Capacities and Sizes of Plastic Injection Moulding Machines

How to choose a Plastic Injection Moulding Machine?

The plastic injection moulding machines, have several parameters, the most important of which include:

• Closing force (Ton)
• Maximum Injection Pressure (MPa, PSI, bar, kgf/cm2)
• Spindle Diameter (in, mm)
• Injection Capacity (cm3, in3, oz)
• Minimum Mould Thickness
• Maximum Mould Opening
• Space between Adjustment Bars

The size specification of the Injection Moulding Machine is determined by the closing force required, depending on the working conditions and the workpiece material. This, in turn, depends on the projected cavity area and the maximum pressure in the injection mould during filling. The projected cavity area is influenced by the area of the part (or parts, if it is a multi-cavity mould) and the feeding system.

The closing force is the force that holds the two mould halves together while the maximum pressure develops in the mould cavity as a result of filling. Although the pressure in the mould cavity is lower than the injection pressure, a high force is still developed on the two mould halves by the product of the pressure of the mould cavity and the projected area of the mould. This force has to be counteracted by the clamping force to ensure that the mould remains closed during injection and to prevent burr formation. Excessive clamping force can damage both mould halves.

How do I know the volume of raw material to be injected?

To calculate the volume of raw material to be injected into each cavity, the amount of material in the feed lines must be calculated. If hot feed pipes are used, then the injected volume matches the volume of the part. The size of the ducts is a function of the size of the workpiece. As a first approximation, the table shows the typical values in % of lines depending on the volume of the part or the sum of the volumes of the parts (in the case of multi-cavity moulds) to be injected.