**5. Conclusion**

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

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

fabrication of tiny micro cups with minimum 0.5 mm in diameter. By providing the different microtools with different surface properties, the high sensitivity of the forming force to the different surface conditions of micro tools has been clearly recognized. Especially, the ironing force and its deviation have the large differences. The surface observation of the drawn cup demonstrates the importance of the tool surface roughness and the material compatibility between the tool and material, in view of the occurrence of adhesion and abrasive wear. In the additional investigation of the influence of material surface roughness, the higher friction force for the bright smooth surface is indicated. This appears to be attributed to the real area of contact during the process, which is strongly dependent on the initial surface geometry of the work material.

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Furthermore, the FE model with surface asperities has been proposed and the availability and the validation of this model are demonstrated. The calculation results of this surface roughness model under the different combination conditions of surface asperities are well corresponded to the experimental results. The general tendency of the interaction of the surface asperities between the tools and the workpieces is explainable in terms of the classic theory of tribology.

Since the sensitivity to the surface properties for the global forming behaviour becomes higher with decreasing the scale dimensions, the proper design of the tool and the material are required more precisely in microforming. In other words, the microscopic geometry of the surface of tools and materials would become a significant parameter of controlling global deformation behaviour in microforming. The tribological optimisation by the surface texturing technology for micro-tooling and materials would be the future tasks.
