Injection molding is a very popular manufacturing process used to quickly and accurately produce plastic parts. In this field, there are two major technologies that are commonly used: runner injection molding and runnerless runner injection molding. These two technologies have different ways of forming molded parts, but they vary greatly in their approach and application. In this article, I will discuss both of these technologies in detail, explaining the differences between the two, as well as the advantages and disadvantages of each.

Process Differences

Runnerless Injection Molding

Runnerless injection molding (RIM), is the process of putting a molding nozzle into the injection mold, then using high pressure air to push the material into the mold. This eliminates waste and quality problems associated with long runners in conventional injection molding. Waste reduction is achieved in two ways: first, by eliminating excessive runners; and second, by eliminating the need to clean the product since no material is used to clean it. The result is improved efficiency and product quality. It is ideal for high precision products, so the products are very precise and high quality.

Runnerless injection molding is a much simpler process than injection molding with runners. It involves feeding, melting, dispensing, filling, packing, cooling, and ejecting the mold. With this method, you can machine very complex and precise parts and still have good production rates and results.

Advantages of Runnerless Injection Molding

1. Waste Reduction: Runnerless injection molding are not used in runnist injection molding, which reduces material use and makes production cheaper for the factory and the environment.

2. Better Part Quality: The lack of runners means fewer defects like flow lines or weld lines. You can see this in the smooth surface finish and mechanical properties of the molded parts.

3. Faster Cycle Times: The injection stage of the mold can be sped up since there are no runners, so runner-based molding can run faster than conventional molding.

Disadvantages of Runnerless Injection Molding

1. Initial Investment: The upfront cost of setting up a hot runner system, compared to a conventional runner system, is likely to be higher, making it difficult for small production runs to justify the expense.

2. Complex Design: Designing and refining hot runner systems is a specialized skill that requires careful consideration of factors as diverse as material options, thermodynamic devices, and mold geometry.

3. Maintenance Requirements: On one hand, runnerless molding eliminates the need to shut down the machine for purging or maintenance. On the other hand, the hot runner system itself requires regular maintenance to keep it running at peak performance and to ensure a long life.

Runner Injection Molding

The best thing about RIM, compared to old injection molding, is that it makes sure the plastic is all melted and goes into the mold in the same way, so the parts look right and fit right. It also has some other good things like making parts that are all the same color and shape, and making them faster.

The process of runner injection molding is made up of the following steps: runner design, plastic injection molder making, melt of plastic, injection, filling, compacting, cooling, and demolding. This technology is used to manufacture products in different shapes, sizes and materials so it’s very popular.

Advantages of Runner Injection Molding

1. Cost-Effectiveness: Injection runner molding is usually preferred for its lower cost especially when large number of effects are rendered simultaneously. A shaped one with many cavities may yield the most aesthetic outcome and hence, the lowest unit cost.

2. Flexibility: Such an approach provides flexibility by bringing the possibility of using not only different geometry but also any materials in the production itself.

3. Cooling Efficiency: The runner system allows for excellent mold cooling with an additional result of its ability to deliver faster cycle times and consistent parts’ quality.

Disadvantages of Runner Injection Molding

1. Waste: One of the drawbacks of runner injection molding is the waste generated by the runner system during the cooling process of the shot. This can lead to higher material costs and concerns about environmental practices.

2. Cycle Time: In terms of cycle, a runner can be considered as additional plastic that is injected into the mold. For molds with very complex runner designs, the cycle time will be longer.

3. Maintenance: Maintaining and cleaning the runner system is labor-intensive and time-consuming, which increases production costs and unfortunately extends lead times.

Different Applications

Runnerless Injection Molding

Unlike runner injection molding, runnerless injection molding is more cost-effective because machines do not have to spend time on designing, making, and maintaining runners. This means it takes less time and uses less material, which improves product quality and process stability. However, this process is limited to small, high-precision, and short-cycle products.

Runner Injection Molding

Injection molding is great for manufacturing because it can make products of different sizes and shapes, and it gives the manufacturer control of the temperature and pressure of the plastic during production, which makes it possible to have high-quality and accurate products. It costs more to do, but you have to make the runner, and it’s more for a big industrial process where you’re making a lot of stuff.

Different Molds

Runnerless injection molding molds use heating and insulating the runners to 100°C or higher so that the non-viscous molten plastic can be held in place, not below but above the nozzle, so that it is transferred directly into the cavity of the injection molding machine when the mold is opened, leaving no gating system.

