G24 a 1 b 1 a b 30 30-70 a 1 30 30 a b b 1 a 1 30 30 a b b 1 APPLICATION EXAMPLES OF FORMING OPERATIONS WITH FIBROFLEX® ELASTOMERS Vee-Bending One of the easiest elastomer-forming operations is that of Vee-bending off a solid punch and into a die cushion of stacked FIBROFLEX® pads. The necessary penetration of the punch and the amount of over-bending depend on the thickness, hardness and type of the material – and furthermore on the bending radius, the length of the free legs on the piece part, and lastly on the Shore hardness of the cushion. Applicable to all kinds of bending operations is the general rule: the smaller the bending radius, the less will be the spring-back of the bend and the shallower is the required penetration of the punch. Especially with larger batch quantities it is advisable to ensure all-round retention of the stacked elastomer cushion; it also pays to make punch and cushion identical in length. Bending of Vee- and U-Shapes Bending of V- and U-shapes can be achieved either with stacked FIBROFLEX® pads of different hardness (Fig. 5), or with the aid of solid and hollow FIBROFLEX® Sections. These may consist of squares, channels or triangular sections. Where solid sections or sheet is used as a cushion, wear of the elastomer material can be reduced through creation of an additional displacement space at the bottom of the cushion retainer box, similar to Fig. 11, where gib inserts are placed along the corners. Hollow cushions, as well as those of a channel configuration, exhibit greater die life and are therefore the preferred choice for bending operations. In the case of a U-shaped bend with straight bottom it may be advisable to insert a packing of 3–5 mm thickness, and of the same width as the flat bottom of the bend, underneath the cushion. This measure increases the forming pressure and helps to achieve a flat bottom on the workpiece (fig. 6). The punch should be relieved on both sides in order to avail compensation possibilities for springback. U-Bends with large radius U-bends with a large bottom radius are difficult to accomplish. Punch penetration must of need be large; springback can be quite considerable. This is illustrated in Figs.In order to achieve good results, the use of hollow FIBROFLEX® sections or of channels becomes almost mandatory. This is illustrated in Figs. 7 and 12. Another alternative consists of machined form cushions in accordance with Fig. 13. The hollow space of the channel-shaped cushion has the effect of increasing the horizontal pressure component in the die; this also holds true for hollow die cushions. In all cases is it necessary to ensure that the cushion retainer box is sufficiently rigid. Displacement possible: a1 = 30-40% of a b1 = 30-40% of b Fig. 5 Displacement possible: a1 = 40 - 50% of a b1 = 50 - 60% of b Fig. 6 Displacement possible: a1 = 50 - 60% of a b1 = 50 - 60% of b Fig.. 7
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