*4.3.1. Simulation conditions*

128 Metal Forming – Process, Tools, Design

*4.2.2. Punch load-stroke curves* 

drawn microcup is observed in following section.

**Figure 19.** Surface images at bottom area of micro-drawn cup wall

Fig.19 compares the surface images of the bottom area of drawn cup wall surface under 2 contact conditions. As shown in the figure, the boundary of the sliding surface and the original surface with rolling traces can be clearly recognized. In comparison of the sliding surfaces, although almost of the whole area of the cup wall is smoothened with die surface for the bright surface condition, mat surface condition has the area, which does not contact

*4.2.3. Surface quality of drawn cups* 

The tests were carried out under the same conditions as previous section. Similarly, punch

Fig. 18 shows the normalized punch-stoke curves, which compares between different

For both materials, the condition Br indicates the higher drawing and ironing force. Although the difference of maximum drawing force is almost no difference between condition Br and Mt for both 1N30-H and 1N30-O aluminium foil, maximum ironing force for the 1N30-H indicates larger difference than that of 1N30-O, as shown in Fig 18(a). In order to investigate the cause of these tendencies of each difference, the surface state of the

**20μm 20μm**

load during the process and surface quality of the cup after drawing were evaluated.

surface conditions of 2 kinds of pure aluminium foils, 1N30-H, and -O.

The simulation was carried out with the condition as mentioned in section 3.2. To study the effect of combination of surface geometry between the blank and the tools on formability, different combinations of surface geometries were analyzed. The combination conditions of the process are given in Table 5. To compare and quantify the effect of the surface topographical interaction between the tool and the material, the punch forces during the process were calculated.


**Table 5.** Combination conditions of surface geometry between blank and tools

Impact of Surface Topography of Tools and Materials in Micro-Sheet Metal Forming 131

Fig.20 (a) shows the effect of roughness amplitude of a tool with same smooth material surface on formability (Condition No.2 and 4) (Shimizu et al., 2009). The curve obtained for the rough tool indicates the higher punch forces than those of the smooth tool. The difference in ironing force is particularly large. This tendency was also observed in the experimental results of the comparison between the untreated tool (smooth) and the airblasted tool (rough), as shown in Fig. 14. From the deformation history in the analysis, it can be seen that, if the tool surface asperity are sharper than the blank surface asperity, the plastic deformation of the blank surface asperity would be easily occurred, due to the intensive surface pressure. In the actual contact behavior during the process, this phenomenon in FE analysis could be translated to the fracture of oxide film layer due to the high normal pressure. It would easily induce the adhesion or the plowing and

Fig. 20 (b) and (c) show the effect of blank roughness amplitude under the same tool surface condition (Shimizu et al., 2009). As for the condition with the smooth amplitude tool (Condition No.3 and 4) as shown in Fig. 20 (b), the punch force of the rough material is lower than that of the smooth material. The similar tendency in the experiment is already shown in Fig. 18(a) and (b). As mentioned from the observed surface images of micro-drawn cup in Fig.19, since the real area of contact under the smoother amplitude blank is much larger than that of rough amplitude blank, the friction force will increase and it results in the

While for the condition with a rough amplitude tool (Condition No.1 and 2) shown in Fig.20 (c), the maximum drawing and ironing force indicates almost the same value between the conditions. This shows the higher impact of the tool surface roughness than the material surface roughness. Since the harder tool surface asperities would plow the softer material surface, the material surface roughness seems to be less influence on the friction resistance

Thus, local interfacial behavior in micro-deep drawing could be explained on the basis of classic theory of conventional tribology. However, a feature of the micro-scale region appears to be the higher sensitivity of the global forming behavior to the microscopic surface properties. Therefore, the proper surface design of tools and work materials in

From the perspective of the significant importance of tribological behaviour under dry friction in micro-sheet metal forming, this chapter has created an overview of the effect of

The advanced development of the micro-deep drawing experimental system has realized the investigation under the actual micro-scale range forming behaviour, such as the

micro-scale becomes significantly more important than in conventional macro-scale.

surface topography of tools and workpieces on micro-sheet formability.

*4.3.2. Simulation results* 

increases the friction.

higher forming force.

**5. Conclusion** 

under the contact with the rough tool surface.

**Figure 20.** FEM results of load-stroke curve under different surface conditions between tool and material (a) Effect of tool surface amplitude (b) Effect of blank surface amplitude with smooth tool, (c) Effect of blank surface amplitude with rough tool
