Injection molding cycle time is a critical parameter in injection molding because it directly impacts production efficiency and costs. A shorter cycle time means more parts can be produced in a given period, enhancing overall productivity. In this post, we will explore the components of the cycle, the factors that influence it, and strategies for optimization.

What is the Injection Molding Cycle Time?

Injection molding cycle time is the total duration required to complete one full cycle of the injection molding process, from closing the mold to opening it again for part ejection. The impact of cycle time on production efficiency and cost is substantial. A reduction in cycle time, even by a small margin, can significantly improve overall productivity. The total injection molding cycle time varies depending on different factors. Generally lasts from seconds to several minutes or more.

Key Components of the Injection Molding Cycle

The injection molding cycle time typically consists of several key phases, with the total duration varying based on factors like part complexity, material properties, and machine capabilities.

Mold Closing Time

Mold closing time is the duration required to close the mold halves and ensure they are properly aligned and clamped together. The mold closing time typically takes about 1-2 seconds for smaller machines(80-200 tons) and 3-4 seconds for larger machines (500-100 tons). This phase involves alignment and clamping. Alignment means ensuring that the mold halves are perfectly aligned to avoid damage and ensure a proper seal. Clamping means applying clamping pressure to hold the mold halves together during injection.

Injection Time

Injection time refers to the period during which molten plastic is injected into the mold cavity. The injection time depends on factors like part volume, injection speed, and material properties. This phase includes plasticization and injection. Plasticization is melting and homogenizing the plastic material in the injection unit. Injection forces the molten plastic into the mold cavity through the injection nozzle and gating system.

Pressure Holding Time

Pressure holding time, also known as packing or holding time, is the period during which pressure is maintained on the injected plastic to compensate for material shrinkage as it cools and solidifies.

Injection Molding Cooling Time

Cooling time is often the longest phase of the cycle, cooling time starts from the end of pressure holding to the start of mold opening. It allows the product to continue cooling and solidifying to prevent deformation upon ejection. The duration depends on factors like part thickness, material properties, and mold cooling design.

Mold Opening Time

Mold opening time is similar to closing time, this usually takes 1-2 seconds for smaller machines and 3-4 seconds for larger ones.

Part Ejection Time

Part ejection time involves removing the molded part from the mold cavity once it has been released during the mold opening phase. The duration can vary widely depending on part geometry and ejection system design.

Injection molding cycle time formula: injection molding cycle time = mold closing time + injection time + pressure holding time + cooling time + mold open time + part ejection time.

What Determines the Cycle Time for Injection Molding?

Several factors influence the cycle time in injection molding.

Material Properties

Different plastics have varying flow characteristics and cooling rates. The temperature at which the plastic is melted affects both injection and cooling times. The rate at which the material cools and solidifies impacts the cooling phase duration.

Part Design

• Wall Thickness: Thicker walls require longer cooling times, while thinner walls cool faster.
• Part Geometry: Complex geometries may require longer injection and cooling times.
• Presence of Ribs, Bosses, or Undercuts: These features can complicate mold filling and cooling, affecting cycle time.

Mold Design

• Cooling System Efficiency: Efficient cooling channels reduce cooling time by dissipating heat quickly.
• Gate Design and Placement: Optimal gate design and placement ensure even filling and reduce defects, impacting cycle time.
• Ejection System Efficiency: Effective ejection systems speed up part removal, reducing cycle time.

Machine Capabilities

• Injection Speed and Pressure: Higher injection speeds and pressures can reduce injection time.
• Cooling Capacity: Machines with better cooling systems can shorten the cooling phase.
• Automation and Robotics: Automated systems and robotics can streamline mold opening, part ejection, and mold closing processes, reducing overall cycle time.

How to reduce the injection molding cycle time?

Mold Design Improvements

Implement conformal cooling channels to enhance that transfer and reduce cooling time. Optimize gate locations and sizes for faster filling. Design parts with uniform wall thickness for even cooling. Use ribs and cores to reduce thick sections that take longer to cool. Design molds with optimal cooling channel layouts.

Material Selection Vonsiderations

choose materials with lower melt temperatures and faster cooling properties. Consider easy flow grade for faster cavity filling. Select materials with lower heat capacity and flow viscosity for quicker filling and cooling.

Process Parameter Optimization:

Increase injection speed where possible without compromising quality. Optimize holding pressure time to the minimum needed for part quality. Fine-tune temperatures, pressures, and speeds for minimum cycle time. Use scientific molding techniques to optimize parameters. Adjust clamping force for secure mold closure without excess force.

Equipment Upgrades:

Invest in modern injection molding machines with advanced features and controls. Use machines with faster clamp movements to reduce mold open/close time. Implement hydraulic accumulators for faster injection. Utilize hot runner systems to reduce material cooling in runners. Upgrade to screws designed for faster melting and more efficient plasticizing.

Additional Strategies:

Implement automation, such as robotic part removal, for faster ejection.
Train operators and process engineers to identify and optimize machine parameters.
Control environmental conditions like humidity and temperature for consistent processing.

Conclusion

Optimization of injection molding cycle time will increase production efficiency and lower production costs. Achieving an optimal cycle time requires a comprehensive approach, considering material selection, part and mold design, and machine capabilities. By focusing on uniform wall thickness, efficient cooling, and regular machine maintenance, manufacturers can significantly reduce cycle times. Investing in advanced technologies and automation further enhances process efficiency and productivity.

FAQ