How can you use hot runner systems to improve injection molding?
Injection molding is a widely used manufacturing process that can produce complex and high-quality plastic parts. However, it also involves some challenges, such as material waste, cycle time, and quality control. One way to overcome these challenges is to use hot runner systems, which are designed to keep the molten plastic in the mold at a constant temperature and flow rate. In this article, you will learn how hot runner systems work, what are their benefits and drawbacks, and how to choose the best one for your injection molding project.
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Kin LeongManufacturing professional, operations influencer, senior project manager, IS/IT Manager, Lean Six Sigma, change…
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Giuseppe di BariMechanical Engineering Manager (25 years) | Senior Designer Team Leader | R&D Project Manager | Continuous Improvement…
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ARUNRAJ Pandiyan🇻🇳Technical Leader_Battery Pack & ESS🔋VinFast🔋 | Manufacturing - Process Engineering | Body in White | |🏅Joining…
A hot runner system is a component of an injection mold that consists of a heated manifold and a set of nozzles that deliver the molten plastic to the mold cavities. Unlike a cold runner system, where the plastic cools and solidifies in the runners and sprues, a hot runner system keeps the plastic in a liquid state until it reaches the cavities. This eliminates the need to eject and trim the runners and sprues, reducing material waste and improving productivity.
Using a hot runner system in injection molding can offer several advantages, such as lower material consumption and cost, faster cycle time and higher output, and better quality and consistency. With no need to regrind and reuse runners and sprues, you can save on material and energy costs while using more expensive or sensitive materials. Additionally, since there is no cooling time for the runners and sprues, you can reduce the cycle time and increase the output. Furthermore, with less thermal variation and shear stress on the plastic, you can improve the quality and consistency of the molded parts while avoiding defects such as sink marks, weld lines, and gate vestiges that are caused by cold runner systems.
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Giuseppe di Bari
Mechanical Engineering Manager (25 years) | Senior Designer Team Leader | R&D Project Manager | Continuous Improvement Developer ⇨ Increasing Team Productivity by 30% & Reducing Product Development time to market by 35%
Hot runner systems offer many benefits for injection molding: Material savings: Since there is no cold runner, there is no need to regrind and reuse the plastic, which can degrade its properties and increase the cost. Cycle time reduction: The molten plastic flows faster and more uniformly in the hot runner system, which reduces the injection pressure and the cooling time. This leads to shorter cycle times and higher productivity. Part quality improvement: The hot runner system ensures a consistent temperature and pressure of the plastic throughout the mold, which reduces warping, shrinkage, and other defects. It also allows for better gate location and design, which minimizes the gate marks and improves the aesthetic appearance of the part
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Kin Leong
Manufacturing professional, operations influencer, senior project manager, IS/IT Manager, Lean Six Sigma, change manager, cultural coach, and automation engineer
From an OEM's perspective, employing a hot runner system in an injection molding tool provides the benefit of leaving a smaller gating mark on the product. Improper or insufficient trimming of gating sprue material can affect the appearance or fitment of a part.
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ARUNRAJ Pandiyan
🇻🇳Technical Leader_Battery Pack & ESS🔋VinFast🔋 | Manufacturing - Process Engineering | Body in White | |🏅Joining - Welding Specialist🇮🇳 | Certified LSSBB® | | Weld Master Certified by Nissan Motors Japan🇯🇵 |
Hot runner systems eliminate the need for a traditional cold runner, reducing material wastage and improving cost-effectiveness. By using hot runners, you only melt the required amount of plastic resin, and the excess can be recycled or reused easily
When considering hot runner systems, it is important to note that they have some drawbacks, such as a higher initial investment and maintenance. Hot runner systems are more complex and require more components and controls, making them costly to install and maintain. Additionally, they are less flexible and compatible than cold runner systems, with factors such as the number and shape of the cavities, the type and viscosity of the plastic, the injection pressure and speed, and the mold temperature and cooling needing to be considered when designing and selecting a hot runner system. It is also important to ensure that the system is properly heated, balanced, and cleaned to avoid problems such as leakage, clogging, and degradation of the plastic.
