25.06.2021
Injection molding machines with enlarged opening stroke

An important (leaflet) feature of an injection molding machine is the opening stroke.
Injection molders must check whether the opening stroke provided is large enough to be able to remove the product from the mold.

If the product is removed with a robot, the opening stroke must be at least two (2) times the product height plus the height of the robot gripper. Free fall is usually maintained at 2.5 times the height of the product, despite free fall becoming less common.

Calculation example

IML (In Mold Labeling)
If a product is provided with an “In-Mold Label”, the label is usually also inserted by the same robot. This is usually done by a plastic “mandrel” in the shape of the core of the product, around which a label is wrapped or placed. This “mandrel” again has the height of the product, so that the minimum opening stroke for In Mold Labeling should not be two (2), but three (3) times the product height. In other words, 3*235mm (product height) + 150mm (grab height) + 20mm (clearance) = 875 mm. With IML, the required opening stroke is therefore greater than the 4400 kN injection molding machine can offer.

Option for enlarged opening stroke
In order to be able to produce a 10 litre bucket with IML, a larger machine with an opening stroke of at least 875 mm would be needed. Because this is an expensive solution, Stork IMM offers the option of increasing the opening stroke for the 3300 kN IMM up to and including the 9000 kN IMM. This option means an opening stroke of 950mm for the 4400kN.
As a result, it is not necessary to buy a machine with a higher closing force.

Exceptions
There are two exceptions to this rule:

• When the 10 litre bucket is produced in two ways, a 6600 kN IMM is required, which already has 940 mm opening stroke. The problem will then resolve itself. This obviously applies to several applications.
• If the opening stroke is too small it is sometimes decided to solve the problem by means of the IML robot. The IML process then gets an intermediate step, which results in significantly more cycle time. When purchasing a new injection molding machine the additional costs of this solution quickly outweigh the loss in cycle time.

More information
If you would like more information about the enlarged opening stroke, please contact your salesperson, call us or write an email to sales@storkimm.com.

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