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Nov 21, 2019

Problems involving pre-opening

An example of the most serious accidents that can occur with the mould, with it in operation, are the problems involving pre-opening.
In this case that we will describe, the cold runner got stuck in the moulding area, which caused the mould to not close completely. This is because the cold runner falls separately from the part, so sometimes it stays on the top of the cam slide. With the cold runner on the top of the movement, the mould cannot close properly/ totally, which will cause the pre-opening to close before the mould does. This locking sequence causes a serious problem since all the internal mechanics have a sequence which must be respected when closing the mould and, when it isn’t, there will be collisions that will damage the mould.


In the 3D scheme below, we can see the correct sequence for the opening and closing of the mould.
Here we can verify that there is a cam slide which, with the pre-opening, will come out of the core at an angle. That is, if we open the mould before retrieving the cam slide, there will be a serious collision between the core and the cam slide, damaging these parts.


Hereupon, we have some options of security measures to resolve the problem and ensure that it does not happen again.
If it is possible to change the part 3D, this will be the best way to avoid this collision, even if the opening and closing order is not performed in the proper order. In other words, change the plastic for the adjustment to be left with a 2° draft in the cavity / core direction, which allows the demoulding without the influence of the pre-opening.


An also important option is the addition of micro switches. These will ensure that the opening and closing order of the mould is performed correctly and, in case there is any problem, it forces the mould to stop immediately, thus preventing collisions and problems in the mould.
However, the best solution for the mould would be to apply the two measures mentioned.


Another additional measure that could help solve the problem would be removing the cold runner along with the part with the robot. However, this does not invalidate the safety measures described above, since we must always prevent these situations to the maximum, to ensure with the utmost certainty that this situation will not be repeated.

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