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.
Suppose we assume the removal of a 10 litre paint bucket 235 mm high. With an opening stroke of 235 mm the core of the mold is just outside of the cavity. When the product is ejected (or blown off) it ends up in the pre-mold. The mold must therefore open the product height at least once, i.e. 470 mm. In theory, the bucket can then be physically removed from the mold exactly, were it not for the fact that the robot gripper also needs some space. Suppose the robot gripper is 150 mm high, then the minimum total opening stroke is (2*235)+150=620 mm. Some clearance is then needed to remain clear of the front and rear mold, about 10 mm on each side. This result is an opening stroke requirement of 640 mm for a 10 litre bucket. A 10 litre bucket can be produced on a Stork 4400 kN machine that has an opening stroke of at least.
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.
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.
If you would like more information about the enlarged opening stroke, please contact your salesperson, call us or write an email to firstname.lastname@example.org.