stated above, the main focus is still at the right section of the part。 With punch stroke equal to 0。5 mm, in the case of the 2◦ taper angle, the material flow within the embossed region show the difficulty in moving down caused by the interrupt zone due to the small taper angle。 Therefore, the material tends to flow outward。 In the case of the 5◦ and 10◦ taper angles, the larger angle causes the material to flow easily。 Therefore, the material flow seems to move directly into the workpiece。 This phenomenon results in an interruption zone on the material flow in the workpiece。 Interruption zone can

Fig。 10。  The effect of distance to edge in terms of material flow pattern at diameter = 3 mm and depth = 2 mm。

be defined as the region where the flow of the material is resisted by a rigid die block, which can be demonstrated in Fig。 13 (oval shape)。 Within this region, higher compression stress and material flow concentration can be observed。 The interruption zone moves further down in the workpiece as the punch with a tapered angle is introduced。 However, for the case of the 10◦ taper angle, higher

flow velocity in the embossed region and the interruption zone can be observed。 It occurs close to the embossed region, which result lower compressive stress in the workpiece compared with the case of the 5◦ taper angle。

It is clearly appear that, at 1。0 mm punch stroke, the material flow feature and stress distribution in the case of the 2◦ taper angle

Fig。 11。  Stress distribution of the embossing stage as the distance to edge increase at diameter = 3 mm and depth = 2 mm。

Fig。 12。  Stress distribution of the embossing process at different tapered angle。

Fig。 13。   Material flow pattern of the embossing process at different tapered angle。

Fig。 14。 The effect of tapered punch to the (a) height of the right section and (b) bulging width。

has a similar manner compared to the results of the 0。5 mm punch stroke。 The material flow is forced outward in the workpiece due to the effect of the small taper angle geometry with a cyclone-shape flow。 Similarly, at 1。5 and 2。0 mm punch strokes, and in the case of the 2◦ taper angle, the material flow in the workpiece is still forced outward。 In contrast, in the case of the 5◦ and 10◦ taper angles, the material flow pattern in both cases are similar。 Specif- ically, the material flow velocity in the embossed region increases as the punch stroke increases。 The flow velocity in the case of the 10◦ taper angle is also lower than the flow velocity in the case of the 5◦ taper angle。 Generally, applying the taper angle has an effect on the material flow, but in this case, because the embossed part is located near the edge, the tapered punch has no significant effect on the formation of bulging and the geometric accuracy of the pin head。 Two parameters were measured on the embossed pin head, i。e。, the height of the edge A and the bulging width。 The bulging width was obtained by subtracting the initial DTE, which is 1。0 mm to the value of B (refer to Fig。 4)。 Based on the result, the effect of the tapered punch to the measured features is still less。 In Fig。 14, a similar pattern can be seen for all the three angles。

Interestingly, the edge of the right section of the workpiece is tilted upward because of the cyclone-type material flow pattern (Fig。 15)。 This phenomenon can only be observed for the tapered punch。 The tilting degree increases as the tapered angle increased。 This is one of the reasons for the increment in the total cumulative bulging width。

The embossed part (Fig。 16) shows a geometrical agreement between the optimized pin head simulated in the FE as shown in Fig。 16(b) and the fabricated pin head in Fig。 16(c)。 This image of the half-cut fabricated pin head was captured using a commercial来:自[优E尔L论W文W网www.youerw.com +QQ752018766-