During injection molding process, after plastic part cools and solidifies in mold cavity, removing it smoothly and completely from mold is crucial for ensuring production efficiency and part quality. demoulding system, like mold's "part removal expert," fulfills this crucial mission. Today, we'll comprehensively analyze design of injection mold demoulding systems.

 

(I) Ensuring Part Integrity
After a part is molded, an improperly designed demoulding system can easily lead to defects such as scratches, deformation, and cracks. A high-quality demoulding system can evenly apply release force, ensuring balanced force distribution during release process, minimizing damage.
(II) Improving Production Efficiency
An efficient demoulding system can quickly and stably remove part from mold, shortening molding cycle. A slow or sluggish release process can directly impact production flow and reduce output per unit time.
(3) Extending Mold Life
A properly designed demolding system can reduce wear and impact between mold components. Conversely, poor demolding can lead to premature failure of mold components, increasing mold repair and replacement costs.

(1) Ensuring Part Quality
During demolding, deformation, cracking, and surface damage to molded part should be avoided. Appropriate demolding method and demolding components should be selected based on part's shape, size, and material properties to ensure uniform distribution of demolding force. For example, for thin-walled parts, a multi-point uniform ejection method should be used to prevent uneven force and deformation.

 

(2) Simple and Reliable Structure
Demolding system should be as simple as possible to facilitate processing, assembly, and maintenance. It should also ensure reliable operation and be less prone to failure during long-term use, minimizing downtime and maintenance.
(3) Sufficient and Uniform Demolding Force
Demolding force should be moderate, allowing for smooth part removal without being excessive enough to damage part or mold. Demolding force should be evenly distributed across appropriate areas of molded part to avoid excessive localized stress.
(4) Facilitating Automated Production
In modern injection molding, degree of automation is increasing. Design of demolding system should consider coordination with automated equipment, such as facilitating part removal by robotic arms and minimizing manual intervention.
(5) Avoiding Interference
Various components of demolding system must not interfere with other mold components during movement, ensuring smooth movement. For example, ejector pin must not collide with core, cavity, or other components during ejection and repositioning.

(1) Ejector Pin Demolding
Ejector pin demolding is one of the most commonly used demolding methods and is suitable for parts of various shapes, especially flat surfaces and shallow cavities.
Ordinary ejector pins: Simple structure and easy to manufacture. Ejector pin diameter is selected based on force requirements of part and should generally not be too small to avoid bending or breaking.
Flat ejector pins: Suitable for ejecting thinner ribs, bosses, and other areas of a part. Its large contact area with part effectively prevents damage during ejection.
(2) Ejector Plate Demolding
Ejector plate demolding, also known as push plate demolding, is suitable for thin-walled cylindrical and box-shaped parts, as well as parts where ejection marks are unacceptable. Large contact area between ejector plate and part ensures uniform ejection and prevents deformation of part.
(3) Ejector Tube Demolding
Ejector tube demolding is suitable for circular or annular parts or parts with holes, such as gears and bearing sleeves. Ejector tube ejects along inner hole or outer surface of part, providing uniform ejection force and minimizing deformation.
(4) Lifter Demolding
Lifter demolding is primarily used when part has internal undercuts. During ejection process, lifter not only achieves axial ejection but also simultaneously performs lateral core pulling, allowing for smooth removal of parts with undercuts.
(5) Core Pull Demolding
When a plastic part has side holes, undercuts, or bosses, core pull demolding is necessary. Core pull mechanisms include motorized, hydraulic, and manual core pulls. Motorized core pulls are reliable, highly automated, and widely used.

(1) Ejector Pin Design
Ejector Pin Diameter: Ejector pin diameter should be determined based on ejection force and material strength of part, generally no less than 3mm. For areas subject to greater force, a larger diameter ejector pin should be selected.
Ejector Pin Length: Ejector pin length must ensure that part can be fully ejected from mold cavity while ensuring sufficient guide length for ejection and repositioning.
Ejector Pin Placement: Ejectors should be evenly distributed in areas of part subject to greater force, areas with greater rigidity, and areas farther from core. Avoid placement in weak areas of part or areas requiring high aesthetic quality.
(2) Reset Mechanism Design
Reset mechanism returns ejector component to its initial position after demolding, preparing it for next injection molding cycle. Common reset mechanisms include reset lever and spring.
Reset lever: Simple structure, reliable reset, and widely used. Reset lever length should match ejector plate stroke.
Spring reset: Suitable for smaller ejection distances, it offers fast reset speed, but spring is prone to fatigue failure and requires regular replacement.
(3) Guide Mechanism Design
Guide mechanism ensures accurate movement of ejector component, preventing misalignment and interference. Common guide mechanisms include guide pin and sleeve guides and ejector plate guide pin guides. Guide mechanism should have excellent wear resistance and guiding accuracy.

(1) Difficulty in Demolding Plastic Parts
Causes: Possible reasons include insufficient demolding angle, excessive friction between plastic part and mold cavity, or insufficient demolding force.
Solution: Appropriately increase demolding angle; polish mold cavity surface to reduce friction; increase number of ejector pins or increase ejector pin diameter to improve demolding force.
(2) Part Deformation
Causes: Uneven ejection force distribution, excessive ejection speed, uneven part cooling, etc.
Solution: Optimize ejector pin layout to evenly distribute ejection force; reduce ejection speed; improve cooling system to ensure even part cooling.
(3) Ejector Pin Bent or Breakage
Causes: Ejector pin diameter is too small, ejector pin length is too long, uneven ejector force, foreign matter in mold, etc.
Solution: Replace ejector pins with larger diameters; shorten ejector pin length or add ejector pin guides; adjust ejector pin layout to ensure even force distribution; regularly clean mold to prevent foreign matter from entering.

Designing ejection system for injection molds is a meticulous and critical task, directly impacting part quality, production efficiency, and mold life. During design process, it's important to comprehensively consider various characteristics of plastic part, adhere to design principles, select appropriate demolding method and components, pay attention to detail design to ensure demolding system operates stably and reliably. This article hopefully provides a useful reference for designing injection mold demolding systems, helping you create higher-quality injection molds.