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Kin Leong
Manufacturing professional, operations influencer, senior project manager, IS/IT Manager, Lean Six Sigma, change manager, cultural coach, and automation engineer
The selection and design of a good hot runner system requires a definitive selection of the injection resin material at the time of tooling. Changing the resin selection may affect the hot runner system resulting in additional cost on tooling modification.
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Giuseppe di Bari
Mechanical Engineering Manager (25 years) | Senior Designer Team Leader | R&D Project Manager | Continuous Improvement Developer ⇨ Increasing Team Productivity by 30% & Reducing Product Development time to market by 35%
Drawbacks: Higher initial cost: it requires more components and complex design than the cold system, which increases the initial investment. This can be offset by long-term savings in material, energy, and labor costs. Higher maintenance: it needs to be cleaned and maintained regularly to prevent clogging, leakage, and degradation of the plastic. This requires more skill/time from the operators. This can be reduced by using proper materials, coatings, and lubricants for the components. Thermal expansion: it expands and contracts due to the temperature changes, which can cause stress/misalignment in the mold. This can affect the part quality and the mold life. It can be minimized by using adequate thermal insulation, and temperature control.
There are two main types of hot runner systems: open and valve gated. The difference between them is how they control the flow of the plastic to the mold cavities. Open hot runner systems use a continuous flow of plastic from the manifold to the nozzles, without any valves or shut-off mechanisms, and the plastic is cut off by the cooling of the mold at the gate. This system is simpler and cheaper, but can cause stringing, drooling, or freezing of the plastic at the gate. On the other hand, valve gated hot runner systems use a valve pin or needle to open and close the flow of plastic from the nozzle to the cavity, and the plastic is cut off by the movement of the valve pin. This system is more complex and expensive, but can offer better control, quality, and aesthetics of the molded parts.
To use hot runner systems effectively and efficiently, you need to make the right selection based on your mold design, material selection, quality requirements, and budget. Additionally, you should optimize the temperature, pressure, and flow rate of the hot runner system with sensors, controllers, and software. Furthermore, regular maintenance is necessary to prevent buildup, blockage, or damage of the components. You can use purging, flushing, or ultrasonic cleaning to remove any residue or contamination from the system. All of these steps will help ensure a uniform and stable delivery of the plastic to the mold cavities.
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ARUNRAJ Pandiyan
🇻🇳Technical Leader_Battery Pack & ESS🔋VinFast🔋 | Manufacturing - Process Engineering | Body in White | |🏅Joining - Welding Specialist🇮🇳 | Certified LSSBB® | | Weld Master Certified by Nissan Motors Japan🇯🇵 |
Hot runner systems are typically easier to maintain than traditional cold runners. The systems are designed for easy cleaning, maintenance, and replacement of individual components, allowing for reduced downtime during mold servicing
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ARUNRAJ Pandiyan
🇻🇳Technical Leader_Battery Pack & ESS🔋VinFast🔋 | Manufacturing - Process Engineering | Body in White | |🏅Joining - Welding Specialist🇮🇳 | Certified LSSBB® | | Weld Master Certified by Nissan Motors Japan🇯🇵 |
It is essential to work with experienced mold designers and hot runner system suppliers to ensure the proper selection, customization, and integration of hot runner systems into your injection molding process
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Giuseppe di Bari
Mechanical Engineering Manager (25 years) | Senior Designer Team Leader | R&D Project Manager | Continuous Improvement Developer ⇨ Increasing Team Productivity by 30% & Reducing Product Development time to market by 35%
Hot runner systems can be even improved by using: Servo-driven valve gate: it uses a servo motor to control the valve gate movement, instead of a mechanical or pneumatic actuator. This allows for more precise control of the gate opening and closing, which can improve the part quality, and reduce the cycle time. Hot runner simulation: a software tool that can simulate the flow, temperature, and pressure of the plastic in the hot runner, as well as the part filling, cooling, and warping. This can help to optimize the hot runner design. Hot runner monitoring: it can measure/record its parameters, such as temperature, pressure, flow, and power consumption. This can help to detect faults, maintain the quality, and improve the efficiency.
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