Mold Cavity Surface Heating for Injection Molding Sink Marks
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Solution Overview
Problem
Conventional injection molding methods often result in the formation of sink marks and burrs on molded articles due to prolonged high-temperature resin contact and overshooting, which increases resin fluidity and viscosity issues.
Innovation Solution
The method involves heating the mold cavity surface to a temperature above the resin's heat distortion temperature and then injecting the resin during a temperature decrease, ensuring the resin maintains high viscosity and reducing contact time at high temperatures to prevent sink marks and burrs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the mold surface is maintained at a predetermined temperature during injection molding, then the resin transfer properties are improved, but sink marks easily develop on the molded article
Solution Approach 1:
The mold surface is heated to a predetermined temperature before resin injection to improve transfer properties. This preliminary heating action ensures the mold is ready to receive the resin in an optimal state, allowing controlled heat transfer during injection without causing sink marks.
Solution Approach 2:
The mold temperature is dynamically controlled during the injection process rather than maintained at a constant high temperature. The temperature is adjusted to optimize resin flow during injection while preventing excessive heat that would cause sink marks during the cooling phase.
2Speed
If a large amount of heat is supplied to rapidly heat the mold, then the heating speed is improved, but the mold temperature overshoots and causes burrs on the molded article
Solution Approach 1:
A temperature detection device continuously monitors the mold surface temperature, and this feedback information is used by the control device to adjust the heating power. When the temperature approaches the predetermined value, the heating is automatically reduced or stopped, preventing temperature overshoot that would cause burrs.
Solution Approach 2:
The heating power parameter is dynamically changed based on the current temperature state. The system transitions from high-power rapid heating to low-power maintenance heating or no heating when the target temperature is reached, ensuring precise temperature control without overshoot.
3Stability of the object's composition
If the resin is maintained at high temperature for a long period, then the resin fluidity is improved, but the resin enters the space between molds causing burrs
Solution Approach 1:
The mold is pre-heated to the optimal temperature before resin injection, creating the ideal conditions for resin flow at the moment of injection. This eliminates the need to maintain high resin temperature for extended periods, reducing the risk of resin entering mold gaps and forming burrs.
Solution Approach 2:
The resin injection process is performed rapidly during the brief optimal window when the mold temperature is ideal for flow but not yet cooled excessively. This quick injection through the cavity minimizes the time resin remains in a highly fluid state, preventing burr formation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses the formation of sink marks and burrs by controlling resin viscosity and contact time, improving the external appearance and quality of molded articles.
Implementation Method 1
a heating step in which a temperature of a cavity surface which forms a cavity of a mold is heated to a temperature equal to or higher than a heat distortion temperature of the resin
Implementation Method 2
an injection step in which, after the heating step, during a decrease in temperature of the cavity surface of the mold, the resin is injected into the cavity
Data Source
AI summary
The injection molding method for injecting a resin into a cavity formed within a mold is provided with a heating step in which the temperature of a cavity surface forming the cavity of the mold is heated to a temperature equal to or higher than a heat distortion temperature of the resin and an injection step in which after the heating step, during a decrease in temperature of the cavity surface of the mold, the resin is injected into the cavity.