**4.2. Effect of material surface properties**

Secondly, the effect of material surface properties is studied. In order to compare the influence of material surface properties on micro-deep drawability, we focused on the aluminium foils, which have the two different surfaces in one foil sheet due to the manufacturing process of 2 layers rolling.

**Figure 17.** Surface images of 1N30 pure aluminum foil (a) bright surface, (b) mat surface

### *4.2.1. Materials and experimental conditions*

As the aluminium foil, pure aluminium (JIS: 1N30) was used as test specimen. Two kinds of pure aluminium of spring-hard material (JIS:1N30-H) and annealed material (JIS: 1N30-O) were investigated. The nominal initial thickness of the both foils were 20μm. Table 3 shows the mechanical properties of the 1N30-H and the 1N30-O pure aluminium foil, which was provided by the supplier.

Fig.17 shows the surface images of the 1N30-H pure aluminium. The bright surface has smooth roughness of 1.02μmRz, while the mat surface has rough surface with 1.64μmRz. The contact between the bright surface and the die surface is defined as contact condition Br, and the condition for mat surface is defined as condition Mt.


**Table 4.** Mechanical properties of pure aluminium foils (JIS: 1N30, 20μm in thickness) used in the experiment.

the tool and material are experimentally demonstrated.

**4.2. Effect of material surface properties** 

manufacturing process of 2 layers rolling.

*4.2.1. Materials and experimental conditions* 

and the condition for mat surface is defined as condition Mt.

provided by the supplier.

The higher value and wider dispersion of the ironing force under the ion-irradiated tool appears to be due to the strong plowing of the wear particles. In fact, Yang et al. reported that WC particles would be exposed by the ion irradiation of WC-Co hard alloy, due to the difference in sputtering rate between the WC and Co (Yang et al., 2008). Since Co particles are removed from the surface, the WC particles lose the binding agents and are easily to drop off from the surface. Therefore the dropped WC particles seem to scratch and plough the surface of work material. Thus, remarkable difference in interfacial behaviour between

Secondly, the effect of material surface properties is studied. In order to compare the influence of material surface properties on micro-deep drawability, we focused on the aluminium foils, which have the two different surfaces in one foil sheet due to the

**Figure 17.** Surface images of 1N30 pure aluminum foil (a) bright surface, (b) mat surface

As the aluminium foil, pure aluminium (JIS: 1N30) was used as test specimen. Two kinds of pure aluminium of spring-hard material (JIS:1N30-H) and annealed material (JIS: 1N30-O) were investigated. The nominal initial thickness of the both foils were 20μm. Table 3 shows the mechanical properties of the 1N30-H and the 1N30-O pure aluminium foil, which was

Fig.17 shows the surface images of the 1N30-H pure aluminium. The bright surface has smooth roughness of 1.02μmRz, while the mat surface has rough surface with 1.64μmRz. The contact between the bright surface and the die surface is defined as contact condition Br,

**Figure 18.** Punch force-stroke curves for comparing different material surface conditions (a) 1N30-H, (b) 1N30-O

The tests were carried out under the same conditions as previous section. Similarly, punch load during the process and surface quality of the cup after drawing were evaluated.

Impact of Surface Topography of Tools and Materials in Micro-Sheet Metal Forming 129

*R*z=0.5μm, P=5μm *R*z=0.05μm, P=5μm

**No.2**

**No.4**

**Blank**

**Die**

**Die**

**Blank**

**Blank**

**Die**

**Die**

**Blank**

**Blank surface geometry**

with the die surface. This suggests that the real area of contact is less in condition Mt than that in condition Br during the ironing, and it would be responsible for the lower friction resistance during the forming. Therefore, it is clear that the initial material surface

In order to discuss the obtained experimental results in detail, and to evaluate the experimental results more generally, FE analysis with proposed surface roughness model is

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

roughness is also responsible for the friction resistance during sheet metal forming.

**4.3. FE analysis with surface roughness model** 

*R*z=0.05μm P=5μm

*R*z=0.5μm P=5μm

**No.1**

**No.3**

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

carried out.

*4.3.1. Simulation conditions* 

process were calculated.

**Tool surface geometry**

### *4.2.2. Punch load-stroke curves*

Fig. 18 shows the normalized punch-stoke curves, which compares between different surface conditions of 2 kinds of pure aluminium foils, 1N30-H, and -O.

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 drawn microcup is observed in following section.

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

#### *4.2.3. Surface quality of drawn cups*

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 with the die surface. This suggests that the real area of contact is less in condition Mt than that in condition Br during the ironing, and it would be responsible for the lower friction resistance during the forming. Therefore, it is clear that the initial material surface roughness is also responsible for the friction resistance during sheet metal forming.
