The most common problem manufacturers will face during over-molding is short shots. It is a situation where the molten plastics can't enter the mold in smooth movements. The materials might get stuck because of various technical issues preventing them from filling the mold. Let's learn the essential things to know about short shots.
What is It?
Short shots in over-molding can cause various issues in your production timeline. It is the condition where the plastic materials don't fill the mold cavity. It will result in the following effects:
• Damaged products
The primary disadvantage of short shots is the damaged or imperfect products from over-molding. Also, you will get incomplete components that you can't assemble with other parts. Poor aesthetics become the final result of short shots in over-molding, which makes the products unfit for market distribution.
• More scraps
Rejected products will result in more scraps or wastes you must throw away from the production site. The more scraps you produce, the higher the rate of your production failure. More scraps will also increase the overall production costs.
• Production delays
Short shots can cause unprecedented production delays, making it harder for you to meet the deadline. The delays can also affect your marketing schedule for the finished products. Also, identifying and fixing the causes of short shots in over-molding will take some time to finish before you can resume production.
Causes
Short shots in over-molding can cause quite a stir in your production processes. You must spend much time fixing the issues and optimizing your over-molding process to prevent the short shots from happening again. Here are common causes of short shot issues:
• Injection speed
The slow injection speed can affect how the equipment fills the molten materials into the mold. It results in the solidification of the molten material before it fills the entire mold cavity. It causes various defects in the final products because of imperfect mold fillings.
• Poor material quality
The plastic quality can also affect how long it can take to fill the mold. Plastics with poor flowability will move slowly inside the equipment, requiring high pressure to keep it flowing well. Poor materials can get stuck inside the injection flow line, preventing them from filling the mold on time.
• Low pressure
The lower the injection pressure, the slower the material flow will be. You must understand each plastic material's characteristics and use sufficient injection pressure to move it. You can create a potential short shot when the pressure is not enough.
• Low temperature
The liquidity of plastic materials during injection molding will depend on the temperature you apply during the process. Some plastics with lower melting points will still work well at low temperatures. However, other plastics will not move smoothly towards the mold when you apply the lower temperature, making them stuck and unable to fill the cavity.
• Mold design
Some mold designs will make it more difficult for the plastic materials to enter the cavity. Molds with some intricate design elements will pose more challenges for the molten plastics to fill the space. Simpler mold designs will have a higher chance of reducing the short shot issue during injection.
These causes can put your injection molding operations at risk. Failing to identify these causes early can result in many short shots happening throughout your production phase. You might need to redo your production process or discard the damaged products.
Best Practices
Short shots in injection molding are a common issue that can ruin your production process. It is the leading cause of product defects and imperfections that can lead to a big failure in your manufacturing production. You can follow these best practices to prevent short shots:
• Mold design optimization
Optimizing the mold design can include changing the gate design, cavity design, and gate location. Also, you can optimize other design aspects, such as part geometry and vent design, which will help move the plastic materials into the mold cavity. By optimizing the mold design, you can improve the smoothness of the material flow during the injection molding process.
• Overmolding parameter tweaking
You must adjust some over-molding parameters to match the best environment for a smooth injection process. Some adjustable molding parameters include injection pressure, speed, mold temperature, and melting temperature. It can help prevent slowdowns during the injection process, which can result in short-shot problems.
• Better material selection
Not all plastic materials will have a smooth flow during the injection process. It will depend on the material's features and characteristics. A better material selection will solve the slowdown problems during the injection process.
• Equipment maintenance
Short shots can also happen because of equipment issues or malfunctions. Maintaining the equipment's best condition will help you keep a smooth injection molding process and prevent problems like short shots. Calibrating the equipment will also help it control the process more accurately according to the set parameters.
• Constant monitoring
It is essential to monitor the over-molding process from start to finish. Spot any issues throughout the process and fix the potential problems soon. Monitoring the injection parameters can also help prevent short-shots.
• Tooling maintenance
Taking care of the tooling of the over-molding process can also help prevent short shots during this process. Ensuring the mold and tooling for the production process are in good condition can bring the best manufacturing performance. It is essential to check for wear and damage on the mold and tooling hardware to ensure everything goes smoothly in your production.
Prevention is always the key to dealing with short shots in over-molding. Adjusting the injection parameters can help maintain a smooth flow for the plastic materials. Understanding the characteristics of the plastic materials can also help you tweak all the key parameters to match the materials.
Conclusion
The best way to prevent short shots in over-molding is to examine the various potential causes of this situation. Maintaining the tools and equipment in your production line will also help minimize the chances of short shots during injection. Constant monitoring and adjustments will keep the smooth-flowing materials inside the injection equipment and prevent short shots.
