A Comprehensive Guide to Injection Mold Gate Design

• A Comprehensive Guide to Injection Mold Gate Design
  • What is the gate in injection molding?
  • The gate design and technology selection of injection molds are of paramount importance.
  • Basic considerations for injection mold gate design
  • Gate types used in injection molding
  • Basic Design Principles of Injection Mold Gate Shape
  • Injection mold gate location design principles
  • Development Trends in Injection Mold Gate Design
  • Why did we choose to partner with Elimold to develop injection molds and molding projects?
  • Conclusion
  • FAQ

Injection molding is a delicate process. It requires precision-machined molds and tightly controlled variables to produce high-quality, consistent parts. Many components of an injection molding machine work together to perform the same melting, injection, and molding actions on repeatedly produced plastic parts. Each component must be carefully designed to ensure that the final molded plastic part perfectly meets requirements. One crucial component is located at the edge of the mold cavity: the gate. Although seemingly small, the gate plays a vital role in the injection molding process. Poor gate design can lead to process delays and inefficiencies. Therefore, understanding and following gate design guidelines is essential before mold design and production.

What is the gate in injection molding?

The gate, part of the runner system, is the inlet for molten plastic to enter the mold cavity. It controls the flow rate and volume of the molten plastic and is responsible for ensuring proper filling and molding of the part. Gates are carefully designed and laid out according to part requirements, surface finish, and design considerations to optimize the molding process and ensure part quality. Because the gate guides the molten plastic into the cavity, the molten plastic also solidifies within the gate during the cooling phase. The gate remains attached to the part as it cools. Therefore, another step is required to remove the gate from the part. This step is called demolding or trimming. Gates can be trimmed manually after the part is removed from the machine or automatically during ejection. The trimming method (manual or automatic) depends on the type of gate used in the process, which we will discuss in the next section.

The gate design and technology selection of injection molds are of paramount importance.

In today’s fiercely competitive global manufacturing industry, every technical detail of the injection molding process has become a key element in building a company’s core competitiveness. Among them, the gating system, as the first “quality valve” controlling melt flow and the “strategic hub” of the molding process, has a technical value far exceeding its physical dimensions. A precisely calculated and optimized gating system can create significant value in three dimensions:

• In terms of quality, a yield improvement of 15-30% can be achieved.
• This will result in a 20-40% reduction in production costs.
• Achieve a 10-25% cycle reduction in efficiency.

Behind these data lies the injection mold manufacturer’s precise control over gate design, material flow, pressure transmission, and cooling processes. Furthermore, the current dual revolution in materials science and process technology is reshaping the injection molding industry. The emergence of new materials such as specialty engineering plastics and bio-based materials presents entirely new challenges to gate design, while the widespread adoption of advanced processes like micro-injection molding and multi-material injection molding provides ample space for gate technology innovation. In response to this industry transformation, Elimold has built a complete matrix of technical solutions and a database. Therefore, our engineering team can provide customized solutions based on customers’ product characteristics, material properties, and production capacity requirements, ranging from classic direct-gating and side-gating systems to advanced hot runner and valve-type gate control technologies.

Basic considerations for injection mold gate design

The design of the injection mold gate is crucial throughout the molding process. A good gate design ensures that the molten plastic flows smoothly and evenly into the mold cavity, thus contributing to the production of high-quality parts. On the other hand, a poor gate design can lead to various problems, such as short runs (incomplete mold filling), warpage, or weak points on the finished part. The importance of gate design is summarized by the mold design engineers at Elimold as follows:

Flow control	The gate controls the flow rate, speed, and pressure of molten plastic entering the mold. This is crucial for ensuring the plastic fills properly and conforms to the mold design, resulting in the manufacture of precise and accurate parts.
Cooling and solidification	The gate design also affects the rate at which parts cool and solidify. A well-designed gate helps with uniform cooling, thereby reducing the likelihood of defects such as warpage or shrinkage.
Cosmetic Surgery Department	The location and type of the gate determine where visible markings (called “gate marks”) will appear on the final part. Depending on the end use of the part, this can be an important aesthetic consideration.
Ejection and degate	The gate design also affects how easily the part is ejected from the mold, and how cleanly the gate is removed from the part or “de-gated”.

Gate types used in injection molding

Besides affecting the shape and surface finish of parts, gates also influence process variables. Therefore, selecting a suitable gate is a crucial consideration during mold design. Before choosing a suitable gate, you must understand some of the most common gate types. The following is a brief overview of some commonly used gates in injection molding:

