Mold-machine combination

The mold should be tuned to the injection molding equipment with respect to mold mounting, injection unit and clamping force. Relevant molding machine data can be found in the figure below. Mold mounting dimensions.

The maximum shot weight of the injection unit is the amount of plastic that can be injected per shot. The weight of the molding should not exceed 70% of the maximum shot weight. The minimum plasticizing capacity depends on the relationship between shot weight and cooling time. For example, molding 300 g in 30 seconds requires a minimum plasticating capacity of 36 kg/hr. The required clamping force of a molding machine is determined by the cavity pressure during the injection/ holding stage and the projected area of the part in the clamp direction. Various factors affect the molding pressure, e.g. length over thickness ratio of the molded part, injection speed and melt viscosity. Typical injection pressures are 40-50 N/mm2, resulting in a required clamp force of 0.4-0.5 tons/cm2.For thin wall moldings the required pressures can be a factor 2 higher resulting in a required clamp force of 1 tons/cm2. With engineering structural foam molding pressures are significantly lower allowing for less robust mold design or the use of aluminum in place of steel in the mold construction.