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What are the 8 common injection mold design defects and their prevention methods?


Injection mold design is a pivotal element in manufacturing that directly impacts the quality and cost-effectiveness of plastic part production. However, even experienced designers encounter challenges that can lead to defects in the final product. This article will explore eight common injection mold design defects and delve into comprehensive prevention methods to help you ensure optimal results.

Common Injection Mold Design Defects

1. Sink Marks

Sink marks, those pesky surface depressions or indentations, can compromise a molded part’s strength and aesthetics. To prevent sink marks, follow these steps:

  • Ensure a uniform wall thickness throughout the region to promote even cooling and minimize shrinkage of different
  • trials.
  • Implement thicker ribs in areas prone to sink marks to maintain consistent material flow.
  • Carefully choose gate locations and optimize injection pressures to reduce the likelihood of sink marks forming.

2. Flash

Flash, where excess material extends beyond the mold parting line, is often due to improper clamping force and pressure settings. To prevent flash, consider these detailed measures:

  • Regularly inspect and maintain the molding machine to ensure optimal clamping force and pressure control.
  • Conduct frequent mold inspections and cleaning to eliminate potential flash sources and keep precise parting lines.

3. Warping

Warping leads to dimensional inaccuracies and weakened parts due to non-uniform cooling and insufficient cooling time. To prevent warping, pay close attention to the following:

  • Strategically place cooling channels within the mold to optimize cooling rates.
  • Ensure a consistent wall thickness in the design to minimize differential cooling.
  • Please select the appropriate material considering its shrinkage characteristics during cooling.

4. Short Shots

Short shots, resulting from incomplete mold filling, create gaps or missing portions in the part. To prevent quick shots, implement these steps:

  • Maintain precise melt temperatures and pressure settings.
  • Adjust injection speed and pressure parameters to guarantee complete mold filling.
  • Perform mold flow analysis to fine-tune the design and optimize the injection process.

5. Ejector Pin Marks

Ejector pin marks, small impressions on the product caused during ejection, can be minimized with these detailed strategies:

  • Position ejector pins strategically to reduce their visibility on the final product.
  • Explore alternative ejection methods like air ejection to avoid traditional pin marks altogether.

6. Voids and Air Traps

Voids and air traps, which compromise structural integrity, can be prevented with the following precise measures:

  • Design effective venting channels to allow trapped air to escape during injection.
  • Position vent channels appropriately and maintain regular cleaning to prevent clogs and obstructions.

7. Wall Thickness Variations

Inconsistent wall thickness can lead to differential cooling, causing warping and uneven shrinkage. Prevent variations by carefully considering these measures:

  • Maintain uniform wall thickness throughout the design.
  • Strategically employ ribs to ensure an even distribution of material and maintain part aesthetics.

8. Undercuts and Draft Angles

Undercuts can impede part ejection, and draft angles can help prevent these issues through the following methods:

  • Apply appropriate draft angles to vertical surfaces for easy ejection and reduced undercuts.
  • Modify part geometry or implement side-actions if draft angles are impractical.

Gate Placement Issues

Proper gate placement is crucial for even material flow and defect avoidance. Ensure the best gate positioning with these detailed considerations:

  • Collaborate with experienced design teams to select the most suitable gate locations.
  • Carefully assess material properties and part geometry to determine optimal gate placement strategies.

Cooling System Problems

An efficient cooling system is essential for consistent, high-quality injection molding. Prevent cooling-related defects with these detailed tactics:

  • Strategically place cooling channels within the mold to optimize heat dissipation.
  • Maintain proper coolant flow rates to ensure efficient cooling and reduce the risk of defects.


Injection mold design is a multifaceted process, and understanding and addressing these common defects is paramount for achieving high-quality production. Collaborate with seasoned mold designers and manufacturers to guarantee the success of your projects. By meticulously implementing these detailed prevention methods, you can significantly reduce defects, lower production costs, and attain the desired results.

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