In injection process, clamping force of injection machine is force to keep mold closed when injection machine push molten plastics in to injection mold. In this post, i will write about: clamping device, calculation of the clamping force, projected area, injection pressure,…
1. Clamping Device.
The clamping device tightens the mold with great force to prevent the mold from opening and closing due to the pressure from injection. Nowadays it is generally run by hydraulic force.
There are two major systems: the direct pressure system and the toggle system:
+ Direct Pressure System:
It is the system in which the mold is tightened directly by the hydraulic force. The clamping force works anywhere as long as it is within clamping stroke range
+ Toggle System:
This is the system using a mechanical device called a “toggle link”.
Clamping force comes from mechanical power, but the force works only when the toggle arm is fully extended. Therefore, it is necessary to adjust the clamping device according to the mold thickness.
The following are the comparison between the direct pressure system and the toggle system:
2. Calculation of the Clamping Force.
The clamping force is proportional to the projected area of the moulding and runner, and must be opposed by the clamping force. although a proportion of the pressure produced by the injection cylinder is transmitted to the cavity, various losses occurring in the heating cylinder, nozzle and gate we can consider that force acts on the mold to make it open can be calculated from the following formula:
Force (N) = Pressure (mpa) x Projected Area (mm2)
+ What is projected area ?
Projected area is area that one line with mold base parting line, for complete calculation, calculate the runner projected area and part projected area is more precision. see picture below to get the imagine og projected area
+ What is injection pressure.