发布时间：2020-01-16 18:44 浏览：
This is an excellent question that touches on a common misconception in mold design and injection molding production.
The simple and direct answer is: Usually, you do not need to specially make a "lengthened" mold for a "longer screw."
Here is a detailed explanation of why and what the correct approach is.
One of the core components of a mold is the ejection system. After the mold opens, a set of ejector pins, sleeves, etc., are needed to push the formed product out. The maximum distance this system can move is the mold's ejection stroke.
"Longer Screw" does not equal "Taller Mold"
The length of a screw is primarily determined by the depth of the mold cavity. The cavity is the hollow space that forms the product's shape.
As long as the mold plates are thick enough to machine a sufficiently deep cavity, and the ejection stroke of the ejector plate is sufficient to push the entire screw out, then producing a longer screw is structurally feasible for the mold.
In other words, the external dimensions (length, width, height) of the mold may remain completely unchanged; only the internal cavity becomes deeper.
When is a "Lengthened" or "Larger" Mold needed?
Situations that typically require changing the mold size (using a larger mold base) include:
Increasing the number of cavities (more parts per cycle): To increase output, you might want to change from "4 cavities" to "16 cavities". This requires a larger mold base to accommodate the additional cavities.
Improving mold structural strength: If the screw is particularly long and thin, the injection pressure can be very high. To prevent the core pin (the rod that forms the screw's internal thread) from bending or the plates from deforming, it might be necessary to thicken the plates, thereby enlarging the mold.
Using a larger injection molding machine: If the new longer screw requires a larger injection molding machine for production, and the new machine has larger platen dimensions and tie-bar spacing, then the mold's external dimensions must also be increased accordingly to fit the machine.
Although the overall mold frame may remain the same, many key internal components need to be redesigned and manufactured:
Redesign and Lengthen the Core Pin: This is the most critical change. The core pin is the component that forms the screw's internal structure and thread. A longer screw requires a correspondingly longer core pin.
Redesign and Deepen the Cavity: The cavity that matches the core pin also needs to be deepened to accommodate the longer screw.
Lengthen the Ejector Pins: The ejector pins that push the screw out must also be lengthened to ensure the entire screw can be smoothly ejected from the deeper cavity.
Possible Increase in Ejection Stroke: This is usually adjusted on the injection molding machine. If the original ejection stroke is insufficient, a longer ejection distance needs to be set on the machine. If the mold's own ejection mechanism has a limited stroke, the ejection system may need to be modified.
Cooling System May Need Optimization: A longer product might mean a longer cooling time. The cooling channels may need to be rearranged to ensure uniform and efficient cooling.
