Injection molding cycle time is a reflection of production efficiency. A comprehensive understanding of this cycle is crucial, as it not only dictates the quality of the final product but also impacts the overall production timeline.
Estimating the Injection Molding Cycle Time: Key Components and Calculations
Injection molding is a cyclical process, and understanding its various stages is essential for optimizing production efficiency. The injection molding cycle time, often synonymous with terms like “injection molding process” or “plastic molding cycle,” comprises several crucial components:
Cycle Components
Material Storage Time & Cooling:
These two processes occur simultaneously. When calculating the molding cycle, the longer of the two is considered. Typically, the cooling time includes the material storage duration.
Injection Pressure Holding Time:
This duration is determined by the polymer’s properties, the product’s shape, and quality requirements such as appearance and dimensions. It’s influenced by factors like injection pressure, injection rate, screw rotation number, back pressure, and temperature. To ensure quality, it’s vital to seek the shortest possible time for this stage.
Injection Process:
Generally divided into three phases – slow, fast, and slow. The formula for estimation is:
T = W/20~50%V + t
T: Total injection time
W: Total injection volume (product weight x number of pieces + sprue weight)
V: Maximum injection speed of the molding machine
t: Time constant required for screw start and stop
Depending on the machine’s tonnage, the time constants vary: 80T~200T takes 1~2s, 200T~500T takes 2~3s, and 500T~1000T takes 3~4s
Pressure Holding Time:
This begins once the mold cavity is filled and lasts until the pressure holding ends. The duration is typically chosen based on the product’s appearance, shrinkage, dimensions, and deformation requirements.
Cooling Time:
This refers to the time from the end of pressure holding to the mold opening. Factors influencing this duration include product shape, wall thickness, mold cooling water design, mold temperature, and melt properties. To ensure optimal product quality, it’s essential to minimize the cooling time. The mold’s cooling water design plays a pivotal role in determining the cooling duration.
Mold Opening & Closing Time:
Influenced by machine size and mold structure. Mold core structures, mold rack transmission mechanisms, and three-plate mold mechanisms can all impact this time. Typically, 80T~200T takes 4~8s, 200T~500T takes 6~10s, and 500T~1000T takes 8~15s.
Product Ejection Time:
Determined by ejection speed, ejection stroke, and ejection method (automatic, manual, or robotic). Automatic ejection is generally used for products with lower appearance requirements. Ejection times typically range from 0.5~2s. When using robotic arms, the mold can start closing once the product is out of its range, taking about 3~8s. Manual ejection usually takes 1~3s longer than robotic ejection.
By understanding these components and their interplay, manufacturers can make informed decisions, optimizing the “injection molding cycle time” and ensuring efficient production.
Optimizing the Injection Molding Cycle Time: Strategies for Efficiency
Reducing the injection molding cycle time, also known as the plastic molding cycle, is a pivotal strategy for enhancing production efficiency and cutting down production costs. It’s an aspect of injection molding that deserves significant attention. Here, we’ll explore various methods to optimize this cycle time.
Mold Opening and Closing Time Optimization
The injection molding cycle can be calculated from the start of one mold closure to the beginning of the next. Mold closure typically has four phases: rapid closure, slow closure, low-pressure protection, and high-pressure lock. Mold opening usually consists of three stages: slow-fast-slow opening. By optimizing the speed and position of mold opening and closing, we can reduce this time. Newly designed injection molding machines come equipped with regenerative mold hydraulic circuits, allowing for faster mold closure speeds.
Injection Time Optimization
Injection begins after the high-pressure lock completes and can be done in multiple stages. To avoid defects like bubbles or burns in the product, it’s advisable to use a high injection speed.
Pressure Holding Time Optimization
Pressure holding starts after injection and is generally lower than the injection pressure. Its primary purpose is to compensate for shrinkage, filling the depressions formed by the cooling melt and ensuring the product is full and free from indentations when de-molded. Once the runner solidifies, further pressure holding becomes redundant. The overall pressure holding time can be determined by weighing the product or ensuring there are no indentations. It’s best to start with a shorter pressure holding time and incrementally increase it until the product weight stabilizes or the indentation level is acceptable.
Cooling Time Optimization
The cooling time parameter on the injection molding machine is the duration from the end of pressure holding to the start of mold opening. The objective of this cooling time is to allow the product to continue cooling and solidifying, ensuring it doesn’t deform when ejected. This time is typically determined through experimentation. It’s advisable to start with a longer cooling time and gradually reduce it until the product remains undistorted upon ejection.
Material Storage Time Optimization
Material storage begins with the cooling time. If the material storage time exceeds the cooling time, it indicates insufficient plasticizing capacity of the screw, affecting the production cycle. Several methods can enhance plasticizing capacity, such as:
- Using barrier screws.
- Employing larger diameter screws.
- Increasing the groove depth of the screw.
- Raising the screw’s rotation speed (not suitable for shear-sensitive plastics like PVC or PET).
- Reducing back pressure to increase plasticizing speed.
- Using hydraulic nozzles to allow plasticizing during mold opening and closing.
- Utilizing equipment that can plasticize throughout the cycle, excluding injection and pressure holding times.
Locking Force Optimization
To prevent flash or excess material around the product, it’s essential to use the lowest possible locking force. This not only reduces the time required for high-pressure locking but also extends the durée de vie du mouleles barres d'attache, les joints à genouillère et les plateaux de la machine de moulage par injection.
Optimisation de la température du fût
Assurer un remplissage par injection en douceur tout en utilisant la température la plus basse possible du tonneau permet de réduire le temps de refroidissement.
Optimisation de l'efficacité du refroidissement
L'optimisation de la conception des canaux d'eau du moule peut améliorer l'efficacité de l'échange thermique et l'uniformité du refroidissement du produit, réduisant ainsi le temps de refroidissement. L'utilisation d'eau réfrigérée pour le refroidissement, tout en garantissant la qualité du produit, peut encore réduire le temps de refroidissement.
Optimisation du temps d'éjection
Pour les petites machines de moulage par injection dont la force d'éjection est minimale, il est possible d'utiliser l'éjection pneumatique, qui est plus rapide que l'éjection hydraulique. Des commandes hydrauliques, pneumatiques ou électriques indépendantes peuvent permettre l'ouverture et l'éjection simultanées du moule. Pour les éjections multiples, l'éjection par vibration de la machine peut être utilisée, ce qui évite aux broches d'éjection de se rétracter complètement à chaque fois, réduisant ainsi le temps d'éjection.
En mettant en œuvre ces stratégies, les fabricants peuvent optimiser de manière significative la durée du cycle de moulage par injection, garantissant ainsi une production efficace et rentable.
Le spécialiste du contrôle des temps de cycle du moulage par injection
Une bonne entreprise de moulage par injection doit savoir comment calculer et réduire les temps de cycle du moulage par injection. La maîtrise de cet aspect n'est pas seulement une question d'efficacité ; il s'agit de fournir une qualité constante, de réduire les coûts et de garantir une production dans les délais. Chez Prototool, nous sommes fiers de notre compréhension approfondie du processus de moulage par injection. Notre expertise en matière de calcul et d'optimisation du cycle de moulage par injection nous permet non seulement de répondre aux demandes de production, mais aussi de les dépasser. Prototool cherche constamment à améliorer et à innover dans l'industrie du moulage par injection. Notre engagement démontre le rôle vital de la connaissance, de l'expérience et du dévouement dans ce domaine. Choisir Prototool, c'est choisir un partenaire qui s'engage à atteindre l'excellence dans toutes les facettes du processus de moulage par injection.
