After reaching the defined mould temperature, the melt is injected and the mould is cooled down. The curves of the temperature for the different mould temperatures citation during injection are shown in Figure 2.Figure 2Mould temperature of the variothermal injection moulding process with different mould temperature for injection moulding.As a consequence of an increasing mould temperature, the cooling of the mould after switching to the cold fluid increases too, due to the higher temperature gradient (the cold fluid stays nearly constant). Whilst for a lower mould temperature, the average temperature change is around 12Ks?1, and it increases with up to 24Ks?1 for a mould temperature of 180��C.

Hence, with the used variothermal tempering process, the temperature of the mould can be above the crystallisation temperature of the PP and the POM or rather above the glass transition temperature of the PC during the injection of the melt. Afterwards, the mould and the melt are cooled down, and a safe ejection of the part can be achieved. For the PA66, the mould temperature is always below the crystallization temperature.2.4. Analytic Approach of the Melt-Mould Contact TemperatureThe contact of the polymer melt with the cold mould surface leads to a rapid cooling and solidification of the surface layer of the part. An analytical approach of the contact temperature is shown in [32]. The contact temperature Tcontact is dependent on the temperature of the mould Tmould, the temperature of the polymer melt Tpolymer, and the thermal diffusivity e:Tcontact=Tmould?emould+Tpolymer?epolymer??emould+epolymer??,e=k?��?cp,(1)with k the thermal conductivity, �� the density, and the specific heat capacity cp of the materials.

The values for the investigated polymers are shown in Table 1. For the mould material, a density of 7850kgm?3, a thermal conductivity of 29Wm?1K?1, and a specific heat capacity of 460Jkg?1K?1 were used.3. Results and Discussion3.1. Analytical Calculated Contact TemperatureFigure 3 shows the analytically calculated contact temperature of the polymers as function of the mould temperature. Due to the high thermal diffusivity of the metal mould, the contact temperature approaches always a marginal higher value as the deployed mould temperature.Figure 3Analytically calculated contact temperature as function of the mould temperature.

Consequently, to achieve a contact temperature Entinostat above the crystallization temperature for the PP, a mould temperature of about 110��C is needed. For the POM, a mould temperature of about 145��C and for the PA66ca. 230��C is required. To reach the glass transition temperature of the PC, a mould temperature of about 140��C is needed. As a consequence, the melt flow length should be increased as the glass or crystallization temperature of the polymer material is transcended.3.2.