How Plastic Injection Molding Problems are Solved by Mold Fill Simulation

Simulation software is the key to striking a perfect balance between several variables that affect the molding process. These variables include:

• Plastic flow rates
• Plastic pressure
• Cooling rates and timing
• Plastic melt temperatures

Any alterations of any kind will influence this complex combination and can permanently affect the molding process and its outcome.   “Accurate mold fill simulations are valuable because they support the same trial-and-error process for discovering the right combination of variables required to produce quality injection molded parts in computer software, which are both faster and less costly”, stated in Prospector article “Overcoming Plastics Injection Molding Problems”.

The end-result is a simulation showing potential problems and allowing for designers to make critical decisions for the part and/or mold design before the mold is ever manufactured.

The Solutions That Are Accomplished By Plastic Injection Molding Simulation

1. “Short-Shots” – this is a mold fill simulation that will show areas of the part that will not completely fill with plastic.

2. The simulation will also show where weld lines develop. Weld lines are areas on the part where two different flow fronts meet – and plastic welds together. These welds can be analyzed to determine if they are structurally sound or not.

3. Plastic injection molding simulation means you can decide if a specific resin will work with a given part design.  The software calculates the pressure inside the filling plastic, which could point towards potential problems for producing a good part.

4. This critical information can help the mold designer determine different gate locations.  Flow distance and  part aesthetics such as visible gate vestiges  or areas where visible knit lines are inappropriate need to be considered when determining gate locations.  Flow distance will also affect the amount of pressure required to fill the mold and in turn, this affects the amount of clamp force required to hold the injection mold shut during the molding process.  The longer the flow distance – the higher your pressures become, and greater clamp force becomes a requirement.

5. Gate sizing is important do to shearing and packing of the molded part.  Every grade of resin has a shear rate limit, and this limit is where the molecular chains are re-stretched too far. Re-stretching too far means the material begins to degrade which causes appearance problems like blushing or decreases in mechanical properties.   Because of the gate sizing issue – the gates need to be placed in the most appropriate locations in order to allow enough melted plastic to fill and pack/hold into the cavity.

6. Cooling lines in a potential mold design can be analyzed.  The heating and cooling of the mold can be simulated through the entire molding cycle over multiple cycles – this helps determine the size and location of cooling lines.  Since cooling lines affect how the part warps, this allows for the potential warpage of the part to be viewed.  The ability to evaluate different cooling arrangements can help deliver a more accurate cycle time estimation. This is because evaluation of each cooling loop, cooling channel size, and plastic frozen percentage will improve mold temperature control to maintain a minimum cycle time.

7. Viewing and using a plastic injection molding simulation means that any air that might be trapped during part filling can be discovered. Once trapped air is located, appropriate venting can be used in the tool. Venting is required so the air in the mold cavity has somewhere to go. If venting is not done properly – the pressurized air produces heat, which produces burn marks on the molded part. It can also restrict the flow of resin which produces parts that are incomplete. These are called “short shots” and are mentioned above.

Mold fill simulation is also helpful in existing molds that may be having production problems.   A simulation analysis points to the easiest fixes for issues like uneven fill times between parts, trouble filling, heating or cooling issues.

The Crescent Industries advantage is clear when you are working with Crescent Industries  engineers. Our engineers utilize 3d mold fill simulation software to evaluate gate locations, runner systems, venting, cooling systems, flow pattern, weld lines and materials for a specific part/mold design.

When you are preparing for your next injection molded project – feel free to contact Crescent Industries – the employee-owned company with over 70 years of injection mold building and plastic injection molding experience.

Crescent Industries
www.crescentind.com