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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 own 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 that significantly impact overall part quality. This section shows you common molding defects, how and why the occur, and ways to minimize or prevent them.

NEW FOR LEVEL 2 MOLDING DEFECTS LESSONS: Each lesson has multiple samples of the molding defect using interactive 3D parts. The examples allow the user to manipulate the simulated part to gain a clear and concise understanding of how each molding defect would appear on a real-life injection molded part.

Video explanations, interactive 3D molding defect examples, simulations, and cause and effect analyses are covered in this section.

Recommended For: Mid-Level Personnel, All Personnel

Length: Lessons are approximately 15-20 minutes long each

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