。 5 [1—3,7]。

Table l

2。5。Die set selection

There are several kinds of die set model in the die making field regularly。 Some time in the particular field, they make special type steel die set for high precision die assembling function。 In this study, we considered the automatic roll feeding of strip for the mass production above one hundred thousand of production part and precision production needed, so we selected special type steel die for high precision production part。 Also the guide post must be installed within the die block and die shoe size allowance with the high accurate guide bushing fit。 It was selected that the die set has six inner guide posts and four outer guide posts for a precision working and high load of pressing。 Fig。 7 shows the result of die design that is called press die assembling drawing。

3。Die making and tryout

3。1。Die making

The SKD 11 high alloy tool steel was selected for punch and die block as a cause of containing of minimized wear among whole of die materials。

Especially, the V1 carbide tool material was selected as a die insert material for the split die components。 In this study, we decided the sizes of punch and die block depending on data base, theoretical background and our own field experiences [7]。 The machining of punch and die block belongs to the precision machine tool working through the raw material cutting, milling, turning, drilling, profiling, heat treating, electronic discharge machining (EDM, Wire-Cut), jig grinding, especially, CNC machining and mirror machining, etc。 Fig。 8 shows the progression of CNC machining center working。

Fig。 9 shows the press die making system。 Fig。 10 shows the CNC machining center for a representative of die making machine tools。

In this study, we used ordinary machine tools, CNC machine tools and EDM, etc。 On the accuracy of each fitting component with combination of the following tolerances, the first case is guide bush and guide post tolerance as the H7(hole) h6(shaft) for a slide fitting。

Fig。 8。 Progression of CNC machining center working

Fig。 9。 Press die making system。

The die set and guide post tolerances are H7(hole) p5(shaft) for a tight fitting。 The Punch plate and punch tolerance are H7(hole) m6(shaft) for a tight fitting with a minor interference。 The second is stripper and punch tolerances as the H7(hole) h6(shaft) for a slide fitting。 The die inserting hole and die inserting

button used the H7(hole) m6(shaft) for a minor tight fitting。 These fitting tolerances are very careful factors

3。2。Try out

Fig。 11 shows the actual strip process layout result from tryout working (200 t power press, l00mm stroke and 40 SPM)。 In this actual process strip layout, we could confirm the real process for making the production part。

Also we checked the every size of production part with a tolerance control。

We could find the jamming problem such as the material strip through the guide tunnel on the die block surface。 Also, when the material strip passing through the die tunnel, the roll feeding device operation was checked very exactly。 The trouble shooting of this problem was come from die setting skill and technology。

At this time, the check of die failures was performed through the production part and strip of every stage with punch and die edge by the surveying and measuring with fine instruments。