**2.1.5 Demolding**

Demolding of microparts becomes a critical issue as failure frequently occurs at the onset of ejection. The interactions of polymer shrinkage and the coefficient of friction between the polymer and the molding tool may have detrimental effects on the component failure during ejection (Pouzada et al., 2006). Moreover, the micro features with high aspect ratios have a larger contact surface between the mould and the polymer which results in higher frictional resistance during part release. Smooth surface finishing is highly desirable for decreasing the friction on the polymer/insert interface (Attia et al., 2009). Coatings are frequently used to improve the roughness properties of the mould cavity and achieve superior surface quality of microparts. For example, if a cavity is coated with diamond-like carbon (DLC), fewer forces are required for the PC and ABS microparts ejection (Griffiths et al., 2008). In order to avoid breaking during ejection, the adhesive bond between polymer and stainless steel mould tool should not exceed the tensile strength of the polymer (Navabpour et.al., 2006). In addition to the experimental techniques, the magnitude of the stress on the polymer/metal interface can be accessed via finite elements stress analysis (Grave et al., 2007).

Considering fragility of the microstructured parts, conventional ejection with pins becomes unlikely and may eventually lead to their irreversible damage. In order to overcome those weaknesses, alternative solutions have to be considered. For example, if geometry of micro parts allows for a positive draft angle, the latter could assist the proper demolding of the microparts (Grave et al., 2007; Wu & Liang, 2005). A concept of more even distribution of ejection forces has been applied when ejection with pins was substituted with the micro ejection block used as striper plate to thrust the microparts (Wu & Liang, 2005). Ejection of the high aspect ratio micro structures, molded within the insert of rough surface finishing, may be successfully accomplished with vacuum assisted demolding (Michaeli et al., 2000). Choice of demolding system at micro scale will eventually depend on the cavity geometry, surface finishing and the material to be molded. In addition, a special attention should be given to correct calculation of the ejection forces and proper design of the ejection system, so far as both of those factors could be detrimental for the micropart quality.
