Jul 17, 2019
At the end of filling phase, in injection molding there is still melt in front of the screw of the plastification unit.
This amount of melt is needed to to compensate the shrinkage within the cavity during the solidification of the melt.
At the end of packing there is still melt left in front of the nozzle. This amount of melt is the so called melt cushion.
It is used to validate the stability of the injection molding process. There shall be only a small variation in the melt cushion from one shot to another.
A difference might indicate an abrasion of the non-return valve.
Oct 12, 2019
There is no clear line between conventional injection molding and micro injection molding.
However, it is common to use the therm micro injection molding when parts being produced starting from 0,001g ( 1 Microgram) up to 0,4g per cavity.
The dimensions of the parts ranging mostly between a few millimeter and one micrometer.
The demand on the part precision is very high.
If cold runner molds are used for micro injection molding the shot weight is defined up to 97% by the cold runner itself.
From the production side machines with screw diameters down to 12mm are available as well as machines using a piston in order to inject the melt.
Cycle times in micro injection molding are obviously very short.
Jan 5, 2019
To fix the injection mold on the machine platens mounting clutches can be used. One of the two ends of the clutch stays on the mold. The other one rests on the platen of the machine. A screw applies the force to hold each side of the mold securely. It is screwed into one of the holes of the platens. It should be noted, that ejection side and injection side of the mold need to be clamped.
Mar 26, 2019
During the injection process, the screw is pushed forward in the injection unit.
The pressure applied to the screw, will cause melted material flowing back into the screw.
To prevent this effect, the tip of a screw is equipped with a movable ring called Non-Return Valve.
During the dosing process, this ring open a gap between screw and screw tip. This allows the melt to enter the area in front of the tip.
During injection stroke, the ring is pushed back and it closes the gap.
This prevents material to flow back into the screw.
Jul 2, 2019
When the mold is placed on the mounting plates of the injection molding machine, it can be opened easily.
The movable side of the mold is moved back from the fixed side with the help of the clamping unit.
The distance between the two halves of the mold is called opening stroke.
The size of the machine defines the possible opening stroke.
With a big enough distance, parts can be ejected easily.
The deeper a core, the larger the necessary opening stroke.
At the same time, the opening stroke should be kept as short as possible in order to reduce the cycle time.
When choosing the machine, the needed opening stroke should be considered.
Therefore, a good machine data sheet should always contain the necessary opening stroke for the mold.
