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Lesson 7: Meld and Weld Lines (Part Design)

When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. Part design features may cause a material flow to split and rejoin as it flows around design features in a mold. In this lesson we will focus on the meld and weld lines formation relative to part wall thickness and gating.

Topics in this lesson include: how different wall thicknesses in a part can affect meld and weld line development; how single or dual hot runners compare in meld and weld line development; and how polymer temperature at a weld line location plays a significant role in its appearance and strength.

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Meld and Weld Lines Part Design

Learn about the causes of common molding defects and how to prevent them. Continue to build your Circle of Knowledge lesson by lesson. 

Goals of Molding Defects (Level 2): 

  • Learn about the various molding defects that can occur during the injection molding process
  • Gain an understanding of how part design, mold design, and process impact molding defects
  • Analyze real-life molded parts and learn the cause-and-effect behaviors of design and process

Section Description: 

Molding defects in injection-molded parts range from minor surface defects to major structural issues impacting overall quality. This section explains common molding defects, how and why they occur, and ways to minimize or prevent them.

Each lesson includes multiple samples of molding defects using interactive 3D parts. The examples allow the user to manipulate the part to gain a clear and concise understanding of how each molding defect would appear on a real-life injection-molded part.

This section covers video explanations, interactive 3D molding defect examples, simulations, and cause-and-effect analyses.

Recommendation: Expert-Level Operators, Technicians, & Designers

Length: Lessons are approximately 15-20 minutes long each

The Kruse Training platform delivers knowledge and expertise developed over three decades in plastic injection molding. Now, companies and individuals can access a state-of-the-art online training program suited for all levels of expertise.