Clamping unit

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Clamping unit (or system) Part of the injection molding machine that provides the capability to open and close the mold, to hold the mold closed during injection, and to eject the part. The clamping unit holds the mold together, opens and closes it automatically, and ejects the finished part.

There are many ways to fasten the tools to the platens, the most common being manual clamps (both halves are bolted to the platens); however hydraulic clamps (chocks are used to hold the tool in place) and magnetic clamps are also used. The magnetic and hydraulic clamps are used where fast tool changes are required.

Robotic arms are often used to remove the molded components; either by side or top entry, but it is more common for parts to drop out of the mold, through a chute and into a container.

Contents 1 Function 2 Clamping Units 2.1 Toggle clamping unit 2.2 Hydraulic clamping unit 2.3 Hydromechanical clamping unit 3 See also

Function

The clamping unit accommodates the mould and must fulfil the following functions:

the closing of the mould

• the closing of the mould

• building-up the clamping force and locking the clamping unit

• retention of the locking force

• opening the mould

• ejection of the moulded part.

Depending on the construction of the machine, the clamping force is produced either by a mechanical locking system (form-fit) or by a direct-hydraulic system (force-fit).

Clamping Units

Clamping mechanism design may be of several designs, either mechanical(toggle), hydraulic or hydromechanical.

Toggle clamping unit

Toggle clamps include various designs. An actuator moves the crosshead forward, extending the toggle links to push the moving platen toward a closed position. At the beginning of the movement, mechanical advantage is low and speed is high; but near the end of the stroke, the reverse is true. Thus, toggle clamps provide both high speed and high force at different points in the cycle when they are desirable. They are actuated either by hydraulic cylinders or ball screws driven by electric motors. Toggle-clamp units seem most suited to relatively low-tonnage machines.

Hydraulic clamping unit

Hydraulic clamps are used on higher-tonnage injection-molding machines, typically in the range 1300 to 8900 kN (150 to 1000 tons). These units are also more flexible than toggle clamps in terms of setting the tonnage at given positions during the stroke.

Hydraulic presses have historically been the only option available to molders until Nissei introduced the first all electric machine in 1983.

Hydromechanical clamping unit

Hydromechanical clamps are designed for large tonnages, usually above 8900 kN (1000 tons); they operate by (1) using hydraulic cylinders to rapidly move the mold toward closing position, (2) locking the position by mechanical means, and (3) using high pressure hydraulic cylinders to finally close the mold and build tonnage.

See also

• Clamping area