Injection molding is a simple plastic production technique that demands high process control. This is because the process parameters have an impact on the production speed, product quality, etc in a significant manner. Pressure is one of the important process parameters that makes a deep impact on injection molding. There are different types of pressure conditions that need to be considered and controlled during the process of injection molding. Injection pressure, packing pressure, back pressure, etc are the impacting pressure considerations in injection molding. Slight fluctuation in one of these pressure values can impact the injection molding process and product quality. This post discusses the role of pressure in injection molding and the impact of pressure values during the injection molding process.
Types of Pressure Values and Their Impact on Injection Molding
The following are different types of pressure experienced in injection molding. Let us discuss their impact on the process, individually.
- Injection Pressure: This is the force applied on the molten plastic material against the opening cross-section of the injection nozzle. It is applied by the lead screw to push the material forward to the nozzle. The injection pressure determines the amount of material that comes out of the nozzle and the velocity.
- Impact of Injection Pressure in Injection Molding: The injection pressure is responsible for filling up the mold cavity with plastic. However, if over-pressurized, it can cause the temperature build-up inside the injection barrel. It leads to an increase in the velocity of material via the tip of the injection nozzle. If the mold is empty, the excessive injection pressure might act as a speeding agent in injection molding. On the other hand, if the mold cavity is filled between 50% and 90%, it can cause premature forced opening of the mold cavity, leading to intense damage.
- Packing Pressure: It is the pressure exerted by packed molecules of molten plastic inside the injection barrel. This packing pressure is responsible for air bubble formation in the molten plastic.
- Impact of Packing Pressure in Injection Molding: The packing pressure often decreases as the initial injection pressure is applied. Before application of injection pressure, it is important to let the material settle and molecules form cohesive bonds to reduce cavities. If holding pressure is not sufficient then cavities and air voids are formed in a material that offers resistance to injection pressure and abrupt pressure rise. Therefore, holding sufficient packing pressure for significant time is important.
- Back Pressure: Backpressure is the resisting pressure inside the injection barrel. It is the resistance force offered by the nozzle surface to the motion of molten material.
- Impact of Packing Pressure in Injection Molding: If the backpressure goes beyond the expected or calculated value, it can restrict the motion of molten plastic. Higher resistance to flow due to backpressure can break the continuity of the injection molding process, this might lead to large cavities in the products, hot spots, reduction in product strength, etc. If it exceeds beyond tolerable pressure of the injection, it can cause thrust of the injection walls or abrupt bursting. Therefore, the impact pressure must be kept in control.
Now that you know the importance of pressure and the impact of slight deflection in pressure values, it is advised that you partner with experienced injection molding service experts like Veejay Plastic. The company offers high-quality injection molding services to the industries like aerospace, defense, etc.
