The following section describes some of the key performance figures for injection molding machines, in particular.
(1) Injection capacity [cm3], [g].
This value represents the maximum value of one shot and, together with the mold clamping force, is representative of the capacity of the injection molding machine and can be expressed in two ways: injection volume [cm3] and injection volume [g].
The injection volume V [cm3] can be expressed as follows: if the screw diameter is D [cm] and the stroke is S [cm], then
V=π/4×D^2×S
(2) Plasticizing capacity [kg/hr].
Indicates how much molding material the heating cylinder plasticises per hour. In practice, plasticizing performance is related to injection volume, back pressure and screw speed, which may affect material temperature uniformity and metering accuracy, especially in precision high-cycle molding.
(3) Injection pressure [kgf/cm2].
Injection pressure P [kgf/cm2] is the pressure acting on the molding material at the end face of the screw.
If the diameter of the injection cylinder is Do [cm], the hydraulic pressure is Po [kgf/cm2] and the screw diameter is D [cm]
P=(Do^2/D^2)×Po
(4) Injection rate [cm3/sec].
Indicates the rate of injection of the molding material from the nozzle, expressed as the maximum volume that flows out in unit time.
The screw diameter is D[cm], injection speed v[cm/sec], injection volume V[cm3] and injection time t[sec].
If the diameter of the injection cylinder is Do [cm] and the hydraulic oil flow rate is Qo [cm3/sec], the injection rate Q [cm3/sec] is
Q=π/4×D^2×v, Q=V/t or Q=Qo×D^2/Do^2
(5) Mould clamping force [tf], forming area [cm2].
This refers to the maximum clamping force and the maximum possible forming area.
The following formula is given as a guide to converting the required clamping force to the action of the material pressure that tries to open the mold
F=α×Pm×(n×A+B)/1000
F: Required clamping force of the molding machine [tf].
α: Safety factor (generally 1.1 - 1.2) [-].
Pm: Average material pressure in the mold [kgf/cm2].
n: Number of molded parts [-].
A: Projected area per molded part [cm2].
B: Projected area of runners, etc. [cm2].
*1: Actual injection pressure P does not match Pm due to pressure drop during the process of filling the mold.
*2: The average in-mold material pressure Pm depends on the type of material. It also varies depending on the design dimensional accuracy of the molded product and the quality requirements (size of sink marks).
*3: Other points to consider when selecting an injection molding machine include the volume of the molded product, size and structure of the mold, and the mold opening and closing stroke.
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