Injection Molding Weld Line Suppression via Bubble Bursting

Solution Overview

Problem

The injection molding method often results in weld lines at merging surfaces of molten resin, leading to imperfections in the external appearance and a decrease in strength of the final product.

Innovation Solution

The method involves providing bubbles into the molten resin, generating fine bubbles using ultrasonic waves, and bursting these bubbles at the merging location to prevent weld line formation by stirring the resin with shock waves or jet streams, ensuring random orientation of fibrous bodies and improved mixing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If molten resin is injected into a closed die to fill the cavity, then the product is fabricated efficiently, but weld lines are formed at merging surfaces causing imperfections and strength decrease

Engineering Contradiction:

Improveproduct fabrication efficiencyVSAvoidexternal appearance quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

Bubbles are introduced into the molten resin before injection into the die. This preliminary action ensures that bubbles are present in the resin before it reaches the merging location, where they will subsequently burst to prevent weld line formation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Bubbles, which are typically considered defects in resin products, are intentionally introduced and then utilized as a beneficial mechanism. The bubbles burst at the merging location to create shock waves that prevent weld line formation, thus converting a potential harm into a useful function.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Productivity

If molten resin is injected into a closed die to fill the cavity, then the product is fabricated efficiently, but weld lines are formed at merging surfaces causing strength decrease

Engineering Contradiction:

Improveproduct fabrication efficiencyVSAvoidproduct tensile strength

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

Bubbles are introduced into the molten resin before injection into the die. This preliminary action ensures that bubbles are present in the resin before it reaches the merging location, where they will subsequently burst to prevent weld line formation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Bubbles, which are typically considered defects in resin products, are intentionally introduced and then utilized as a beneficial mechanism. The bubbles burst at the merging location to create shock waves that prevent weld line formation, thus converting a potential harm into a useful function.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Manufacturing precision

If bubbles are introduced into molten resin and ultrasonic waves are applied to generate fine bubbles, then weld line formation is suppressed, but process complexity increases

Engineering Contradiction:

Improveweld line suppressionVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Ultrasonic waves are applied to the molten resin to generate fine bubbles. The mechanical vibration from the ultrasonic waves causes the introduced bubbles to fragment into fine bubbles that can effectively burst at the merging location to prevent weld lines.

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

Bubbles serve as an intermediary medium that transfers the ultrasonic energy into localized shock waves at the merging location. The bubbles act as a mediator between the ultrasonic vibration source and the resin merging front, enabling weld line suppression.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 weld lines, enhancing the external appearance and tensile strength of the resin product while maintaining a simple and efficient process.

Implementation Method 1

generating fine bubbles with the provided bubbles before the molten resin is injected

Methodology Applied

Scientific EffectUltrasonic vibration: Ultrasonic Vibration

Implementation Method 2

bursting the fine bubbles of the injected molten resin containing the fine bubbles in a merging location where the molten resin merges

Methodology Applied

Scientific EffectBubble bursting: Cavitation

Data Source

PatentUS11338474B2Injection molding method

Publication Date: 2022.05.24 SUBARU CORP

AI summary

An injection molding method uses a die with a cavity into which molten resin is to be injected to fill the cavity. The die has a shape that causes the molten resin injected into the cavity to branch and merge. The injection molding method includes providing bubbles into the molten resin before the molten resin is injected, generating fine bubbles with the provided bubbles before the molten resin is injected, injecting the molten resin containing the fine bubbles, and bursting the fine bubbles of the injected molten resin containing the fine bubbles in a merging location where the molten resin merges.