Machine Size

Machine size requirements for molding a given part is determined by several factors. The first variable to be considered is the projected area of the molded part. Projected area is defined by the maximum area, (including all cavities), parallel to the clamping force (i.e., the platens). A part behind another part as in stack molds, does not require extra clamping force. Clamping force required per square inch of projected area is a factor of the amount of pressure required to fill the cavity. Wall section, gating method and material viscosity are a few of the variables considered when accurately calculating tonnage requirements. For the purpose of this estimator a rule of thumb of between 2 and 5 tons per square inch of projected area can be used. As an example if a 3 inches by 6 inches box made of ABS is molded in a two cavity mold the calculation would be as follows, 3 times 6 = 18 in2, times 2 cavities equal 36 in2. 2 tons per square inch would be 90 tons. The depth of the box would not be considered projected area because the sides are not perpendicular to the clamping force. Other factors such as mold base size and shot size should be considered in true tonnage requirement calculations.

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