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common causes of short shots

5 Key Reasons Behind Short Shots in Injection Molding

Perceive the impact of high viscosity, inadequate venting, improper settings, low fill volume, and insufficient pressure on injection molding short shots.

High material viscosity affects plastic flow, injection speed, and mold filling. Inadequate venting can lead to air traps and hinder plastic flow. Improper machine settings impact injection pressure, speed, and material packing. Low fill volume results in incomplete mold cavity filling and compromises product quality. Insufficient pack and hold pressure causes incomplete filling and premature solidification. Understanding these five key reasons is essential for optimizing injection molding processes and achieving high-quality production. Mastering these factors will help you prevent short shots and enhance the overall efficiency of your manufacturing operation.

Material Viscosity

High material viscosity hinders the smooth flow of plastic during the injection molding process, leading to various flow problems within the mold cavity. Material viscosity, often quantified by the Melt Flow Index (MFI), greatly influences the filling of the mold cavities. When the plastic material exhibits high viscosity, the injection speed required to fill the mold increases, potentially causing issues like short shots where the mold is incompletely filled.

To address these challenges, careful consideration of material viscosity is vital during the mold design phase. Choosing a plastic material with an appropriate viscosity for the specific mold design can help optimize the filling process and reduce the occurrence of short shots. Additionally, adjusting the material melt temperature within the recommended range can help lower viscosity and improve the flow of the plastic during injection molding, ensuring consistent material properties for uniform filling of the mold cavities.

Proper management of material viscosity is essential to prevent flow-related defects and ensure successful injection molding outcomes.

Improper Venting

lack of proper ventilation

Insufficient venting in molds during injection molding can lead to air traps, causing short shots by hindering proper plastic flow. Improper venting can result in air becoming trapped within the mold cavity, preventing the plastic material from filling the entire space adequately. This leads to incomplete mold filling and the formation of trapped air pockets, ultimately affecting part quality.

To address this issue, it's essential to pay attention to vent design and placement. Effective venting allows air to escape during the injection process, maintaining consistent pressure and promoting proper plastic flow. Venting adjustments play a significant role in optimizing the mold filling process, reducing the likelihood of short shots occurring in the final molded products.

Inadequate Machine Settings

machine settings not optimized

Inadequate machine settings during injection molding can have a substantial impact on the production process and lead to short shots in the final molded products. It is important to pay attention to various machine settings to ensure best results. Here are key factors related to machine settings that can contribute to short shots:

Machine Setting Impact on Short Shots
Injection Pressure Insufficient pressure can lead to incomplete filling of the mold.
Injection Speed Slow injection speed may result in inadequate material flow.
Pack and Hold Pressure Improper pressure settings can cause insufficient material packing.
Melt and Mold Temperature Low temperatures hinder plastic flow and can lead to premature solidification.

To avoid short shots, it is essential to maintain proper machine calibration, provide adequate operator training, adjust settings for the required fill volume, and ensure that the plastic flows correctly during the injection process. Paying attention to these details can greatly improve the quality of molded products and reduce the occurrence of short shots.

Low Fill Volume

insufficient liquid content detected

Low fill volume in injection molding can result in incomplete mold cavity filling, leading to short shots in the final molded products. When the injection of plastic material is insufficient due to low fill volume, it causes voids or incomplete parts, compromising the overall quality of the product. To prevent short shots caused by low fill volume, it's essential to guarantee proper adjustment of fill volume settings.

Here is how low fill volume contributes to short shots:

  1. Inadequate Injection Pressure: Low fill volume leads to insufficient injection pressure, which hinders the material flow into the mold cavities.
  2. Incomplete Filling of Mold Cavities: Insufficient material flow resulting from low fill volume can cause incomplete filling of mold cavities, leading to short shots in the final product.
  3. Defects and Compromised Product Quality: The lack of material due to low fill volume can result in defects and compromise the quality of the molded products.

Insufficient Pack and Hold Pressure

insufficient pressure causes issues

To optimize proper mold filling during the injection molding process, it's essential to optimize the pack and hold pressure settings. Insufficient pack and hold pressure can result in incomplete filling of the mold cavity, leading to short shots in injection molded products. Low pressure settings can cause the molten plastic to solidify before completely filling the mold cavity, resulting in defects in the final product. Adjusting the machine pressure settings is pivotal to guarantee adequate pack and hold pressure, which is necessary for achieving complete part formation.

Maintaining the proper pack and hold pressure is pivotal for packing the mold cavity uniformly and reducing the risk of short shots. By ensuring that the pressure is at the correct level, you can enhance the quality of injection molded parts and minimize the occurrence of defects. It's essential to monitor and adjust the pack and hold pressure throughout the injection molding process to guarantee optimal mold filling and avoid issues related to incomplete filling and short shots.

Frequently Asked Questions

What Is the Reason for Short Shot During the Injection Molding Can Be?

Short shots during injection molding occur due to factors like insufficient pressure, incorrect temperatures, slow injection speed, poor ventilation, and inadequate wall thickness. Detecting short shots involves visual inspection and dimensional analysis.

Look for voids, sink marks, out-of-spec dimensions, warping, and other defects indicating incomplete mold cavity filling. Correcting short shots involves adjusting injection pressure, speed, temperature, mold design, and material selection to guarantee complete filling.

What Is the Cause of Short Shots?

When dealing with short shots in injection molding, the cause is often linked to factors such as insufficient injection pressure, incorrect temperature settings, slow injection speed, poor ventilation, or inadequate wall thickness.

These issues can lead to incomplete filling of the mold cavity, resulting in defects like voids, sink marks, or warping.

Detecting and rectifying these causes promptly is essential for ensuring the quality and integrity of the final product.

How to Avoid Short Shots in Injection Molding?

To avoid short shots in injection molding, adjust settings for injection pressure, temperature, and ventilation.

Optimize injection speed to prevent premature hardening and guarantee complete mold cavity filling.

Choose appropriate plastic materials and design molds compatible with part shapes.

Enhance ventilation by enlarging vents and adjusting airflow.

Modify wall thickness to promote proper plastic distribution and prevent short shots.

These measures will help you achieve successful mold filling and prevent short shots.

What Causes a Short Fill?

When a short fill happens in injection molding, it's due to the mold cavity not being completely filled with molten plastic. Factors like low injection pressure, wrong temperature settings, slow injection speed, poor ventilation, and inadequate wall thickness can lead to these issues.

Detecting short fills requires visual inspection, dimensional analysis, defect evaluation, and real-time monitoring. It's important to address these issues promptly by adjusting injection parameters, optimizing mold design, and selecting appropriate plastic materials.


In conclusion, addressing the key factors behind short shots in injection molding is essential for achieving high-quality production.

For example, a case study showed that by optimizing machine settings and adjusting pack and hold pressure, a manufacturer was able to greatly reduce short shots and improve overall part quality.

By understanding and addressing these factors, manufacturers can guarantee efficient and successful injection molding processes.

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