Edge gate	Edge gates are located at the edge of the part. Also known as side gates or sprues, these gates are only suitable for flat parts and parts requiring easy trimming due to their thinness and ease of trimming. Removing this type of gate requires manual operation, which increases production cycle time.
Needle gate	The pin gate is located on side B of the mold. The gate itself is very thin, but the scrap rate is high because the runner is relatively large compared to the gate. Due to the thin gate tip, the pin gate is ideal for complex parts where gate marks and markings need to be minimized. The gate is automatically trimmed and removed as the part is ejected from the mold.
Hot runner gate	Hot runner systems maintain the state and temperature of molten plastic as it flows from the barrel into the mold cavity. Hot runner systems typically use two types of gates: hot gates and valve gates . Hot gates function similarly to regular gates, controlling the flow of molten plastic from the runner into the mold cavity. However, hot gates are prone to gate residue, which may require post-processing of the parts. Valve gates, on the other hand , have internal pins that allow for more precise control of the molten plastic flow. Pulling the pin backward allows material to flow, while pushing it forward cuts off the flow. Valve gates reduce gate residue and improve process efficiency.
Diaphragm gate	When high concentricity is required for parts, diaphragm gates are typically used. These gates are commonly found in the production of cylindrical parts that are open at both ends. When used properly, diaphragm gates can prevent defects such as weld seams and help improve the quality of the final part.
Fan-shaped gate	When high concentricity is required for parts, diaphragm gates are typically used. These gates are commonly found in the production of cylindrical parts that are open at both ends. When used properly, diaphragm gates can prevent defects such as weld seams and help improve the quality of the final part.
Tunnel gate	The tunnel gate or submersible gate is located below the parting line and can be automatically trimmed during ejection. It tapers gradually in the gate area close to the part and separates from the part, leaving little residue.
Curved gate	Similar to tunnel gates, curved gates are machined below the parting line and automatically trimmed. The difference lies in their structure; curved gates are curved, making ejection more difficult. However, they allow pouring in areas inaccessible by tunnel gates.

Basic Design Principles of Injection Mold Gate Shape

To facilitate the removal of solidified material from the gate, the gate is typically designed in a conical shape with a cone angle α between 2° and 4°. For plastics with poor melt flowability, α can be 6° to 10°, and the inner wall surface roughness is generally around Ra 0.8 μm. The inlet diameter is typically 4 to 8 mm. If the melt flowability is good and the product size is small, we tend to choose a smaller diameter; conversely, it is better to choose a larger diameter.

Generally, the gate size should be small rather than large. Start with a smaller size and then adjust it during trial molding based on the cavity filling. This is especially important in multi-cavity molds, where adjusting the gate size ensures simultaneous and uniform injection into all cavities. A smaller gate also increases the melting speed and temperature, which is beneficial for filling, and it facilitates removal. However, for products with very thick walls, a gate that is too small can cause premature solidification at the gate area, resulting in insufficient filling and product defects. Therefore, the specific gate size should be determined based on the specific gate design.

Injection mold gate location design principles

Determine the gate location to ensure all corners of the cavity are filled simultaneously. The plastic flow rate should remain uniform and stable throughout all stages of injection molding. Therefore, the gate should be designed at the thicker part of the product wall, allowing the molten plastic to flow from the thicker part to the thinner part, facilitating complete filling of the mold.

The gate should be chosen in a location that minimizes the plastic filling process to reduce pressure loss. The gate should be positioned to facilitate gas venting, and the gate should not directly guide the melt into the mold cavity to avoid swirling flows and swirl marks, especially in narrow gate configurations. Potential issues such as weld marks, bubbles, depressions, under-injection, and material spraying should also be considered.

Furthermore, when designing the gate location, it’s crucial to avoid visible weld seams on the product surface. If weld seams cannot be avoided, their impact should be minimized during gate location design. Especially for round or cylindrical parts, a cold slug well should be added at the molten metal pouring point to prevent weld seams from forming.

When the product has a large surface area, avoid placing the gate on only one side. This ensures even distribution of injection force and a placement that doesn’t affect the product’s appearance. Additionally, gates should not be placed on parts of the product subjected to bending or impact loads, as these areas often have lower strength.

Finally, in injection molds with long and thin cores, the gate should be located away from the core to prevent deformation caused by material flow. You can use compound gates for large or flat plastic parts to prevent skewing, deformation, and material shortage.

Development Trends in Injection Mold Gate Design

With the deepening application of Industry 4.0 and intelligent manufacturing in the injection molding industry, mold gate design is also showing some new trends. The main trend is the widespread use of simulation technologies (such as Moldflow), which allows engineers to simulate the melt filling process, pressure distribution, and temperature changes under different gate designs before mold manufacturing. This enables them to accurately predict potential product defects, optimize gate types and parameters in advance, reduce trial molding, and improve mold development efficiency. Another factor is the increasing market demand for personalized customization and small-batch, multi-variety production, which places higher demands on the flexibility of injection molds. Many new adjustable gate technologies (such as valve gates) are gradually being applied.

Why did we choose to partner with Elimold to develop injection molds and molding projects?

The complexity of gate design is often underestimated. Elimold’s engineering and project database shows that improper gate design can lead to 47 types of molding defects, including flow marks, short shots, and silver streaks. The average direct economic loss from each mold modification is as high as $5,000 to $15,000, not to mention the delayed delivery times and lost market opportunities. Based on a deep understanding of injection mold manufacturing and injection molding technology, the Elimold team has built an engineering and project database of over 10,000 mold cases through years of technical accumulation, forming a complete technical support system from conceptual design to mass production optimization. If you need a mold manufacturer to develop new molds and require high-volume production capabilities, please contact Elimold now.

Conclusion

injection molds is crucial to the efficiency of the entire process. Improperly designed gate locations can lead to part defects, residues, molten plastic flowing back into the runner, and many other problems that may reduce part quality and increase production costs.

to fully consider the gate location design before starting mold design . Since each customer’s product structure and materials are different, there is no single correct answer for the gate location. Choosing the right gate location requires mold designers to have a certain amount of practical experience.

FAQ