Molding Cycle

Runnerless Injection Molding Molds: When calculating the molding cycle, if the cooling time of the gating system is included, the molding cycle is generally 3-8 seconds. If manually taken out, it may take 1-3 seconds longer than mechanical product removal.

Runner Injection Molding Molds: Because there is no cooling time for the gating system, the molded parts can be ejected promptly after solidification. Therefore, many thin-wall parts produced by hot runner molds can be molded in less than 5 seconds.

Material Saving

Runnerless Injection Molding Molds: The cost of raw materials for injection molds is a significant part of the overall cost because cold runners are needed in the molding equipment. This means that the mold will use more material than a hot runner mold to compensate for the scrap generated by the cold runner in the hot runner molding process.

Runner Injection Molding Molds: There are no cold runners at all in a pure hot runner system, so there is no scrap or waste produced. This is the single biggest thing that affects the cost of raw materials. In fact, there was a period of rapid growth for the major hot runner manufacturers around the world when oil and plastic raw material prices were high. With hot runner technology, you can pay less and reduce material waste because the parts will melt quickly and you won’t need extra material.

Product Quality

Molds for Injection Molding without Runner: When the resin is not heated as it flows through the mold, there are differences in heating of the resin, so there are parts of the molded product that do not meet the standards, resulting in many defective products. The mold is significantly different from the product mold because of the SS injector, so the quality of the mold is inferior.

Molds for Injection Molding with Runner: In hot runner molds, the plastic flow in the runner system is heated and controlled. The plastic is then cut into each cavity that is being formed. With hot runner technology, the quality is more uniform and there are fewer defective products. In addition, the gate quality of the molded parts is good, the molding stress is low (after demolding), and the deformation of the parts is small.

Subsequent Processes

Runnerless Injection Molding Molds: When you’re running a mold with a mold program, you need to make sure that you have plenty of time to get the parts out. You need to slow down the ejection speed so that the parts have enough time to come off the mold. This will help to prevent burning, spring back, and other problems with the parts sticking in the mold.

Runner Injection Molding Molds: The parts are done when they come out of the hot runner mold. The mold also cuts the sprue and the runner off the parts. The cold runner is the sprue and runner that you throw away. This is the way that the robot makes parts.

Mold Cost

Runnerless Injection Molding Molds: The molds used in the traditional method are priced normally and do not include the cost of installing hot runner components, which is only the cost of calculating process losses. The cost of molding is in good shape.

Runner Injection Molding Molds: Hot runner components are quite expensive. In addition, the cost of hot runner molds can be significantly increased due to design. It is not economically feasible to manufacture parts if the number of parts is small and the cost of mold tools is high.

Equipment Maintenance

Runnerless Injection Molding Molds: Check immediately what needs to be repaired. Find the problem, which may be a leak or a damaged part, and replace it right away.

Runner Injection Molding Molds: Unlike the first type, which is operated mechanically, the second type is difficult to operate and maintain. If you don’t use it correctly, you can damage the parts and people can’t continue to produce, which will cause a lot of economic losses.

Making the Right Choice

When deciding between runnerless injection molding and runner injection molding, several factors must be considered:

Production Volume: When it comes to parts that have long production runs and require expensive materials and cycle times, runnerless is less expensive in the long run, but has higher upfront costs.

Part Complexity: If you have parts with complex geometries or visual requirements, you might find that the flexibility and precision of runnerless injection molding outweigh the cost difference.

Budget Constraints: Initially, you can make parts with a runner and then, as you get more parts and more money, you can switch to a runnerless system.

Material Selection: You can make parts with a runner or without a runner using different kinds of plastic. Some plastics flow better, some are thicker, and some change with temperature.

Maintenance Capability: Remember to consider your team’s abilities and the resources you have available to troubleshoot and maintain your molds. This will help you decide whether to use a mold with runners or a runnerless mold.

Conclusion

There are two important processes in the injection molding industry: runnerless injection molding and runner injection molding. Each has its own advantages and challenges. With the development of new materials and processing technologies, both processes have broad application prospects and will be more widely used and promoted in the future.

In short, both runner injection molding and runnerless injection molding are good ways to make plastic parts. Each has its own good things and bad things. Runner injection molding is good because it is cheap and you can make all kinds of parts. Runnerless injection molding is good because the parts come out better and you don’t waste as much material. Which one you choose depends on how many parts you want to make, how hard they are to make, and how much money you have. If you understand the differences between these ways to make parts, you can decide which one is best for you and make the parts you want.